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1.
Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi,
especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on
the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous
forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production
of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching
data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty
acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2ω6,9 was used as an indicator to estimate
the total fungal biomass. Higher N deposition (20 kg N ha−1 y−1 compared with 10 kg N ha−1 y−1) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the
PLFA 16:1ω5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively
correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1ω9, a17:0 and 18:1ω7, while
some were negatively affected by pH, such as i15:0, 16:1ω7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect
on the PLFAs 16:1ω7c and 16:1ω9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive
to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2ω6,9. Low amounts of EM mycelia covaried
with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at
increased N input. 相似文献
2.
Changes in plant inputs under changing atmospheric CO2 can be expected to alter the size and/or functional characteristics of soil microbial communities which can determine whether soils are a C sink or source. Stable isotope probing was used to trace autotrophically fixed 13C into phospholipid fatty acid (PLFA) biomarkers in Mojave Desert soils planted with the desert shrub, Larrea tridentata. Seedlings were pulse‐labeled with 13CO2 under ambient and elevated CO2 in controlled environmental growth chambers. The label was chased into the soil by extracting soil PLFAs after labeling at Days 0, 2, 10, 24, and 49. Eighteen of 29 PLFAs identified showed 13C enrichment relative to nonlabeled control soils. Patterns of PLFA enrichment varied temporally and were similar for various PLFAs found within a microbial functional group. Enrichment of PLFA 13C generally occurred within the first 2 days in general and fungal biomarkers, followed by increasingly greater enrichment in bacterial biomarkers as the study progressed (Gram‐negative, Gram‐positive, actinobacteria). While treatment CO2 level did not affect total PLFA‐C concentrations, microbial functional group abundances and distribution responded to treatment CO2 level and these shifts persisted throughout the study. Specifically, ratios of bacterial‐to‐total PLFA‐C decreased and fungal‐to‐bacterial PLFA‐C increased under elevated CO2 compared with ambient conditions. Differences in the timing of 13C incorporation into lipid biomarkers coupled with changes in microbial functional groups indicate that microbial community characteristics in Mojave Desert soils have shifted in response to long‐term exposure to increased atmospheric CO2. 相似文献
3.
HAEGEUN CHUNG DONALD R. ZAK PETER B. REICH‡ DAVID S. ELLSWORTH 《Global Change Biology》2007,13(5):980-989
We determined soil microbial community composition and function in a field experiment in which plant communities of increasing species richness were exposed to factorial elevated CO2 and nitrogen (N) deposition treatments. Because elevated CO2 and N deposition increased plant productivity to a greater extent in more diverse plant assemblages, it is plausible that heterotrophic microbial communities would experience greater substrate availability, potentially increasing microbial activity, and accelerating soil carbon (C) and N cycling. We, therefore, hypothesized that the response of microbial communities to elevated CO2 and N deposition is contingent on the species richness of plant communities. Microbial community composition was determined by phospholipid fatty acid analysis, and function was measured using the activity of key extracellular enzymes involved in litter decomposition. Higher plant species richness, as a main effect, fostered greater microbial biomass, cellulolytic and chitinolytic capacity, as well as the abundance of saprophytic and arbuscular mycorrhizal (AM) fungi. Moreover, the effect of plant species richness on microbial communities was significantly modified by elevated CO2 and N deposition. For instance, microbial biomass and fungal abundance increased with greater species richness, but only under combinations of elevated CO2 and ambient N, or ambient CO2 and N deposition. Cellobiohydrolase activity increased with higher plant species richness, and this trend was amplified by elevated CO2. In most cases, the effect of plant species richness remained significant even after accounting for the influence of plant biomass. Taken together, our results demonstrate that plant species richness can directly regulate microbial activity and community composition, and that plant species richness is a significant determinant of microbial response to elevated CO2 and N deposition. The strong positive effect of plant species richness on cellulolytic capacity and microbial biomass indicate that the rates of soil C cycling may decline with decreasing plant species richness. 相似文献
4.
The natural abundance of 15N in plant biomass has been used to infer how N dynamics change with elevated atmospheric CO2 and changing water availability. However, it remains unclear if atmospheric CO2 effects on plant biomass 15N are driven by CO2-induced changes in soil moisture. We tested whether 15N abundance (expressed as δ15N) in plant biomass would increase with increasing soil moisture content at two atmospheric CO2 levels. In a greenhouse experiment we grew sunflower (Helianthus annuus) at ambient and elevated CO2 (760 ppm) with three soil moisture levels maintained at 45, 65, and 85% of field capacity, thereby eliminating potential
CO2-induced soil moisture effects. The δ15N value of total plant biomass increased significantly with increased soil moisture content at both CO2 levels, possibly due to increased uptake of 15N-rich organic N. Although not adequately replicated, plant biomass δ15N was lower under elevated than under ambient CO2 after adjusting for plant N uptake effects. Thus, increases in soil moisture can increase plant biomass δ15N, while elevated CO2 can decrease plant biomass δ15N other than by modifying soil moisture. 相似文献
5.
We estimated the biomass and growth of arbuscular mycorrhizal (AM) mycelium in sand dunes using signature fatty acids. Mesh
bags and tubes, containing initially mycelium-free sand, were buried in the field near the roots of the dune grass Ammophila arenaria L. AM fungal mycelia were detected at a distance of about 8.5 cm from the roots after 68 days of growth by use of neutral
lipid fatty acid (NLFA) 16:1ω5. The average rate of mycelium extension during September and October was estimated as 1.2 mm
day−1. The lipid and fatty acid compositions of AM fungal mycelia of isolates and from sand dunes were analysed and showed all
to be of a similar composition. Phospholipid fatty acids (PLFAs) can be used as indicators of microbial biomass. The mycelium
of G. intraradices growing in glass beads contained 8.3 nmol PLFAs per mg dry biomass, and about 15% of the PLFAs in G. intraradices, G. claroideum and AM fungal mycelium extracted from sand dunes, consisted of the signature PLFA 16:1ω5. We thus suggest a conversion factor
of 1.2 nmol PLFA 16:1ω5 per mg dry biomass. Calculations using this conversion factor indicated up to 34 μg dry AM fungal
biomass per g sand in the sand dunes, which was less than one tenth of that found in an experimental system with Glomus spp. growing with cucumber as plant associate in agricultural soil. The PLFA results from different systems indicated that
the biomass of the AM fungi constitutes a considerable part of the total soil microbial biomass. Calculations based on ATP
of AM fungi in an experimental growth system indicated that the biomass of the AM fungi constituted approximately 30% of the
total microbial biomass.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
以藏嵩草沼泽化草甸为研究对象,利用磷脂脂肪酸(PLFA)技术,研究连续6年N素添加对地上植被群落数量特征、土壤微生物群落结构的影响。结果表明:①藏嵩草沼泽化草甸群落生物量、枯枝落叶对施肥处理无明显响应,且莎草科植物对土壤氮素的吸收和利用率较低。②施肥增加了0-10 cm土壤微生物类群PLFAs丰富度尤其细菌和革兰氏阳性菌PLFAs,降低了10-20 cm PLFAs丰富度;③磷脂脂肪酸饱和脂肪酸/单烯不饱和脂肪酸、细菌PLFAs/真菌PLFAs的比值随土壤层次增加而增加;④0-10 cm土层革兰氏阳性菌、真菌PLFAs含量与pH、土壤速效磷、速效氮、土壤有机质显著正相关(P0.05或P0.01);10-20 cm土层,细菌、革兰氏阳性菌、真菌和总PLFAs含量与土壤有机质含量显著正相关(P0.05或P0.01)。表明藏嵩草沼泽化草甸微生物PLFAs含量和丰富度对施肥的响应存在明显的土层梯度效应,土壤微生物PLFAs含量和丰富度主要受表层土壤初始养分含量的影响。 相似文献
7.
Elevated Atmospheric CO2 Alters Soil Microbial Communities Associated with Trembling Aspen (Populus tremuloides) Roots 总被引:4,自引:0,他引:4
Global atmospheric CO2 levels are expected to double within the next 50 years. To assess the effects of increased atmospheric CO2 on soil ecosystems, cloned trembling aspen (Populus tremuloides) seedlings were grown individually in 1 m3 open bottom root boxes under either elevated (720 ppm, ELEV) or ambient CO2 (360 ppm, AMB). After 5 years, soil cores (40 cm depth) were collected from the root boxes and divided into 0–20 cm and 20–40
cm fractions. ELEV treatment resulted in significant decreases in both soil nitrate and total soil nitrogen in both the 0–20
cm and 20–40 cm soil fractions, with a 47% decrease in soil nitrate and a 50% decrease in total soil nitrogen occurring in
the 0–20 cm fraction. ELEV treatment did not result in a significant change in the amount of soil microbial biomass. However,
analysis of indicator phospholipid fatty acids (PLFA) indicated that ELEV treatment did result in significant increases in
PLFA indicators for fungi and Gram-negative bacteria in the 0–20 cm fraction. Terminal restriction fragment length polymorphism
(T-RFLP) analysis was used to analyze the composition of the soil bacterial communities (using primers targeting the 16SrRNA
gene) and the soil fungal communities (using primers targeting the intergenic transcribed spacer region). T-RFLP analysis
revealed shifts in both bacterial and fungal community structure, as well as increases in both bacterial and fungal species
richness with ELEV treatment. These results indicated that increased atmospheric CO2 had significant effects on both soil nutrient availability and the community composition of soil microbes associated with
aspen roots. 相似文献
8.
Increased use of stable isotope analysis to examine food-web dynamics, migration, transfer of nutrients, and behavior will likely result in expansion of stable isotope studies investigating human-induced global changes. Recent elevation of atmospheric CO2 concentration, related primarily to fossil fuel combustion, has reduced atmospheric CO2 δ13C (13C/12C), and this change in isotopic baseline has, in turn, reduced plant and animal tissue δ13C of terrestrial and aquatic organisms. Such depletion in CO2 δ13C and its effects on tissue δ13C may introduce bias into δ13C investigations, and if this variation is not controlled, may confound interpretation of results obtained from tissue samples collected over a temporal span. To control for this source of variation, we used a high-precision record of atmospheric CO2 δ13C from ice cores and direct atmospheric measurements to model modern change in CO2 δ13C. From this model, we estimated a correction factor that controls for atmospheric change; this correction reduces bias associated with changes in atmospheric isotopic baseline and facilitates comparison of tissue δ13C collected over multiple years. To exemplify the importance of accounting for atmospheric CO2 δ13C depletion, we applied the correction to a dataset of collagen δ13C obtained from mountain lion (Puma concolor) bone samples collected in California between 1893 and 1995. Before correction, in three of four ecoregions collagen δ13C decreased significantly concurrent with depletion of atmospheric CO2 δ13C (n ≥ 32, P ≤ 0.01). Application of the correction to collagen δ13C data removed trends from regions demonstrating significant declines, and measurement error associated with the correction did not add substantial variation to adjusted estimates. Controlling for long-term atmospheric variation and correcting tissue samples for changes in isotopic baseline facilitate analysis of samples that span a large temporal range. 相似文献
9.
Mycorrhizal Hyphal Turnover as a Dominant Process for Carbon Input into Soil Organic Matter 总被引:1,自引:0,他引:1
Douglas L. Godbold Marcel R. Hoosbeek Martin Lukac M. Francesca Cotrufo Ivan A. Janssens Reinhart Ceulemans Andrea Polle Eef J. Velthorst Giuseppe Scarascia-Mugnozza Paolo De Angelis Franco Miglietta Alessandro Peressotti 《Plant and Soil》2006,281(1-2):15-24
The atmospheric concentration of CO2 is predicted to reach double current levels by 2075. Detritus from aboveground and belowground plant parts constitutes the
primary source of C for soil organic matter (SOM), and accumulation of SOM in forests may provide a significant mechanism
to mitigate increasing atmospheric CO2 concentrations. In a poplar (three species) plantation exposed to ambient (380 ppm) and elevated (580 ppm) atmospheric CO2 concentrations using a Free Air Carbon Dioxide Enrichment (FACE) system, the relative importance of leaf litter decomposition,
fine root and fungal turnover for C incorporation into SOM was investigated. A technique using cores of soil in which a C4 crop has been grown (δ13C −18.1‰) inserted into the plantation and detritus from C3 trees (δ13C −27 to −30‰) was used to distinguish between old (native soil) and new (tree derived) soil C. In-growth cores using a fine
mesh (39 μm) to prevent in-growth of roots, but allow in-growth of fungal hyphae were used to assess contribution of fine
roots and the mycorrhizal external mycelium to soil C during a period of three growing seasons (1999–2001). Across all species
and treatments, the mycorrhizal external mycelium was the dominant pathway (62%) through which carbon entered the SOM pool,
exceeding the input via leaf litter and fine root turnover. The input via the mycorrhizal external mycelium was not influenced
by elevated CO2, but elevated atmospheric CO2 enhanced soil C inputs via fine root turnover. The turnover of the mycorrhizal external mycelium may be a fundamental mechanism
for the transfer of root-derived C to SOM. 相似文献
10.
Lucía Carrasco Andreas Gattinger Andreas Fließbach Antonio Roldán Michael Schloter Fuensanta Caravaca 《Microbial ecology》2010,60(2):265-271
The objective of this study was to compare the microbial community composition and biomass associated with the rhizosphere
of a perennial gramineous species (Lygeum spartum L.) with that of an annual (Piptatherum miliaceum L.), both growing in semiarid mine tailings. We also established their relationship with the contents of potentially toxic
metals as well as with indicators of soil quality. The total phospholipid fatty acid (PLFA) amount was significantly higher
in the rhizosphere soil of the annual species than in the rhizosphere soil of the perennial species. The fungal/bacterial
PLFA ratio was significantly greater in the perennial species compared to the annual species. The fatty acid 16:1ω5c, the
fungal/bacterial PLFA ratio and monounsaturated/saturated PLFA ratio were correlated negatively with the soluble contents
of toxic metals. The cyc/prec (cy17:0 + cy19:0/16:1ω7 + 18:1ω7) ratio was correlated positively with the soluble contents
of Pb, Zn, Al, Ni, Cd, and Cu. The results of the PLFA analysis for profiling microbial communities and their stress status
of both the plant species indicate that perennial and annual gramineous species appear equally suitable for use in programmes
of revegetation of semiarid mine tailings. 相似文献
11.
The mechanisms behind the 13C enrichment of organic matter with increasing soil depth in forests are unclear. To determine if 13C discrimination during respiration could contribute to this pattern, we compared δ13C signatures of respired CO2 from sieved mineral soil, litter layer and litterfall with measurements of δ13C and δ15N of mineral soil, litter layer, litterfall, roots and fungal mycelia sampled from a 68-year-old Norway spruce forest stand
planted on previously cultivated land. Because the land was subjected to ploughing before establishment of the forest stand,
shifts in δ13C in the top 20 cm reflect processes that have been active since the beginning of the reforestation process. As 13C-depleted organic matter accumulated in the upper soil, a 1.0‰ δ13C gradient from −28.5‰ in the litter layer to −27.6‰ at a depth of 2–6 cm was formed. This can be explained by the 1‰ drop
in δ13C of atmospheric CO2 since the beginning of reforestation together with the mixing of new C (forest) and old C (farmland). However, the isotopic
change of the atmospheric CO2 explains only a portion of the additional 1.0‰ increase in δ13C below a depth of 20 cm. The δ13C of the respired CO2 was similar to that of the organic matter in the upper soil layers but became increasingly 13C enriched with depth, up to 2.5‰ relative to the organic matter. We hypothesise that this 13C enrichment of the CO2 as well as the residual increase in δ13C of the organic matter below a soil depth of 20 cm results from the increased contribution of 13C-enriched microbially derived C with depth. Our results suggest that 13C discrimination during microbial respiration does not contribute to the 13C enrichment of organic matter in soils. We therefore recommend that these results should be taken into consideration when
natural variations in δ13C of respired CO2 are used to separate different components of soil respiration or ecosystem respiration. 相似文献
12.
Effects of long term CO2 enrichment on microbial community structure in calcareous grassland 总被引:1,自引:0,他引:1
Diana Ebersberger Nicola Wermbter Pascal A. Niklaus Ellen Kandeler 《Plant and Soil》2004,264(1-2):313-323
Elevated CO2 generally increases plant productivity, and has been found to alter plant community composition in many ecosystems. Because soil microbes depend on plant-derived C and are often associated with specific plant species, elevated CO2 has the potential to alter structure and functioning of soil microbial communities. We investigated soil microbial community structure of a species-rich semi-natural calcareous grassland that had been exposed to elevated CO2 (600 μL L?1) for 6 growing seasons. We analysed microbial community structure using phospholipid fatty acid (PLFA) profiles and DNA fingerprints obtained by Denaturing Gradient Gel Electrophoresis (DGGE) of 16S rDNA fragments amplified by the Polymerase Chain Reaction (PCR). PLFA profiles were not affected by CO2 enrichment and the ratio of fungal and bacterial PLFA did not change. Ordination analysis of DNA fingerprints revealed a significant relation between CO2 enrichment and variation in DNA fingerprints in summer (P=0.01), but not in spring. This variation was due to changes in low-intensity bands, while dominant bands did not differ between CO2 treatments. Diversity of the bacterial community, as assessed by number of bands in DNA fingerprints and calculation of Shannon diversity indices, was not affected by elevated CO2. Overall, only minor effects on microbial community structure were detected, corroborating earlier findings that soil carbon inputs did probably change much less than suggested by plant photosynthetic responses. 相似文献
13.
Rising atmospheric CO2 levels alter the physiology of many plant species, but little is known of changes to root dynamics that may impact soil microbial mediation of greenhouse gas emissions from wetlands. We grew co-occurring wetland plant species that included an invasive reed canary grass (Phalaris arundinacea L.) and a native woolgrass (Scirpus cyperinus L.) in a controlled greenhouse facility under ambient (380 ppm) and elevated atmospheric CO2 (700 ppm). We hypothesized that elevated atmospheric CO2 would increase the abundance of both archaeal methanogen and bacterial methanotroph populations through stimulation of plant root and shoot biomass. We found that methane levels emitted from S. cyperinus shoots increased 1.5-fold under elevated CO2, while no changes in methane levels were detected from P. arundincea. The increase in methane emissions was not explained by enhanced root or shoot growth of S. cyperinus. Principal components analysis of the total phospholipid fatty acid (PLFA) recovered from microbial cell membranes revealed that elevated CO2 levels shifted the composition of the microbial community under S. cyperinus, while no changes were detected under P. arundinacea. More detailed analysis of microbial abundance showed no impact of elevated CO2 on a fatty acid indicative of methanotrophic bacteria (18:2ω6c), and no changes were detected in the terminal restriction fragment length polymorphism (T-RFLP) relative abundance profiles of acetate-utilizing archaeal methanogens. Plant carbon depleted in 13C was traced into the PLFAs of soil microorganisms as a measure of the plant contribution to microbial PLFA. The relative contribution of plant-derived carbon to PLFA carbon was larger in S. cyperinus compared with P. arundinacea in four PLFAs (i14:0, i15:0, a15:0, and 18:1ω9t). The δ13C isotopic values indicate that the contribution of plant-derived carbon to microbial lipids could differ in rhizospheres of CO2-responsive plant species, such as S. cyperinus in this study. The results from this study show that the CO2–methane link found in S. cyperinus can occur without a corresponding change in methanogen and methanotroph relative abundances, but PLFA analysis indicated shifts in the community profile of bacteria and fungi that were unique to rhizospheres under elevated CO2. 相似文献
14.
Concentrations and natural isotope abundance of total sulfur and nitrogen as well as sulfate and nitrate concentrations were
measured in needles of different age classes and in soil samples of different horizons from a healthy and a declining Norway
spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), in order to study the fate of atmospheric depositions of
sulfur and nitrogen compounds.
The mean δ15N of the needles ranged between −3.7 and −2.1 ‰ and for δ34S a range between −0.4 and +0.9 ‰ was observed. δ34S and sulfur concentrations in the needles of both stands increased continuously with needle age and thus, were closely correlated.
The δ15N values of the needles showed an initial decrease followed by an increase with needle age. The healthy stand showed more
negative δ15N values in old needles than the declining stand. Nitrogen concentrations decreased with needle age.
For soil samples at both sites the mean δ15N and δ34S values increased from −3 ‰ (δ15N) or +0.9 ‰ (δ34S) in the uppermost organic layer to about +4 ‰ (δ15N) or +4.5 ‰ (δ34S) in the mineral soil. This depth-dependent increase in abundance of 15N and 34S was accompanied by a decrease in total nitrogen and sulfur concentrations in the soil. δ15N values and nitrogen concentrations were closely correlated (slope −0.0061 ‰ δ15N per μmol eq N gdw
−1), and δ34S values were linearly correlated with sulfur concentrations (slope −0.0576 ‰ δ34S per μmol eq S gdw
−1). It follows that in the same soil samples sulfur concentrations were linearly correlated with the nitrogen concentrations
(slope 0.0527), and δ34S values were linearly correlated with δ15N values (slope 0.459). A correlation of the sulfur and nitrogen isotope abundances on a Δ basis (which considers the different
relative frequencies of 15N and 34S), however, revealed an isotope fractionation that was higher by a factor of 5 for sulfur than for nitrogen (slope 5.292).
These correlations indicate a long term synchronous mineralization of organic nitrogen and sulfur compounds in the soil accompanied
by element-specific isotope fractionations.
Based on different sulfur isotope abundance of the soil (δ34S=0.9 ‰ for total sulfur of the organic layer was assumed to be equivalent to about −1.0 ‰ for soil sulfate) and of the atmospheric
SO2 deposition (δ34S=2.0 ‰ at the healthy site and 2.3 ‰ at the declining site) the contribution of atmospheric SO2 to total sulfur of the needles was estimated. This contribution increased from about 20 % in current-year needles to more
than 50 % in 3-year-old needles. The proportion of sulfur from atmospheric deposition was equivalent to the age dependent
sulfate accumulation in the needles. In contrast to the accumulation of atmospheric sulfur compounds nitrogen compounds from
atmospheric deposition were metabolized and were used for growth. The implications of both responses to atmospheric deposition
are discussed. 相似文献
15.
XIAOJUAN FENG ANDRÉ J. SIMPSON WILLIAM H. SCHLESINGER MYRNA J. SIMPSON 《Global Change Biology》2010,16(7):2104-2116
The dynamics and fate of terrestrial organic matter (OM) under elevated atmospheric CO2 and nitrogen (N) fertilization are important aspects of long‐term carbon sequestration. Despite numerous studies, questions still remain as to whether the chemical composition of OM may alter with these environmental changes. In this study, we employed molecular‐level methods to investigate the composition and degradation of various OM components in the forest floor (O horizon) and mineral soil (0–15 cm) from the Duke forest free air CO2 enrichment (FACE) experiment. We measured microbial responses to elevated CO2 and N fertilization in the mineral soil using phospholipid fatty acid (PLFA) profiles. Increased fresh carbon inputs into the forest floor under elevated CO2 were observed at the molecular‐level by two degradation parameters of plant‐derived steroids and cutin‐derived compounds. The ratios of fungal to bacterial PLFAs and Gram‐negative to Gram‐positive bacterial PLFAs decreased in the mineral soil with N fertilization, indicating an altered soil microbial community composition. Moreover, the acid to aldehyde ratios of lignin‐derived phenols increased with N fertilization, suggesting enhanced lignin degradation in the mineral soil. 1H nuclear magnetic resonance (NMR) spectra of soil humic substances revealed an enrichment of leaf‐derived alkyl structures with both elevated CO2 and N fertilization. We suggest that microbial decomposition of SOM constituents such as lignin and hydrolysable lipids was promoted under both elevated CO2 and N fertilization, which led to the enrichment of plant‐derived recalcitrant structures (such as alkyl carbon) in the soil. 相似文献
16.
Linda T. A. van Diepen Erik A. Lilleskov Kurt S. Pregitzer R. Michael Miller 《Ecosystems》2010,13(5):683-695
Increased nitrogen (N) deposition caused by human activities has altered ecosystem functioning and biodiversity. To understand
the effects of altered N availability, we measured the abundance of arbuscular mycorrhizal fungi (AMF) and the microbial community
in northern hardwood forests exposed to long-term (12 years) simulated N deposition (30 kg N ha−1 y−1) using phospholipid fatty acid (PLFA) analysis and hyphal in-growth bags. Intra- and extraradical AMF biomass and total microbial
biomass were significantly decreased by simulated N deposition by 36, 41, and 24%, respectively. Both methods of extraradical
AMF biomass estimation (soil PLFA 16:1ω5c and hyphal in-growth bags) showed comparable treatment responses, and extraradical
biomass represented the majority of total (intra-plus extraradical) AMF biomass. N deposition also significantly affected
the microbial community structure, leading to a 10% decrease in fungal to bacterial biomass ratios. Our observed decline in
AMF and total microbial biomass together with changes in microbial community structure could have substantial impacts on the
nutrient and carbon cycling within northern hardwood forest ecosystems. 相似文献
17.
Christine L. Goodale Steven A. Thomas Guinevere Fredriksen Emily M. Elliott Kathryn M. Flinn Thomas J. Butler M. Todd Walter 《Biogeochemistry》2009,93(3):197-218
Atmospheric deposition contributes a large fraction of the annual nitrogen (N) input to the basin of the Susquehanna River,
a river that provides two-thirds of the annual N load to the Chesapeake Bay. Yet, there are few measurements of the retention
of atmospheric N in the Upper Susquehanna’s forested headwaters. We characterized the amount, form (nitrate, ammonium, and
dissolved organic nitrogen), isotopic composition (δ15N- and δ18O-nitrate), and seasonality of stream N over 2 years for 7–13 catchments. We expected high rates of N retention and seasonal
nitrate patterns typical of other seasonally snow-covered catchments: dormant season maxima and growing season minima. Coarse
estimates of N export indicated high rates of inorganic N retention (>95%), yet streams had unexpected seasonal nitrate patterns,
with summer peaks (14–96 μmol L−1), October crashes (<1 μmol L−1), and modest rebounds during the dormant season (<1–20 μmol L−1). Stream δ18O-nitrate values indicated microbial nitrification as the primary source of stream nitrate, although snowmelt or other atmospheric
source contributed up to 47% of stream nitrate in some March samples. The autumn nitrate crash coincided with leaffall, likely
due to in-stream heterotrophic uptake of N. Hypothesized sources of the summer nitrate peaks include: delayed release of nitrate
previously flushed to groundwater, weathering of geologic N, and summer increases in net nitrate production. Measurements
of shale δ15N and soil-, well-, and streamwater nitrate within one catchment point toward a summer increase in soil net nitrification
as the driver of this pattern. Rather than seasonal plant demand, processes governing the seasonal production, retention,
and transport of nitrate in soils may drive nitrate seasonality in this and many other systems. 相似文献
18.
Jianping Wu Wenfei Liu Houbao Fan Guomin Huang Songze Wan Yinghong Yuan Chunfeng Ji 《Ecology and evolution》2013,3(11):3895-3905
Atmospheric nitrogen (N) deposition greatly affects ecosystem processes and properties. However, few studies have simultaneously examined the responses of both the above- and belowground communities to N deposition. Here, we investigated the effects of 8 years of simulated N deposition on soil microbial communities and plant diversity in a subtropical forest. The quantities of experimental N added (g of N m−2 year−1) and treatment codes were 0 (N0, control), 6 (N1), 12 (N2), and 24 (N3). Phospholipid fatty acids (PLFAs) analysis was used to characterize the soil microbial community while plant diversity and coverage were determined in the permanent field plots. Microbial abundance was reduced by the N3 treatment, and plant species richness and coverage were reduced by both N2 and N3 treatments. Declines in plant species richness were associated with decreased abundance of arbuscular mycorrhizal fungi, increased bacterial stress index, and reduced soil pH. The plasticity of soil microbial community would be more related to the different responses among treatments when compared with plant community. These results indicate that long-term N deposition has greater effects on the understory plant community than on the soil microbial community and different conservation strategies should be considered. 相似文献
19.
Barbara Drigo George A. Kowalchuk Brigitte A. Knapp Agata S. Pijl Henricus T. S. Boschker Johannes A. van Veen 《Global Change Biology》2013,19(2):621-636
Carbon (C) uptake by terrestrial ecosystems represents an important option for partially mitigating anthropogenic CO2 emissions. Short‐term atmospheric elevated CO2 exposure has been shown to create major shifts in C flow routes and diversity of the active soil‐borne microbial community. Long‐term increases in CO2 have been hypothesized to have subtle effects due to the potential adaptation of soil microorganism to the increased flow of organic C. Here, we studied the effects of prolonged elevated atmospheric CO2 exposure on microbial C flow and microbial communities in the rhizosphere. Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown at defined atmospheric conditions differing in CO2 concentration (350 and 700 ppm) for 3 years. During this period, C flow was assessed repeatedly (after 6 months, 1, 2, and 3 years) by 13C pulse‐chase experiments, and label was tracked through the rhizosphere bacterial, general fungal, and arbuscular mycorrhizal fungal (AMF) communities. Fatty acid biomarker analyses and RNA‐stable isotope probing (RNA‐SIP), in combination with real‐time PCR and PCR‐DGGE, were used to examine microbial community dynamics and abundance. Throughout the experiment the influence of elevated CO2 was highly plant dependent, with the mycorrhizal plant exerting a greater influence on both bacterial and fungal communities. Biomarker data confirmed that rhizodeposited C was first processed by AMF and subsequently transferred to bacterial and fungal communities in the rhizosphere soil. Over the course of 3 years, elevated CO2 caused a continuous increase in the 13C enrichment retained in AMF and an increasing delay in the transfer of C to the bacterial community. These results show that, not only do elevated atmospheric CO2 conditions induce changes in rhizosphere C flow and dynamics but also continue to develop over multiple seasons, thereby affecting terrestrial ecosystems C utilization processes. 相似文献
20.
氮素添加对贝加尔针茅草原土壤团聚体微生物群落的影响 总被引:1,自引:0,他引:1
大气氮沉降增加作为全球气候变化的重要因素,其对土壤生态系统影响的研究受到了生态学家的广泛关注。土壤微生物是有机物分解和养分循环的主要参与者,在维持土壤的功能多样性和可持续发展方面发挥着重要的作用。氮沉降的激增会引起土壤微生物群落结构和功能的改变。土壤中营养物质在不同团聚体组分中分布的不均匀,为微生物提供了空间异质微生境。为揭示草原土壤不同粒径团聚体中微生物群落分布及其对氮素添加响应特征。自2010年起,在内蒙古贝加尔针茅草原典型地段设置N0(0 kg hm-2 a-1)、N15(15 kg hm-2 a-1)、N30(30 kg hm-2 a-1)、N50(50 kg hm-2 a-1)、N100(100 kg hm-2 a-1)、N150(150 kg hm-2 a-1)6个氮素添加处理模拟氮沉降野外控制试验。采用磷脂脂肪酸(phospholipid fatty acid,PLFA)法测定>2 mm、0.25-2 mm和<0.25 mm 3个粒径土壤团聚体中微生物PLFA含量,探讨氮素添加对土壤团聚体微生物群落结构的影响。结果表明:氮素添加提高了土壤碳、氮含量,降低了土壤pH。氮素添加显著提高了0.25-2 mm土壤团聚体微生物群落磷脂脂肪酸总量、真菌磷脂脂肪酸含量和真菌/细菌(Fungi/bacteria,F/B)、革兰氏阳性菌/革兰氏阴性菌(Gram-positive bacteria/gram-negative bacteria,G+/G-)的比值(P<0.05),降低了土壤团聚体微生物Margalef丰富度指数(P<0.05)。相关性分析表明,土壤团聚体微生物总PLFAs、真菌PLFAs含量、G+/G-、F/B与土壤有机碳、全氮含量呈显著正相关关系,与C/N值负相关。综合研究表明,连续8年氮素添加显著提高了土壤有机碳和全氮含量、降低了土壤pH;提高了0.25-2 mm土壤团聚体真菌群落,土壤有机碳、全氮的固持与真菌群落的增加有关。 相似文献