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Journal ArticleDOI

Separating root and soil microbial contributions to soil respiration: A review of methods and observations

01 Jan 2000-Biogeochemistry (Kluwer Academic Publishers)-Vol. 48, Iss: 1, pp 115-146
TL;DR: In this article, three primary methods have been used to distinguish hetero- versus autotrophic soil respiration including integration of components contributing to in situ forest soil CO2 efflux (i.e., litter, roots, soil), comparison of soils with and without root exclusion, and application of stable or radioactive isotope methods.
Abstract: Forest soil respiration is the sum of heterotrophic (microbes, soil fauna) and auto- trophic (root) respiration. The contribution of each group needs to be understood to evaluate implications of environmental change on soil carbon cycling and sequestration. Three primary methods have been used to distinguish hetero- versus autotrophic soil respiration including: integration of components contributing to in situ forest soil CO2 efflux (i.e., litter, roots, soil), comparison of soils with and without root exclusion, and application of stable or radioactive isotope methods. Each approach has advantages and disadvantages, but isotope based methods provide quantitative answers with the least amount of disturbance to the soil and roots. Pub- lished data from all methods indicate that root/rhizosphere respiration can account for as little as 10 percent to greater than 90 percent of total in situ soil respiration depending on vegetation type and season of the year. Studies which have integrated percent root contribution to total soil respiration throughout an entire year or growing season show mean values of 45.8 and 60.4 percent for forest and nonforest vegetation, respectively. Such average annual values must be extrapolated with caution, however, because the root contribution to total soil respiration is commonly higher during the growing season and lower during the dormant periods of the year. Abbreviations: TScer -t otal soil CO 2 efflux rate; f - fractional root contribution to TS cer; RC - root contribution to TScer

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Citations
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Journal ArticleDOI
01 Jun 2007-Ecology
TL;DR: Survey, experimental, and meta-analytical results suggest that certain bacterial phyla can be differentiated into copiotrophic and oligotrophic categories that correspond to the r- and K-selected categories used to describe the ecological attributes of plants and animals.
Abstract: Although researchers have begun cataloging the incredible diversity of bacteria found in soil, we are largely unable to interpret this information in an ecological context, including which groups of bacteria are most abundant in different soils and why. With this study, we examined how the abundances of major soil bacterial phyla correspond to the biotic and abiotic characteristics of the soil environment to determine if they can be divided into ecologically meaningful categories. To do this, we collected 71 unique soil samples from a wide range of ecosystems across North America and looked for relationships between soil properties and the relative abundances of six dominant bacterial phyla (Acidobacteria, Bacteroidetes, Firmicutes, Actinobacteria, alpha-Proteobacteria, and the beta-Proteobacteria). Of the soil properties measured, net carbon (C) mineralization rate (an index of C availability) was the best predictor of phylum-level abundances. There was a negative correlation between Acidobacteria abundance and C mineralization rates (r2 = 0.26, P < 0.001), while the abundances of beta-Proteobacteria and Bacteroidetes were positively correlated with C mineralization rates (r2 = 0.35, P < 0.001 and r2 = 0.34, P < 0.001, respectively). These patterns were explored further using both experimental and meta-analytical approaches. We amended soil cores from a specific site with varying levels of sucrose over a 12-month period to maintain a gradient of elevated C availabilities. This experiment confirmed our survey results: there was a negative relationship between C amendment level and the abundance of Acidobacteria (r2 = 0.42, P < 0.01) and a positive relationship for both Bacteroidetes and beta-Proteobacteria (r2 = 0.38 and 0.70, respectively; P < 0.01 for each). Further support for a relationship between the relative abundances of these bacterial phyla and C availability was garnered from an analysis of published bacterial clone libraries from bulk and rhizosphere soils. Together our survey, experimental, and meta-analytical results suggest that certain bacterial phyla can be differentiated into copiotrophic and oligotrophic categories that correspond to the r- and K-selected categories used to describe the ecological attributes of plants and animals. By applying the copiotroph-oligotroph concept to soil microorganisms we can make specific predictions about the ecological attributes of various bacterial taxa and better understand the structure and function of soil bacterial communities.

3,423 citations


Cites background from "Separating root and soil microbial ..."

  • ...…et al. 2004, Knorr et al. 2005), we selected these amendment levels to reflect a supply of labile carbon that equates with a broad range of published soil CO2 efflux rates (Rustad et al. 2001), assuming that 50% of total soil CO2 efflux is derived from microbial mineralization (Hanson et al. 2000)....

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  • ...Average annual soil moisture deficit (in mm H2O) was estimated as the sum of the differences between mean monthly potential evapotranspiration (PET) and mean monthly precipitation....

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Journal ArticleDOI
14 Jun 2001-Nature
TL;DR: Girdling reduced soil respiration within 1–2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days, which clearly show that the flux of current assimilates to roots is a key driver of soil resppiration.
Abstract: The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertain. To separate mycorrhizal root respiration from heterotrophic respiration in aboreal pine forest, we conducted a large-scale tree-girdling experiment, comprising 9 plots each containing about 120 trees. Tree-girdling involves stripping the stem bark to the depth of the current xylem at breast height terminating the supply of current photosynthates to roots and their mycorrhizal fungi without physically disturbing the delicate root-microbe-soil system. Here we report that girdling reduced soil respiration within 1-2 months by about 54% relative to respiration on ungirdled control plots, and that decreases of up to 37% were detected within 5 days. These values clearly show that the flux of current assimilates to roots is a key driver of soil respiration; they are conservative estimates of root respiration, however, because girdling increased the use of starch reserves in the roots. Our results indicate that models of soil respiration should incorporate measures of photosynthesis and of seasonal patterns of photosynthate allocation to roots.

1,794 citations


Cites background from "Separating root and soil microbial ..."

  • ...gif" NDATA ITEM> ]> The respiratory activities of plant roots, of their mycorrhizal fungi and of the free-living microbial heterotrophs (decomposers) in soils are significant components of the global carbon balance, but their relative contributions remain uncertai...

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Journal ArticleDOI
TL;DR: Some of the lessons learned from the long-term investment in Free-Air CO(2) Enrichment experiments are described, where many of these lessons have been most clearly demonstrated in crop systems, and have important implications for natural systems.
Abstract: Plant responses to the projected future levels of CO2 were first characterized in short-term experiments lasting days to weeks. However, longer term acclimation responses to elevated CO2 were subsequently discovered to be very important in determining plant and ecosystem function. Free-Air CO2 Enrichment (FACE) experiments are the culmination of efforts to assess the impact of elevated CO2 on plants over multiple seasons and, in the case of crops, over their entire lifetime. FACE has been used to expose vegetation to elevated concentrations of atmospheric CO2 under completely open-air conditions for nearly two decades. This review describes some of the lessons learned from the long-term investment in these experiments. First, elevated CO2 stimulates photosynthetic carbon gain and net primary production over the long term despite down-regulation of Rubisco activity. Second, elevated CO2 improves nitrogen use efficiency and, third, decreases water use at both the leaf and canopy scale. Fourth, elevated CO2 stimulates dark respiration via a transcriptional reprogramming of metabolism. Fifth, elevated CO2 does not directly stimulate C4 photosynthesis, but can indirectly stimulate carbon gain in times and places of drought. Finally, the stimulation of yield by elevated CO2 in crop species is much smaller than expected. While many of these lessons have been most clearly demonstrated in crop systems, all of the lessons have important implications for natural systems.

1,377 citations


Cites background from "Separating root and soil microbial ..."

  • ...There are unique challenges to measuring the respiration of leaves, stems, and roots (Hanson et al., 2000; Davey et al., 2004; Moore et al., 2008) and the relationship between plant productivity and respiration is variable in each of these tissues (Litton et al., 2007)....

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  • ...There are unique challenges to measuring the respiration of leaves, stems, and roots (Hanson et al., 2000; Davey et al., 2004; Moore et al., 2008) and the relationship between plant productivity and respiration is variable in each of these tissues (Litton et al....

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Journal ArticleDOI
TL;DR: A meta-analysis suggests that nitrogen deposition impedes organic matter decomposition, and thus stimulates carbon sequestration, in temperate forest soils where nitrogen is not limiting microbial growth as mentioned in this paper, and the concomitant reduction in soil carbon emissions is substantial, and equivalent in magnitude to the amount of carbon taken up by trees owing to nitrogen fertilization.
Abstract: The use of fossil fuels and fertilizers has increased the amount of biologically reactive nitrogen in the atmosphere over the past century. As a consequence, forests in industrialized regions have experienced greater rates of nitrogen deposition in recent decades. This unintended fertilization has stimulated forest growth, but has also affected soil microbial activity, and thus the recycling of soil carbon and nutrients. A meta-analysis suggests that nitrogen deposition impedes organic matter decomposition, and thus stimulates carbon sequestration, in temperate forest soils where nitrogen is not limiting microbial growth. The concomitant reduction in soil carbon emissions is substantial, and equivalent in magnitude to the amount of carbon taken up by trees owing to nitrogen fertilization. As atmospheric nitrogen levels continue to rise, increased nitrogen deposition could spread to older, more weathered soils, as found in the tropics; however, soil carbon cycling in tropical forests cannot yet be assessed.

1,275 citations

Journal ArticleDOI
TL;DR: Evidence is brought together to show that roots can directly regulate most aspects of rhizosphere C flow either by regulating the exudation process itself or by directly regulating the recapture of exudates from soil.
Abstract: The loss of carbon from roots (rhizodeposition) and the consequent proliferation of microorganisms in the surrounding soil, coupled with the physical presence of a root and processes associated with nutrient uptake, gives rise to a unique zone of soil called the rhizosphere. In this review, we bring together evidence to show that roots can directly regulate most aspects of rhizosphere C flow either by regulating the exudation process itself or by directly regulating the recapture of exudates from soil. Root exudates have been hypothesized to be involved in the enhanced mobilization and acquisition of many nutrients from soil or the external detoxification of metals. With few exceptions, there is little mechanistic evidence from soil-based systems to support these propositions. We conclude that much more integrated work in realistic systems is required to quantify the functional significance of these processes in the field. We need to further unravel the complexities of the rhizosphere in order to fully engage with key scientific ideas such as the development of sustainable agricultural systems and the response of ecosystems to climate change. Contents I. Introduction 460 II. What is rhizodeposition? 460 III. Regulation of rhizodeposition 460 IV. How large is the root exudation C flux? 463 V. How responsive is the root exudation C flux? 463 VI. How responsive is the microbial community to root exudation? 464 VII. The role of root exudates in nutrient acquisition 464 VIII. Mycorrhizal fungi and rhizodeposition 471 IX. Future thoughts 474 Acknowledgements 474 References 474.

1,190 citations


Cites background from "Separating root and soil microbial ..."

  • ...A range of 14C and 13C tracer studies have shown that approximately 5–20% of net fixed C can be accounted for in rhizosphere respiration (Hanson et al., 2000; Nguyen, 2003)....

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References
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Journal ArticleDOI
01 Apr 1992-Tellus B
TL;DR: In this article, measured rates of soil respiration from terrestrial and wetland ecosystems were used to define the annual global CO 2 flux from soils, to identify uncertainties in the global flux estimate, and to investigate the influences of temperature, precipitation, and vegetation.
Abstract: We review measured rates of soil respiration from terrestrial and wetland ecosystems to define the annual global CO 2 flux from soils, to identify uncertainties in the global flux estimate, and to investigate the influences of temperature, precipitation, and vegetation on soil respiration rates. The annual global CO 2 flux from soils is estimated to average (± S.D.) 68 ± 4 PgC/ yr, based on extrapolations from biome land areas. Relatively few measurements of soil respiration exist from arid, semi-arid, and tropical regions; these regions should be priorities for additional research. On a global scale, soil respiration rates are positively correlated with mean annual air temperatures and mean annual precipitation. There is a close correlation between mean annual net primary productivity (NPP) of different vegetation biomes and their mean annual soil respiration rates, with soil respiration averaging 24% higher than mean annual NPP. This difference represents a minimum estimate of the contribution of root respiration to the total soil CO 2 efflux. Estimates of soil C turnover rates range from 500 years in tundra and peaty wetlands to 10 years in tropical savannas. We also evaluate the potential impacts of human activities on soil respiration rates, with particular focus on land use changes, soil fertilization, irrigation and drainage, and climate changes. The impacts of human activities on soil respiration rates are poorly documented, and vary among sites. Of particular importance are potential changes in temperatures and precipitation. Based on a review of in situ measurements, the Q 10 value for total soil respiration has a median value of 2.4. Increased soil respiration with global warming is likely to provide a positive feedback to the greenhouse effect. DOI: 10.1034/j.1600-0889.1992.t01-1-00001.x

3,271 citations


"Separating root and soil microbial ..." refers background or result in this paper

  • ...Reduced rates of heterotrophic respiration in the analysis provided by Raich and Schlesinger (1992) would have increased their estimates of the soil turnover time for an average forest ecosystem....

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  • ...The conclusion of a mean RC near 50 percent differs substantially from the prior estimate of RC used by Raich and Schlesinger (1992) in their global analysis of the impact of warming on soil respiration and soil carbon turnover rates....

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Journal ArticleDOI
TL;DR: The fractionation of carbon isotopes that occurs during photosynthesis is one of the most useful techniques for investigating the efficiency of CO2 uptake and indicates that different strategies are needed for improving wateruse efficiency in different kinds of plants.
Abstract: he efficiency of photosynthesis continues to interest biochemists, biologists, and plant physiologists. Scientists interested in CO2 uptake are concerned about the extent to which the uptake rate is limited by such factors as stomatal diffusion and the chemistry of the CO2 absorption process. The fractionation of carbon isotopes that occurs during photosynthesis is one of the most useful techniques for investigating the efficiency of CO2 uptake. Atmospheric carbon dioxide contains approximately 1.1% of the nonradioactive isotope carbon-13 and 98.9% of carbon-12. During photosynthesis, plants discriminate against C because of small differences in chemical and physical properties imparted by the difference in mass. This discrimination can be used to assign plants to various photosynthetic groups. The isotope fractionation also reflects limitations on photosynthetic efficiency imposed by the various diffusional and chemical components of CO2 uptake. When analyzed in detail, this fractionation provides information .about water use efficiency and indicates that different strategies are needed for improving wateruse efficiency in different kinds of plants. Isotope fractionation in simple physical and chemical processes is well understood and is commonly Current studies include

2,019 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide a brief review for policymakers who are concerned that changes in soil respiration may contribute to the rise in CO2 in Earth's atmosphere, while simultaneously leaving a greater store of carbon in the soil.
Abstract: Soil respiration is the primary path by which CO2fixed by land plants returns to the atmosphere. Estimated at approximately 75 × 1015gC/yr, this large natural flux is likely to increase due changes in the Earth's condition. The objective of this paper is to provide a brief scientific review for policymakers who are concerned that changes in soil respiration may contribute to the rise in CO2in Earth's atmosphere. Rising concentrations of CO2in the atmosphere will increase the flux of CO2from soils, while simultaneously leaving a greater store of carbon in the soil. Traditional tillage cultivation and rising temperature increase the flux of CO2from soils without increasing the stock of soil organic matter. Increasing deposition of nitrogen from the atmosphere may lead to the sequestration of carbon in vegetation and soils. The response of the land biosphere to simultaneous changes in all of these factors is unknown, but a large increase in the soil carbon pool seems unlikely to moderate the rise in atmospheric CO2during the next century.

1,646 citations


"Separating root and soil microbial ..." refers methods in this paper

  • ...As the distinctive13C label is added to the FACE plot, the CO2 fertilization effect may increase root respiration (Schlesinger & Andrews 1999)....

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Journal ArticleDOI
01 May 1991-Nature
TL;DR: In this article, the Rothamsted model is used to calculate the amount of CO2 that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant.
Abstract: ONE effect of global warming will be to accelerate the decomposition of soil organic matter, thereby releasing CO2 to the atmosphere, which will further enhance the warming trend1–7. Such a feedback mechanism could be quantitatively important, because CO2 is thought to be responsible for ∼55% of the increase in radiative forcing arising from anthropogenic emissions of gases to the atmosphere8, and there is about twice as much carbon in the top metre of soil as in the atmosphere9. Here we use the Rothamsted model for the turnover of organic matter in soil3 to calculate the amount of CO2 that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant. If world temperatures rise by 0.03 °C yr−1 (the increase considered as most likely by the Intergovernmental Panel on Climate Change8), we estimate that the additional release of CO2 from soil organic matter over the next 60 years will be 61 × 1015 gC. This is ∼19% of the CO2 that will be released by combustion of fossil fuel during the next 60 years if present use of fuel continues unabated.

1,003 citations


"Separating root and soil microbial ..." refers background in this paper

  • ...Much discussion centers on the feasibility of this approach (Anderson 1991; Dixon & Turner 1991; Jenkinson et al. 1991; Johnson & Kern 1991; Raich & Nadelhoffer 1989; Schlesinger 1990; Smith et al. 1997; Winjum et al. 1992)....

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Journal ArticleDOI
TL;DR: In this article, a review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration.
Abstract: This review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration. Both these processes have been evaluated through indirect assessments as well as through direct measurements under the field conditions. The techniques used suffer in general from difficulties in creating conditions of natural environment during the process of measurement. Generalizations regarding the magnitude of rates in different ecosystems are difficult because of limited results or non-comparability of results from different methods. Temperature and moisture and their interactions markedly influence both the processes. The surface feeders and soil animals have a marked influence on the decomposition. Partitioning of soil respiration into components due to live roots, microbes, and soil fauna has eluded a satisfactory solution so far.

734 citations