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Soil Respiration (soil + respiration)

Distribution by Scientific Domains

Life Sciences	82%
Earth and Environmental Science	12%

Selected Abstracts

Effects of the herbicide hexazinone on nutrient cycling in a low-pH blueberry soil

ENVIRONMENTAL TOXICOLOGY, Issue 2 2004
D. M. Vienneau
Abstract The herbicide hexazinone was applied as the commercial formulation Velpar® L at field-rate (FR) concentrations of FR (14.77 ,g ai g,1), FR×5 (73.85 ,g ai g,1), FR×10 (147.70 ,g ai g,1), FR×50 (738.50 ,g ai g,1), and FR×100 (1477.00 ,g ai g,1) to acidic soil, pH 4.12, taken from a lowbush blueberry field. Hexazinone was tested for inhibitory effects on various transformations of the nitrogen cycle and soil respiration. Nitrogen fixation was unaffected by hexazinone levels up to FR×100 following a 4-week incubation period. Ammonification was initially inhibited by all levels of hexazinone, but after 4 weeks, ammonification in all treatment systems was equal to or greater than the control. Nitrification was more sensitive to hexazinone; however, application at a field-rate level caused no inhibition. Inhibitory effects were noted above FR after a 2-month endpoint analysis and above FR×5 after a 6-month endpoint analysis. Hexazinone concentrations up to and including FR×100 stimulated denitrification. Soil respiration was also stimulated over a 3-week period when applied at a level up to 100 times the recommended field rate. In general, it was found that when applied at the recommended field application rate, hexazinone does not adversely affect the nitrogen cycle or soil respiration in acidic lowbush blueberry soils. © 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 115,122, 2004 [source]

The sensitivity of annual grassland carbon cycling to the quantity and timing of rainfall

GLOBAL CHANGE BIOLOGY, Issue 6 2008
WENDY W. CHOU
Abstract Global climate models predict significant changes to the rainfall regimes of the grassland biome, where C cycling is particularly sensitive to the amount and timing of precipitation. We explored the effects of both natural interannual rainfall variability and experimental rainfall additions on net C storage and loss in annual grasslands. Soil respiration and net primary productivity (NPP) were measured in treatment and control plots over four growing seasons (water years, or WYs) that varied in wet-season length and the quantity of rainfall. In treatment plots, we increased total rainfall by 50% above ambient levels and simulated one early- and one late-season storm. The early- and late-season rain events significantly increased soil respiration for 2,4 weeks after wetting, while augmentation of wet-season rainfall had no significant effect. Interannual variability in precipitation had large and significant effects on C cycling. We observed a significant positive relationship between annual rainfall and aboveground NPP across the study (P=0.01, r2=0.69). Changes in the seasonal timing of rainfall significantly affected soil respiration. Abundant rainfall late in the wet season in WY 2004, a year with average total rainfall, led to greater net ecosystem C losses due to a ,50% increase in soil respiration relative to other years. Our results suggest that C cycling in annual grasslands will be less sensitive to changes in rainfall quantity and more affected by altered seasonal timing of rainfall, with a longer or later wet season resulting in significant C losses from annual grasslands. [source]

Long-term carbon exchange in a sparse, seasonally dry tussock grassland

GLOBAL CHANGE BIOLOGY, Issue 10 2004
John E. Hunt
Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source]

Organic carbon and carbon isotopes in modern and 100-year-old-soil archives of the Russian steppe

GLOBAL CHANGE BIOLOGY, Issue 10 2002
Margaret S. Torn
Abstract Archived soils can provide valuable information about changes in the carbon and carbon isotope content of soils during the past century. We characterized soil carbon dynamics in a Russian steppe preserve using a 100-year-old-soil archive and modern samples collected from the same site. The site has been protected since 1885 to the present, during which time the region has experienced widespread conversion to cultivation, a decrease in fire frequency, and a trend of increasing precipitation. In the preserve, the amount of organic carbon did not change appreciably between the 1900 and 1997 sampling dates, with 32 kg C/m2 in the top meter and a third of that in the top 20 cm. Carbon and nitrogen stocks varied by less than 6% between two replicate modern soil pits or between the modern sites and the archive. Radiocarbon content decreased with depth in all sites and the modern SOM had positive , values near the surface due to nuclear weapons testing in the early 1960s. In the upper 10 cm, most of the SOM had a turnover time of 6,10 years, according to a model fit to the radiocarbon content. Below about 10 cm, the organic matter was almost all passive material with long (millennial) turnover times. Soil respiration ,14CO2 on a summer day was 106,109,, an isotopic disequilibrium of about 9, relative to atmospheric 14CO2. In both the modern and archive soil, the relative abundance of 13C in organic matter increased with depth by 2, in the upper meter from ,13C = --26, at 5 cm to --24, below a meter. In addition, the slope of ,13C vs. depth below 5 cm was the same for both soils. Given the age of the soil archive, these results give clear evidence that the depth gradients are not due to depletion of atmospheric 13CO2 by fossil fuel emissions but must instead be caused by isotopic fractionation between plant litter inputs and preservation of SOM. Overall, the data show that these soils have a large reservoir of recalcitrant C and stocks had not changed between sampling dates 100 years apart. [source]

Effects of glucose, cellulose, and humic acids on soil microbial eco-physiology

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2004
Oliver Dilly
Abstract Microbial eco-physiology in soils is regulated by substrate quality of the organic matter. This regulation was studied for a forest and an agricultural soil by the combination of activity and biomass techniques. Soil respiration was stimulated by the substrate quality in the order, humic acid < cellulose < glucose over 20 days. Concurrently, substrate addition increased the respiratory quotient (RQ), defined as the ratio of mol CO2 evolution per mol O2 uptake. Anabolic processes were mainly induced by glucose addition. Soil preconditioned with glucose showed a decrease in the RQ value during glucose-induced microbial growth in comparison to non-amended control. The decrease in the RQ value induced by preconditioning with cellulose and humic acid was lower. Glucose, cellulose, and humic acid addition modified the microbial biomass as estimated by fumigation-extraction (FE), substrate-induced respiration (SIR), and ATP content. Since each biomass estimate refers to specific microbial components, shifts in microbial eco-physiology and community structure induced by substrate quality were reflected by SIR : FE and SIR : ATP ratios. The active and glucose-responsive biomass in the forest soil which was earlier suggested as being dominated by K-strategists was increased in the order, humic acid < cellulose < glucose. Einfluss von Zugaben von Glucose-, Cellulose und Huminsäuren auf die mikrobielle Ökophysiologie im Boden Die Ökophysiologie der mikrobiellen Gemeinschaften in Böden ist abhängig von der Substratqualität der organischen Substanz. Dies wurde nach Zugabe von Substraten für zwei Böden, einer unter Buchenwald und einer unter Acker, anhand einer Kombination von biochemischen und physiologischen Aktivitäts- und Biomassetechniken analysiert. Die Substratzugabe erhöhte die Bodenatmung über 20 Tage hinweg in der Reihenfolge Huminsäuren < Cellulose < Glucose. Gleichzeitig wurde auch der respiratorische Quotient (RQ), definiert als das Verhältnis von CO2 -Freisetzung zu O2 -Aufnahme, durch die Substratzugabe erhöht und anabolische Prozesse induziert. Das mikrobielle Wachstum wurde in erster Linie durch Glucose stimuliert. Der mit Glucose als Substrat versetzte Boden zeigte eine Abnahme des RQ während eines glucose-induzierten Wachstums im Vergleich zur Kontrolle. Eine solche Abnahme war bei der Huminsäure- und Cellulosebehandlung geringer. Die Zugabe von Glucose, Cellulose und Huminsäuren veränderte schließlich die mikrobielle Biomasse, welche mittels Fumigation-Extraktion, substratinduzierter Atmung und ATP-Gehalt ermittelt wurde. Da jede Technik spezifische mikrobielle Komponenten erfasst, wurden Veränderungen in der mikrobiellen Ökophysiologie und der Struktur der mikrobiellen Gemeinschaften durch die Substrate induziert, die in dem SIR:FE- und SIR:ATP-Verhältnis erkennbar waren. Die aktive und glucoseaktivierbare Biomasse in einem von K-Strategen dominierten Waldboden nahm von Huminsäure-, über Cellulose- und Glucosezugabe hin zu. [source]

Leaf age affects the seasonal pattern of photosynthetic capacityand net ecosystem exchange of carbon in a deciduous forest

PLANT CELL & ENVIRONMENT, Issue 6 2001
K. B. Wilson
Abstract Temporal trends in photosynthetic capacity are a critical factorin determining the seasonality and magnitude of ecosystem carbonfluxes. At a mixed deciduous forest in the south-eastern United States (Walker Branch Watershed, Oak Ridge, TN, USA), we independently measured seasonal trends in photosynthetic capacity (using single-leaf gas exchange techniques) and the whole-canopycarbon flux (using the eddy covariance method). Soil respiration was also measured using chambers and an eddy covariance system beneath the canopy. These independent chamber and eddy covariance measurements, along with a biophysical model (CANOAK), areused to examine how leaf age affects the seasonal pattern of carbon uptake during the growing season. When the measured seasonality in photosynthetic capacity is representedin the CANOAK simulations, there is good agreement with the eddy covariance data on the seasonal trends in carbon uptake. Removing the temporal trends in the simulations by using the early season maximum value of photosynthetic capacity over the entire growing season over estimates the annual carbon uptake by about 300 g C m,2 year,1, halfthe total estimated annual net ecosystem exchange. Alternatively, use of the mean value of photosynthetic capacity incorrectly simulates the seasonality in carbon uptake by the forest. In addition to changes related to leaf development and senescence, photosynthetic capacitydecreased in the middle and late summer, even when leaf nitrogenwas essentially constant. When only these middle and late summer reductions were neglected in the model simulations, CANOAK still overestimated the carbon uptake by an amount comparable to 25% ofthe total annual net ecosystem exchange. [source]

Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in Lapland

ECOGRAPHY, Issue 4 2003
Otso Suominen
Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground-dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H') of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H'/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites. [source]

Effects of the herbicide hexazinone on nutrient cycling in a low-pH blueberry soil

Gross rates of ammonification and nitrification at a nitrogen-saturated spruce (Picea abies (L.)Karst.) stand in southern Germany

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2010
P. Rosenkranz
We investigated the magnitudes of temporal and spatial variabilities of gross ammonification and nitrification, in an N-saturated temperate forest ecosystem. Forest soil gross ammonification, gross nitrification and heterotrophic soil respiration were measured in the forest floor and uppermost mineral layer over a period of 3 years. Total annual gross fluxes for the organic layer and uppermost mineral horizon (0,4 cm) were in the range of 800,980 kg N ha,1 year,1 for gross ammonification and 480,590 kg N ha,1 year,1 for gross nitrification. Annual heterotrophic soil respiration was 8000,8900 kg C ha,1 year,1. Highest soil C and N turnover rates occurred in summer, and a consistent pattern was observed throughout the observation period, with highest values for plots located at a clear-cut area and lowest values for plots located at an unmanaged, approximately 100-year-old, spruce control site. Soil moisture, soil temperature and substrate availability accounted for most of the observed variability of C and N turnover rates. Because gross rates of inorganic N production were more than an order of magnitude larger than ecosystem N losses along hydrological and gaseous pathways, our study underlines the importance of internal microbial N turnover processes for ecosystem N cycling and retention. [source]

Towards a predictive understanding of belowground process responses to climate change: have we moved any closer?

FUNCTIONAL ECOLOGY, Issue 6 2008
Elise Pendall
Summary 1Belowground processes, including root production and exudation, microbial activity and community dynamics, and biogeochemical cycling interact to help regulate climate change. Feedbacks associated with these processes, such as warming-enhanced decomposition rates, give rise to major uncertainties in predictions of future climate. 2Uncertainties associated with these processes are more likely to be reduced if two key challenges can be met: increasing interdisciplinarity among researchers, and measuring belowground ecosystem structure and function at relevant spatial and temporal scales. For instance, recognizing the relationship between belowground primary production and soil respiration enhances modelling of global-scale C cycle temperature responses. At the opposite end of the spectrum, applying genomic techniques at the scale of microns improves mechanistic understanding of root,microbe interactions. 3Progress has been made in understanding interactions of belowground processes with climate change, although challenges remain. We highlight some of these advances and provide directions for key research needs in this Special Feature of Functional Ecology, which results from a symposium that was convened at the Soil Science Society of America National Meeting in November, 2006. [source]

The response of heterotrophic activity and carbon cycling to nitrogen additions and warming in two tropical soils

GLOBAL CHANGE BIOLOGY, Issue 9 2010
DANIELA F. CUSACK
Abstract Nitrogen (N) deposition is projected to increase significantly in tropical regions in the coming decades, where changes in climate are also expected. Additional N and warming each have the potential to alter soil carbon (C) storage via changes in microbial activity and decomposition, but little is known about the combined effects of these global change factors in tropical ecosystems. In this study, we used controlled laboratory incubations of soils from a long-term N fertilization experiment to explore the sensitivity of soil C to increased N in two N-rich tropical forests. We found that fertilization corresponded to significant increases in bulk soil C concentrations, and decreases in C loss via heterotrophic respiration (P< 0.05). The increase in soil C was not uniform among C pools, however. The active soil C pool decomposed faster with fertilization, while slowly cycling C pools had longer turnover times. These changes in soil C cycling with N additions corresponded to the responses of two groups of microbial extracellular enzymes. Smaller active C pools corresponded to increased hydrolytic enzyme activities; longer turnover times of the slowly cycling C pool corresponded to reduced activity of oxidative enzymes, which degrade more complex C compounds, in fertilized soils. Warming increased soil respiration overall, and N fertilization significantly increased the temperature sensitivity of slowly cycling C pools in both forests. In the lower elevation forest, respired CO2 from fertilized cores had significantly higher ,14C values than control soils, indicating losses of relatively older soil C. These results indicate that soil C storage is sensitive to both N deposition and warming in N-rich tropical soils, with interacting effects of these two global change factors. N deposition has the potential to increase total soil C stocks in tropical forests, but the long-term stability of this added C will likely depend on future changes in temperature. [source]

Increased temperature and precipitation interact to affect root production, mortality, and turnover in a temperate steppe: implications for ecosystem C cycling

GLOBAL CHANGE BIOLOGY, Issue 4 2010
WENMING BAI
Abstract Fine root production and turnover play important roles in regulating carbon (C) cycling in terrestrial ecosystems. In order to examine effects of climate change on root production and turnover, a field experiment with increased temperature and precipitation had been conducted in a semiarid temperate steppe in northern China since April 2005. Experimental warming decreased annual root production, mortality, and mean standing crop by 10.3%, 12.1%, 7.0%, respectively, while root turnover was not affected in 2006 and 2007 by the warming. Annual root production and turnover was 5.9% and 10.3% greater in the elevated than ambient precipitation plots. Changes in root production and mortality in response to increased temperature and precipitation could be largely attributed to the changes in gross ecosystem productivity (GEP) and belowground/aboveground C allocation. There were significant interactive effects of warming and increased precipitation on root productivity, mortality, and standing crop. Experimental warming had positive and negative effects on the three root variables (root production, mortality, standing crop) under ambient and increased precipitation, respectively. Increased precipitation stimulated and suppressed the three root variables in the unwarmed and warmed subplots, respectively. The positive dependence of soil respiration and ecosystem respiration upon root productivity and mortality highlights the important role of root dynamics in ecosystem C cycling. The nonadditive effects of increased temperature and precipitation on root productivity, mortality, and standing crop observed in this study are critical for model projections of climate,ecosystem feedbacks. These findings indicate that carbon allocation is a focal point for future research and that results from single factor experiments should be treated with caution because of factor interactions. [source]

Responses of dryland soil respiration and soil carbon pool size to abrupt vs. gradual and individual vs. combined changes in soil temperature, precipitation, and atmospheric [CO2]: a simulation analysis

GLOBAL CHANGE BIOLOGY, Issue 9 2009
WEIJUN SHEN
Abstract With the large extent and great amount of soil carbon (C) storage, drylands play an important role in terrestrial C balance and feedbacks to climate change. Yet, how dryland soils respond to gradual and concomitant changes in multiple global change drivers [e.g., temperature (Ts), precipitation (Ppt), and atmospheric [CO2] (CO2)] has rarely been studied. We used a process-based ecosystem model patch arid land simulator to simulate dryland soil respiration (Rs) and C pool size (Cs) changes to abrupt vs. gradual and single vs. combined alterations in Ts, Ppt and CO2 at multiple treatment levels. Results showed that abrupt perturbations generally resulted in larger Rs and had longer differentiated impacts than did gradual perturbations. Rs was stimulated by increases in Ts, Ppt, and CO2 in a nonlinear fashion (e.g., parabolically or asymptotically) but suppressed by Ppt reduction. Warming mainly stimulated heterotrophic Rs (i.e., Rh) whereas Ppt and CO2 influenced autotrophic Rs (i.e., Ra). The combined effects of warming, Ppt, and CO2 were nonadditive of primary single-factor effects as a result of substantial interactions among these factors. Warming amplified the effects of both Ppt addition and CO2 elevation whereas Ppt addition and CO2 elevation counteracted with each other. Precipitation reduction either magnified or suppressed warming and CO2 effects, depending on the magnitude of factor's alteration and the components of Rs (Ra or Rh) being examined. Overall, Ppt had dominant influence on dryland Rs and Cs over Ts and CO2. Increasing Ppt individually or in combination with Ts and CO2 benefited soil C sequestration. We therefore suggested that global change experimental studies for dryland ecosystems should focus more on the effects of precipitation regime changes and the combined effects of Ppt with other global change factors (e.g., Ts, CO2, and N deposition). [source]

Litter decomposition in grasslands of Central North America (US Great Plains)

GLOBAL CHANGE BIOLOGY, Issue 5 2009
ELIANA 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 soil frost on soil respiration and its radiocarbon signature in a Norway spruce forest soil

GLOBAL CHANGE BIOLOGY, Issue 4 2009
JAN MUHR
Abstract Apart from a general increase of mean annual air temperature, climate models predict a regional increase of the frequency and intensity of soil frost with possibly strong effects on C cycling of soils. In this study, we induced mild soil frost (up to ,5 °C in a depth of 5 cm below surface) in a Norway spruce forest soil by removing the natural snow cover in the winter of 2005/2006. Soil frost lasted from January to April 2006 and was detected down to 15 cm depth. Soil frost effectively reduced soil respiration in the snow removal plots in comparison to undisturbed control plots. On an annual basis 6.2 t C ha,1 a,1 were emitted in the control plots compared with 5.1 t C ha,1 a,1 in the snow removal plots. Only 14% of this difference was attributed to reduced soil respiration during the soil frost period itself, whereas 63% of this difference originated from differences during the summer of 2006. Radiocarbon (,14C) signature of CO2 revealed a considerable reduction of heterotrophic respiration on the snow removal plots, only partly compensated for by a slight increase of rhizosphere respiration. Similar CO2 concentrations in the uppermost mineral horizons of both treatments indicate that differences between the treatments originated from the organic horizons. Extremely low water contents between June and October of 2006 may have inhibited the recovery of the heterotrophic organisms from the frost period, thereby enhancing the differences between the control and snow removal plots. We conclude that soil frost triggered a change in the composition of the microbial community, leading to an increased sensitivity of heterotrophic respiration to summer drought. A CO2 pulse during thawing, such as described for arable soils several times throughout the literature, with the potential to partly compensate for reduced soil respiration during soil frost, appears to be lacking for this soil. Our results from this experiment indicate that soil frost reduces C emission from forest soils, whereas mild winters may enhance C losses from forest soils. [source]

Soil carbon fluxes and stocks in a Great Lakes forest chronosequence

GLOBAL CHANGE BIOLOGY, Issue 1 2009
JIANWU TANG
Abstract We measured soil respiration and soil carbon stocks, as well as micrometeorological variables in a chronosequence of deciduous forests in Wisconsin and Michigan. The chronosequence consisted of (1) four recently disturbed stands, including a clearcut and repeatedly burned stand (burn), a blowdown and partial salvage stand (blowdown), a clearcut with sparse residual overstory (residual), and a regenerated stand from a complete clearcut (regenerated); (2) four young aspen (Populus tremuloides) stands in average age of 10 years; (3) four intermediate aspen stands in average age of 26 years; (4) four mature northern hardwood stands in average age of 73 years; and (5) an old-growth stand approximately 350-years old. We fitted site-based models and used continuous measurements of soil temperature to estimate cumulative soil respiration for the growing season of 2005 (days 133,295). Cumulative soil respiration in the growing season was estimated to be 513, 680, 747, 747, 794, 802, 690, and 571 g C m,2 in the burn, blowdown, residual, regenerated, young, intermediate, mature, and old-growth stands, respectively. The measured apparent temperature sensitivity of soil respiration was the highest in the regenerated stand, and declined from the young stands to the old-growth. Both, cumulative soil respiration and basal soil respiration at 10 °C, increased during stand establishment, peaked at intermediate age, and then decreased with age. Total soil carbon at 0,60 cm initially decreased after harvest, and increased after stands established. The old-growth stand accumulated carbon in deep layers of soils, but not in the surface soils. Our study suggests a complexity of long-term soil carbon dynamics, both in vertical depth and temporal scale. [source]

Contrasting effects of repeated summer drought on soil carbon efflux in hydric and mesic heathland soils

GLOBAL CHANGE BIOLOGY, Issue 10 2008
ALWYN SOWERBY
Abstract Current predictions of climate change include altered rainfall patterns throughout Europe, continental USA and areas such as the Amazon. The effect of this on soil carbon efflux remains unclear although several modelling studies have highlighted the potential importance of drought for carbon storage. To test the importance of drought, and more importantly repeated drought year-on-year, we used automated retractable curtains to exclude rain and produce repeated summer drought in three heathlands at varying moisture conditions. This included a hydric system limited by water-excess (in the UK) and two mesic systems with seasonal water limitation in Denmark (DK) and the Netherlands (NL). The experimental rainfall reductions were set to reflect single year droughts observed in the last decade with exclusion of rain for 2,3 months of the year resulting in a 20,26% reduction in annual rainfall and 23,38% reduction in mean soil moisture during the drought period. Unexpectedly, sustained reduction in soil moisture over winter (between drought periods) was also observed at all three sites, along with a reduction in the maximum water-holding capacity attained. Three hypotheses are discussed which may have contributed to this lack of recovery in soil moisture: hydrophobicity of soil organic matter, increased water use by plants and increased cracking of the soil. The responses of soil respiration to this change in soil moisture varied among the sites: decreased rates were observed at the water-limited NL and DK sites whilst they increased at the UK site. Reduced sensitivity of soil respiration to soil temperature was observed at soil moisture contents above 55% at the UK site and below 20% and 13% at the NL and DK sites, respectively. Soil respiration rates recovered to predrought levels in the NL and DK sites during the winter re-wetting period that indicates any change in soil C storage due to changes in soil C efflux may be short lived in these mesic systems. In contrast, in the hydric UK site after 2 years of drought treatment, the persistent reduction in soil moisture throughout the year resulted in a year-round increase in soil respiration flux, a response that accelerated over time to 40% above control levels. These findings suggest that carbon-rich soils with high organic matter content may act as a significant source of CO2 to the atmosphere following repeated summer drought. Nonrecovery of soil moisture and a persistent increase in soil respiration may be the primary mechanism underlying the reported substantial losses of soil carbon from UK organic soils over the last 20 years. These findings indicate that the water status of an ecosystem will be a critical factor to consider in determining the impact of drought on the soil carbon fluxes and storage. [source]

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change

GLOBAL CHANGE BIOLOGY, Issue 7 2008
PHILIP A. FAY
Abstract Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected soil water content (SWC) and three aspects of ecosystem function: leaf photosynthetic carbon gain (), aboveground net primary productivity (ANPP), and soil respiration (). We utilized rainout shelter-covered mesocosms (2.6 m3) containing assemblages of tallgrass prairie grasses and forbs. These were hand watered with 16 I×Q treatment combinations, using event sizes from 4 to 53 mm. Increasing Q by 250% (400,1000 mm yr,1) increased mean soil moisture and all three processes as expected, but only by 20,55% (P,0.004), suggesting diminishing returns in ecosystem function as Q increased. Increasing I (from 3 to 15 days between rainfall inputs) caused both positive () and negative () changes in ecosystem processes (20,70%, P,0.01), within and across levels of Q, indicating that I strongly influenced the effects of Q, and shifted the system towards increased net carbon uptake. Variation in SE at shorter I produced greater response in soil moisture and ecosystem processes than did variation in SE at longer I, suggesting greater stability in ecosystem function at longer I and a priming effect at shorter I. Significant differences in ANPP and between treatments differing in I and Q but sharing the same SE showed that the prevailing pattern of rainfall influenced the responses to a given event size. Grassland ecosystem responses to extreme rainfall patterns expected with climate change are, therefore, likely to be variable, depending on how I, Q, and SE combine, but will likely result in changes in ecosystem carbon cycling. [source]

The sensitivity of annual grassland carbon cycling to the quantity and timing of rainfall

On the variability of respiration in terrestrial ecosystems: moving beyond Q10

GLOBAL CHANGE BIOLOGY, Issue 2 2006
ERIC A. DAVIDSON
Abstract Respiration, which is the second most important carbon flux in ecosystems following gross primary productivity, is typically represented in biogeochemical models by simple temperature dependence equations. These equations were established in the 19th century and have been modified very little since then. Recent applications of these equations to data on soil respiration have produced highly variable apparent temperature sensitivities. This paper searches for reasons for this variability, ranging from biochemical reactions to ecosystem-scale substrate supply. For a simple membrane-bound enzymatic system that follows Michaelis,Menten kinetics, the temperature sensitivities of maximum enzyme activity (Vmax) and the half-saturation constant that reflects the affinity of the enzyme for the substrate (Km) can cancel each other to produce no net temperature dependence of the enzyme. Alternatively, when diffusion of substrates covaries with temperature, then the combined temperature sensitivity can be higher than that of each individual process. We also present examples to show that soluble carbon substrate supply is likely to be important at scales ranging from transport across membranes, diffusion through soil water films, allocation to aboveground and belowground plant tissues, phenological patterns of carbon allocation and growth, and intersite differences in productivity. Robust models of soil respiration will require that the direct effects of substrate supply, temperature, and desiccation stress be separated from the indirect effects of temperature and soil water content on substrate diffusion and availability. We speculate that apparent Q10 values of respiration that are significantly above about 2.5 probably indicate that some unidentified process of substrate supply is confounded with observed temperature variation. [source]

Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon

GLOBAL CHANGE BIOLOGY, Issue 2 2006
Edward A.G. Schuur
Abstract Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (,14C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently-fixed C that fuels plant or microbial metabolism has ,14C values close to that of current atmospheric CO2, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the ,14C of C respired by recently excised black spruce roots averaged 14, greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The ,14C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60, higher than the contemporary atmosphere ,14CO2, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic ,14C end members with measurements of the ,14C of total soil respiration, we calculated that 47,63% of soil CO2 emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high ,14C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration. [source]

Patterns of rhizosphere carbon flux in sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) saplings

GLOBAL CHANGE BIOLOGY, Issue 6 2005
Richard P. Phillips
Abstract Despite its importance in the terrestrial C cycle rhizosphere carbon flux (RCF) has rarely been measured for intact root,soil systems. We measured RCF for 8-year-old saplings of sugar maple (Acer saccharum) and yellow birch (Betula allegheniensis) collected from the Hubbard Brook Experimental Forest (HBEF), NH and transplanted into pots with native soil horizons intact. Five saplings of each species were pulse labeled with 13CO2 at ambient CO2 concentrations for 4,6 h, and the 13C label was chased through rhizosphere and bulk soil pools in organic and mineral horizons for 7 days. We hypothesized yellow birch roots would supply more labile C to the rhizosphere than sugar maple roots based on the presumed greater C requirements of ectomycorrhizal roots. We observed appearance of the label in rhizosphere soil of both species within the first 24 h, and a striking difference between species in the timing of 13C release to soil. In sugar maple, peak concentration of the label appeared 1 day after labeling and declined over time whereas in birch the label increased in concentration over the 7-day chase period. The sum of root and rhizomicrobial respiration in the pots was 19% and 26% of total soil respiration in sugar maple and yellow birch, respectively. Our estimate of the total amount of RCF released by roots was 6.9,7.1% of assimilated C in sugar maple and 11.2,13.0% of assimilated C in yellow birch. These fluxes extrapolate to 55,57 and 90,104 g C m,2 yr,1 from sugar maple and yellow birch roots, respectively. These results suggest RCF from both arbuscular mycorrhizal and ectomycorrhizal roots represents a substantial flux of C to soil in northern hardwood forests with important implications for soil microbial activity, nutrient availability and C storage. [source]

Annual Q10 of soil respiration reflects plant phenological patterns as well as temperature sensitivity

GLOBAL CHANGE BIOLOGY, Issue 2 2004
J. Curiel yuste
Abstract The temperature sensitivity of soil respiration (SR) is often estimated from the seasonal changes in the flux relative to those in soil temperature, and subsequently used in models to interpolate or predict soil fluxes. However, temperature sensitivities derived from seasonal changes in SR (from here on denoted seasonal Q10) may not solely reflect the temperature sensitivity of SR, because seasonal changes in SR can also be affected by other seasonally fluctuating conditions and processes. In this manuscript, we present a case study of how the seasonal Q10 of SR can be decoupled from the temperature sensitivity of SR. In a mixed temperate forest, we measured SR under vegetations with different leaf strategies: pure evergreen, pure deciduous, and mixed. Seasonal Q10 was much higher under deciduous than under evergreen canopies. However, at a shorter time scale, both vegetation types exhibited very similar Q10 values, indicating that the large differences in seasonal Q10 do not represent differences in the temperature sensitivity of the soil metabolism. The seasonal Q10 depends strongly on the amplitude of the seasonal changes in SR (SRs), which, under the particular climatic and edaphic conditions of our forest study site, were significantly larger in deciduous forest. In turn, SRs was positively correlated with the seasonal changes in leaf area index (LAIs), a measure of the deciduousness of the vegetation. Thus, in this temperate maritime forest, seasonal Q10 of SR was strongly influenced by the deciduousness of the vegetation. We conclude that the large differences in seasonal Q10 were not entirely due to different temperature sensitivities, but also to different seasonal patterns of plant activity in the evergreen and deciduous plants of this site. Some coniferous forests may be more seasonal than the one we studied, and the deciduous,evergreen differences observed here may not be broadly applicable, but this case study demonstrates that variation of plant phenological process can significantly contribute to the seasonality of SR, and, hence, calculated Q10 values. Where this occurs, the seasonal Q10 value for SR does not accurately represent temperature sensitivity. Because the strong seasonal correlation between SR and temperature does not necessarily imply a causal relationship, Q10 values derived form annual patterns of SR should be used with caution when predicting future responses of SR to climatic change. [source]

The contribution of bryophytes to the carbon exchange for a temperate rainforest

GLOBAL CHANGE BIOLOGY, Issue 8 2003
Evan H. DeLucia
Abstract Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100,400-year-old rimu (Dacrydium cupressimum) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis , whole-plant respiration) per unit ground area at saturating irradiance was 1.9 ,mol m,2 s,1 and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m,2, compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of ,1010 g m,2. To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or ,11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [source]

Contrasting soil respiration in young and old-growth ponderosa pine forests

GLOBAL CHANGE BIOLOGY, Issue 12 2002
J. IRVINE
Abstract Three years of fully automated and manual measurements of soil CO2 efflux, soil moisture and temperature were used to explore the diel, seasonal and inter-annual patterns of soil efflux in an old-growth (250-year-old, O site) and recently regenerating (14-year-old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO2 efflux at both sites showed large inter-annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO2 efflux at the O site showed a strong positive correlation between diel mean soil CO2 efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site-specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO2 efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m,2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes. [source]

Linkages of plant traits to soil properties and the functioning of temperate grassland

JOURNAL OF ECOLOGY, Issue 5 2010
Kate H. Orwin
Summary 1.,Global change is likely to alter plant community structure, with consequences for the structure and functioning of the below-ground community and potential feedbacks to climate change. Understanding the mechanisms behind these plant,soil interactions and feedbacks to the Earth-system is therefore crucial. One approach to understanding such mechanisms is to use plant traits as predictors of functioning. 2.,We used a field-based monoculture experiment involving nine grassland species that had been growing on the same base soil for 7 years to test whether leaf, litter and root traits associated with different plant growth strategies can be linked to an extensive range of soil properties relevant to carbon, nitrogen and phosphorus cycling. Soil properties included the biomass and structure of the soil microbial community, soil nutrients, soil microclimate and soil process rates. 3.,Plant species with a high relative growth rate (RGR) were associated with high leaf and litter quality (e.g. low toughness, high nitrogen concentrations), an elevated biomass of bacteria relative to fungi in soil, high rates of soil nitrogen mineralization and concentrations of extractable inorganic nitrogen, and to some extent higher available phosphorus pools. 4.,In contrast to current theory, species with a high RGR and litter quality were associated with soils with a lower rate of soil respiration and slow decomposition rates. This indicates that predicting processes that influence carbon cycling from plant traits may be more complex than predicting processes that influence nitrogen and phosphorus cycling. 5.,Root traits did not show strong relationships to RGR, leaf or litter traits, but were strongly correlated with several soil properties, particularly the biomass of bacteria relative to fungi in soil and measures relating to soil carbon cycling. 6.,Synthesis. Our results indicate that plant species from a single habitat can result in significant divergence in soil properties and functioning when grown in monoculture, and that many of these changes are strongly and predictably linked to variation in plant traits associated with different growth strategies. Traits therefore have the potential to be a powerful tool for understanding the mechanisms behind plant,soil interactions and ecosystem functioning, and for predicting how changes in plant species composition associated with global change will feedback to the Earth-system. [source]

The contribution of stone cover to biological activity in the Negev desert, Israel

LAND DEGRADATION AND DEVELOPMENT, Issue 1 2001
I. Lahav (Lavian)
Abstract Ancient valley agriculture in the northern Negev highlands was based on the principle of directed collection of water and eroded material from the slopes and their consequent flow towards the valleys. The stones on these slopes were therefore removed and/or collected into piles known as ,grape mounds'. The aim of this study was to understand the contribution of stone cover and slope-facing to biological activity in soil. Soil samples from a depth of 0,5,mm from the soil surface were collected during the study period (December 1994,March 1996) from northern and southern hill slopes, from under limestones and between stones. Soil moisture, organic matter, chlorophyll-a and soil respiration were determined. The results obtained in field and laboratory studies demonstrated differences between the northern and southern slopes. The stone cover on the northern slope made up 33 per cent and in the southern slope 23 per cent, stone size ranging from 15,50,cm2 and 15,35,cm2, respectively. Soil moisture content varied from 12 per cent in December 1994 on both slopes to one-quarter of the initial value during the dry period. Organic matter content reached a maximal level of 14 per cent and 16 per cent on the northern and southern slopes, respectively. Values of chlorophyll-a on both the northern and southern slopes were 0.38,,g,g,1 dry soil during the wet season, decreasing to 0.05,,g,g,1 dry soil during the dry period. Soil samples from under the stones on both slopes produced high levels of CO2, ranging between 50 and 100,,g CO2,g;,1 dry soil h,1, whereas in the control samples the levels ranged between 30 and 70,,g CO2,g,1 dry soil h,1. In conclusion, the stone cover apparently plays an important role in the maintenance of biological activity through its contribution to slope biotope stability. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: extending observations beyond the first year

PLANT CELL & ENVIRONMENT, Issue 8 2003
BHUPINDERPAL-SINGH
ABSTRACT Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789,792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the ,13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change. [source]

A numerical evaluation of chamber methodologies used in measuring the ,13C of soil respiration

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2009
Nick Nickerson
Measurement of the ,13C value of soil-respired CO2 (,r) has become a commonplace method through which ecosystem function and C dynamics can be better understood. Despite its proven utility there is currently no consensus on the most robust method with which to measure ,r. Static and dynamic chamber systems are both commonly used for this purpose; however, the literature on these methods provides evidence suggesting that measurements of ,r made with these chamber systems are neither repeatable (self-consistent) nor comparable across methodologies. Here we use a three-dimensional (3-D) numerical soil-atmosphere-chamber model to test these chamber systems in a ,surrogate reality'. Our simulations show that each chamber methodology is inherently biased and that no chamber methodology can accurately predict the true ,r signature under field conditions. If researchers intend to use ,r to study insitu ecosystem processes, the issues with these chamber systems need to be corrected either by using diffusive theory or by designing a new, unbiased ,r measurement system. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Use of labelled nitrogen to measure gross and net rates of mineralization and microbial activity in permanent pastures following fertilizer applications at different time intervals,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2002
David J. Hatch
Measurements of some of the main internal N-cycling processes in soil were obtained by labelling the inorganic N pool with the stable isotope of nitrogen (15N). The 15N mean pool dilution technique, combined with other field measurements, enabled gross and net N-mineralization rates to be resolved in grassland soils, which had previously either received fertilizer N (F), or had remained unfertilized (U) for many years. The two soils were subdivided into plots that received N at different time intervals (over 3 weeks), prior to 15N measurements being made. By this novel approach, possible ,priming' effects over time were investigated to try to overcome some of the temporal problems of isotopic labelling of soil N (native plus fertilizer) and to identify possible changes in a range of primary N-transformation processes. The results suggested that an overall stimulation of microbially mediated processes occurred with all N treatments, but there were inconsistencies associated with the release of N, both in the timing and the degree to which different processes responded to the application of fertilizer N. The rates of these processes were, however, within the range of previously reported data and the 15N measurements were not adversely affected by the differences in N pools created by the treatments. Thus, the mean pool dilution technique was shown to be applicable to agricultural soils, under conditions relevant to grass swards receiving fertilizer. For example, between the,U and F treatments, the size of inorganic N pools increased by five-fold and gross rates of mineralization reached 3.5 and 4.8,µg N g,1 (dry soil) d,1, respectively, but did not vary greatly with the timing of N applications. A correlation (r2,=,0.57) was found between soil respiration (which is relatively simple to measure) and net mineralization (which is more time consuming), suggesting that the former might be used as an indicator of the latter. Although this relationship was stronger in previously unfertilized soils, the similarities found with fertilized soils suggest that this approach could be used to obtain information of wider agronomic value and would, therefore, warrant further work under a range of soil conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source]