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Litter Decomposition (litter + decomposition)
Kinds of Litter Decomposition Terms modified by Litter Decomposition Selected AbstractsLitter Decomposition Within the Canopy and Forest Floor of Three Tree Species in a Tropical Lowland Rain forest, Costa RicaBIOTROPICA, Issue 3 2010Catherine L. Cardelús ABSTRACT The rain forest canopy hosts a large percentage of the world's plant biodiversity, which is maintained, in large part, by internal nutrient cycling. This is the first study to examine the effects of site (canopy, forest floor) and tree species (Dipteryx panamensis, Lecythis ampla, Hyeronima alchorneoides) on decay rates of a common substrate and in situ leaf litter in a tropical forest in Costa Rica. Decay rates were slower for both substrates within the canopy than on the forest floor. The slower rate of mass loss of the common substrate in the canopy was due to differences in microclimate between sites. Canopy litter decay rates were negatively correlated with litter lignin:P ratios, while forest floor decay rates were negatively correlated with lignin concentrations, indicating that the control of litter decay rates in the canopy is P availability while that of the forest floor is carbon quality. The slower cycling rates within the canopy are consistent with lower foliar nutrient concentrations of epiphytes compared with forest floor-rooted plants. Litter decay rates, but not common substrate decay rates, varied among tree species. The lack of variation in common substrate decay among tree species eliminated microclimatic variation as a possible cause for differences in litter decay and points to variation in litter quality, nutrient availability and decomposer community of tree species as the causal factors. The host tree contribution to canopy nutrient cycling via litter quality and inputs may influence the quality and quantity of canopy soil resources. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] Extracellular Enzyme Activities and Carbon Chemistry as Drivers of Tropical Plant Litter DecompositionBIOTROPICA, Issue 3 2004Steven D. Allison ABSTRACT Litter quality parameters such as nitrogen and lignin content correlate with decomposition rates at coarse scales, but fine-scale mechanisms driving litter decomposition have proven more difficult to generalize. One potentially important driver of decomposition is the activity of extracellular enzymes that catalyze the degradation of complex compounds present in litter. To address the importance of this mechanism, we collected 15 Hawaiian plant litter types and decomposed them in fertilized and control plots for up to two years. We measured litter nutrient content and carbon chemistry prior to decomposition, as well as extracellular enzyme activities, mass loss, and litter nutrient content over time. We found that water-soluble carbon content, cellobiohydrolase activities, and polyphenol oxidase activities were significantly correlated with mass loss. Enzyme activities and decomposition rate constants both varied significantly by litter type, and fertilization increased mass loss rates in five litter types. Some litter types that decayed faster under fertilization also showed time-dependent increases in carbon-degrading enzyme activities, but others decayed faster independent of enzyme changes. These results suggest that extracellular enzyme activities partially determine litter decomposition rates, but high soluble carbon content may circumvent the requirement for enzyme-catalyzed decomposition. [source] Leaf Litter Decomposition and Monodominance in the Peltogyne Forest of Marací Island, Brazil1BIOTROPICA, Issue 3 2002Dora M. Villela ABSTRACT The forest type dominated by Peltogyne gracilipes (Caesalpiniaceae) on the riverine Marací Island is the least speciesrich of any recorded for Brazilian Amazonia. Because the forest has high soil and foliar Mg concentrations, and Mg is known to be toxic to plant growth at high concentrations, this study tested the hypothesis that dominance by Peltogyne is related to Mg leaf litter amounts and decomposition. We predicted that decomposition of Peltogyne leaves would differ from that of other species, and that their decomposition would result in a pulse of Mg release. Three plots (50 × 50 m) were established in each of three forest types: Peltogyne -rich forest (PRF; dominated by P. gracilipes),Peltogyne-poor forest (PPF), and forest without Peltogyne (FWP). Three leaf litter decomposition experiments tested if decomposition of mixed leaf litter in coarse- mesh (CM) litterbags differed among forests (experiment 1); whether or not decomposition and nutrient release of Ecclinusa guianensis, Lueheopsis duckeana, and Peltogyne in CM litterbags differed among forests and species (experiment 2); and using fine-mesh (FM) litterbags, investigated the differences in the influence of fauna! activity on Ecclinusa and Peltogyne decomposition (experiment 3). Decomposition was independent of the presence and dominance of Peltogyne, since decomposition rates in both PRF and FWP were in general lower than in PPF. These differences appeared to be related to fauna] activity. The decomposition of Peltogyne leaves was lower than that of the other species tested and was more affected by microbial and physical action. It is possible that the monodominance of Peltogyne is related to its deciduousness and faster decomposition in the dry season, which coincides with a large leaf fall. Magnesium was lost quickly from the Peltogyne leaves and the resultant pulses of Mg into the soil during the heavy rains at the beginning of the wet season may be deleterious for other species that are not adapted to high solution Mg concentrations. Results obtained were consistent with the hypothesis that Peltogyne dominance is related to the pattern of its leaf decomposition and the seasonal pulses of toxic Mg. RESUMO A floresta dominada por Peltogyne gracilipes (Caesalpiniaceae) na Ilha fluvial de Maracáé a mais pobre em espécies reportada para a Amazõnia brasileira. Devido a esta floresta possuir altas concentra¸ões de Mg no solo e nas folhas, e pelo fato de Mg ser conhecidamente tóxico para o crescimento das plantas quando em altas concentra¸ões, este estudo testou a hipótese de que a dominãncia de Peltogyne está relacionada com as quantidades de Mg e com a decomposi¸ão das folhas da serrapilheira. Esperou-se encontrar um padrão de decomposi¸ão diferente para folhas de Peltogyne, e que as folhas de Peltogyne apresentassem um pulso de libera¸ão de Mg. Três parcelas (50 × 50 m) foram estabelecidas em cada um dos três tipos florestais: floresta rica em Peltogyne (PRF; dominada por P. gracilipes), floresta pobre em Peltogyne (PPF) e floresta sem Peltogyne (FWP). Três experimentos de decomposi¸ão de folhas da serrapilheira testaram se a decomposi¸ão de folhas mistas da serrapilheira em sacos de serrapilheira de malha grossa (CM) difere entre florestas (experimento 1), se a decomposi¸ão e a libera¸ão de nutrientes de Ecclinusa guianensis, Lueheopsis duckeana, e Peltogyne em sacos de serrapilheira CM difere entre florestas e entre espécies (experimento 2), e usou sacos de serrapilheira de malha fina (FM) para investigar as diferen¸as na influência da atividade da fauna na decomposi¸ão de Ecclinusa e Peltogyne (experimento 3). A decomposi¸ão foi independente da presen¸a e dominãncia de Peltogyne, já que as taxas de decomposi¸ão em PRF e FWP foram em geral menores que em PPF. Estas diferencas parecem estar relacionadas à atividade da fauna. A decomposi¸ão de folhas de Peltogyne foi menor que a das demais espécies testadas e foi mais afetada pela a¸ão microbiológica e flsica. é possível que a dominãncia de Peltogyne esteja relacionada com a sua deciduidade e com a rápida decomposi¸ão na esta¸ão seca, a qual coincide com uma grande queda de folhas. Magnésio foi perdido rapidamente das folhas de Peltogyne e os pulsos resultantes de Mg no solo durante as fortes chuvas no início da esta¸ão chuvosa podem ser deletérios para outras espécies que não estão adaptadas as altas concentra¸ões deste íon. Os resultados obtidos foram consistentes com a hipótese de que a dominãncia de Peltogyne está relacionada com o padrão de decomposi¸ão de suas folhas e com os pulsos sazonais de Mg tóxico. [source] Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shreddersFRESHWATER BIOLOGY, Issue 8 2007J. F. GONÇALVES JR Summary 1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions. 2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day,1 and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046,0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 ,g g,1, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 ,g g,1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g,1). 3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves. 4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L,1), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source. [source] Litter decomposition in grasslands of Central North America (US Great Plains)GLOBAL CHANGE BIOLOGY, Issue 5 2009ELIANA E. BONTTI Abstract One of the major concerns about global warming is the potential for an increase in decomposition and soil respiration rates, increasing CO2 emissions and creating a positive feedback between global warming and soil respiration. This is particularly important in ecosystems with large belowground biomass, such as grasslands where over 90% of the carbon is allocated belowground. A better understanding of the relative influence of climate and litter quality on litter decomposition is needed to predict these changes accurately in grasslands. The Long-Term Intersite Decomposition Experiment Team (LIDET) dataset was used to evaluate the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon : nitrogen, and lignin : nitrogen ratios) on leaf and root decomposition in the US Great Plains. Wooden dowels were used to provide a homogeneous litter quality to evaluate the relative importance of above and belowground environments on decomposition. Contrary to expectations, temperature did not explain variation in root and leaf decomposition, whereas precipitation partially explained variation in root decomposition. Percent lignin was the best predictor of leaf and root decomposition. It also explained most variation in root decomposition in models which combined litter quality and climatic variables. Despite the lack of relationship between temperature and root decomposition, temperature could indirectly affect root decomposition through decreased litter quality and increased water deficits. These results suggest that carbon flux from root decomposition in grasslands would increase, as result of increasing temperature, only if precipitation is not limiting. However, where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands. Under homogeneous litter quality, belowground decomposition was faster than aboveground and was best predicted by mean annual precipitation, which also suggests that the high moisture in soil accelerates decomposition belowground. [source] Litter decomposition in a sandy Monte desert of western Argentina: Influences of vegetation patches and summer rainfallAUSTRAL ECOLOGY, Issue 7 2006EDUARDO PUCHETA Abstract: We tested the hypothesis that shrub canopies interact with monthly rain pulses to control litter decomposition in a sandy Monte desert, in Argentina. We assessed (i) the potential for litter decomposition of soils beneath the canopies of two dominant shrub species (Larrea divaricata and Bulnesia retama, Zygophyllaceae R. Br.) and from bare-ground microsites or ,openings'; (ii) litter decomposition at different spatial patches over the summer rainy season; and (iii) the interaction between vegetation patches and monthly rain pulses on short-term litter decomposition, or decomposition pulses. In a greenhouse experiment, we found buried litter decomposition to be higher in soils from under the canopies of a dominant shrub species compared with soils from openings and sterilized controls. This, and higher nutrient concentration under shrub soils, suggest undercanopy soils may support a microbial community capable of decomposing litter at higher rates than soils in bare openings. However, ,eld trials showed that shrub patches did not affect leaf litter decomposition over the rainy season, at least for short periods. We found an interaction between shrub patches and incubation time at the end of the ,eld experiment, with higher litter decomposition rates under B. retama canopies. In a monthly ,eld experiment, we found monthly rain pulses signi,cantly explained decomposition pulses, irrespective of patch type. Our ,ndings support the hypothesis that shrub soils have a greater potential for litter decomposition, but this is not directly translated to the ,eld possibly due to interactions with abiotic factors. Rain pulses create conditions for decomposition pulses to occur at shorter time scales, whereas rainfall may interact with a dominant shrub undercanopy to control litter mass loss over longer time scales. [source] Magnitude and variability of process rates in fungal diversity-litter decomposition relationshipsECOLOGY LETTERS, Issue 11 2005Christian K. Dang Abstract There is compelling evidence that losses in plant diversity can alter ecosystem functioning, particularly by reducing primary production. However, impacts of biodiversity loss on decomposition, the complementary process in the carbon cycle, are highly uncertain. By manipulating fungal decomposer diversity in stream microcosm experiments we found that rates of litter decomposition and associated fungal spore production are unaffected by changes in decomposer diversity under benign and harsher environmental conditions. This result calls for caution when generalizing outcomes of biodiversity experiments across systems. In contrast to their magnitude, the variability of process rates among communities increased when species numbers were reduced. This was most likely caused by a portfolio effect (i.e. statistical averaging), with the uneven species distribution typical of natural communities tending to weaken that effect. Curbing species extinctions to maintain ecosystem functioning thus can be important even in situations where process rates are unaffected. [source] Accumulation and solubility of metals during leaf litter decomposition in non-polluted and polluted soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009S. Scheid Summary The decomposition of alder (Alnus glutinosa) and poplar (Populus tremula) leaf litter placed in direct contact with non-polluted and metal-polluted soil was investigated over 25 months in a controlled model-ecosystem experiment using the litterbag method. In addition to mass loss, we monitored the total and soluble concentrations of carbon, Cu, Zn, Cd and Pb. Leaves from trees grown on polluted soil had larger initial Zn, Cd and dissolved organic carbon concentrations. Neither the origin of the leaves (from trees grown on non-polluted or polluted soil) nor the placement of the leaves in polluted or unpolluted soil affected the decomposition process. Total metal contents increased in leaves placed on polluted soil over time. The solubility of metals in the leaf litter decreased over time, indicating that leaves acted as a temporary pool for metals from the soil in direct contact with the leaves. The sorbed metals were strongly bound in the litter even after two years of decomposition. The strong binding and thus reduced bioavailability of the metals provides an explanation for why they had no observable effects on litter decomposition. [source] Alkaloids may not be responsible for endophyte-associated reductions in tall fescue decomposition ratesFUNCTIONAL ECOLOGY, Issue 2 2010Jacob A. Siegrist Summary 1. ,Fungal endophyte , grass symbioses can have dramatic ecological effects, altering individual plant physiology, plant and animal community structure and function, and ecosystem processes such as litter decomposition and nutrient cycling. 2. ,Within the tall fescue (Schedonorus arundinaceus) , fungal endophyte (Neotyphodium coenophialum) symbiosis, fungal produced alkaloids are often invoked as the putative mechanism driving these ecological responses. Yet few measurements of alkaloids exist in the ecological literature. In this study, we quantified alkaloid levels in live, standing dead and decomposing endophyte-infected (E+) and ,free (E,) plant material and simultaneously evaluated the direct and indirect effects of endophyte presence on tall fescue decomposition. 3. ,Loline and ergot alkaloid levels were consistently high in live E+ (common toxic strain of N. coenophialum) tall fescue biomass throughout the sampling period (May,November 2007), whereas, E, live and standing dead material had non-detectable alkaloid concentrations. Standing dead E+ biomass had significantly reduced alkaloid levels (6,19x lower than the levels measured in the corresponding live E+ biomass) that were equivalent to E, live and dead for loline but were still somewhat higher than E, material for ergots. 4. ,In an effort to test the role of alkaloids in directly inhibiting decomposition, as has been suggested by previous studies, we conducted a litter bag experiment using green, alkaloid-laden E+ and alkaloid-free E, tall fescue plant material. We incubated E+ and E, litter bags in both E+ and E, tall fescue stands for 170 days, and measured mass loss, carbon and nitrogen content, and ergot and loline alkaloid concentrations over the incubation period. 5. ,Consistent with previous reports, both direct and indirect effects of endophyte presence on litter decomposition were observed: endophyte presence in the litter and surrounding microenvironment significantly reduced decomposition rates. Surprisingly, despite large differences in alkaloid content between E+ and E, litter from Day 0,Day 21 of the incubation, direct effects of the endophyte on litter decomposition, while significant, were relatively small (differences in mass loss between E+ and E, litter were never >3%). Alkaloids were gone from E+ material by day 56. 6. ,We propose that results from this study indicating alkaloids are largely absent in standing dead material (the typical input to the decomposition process), and that despite being present in our litter bag experiment, failed to produce large differences in mass loss between E+ and E, material questions the supposition that fungal produced alkaloids directly inhibit decomposition. Additional studies exploring the mechanisms behind the direct and indirect effects of endophytes on this ecosystem process are needed. [source] Among- and within-species variation in plant litter decomposition in contrasting long-term chronosequencesFUNCTIONAL ECOLOGY, Issue 2 2009David A. Wardle Summary 1Following major disturbances ecosystem development occurs but in the prolonged absence of disturbance a decline (retrogressive) phase follows in which productivity and nutrient availability diminishes. Although it is recognized that litter quality and decomposition rates decrease as retrogression proceeds, little is known about the extent to which this is driven among- vs. within-species variation across these sequences. 2We selected six long-term chronosequences that each included retrogressive stages, in New Zealand, Hawaii, Sweden, Alaska and Australia. Two involve significant species turnover across the sequence so that different species dominate at different stages, two involve low species turnover so that the same dominant species occur at all stages, and two involve some turnover of species but with certain species persisting throughout most of the sequence. 3For each chronosequence, we collected litter from each dominant plant species at each stage of that sequence. For each litter collection we measured concentrations of N and P, and performed laboratory decomposition bioassays to measure mass loss, N and P loss, and the response of mass loss to mixture with litters of coexisting species. 4We found that litter N and P concentrations often declined with increasing ecosystem age, both among- and within-species. However, the relative importance of among- and within-species effects varied across the six chronosequences. Rates of litter mass, N, and P loss during decomposition sometimes decreased with increasing ecosystem age, but most often at the among-species rather than the within-species level. 5Litter mixing effects often varied across chronosequence stages, but the magnitude and direction of these effects was inconsistent among sequences. Variation in litter mixing effects across chronosequence stages was driven mainly by among- rather than within-species variation. 6Although several recent studies have emphasized the role of within-species variation on ecosystem properties, our results point to among-species variation as a consistently important ecological driver, with within-species variation being important only for some variables and in some instances. As such they highlight that decomposition processes are most likely to be highly responsive to gradients of soil fertility (such as across chronosequences) when significant species turnover occurs across the gradient. [source] Do woodlice and earthworms interact synergistically in leaf litter decomposition?FUNCTIONAL ECOLOGY, Issue 1 2005MARTIN ZIMMER Summary 1In laboratory microcosms, we investigated the influence of diversity of both leaf litter and detritivores on decomposition processes. Either woodlice or earthworms, or a combination of woodlice and earthworms, fed on leaf litter of either oak or alder, or oak and alder for 8 weeks. Mass loss of leaf litter, soil microbial respiration and soil nutrient concentrations were determined every 2 weeks. 2For four out of seven decomposition parameters, the joint effects of woodlice and earthworms were stronger than the sum of single-species effects when they had fed on alder litter. When feeding on oak litter, however, woodlice and earthworms together revealed lower decomposition rates than predicted from their single effects. Joint effects of detritivores on decomposition of mixed litter were always lower than predicted from the sum of their effects. 3In mixed-litter assays, we obtained intermediate values of decomposition parameters, indicating that doubling the species richness of leaf litter from one to two species did not promote decomposition processes. Effects of mixing litter were, thus, mostly additive; essentially only when earthworms fed on mixed litter we observed, mostly positive, non-additive effects of diverse litter. 4Our findings provide evidence for a potential effect on ecosystem functioning through joint action of detritivores even at low species diversity, while litter diversity seems to be less significant. On high-quality litter, isopods and earthworms are not functionally redundant but act synergistically on litter decomposition. The effects of detritivore diversity on ecosystem processes, however, are context-specific and depend on the quality and diversity of the available food sources, and on species-specific characteristics of the detritivores. [source] Moisture availability influences the effect of ultraviolet-B radiation on leaf litter decompositionGLOBAL CHANGE BIOLOGY, Issue 1 2010W. KOLBY SMITH Abstract Altered surface ultraviolet-B (UV-B) radiation resulting from a combination of factors that include changes in stratospheric ozone concentrations, cloud cover, and aerosol conditions may affect litter decomposition and, thus, terrestrial nutrient cycling on a global scale. Although litter decomposition rates vary across biomes, patterns of decomposition suggest that UV-B radiation accelerates litter decay in xeric environments where precipitation is infrequent. However, under more frequent precipitation regimes where litter decay rates are characteristically high, the effect of UV-B radiation on litter decomposition has not been fully elucidated. To evaluate this association between moisture regime and UV-B exposure, a litter decomposition experiment was designed for aspen (Populus tremuloides) leaf litter, where conditions that influence both abiotic (photodegradation) and biotic (microbial) processes could be manipulated quantitatively. We found that experimentally increasing UV-B exposure (0, 7.4, and 11.2 kJ m,2 day,1, respectively) did not consistently increase litter decomposition rates across simulated precipitation frequencies of 4, 12, and 24 days. Instead, a UV-B exposure of 11.2 kJ m,2 day,1 resulted in a 13% decrease in decomposition rates under the 4-day precipitation frequency, but an increase of 80% under the 24-day frequency. Furthermore, the same UV-B dose increased litter decomposition rates under the 24-day precipitation frequency by 78% even in conditions where microbial activity was suppressed. Therefore, under more xeric conditions, greater exposure to UV-B radiation increased decomposition rates, presumably through photodegradation. In contrast, when decomposition was not moisture-limited, greater UV-B exposure slowed decomposition rates, most likely from the resulting inhibition of microbial activity. Ultimately, these experimental results highlight UV-B radiation as a potential driver of decomposition, as well as indicate that both the direction and magnitude of the UV-B effect is dependent on moisture availability, a factor that may change according to future patterns in global precipitation. [source] Litter decomposition in grasslands of Central North America (US Great Plains)GLOBAL CHANGE BIOLOGY, Issue 5 2009ELIANA E. BONTTI Abstract One of the major concerns about global warming is the potential for an increase in decomposition and soil respiration rates, increasing CO2 emissions and creating a positive feedback between global warming and soil respiration. This is particularly important in ecosystems with large belowground biomass, such as grasslands where over 90% of the carbon is allocated belowground. A better understanding of the relative influence of climate and litter quality on litter decomposition is needed to predict these changes accurately in grasslands. The Long-Term Intersite Decomposition Experiment Team (LIDET) dataset was used to evaluate the influence of climatic variables (temperature, precipitation, actual evapotranspiration, and climate decomposition index), and litter quality (lignin content, carbon : nitrogen, and lignin : nitrogen ratios) on leaf and root decomposition in the US Great Plains. Wooden dowels were used to provide a homogeneous litter quality to evaluate the relative importance of above and belowground environments on decomposition. Contrary to expectations, temperature did not explain variation in root and leaf decomposition, whereas precipitation partially explained variation in root decomposition. Percent lignin was the best predictor of leaf and root decomposition. It also explained most variation in root decomposition in models which combined litter quality and climatic variables. Despite the lack of relationship between temperature and root decomposition, temperature could indirectly affect root decomposition through decreased litter quality and increased water deficits. These results suggest that carbon flux from root decomposition in grasslands would increase, as result of increasing temperature, only if precipitation is not limiting. However, where precipitation is limiting, increased temperature would decrease root decomposition, thus likely increasing carbon storage in grasslands. Under homogeneous litter quality, belowground decomposition was faster than aboveground and was best predicted by mean annual precipitation, which also suggests that the high moisture in soil accelerates decomposition belowground. [source] Effects of ultraviolet radiation on litter decomposition depend on precipitation and litter chemistry in a shortgrass steppe ecosystemGLOBAL CHANGE BIOLOGY, Issue 10 2007LESLIE A. BRANDT Abstract We examined the effect of altered levels of ultraviolet (UV) radiation (280,400 nm) and different amounts of precipitation on the decomposition rates of litter of contrasting carbon to nitrogen ratio (C : N) in a 3-year field experiment in a shortgrass steppe (SGS) ecosystem. UV radiation was either blocked or passed under clear plastic tents where precipitation was applied to simulate a very dry or very wet year. These treatments minimized or maximized the abiotic component (UV) or the biotic component (biological activity of decomposer organisms) of decomposition to assess potential interactions between the two. Initial litter chemistry varied in response to having been grown under ambient or elevated atmospheric CO2 concentrations. While precipitation and litter chemistry were the most important drivers in decomposition in this system, UV radiation increased decomposition rates under dry conditions in litter with higher C : N ratios. Exposure to UV radiation slightly increased the amount of holocellulose that was lost from the litter. UV exposure did not affect the decomposition of the lignin fraction. Increased decomposition with UV radiation was accompanied by a decrease in N immobilization over the summer months. These results suggest that the effects of UV radiation on decomposition rates may be primarily abiotic, caused by direct photochemical degradation of the litter. Our results demonstrate that the role of UV radiation in litter decomposition in semiarid systems depends on the aridity of the system and the chemistry of the litter. [source] Vegetation responses in Alaskan arctic tundra after 8 years of a summer warming and winter snow manipulation experimentGLOBAL CHANGE BIOLOGY, Issue 4 2005C.-H. A. Wahren Abstract We used snow fences and small (1 m2) open-topped fiberglass chambers (OTCs) to study the effects of changes in winter snow cover and summer air temperatures on arctic tundra. In 1994, two 60 m long, 2.8 m high snow fences, one in moist and the other in dry tundra, were erected at Toolik Lake, Alaska. OTCs paired with unwarmed plots, were placed along each experimental snow gradient and in control areas adjacent to the snowdrifts. After 8 years, the vegetation of the two sites, including that in control plots, had changed significantly. At both sites, the cover of shrubs, live vegetation, and litter, together with canopy height, had all increased, while lichen cover and diversity had decreased. At the moist site, bryophytes decreased in cover, while an increase in graminoids was almost entirely because of the response of the sedge Eriophorum vaginatum. These community changes were consistent with results found in studies of responses to warming and increased nutrient availability in the Arctic. However, during the time period of the experiment, summer temperature did not increase, but summer precipitation increased by 28%. The snow addition treatment affected species abundance, canopy height, and diversity, whereas the summer warming treatment had few measurable effects on vegetation. The interannual temperature fluctuation was considerably larger than the temperature increases within OTCs (<2°C), however. Snow addition also had a greater effect on microclimate by insulating vegetation from winter wind and temperature extremes, modifying winter soil temperatures, and increasing spring run-off. Most increases in shrub cover and canopy height occurred in the medium snow-depth zone (0.5,2 m) of the moist site, and the medium to deep snow-depth zone (2,3 m) of the dry site. At the moist tundra site, deciduous shrubs, particularly Betula nana, increased in cover, while evergreen shrubs decreased. These differential responses were likely because of the larger production to biomass ratio in deciduous shrubs, combined with their more flexible growth response under changing environmental conditions. At the dry site, where deciduous shrubs were a minor part of the vegetation, evergreen shrubs increased in both cover and canopy height. These changes in abundance of functional groups are expected to affect most ecological processes, particularly the rate of litter decomposition, nutrient cycling, and both soil carbon and nitrogen pools. Also, changes in canopy structure, associated with increases in shrub abundance, are expected to alter the summer energy balance by increasing net radiation and evapotranspiration, thus altering soil moisture regimes. [source] UV-B effect on Quercus robur leaf litter decomposition persists over four yearsGLOBAL CHANGE BIOLOGY, Issue 4 2001K. K. Newsham Summary The effects of elevated UV-B (280,315 nm) radiation on the long-term decomposition of Quercus robur leaf litter were assessed at an outdoor facility in the UK by exposing saplings to elevated UV-B radiation (corresponding to a 30% increase above the ambient level of erythemally weighted UV-B, equivalent to that resulting from a c. 18% reduction in ozone column) under arrays of cellulose diacetate-filtered fluorescent UV-B lamps that also produced UV-A radiation (315,400 nm). Saplings were also exposed to elevated UV-A radiation alone under arrays of polyester-filtered fluorescent lamps and to ambient solar radiation under arrays of nonenergized lamps. After 8 months of irradiation, abscised leaves were placed into litter bags and allowed to decompose in the litter layer of a mixed deciduous woodland for 4.08 years. The dry weight loss of leaf litter from saplings irradiated with elevated UV-B and UV-A radiation during growth was 17% greater than that of leaf litter irradiated with elevated UV-A radiation alone. Annual fractional weight loss of litter (k), and the estimated time taken for 95% of material to decay (3/k) were respectively increased and decreased by 27% for leaf litter exposed during growth to elevated UV-B and UV-A radiation, relative to that exposed to UV-A alone. The present data corroborate those from a previous study indicating that UV-B radiation applied during growth accelerates the subsequent decomposition of Q. robur leaf litter in soil, but indicate that this effect persists for over four years after abscission. [source] Decomposition of litter in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern AustraliaHYDROLOGICAL PROCESSES, Issue 17 2002R. H. Crockford This study of litter decomposition was part of an extensive project examining the partitioning of rainfall, the associated chemistry, and litterfall in a dry sclerophyll eucalypt forest and a Pinus radiata plantation in southeastern Australia. The eucalypt species studied were Eucalyptus rossii, E. mannifera and E. dives. The components tested were Pinus radiata needles, leaves of the three eucalypt species, and the bark of E. rossii and E. mannifera. During the first 16 weeks of the decomposition experiment there was a rapid decrease in the concentrations of potassium, magnesium, sodium and phosphorus; this was attributed to leaching. During this period, concentrations of nitrogen and calcium increased for most components. After this period, decomposition became the dominant process, during which the concentrations of most elements increased. By the end of the experiment there was, compared with the initial values, a marked reduction in concentrations of sodium, magnesium and potassium for all eucalypt and pine litter. Calcium concentrations increased through time, with eucalypt bark showing a mid-period decline. Phosphorus concentrations decreased for the eucalypt leaves but increased substantially for the pine needles and the eucalypt bark. For all components of both the eucalypts and pines, total nitrogen concentrations rose consistently throughout the decomposition period. This was attributed to the formation of nitrogen-substituted lignin, which was more resistant to decomposition than the other nitrogen-containing compounds, as well as some nitrogen being stored in the micro-organisms responsible for decomposition. Because of loss of fragmented litter from the litter bags after 16 weeks, the weight changes could not be confidently measured after this period. Copyright © 2002 John Wiley & Sons, Ltd. [source] USING STREAM BIOASSESSMENT PROTOCOLS TO MONITOR IMPACTS OF A CONFINED SWINE OPERATION,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2006Jeffrey Jack ABSTRACT: The processing of waste from confined animal feeding operations (CAFOs) presents a major environmental challenge. Treatment of waste and subsequent land application is a common best management practice (BMP) for these operations in Kentucky, USA, but there are few data assessing the effect of runoff from such operations on aquatic communities. The authors sampled a stream bordering a CAFO with a land application program to determine if runoff from the fertilized fields was adversely affecting stream communities. Water chemistry, periphyton, and macroinvertebrate samples from riffle habitats downstream of the CAFO were compared to samples collected from an upstream site and a control stream in 1999 and 2000. Riffle communities downstream of the fertilized fields had higher chlorophyll a levels than other sites, but there were no significant differences in macroinvertebrate numbers or in biometrics such as taxa richness among the sites. The BMP in place at this site may be effective in reducing this CAFO's impact on the stream; however, similar assessments at other CAFO sites should be done to assess their impacts. Functional measures such as nutrient retention and litter decomposition of streams impacted by CAFOs should also be investigated to ensure that these operations are not adversely affecting stream communities. [source] Evidence that saprotrophic fungi mobilise carbon and mycorrhizal fungi mobilise nitrogen during litter decompositionNEW PHYTOLOGIST, Issue 3 2007Erik A. Hobbie No abstract is available for this article. [source] Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forestNEW PHYTOLOGIST, Issue 3 2007Björn D. Lindahl Summary ,,Our understanding of how saprotrophic and mycorrhizal fungi interact to re-circulate carbon and nutrients from plant litter and soil organic matter is limited by poor understanding of their spatiotemporal dynamics. ,,In order to investigate how different functional groups of fungi contribute to carbon and nitrogen cycling at different stages of decomposition, we studied changes in fungal community composition along vertical profiles through a Pinus sylvestris forest soil. We combined molecular identification methods with 14C dating of the organic matter, analyses of carbon:nitrogen (C:N) ratios and 15N natural abundance measurements. ,,Saprotrophic fungi were primarily confined to relatively recently (< 4 yr) shed litter components on the surface of the forest floor, where organic carbon was mineralized while nitrogen was retained. Mycorrhizal fungi dominated in the underlying, more decomposed litter and humus, where they apparently mobilized N and made it available to their host plants. ,,Our observations show that the degrading and nutrient-mobilizing components of the fungal community are spatially separated. This has important implications for biogeochemical studies of boreal forest ecosystems. [source] Insect herbivores and their frass affect Quercus rubra leaf quality and initial stages of subsequent litter decompositionOIKOS, Issue 1 2008Christopher J. Frost Defoliation-induced changes in plant foliage are ubiquitous, though factors mediating induction and the extent of their influence on ecosystem processes such as leaf litter decomposition are poorly understood. Soil nitrogen (N) availability, which can be affected by insect herbivore frass (feces), influences phytochemical induction. We conducted experiments to test the hypotheses that insect frass deposition would (1) reduce phytochemical induction following herbivory and (2) increase the decomposition and nutrient release of the subsequent leaf litter. During the 2002 growing season, 80 Quercus rubra saplings were subjected to a factorial experiment with herbivore and frass manipulations. Leaf samples were collected throughout the growing season to measure the effects of frass deposition on phytochemical induction. In live foliage, herbivore damage increased tannin concentrations early, reduced foliar N concentrations throughout the growing season, and lowered lignin concentrations in the late season. Frass deposition apparently reduced leaf lignin concentrations, but otherwise did not influence leaf chemistry. Following natural senescence, litter samples from the treatment groups were decomposed in replicated litterbags for 18 months at the Coweeta Hydrologic Laboratory, NC. In the dead litter samples, initial tannin concentrations were lower in the herbivore damage group and higher in the frass addition group relative to their respective controls. Tannin and N release rates in the first nine months of decomposition were also affected by both damage and frass. However, decomposition rates did not differ among treatment groups. Thus, nutrient dynamics important for some ecosystem processes may be independent from the physical loss of litter mass. Overall, while lingering effects of damage and even frass deposition can therefore carry over and affect ecosystem processes during decomposition, their effects appear short lived relative to abiotic forces that tend to homogenize the decomposition process. [source] The interaction of plant genotype and herbivory decelerate leaf litter decomposition and alter nutrient dynamicsOIKOS, Issue 1 2005Jennifer A. Schweitzer We examined how plant genetic variation and a common herbivore (the leaf-galling aphid, Pemphigus betae) influenced leaf litter quality, decomposition, and nutrient dynamics in a dominant riparian tree (Populus spp.). Based on both observational studies and a herbivore exclusion experiment using trees of known genotype, we found four major patterns: 1) the quality of galled vs non-galled or gall-excluded litter significantly differed in the concentration of condensed tannins, lignin, nitrogen and phosphorus; 2) the difference in litter quality resulted in galled litter decomposing at rates 34 to 40% slower than non-galled litter; 3) plant genotype and herbivory had similar effects on the magnitude of decomposition rate constants; and 4) plant genotype mediated the herbivore effects on leaf litter quality and decomposition, as there were genotype-specific responses to herbivory independent of herbivore density. In contrast to other studies that have demonstrated accelerated ecosystem properties in response to arthropod herbivory, our findings argue that herbivore-induced secondary compounds decelerated ecosystem properties though their "after-life" effects on litter quality. Furthermore, these data are among the first to suggest that genotype-specific responses to herbivores can have a major impact on decomposition and nutrient flux, which likely has important consequences for the spatial distribution of nutrients at the landscape level. Due to the magnitude of these effects, we contend that it is important to incorporate a genetic perspective into ecosystem studies. [source] Phenotypic diversity and litter chemistry affect nutrient dynamics during litter decomposition in a two species mixOIKOS, Issue 1 2004Michael D. Madritch We have previously demonstrated that the intraspecific diversity of leaf litter can influence ecosystem functioning during litter decomposition in the field. It is unknown whether the effects of phenotypic diversity persist when litter from an additional species is present. We used laboratory microcosms to determine whether the intraspecific diversity effects of turkey oak leaf litter on nutrient dynamics are confounded by the presence of naturally co-occurring longleaf pine litter. We varied the phenotypic diversity of oak litter (1, 3, and 6 phenotype combinations) in the presence and absence of pine litter and measured fluxes of carbon and nitrogen over a 42-week period. The average soil C:N ratio peaked at intermediate levels of oak phenotypic diversity and the total amount of dissolved organic carbon leached from microcosms decreased (marginally) with increasing oak phenotypic diversity. The soil carbon content, and the total amount of ammonium, nitrate, and dissolved organic carbon leached from microcosms were all influenced by initial litter chemistry. Our results suggest that the effects of phenotypic diversity can persist in the presence of another species, however specific litter chemistries (condensed and hydrolysable tannins, simple phenolics, C:N ratios) are more important than phenotypic litter diversity to most nutrient fluxes during litter decomposition. [source] Decomposition dynamics in mixed-species leaf litterOIKOS, Issue 2 2004Tracy B. Gartner Literature on plant leaf litter decomposition is substantial, but only in recent years have potential interactions among leaves of different species during decomposition been examined. We review emerging research on patterns of mass loss, changes in nutrient concentration, and decomposer abundance and activity when leaves of different species are decaying in mixtures. Approximately 30 papers have been published that directly examine decomposition in leaf mixtures as well as in all component species decaying alone. From these litter-mix experiments, it is clear that decomposition patterns are not always predictable from single-species dynamics. (Characteristics of decomposition in litter-mixes that deviate from responses predicted from decomposition of single-species litters alone are designated "non-additive"; "additive" responses in mixes are predictable from component species decaying alone.) Non-additive patterns of mass loss were observed in 67% of tested mixtures; mass loss is often (though not always) increased when litters of different species are mixed. Observed mass loss in some mixtures is as much as 65% more extensive than expected from decomposition of single-species litter, but more often mass loss in mixtures exceeds expected decay by 20% or less. Nutrient transfer among leaves of different species is striking, with 76% of the mixtures showing non-additive dynamics of nutrient concentrations. Non-additive patterns in the abundance and activity of decomposers were observed in 55% and 65% of leaf mixes, respectively. We discuss some methodological details that likely contribute to conflicting results among mixed-litter studies to date. Enough information is available to begin formulating mechanistic hypotheses to explain patterns in litter-mix experiments. Emerging patterns in the mixed-litter decomposition literature have implications for relationships between biodiversity and ecosystem function (in this case, the function being decomposition), and for potential mechanisms through which invasive plant species could alter carbon and nutrient dynamics in ecosystems. [source] Environmental factors affecting Phragmites australis litter decomposition in Mediterranean and Black Sea transitional watersAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2008F. Sangiorgio Abstract 1. Leaf litter decomposition rates in aquatic ecosystems are known to be related to many abiotic and biotic factors. 2. Field experiments were carried out during spring 2005 in 16 ecosystems, each with four sampling sites, using the litter bag technique to investigate the influence of abiotic factors on patterns of reed litter breakdown in different physiographic, hydrological and physico-chemical gradients occurring in transitional water ecosystems in the Eastern Mediterranean and Black Sea. 3. Significant differences in leaf litter decomposition were observed among the studied ecosystems along univariate gradients of tidal range, water temperature, salinity and sinuosity index. 4. Overall, 71% of variance in the litter breakdown rate was explained by the hydrological, physico-chemical and physiographic components. Specifically, tidal range, salinity and sinuosity index are among the key factors in the most commonly used typological schemes for classifying transitional water ecosystems (i.e. Confinement Concept and Venice System), due to their influence on abundance and distribution of benthic macroinvertebrates and other guilds. 5. The patterns observed at the regional scale of the study suggest that certain key abiotic factors are likely to play a major role as drivers of plant detritus decomposition processes, through their influence on the overall metabolism of microorganisms and benthic macroinvertebrates. 6. These observations have implications for the identification of reference conditions for transitional water ecosystems in the studied area, on which all processes of classification and conservation of their ecological status are based. Copyright © 2008 John Wiley & Sons, Ltd. [source] Non-symbiotic nitrogen fixation during leaf litter decomposition in an old-growth temperate rain forest of Chiloé Island, southern Chile: Effects of single versus mixed species litterAUSTRAL ECOLOGY, Issue 2 2010CECILIA A. PÉREZ Abstract Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old-growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy-rich substrate that favours the occurrence of this energy demanding process. Following the niche ,complementarity hypothesis', we expected that decomposing leaf litter of a single tree species would support lower rates of non-symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50,79) in an old-growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova, Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h,1 g,1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h,1 g,1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h,1 g,1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h,1g,1). We interpret these results as follows: in N-poor litter and high lignin content of leaves (e.g. N. nitida) free-living N fixers would be at competitive advantage over non-fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization. [source] Direct and indirect effects of climate on decomposition in native ecosystems from central ArgentinaAUSTRAL ECOLOGY, Issue 7 2007NATALIA PÉREZ-HARGUINDEGUY Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central-western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems. [source] Litter decomposition in a sandy Monte desert of western Argentina: Influences of vegetation patches and summer rainfallAUSTRAL ECOLOGY, Issue 7 2006EDUARDO PUCHETA Abstract: We tested the hypothesis that shrub canopies interact with monthly rain pulses to control litter decomposition in a sandy Monte desert, in Argentina. We assessed (i) the potential for litter decomposition of soils beneath the canopies of two dominant shrub species (Larrea divaricata and Bulnesia retama, Zygophyllaceae R. Br.) and from bare-ground microsites or ,openings'; (ii) litter decomposition at different spatial patches over the summer rainy season; and (iii) the interaction between vegetation patches and monthly rain pulses on short-term litter decomposition, or decomposition pulses. In a greenhouse experiment, we found buried litter decomposition to be higher in soils from under the canopies of a dominant shrub species compared with soils from openings and sterilized controls. This, and higher nutrient concentration under shrub soils, suggest undercanopy soils may support a microbial community capable of decomposing litter at higher rates than soils in bare openings. However, ,eld trials showed that shrub patches did not affect leaf litter decomposition over the rainy season, at least for short periods. We found an interaction between shrub patches and incubation time at the end of the ,eld experiment, with higher litter decomposition rates under B. retama canopies. In a monthly ,eld experiment, we found monthly rain pulses signi,cantly explained decomposition pulses, irrespective of patch type. Our ,ndings support the hypothesis that shrub soils have a greater potential for litter decomposition, but this is not directly translated to the ,eld possibly due to interactions with abiotic factors. Rain pulses create conditions for decomposition pulses to occur at shorter time scales, whereas rainfall may interact with a dominant shrub undercanopy to control litter mass loss over longer time scales. [source] Evaluation of macrofaunal effects on leaf litter breakdown rates in aquatic and terrestrial habitatsAUSTRAL ECOLOGY, Issue 6 2006AUGUSTO C. DE A. RIBAS Abstract Decomposition of the organic matter is a key process in the functioning of aquatic and terrestrial ecosystems, although different factors influence processing rates between and within these habitats. Most patterns were described for temperate regions, with fewer studies in tropical, warmer sites. In this study, we carried out a factorial experiment to compare processing rates of mixed species of leaf litter between terrestrial and aquatic habitats at a tropical site, using ,ne and coarse mesh cages to allow or prevent colonization by macroinvertebrates. The experiment was followed for 10 weeks, and loss of leaf litter mass through time was evaluated using exponential models. We found no interaction between habitat and mesh size and leaf litter breakdown rates did not differ between ,ne and coarse mesh cages, suggesting that macroinvertebrates do not influence leaf litter decomposition in either habitat at our studied site. Leaf breakdown rates were faster in aquatic than in terrestrial habitats and the magnitude of these differences were comparable to studies in temperate regions, suggesting that equivalent factors can influence between-habitat differences detected in our study. [source] The role of microarthropods in terrestrial decomposition: a meta-analysis of 40 years of litterbag studiesBIOLOGICAL REVIEWS, Issue 3 2009Christian Kampichler ABSTRACT Litterbags have been utilized in soil ecology for about 50 years. They are useful because they confine organic material and thus enable the study of decomposition dynamics (mass loss and/or nutrient loss through time, colonization by soil biota) in situ, i.e. under field conditions. Researchers can easily restrict or permit access to certain size classes of soil fauna to determine their contribution to litter mass loss by choosing adequate mesh size or applying specific biocides. In particular, the mesofauna has received much attention since it comprises two very abundant and diverse microarthropod groups, the Collembola (springtails) and Acari (mites). We comprehensively searched the literature from the mid-1960s to the end of 2005 for reports on litterbag experiments investigating the role of microarthropods in terrestrial decomposition. Thirty papers reporting 101 experiments satisfied our selection criteria and were included in the database. Our meta-analysis revealed that microarthropods have a moderate but significant effect on mass loss. We discuss in detail the interactions of the microarthropod effect with study characteristics such as experimental design (e.g. number of bags, duration of experiment), type of exposed organic matter, climatic zone and land use of the study site. No publication bias was detected; however, we noticed a significant decrease in the microarthropod effect with publication year, indicating that, in the first decades of litterbag use, soil zoologists may have studied "promising" sites with a higher a priori probability of positive microarthropod effects on litter mass loss. A general weakness is that the treatments differ not only with respect to the presence or absence of microarthropods, but also with regard to mesh size (small to exclude microarthropods, wide to permit their access) or presence (to exclude microarthropods) and absence (to permit their access) of an insecticide. Consequently, the difference between the decomposition rates in the treatments is not a pure microarthropod effect but will be influenced by the additive effects of mesh size and insecticide. The relative contribution of the "true" microarthropod effect remains unknown without additional treatments controlling for the differential mesh size/insecticide effect. A meta-analysis including only those studies using different mesh size and for which the data were corrected by subtracting an estimated mesh size effect based on data from the literature yielded a significantly negative microarthropod effect on litter decomposition. These results cast doubt on the widely accepted hypothesis that microarthropods generally exert a positive effect on litter mass loss. We conclude that after 40 years of litterbag studies our knowledge on the role of microarthropods in litter mass loss remains limited and that the inclusion of a third treatment in future studies is a promising way to retain litterbags as a meaningful tool of soil biological studies. [source] | |||||||||||||