Elevated CO2 stimulates microbial growth and exoenzymes in soil aggregates (original) (raw)
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Global Change Biology, 2009
Increased belowground carbon (C) transfer by plant roots at elevated CO 2 may change properties of the microbial community in the rhizosphere. Previous investigations that focused on total soil organic C or total microbial C showed contrasting results: small increase, small decrease or no changes. We evaluated the effect of 5 years of elevated CO 2 (550 ppm) on four extracellular enzymes: b-glucosidase, chitinase, phosphatase, and sulfatase. We expected microorganisms to be differently localized in aggregates of various sizes and, therefore analyzed microbial biomass (C mic by SIR) and enzyme activities in three aggregate-size classes: large macro-(42 mm), small macro-(0.25-2 mm), and microaggregates (o0.25 mm). To estimate the potential enzyme production, we activated microorganisms by substrate (glucose and nutrients) amendment. Although C total and C mic as well as the activities of b-glucosidase, phosphatase, and sulfatase were unaffected in bulk soil and in aggregate-size classes by elevated CO 2 , significant changes were observed in potential enzyme production after substrate amendment. After adding glucose, enzyme activities under elevated CO 2 were 1.2-1.9-fold higher than under ambient CO 2 . This indicates the increased activity of microorganisms, which leads to accelerated C turnover in soil under elevated CO 2 . Significantly higher chitinase activity in bulk soil and in large macroaggregates under elevated CO 2 revealed an increased contribution of fungi to turnover processes. At the same time, less chitinase activity in microaggregates underlined microaggregate stability and the difficulties for fungal hyphae penetrating them. We conclude that quantitative and qualitative changes of C input by plants into the soil at elevated CO 2 affect microbial community functioning, but not its total content. Future studies should therefore focus more on the changes of functions and activities, but less on the pools.
European Journal of Soil Science, 2007
To gain insight into microbial function following increased atmospheric CO 2 concentration, we investigated the influence of 9 years of enriched CO 2 (600 ml litre À1) on the function and structural diversity of soil microorganisms in a grassland ecosystem under free air carbon dioxide enrichment (FACE), as affected by plant species (Trifolium repens L. and Lolium perenne L. in monocultures and mixed culture) and nitrogen (N) supply. We measured biomass and activities of enzymes covering cycles of the most important elements (C, N and P). The microbial community was profiled by molecular techniques of phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analysis. The enrichment in CO 2 increased soil microbial biomass (þ48.1%) as well as activities of invertase (þ36.2%), xylanase (þ22.9%), urease (þ23.8%), protease (þ40.2%) and alkaline phosphomonoesterase (þ54.1%) in spring 2002. In autumn, the stimulation of microbial biomass was 25% less and that of enzymes 3-12% less than in spring. Strong correlations between activities of invertase, protease, urease and alkaline phosphomonoesterase and microbial biomass were found. The stimulation of microbial activity in the enriched atmosphere was probably caused by changes in the quantity and kind of root litter and rhizodeposition. The response of soil microorganisms to enriched CO 2 was most pronounced under Trifolium monoculture and under greater N supply. The PLFA analysis revealed that total PLFA contents were greater by 24.7% on average, whereby the proportion of bioindicators representative of Gram-negative bacteria increased significantly in the enriched CO 2 under less N-fertilized Lolium culture. Discriminant analysis showed marked differences between the PLFA profiles of the three plant communities. Shannon diversity indices calculated from DGGE patterns were greater (þ12.5%) in the enriched CO 2 , indicating increased soil bacterial diversity. We conclude that greater microbial biomass and enzyme activity buffer the potential increase in C sequestration occurring from greater C addition in enriched CO 2 due to greater mineralization of soil organic matter.
FEMS Microbiology Ecology, 2000
Increased root exudation under elevated atmospheric CO 2 and the contrasting environments in soil macro-and microaggregates could affect microbial growth strategies. We investigated the effect of elevated CO 2 on the contribution of fast-(r-strategists) and slow-growing (K-strategists) microorganisms in soil macroand microaggregates. We fractionated the bulk soil from the ambient and elevated (for 5 years) CO 2 treatments of FACE-Hohenheim (Stuttgart) into large macro-(4 2 mm), small macro-(0.25-2.00 mm), and microaggregates (o 0.25 mm) using 'optimal moist' sieving. Microbial biomass (C mic ), the maximum specific growth rate (m), growing microbial biomass (GMB) and lagperiod (t lag ) were estimated by the kinetics of CO 2 emission from bulk soil and aggregates amended with glucose and nutrients. Although C org and C mic were unaffected by elevated CO 2 , m values were significantly higher under elevated than ambient CO 2 for bulk soil, small macroaggregates, and microaggregates. Substrate-induced respiratory response increased with decreasing aggregate size under both CO 2 treatments. Based on changes in m, GMB and lag period, we conclude that elevated atmospheric CO 2 stimulated the r-selected microorganisms, especially in soil microaggregates. Such an increase in r-selected microorganisms indicates acceleration of available C mineralization in soil, which may counterbalance the additional C input by roots in soils in a future elevated atmospheric CO 2 environment.
New Phytologist, 2000
There is considerable uncertainty about how rates of soil carbon (C) and nitrogen (N) cycling will change as CO # accumulates in the Earth's atmosphere. We summarized data from 47 published reports on soil C and N cycling under elevated CO # in an attempt to generalize whether rates will increase, decrease, or not change. Our synthesis centres on changes in soil respiration, microbial respiration, microbial biomass, gross N mineralization, microbial immobilization and net N mineralization, because these pools and processes represent important control points for the below-ground flow of C and N. To determine whether differences in C allocation between plant life forms influence soil C and N cycling in a predictable manner, we summarized responses beneath graminoid, herbaceous and woody plants grown under ambient and elevated atmospheric CO # . The below-ground pools and processes that we summarized are characterized by a high degree of variability (coefficient of variation 80-800%), making generalizations within and between plant life forms difficult. With few exceptions, rates of soil and microbial respiration were more rapid under elevated CO # , indicating that (1) greater plant growth under elevated CO # enhanced the amount of C entering the soil, and (2) additional substrate was being metabolized by soil microorganisms. However, microbial biomass, gross N mineralization, microbial immobilization and net N mineralization are characterized by large increases and declines under elevated CO # , contributing to a high degree of variability within and between plant life forms. From this analysis we conclude that there are insufficient data to predict how microbial activity and rates of soil C and N cycling will change as the atmospheric CO # concentration continues to rise. We argue that current gaps in our understanding of fine-root biology limit our ability to predict the response of soil microorganisms to rising atmospheric CO # , and that understanding differences in fine-root longevity and biochemistry between plant species are necessary for developing a predictive model of soil C and N cycling under elevated CO # .
Global Change Biology, 2010
Increasing the belowground translocation of assimilated carbon by plants grown under elevated CO 2 can cause a shift in the structure and activity of the microbial community responsible for the turnover of organic matter in soil. We investigated the long-term effect of elevated CO 2 in the atmosphere on microbial biomass and specific growth rates in root-free and rhizosphere soil. The experiments were conducted under two free air carbon dioxide enrichment (FACE) systems: in Hohenheim and Braunschweig, as well as in the intensively managed forest mesocosm of the Biosphere 2 Laboratory (B2L) in Oracle, AZ. Specific microbial growth rates (l) were determined using the substrateinduced respiration response after glucose and/or yeast extract addition to the soil. For B2L and both FACE systems, up to 58% higher l were observed under elevated vs. ambient CO 2 , depending on site, plant species and N fertilization. The l-values increased linearly with atmospheric CO 2 concentration at all three sites. The effect of elevated CO 2 on rhizosphere microorganisms was plant dependent and increased for: Brassica napus 5 Triticum aestivumoBeta vulgarisoPopulus deltoides. N deficiency affected microbial growth rates directly (N limitation) and indirectly (changing the quantity of fine roots). So, 50% decrease in N fertilization caused the overall increase or decrease of microbial growth rates depending on plant species. The l-value increase was lower for microorganisms growing on yeast extract then for those growing on glucose, i.e. the effect of elevated CO 2 was smoothed on rich vs. simple substrate. So, the r/K strategies ratio can be better revealed by studying growth on simple (glucose) than on rich substrate mixtures (yeast extract). Our results clearly showed that the functional characteristics of the soil microbial community (i.e. specific growth rates) rather than total microbial biomass amount are sensitive to increased atmospheric CO 2 . We conclude that the more abundant available organics released by roots at elevated CO 2 altered the ecological strategy of the soil microbial community specifically a shift to a higher contribution of fast-growing r-selected species was observed. These changes in functional structure of the soil microbial community may counterbalance higher C input into the soil under elevated atmospheric CO 2 concentration.
Effects of elevated atmospheric CO2 concentrations on soil microorganisms
Journal of microbiology (Seoul, Korea), 2004
Effects of elevated CO(2) on soil microorganisms are known to be mediated by various interactions with plants, for which such effects are relatively poorly documented. In this review, we summarize and synthesize results from studies assessing impacts of elevated CO(2) on soil ecosystems, focusing primarily on plants and a variety the of microbial processes. The processes considered include changes in microbial biomass of C and N, microbial number, respiration rates, organic matter decomposition, soil enzyme activities, microbial community composition, and functional groups of bacteria mediating trace gas emission such as methane and nitrous oxide. Elevated CO(2) in atmosphere may enhance certain microbial processes such as CH(4) emission from wetlands due to enhanced carbon supply from plants. However, responses of extracellular enzyme activities and microbial community structure are still controversy, because interferences with other factors such as the types of plants, nutrient av...
Soil microbial responses to increased concentrations of atmospheric CO2
Global Change Biology, 1997
Terrestrial ecosystems respond to an increased concentration of atmospheric CO 2 . While elevated atmospheric CO 2 has been shown to alter plant growth and productivity, it also affects ecosystem structure and function by changing below-ground processes. Knowledge of how soil microbiota respond to elevated atmospheric CO 2 is of paramount importance for understanding global carbon and nutrient cycling and for predicting changes at the ecosystem-level. An increase in the atmospheric CO 2 concentration not only alters the weight, length, and architecture of plant roots, but also affects the biotic and abiotic environment of the root system. Since the concentration of CO 2 in soil is already 10-50 times higher than that in the atmosphere, it is unlikely that increasing atmospheric CO 2 will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO 2 will affect the microbe-soil-plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil water deficit. Consequently, the increased amounts and altered composition of rhizosphere-released materials will have the potential to alter both population and community structure, and activity of soil-and rhizosphere-associated microorganisms. This occurrence could in turn affect plant health and productivity and plant community structure. This review covers current knowledge about the response of soil microbes to elevated concentrations of atmospheric CO 2 .
Atmospheric CO2 and the composition and function of soil microbial communities
Ecological Applications, 2000
Elevated atmospheric CO 2 has the potential to increase the production and alter the chemistry of organic substrates entering soil from plant production, the magnitude of which is constrained by soil-N availability. Because microbial growth in soil is limited by substrate inputs from plant production, we reasoned that changes in the amount and chemistry of these organic substrates could affect the composition of soil microbial communities and the cycling of N in soil. We studied microbial community composition and soil-N transformations beneath Populus tremuloides Michx. growing under experimental atmospheric CO 2 (35.7 and 70.7 Pa) and soil-N-availability (low N ϭ 61 ng N·g Ϫ1 ·d Ϫ1 and high N ϭ 319 ng N·g Ϫ1 ·d Ϫ1 ) treatments. Atmospheric CO 2 concentration was modified in large, open-top chambers, and we altered soil-N availability in open-bottom root boxes by mixing different proportions of A and C horizon material. We used phospholipid fatty-acid analysis to gain insight into microbial community composition and coupled this analysis to measurements of soil-N transformations using 15 N-pool dilution techniques. The information presented here is part of an integrated experiment designed to elucidate the physiological mechanisms controlling the flow of C and N in the plant-soil system. Our objectives were (1) to determine whether changes in plant growth and tissue chemistry alter microbial community composition and soil-N cycling in response to increasing atmospheric CO 2 and soil-N availability and (2) to integrate the results of our experiment into a synthesis of elevated atmospheric CO 2 and the cycling of C and N in terrestrial ecosystems.