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1.
Atmospheric CO 2 and O 3 concentrations are increasing due to human activity and both trace gases have the potential to alter C cycling in forest
ecosystems. Because soil microorganisms depend on plant litter as a source of energy for metabolism, changes in the amount
or the biochemistry of plant litter produced under elevated CO 2 and O 3 could alter microbial community function and composition. Previously, we have observed that elevated CO 2 increased the microbial metabolism of cellulose and chitin, whereas elevated O 3 dampened this response. We hypothesized that this change in metabolism under CO 2 and O 3 enrichment would be accompanied by a concomitant change in fungal community composition. We tested our hypothesis at the
free-air CO 2 and O 3 enrichment (FACE) experiment at Rhinelander, Wisconsin, in which Populus tremuloides, Betula papyrifera, and Acer saccharum were grown under factorial CO 2 and O 3 treatments. We employed extracellular enzyme analysis to assay microbial metabolism, phospholipid fatty acid (PLFA) analysis
to determine changes in microbial community composition, and polymerase chain reaction–denaturing gradient gel electrophoresis
(PCR–DGGE) to analyze the fungal community composition. The activities of 1,4-β-glucosidase (+37%) and 1,4,-β- N-acetylglucosaminidase (+84%) were significantly increased under elevated CO 2, whereas 1,4-β-glucosidase activity (−25%) was significantly suppressed by elevated O 3. There was no significant main effect of elevated CO 2 or O 3 on fungal relative abundance, as measured by PLFA. We identified 39 fungal taxonomic units from soil using DGGE, and found
that O 3 enrichment significantly altered fungal community composition. We conclude that fungal metabolism is altered under elevated
CO 2 and O 3, and that there was a concomitant change in fungal community composition under elevated O 3. Thus, changes in plant inputs to soil under elevated CO 2 and O 3 can propagate through the microbial food web to alter the cycling of C in soil. 相似文献
2.
The role of nutrient availability in the decay of Typha latifolia and Cladium jamaicense litter and associated microbial responses were studied under controlled experimental conditions. The experimental setup consisted of three 14 m 2 mesocosms: (i) an experimentally enriched (N&P) mesocosm containing organic soil, (ii) a mesocosm with organic soil but no external enrichment, and (iii) a mesocosm with no external nutrient inputs and a mineral soil, each equally divided into two areas predominated by T. latifolia and C. jamaicense. Air dried senesced material of each plant species from the three units were placed in litterbags and were introduced back into their respective communities on the soil and water interface. Litter from T. latifolia degraded significantly faster than that of C. jamaicense. The half life of T. latifolia litter averaged approximately 274 days, C. jamaicense litter half life was extrapolated to approximately 377 days. Nutrient enrichment significantly increased the decay rates of T. latifolia, the nutrient effect on C. jamaicense decomposition was less apparent. The microbial biomass carbon in T. latifolia and C. jamaicense litter increased significantly as the litter decomposed. No significant differences between the litter types or amongst mesocosms were found. The relative activities of the extracellular enzymes acid phosphatase and β-glucosidase were significantly ( P < 0.001 and P = 0.0284, respectively) affected by litter type and mesocosm over time. Litter associated alkaline phosphatase activity was largest in the mineral mesocosm, followed by the organic control and then organic enriched irrespective of litter type, β-glucosidase activity showed an inverse effect, enriched organic > organic control > mineral. The litter CO 2 and CH 4 microbial production rates showed a significant litter type and mesocosm effect ( P = 0.0003 and 0.001, respectively). T. latifolia litter had larger associated methanogenic and microbial respiration rates than C. jamaicense litter. Nutrient enrichment enhanced both forms of microbial metabolic activities (CO 2 and CH 4 production). The effect of nutrient enrichment was primarily evident in the initial (3–6 months) period of decay, extracellular enzyme activities and the litter associated microbial metabolic activities showed most response during this decay stage. 相似文献
3.
CO 2 production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation – the direct breakdown of organic matter (OM) by solar irradiance – has been found to contribute to litter mass loss in dry ecosystems. Previous small‐scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO 2. However, the contribution of photodegradation to total CO 2 losses at ecosystems scales is unknown. This study determined the proportion of the total CO 2 losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO 2 production was examined by comparing daytime CO 2 fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO 2 gradient technique, and with night‐time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO 2 fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO 2 flux from the peatland and almost 60% of the dry season CO 2 flux from the grassland, and up to 62% and 92% of the summer mid‐day CO 2 fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO 2 exchange into its gross components by assuming that total daytime CO 2 losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem–atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon–climate models. 相似文献
4.
Permafrost thaw can alter the soil environment through changes in soil moisture, frequently resulting in soil saturation, a shift to anaerobic decomposition, and changes in the plant community. These changes, along with thawing of previously frozen organic material, can alter the form and magnitude of greenhouse gas production from permafrost ecosystems. We synthesized existing methane (CH 4) and carbon dioxide (CO 2) production measurements from anaerobic incubations of boreal and tundra soils from the geographic permafrost region to evaluate large‐scale controls of anaerobic CO 2 and CH 4 production and compare the relative importance of landscape‐level factors (e.g., vegetation type and landscape position), soil properties (e.g., pH, depth, and soil type), and soil environmental conditions (e.g., temperature and relative water table position). We found fivefold higher maximum CH 4 production per gram soil carbon from organic soils than mineral soils. Maximum CH 4 production from soils in the active layer (ground that thaws and refreezes annually) was nearly four times that of permafrost per gram soil carbon, and CH 4 production per gram soil carbon was two times greater from sites without permafrost than sites with permafrost. Maximum CH 4 and median anaerobic CO 2 production decreased with depth, while CO 2:CH 4 production increased with depth. Maximum CH 4 production was highest in soils with herbaceous vegetation and soils that were either consistently or periodically inundated. This synthesis identifies the need to consider biome, landscape position, and vascular/moss vegetation types when modeling CH 4 production in permafrost ecosystems and suggests the need for longer‐term anaerobic incubations to fully capture CH 4 dynamics. Our results demonstrate that as climate warms in arctic and boreal regions, rates of anaerobic CO 2 and CH 4 production will increase, not only as a result of increased temperature, but also from shifts in vegetation and increased ground saturation that will accompany permafrost thaw. 相似文献
5.
Rising atmospheric carbon dioxide has the potential to alter leaf litter chemistry, potentially affecting decomposition and rates of carbon and nitrogen cycling in forest ecosystems. This study was conducted to determine whether growth under elevated atmospheric CO 2 altered the quality and microbial decomposition of leaf litter of a widely distributed northern hardwood species at sites of low and high soil nitrogen availability. In addition, we assessed whether the carbon–nutrient balance (CNB) and growth differentiation balance (GDB) hypotheses could be extended to predict changes in litter quality in response to resource availability. Sugar maple ( Acer saccharum) was grown in the field in open‐top chambers at 36 and 55 Pa partial pressure CO 2, and initial soil mineralization rates of 45 and 348 μg N g ?1 d ?1. Naturally senesced leaf litter was assessed for chemical composition and incubated in the laboratory for 111 d. Microbial respiration and the production of dissolved organic carbon (DOC) were quantified as estimates of decomposition. Elevated CO 2 and low soil nitrogen resulted in higher litter concentrations of nonstructural carbohydrates and condensed tannins, higher C/N ratios and lower N concentrations. Soil N availability appears to have had a greater effect on litter quality than did atmospheric CO 2, although the treatments were additive, with highest concentrations of nonstructural carbohydrates and condensed tannins occurring under elevated CO 2–low soil N. Rates of microbial respiration and the production of DOC were insensitive to differences in litter quality. In general, concentrations of litter constituents, except for starch, were highly correlated to those in live foliage, and the CNB/GDB hypotheses proved useful in predicting changes in litter quality. We conclude the chemical composition of sugar maple litter will change in the future in response to rising atmospheric CO 2, and that soil N availability will exert a major control. It appears that microbial metabolism will not be directly affected by changes in litter quality, although conclusions regarding decomposition as a whole must consider the entire soil food web. 相似文献
6.
Hydrogenotrophic methanogens can use gaseous substrates, such as H 2 and CO 2, in CH 4 production. H 2 gas is used to reduce CO 2. We have successfully operated a hollow-fiber membrane biofilm reactor (Hf-MBfR) for stable and continuous CH 4 production from CO 2 and H 2. CO 2 and H 2 were diffused into the culture medium through the membrane without bubble formation in the Hf-MBfR, which was operated at pH 4.5–5.5 over 70 days. Focusing on the presence of hydrogenotrophic methanogens, we analyzed the structure of the microbial community in the reactor. Denaturing gradient gel electrophoresis (DGGE) was conducted with bacterial and archaeal 16S rDNA primers. Real-time qPCR was used to track changes in the community composition of methanogens over the course of operation. Finally, the microbial community and its diversity at the time of maximum CH 4 production were analyzed by pyrosequencing methods. Genus Methanobacterium, related to hydrogenotrophic methanogens, dominated the microbial community, but acetate consumption by bacteria, such as unclassified Clostridium sp., restricted the development of acetoclastic methanogens in the acidic CH 4 production process. The results show that acidic operation of a CH 4 production reactor without any pH adjustment inhibited acetogenic growth and enriched the hydrogenotrophic methanogens, decreasing the growth of acetoclastic methanogens. 相似文献
7.
土壤是地球表层最为重要的碳库也是温室气体的源或汇。自工业革命以来,对土壤温室气体的容量、收支平衡和通量等已有较多研究和估算,但对关键过程及其源/汇的研究却十分有限。微生物是土壤碳氮转化的主要驱动者, 在生态系统碳氮循环过程中扮演重要的角色,对全球气候变化有着响应的响应、适应及反馈,然而其个体数量,群落结构和多样性如何与气候扰动相互关联、进而怎样影响生态系统过程的问题仍有待进一步探索。从微生物介导的碳氮循环过程入手,重点讨论微生物对气候变化包括温室气体(CO 2,CH 4,N 2O)增加、全球变暖、大气氮沉降等的响应和反馈,并由此提出削减温室气体排放的可能途径和今后发展的方向。 相似文献
8.
Temperature sensitivity of anaerobic carbon mineralization in wetlands remains poorly represented in most climate models and is especially unconstrained for warmer subtropical and tropical systems which account for a large proportion of global methane emissions. Several studies of experimental warming have documented thermal acclimation of soil respiration involving adjustments in microbial physiology or carbon use efficiency (CUE), with an initial decline in CUE with warming followed by a partial recovery in CUE at a later stage. The variable CUE implies that the rate of warming may impact microbial acclimation and the rate of carbon‐dioxide (CO 2) and methane (CH 4) production. Here, we assessed the effects of warming rate on the decomposition of subtropical peats, by applying either a large single‐step (10°C within a day) or a slow ramping (0.1°C/day for 100 days) temperature increase. The extent of thermal acclimation was tested by monitoring CO 2 and CH 4 production, CUE, and microbial biomass. Total gaseous C loss, CUE, and MBC were greater in the slow (ramp) warming treatment. However, greater values of CH 4–C:CO 2–C ratios lead to a greater global warming potential in the fast (step) warming treatment. The effect of gradual warming on decomposition was more pronounced in recalcitrant and nutrient‐limited soils. Stable carbon isotopes of CH 4 and CO 2 further indicated the possibility of different carbon processing pathways under the contrasting warming rates. Different responses in fast vs. slow warming treatment combined with different endpoints may indicate alternate pathways with long‐term consequences. Incorporations of experimental results into organic matter decomposition models suggest that parameter uncertainties in CUE and CH 4–C:CO 2–C ratios have a larger impact on long‐term soil organic carbon and global warming potential than uncertainty in model structure, and shows that particular rates of warming are central to understand the response of wetland soils to global climate change. 相似文献
9.
The impact of salt-water intrusion on microbial organic carbon (C) mineralization in tidal freshwater marsh (TFM) soils was investigated in a year-long laboratory experiment in which intact soils were exposed to a simulated tidal cycle of freshwater or dilute salt-water. Gas fluxes [carbon dioxide (CO 2) and methane (CH 4)], rates of microbial processes (sulfate reduction and methanogenesis), and porewater and solid phase biogeochemistry were measured throughout the experiment. Flux rates of CO 2 and, surprisingly, CH 4 increased significantly following salt-water intrusion, and remained elevated relative to freshwater cores for 6 and 5 months, respectively. Following salt-water intrusion, rates of sulfate reduction increased significantly and remained higher than rates in the freshwater controls throughout the experiment. Rates of acetoclastic methanogenesis were higher than rates of hydrogenotrophic methanogenesis, but the rates did not differ by salinity treatment. Soil organic C content decreased significantly in soils experiencing salt-water intrusion. Estimates of total organic C mineralized in freshwater and salt-water amended soils over the 1-year experiment using gas flux measurements (18.2 and 24.9 mol C m ?2, respectively) were similar to estimates obtained from microbial rates (37.8 and 56.2 mol C m ?2, respectively), and to losses in soil organic C content (0 and 44.1 mol C m ?2, respectively). These findings indicate that salt-water intrusion stimulates microbial decomposition, accelerates the loss of organic C from TFM soils, and may put TFMs at risk of permanent inundation. 相似文献
10.
A bstract
We examined aerobic and anaerobic microbial carbon dioxide (CO 2) and methane (CH 4) exchange in peat samples representing different profiles at natural, mined, mined-abandoned, and restored northern peatlands
and characterized the nutrient and substrate chemistry and microbial biomass of these soils. Mining and abandonment led to
reduced nutrient and substrate availability and occasionally drier conditions in surface peat resulting in a drastic reduction
in CO 2 and CH 4 production, in agreement with previous studies. Owing mainly to wetter conditions, CH 4 production and oxidation were faster in restored block-cut than natural sites, whereas in one restored site, increased substrate
and nutrient availability led to much more rapid rates of CO 2 production. Our work in restored block-cut sites compliments that in vacuum-harvested peatlands undergoing more recent active
restoration attempts. The sites we examined covered a large range of soil C substrate quality, nutrient availability, microbial
biomass, and microbial activities, allowing us to draw general conclusions about controls on microbial CO 2 and CH 4 dynamics using stepwise regression analysis among all sites and soil depths. Aerobic and anaerobic decomposition of peat
was constrained by organic matter quality, particularly phosphorus (P) and carbon (C) chemistry, and closely linked to the
size of the microbial biomass supported by these limiting resources. Methane production was more dominantly controlled by
field moisture content (a proxy for anaerobism), even after 20 days of anaerobic laboratory incubation, and to a lesser extent
by C substrate availability. As methanogens likely represented only a small proportion of the total microbial biomass, there
were no links between total microbial biomass and CH 4 production. Methane oxidation was controlled by the same factors influencing CH 4 production, leading to the conclusion that CH 4 oxidation is primarily controlled by substrate (that is, CH 4) availability. Although restoring hydrology similar to natural sites may re-establish CH 4 dynamics, there is geographic or site-specific variability in the ability to restore peat decomposition dynamics. 相似文献
11.
Rates of atmospheric CH 4 consumption of soils in temperate forest were compared in plots continuously enriched with CO 2 at 200 µL L ?1 above ambient and in control plots exposed to the ambient atmosphere of 360 µL CO 2 L ?1. The purpose was to determine if ecosystem atmospheric CO 2 enrichment would alter soil microbial CH 4 consumption at the forest floor and if the effect of CO 2 would change with time or with environmental conditions. Reduced CH 4 consumption was observed in CO 2‐enriched plots relative to control plots on 46 out of 48 sampling dates, such that CO 2‐enriched plots showed annual reductions in CH 4 consumption of 16% in 1998 and 30% in 1999. No significant differences were observed in soil moisture, temperature, pH, inorganic‐N or rates of N‐mineralization between CO 2‐enriched and control plots, indicating that differences in CH 4 consumption between treatments were likely the result of changes in the composition or size of the CH 4‐oxidizing microbial community. A repeated measures analysis of variance that included soil moisture, soil temperature (from 0 to 30 cm), and time as covariates indicated that the reduction of CH 4 consumption under elevated CO 2 was enhanced at higher soil temperatures. Additionally, the effect of elevated CO 2 on CH 4 consumption increased with time during the two‐year study. Overall, these data suggest that rising atmospheric CO 2 will reduce atmospheric CH 4 consumption in temperate forests and that the effect will be greater in warmer climates. A 30% reduction in atmospheric CH 4 consumption by temperate forest soils in response to rising atmospheric CO 2 will result in a 10% reduction in the sink strength of temperate forest soils in the atmospheric CH 4 budget and a positive feedback to the greenhouse effect. 相似文献
12.
Understanding the impacts of leaks from geologic carbon sequestration, also known as carbon capture and storage, is key to developing effective strategies for carbon dioxide (CO 2) emissions management and mitigation of potential negative effects. Here, we provide the first report on the potential effects of leaks from carbon capture and storage sites on microbial functional groups in surface and near-surface soils. Using a simulated subsurface CO 2 storage leak scenario, we demonstrate how CO 2 flow upward through the soil column altered both the abundance (DNA) and activity (mRNA) of microbial functional groups mediating carbon and nitrogen transformations. These microbial responses were found to be seasonally dependent and correlated to shifts in atmospheric conditions. While both DNA and mRNA levels were affected by elevated CO 2, they did not react equally, suggesting two separate mechanisms for soil microbial community response to high CO 2 levels. The results did not always agree with previous studies on elevated atmospheric (rather than subsurface) CO 2 using FACE (Free-Air CO 2 Enrichment) systems, suggesting that microbial community response to CO 2 seepage from the subsurface might differ from its response to atmospheric CO 2 increases. 相似文献
13.
Anaerobic microbial activity in northern peat soils most often results in more carbon dioxide (CO 2 ) production than methane (CH 4) production. This study examined why methanogenic conditions (i.e., equal molar amounts of CH 4 production and CO 2 production) prevail so infrequently. We used peat soils from two ombrotrophic bogs and from two rheotrophic fens. The former two represented a relatively dry bog hummock and a wet bog hollow, and the latter two represented a forested fen and a sedge-dominated fen. We quantified gas production rates in soil samples incubated in vitro with and without added metabolic substrates (glucose, ethanol, H 2/CO 2). None of the peat soils exhibited methanogenic conditions when incubated in vitro for a short time (< 5 days) and without added substrates. Incubating some samples > 50 days without added substrates led to methanogenic conditions in only one of four experiments. The anaerobic CO 2:CH 4 production ratio ranged from 5:1 to 40:1 in peat soil without additions and was larger in samples from the dry bog hummock and forested fen than the wet bog hollow and sedge fen. Adding ethanol or glucose separately to peat soils led to methanogenic conditions within 5 days after the addition by stimulating rates of CH 4 production, suggesting CH 4 production from both hydrogenotrophic and acetoclastic methanogenesis. Our results suggest that methanogenic conditions in peat soils rely on a constant supply of easily decomposable metabolic substrates. Sample handling and incubation procedures might obscure methanogenic conditions in peat soil incubated in vitro. 相似文献
14.
As atmospheric CO 2 concentrations continue to rise and impact plant communities, concomitant shifts in belowground microbial processes are likely, but poorly understood. We measured monthly porewater concentrations of sulfate, sulfide, methane (CH 4), dissolved inorganic carbon and dissolved organic carbon over a 5-year period in a brackish marsh. Samples were collected using porewater wells (i.e., sippers) in a Schoenoplectus americanus-dominated (C 3 sedge) community, a Spartina patens-dominated (C 4 grass) community and a mixed (C 3 and C 4) community within the marsh. Plant communities were exposed to ambient and elevated (ambient + 340 ppm) CO 2 levels for 15 years prior to porewater sampling, and the treatments continued over the course of our sampling. Sulfate reduction was stimulated by elevated CO 2 in the C 3-dominated community, but not in the C 4-dominated community. Elevated CO 2 also resulted in higher porewater concentrations of CH 4 and dissolved organic carbon in the C 3-dominated system, though inhibition of CH 4 production by sulfate reduction appears to temper the porewater CH 4 response. These patterns mirror the typical divergent responses of C 3 and C 4 plants to elevated CO 2 seen in this ecosystem. Porewater concentrations of nitrogen (as ammonium) and phosphorus did not decrease despite increased plant biomass in the C 3-dominated community, suggesting nutrients do not strongly limit the sustained vegetation response to elevated CO 2. Overall, our data demonstrate that elevated CO 2 drives changes in porewater chemistry and suggest that increased plant productivity likely stimulates microbial decomposition through increases in dissolved organic carbon availability. 相似文献
15.
Background and aimsThe litter layer is a major source of CO2, and it also influences soil-atmosphere exchange of N2O and CH4. So far, it is not clear how much of soil greenhouse gas (GHG) emission derives from the litter layer itself or is litter-induced. The present study investigates how the litter layer controls soil GHG fluxes and microbial decomposer communities in a temperate beech forest. MethodsWe removed the litter layer in an Austrian beech forest and studied responses of soil CO2, CH4 and N2O fluxes and the microbial community via phospholipid fatty acids (PLFA). Soil GHG fluxes were determined with static chambers on 22 occasions from July 2012 to February 2013, and soil samples collected at 8 sampling events. ResultsLitter removal reduced CO2 emissions by 30 % and increased temperature sensitivity (Q10) of CO2 fluxes. Diffusion of CH4 into soil was facilitated by litter removal and CH4 uptake increased by 16 %. This effect was strongest in autumn and winter when soil moisture was high. Soils without litter turned from net N2O sources to slight N2O sinks because N2O emissions peaked after rain events in summer and autumn, which was not the case in litter-removal plots. Microbial composition was only transiently affected by litter removal but strongly influenced by seasonality. ConclusionsLitter layers must be considered in calculating forest GHG budgets, and their influence on temperature sensitivity of soil GHG fluxes taken into account for future climate scenarios. 相似文献
16.
Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of CO 2, N 2O and CH 4 from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil GHG emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in CH 4 emissions while temporarily increasing N 2O fluxes. Interestingly, N 2O fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of CO 2 were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different GHG production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas CO 2 emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions. 相似文献
17.
Differences in paths of carbon flow have been found in soils of the tall (TS) and short (SS) Spartina alterniflora marshes of Sapelo Island, Ga. Gaseous end products of [ U- 14C]glucose metabolism were 14CO 2 and 14CH 4 in the SS region and primarily 14CO 2 in the TS region. Sulfate concentration did not demonstrably affect glucose catabolism or the distribution of end products in either zone. [ U- 14C]acetate was converted to 14CO 2 and 14CH 4 in the SS soils and almost exclusively to 14CO 2 in the TS soils. Sulfate concentration did not affect acetate metabolism in the SS soils; however, a noticeable effect of sulfate dilution was seen in TS soils. Sulfate dilution in TS samples resulted in increased methane formation. Total glucose and acetate metabolism were similar in TS and SS soils despite differences in end products. A microbial community characterized by fermentative/sulfate-reducing processes has developed in TS soils as opposed to the fermentative/methanogenic/sulfate-reducing community found in SS soils. 相似文献
18.
In nutrient impoverished landscapes in southwest Australia, terrestrial litter appears to be important in phosphorus (P) turnover and in the gradual accumulation of P in wetland systems. Little is known about the fate of P leached from litter during the wet season and the associated effects of soil microclimate on microbial activity. The effects of temperature, moisture, and litter leaching on soil microbial activity were studied on a transect across a seasonal wetland in southwestern Australia, after the onset of the wet season. Heterotrophic respiration (CO 2 efflux) was higher in the dried lakebed and riparian areas than in upland soils, and higher during the day than at night. There were significant variations in CO 2 efflux with time of sampling, largely caused by the effect of temperature. The addition of litter leachate significantly increased CO 2 efflux, more significantly in soils from upland sites, which had lower moisture and nutrient contents. There was a difference in response of microbial respiration between upland soils and wetland sediments to litter leachate and wetter, warmer conditions. In general, the litter leachate enhanced heterotrophic microbial respiration, and more significantly at warmer conditions (31 °C). The relative fungal to bacterial ratio was 2.9 – 3.2 for surface litter and 0.7–1.0 for soils, suggesting a fungal dominance in heterotrophic respiration of surface litter, but increased bacterial dominance in soils, especially in exposed sediments in the lakebed. 相似文献
19.
微生物固碳在减缓全球气候变化、实现人类可持续发展方面具有重要的意义,通过揭示长期不同施肥制度对土壤固碳细菌的影响规律,可以为我国稻田土壤科学施肥,稻田固碳和温室气体减排的共轭双赢作用提供重要的理论依据。以湖南宁乡国家级稻田肥力变化长期定位试验为平台,采用PCR-克隆测序和实时荧光定量(Real-time)PCR技术,研究不施肥(CK),氮磷钾肥(NPK)和秸秆还田(NPKS)3种长期施肥制度对稻田土壤固碳细菌群落结构及数量的影响。通过分析固碳细菌cbbL基因文库发现,长期施肥导致土壤固碳细菌种群结构产生了明显差异,NPK和NPKS处理中兼性自养固碳菌群落优势增加而严格自养固碳菌生长受到抑制。LUBSHUFF软件统计分析显示cbbL基因文库在CK、NPK及NPKS处理间均存在显著性差异。 3种施肥处理的稻田土壤细菌cbbL基因拷贝数为3.35?108 —5.61?108每克土,施肥后,土壤细菌cbbL基因数量增加,其中NPKS处理cbbL数量最多,是CK处理的1.5倍左右。稀疏曲线则显示长期施化肥导致细菌cbbL基因多样性高于NPKS,而NPKS高于CK。上述结果表明了长期施肥对土壤固碳细菌群落结构,多样性及数量均有显著的影响。本研究结果可为深入探讨稻田土壤微生物固碳潜力及其影响机理提供有力的依据。 相似文献
20.
Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple ( Acer rubrum) forest on deep peat soil. Direct measurements of CH 4 and CO 2 fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m ? 2 s ? 1 for CO 2 and 0.58 nmol m ? 2 s ? 1 for CH 4 (371 to 403 g C m ? 2 year ? 1). Carbon in aboveground litter (144 g C m ? 2 year ? 1) was 84% greater than C in root production (78 g C m ? 2 year ? 1). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m ? 2 year ? 1. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal. 相似文献
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