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N Ratio (n + ratio)
Selected AbstractsInfluence of former agricultural land use on net nitrate production in forest soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2002J. H. Jussy Summary Except where nitrate is added to the soil artificially, nitrate is leached from forest soils only if it is produced. Although the factors influencing nitrification have been widely studied, nitrification activity still cannot be simply predicted from ecosystem characteristics. In France, about half of the present forest area was agricultural in 1850. Previous work suggested that former cultivation could be a major factor influencing nitrogen availability in forest soils. Using laboratory incubations, we compared the net production of ammonium and nitrate in soils from formerly manured lands planted with conifers 70,100 years ago with that in soils of surrounding ancient coniferous forests. Net nitrate production, available P content, and natural abundance of nitrogen 15, ,15N, were greater in soils from formerly manured plots than other land, whereas the C:N ratio of the soil was less. The difference in net nitrate production between previously manured sites and adjacent ancient forests was related to differences in ,15N values in the soil but not evidently to other soil properties. Because soil ,15N increases with the intensity of organic manuring, these results suggest that nitrification in forest soils depends on previous manurial practices under agriculture. In this context, the soil ,15N might be used as an indicator of both previous agricultural land use and potential nitrification. Because a significant proportion of West European forests grow on previously cultivated soils, past land use should be taken into account when evaluating the risks of nitrate leaching from forests. [source] Palatability of macrophytes to the invasive freshwater snail Pomacea canaliculata: differential effects of multiple plant traitsFRESHWATER BIOLOGY, Issue 10 2010PAK KI WONG Summary 1.,By selective grazing, invasive grazers can alter macrophyte-herbivore relationships in shallow freshwater bodies. Evaluating the palatability of macrophytes and understanding the determinants of plant palatability can help predict grazing impact. In no-choice feeding assays, we tested the palatability of 21 species of freshwater macrophytes to the invasive freshwater apple snail Pomacea canaliculata. 2.,Daily feeding rate varied greatly with plant species, ranging from 1.1 to 22% of snail body mass. We assessed six plant properties and examined their correlation with feeding rate. Total nitrogen content was positively related, and C:N ratio and dry matter content (DMC) negatively related, to snail feeding rate. There was no significant correlation between snail feeding rate and plant phenolic content, but the feeding rate on Myriophyllum aquaticum (the plant with the highest phenolic content) was very low. 3.,We repeated the feeding assays for 15 species that were not palatable as fresh leaves with reconstituted plant tissues formed by mixing ground up dried leaves with agar. The feeding rate still differed greatly among macrophyte species. Phragmites australis and Vallisneria natans (two species with the highest DMC) were eaten much more as reconstituted plant than as fresh leaves, indicating that structure (i.e. DMC) may be important in their defence against snail herbivory. For two plants (M. aquaticum and Alternanthera philoxeroides) that had moderate amounts of nitrogen/phosphorus but were consumed very little as fresh and reconstituted tissues, we incorporated their extracts into a palatable agar-based food. The extracts from both species greatly reduced snail feeding rate, indicating the presence of chemical defences in these two species. 4.,These results indicated that feeding was affected by several plant traits. The snail favoured plants with a high nitrogen content and avoided plants with a high DMC. Only a few plants possessed chemical feeding deterrents that were effective against this snail. Given the invasive spread of P. canaliculata in Asia, ecologists and managers should consider plant palatability when selecting plants for use in wetland restoration and when predicting the impact of further invasion by this species. [source] Photoheterotrophy and light-dependent uptake of organic and organic nitrogenous compounds by Planktothrix rubescens under low irradianceFRESHWATER BIOLOGY, Issue 10 2003Tatiana Zotina Summary 1. Planktothrix rubescens is the dominant photoautotrophic organism in Lake Zürich, a prealpine, deep, mesotrophic freshwater lake with an oxic hypolimnion. Over long periods of the year, P. rubescens accumulates at the metalimnion and growth occurs in situ at irradiance near the photosynthesis compensation point. Experiments were conducted to evaluate the contribution of photoheterotrophy, heterotrophy and light-dependent uptake of nitrogenous organic compounds to the carbon and nitrogen budget of this cyanobacterium under conditions of restricted availability of light quanta. 2. We used both purified natural populations of P. rubescens from the depth of 9 m and an axenic culture grown under low irradiance at 11 ,mol m,2 s,1 on a light : dark cycle (10 : 14 h) to determine the uptake rates of various amino acids, urea, glucose, fructose, acetate and inorganic carbon. The components were added to artificial lake water in low amounts that simulated the naturally occurring potential concentrations. 3. The uptake rates of acetate and amino acids (glycine, serine, glutamate and aspartate) were strongly enhanced at low irradiance as compared with the dark. However, no difference was observed in the uptake of arginine, which was taken up at high rates under both treatments. The uptake rates of glucose, fructose and urea were very low under all conditions. Similar results were obtained for both axenic P. rubescens and for purified natural populations of P. rubescens that were separated from bacterioplankton and other phytoplankton. 4. Metalimnetic P. rubescens that was stratified at low irradiance for weeks exhibited much higher uptake rates than filaments that were entrained in the deepening surface mixed layer and experienced higher irradiance. The added organic compounds contributed up to 62% to the total carbon uptake of metalimnetic P. rubescens. On the basis of a molar C : N ratio of 4.9, the nitrogen uptake as organic compounds satisfied up to 84% of the nitrogen demand. 5. The experiments indicate that photoheterotrophy and light-dependent uptake of nitrogenous organic compounds may contribute significantly to the carbon and nitrogen budget of filaments at low irradiance typical for growth of P. rubescens in the metalimnion and at the bottom of the surface mixed layer. [source] Allochthonous and autochthonous particulate organic matter in floodplains of the River Danube: the importance of hydrological connectivityFRESHWATER BIOLOGY, Issue 2 2003Thomas Hein SUMMARY 1.,The elemental composition, the proportion of living organic carbon and the carbon stable isotope signatures of particulate organic matter (POM) were determined in a large river floodplain system in order to elucidate the major carbon sources in relation to the hydrological conditions over a 13-month period. 2.,Two floodplain segments and the main channel of the River Danube downstream of Vienna (Austria), were compared on the basis of discharge and water age estimations. The more dynamic floodplain was connected to the main channel for 46% of the study period and drained up to 12% of total discharge at high water. 3.,The mean C : N ratio and ,13C signature of the POM increased from the floodplain site that was more isolated from the river (6.6; ,33,) to the main channel (8.4; ,25,). At the dynamic floodplain site, the C : N ratio and the ,13C signature of the POM increased with hydrological connectivity (expressed as water age). 4.,Only during flood events (4% frequency of occurrence), a considerable input of riverine POM was observed. This input was indicated by a C : N ratio of the POM pool of more than 10, the amount of detrital carbon (>80% of the total POM pool) and a ,13C signature of POM of more than ,25, in the dynamic floodplain. 5.,Plankton derived carbon, indicated by C : N ratios less than eight and ,13C values lower than ,25,, dominated the particulate organic carbon (POC) pool at both floodplain sites, emphasising the importance of local (autochthonous) production. Phytoplankton was the major plankton compartment at the dynamic site, with highest biomasses at medium water ages. 6.,At the dynamic floodplain site, the Danube Restoration Project has enhanced the duration of upstream surface connection with the main channel from 4 to 46% frequency of occurrence. Therefore, the export of living POC to the main channel is now established during phases of maximum phytoplankton production and doubled the estimated total export of non-refractory POM compared with prerestoration conditions. [source] Effects of augmentation of coarse particulate organic matter on metabolism and nutrient retention in hyporheic sedimentsFRESHWATER BIOLOGY, Issue 10 2002C. L. Crenshaw SUMMARY 1.,Metabolic and biogeochemical processes in hyporheic zones may depend on inputs of coarse particulate organic matter. Our research focused on how differing quantity and quality of organic matter affects metabolism and nutrient retention in the hyporheic zone of a first-order Appalachian stream. 2.,Sixteen plots were established on a tributary of Hugh White Creek, NC, U.S.A. Sediment was extracted and treated with leaves, wood, plastic strips or remained unamended. Following treatment, sediment was returned to the stream and, approximately 3 months later, samples were removed from each plot. 3.,Aerobic and anaerobic metabolism were measured as the change in O2 and CO2 in recirculating microcosms. At the same time, we monitored other possible terminal electron accepting processes and changes in nutrient concentrations. Aerobic metabolism was low in all treatments and respiratory quotients calculated for all treatments indicated that metabolism was dominated by anaerobic processes. 4.,Rates of anaerobic respiration and total (combined aerobic and anaerobic) respiration were significantly greater (P < 0.05) in plots treated with leaf organic matter compared to controls. 5.,Addition of leaves, which had a low C:N ratio, stimulated respiration in hyporheic sediments. Anaerobic processes dominated metabolism in both control and amended sediments. Enhanced metabolic rates increased retention of many solutes, indicating that energy flow and nutrient dynamics in the subsurface of streams may depend upon the quantity and quality of imported carbon. [source] Plant species traits and capacity for resource reduction predict yield and abundance under competition in nitrogen-limited grasslandFUNCTIONAL ECOLOGY, Issue 3 2006J. FARGIONE Summary 1The objective of this study is to test whether plant traits that are predicted by resource-competition theory to lead to competitive dominance are correlated with competitive response and abundance in a nitrogen-limited grassland. We collected species trait and soil nutrient data on non-leguminous perennial prairie plant species in replicated monoculture plots established for this purpose. 2The soil nitrate concentration of 13 species grown in long-term (5-year) monocultures (a measure of R*) was correlated with their relative yield (a measure of competitive response) and with their abundance in competition. The trait best correlated with a species' relative yield was root length density (RLD), and the trait best correlated with abundance in competition was biomass : N ratio. 3The traits that best predicted nitrate R* were the biomass : N ratio and allocation to fine roots, where species with higher biomass : N and allocation to fine roots had lower R*. Easily measured species traits may therefore be useful proxy measures for R*. 4The dominance of species with lower nitrate R* levels and higher RLD and biomass : N in monoculture is qualitatively consistent with the prediction of resource-competition theory that the species most efficient at acquiring, retaining and using the major limiting resource will be the best competitors. Additional mechanisms are needed to explain how these species coexist. [source] Solar UVB and warming affect decomposition and earthworms in a fen ecosystem in Tierra del Fuego, ArgentinaGLOBAL CHANGE BIOLOGY, Issue 10 2009JOHANN G. ZALLER Abstract Combined effects of co-occurring global climate changes on ecosystem responses are generally poorly understood. Here, we present results from a 2-year field experiment in a Carex fen ecosystem on the southernmost tip of South America, where we examined the effects of solar ultraviolet B (UVB, 280,315 nm) and warming on above- and belowground plant production, C : N ratios, decomposition rates and earthworm population sizes. Solar UVB radiation was manipulated using transparent plastic filter films to create a near-ambient (90% of ambient UVB) or a reduced solar UVB treatment (15% of ambient UVB). The warming treatment was imposed passively by wrapping the same filter material around the plots resulting in a mean air and soil temperature increase of about 1.2 °C. Aboveground plant production was not affected by warming, and marginally reduced at near-ambient UVB only in the second season. Aboveground plant biomass also tended to have a lower C : N ratio under near-ambient UVB and was differently affected at the two temperatures (marginal UVB × temperature interaction). Leaf decomposition of one dominant sedge species (Carex curta) tended to be faster at near-ambient UVB than at reduced UVB. Leaf decomposition of a codominant species (Carex decidua) was significantly faster at near-ambient UVB; root decomposition of this species tended to be lower at increased temperature and interacted with UVB. We found, for the first time in a field experiment that epigeic earthworm density and biomass was 36% decreased by warming but remained unaffected by UVB radiation. Our results show that present-day solar UVB radiation and modest warming can adversely affect ecosystem functioning and engineers of this fen. However, results on plant biomass production also showed that treatment manipulations of co-occurring global change factors can be overridden by the local climatic situation in a given study year. [source] Combined effects of elevated temperatures and reduced leaf litter quality on the life-history parameters of a saprophagous macroarthropodGLOBAL CHANGE BIOLOGY, Issue 1 2009JEAN-FRANCOIS DAVID Abstract Because soil macroinvertebrates strongly modify decomposition processes, it is important to know how their abundance will respond to global change. We investigated in laboratory microcosms, the effects of elevated temperatures and reduced leaf litter quality on the life-history traits of a saprophagous macroarthropod (development time, growth, survival and reproduction). Millipedes (Polydesmus angustus) from an Atlantic temperate forest were reared throughout their life cycle (,16 months) under two temperature regimes differing on average by 3.3 °C; in a factorial design, they were fed either on Atlantic leaf litter or on Mediterranean leaf litter with a higher C : N ratio; humidity was consistently high. The components of the population growth rate (r) were affected positively by the temperature rise and negatively by the switch from Atlantic to Mediterranean leaf litter. When both treatments were combined, litter effects offset temperature effects. These results show that the short-term response of saprophagous macroarthropods to warming is positive but depends on the availability of high-quality litter, which is difficult to predict in the global change context. In a parallel experiment, conspecific millipedes from a Mediterranean population, which have evolved for a long time in a warmer climate and on poor-quality litter, were reared at elevated temperatures on Mediterranean leaf litter. All components of r were higher than in the Atlantic population under the same conditions. This suggests that in the longer term, macroarthropods can overcome detrimental trophic interactions. Based on our study and the literature, we conclude that for decades the positive effects of warming on saprophagous macrofauna should exceed the negative effects of changes in litter quality. The abundance of those organisms in temperate forests could increase, which is confirmed by latitudinal patterns in Europe. Studies aimed at predicting the impacts of global change on decomposition will need to consider interactions with soil macroinvertebrates. [source] Loss of forb diversity in relation to nitrogen deposition in the UK: regional trends and potential controlsGLOBAL CHANGE BIOLOGY, Issue 10 2006CARLY J. STEVENS Abstract In this study we investigate the impact of nitrogen (N) deposition on the diversity of three different vegetation functional groups , forbs, grasses and mosses , using a field survey of acid grasslands across Great Britain. Our aim is to identify the vegetation types that are most vulnerable to enhanced N deposition, and to shed light on the mechanisms that may be driving N-initiated species changes in the UK. Sixty-eight randomly selected grasslands belonging to the UK National Vegetation Classification group U4 (Festuca ovina,Agrostis capillaris,Galium saxatile grassland) were studied along a gradient of atmospheric N deposition ranging from 6 to 36 kg N ha,1 yr,1. At each site, vegetation was surveyed and samples were taken from the topsoil and subsoil. Aboveground plant material was collected from three species: a forb, grass and moss. Both the species richness and cover of forbs declined strongly with increasing N deposition, from greater than eight species/20% cover per m2 quadrat at low levels of N to fewer than two species/5% cover at the highest N deposition levels. Grasses showed a weak but significant decline in species richness, and a trend toward increasing cover with increasing N input. Mosses showed no trends in either species richness or cover. Most of the decline in plant species richness could be accounted for by the level of ammonium deposition. Soil KCl-extractable ammonium concentration showed a significant positive correlation with N input, but there was no relationship between N deposition and extractable nitrate. In the soil O/A horizon, there was no relationship between N deposition and %N, and only a very weak positive relationship between the level of N deposition and the C : N ratio. Finally, in the vegetation, there was no relationship between N deposition and either shoot tissue N concentration or N : P ratio for any of the three reference species. Combining our regional survey with the results of published N-addition experiments provides compelling evidence that there has been a significant decline in the species richness and cover of forbs across Great Britain, and that the primary cause is competition due to an increase in the cover of grasses in response to enhanced deposition of reactive N, primarily NH4+. [source] Electron Transport System (ETS) Activity in Alder Leaf Litter in Two Contrasting Headwater StreamsINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4-5 2007Tadeusz Fleituch Abstract Decomposition rates, carbon and nitrogen concentrations and respiration electron transport (ETS) activity in alder leaf litter were examined by bag exposition method in two contrasting 2nd order streams. Oberer Seebach, Austria (alpine, limestone, karstic) and Goscibia, Poland (sub mountain, flysh) contrasted in catchment geology, channel hydrology, thermal regime and water chemistry. Despite differences in water temperature, the breakdown rates did not show statistical differences. However, the C:N ratio in alder leaf litter varied significantly between two sites. The potential ETS activity was significantly higher in the colder Goscibia and weakly related to stream thermal regimes. The effect of temperature on ETS of alder leaves was not the dominating factor. It was masked by variation of other factors like stream chemistry and the contribution of fine sediments, which are related to stream morphology and channel hydrology. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Geochemistry of peridotite xenoliths in alkali basalts from Jeju Island, KoreaISLAND ARC, Issue 4 2002SEONG HEE CHOI Abstract Ultramafic xenoliths in alkali basalts from Jeju Island, Korea, are mostly spinel lherzolites with subordinate amounts of spinel harzburgites and pyroxenites. The compositions of major oxides and compatible to moderately incompatible elements of the Jeju peridotite xenoliths suggest that they are residues after various extents of melting. The estimated degrees of partial melting from compositionally homogeneous and unfractionated mantle to form the residual xenoliths reach 30%. However, their complex patterns of chondrite-normalized rare earth element, from light rare earth element (LREE)-depleted through spoon-shaped to LREE-enriched, reflect an additional process. Metasomatism by a small amount of melt/fluid enriched in LREE followed the former melt removal, which resulted in the enrichment of the incompatible trace elements. Sr and Nd isotopic ratios of the Jeju xenoliths display a wide scatter from depleted mid-oceanic ridge basalt (MORB)-like to near bulk-earth estimates along the MORB,oceanic island basalt (OIB) mantle array. The varieties in modal proportions of minerals, (La/Yb)N ratio and Sr-Nd isotopes for the xenoliths demonstrate that the lithospheric mantle beneath Jeju Island is heterogeneous. The heterogeneity is a probable result of its long-term growth and enrichment history. [source] Optimization of C:N ratio and minimal initial carbon source for poly(3-hydroxybutyrate) production by Bacillus megateriumJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2009Débora Jung Luvizetto Faccin Abstract BACKGROUND: The aim of this research was the optimization of poly(3-hydroxybutyrate),P(3HB),production in submerged cultures of Bacillus megaterium in a mineral medium using sucrose as carbon source and nitrogen as the limiting substrate. Small-scale experiments were carried out in shake flasks at 30 °C and 160 rpm in order to evaluate the best initial sucrose concentration and carbon:nitrogen ratio to maximize biomass accumulation and biopolymer production. An objective function in terms of residual sucrose and P(3HB) production was proposed in order to optimize the amount of carbon source used and the production of P(3HB). RESULTS: High production of P(3HB) was obtained, with approximately 70% (CDW) accumulation in cells without nitrogen limitation and strongly correlated with the pH of the culture. Scaling-up the system to cultures in a bioreactor, with or without pH control, a reduction of P(3HB) accumulation (around 30% CDW) was observed when compared with shaker cultures, suggesting a possible role of oxygen limitation as a stress signaling for P(3HB) synthesis. CONCLUSIONS: Results of our experiments showed that Bacillus megaterium was able to produce P(3HB) at one of the highest production rates so far reported for this bacterium, making this microorganism very interesting for industrial applications. Comparisons of shaker and bench-scale bioreactor experiments show both the importance of pH and aeration strategies. It is likely that complex aeration strategies linked to cell metabolism will be necessary for further developments using this bacterium. Copyright © 2009 Society of Chemical Industry [source] Soil N dynamics in relation to leaf litter quality and soil fertility in north-western Patagonian forestsJOURNAL OF ECOLOGY, Issue 2 2003Patricia Satti Summary 1We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens. Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality. N dynamics were assessed in two consecutive years with contrasting precipitation. 2Net N mineralization was lower in stands of the three conifers and one of three broad-leaf evergreen species than in stands of the other six broad-leaf species (40,77 vs. 87,250 mg N kg,1 after 16-week incubations) and higher in the wetter year. 3The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year. Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture. 4Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species. Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses. 5Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23,28) in all broad-leaf species made it a poor predictor of the differences found within this group. Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N. [source] How to account for the lipid effect on carbon stable-isotope ratio (,13C): sample treatment effects and model biasJOURNAL OF FISH BIOLOGY, Issue 4 2008K. Mintenbeck This study investigated the impact of lipid extraction, CaCO3 removal and of both treatments combined on fish tissue ,13C, ,15N and C:N ratio. Furthermore, the suitability of empirical ,13C lipid normalization and correction models was examined. ,15N was affected by lipid extraction (increase of up to 1·65,) and by the combination of both treatments, while acidification alone showed no effect. The observed shift in ,15N represents a significant bias in trophic level estimates, i.e. lipid-extracted samples are not suitable for ,15N analysis. C:N and ,13C were significantly affected by lipid extraction, proportional to initial tissue lipid content. For both variables, rates of change with lipid content (,C:N and ,,13C) were species specific. All tested lipid normalization and correction models produced biased estimates of fish tissue ,13C, probably due to a non-representative database and incorrect assumptions and generalizations the models were based on. Improved models need a priori more extensive and detailed studies of the relationships between lipid content, C:N and ,13C, as well as of the underlying biochemical processes. [source] IMPACT OF IRON LIMITATION ON THE PHOTOSYNTHETIC APPARATUS OF THE DIATOM CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)JOURNAL OF PHYCOLOGY, Issue 6 2001Margaret Davey Iron starvation induced marked increases in flavodoxin abundance and decreases in light-saturated and light-limited photosynthesis rates in the diatom Chaetoceros muelleri. Consistent with the substitution of flavodoxin for ferredoxin as an early response to iron starvation, increases of flavodoxin abundance were observed before declines of cell division rate or chl a specific photosynthesis rates. Changes in the abundance of flavodoxin after the addition of iron to iron-starved cells indicated that flavodoxin was not actively degraded under iron-replete conditions. Greater declines in light-saturated oxygen evolution rates than dark oxygen consumption rates indicated that the mitochondrial electron transfer chain was not affected as greatly by iron starvation as the photosynthetic electron transfer chain. The carbon:nitrogen ratio was unaffected by iron starvation, suggesting that photosynthetic electron transfer was a primary target of iron starvation and that reductions in nitrate assimilation were due to energy limitation (the C:N ratio would be expected to rise under nitrogen-limited but energy-replete conditions). Parallel changes were observed in the maximum light-saturated photosynthesis rate and the light-limited initial slope of the photosynthesis-light curve during iron starvation and recovery. The lowest photosynthesis rates were observed in iron-starved cells and the highest values in iron-replete cells. The light saturation parameter, Ik, was not affected by iron starvation, nor was the chl-to-C ratio markedly reduced. These observations were consistent with iron starvation having a similar or greater effect on photochemical charge separation in PSII than on downstream electron transfer steps. Declines of the ratio of variable to maximum fluorescence in iron-starved cells were consistent with PSII being a primary target of iron starvation. The functional cross-section of PSII was affected only marginally (<20%) by iron starvation, with the largest values observed in iron-starved cells. The rate constant for electron transfer calculated from fast repetition rate fluorescence was found to covary with the light-saturated photosynthesis rate; it was lowest in the most severely starved cells. [source] Abiotic soil properties and the occurrence of Rhizoctonia crown and root rot in sugar beetJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2009Jürgen Kühn Abstract Since 1993, Rhizoctonia crown and root rot (Rhizoctonia solani AG 2,2 IIIB) has represented an increasing problem for sugar beet production in Germany. Up to now, the outbreak of the infection and the spread of the disease within a field cannot be predicted and effective countermeasures are not available. Although little is known about the living conditions of R. solani in soils, abiotic soil properties are likely to influence the disease occurrence. Investigations were carried out based on 60 pairwise comparisons, each consisting of a disease-affected and an adjacent nonaffected patch on farmers' fields in 2002 and 2003. Soil samples from the top soil layer (0,30,cm) were collected before harvest, and eight of the most frequently mentioned soil properties potentially influencing Rhizoctonia crown and root rot infection were examined: bulk density, texture, carbonate carbon, potassium, phosphorus, organic carbon, total nitrogen, and pH. The occurrence of the disease was significantly related to the soil C : N ratio, indicating the influence of soil organic matter on the disease occurrence. Examinations of soil thin sections showed that organic-matter particles in the soil serve as a substrate for R. solani. All other soil physical and chemical properties examined did not differ between the disease-affected and nonaffected patches and seem to be of minor importance. [source] Use of mid-infrared spectroscopy in the diffuse-reflectance mode for the prediction of the composition of organic matter in soil and litterJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2008Bernard Ludwig Abstract Mid-infrared spectroscopy (MIRS) is assumed to be superior to near-infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid-infrared region including part of the near-infrared region (7000,400,cm,1) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by 13C CPMAS-NMR spectroscopy. A partial least-square method and cross-validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid-infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF , 0.70, 0.8 , a , 1.2, r , 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O-alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl,to,aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse-reflectance mode were generally not superior to those of NIRS. [source] Soil properties and tree growth along an altitudinal transect in Ecuadorian tropical montane forestJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2008Wolfgang Wilcke Abstract In tropical montane forests, soil properties change with increasing altitude, and tree-growth decreases. In a tropical montane forest in Ecuador, we determined soil and tree properties along an altitudinal transect between 1960 and 2450 m asl. In different vegetation units, all horizons of three replicate profiles at each of eight sites were sampled and height, basal area, and diameter growth of trees were recorded. We determined pH and total concentrations of Al, C, Ca, K, Mg, Mn, N, Na, P, S, Zn, polyphenols, and lignin in all soil horizons and in the mineral soil additionally the effective cation-exchange capacity (CEC). The soils were Cambisols, Planosols, and Histosols. The concentrations of Mg, Mn, N, P, and S in the O horizons and of Al, C, and all nutrients except Ca in the A horizons correlated significantly negatively with altitude. The C : N, C : P, and C : S ratios increased, and the lignin concentrations decreased in O and A horizons with increasing altitude. Forest stature, tree basal area, and tree growth decreased with altitude. An ANOVA analysis indicated that macronutrients (e.g., N, P, Ca) and micronutrients (e.g., Mn) in the O layer and in the soil mineral A horizon were correlated with tree growth. Furthermore, lignin concentrations in the O layer and the C : N ratio in soil affected tree growth. These effects were consistent, even if the effect of altitude was accounted for in a hierarchical statistical model. This suggests a contribution of nutrient deficiencies to reduced tree growth possibly caused by reduced organic-matter turnover at higher altitudes. [source] A rapid method for assessment of plant residue qualityJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2003Praveen-Kumar Abstract A simple, reproducible and new method (modified dehydrogenase activity measurement after 72 h; DHA 72) was developed to assess plant residue quality for decomposition. The method resulted in similar assessments of residue quality than measurements of the C:N ratio, lignin:N ratio, and lignin and polyphenol concentration (PRQI). Among 25 plant residues tested, there was a large variation of DHA 72 as found in other well-established methods. Based on cluster analysis, plant residues were grouped in four different classes; highly decomposable, moderately decomposable, slowly decomposable, and least decomposable. It is concluded that DHA 72 can very well be used to screen plant residues for residue quality judgment. The proposed method is very simple and easy to handle. [source] Soil biochemical and chemical changes in relation to mature spruce (Picea abies) forest conversion and regenerationJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2003Zheke Zhong Abstract To investigate soil changes from forest conversion and regeneration, soil net N mineralization, potential nitrification, microbial biomass N, L-asparaginase, L-glutaminase, and other chemical and biological properties were examined in three adjacent stands: mature pure and dense Norway spruce (Picea abies (L.) Karst) (110 yr) (stand I), mature Norway spruce mixed with young beech (Fagus sylvatica) (5 yr) (stand II), and young Norway spruce (16 yr) (stand III). The latter two stands were converted or regenerated from the mature Norway spruce stand as former. The studied soils were characterized as having a very low pH value (2.9 , 3.5 in 0.01 M CaCl2), a high total N content (1.06 , 1.94,%), a high metabolic quotient (qCO2) (6.7 , 16.9 g CO2 kg,1 h,1), a low microbial biomass N (1.1 , 3.3,% of total N, except LOf1 at stand III), and a relatively high net N mineralization (175 , 1213 mg N kg,1 in LOf1 and Of2, 4 weeks incubation). In the converted forest (stand II), C,:,N ratio and qCO2 values in the LOf1 layer decreased significantly, and base saturation and exchangeable Ca showed a somewhat increment in mineral soil. In the regenerated forest (stand III), the total N storage in the surface layers decreased by 30,%. The surface organic layers (LOf1, Of2) possessed a very high net N mineralization (1.5 , 3 times higher than those in other two stands), high microbial biomass (C, N), and high basal respiration and qCO2 values. Meanwhile, in the Oh layer, the base saturation and the exchangeable Ca decreased. All studied substrates showed little net nitrification after the first period of incubation (2 weeks). In the later period of incubation (7 , 11 weeks), a considerable amount of NO3 -N accumulated (20 , 100,% of total cumulative mineral N) in the soils from the two pure spruce stands (I, III). In contrast, there was almost no net NO3 -N accumulation in the soils from the converted mixed stand (II) indicating that there was a difference in microorganisms in the two types of forest ecosystems. Soil microbial biomass N, mineral N, net N mineralization, L-asparaginase, and L-glutaminase were correlated and associated with forest management. Chemische und biochemische Veränderungen der Bodeneigenschaften durch Verjüngung und Waldumbau eines Fichtenaltbestandes Um die durch den Waldumbau und die Regeneration bedingten Standortsveränderungen zu untersuchen, wurden die Netto-Stickstoffmineralisierung, die potenzielle Nitrifikation, der mikrobiell gebundene Stickstoff (Nmic), L-Asparaginase, L-Glutaminase sowie weitere chemische und biologische Parameter an drei benachbarten Standorten untersucht: Standort I, reiner Fichtenaltbestand (Picea abies (L.) Karst ,110 Jahre); Standort II, Fichtenaltbestand mit Buchenunterbau (Fagus sylvatica , 5 Jahre); Standort III, reine Fichtenaufforstung (16 Jahre). Die Standorte II und III entstanden infolge des Waldumbaus aus reinen Fichtenaltbeständen. Die untersuchten Böden sind gekennzeichnet durch sehr niedrige pH-Werte (pH(H2O) 3, 7 , 4, 2, pH (CaCl2) 2, 9 , 3, 5), hohe Gesamtstickstoffgehalte (1, 06 , 1, 94,%), hohe metabolische Quotienten (6, 7,16, 9g CO2 kg,1 h,1), geringe Nmic -Gehalte (1, 1 , 3, 3,% des Gesamt-N, ausgenommen LOf1 von Standort III) und eine relativ hohe N-Nettomineralisation (175 , 1213 mg N Kg,1 in LOf1 und Of2, nach 4 Wochen Inkubation). Am Standort II nahm das C,:,N-Verhältnis und der qCO2 im LOf1 -Horizont deutlich ab, wohingegen der Gehalt an austauschbarem Ca sowie die Basensättigung im Mineralboden geringfügig zunahmen. Am Standort III nahm der N-Vorrat (Auflagehumus + Mineralboden 0 , 10,cm) um 30,% ab. In den LOf1 - und Of2 -Lagen des Auflagehumus dieses Standortes traten eine hohe N-Nettomineralisation (1, 5- bis 3fach höher als in den Standorten I und II), hohe Gehalte an mikrobiell gebundenem C und N, eine erhöhte Basalatmung sowie erhöhte qCO2 -Werte auf. In den Oh-Lagen hingegen nahm die Basensättigung ab. Alle untersuchten Standorte zeigten in der ersten Periode der Inkubation (0 bis 2 Wochen) eine geringe Netto-Nitrifikation. An den Standorten I und III fand in der späteren Periode (7. bis 11. Woche) eine Anreicherung an NO3 (20 , 100,% des gesamten mineralischen N-Vorrates) statt. Im Gegensatz dazu wurde am Standort II keine NO3 -N- Anreicherung festgestellt. Dies deutet auf einen Unterschied in der Zusammensetzung der mikrobiellen Gemeinschaften in den zwei verschiedenen Forstökosystemen hin. Nmic, N-Nettomineralisation, L-Asparaginase und L-Glutaminase korrelieren miteinander und zeigen eine enge Beziehung zu den Bewirtschaftungsformen. [source] Recalcitrant soil organic materials mineralize more efficiently at higher temperaturesJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2003Roland Bol Abstract As concentrations of atmospheric CO2 increase, it is important to know whether this may result in feedbacks that could modify the rate of increase of CO2 in the atmosphere. Soil organic matter (SOM) represents one of the largest pools of C and mineralization rates are known to be temperature dependent. In this study, we investigated whether different OM fractions present in a forest soil (F/A1 horizon) would respond in a similar manner to elevated temperatures. We examined the trends in isotopic content (12C, 13C, and 14C) of soil respired CO2 at various temperatures (10, 20, and 35 0C) over a two year period in the laboratory. We also examined the total C, total N, and C,:,N ratio in the remaining soil and isolated humic fractions, and the distribution of the individual amino acids in the soil after 5 years of laboratory incubation at the various temperatures. We found that the rate at which C mineralization increases with temperature was occasionally greater than predicted by most models, more C from recalcitrant OM pools being mineralized at the higher temperature. This confirmed that the relationship between soil organic matter decomposition and temperature was complex and that the different pools of organic matter did respond in differing ways to elevated temperatures. Rekalizitrante organische Bodensubstanz mineralisiert bei höheren Temperaturen effizienter Vor dem Hintergrund ansteigender atmosphärischer CO2 -Konzentrationen gewinnt die Erforschung möglicher Rückkopplungs-Mechanismen zunehmend an Bedeutung. Die organische Bodensubstanz stellt eines der größten terrestrischen C-Reservoirs dar. Die Rate der C-Mineralisation aus der organischen Bodensubstanz gilt allgemein als temperaturabhängig. In der hier vorgestellten Untersuchung sollte geprüft werden, ob verschiedene Fraktionen der organischen Bodensubstanz eines Waldstandortes (F/A1-Horizont) ähnlich stark auf erhöhte Temperaturen reagieren. Über einen Zeitraum von zwei Jahren wurde unter Laborbedingungen die Veränderung der Isotopen-Gehalte (12C, 13C und 14C) des bei verschiedenen Temperaturen (10, 20 und 35 °C) inkubierten Bodens untersucht. Ebenfalls erfasst wurden Gesamt-C, Gesamt-N und C,:,N-Verhältnis im Gesamt-Boden und in isolierten Humus-Fraktionen sowie das Verteilungsmuster der Aminosäuren im Boden nach fünfjähriger Inkubationsdauer. Die Ergebnisse zeigen, dass die temperaturbedingte Erhöhung der Mineralisationsrate in einigen Fällen deutlich stärker ausgeprägt ist, als anhand von Modellberechnungen erwartet wurde. Ursache hierfür ist unter erhöhten Temperaturen intensivere C-Mineralisation aus rekalzitranter organischer Bodensubstanz. Dies bestätigt unsere Vermutung, dass es keinen einfachen Zusammenhang zwischen Mineralisationsrate und Temperatur gibt, da verschiedene Humusbestandteile unterschiedlich auf erhöhte Temperaturen reagieren. [source] Importance of soils, topography and geographic distance in structuring central Amazonian tree communitiesJOURNAL OF VEGETATION SCIENCE, Issue 6 2008Stephanie A. Bohlman Abstract Question: What is the relative contribution of geographic distance, soil and topographic variables in determining the community floristic patterns and individual tree species abundances in the nutrient-poor soils of central Amazonia? Location: Central Amazonia near Manaus, Brazil. Methods: Our analysis was based on data for 1105 tree species (, 10 cm dbh) within 40 1-ha plots over a ca. 1000-km2 area. Slope and 26 soil-surface parameters were measured for each plot. A main soil-fertility gradient (encompassing soil texture, cation content, nitrogen and carbon) and five other uncorrelated soil and topographic variables were used as potential predictors of plant-community composition. Mantel tests and multiple regressions on distance matrices were used to detect relationships at the community level, and ordinary least square (OLS) and conditional autoregressive (CAR) models were used to detect relationships for individual species abundances. Results: Floristic similarity declined rapidly with distance over small spatial scales (0,5 km), but remained constant (ca. 44%) over distances of 5 to 30 km, which indicates lower beta diversity than in western Amazonian forests. Distance explained 1/3 to 1/2 more variance in floristics measures than environmental variables. Community composition was most strongly related to the main soil-fertility gradient and C:N ratio. The main fertility gradient and pH had the greatest impact of species abundances. About 30% of individual tree species were significantly related to one or more soil/topographic parameters. Conclusions: Geographic distance and the main fertility gradient are the best predictors of community floristic composition, but other soil variables, particularly C:N ratio, pH, and slope, have strong relationships with a significant portion of the tree community. [source] Soil restorative effects of mulching on aggregation and carbon sequestration in a Miamian soil in central OhioLAND DEGRADATION AND DEVELOPMENT, Issue 5 2003G. S. Saroa Abstract Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16,Mg,ha,1,yr,1 without crop cultivation. Soil samples from 0,5,cm and 5,10,cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0,5,cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per,cent after 4 years of mulching and 52 per,cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2,mm size after 4 years and up to 0,5,mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45,51 per,cent, silt by 34,36 per,cent, and to sand fraction by 15,19 per,cent. Bulk of the TSN (62,67 per,cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd. [source] Symbiont-mediated changes in Lolium arundinaceum inducible defenses: evidence from changes in gene expression and leaf compositionNEW PHYTOLOGIST, Issue 3 2007Terrence J. Sullivan Summary ,,Plants have multiple strategies to deal with herbivory, ranging from chemical or physical defenses to tolerating damage and allocating resources for regrowth. Grasses usually tolerate herbivory, but for some cool-season grasses, their strategy may depend upon their interactions with intracellular symbionts. Neotyphodium endophytes are common symbionts in pooid grasses, and, for some host species, they provide chemical defenses against both vertebrate and invertebrate herbivores. ,,Here, it was tested whether defenses provided by Neotyphodium coenophialum in Lolium arundinaceum (tall fescue) are inducible by both mechanical damage and herbivory from an invertebrate herbivore, Spodoptera frugiperda (fall armyworm), via a bioassay and by quantifying mRNA expression for lolC, a gene required for loline biosysnthesis. ,,Both mechanical and herbivore damage had a negative effect on the reproduction of a subsequent herbivore, Rhopalosiphum padi (bird cherry-oat aphid), and herbivore damage caused an up-regulation of lolC. Uninfected grass hosts also had significantly higher foliar N% and lower C : N ratio compared with infected hosts, suggesting greater allocation to growth rather than defense. ,,For L. arundinaceum, N. coenophialum appears to switch its host's defensive strategy from tolerance via compensation to resistance. [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] Arabidopsis transcript and metabolite profiles: ecotype-specific responses to open-air elevated [CO2]PLANT CELL & ENVIRONMENT, Issue 11 2008PINGHUA LI ABSTRACT A Free-Air CO2 Enrichment (FACE) experiment compared the physiological parameters, transcript and metabolite profiles of Arabidopsis thaliana Columbia-0 (Col-0) and Cape Verde Island (Cvi-0) at ambient (,0.375 mg g,1) and elevated (,0.550 mg g,1) CO2 ([CO2]). Photoassimilate pool sizes were enhanced in high [CO2] in an ecotype-specific manner. Short-term growth at elevated [CO2] stimulated carbon gain irrespective of down-regulation of plastid functions and altered expression of genes involved in nitrogen metabolism resembling patterns observed under N-deficiency. The study confirmed well-known characteristics, but the use of a time course, ecotypic genetic differences, metabolite analysis and the focus on clusters of functional categories provided new aspects about responses to elevated [CO2]. Longer-term Cvi-0 responded by down-regulating functions favouring carbon accumulation, and both ecotypes showed altered expression of genes for defence, redox control, transport, signalling, transcription and chromatin remodelling. Overall, carbon fixation with a smaller commitment of resources in elevated [CO2] appeared beneficial, with the extra C only partially utilized possibly due to disturbance of the C : N ratio. To different degrees, both ecotypes perceived elevated [CO2] as a metabolic perturbation that necessitated increased functions consuming or storing photoassimilate, with Cvi-0 emerging as more capable of acclimating. Elevated [CO2] in Arabidopsis favoured adjustments in reactive oxygen species (ROS) homeostasis and signalling that defined genotypic markers. [source] Nitrogen and carbon source,sink relationships in trees at the Himalayan treelines compared with lower elevationsPLANT CELL & ENVIRONMENT, Issue 10 2008MAI-HE LI ABSTRACT No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source,sink ratio of carbon; or (3) a sufficient C,N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source,sink relationship. [source] Seasonal variations in nitrate reductase activity and internal N pools in intertidal brown algae are correlated with ambient nitrate concentrationsPLANT CELL & ENVIRONMENT, Issue 6 2007ERICA B. YOUNG ABSTRACT Nitrogen metabolism was examined in the intertidal seaweeds Fucus vesiculosus, Fucus serratus, Fucus spiralis and Laminaria digitata in a temperate Irish sea lough. Internal NO3 - storage, total N content and nitrate reductase activity (NRA) were most affected by ambient NO3 - , with highest values in winter, when ambient NO3 - was maximum, and declined with NO3 - during summer. In all species, NRA was six times higher in winter than in summer, and was markedly higher in Fucus species (e.g. 256 ± 33 nmol NO3 - min,1 g,1 in F. vesiculosus versus 55 ± 17 nmol NO3 - min,1 g,1 in L. digitata). Temperature and light were less important factors for N metabolism, but influenced in situ photosynthesis and respiration rates. NO3 - assimilating capacity (calculated from NRA) exceeded N demand (calculated from net photosynthesis rates and C : N ratios) by a factor of 0.7,50.0, yet seaweeds stored significant NO3 - (up to 40,86 µmol g,1). C : N ratio also increased with height in the intertidal zone (lowest in L. digitata and highest in F. spiralis), indicating that tidal emersion also significantly constrained N metabolism. These results suggest that, in contrast to the tight relationship between N and C metabolism in many microalgae, N and C metabolism could be uncoupled in marine macroalgae, which might be an important adaptation to the intertidal environment. [source] Diminishing Spatial Heterogeneity in Soil Organic Matter across a Prairie Restoration ChronosequenceRESTORATION ECOLOGY, Issue 2 2005Diana R. Lane Abstract Habitat restoration resulting in changes in plant community composition or species dominance can affect the spatial pattern and variability of soil nutrients. Questions about how these changes in soil spatial heterogeneity develop over time at restoration sites, however, remain unaddressed. In this study, a geostatistical approach was used to quantify changes over time in the spatial heterogeneity of soil organic matter (SOM) across a 26-year chronosequence of tallgrass prairie restoration sites at FermiLab, outside of Chicago, Illinois. We used total soil N and C as an index of the quantity of SOM. We also examined changes in C:N ratio, which can influence the turnover of SOM. Specifically, the spatial structure of total N, total C, and C:N ratio in the top 10 cm of soil was quantified at a macroscale (minimum spacing of 1.5 m) and a microscale (minimum spacing of 0.2 m). The magnitude of spatial heterogeneity (MSH) was characterized as the proportion of total sample variation explained by spatially structured variation. At the macroscale, the MSH for total N decreased with time since restoration (r2= 0.99, p < 0.001). The decrease in spatial heterogeneity over time corresponded with a significant increase in the dominance of the C4 grasses. At the microscale, there was significant spatial structure for total N at the 4-year-old, 16-year-old, and 26-year-old sites, and significant spatial structure for total C at the 16-year-old and 26-year-old sites. These results suggest that an increase in dominance of C4 grasses across the chronosequence is homogenizing organic matter variability at the field scale while creating fine-scale patterns associated with the spacing of vegetation. Areas of higher soil moisture were associated with higher soil N and C at the two oldest restoration sites and at the native prairie site, potentially suggesting patches of increased belowground productivity in areas of higher soil moisture. This study is one of the first to report significant changes over time in the spatial structure of organic matter in response to successional changes initiated by restoration. [source] Land use legacies in post-agricultural forests in the Doupovské Mountains, Czech RepublicAPPLIED VEGETATION SCIENCE, Issue 2 2009Martin Kopecký Abstract Questions: Do differences in previous land use cause long-lasting changes in soil chemistry? Is vegetation composition affected by the previous land use after 50 years of secondary succession? Is the effect of previous land use caused by pre-existing differences in environmental conditions or mediated through changes in soil chemistry? How important is the effect of previous land use in relation to other factors? Location: Doupovské Mountains, Czech Republic. Methods: A stratified random sampling design was used to collect 91 vegetation relevés with accompanying soil samples. The effects of previous land use (arable field, meadow, pasture) on soil pH, organic carbon (C), total nitrogen (N), C:N ratio and available phosphorus were tested by an analysis of covariance. A canonical correspondence analysis and variation partitioning procedure were used to reveal relationships among previous land use, environmental factors and species composition. Results: Organic C, total N and C:N ratio were significantly influenced by previous land use, while available phosphorus and soil pH were not. Previous land use explained a significant part of the variation in species composition and its effects only partly overlapped with the effects of soil chemistry and terrain attributes. However, the species composition of post-agricultural forests was mostly determined by environmental factors not modified by previous land use. Conclusions: Forest communities that originate on abandoned agricultural land are primarily determined by natural environmental conditions. Nevertheless, the type of previous land use also modifies the species assemblages of these forests and needs to be considered as an important determinant of their composition. [source] | |||||||||||||||||||||||||||||||