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1.
Christelle Collignon Christophe Calvaruso Marie-Pierre Turpault 《Plant and Soil》2011,338(1-2):355-366
Anthropogenic nitrogen (N) deposition significantly affects forest soil microbial biomass and extracellular enzymatic activities (EEA). However, the influence of mixed N fertilizations on soil microbial biomass and EEA remains unclear. In this work, NH4NO3 was chosen as inorganic N, while urea and glycine were chosen as organic N. They were used to fertilize subtropical forest soil monthly for 1 year with different ratios (inorganic N : organic N?=?10 : 0, 7 : 3, 3 : 7 and 1 : 9 respectively.) and N inputs were equivalent to 7.2 g?N?m?2?y?1. Soil samples were harvested every 2 months. Subsequently, soil microbial biomass and enzymatic activities were assayed. Multiple regression analysis (MRA) and principle components analysis (PCA) were utilized to illustrate the relationship between soil microbial biomass and EEA. Results showed that soil EEA displayed different changes in response to various mixed N fertilizations. Invertase, cellulase, cellobiohydrolase, alkaline phosphatase, and catalase activities under mixed N fertilization were higher than those of single inorganic N (NH4NO3) fertilization. Polyphenol oxidase activities were depressed after inorganic N fertilization and accelerated after mixed N fertilization. Acid phosphatase activities were accelerated in all N fertilization plots, while the influence of various mixed N fertilizations were not significant. Soil microbial biomass was enhanced by mixed N fertilization, while no significant changes were observed after inorganic N fertilization. The result revealed that although N fertilization may alleviate soil N-limitation, single inorganic N fertilization may disturb the balance of inorganic N and organic N, and depress the increases of soil enzymatic activities and microbial biomass in the end. Soil enzymes activities and microbial biomass showed the highest activities after medium organic N fertilization (inorganic : organic N?=?3 : 7), which might be the most suitable N fertilizer for soil microbes. Meanwhile, PCA showed that the alleviation of N-limited reached a maximum after medium organic N fertilization. All results indicated that soil EEA, microbial biomass, and their relationship are all affected by N type and inorganic to organic N ratio. 相似文献
2.
Alternate partial root-zone irrigation induced dry/wet cycles of soils stimulate N mineralization and improve N nutrition in tomatoes 总被引:3,自引:0,他引:3
Yaosheng Wang Fulai Liu Andreas de Neergaard Lars S. Jensen Jesper Luxhøi Christian R. Jensen 《Plant and Soil》2010,337(1-2):167-177
Given the same amount of irrigation volume, applying alternate partial root-zone irrigation (PRI) has improved crop N nutrition as compared to deficit irrigation (DI), yet the mechanisms underlying this effect remain unknown. Therefore, the objective of this study was to investigate whether PRI induced soil dry/wet cycles facilitate soil organic N mineralization hereby contributing to the improvement of N nutrition in tomatoes. The plants were grown in split-root pots in a climate-controlled glasshouse and were subjected to PRI and DI treatments during early fruiting stage. 15N-labeled maize residues were incorporated into the soils. Results showed that PRI resulted in 25% higher net 15N mineralization than did DI, indicating that the enhanced mineralization of soil organic N alone could account for the 16% increase of N accumulation in the PRI than in the DI plants. The higher net N mineralization under PRI was coincided with an intensified soil microbial activity. In addition, even though soil chloroform fumigation labile carbon (CFL-C, as an index of microbial biomass) was similar for the two irrigation treatments, a significant increase of chloroform fumigation labile nitrogen (CFL-N) was found in the PRI wetting soil. Consequently, the C:N ratio of the chloroform fumigation labile pool was remarkably modified by the PRI treatment, which might indicate physiological changes of soil microbes or changes in labiality of soil organic C and N due to the dry/wet cycles of soils, altering conditions for net N mineralization. Moreover, in both soil compartments PRI caused significantly less extractable organic carbon (EOC) as compared with DI; whilst in the PRI wetting soil significantly higher extractable organic nitrogen (EON) was observed. A low EOC:EON ratio in the PRI wetting soil may indicate an increasing net mineralization of the organic N as a result of microbial metabolism. Conclusively, PRI induced greater microbial activity and higher microbial substrates availability are seemingly responsible for the enhanced net N mineralization and improved N nutrition in tomato plants. 相似文献
3.
Microbial biomass and nitrogen cycling responses to fertilization and litter removal in young northern hardwood forests 总被引:15,自引:1,他引:14
The influence of site fertility on soil microbial biomass and activity is not well understood but is likely to be complex because of interactions with plant responses to nutrient availability. We examined the effects of long-term (8 yr) fertilization and litter removal on forest floor microbial biomass and N and C transformations to test the hypothesis that higher soil resource availability stimulates microbial activity. Microbial biomass and respiration decreased by 20–30 % in response to fertilization. Microbial C averaged 3.8 mg C/g soil in fertilized, 5.8 mg C/g in control, and 5.5 mg C/g in litter removal plots. Microbial respiration was 200 µg CO2-C g–1 d–1 in fertilized plots, compared to 270 µg CO2-C g–1 d–1 in controls. Gross N mineralization and N immobilization did not differ among treatments, despite higher litter nutrient concentrations in fertilized plots and the removal of substantial quantities of C and N in litter removal plots. Net N mineralization was significantly reduced by fertilization. Gross nitrification and NO3
– immobilization both were increased by fertilization. Nitrate thus became a more important part of microbial N cycling in fertilized plots even though NH4
+ availability was not stimulated by fertilization.Soil microorganisms did not mineralize more C or N in response to fertilization and higher litter quality; instead, results suggest a difference in the physiological status of microbial biomass in fertilized plots that influenced N transformations. Respiration quotients (qCO2, respiration per unit biomass) were higher in fertilized plots (56 µg CO2-C mg C–1 d–1) than control (48 µg CO2-C mg C–1 d –1) or litter removal (45 µg CO2-C mg C–1 d–1), corresponding to higher microbial growth efficiency, higher proportions of gross mineralization immobilized, and lower net N mineralization in fertilized plots. While microbial biomass is an important labile nutrient pool, patterns of microbial growth and turnover were distinct from this pool and were more important to microbial function in nitrogen cycling. 相似文献
4.
Yanna Lü Congyan Wang Yanyan Jia Jingjing Du Xu Ma Wenwen Wang Gaozhong Pu Xingjun Tian 《Ecological Research》2013,28(3):447-457
Numerous studies reported that inorganic nitrogen (N) deposition strongly affected forest ecosystems. However, organic N is also an important component of atmospheric N deposition. The influence of organic N deposition on soil microbial biomass and extracellular enzymatic activities (EEA) in subtropical forests remains unclear. Coniferous forest (CF) and broad-leaved forest (BF) were chosen from the Zijin Mountain in China. Five forms of organic N (urea, glycine, serine, nonylamine, and a mixture of all four) were used to fertilize the soils in CF and BF every month for 1 year. Soil samples were collected every 2 months. Subsequently, soil microbial biomass and EEA were assayed. Results showed that the microbial biomass and EEA of soils fertilized with urea and amino acids increased significantly, whereas those fertilized with nonylamine and mixed N decreased significantly. Urea and amino acid fertilizations had a more positive influence on EEA of BF than on those of CF. Nonylamine fertilization had a more negative influence on EEA of CF than on those of BF. Organic N fertilization shifted soil microbial biomass away from the excretion of N-degrading enzymes and toward the excretion of C-degrading enzymes. These results suggest that organic N type is an important factor that affects soil microbial biomass, EEA, and their relationship. Organic N deposition may seriously affect soil C and N cycling, as well as carbon dioxide releasing from the soils by influencing microbial activities and biomass. This study thereby provides evidence that soil microorganisms have strong feedback to different forms of organic N deposition. 相似文献
5.
Ellen H. Esch Daniel L. Hernández Jae R. Pasari Rose S. G. Kantor Paul C. Selmants 《Plant and Soil》2013,366(1-2):671-682
Background and aims
Exotic species, nitrogen (N) deposition, and grazing are major drivers of change in grasslands. However little is known about the interactive effects of these factors on below-ground microbial communities.Methods
We simulated realistic N deposition increases with low-level fertilization and manipulated grazing with fencing in a split-plot experiment in California’s largest serpentine grassland. We also monitored grazing intensity using camera traps and measured total available N to assess grazing and nutrient enrichment effects on microbial extracellular enzyme activity (EEA), microbial N mineralization, and respiration rates in soil.Results
Continuous measures of grazing intensity and N availability showed that increased grazing and N were correlated with increased microbial activity and were stronger predictors than the categorical grazing and fertilization measures. Exotic cover was also generally correlated with increased microbial activity resulting from exotic-driven nutrient cycling alterations. Seasonal effects, on abiotic factors and plant phenology, were also an important factor in EEA with lower activity occurring at peak plant biomass.Conclusions
In combination with previous studies from this serpentine grassland, our results suggest that grazing intensity and soil N availability may affect the soil microbial community indirectly via effects on exotic cover and associated changes in nutrient cycling while grazing directly impacts soil community function. 相似文献6.
Herbivore influence on soil microbial biomass and nitrogen mineralization in a northern grassland ecosystem: Yellowstone National Park 总被引:8,自引:0,他引:8
Microorganisms are largely responsible for soil nutrient cycling and energy flow in terrestrial ecosystems. Although soil
microorganisms are affected by topography and grazing, little is known about how these two variables may interact to influence
microbial processes. Even less is known about how these variables influence microorganisms in systems that contain large populations
of free-roaming ungulates. In this study, we compared microbial biomass size and activity, as measured by in situ net N mineralization,
inside and outside 35- to 40-year exclosures across a topographic gradient in northern Yellowstone National Park. The objective
was to determine the relative effect of topography and large grazers on microbial biomass and nitrogen mineralization. Microbial
C and N varied by almost an order of magnitude across sites. Topographic depressions that contained high plant biomass and
fine-textured soils supported the greatest microbial biomass. We found that plant biomass accurately predicted microbial biomass
across our sites suggesting that carbon inputs from plants constrained microbial biomass. Chronic grazing neither depleted
soil C nor reduced microbial biomass. We hypothesize that microbial populations in grazed grasslands are sustained mainly
by inputs of labile C from dung deposition and increased root turnover or root exudation beneath grazed plants. Mineral N
fluxes were affected more by grazing than topography. Net N mineralization rates were highest in grazed grassland and increased
from dry, unproductive to mesic, highly productive communities. Overall, our results indicate that topography mainly influences
microbial biomass size, while mineral N fluxes (microbial activity) are affected more by grazing in this grassland ecosystem.
Received: 4 June 1997 / Accepted: 16 December 1997 相似文献
7.
Yanjun Zhang Junliang Zou Delong Meng Shuina Dang Jinhong Zhou Bruce Osborne Yuanyuan Ren Ting Liang Keke Yu 《Ecology and evolution》2020,10(24):13602
Litter inputs can influence soil respiration directly through labile C availability and, indirectly, through the activity of soil microorganisms and modifications in soil microclimate; however, their relative contributions and the magnitude of any effect remain poorly understood. We synthesized 66 recently published papers on forest ecosystems using a meta‐analysis approach to investigate the effect of litter inputs on soil respiration and the underlying mechanisms involved. Our results showed that litter inputs had a strong positive impact on soil respiration, labile C availability, and the abundance of soil microorganisms, with less of an impact related to soil moisture and temperature. Overall, soil respiration was increased by 36% and 55%, respectively, in response to natural and doubled litter inputs. The increase in soil respiration induced by litter inputs showed a tendency for coniferous forests (50.7%)> broad‐leaved forests (41.3%)> mixed forests (31.9%). This stimulation effect also depended on stand age with 30‐ to 100‐year‐old forests (53.3%) and ≥100‐year‐old forests (50.2%) both 1.5 times larger than ≤30‐year‐old forests (34.5%). Soil microbial biomass carbon and soil dissolved organic carbon increased by 21.0%‐33.6% and 60.3%‐87.7%, respectively, in response to natural and doubled litter inputs, while soil respiration increased linearly with corresponding increases in soil microbial biomass carbon and soil dissolved organic carbon. Natural and doubled litter inputs increased the total phospholipid fatty acid (PLFA) content by 6.6% and 19.7%, respectively, but decreased the fungal/bacterial PLFA ratio by 26.9% and 18.7%, respectively. Soil respiration also increased linearly with increases in total PLFA and decreased linearly with decreases in the fungal/bacterial PLFA ratio. The contribution of litter inputs to an increase in soil respiration showed a trend of total PLFA > fungal/bacterial PLFA ratio > soil dissolved organic carbon > soil microbial biomass carbon. Therefore, in addition to forest type and stand age, labile C availability and soil microorganisms are also important factors that influence soil respiration in response to litter inputs, with soil microorganisms being more important than labile C availability. 相似文献
8.
Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest 总被引:15,自引:0,他引:15
STEVEN D. ALLISON † CLAUDIA I. CZIMCZIK† KATHLEEN K. TRESEDER † 《Global Change Biology》2008,14(5):1156-1168
Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high‐latitude ecosystems. However, the effects of increasing nutrient availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)‐degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 ± 1.4 to 5.2 ± 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose‐degrading enzyme and suppressed the activities of protein‐ and chitin‐degrading enzymes but had no effect on soil respiration rates or 14C signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds. 相似文献
9.
How microbial communities respond to increases in available nitrogen (N) will influence carbon (C) and nutrient cycles. Most studies addressing N fertilization focus on mid-latitude ecosystems, where complex aboveground–belowground interactions can obscure the response of the soil microbial community, and little is known about how soil microbial communities of polar systems, particularly polar deserts, will respond. The low C content and comparatively simpler (low biomass and biodiversity) soil communities of the McMurdo Dry Valleys of Antarctica may allow easier identification of the mechanisms by which N fertilization influences microbial communities. Therefore, we conducted a microcosm incubation using three levels of N fertilization, added in solution to simulate a pulse of increased soil moisture, and measured microbial biomass and respiration over the course of 4.5 months. Soil characteristics, including soil pH, conductivity, cation content, chlorophyll a, and organic C content were measured. Soils from two sites that differed in stoichiometry were used to examine how in situ C:N:P influenced the N-addition response. We hypothesized that negative influences of N enrichment would result from increased salinity and ion content, while positive influences would result from enhanced C availability and turnover. We observed that microbes were moderately influenced by N addition, including stimulation and inhibition with increasing levels of N. Mechanisms identified include direct inhibition due to N toxicity and stimulation due to release from N, rather than C, limitation. Our results suggest that, by influencing microbial biomass and activity, N fertilization will influence C cycling in soils with very low C content. 相似文献
10.
Differential effects of warming and nitrogen fertilization on soil respiration and microbial dynamics in switchgrass croplands 下载免费PDF全文
Jianwei Li Siyang Jian Jason P. de Koff Chad S. Lane Gangsheng Wang Melanie A. Mayes Dafeng Hui 《Global Change Biology Bioenergy》2018,10(8):565-576
The mechanistic understanding of warming and nitrogen (N) fertilization, alone or in combination, on microbially mediated decomposition is limited. In this study, soil samples were collected from previously harvested switchgrass (Panicum virgatum L.) plots that had been treated with high N fertilizer (HN: 67 kg N ha?1) and those that had received no N fertilizer (NN) over a 3‐year period. The samples were incubated for 180 days at 15 °C and 20 °C, during which heterotrophic respiration, δ13C of CO2, microbial biomass (MB), specific soil respiration rate (Rs: respiration per unit of microbial biomass), and exoenzyme activities were quantified at 10 different collections time. Employing switchgrass tissues (referred to as litter) with naturally abundant 13C allowed us to partition CO2 respiration derived from soil and amended litter. Cumulative soil respiration increased significantly by 16.4% and 4.2% under warming and N fertilization, respectively. Respiration derived from soil was elevated significantly with warming, while oxidase, the agent for recalcitrant soil substrate decomposition, was not significantly affected by warming. Warming, however, significantly enhanced MB and Rs indicating a decrease in microbial growth efficiency (MGE). On the contrary, respiration derived from amended litter was elevated with N fertilization, which was consistent with the significantly elevated hydrolase. N fertilization, however, had little effect on MB and Rs, suggesting little change in microbial physiology. Temperature and N fertilization showed minimal interactive effects likely due to little differences in soil N availability between NN and HN samples, which is partly attributable to switchgrass biomass N accumulation (equivalent to ~53% of fertilizer N). Overall, the differential individual effects of warming and N fertilization may be driven by physiological adaptation and stimulated exoenzyme kinetics, respectively. The study shed insights on distinct microbial acquisition of different substrates under global temperature increase and N enrichment. 相似文献
11.
Disturbed grassland soils are often cited as having the potential to store large amounts of carbon (C). Fertilization of grasslands
can promote soil C storage, but little is known about the generation of recalcitrant pools of soil organic matter (SOM) with
management treatments, which is critical for long-term soil C storage. We used a combination of soil incubations, size fractionation
and acid hydrolysis of SOM, [C], [N], and stable isotopic analyses, and biomass quality indices to examine how fertilization
and haying can impact SOM dynamics in Kansan grassland soils. Fertilized soils possessed 113% of the C possessed by soils
subjected to other treatments, an increase predominantly harbored in the largest size fraction (212–2,000 μm). This fraction
is frequently associated with more labile material. Haying and fertilization/haying, treatments that more accurately mimic
true management techniques, did not induce any increase in soil C. The difference in 15N-enrichment between size fractions was consistent with a decoupling of SOM processing between pools with fertilization, congruent
with gains of SOM in the largest size fraction promoted by fertilization not moving readily into smaller fractions that frequently
harbor more recalcitrant material. Litterfall and root biomass C inputs increased 104% with fertilization over control plots,
and this material possessed lower C:N ratios. Models of incubation mineralization kinetics indicate that fertilized soils
have larger pools of labile organic C. Model estimates of turnover rates of the labile and recalcitrant C pools did not differ
between treatments (65.5 ± 7.2 and 2.9 ± 0.3 μg C d−1, respectively). Although fertilization may promote greater organic inputs into these soils, much of that material is transformed
into relatively labile forms of soil C; these data highlight the challenges of managing grasslands for long-term soil C sequestration. 相似文献
12.
Combined effects of atmospheric CO<Subscript>2</Subscript> and N availability on the belowground carbon and nitrogen dynamics of aspen mesocosms 总被引:1,自引:0,他引:1
It is uncertain whether elevated atmospheric CO2 will increase C storage in terrestrial ecosystems without concomitant increases in plant access to N. Elevated CO2 may alter microbial activities that regulate soil N availability by changing the amount or composition of organic substrates
produced by roots. Our objective was to determine the potential for elevated CO2 to change N availability in an experimental plant-soil system by affecting the acquisition of root-derived C by soil microbes.
We grew Populus tremuloides (trembling aspen) cuttings for 2 years under two levels of atmospheric CO2 (36.7 and 71.5 Pa) and at two levels of soil N (210 and 970 μg N g–1). Ambient and twice-ambient CO2 concentrations were applied using open-top chambers, and soil N availability was manipulated by mixing soils differing in
organic N content. From June to October of the second growing season, we measured midday rates of soil respiration. In August,
we pulse-labeled plants with 14CO2 and measured soil 14CO2 respiration and the 14C contents of plants, soils, and microorganisms after a 6-day chase period. In conjunction with the August radio-labeling
and again in October, we used 15N pool dilution techniques to measure in situ rates of gross N mineralization, N immobilization by microbes, and plant N uptake.
At both levels of soil N availability, elevated CO2 significantly increased whole-plant and root biomass, and marginally increased whole-plant N capital. Significant increases
in soil respiration were closely linked to increases in root biomass under elevated CO2. CO2 enrichment had no significant effect on the allometric distribution of biomass or 14C among plant components, total 14C allocation belowground, or cumulative (6-day) 14CO2 soil respiration. Elevated CO2 significantly increased microbial 14C contents, indicating greater availability of microbial substrates derived from roots. The near doubling of microbial 14C contents at elevated CO2 was a relatively small quantitative change in the belowground C cycle of our experimental system, but represents an ecologically
significant effect on the dynamics of microbial growth. Rates of plant N uptake during both 6-day periods in August and October
were significantly greater at elevated CO2, and were closely related to fine-root biomass. Gross N mineralization was not affected by elevated CO2. Despite significantly greater rates of N immobilization under elevated CO2, standing pools of microbial N were not affected by elevated CO2, suggesting that N was cycling through microbes more rapidly. Our results contained elements of both positive and negative
feedback hypotheses, and may be most relevant to young, aggrading ecosystems, where soil resources are not yet fully exploited
by plant roots. If the turnover of microbial N increases, higher rates of N immobilization may not decrease N availability
to plants under elevated CO2.
Received: 12 February 1999 / Accepted: 2 March 2000 相似文献
13.
The impacts of crop rotation and inorganic nitrogen fertilization on soil microbial biomass C (SMBC) and N (SMBN) and water-soluble
organic C (WSOC) were studied in a Guinea savanna Alfisol of Nigeria. In 2001, fields of grain legumes (soybean and cowpea),
herbaceous legume (Centrosema pascuorum) and a natural fallow were established. In 2002, maize was planted with N fertilizer rates of 0, 20, 40 and 60 kg N ha−1 in a split-plot arrangement fitted to a randomized complete block design with legumes and fallow as main plots and N fertilizer
levels as subplots. Surface soil samples were taken at 4 weeks after planting and tasselling stage of the maize. Inorganic
N fertilization had no significant (P>0.05) effect on SMBC, SMBN and WSOC, while crop rotation significantly (P<0.0001) affected both SMBC and WSOC. These results demonstrate that crop rotation do not necessarily influence the gross
soil microbial biomass, but may affect physiologically distinct subcomponent of the microbial biomass. The soils under the
various rotations had a predominance of fungi community as indicated by their wide biomass C/N ratio ranging from 9.2 to 20.9
suggesting fungi to be mainly responsible for decomposition in these soils. Soil microbial biomass and WSOC showed significant
(P<0.05) correlation with both soil pH and organic carbon but no relationship with total N. Based on these results, it appears
that the soil pH and organic carbon determined the flux of the soil microbial biomass and amount of WSOC in these soils. 相似文献
14.
Questions: What are the effects of repeated disturbance and N‐fertilization on plant community structure in a mountain birch forest? What is the role of enhanced nutrient availability in recovery of understorey vegetation after repeated disturbance? How are responses of soil micro‐organisms to disturbance and N‐fertilization reflected in nutrient allocation patterns and recovery of understorey vegetation after disturbance? Location: Subarctic mountain birch forest, Finland. Methods: We conducted a fully factorial experiment with annual treatments of disturbance (two levels) and N‐fertilization (four levels) during 1998–2002. We monitored treatment effects on above‐ground plant biomass, plant community structure and plant and soil nutrient concentrations. Results: Both disturbance and N‐fertilization increased the relative biomass of graminoids. The increase of relative biomass of graminoids in the disturbance treatment was over twice that of the highest N‐fertilization level, and N‐fertilization further increased their relative biomass after disturbance. As repeated disturbance broke the dominance of evergreen dwarf shrubs, it resulted in a situation where deciduous species, graminoids and herbs dominated the plant community. Although relative biomass of deciduous dwarf shrubs declined with N‐fertilization, it did not cause a shift in plant community structure, as evergreen dwarf shrubs remained dominant. Both disturbance and N‐fertilization increased the N concentration in vascular plants, whereas microbial biomass N and C were not affected by the treatments. Concentrations of NH4+, dissolved organic N (DON) and dissolved organic C (DOC) increased in the soil after N‐fertilization, whereas concentrations of NH4+ and DON decreased after disturbance. Conclusions: Disturbances caused by e.g. humans or herbivores contribute more to changes in the understorey vegetation structure than increased levels of N in subarctic vegetation. Fertilization accelerated the recovery potential after repeated disturbance in graminoids. Microbial activities did not limit plant growth. 相似文献
15.
Annual burning of a tallgrass prairie inhibits C and N cycling in soil,increasing recalcitrant pyrogenic organic matter storage while reducing N availability 下载免费PDF全文
Grassland ecosystems store an estimated 30% of the world's total soil C and are frequently disturbed by wildfires or fire management. Aboveground litter decomposition is one of the main processes that form soil organic matter (SOM). However, during a fire biomass is removed or partially combusted and litter inputs to the soil are substituted with inputs of pyrogenic organic matter (py‐OM). Py‐OM accounts for a more recalcitrant plant input to SOM than fresh litter, and the historical frequency of burning may alter C and N retention of both fresh litter and py‐OM inputs to the soil. We compared the fate of these two forms of plant material by incubating 13C‐ and 15N‐labeled Andropogon gerardii litter and py‐OM at both an annually burned and an infrequently burned tallgrass prairie site for 11 months. We traced litter and py‐OM C and N into uncomplexed and organo‐mineral SOM fractions and CO2 fluxes and determined how fire history affects the fate of these two forms of aboveground biomass. Evidence from CO2 fluxes and SOM C:N ratios indicates that the litter was microbially transformed during decomposition while, besides an initial labile fraction, py‐OM added to SOM largely untransformed by soil microbes. Additionally, at the N‐limited annually burned site, litter N was tightly conserved. Together, these results demonstrate how, although py‐OM may contribute to C and N sequestration in the soil due to its resistance to microbial degradation, a long history of annual removal of fresh litter and input of py‐OM infers N limitation due to the inhibition of microbial decomposition of aboveground plant inputs to the soil. These results provide new insight into how fire may impact plant inputs to the soil, and the effects of py‐OM on SOM formation and ecosystem C and N cycling. 相似文献
16.
Pulse additions of soil carbon and nitrogen affect soil nitrogen dynamics in an arid Colorado Plateau shrubland 总被引:4,自引:0,他引:4
Biogeochemical cycles in arid and semi-arid ecosystems depend upon the ability of soil microbes to use pulses of resources.
Brief periods of high activity generally occur after precipitation events that provide access to energy and nutrients (carbon
and nitrogen) for soil organisms. To better understand pulse-driven dynamics of microbial soil nitrogen (N) cycling in an
arid Colorado Plateau ecosystem, we simulated a pulsed addition of labile carbon (C) and N in the field under the canopies
of the major plant species in plant interspaces. Soil microbial activity and N cycling responded positively to added C while
NH4+–N additions resulted in an accumulation of soil NO3−. Increases in microbial activity were reflected in higher rates of respiration and N immobilization with C addition. When
both C and N were added to soils, N losses via NH3 volatilization decreased. There was no effect of soil C or N availability on microbial biomass N suggesting that the level
of microbial activity (respiration) may be more important than population size (biomass) in controlling short-term dynamics
of inorganic and labile organic N. The effects of C and N pulses on soil microbial function and pools of NH4+–N and labile organic N were observed to last only for the duration of the moisture pulse created by treatment addition, while
the effect on the NO3−–N pool persisted after soils dried to pre-pulse moisture levels. We observed that increases in available C lead to greater
ecosystem immobilization and retention of N in soil microbial biomass and also lowered rates of gaseous N loss. With the exception
of trace gas N losses, the lack of interaction between available C and N on controlling N dynamics, and the subsequent reduction
in plant available N with C addition has implications for the competitive relationships between plants species, plants and
microbes, or both. 相似文献
17.
Soil organic material (SOM) is usually enriched in 15N in deeper soil layers. This has been explained by discrimination against the heavier isotope during decomposition or by
the accumulation of 15N-enriched microbial biomass versus plant biomass in older SOM. In particular, ectomycorrhizal (EM) fungi have been suggested
to accumulate in old SOM since this group is among the most 15N-enriched components of the microbial community. In the present study we investigated the microbial community in soil samples
along a chronosequence (7,800 years) of sites undergoing isostatic rebound in northern Sweden. The composition of the microbial
community was analyzed and related to the δ15N and δ13C isotope values of the SOM in soil profiles. A significant change in the composition of the microbial community was found
during the first 2,000 years, and this was positively related to an increase in the δ15N values of the E and B horizons in the mineral soil. The proportion of fungal phospholipid fatty acids increased with time
in the chronosequence and was positively related to the 15N enrichment of the SOM. The increase in δ13C in the SOM was much less than the increase in δ15N, and δ13C values in the mineral soil were only weakly related to soil age. The C:N ratio and the pH of the soil were important factors
determining the composition of the microbial community. We suggest that the N being transported from the soil to aboveground
tissue by EM fungi is a driver for 15N enrichment of soil profiles. 相似文献
18.
Distribution of ecosystem C and N within contrasting vegetation types in a semiarid rangeland in the Great Basin,USA 总被引:1,自引:0,他引:1
Toby D. Hooker John M. Stark Urszula Norton A. Joshua Leffler Michael Peek Ron Ryel 《Biogeochemistry》2008,90(3):291-308
Semiarid sagebrush ecosystems are being transformed by wildfire, rangeland improvement techniques, and exotic plant invasions,
but the effects on ecosystem C and N dynamics are poorly understood. We compared ecosystem C and N pools to 1 m depth among
historically grazed Wyoming big sagebrush, introduced perennial crested wheatgrass, and invasive annual cheatgrass communities,
to examine whether the quantity and quality of plant inputs to soil differs among vegetation types. Natural abundance δ15N isotope ratios were used to examine differences in ecosystem N balance. Sagebrush-dominated sites had greater C and N storage
in plant biomass compared to perennial or annual grass systems, but this was predominantly due to woody biomass accumulation.
Plant C and N inputs to soil were greatest for cheatgrass compared to sagebrush and crested wheatgrass systems, largely because
of slower root turnover in perennial plants. The organic matter quality of roots and leaf litter (as C:N ratios) was similar
among vegetation types, but lignin:N ratios were greater for sagebrush than grasses. While cheatgrass invasion has been predicted
to result in net C loss and ecosystem degradation, we observed that surface soil organic C and N pools were greater in cheatgrass
and crested wheatgrass than sagebrush-dominated sites. Greater biomass turnover in cheatgrass and crested wheatgrass versus
sagebrush stands may result in faster rates of soil C and N cycling, with redistribution of actively cycled N towards the
soil surface. Plant biomass and surface soil δ15N ratios were enriched in cheatgrass and crested wheatgrass relative to sagebrush-dominated sites. Source pools of plant available
N could become 15N enriched if faster soil N cycling rates lead to greater N trace gas losses. In the absence of wildfire, if cheatgrass invasion
does lead to degradation of ecosystem function, this may be due to faster nutrient cycling and greater nutrient losses, rather
than reduced organic matter inputs. 相似文献
19.
Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term
changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic
matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the
short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production,
and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant
residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N
ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases
in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual
burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation.
Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE.
No single factor dominates the impact of fire on tallgrass plant production. 相似文献
20.
Ungulate stimulation of nitrogen cycling and retention in Yellowstone Park grasslands 总被引:4,自引:0,他引:4
We studied how ungulates and a large variation in site conditions influenced grassland nitrogen (N) dynamics in Yellowstone
National Park. In contrast to most grassland N studies that have examined one or two soil N processes, we investigated four
rates, net N mineralization, nitrification, denitrification, and inorganic N leaching, at seven paired sites inside and outside
long-term (33+ year) exclosures. Our focus was how N fluxes were related to one another among highly variable grasslands and
how grazers influenced those relationships. In addition, we examined variation in soil δ15N among grasslands and the relationships between soil 15N abundance and N processes. Previously, ungulates were reported to facilitate net N mineralization across variable Yellowstone
grasslands and denitrification at mesic sites. In this study, we found that herbivores also promoted nitrification among diverse
grasslands. Furthermore, net N mineralization, nitrification, and denitrification (kg N ha–1 year–1, each variable) were postively and linearly related to one another among all grasslands (grazed and fenced), and grazers
reduced the nitrification/net N mineralization and denitrification/net N mineralization ratios, indicating that ungulates
inhibited the proportion of available NH4
+ that was nitrified and denitrified. There was no relationship between net N mineralization or nitrification with leaching
(indexed by inorganic N adsorbed to resin buried at the bottom of rooting zones) and leaching was unaffected by grazers. Soil
δ15N was positively and linearly related to in situ net N mineralization and nitrification in ungrazed grasslands; however, there
was no relationship between isotopic composition of N and those rates among grazed grasslands. The results suggested that
grazers simultaneously increased N availability (stimulated net N mineralization and nitrification per unit area) and N conservation
(reduced N loss from the soil per unit net N mineralization) in Yellowstone grasslands. Grazers promoted N retention by stimulating
microbial productivity, probably caused by herbivores promoting labile soil C. Process-level evidence for N retention by grazers
was supported by soil δ15N data. Grazed grassland with high rates of N cycling had substantially lower soil δ15N relative to values expected for ungrazed grassland with comparable net N mineralization and nitrification rates. These soil
15N results suggest that ungulates inhibited N loss at those sites. Such documented evidence for consumer control of N availability
to plants, microbial productivity, and N retention in Yellowstone Park is further testimony for the widespread regulation
of grassland processes by large herbivores.
Received: 5 May 1999 / Accepted: 1 November 1999 相似文献