The impact of long-term CO2 enrichment and moisture levels on soil microbial community structure and enzyme activities (original) (raw)
Related papers
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.
Soil Biology and Biochemistry, 2006
Although elevation of CO 2 has been reported to impact soil microbial functions, little information is available on the spatial and temporal variation of this effect. The objective of this study was to determine the microbial response in a northern Colorado shortgrass steppe to a 5-year elevation of atmospheric CO 2 as well as the reversibility of the microbial response during a period of several months after shutting off the CO 2 amendment. The experiment was comprised of nine experimental plots: three chambered plots maintained at ambient CO 2 levels of 360 mmol mol À1 (ambient treatment), three chambered plots maintained at 720 mmol mol À1 CO 2 (elevated treatment) and three unchambered plots of equal ground area used as controls to monitor the chamber effect.
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.
Effects of long term CO 2 enrichment on microbial community structure in calcareous grassland
Plant and Soil, 2000
Dissertation zur Erlangung des Grades eines Doktors der Agrarwissenschaften vorgelegt der Fakultät Agrarwissenschaften von Diana Ebersberger Diplom-Geographin aus Neustadt an der Weinstraße 2003 Die vorliegende Arbeit wurde am 04.07.2003 von der Fakultät Agrarwissenschaften der Universität Hohenheim als "Dissertation zur Erlangung des Grades eines Doktors der Agrarwissenschaften" angenommen. Tag der mündlichen Prüfung: 15.
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.
Soil organic matter (SOM) dynamics ultimately govern the ability of soil to provide long-term C sequestration and the nutrients required for ecosystem productivity. Predicting belowground responses to elevated CO 2 requires an integrated understanding of SOM transformations and the microbial activity that governs them. It remains unclear how the microorganisms upon which these transformations depend will function in an elevated CO 2 world. This study examines SOM transformations and microbial metabolism in soils from the Duke Free Air Carbon Enrichment site in North Carolina, USA. We assessed microbial respiration and net nitrogen (N) mineralization in soils with and without elevated CO 2 exposure during a 100-day incubation. We also traced the depleted C isotopic signature of the supplemental CO 2 into SOM and the soils' phospholipid fatty acids (PLFA), which serve as biomarkers for living cells. Cumulative net N mineralization in elevated CO 2 soils was 50% that in control soils after a 100-day incubation. Respiration was not altered with elevated CO 2 . C : N ratios of bulk SOM did not change with elevated CO 2 , but incubation data suggest that the C : N ratios of mineralized organic matter increased with elevated CO 2 . Values of SOM d 13 C were depleted with elevated CO 2 (À26.7 AE 0.2 vs. À30.2 AE 0.3%), reflecting the depleted signature of the supplemental CO 2 . We compared d 13 C of individual PLFA with the d 13 C of SOM to discern incorporation of the depleted C isotopic signature into soil microbial groups in elevated CO 2 plots. PLFA i15:0, a15:0, and 10Met18:0 reflected significant incorporation of recently produced photosynthate, suggesting that the bacterial groups defined by these biomarkers are active metabolizers in elevated CO 2 soils. At least one of these groups (actinomycetes, 10Met18:0) specializes in metabolizing less labile substrates. Because control plots did not receive an equivalent 13 C tracer, we cannot determine from these data whether this group of organisms was stimulated by elevated CO 2 compared with these organisms in control soils. Stimulation of this group, if it occurred in the elevated CO 2 plot, would be consistent with a decline in the availability of mineralizable organic matter with elevated CO 2 , which incubation data suggest may be the case in these soils.
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...
Assessing the impact of elevated CO2 on soil microbial activity in a Mediterranean model ecosystem
Plant and Soil, 1995
The fate, as well as the consequence for plant nutrition, of the additional carbon entering soil under elevated C O 2 is largely determined by the activity of soil microorganisms. However, most elevated CO2 studies have documented changes (generally increases) in microbial biomass and total infection by symbiotic organisms, which is only a first step in the understanding of the modification of soil processes. Using a Mediterranean model ecosystem, we complemented these variables by analyzing changes in enzymatic activities, hyphal lengths, and bacterial substrate assimilation, to tentatively identify the specific components affected under elevated CO2 and those which suggest changes in soil organic matter pools. We also investigated changes in the functional structures of arbuscular mycorrhizas. Most of the microbial variables assessed showed significant and substantial increase under elevated CO2, of the same order or less than those observed for root mass and length. The increase in dehydrogenase activity indicates that the larger biomass of microbes was accompanied by an increase in their activity. The increase in hyphal length (predominantly of saprophytic fungi), and xylanase, cellulase and phosphatase activities, suggests an overall stimulation of organic matter decomposition. The higher number of substrates utilized by microorganisms from the soil under elevated CO2 was significant for the amine/amide group. Total arbuscular and vesicular mycorrhizal infection of roots was higher under elevated CO2, but the proportion of functional structures was not modified. These insights into the CO2-induced changes in soil biological activity point towards potential areas of investigation complementary to a direct analysis of the soil organic matter pools.
Applied Soil Ecology, 2005
Microorganisms are the regulators of decomposition processes occurring in soil, they also constitute a labile fraction of potentially available N. Microbial mineralization and nutrient cycling could be affected through altered plant inputs at elevated CO 2. An understanding of microbial biomass and microbial activity in response to belowground processes induced by elevated CO 2 is thus crucial in order to predict the long-term response of ecosystems to climatic changes. Microbial biomass, microbial respiration, inorganic N, extractable P and six enzymatic activities related to C, N, P and S cycling (b-glucosidase, cellulase, chitinase, protease, acid phosphatase and arylsulphatase) were investigated in soils of a poplar plantation exposed to elevated CO 2. Clones of Populus alba, Populus nigra and Populus x euramericana were grown in six 314 m 2 plots treated either with atmospheric (control) or enriched (550 mmol mol À1 CO 2 ) CO 2 concentration with FACE technology (free-air CO 2 enrichment). Chemical and biochemical parameters were monitored throughout a year in soil samples collected at five sampling dates starting from Autumn 2000 to Autumn 2001.
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.