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1.
Many previous studies have demonstrated that heterotrophic nitrification processes play an important role in the production of NO3− in acidic soils. However, it is not clear whether a low concentration of nitrogenous organic compounds support heterotrophic nitrification processes in natural soils. In this study, we performed an 15N tracer experiment with a glycine concentration gradient (20, 40, 80, and 160 mg N kg−1) to investigate the effect of the organic nitrogen concentration on the heterotrophic nitrification rate and its relative contribution to the total nitrification of the studied acidic forest soil. This experiment demonstrated that 15N–NO3− accumulated over time with all nitrogen treatments in the presence of acetylene, confirming that heterotrophic nitrification occurred even at a low organic nitrogen concentration (20 mg kg−1) in the studied acidic forest soil. In the presence of acetylene, the 15N–NO3− concentration in the 20 and 40 mg kg−1 glycine-N treatments was significantly lower than in the 80 and 160 mg kg−1 glycine-N treatments (p < 0.05), indicating that a high organic nitrogen concentration stimulated the heterotrophic nitrification rate. There was no significant difference in the average contribution of heterotrophic nitrification to total nitrification among the different nitrogen treatments, suggesting that the organic nitrogen concentration did not affect the relative contribution of heterotrophic nitrification to total nitrification in the studied acidic soil. Our results confirmed that a low concentration of organic N (20 mg kg−1) supported heterotrophic nitrification in the studied soil. The organic nitrogen concentration stimulates the heterotrophic nitrification rate, but does not affect the relative contribution of heterotrophic nitrification to total nitrification in the studied acidic soil.  相似文献   

2.
Impact of Pheidole sp., reportedly important in insect pest suppression in agroecosystems was studied on supporting agroecosystem services. This tropical ant species was found to be common and abundant in agroecosystems, with a high nest density and preference for the central, crop-growing zone of annual cropping systems. Physico-chemical characteristics of the debris soil were examined from nests located by the roadside and within two managed ecosystems. The debris soil had significantly higher concentrations of total C, N, P and NO3-N along with higher water-holding capacity and moderate-sized soil particles in comparison to the control soil. The pH of the Pheidole sp. debris soil was shifted towards reduced alkaline conditions. Results reveal that annually, 2.44 kg/ha C, 0.071 kg/ha P, 0.628 kg/ha N and 0.009 kg/ha NO3-N are added to the soil through the accumulation of organic refuse at the nest rim. This contributes to soil nutrient enhancement and is suggested to enhance ecosystem productivity. The high nutrient content of nest debris soil is linked to the predominance of arthropod carcasses (93.7% of the total organic refuse) in the refuse piles derived from the animal-based food (70.3%) brought to the nests by the foragers. Plant-based food was 29.6% (seeds, leaves, roots, etc.) of the total indicating a minor role of Pheidole sp. as a seed harvester. The results suggest an important role of Pheidole sp. in regulating the soil nutrients as an ecosystem engineer.  相似文献   

3.
The distribution of heterotrophic bacteria on organic debris and roots of rice plants in a paddy field were studied. The heterotrophic bacteria consisted of two main groups: those which grew on full-strength nutrient broth (NB) and those which did not grow on NB but on a 100-fold dilution of NB (DNB). The latter group was called ‘DNB organisms’ and were considered to be oligotrophic. In both manured and unmanured soils, DNB organisms were predominant in the bacterial communities on organic debris and the rice roots throughout most of the entire period of rice cultivation, although a transient decrease in the proportion of DNB organisms was observed immediately after an application of manure. Morphological and physiological characteristics of DNB isolates from organic debris and rice roots were studied: five types of cell shape were observed, (1) regular rods, (2) filament-forming rods, (3) irregular rods, (4) prosthecate organisms and (5) large oval cells. Regular rods (42% of the total DNB isolates) and irregular rods (46%) were abundant. The ecological roles of DNB organisms in paddy soil are discussed in relation to their physiological characteristics.  相似文献   

4.
Abstract

A series of experiments has been conducted on the N2 fixation in the paddy soils by the authors (1–4). The amount of organic substrates for microorganisms and the degree of reduction of the soil are found to be two major factors affecting the N2-fixing activity of the heterotrophic microorganisms in the submerged soil. Organic debris, rice root and their neighboring soils are identified to be the important micro-sites for the heterotrophic N2 fixers. The organic debris and the rice root are considered to play dual roles by supplying the organic substances; (1) increase of the population of the heterotrophic N2 fixers—the amount of nitrogenase, (2) preparation of the reduced conditions favorable for the nitrogenase activity.

However, it is not yet clearly known which of these two roles of the organic substrates is more essential to the N2-fixing activity in the paddy soil. In addition, it is expected that there must be some differences between the organic debris and rice root in their contribution to the N2 fixation in the paddy soil.

An experiment was carried out to clarify these problems. Moist soil sample was collected from the plough layer of the paddy field at Central Agric. Exp. Sta. in Konosu City, Saitama Pref., passed through a 5 mm sieve and placed in pots (3 kg moist soil/pot). Ammonium sulfate, calcium superphosphate, and potassium chloride at the rate of 0.4-0.4-0.4 (N-P2O5-K20) g/pot were incorporated into the soil 7 days before transplanting. Split application of ammonium sulfate at the rates of 0.2 and 0.4 g N/pot were also incorporated at 30 and 41 days after transplanting respectively. These pots were divided into three series; planted (P-series), non-planted (N-series), and non-planted and applied with organic manure (O-series). In case of O-series, 60 g of fairly rotted organic manure was applied to each pot. Each pot of P-series was planted with two 4O-day-old seedlings of rice plant at 7 days after submergence. The Nseries was regarded as a control. Each series was not replicated in this preliminary experiment.  相似文献   

5.
The presence of tree roots and symbiotic mycorrhizal fungi is recognized to have a substantial impact on carbon dynamics in soils. In this study the effect of Pinus sylvestris seedlings and the ectomycorrhizal fungus Hebeloma crustuliniforme on a number of biogeochemical variables, mainly related to labile carbon pools was investigated. The impact of K limitation as a potential regulatory factor was also examined. Columns filled with E horizon ±plants and ±mycorrhizal fungi were incubated for 18.5 months. The results demonstrate that plants, as well as mycorrhizal fungi, significantly increased the concentrations of some simple organic acids, including oxalate, in soil solution. Observations for dissolved organic carbon were slightly contradictory but the cumulative amount found in drainage water was ∼20% higher in planted versus non-planted columns. Soil from planted treatments also showed more rapid mineralisation kinetics for oxalate. However carbon utilization (mineralisation vs. biomass) of oxalate and glucose by the soil microbial biomass was less influenced by plants. At harvest a component integration study of soil autotrophic and heterotrophic respiration was performed which revealed that both plant and mycorrhiza had a positive effect on the heterotrophic respiration. Potassium omission had little effect on the variables studied with the exception of the maximum mineralisation rate for oxalate, which increased when K was withdrawn. The results are discussed in the context of the dynamics of labile soil carbon pools and ecosystem C fluxes.  相似文献   

6.
A major forest disturbance such as clearcutting may bring on a flush of mineral N in organic forest floor horizons, but the magnitude of this flush can vary markedly from one ecosystem to another. For example, it was previously established that clearcutting in a high elevation Engelmann spruce-subalpine fir (ESSF) ecosystem results in significantly higher NH4+ and NO3− concentrations, whereas clearcutting in an old-growth coastal western hemlock (CWH) ecosystem has little effect on mineral N dynamics. We hypothesized that the higher mineral N flush observed in the ESSF ecosystem is due to a greater temperature sensitivity of mineral N transformation rates, and to a lower proportion of heterotrophic nitrifiers, compared to the CWH ecosystem. To test these two hypotheses, we sampled forest floors several times over the growing season from clearcut and old-growth plots in both ecosystems, and measured gross mineral N transformation rates at field temperatures and at 10 °C above field temperatures, as well as with and without acetylene to inhibit autotrophic nitrifiers. Gross NH4+ transformations rates ranged between 20 and 120 μg N (g forest floor)−1 day−1 at the ESSF site, and between 15 and 40 μg N (g forest floor)−1 day−1 at the CWH site. Higher temperature increased gross NH4+ transformation rates in forest floor samples at both sites, but the average Q10 value was higher at the ESSF site (3.15) than at the CWH site (1.25). Temperature sensitivity at the ESSF site was greater in clearcut plots (Q10=4.31) than in old-growth plots (Q10=1.98). Gross NO3− transformation rates ranged between 10 and 32 μg N (g forest floor)−1 day−1 at the ESSF site, and between 10 and 24 μg N (g forest floor)−1 day−1 at the CWH site, but there were no significant effects of temperature or clearcutting on gross NO3− transformation rates at either site. Likewise, there were no significant differences in the proportion of heterotrophic nitrifiers between sites. Overall, our results support the view that the temperature sensitivity of microbial processes may explain the magnitude of the NH4+ flush in some coniferous ecosystems, but we lack the evidence relating the magnitude of the NO3− flush to the proportion of heterotrophic nitrifiers.  相似文献   

7.
In traditional environmental risk assessment for soils, interactions between biota, contaminants and soil functioning are seldom taken into account. Also, single species toxicity tests are conducted with a fixed number of test animals. The objective of this study was to investigate effects of zinc (0–620 mg Zn kg?1 dry soil) on soil ecosystem processes at different densities of the earthworm Lumbricus rubellus. Experiments were conducted using 1-liter microcosms equipped with respirometers. The presence of L. rubellus stimulated relevant soil processes and parameters: litter fragmentation, leaf litter mass loss from the soil surface, soil organic matter (SOM) content and soil respiration. Zinc was not lethal to L. rubellus, but negatively impacted soil respiration at the highest concentrations. Litter mass loss from the soil surface was also decreased by zinc and there was a significant interaction with worm density. The results of the study demonstrate that the impact of zinc on soil processes depends on the presence and densities of key soil organisms such as earthworms that influence decomposition and SOM content. The outcome of this research can be used to make existing models for site-specific risk assessment more ecologically relevant, linking effects of contaminants on soil fauna populations with effects on ecosystem functioning.  相似文献   

8.
We studied a semi-natural forest in Northern Italy that was set aside more than 50 years ago, in order to better understand the soil carbon cycle and in particular the partitioning of soil respiration between autotrophic and heterotrophic respiration. Here we report on soil organic carbon, root density, and estimates of annual fluxes of soil CO2 as measured with a mobile chamber system at 16 permanent collars about monthly during the course of a year. We partitioned between autotrophic and heterotrophic respiration by the indirect regression method, which enabled us to obtain the seasonal pattern of single components.The soil pool of organic carbon, with 15.8 (±4.5) kg m?2, was very high over the entire depth of 45 cm. The annual respiration rates ranged from 0.6 to 6.9 μmol CO2 m?2 s?1 with an average value of 3.4 (±2.3) μmol CO2 m?2 s?1, and a cumulative flux of 1.1 kg C m?2 yr?1. The heterotrophic component accounted for 66% of annual CO2 efflux. Soil temperature largely controlled the heterotrophic respiration (R2 = 0.93), while the autotrophic component followed irradiation, pointing to the role of photosynthesis in modulating the annual course of soil respiration.Most studies on soil respiration partitioning indicate autotrophic root respiration as a first control of the spatial variability of the overall respiration, which originates mainly from the uppermost soil layers. Instead, in our forest the spatial variability of soil respiration was mainly linked to soil carbon, and deeper layers seemed to provide a significant contribution to soil respiration, a feature that may be typical for an undisturbed, naturally maturing ecosystem with well developed pedobiological processes and high carbon stocks.  相似文献   

9.
Plant effects on ecosystem processes are mediated through plant-microbial interactions belowground and soil enzyme assays are commonly used to directly relate microbial activity to ecosystem processes. Live plants influence microbial biomass and activity via differences in rhizosphere processes and detrital inputs. I utilized six grass species of varying litter chemistry in a factorial greenhouse experiment to evaluate the relative effect of live plants and detrital inputs on substrate-induced respiration (SIR, a measure of active microbial biomass), basal respiration, dissolved organic carbon (DOC), and the activities of β-glucosidase, β-glucosaminidase, and acid phosphatase. To minimize confounding variables, I used organic-free potting media, held soil moisture constant, and fertilized weekly. SIR and enzyme activities were 2-15 times greater in litter-addition than plant-addition treatments. Combining live plants with litter did not stimulate microbial biomass or activity above that in litter-only treatments, and β-glucosidase activity was significantly lower. Species-specific differences in litter N (%) and plant biomass were related to differences in β-glucosaminidase and acid phosphatase activity, respectively, but had no apparent effect on β-glucosidase, SIR, or basal respiration. DOC was negatively related to litter C:N, and positively related to plant biomass. Species identity and living plants were not as important as litter additions in stimulating microbial activity, suggesting that plant effects on soil enzymatic activity were driven primarily by detrital inputs, although the strength of litter effects may be moderated by the effect of growing plants.  相似文献   

10.
Net carbon flux partitioning was used to disentangle abiotic and biotic drivers of all important component fluxes influencing the overall sink strength of a Mediterranean ecosystem during a rapid spring to summer transition. Between May and June 2006 we analyzed how seasonal drought affected ecosystem assimilation and respiration fluxes in an evergreen oak woodland and attributed variations in the component fluxes (trees, understory, soil microorganisms and roots) to observations at the ecosystem scale. We observed a two thirds decrease in both ecosystem carbon assimilation and respiration (Reco) within only 15 days time. The impact of decreasing Reco on the ecosystem carbon balance was smaller than the impact of decreasing primary productivity. Flux partitioning of GPP and Reco into their component fluxes from trees, understory, soil microorganisms and roots showed that declining ecosystem sink strength was due to a large drought and temperature-induced decrease in understory carbon uptake (from 56% to 21%). Hence, the shallow-rooted annuals mainly composing the understory have a surprisingly large impact on the source/sink behavior of this open evergreen oak woodland during spring to summer transition and the timing of the onset of drought might have a large effect on the annual carbon budget. In response to seasonal drought Reco was increasingly dominated by respiration of heterotrophic soil microorganisms, while the root flux was found to be of minor importance. Soil respiration flux decreased with drought but its contribution to total daily CO2-exchange increased by 11.5%. This partitioning approach disentangled changes in respiratory and photosynthetic ecosystem fluxes that were not apparent from the eddy-covariance or the soil respiration data alone. By the novel combination of understory vs. overstory carbon flux partitioning with soil respiration data from trenched and control plots, we gained a detailed understanding of factors controlling net carbon exchange of Mediterranean ecosystems.  相似文献   

11.

Background, aim, and scope  

Mining activities disturb land and reduce its capacity to support a complete functional ecosystem. Reclamation activities in this case are not easy due to the large amount of soil required. This is why mining debris are usually used as surrogate of soil, despite their unsuitable physicochemical properties. However, these properties can be improved with the amendment using an organic source, usually sewage sludge. Nevertheless, the use of sludge might lead to impacts on soil and water ecosystems because of its physicochemical properties and pollutant content. The aim of this study is to assess the suitability of the use of mining debris amended with sewage sludge as practice for the reclamation of land degraded by limestone-quarrying activities.  相似文献   

12.
In order to assess the capacity of the boreal forest ecosystem to intercept atmospheric carbon over a period of years, a climate-driven growth model (FinnFor, process-based) was applied to calculate the seasonal and inter-annual variability of net ecosystem CO2 exchange (NEE) and component carbon fluxes (gross primary production - GPP and total ecosystem respiration - TER) against a 10-year (1999-2008) period of eddy covariance (EC) measurements in a Scots pine (Pinus sylvestris L.) stand in Eastern Finland. Furthermore, the role of climatic factors, leaf area index (LAI) and physiological responses of trees regarding the ecosystem carbon fixation processes were evaluated. An hourly time-step was used to simulate the carbon exchange based on measured tree/stand characteristics and meteorological input for the experimental site, and the dynamic LAI was used throughout the 10-year simulations. The model predicted well the annual course of NEE compared to the measured values for most of the years, with the development of LAI (2.4-3.3 m2 m−2, as simulated). The simulated NEE over the study period shows that, on average, 62% of the variation refers to daily and 88% to monthly measured NEE. Both modeled and measured daily NEE showed similar responses to the temperature, photosynthetically active radiation and vapor pressure deficit during the growing seasons. In the simulation, the annual amount of GPP varied from 720.8 to 910.4 g C m−2 with a mean value of 825.3 g C m−2, and the annual mean TER/GPP ratio was 0.79, close to the measured value. Carbon efflux from the forest floor was the dominant contributor to the forest ecosystem respiration. The inter-annual variation of GPP mostly corresponded to the development of LAI, temperature sum and total incoming radiation over the 10-year simulation period. It was suggested that the process-based model could be applied to study the carbon processes for natural and management-induced dynamics of Scots pine forest ecosystem over longer periods across a wider climate gradient in the boreal zone.  相似文献   

13.
Nitrogen (N) cycling in terrestrial ecosystems is complex since it involves the closely interwoven processes of both N uptake by plants and microbial turnover of a variety of N metabolites. Major interactions between plants and microorganisms involve competition for the same N species, provision of plant nutrients by microorganisms and labile carbon (C) supply to microorganisms by plants via root exudation. Despite these close links between microbial N metabolism and plant N uptake, only a few studies have tried to overcome isolated views of plant N acquisition or microbial N fluxes. In this study we studied competitive patterns of N fluxes in a mountainous beech forest ecosystem between both plants and microorganisms by reducing rhizodeposition by tree girdling. Besides labile C and N pools in soil, we investigated total microbial biomass in soil, microbial N turnover (N mineralization, nitrification, denitrification, microbial immobilization) as well as microbial community structure using denitrifiers and mycorrhizal fungi as model organisms for important functional groups. Furthermore, plant uptake of organic and inorganic N and N metabolite profiles in roots were determined.Surprisingly plants preferred organic N over inorganic N and nitrate (NO3−) over ammonium (NH4+) in all treatments. Microbial N turnover and microbial biomass were in general negatively correlated to plant N acquisition and plant N pools, thus indicating strong competition for N between plants and free living microorganisms. The abundance of the dominant mycorrhizal fungi Cenococcum geophilum was negatively correlated to total soil microbial biomass but positively correlated to glutamine uptake by beech and amino acid concentration in fine roots indicating a significant role of this mycorrhizal fungus in the acquisition of organic N by beech. Tree girdling in general resulted in a decrease of dissolved organic carbon and total microbial biomass in soil while the abundance of C. geophilum remained unaffected, and N uptake by plants was increased. Overall, the girdling-induced decline of rhizodeposition altered the competitive balance of N partitioning in favour of beech and its most abundant mycorrhizal symbiont and at the expense of heterotrophic N turnover by free living microorganisms in soil. Similar to tree girdling, drought periods followed by intensive drying/rewetting events seemed to have favoured N acquisition by plants at the expense of free living microorganisms.  相似文献   

14.
Forest debris on ground surface can interact with soil biota and consequently change ecosystem processes across heterogeneous landscape. We examined the interactions between forest debris and litter decomposition in riparian and upland sites within a tropical wet forest. Our experiment included control and debris-removal treatments. Debris-removal reduced leaf litter decomposition rates in both the riparian and upland sites. Debris-removal also reduced soil microbial biomass C in the upland site, but had no effect on microbial biomass C in the riparian site. In contrast, debris-removal altered the density of selected arthropod groups in the riparian site. Litter decomposition rates correlated with both soil microbial biomass and the density of millipedes in a multiple stepwise regression model. Removal of forest debris can substantially reduce rates of leaf litter decomposition through suppressing soil activities. This influence can be further modified by landscape position. Forest debris plays an essential role in maintaining soil activities and ecosystem functioning in this tropical wet forest.  相似文献   

15.
Limitations to the respiratory activity of heterotrophic soil microorganisms exert important controls of CO2 efflux from soils. In the northeastern US, ecosystem nutrient status varies across the landscape and changes with forest succession following disturbance, likely impacting soil microbial processes regulating the transformation and emission of carbon (C). We tested whether nitrogen (N) or phosphorus (P) limit the mineralization of soil organic C (SOC) or that of added C sources in the Oe horizon of successional and mature northern hardwood forests in three locations in central New Hampshire, USA. Added N reduced mineralization of C from SOC and from added leaf litter and cellulose. Added P did not affect mineralization from SOC; however, it did enhance mineralization of litter- and cellulose- C in organic horizons from all forest locations. Added N increased microbial biomass N and K2SO4-extractable DON pools, but added P had no effect. Microbial biomass C increased with litter addition but did not respond to either nutrient. The direction of responses to added nutrients was consistent among sites and between forest ages. We conclude that in these organic horizons limitation by N promotes mineralization of C from SOC, whereas limitation by P constrains mineralization of C from new organic inputs. We also suggest that N suppresses respiration in these organic horizons either by relieving the N limitation of microbial biomass synthesis, or by slowing turnover of C through the microbial pool; concurrent measures of microbial growth and turnover are needed to resolve this question.  相似文献   

16.
Gas and volatile organic compounds (VOCs) release in soil is known to be linked to microbial activity and can differently affect the life of organisms in soil. Electronic noses (E-noses) are sensing devices composed of sensor arrays able to measure and monitor gases and VOCs in air. This is the first report on the use of such a sensing device to measure specifically microbial activity in soil. In the present study, γ-irradiated sterilised soil was inoculated with Pseudomonas fluorescens. To be sure for a rapid microbial growth and activity, two pulses of nutrient solution with organic and inorganic C, N, P and S sources were added to soil and the resulting microcosms were incubated for 23 d. During the incubation, respiration and enzyme activities of acid phosphatase, β-glucosidase, fluorescein diacetate hydrolase and protease, were measured, and microbial growth as global biomass of vital cells based on substrate-induced respiration (SIR-Cmic) and enumeration of viable and culturable cells by means of dilution plate counts (CFU) were also monitored. Concurrently, VOCs and/or gas evolution in the headspace of the soil microcosms were measured through the E-nose, upon their adsorption on quartz crystal microbalances (QCMs) comprising the sensory device. The E-nose typically generated an odorant image (olfactory fingerprint) representative of the analysed samples (soils) and resulting from the concurrent perception of all or most of the analytes in headspace, as it commonly happens when several selective but not specific sensors are used together (array). The basic hypothesis of this study was that different soil ecosystems expressing distinct microbial metabolic activities, tested through respiration and enzyme activities, might generate different olfactory fingerprints in headspace. Furthermore, the possibility to detect several substances at the same time, released from the soil ecosystems, possibly deriving from both abiotic and biotic (microbial metabolism) processes provides an “odorant image” representative of the whole ecosystem under study. The E-nose here used succeeded in discriminating between inoculated and non-inoculated ecosystems and in distinguishing different metabolic and growth phases of the inoculated bacteria during incubation. Specifically, E-nose responses were proved highly and significantly correlated with all hydrolytic activities linked to the mobilisation of nutrients from soil organic matter and their cycling, with CO2 fluxes (respiration and presumed heterotrophic fixation) and with P. fluorescens population dynamics during exponential, stationary and starvation phases measured by SIR-Cmic and CFUs. Interestingly, the E-nose successfully detected soil microbial activity stimulated by nutrient supply, even though none of the catalytic activities tested directly produced VOCs and/or gases. The E-nose technology was then proved able to supply a real holistic image of microbial activity in the entire gnotobiotic and axenic soil ecosystems.  相似文献   

17.
Although two species of chemolithoautotrophic bacteria, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, are widely considered to be the main microorganisms that control the process of bioleaching of heavy metals from sewage sludge, little is known about the effect of dissolved organic matter (DOM) present in sewage sludge on bacterial oxidation of energy substrate. Batch cultures studies showed that sludge DOM significantly inhibited ferrous iron and sulfur oxidation by Acidithiobacillus ferrooxidans LX5 and Acidithiobacillus thiooxidans TS6, respectively. The toxicity of sludge DOM appeared when the concentration was higher than 150 mg DOC L?1. Among the organic compounds tested, the monocarboxylic organic acids including formic acid, acetic acid, propionic acid, and butyric acid exhibited a marked toxicity to Acidithiobacillus species. Of these organic acids, formic acid was the most toxic one as indicating that iron and sulfur oxidation almost were entirely inhibited at a concentration of 1.67 mM. In addition, it was found that A. ferrooxidans LX5 was more sensitive to glucose, starch, and citric acid than A. thiooxidans TS6, while the former seemed to be more acetic, propionic, and butyric acid resistant than the latter. In the selected 150 mg DOC L?1 of DOM derived from Sludge-H, the concentrations of formic acid and acetic acid were 8.94 mM and 2.09 mM, respectively, being a contributing factor causing 95% inhibition of iron oxidation and 70% inhibition of sulfur oxidation. To exploit specific heterotrophic microorganisms to eliminate these toxic organic compounds should be further studied.  相似文献   

18.
General concern about climate change has led to growing interest in the responses of terrestrial ecosystems to elevated concentrations of CO2 in the atmosphere. Experimentation during the last two to three decades using a large variety of approaches has provided sufficient information to conclude that enrichment of atmospheric CO2 may have severe impact on terrestrial ecosystems. This impact is mainly due to the changes in the organic C dynamics as a result of the effects of elevated CO2 on the primary source of organic C in soil, i.e., plant photosynthesis. As the majority of life in soil is heterotrophic and dependent on the input of plant-derived organic C, the activity and functioning of soil organisms will greatly be influenced by changes in the atmospheric CO2 concentration. In this review, we examine the current state of the art with respect to effects of elevated atmospheric CO2 on soil microbial communities, with a focus on microbial community structure. On the basis of the existing information, we conclude that the main effects of elevated atmospheric CO2 on soil microbiota occur via plant metabolism and root secretion, especially in C3 plants, thereby directly affecting the mycorrhizal, bacterial, and fungal communities in the close vicinity of the root. There is little or no direct effect on the microbial community of the bulk soil. In particular, we have explored the impact of these changes on rhizosphere interactions and ecosystem processes, including food web interactions.  相似文献   

19.
Soils are the central organizer of the terrestrial ecosystem. Their colloidal and particulate constituents, be they minerals, organic matter, and microorganisms, are not separate entities; rather, they are constantly interacting with each other. Interactions of these components control biogeochemical reactions, namely, the formation of short-range-ordered metal oxides, catalysis of humic substance formation, enzymatic stability and activity, mineral transformation, aggregate turnover, biogeochemical cycling of C, N, P, and S, and the fate and transformation of organic and inorganic pollutants. Furthermore, the impacts of mineral–organic matter–microorganism interactions and associated biogeochemical reactions and processes on biodiversity, species composition, and sustainability of the terrestrial ecosystem deserve close attention for years to come. This paper integrates the frontiers of knowledge on this subject matter, which is essential to uncovering the dynamics and mechanisms of terrestrial ecosystem processes and to developing innovative management strategies to sustain ecosystem health on the global scale.  相似文献   

20.
《Pedobiologia》2014,57(4-6):263-269
Nitrogen (N) availability is an important factor that determines ecosystem productivity and respiration, especially in N-limited alpine ecosystems. However, the magnitude of this response depends on the timing and amounts of N input. Moreover, we have only a limited understanding of the potential effects of the timing of N fertilization on ecosystem carbon (C) and N processes, and activities of the soil microbes. A nitrogen fertilization experiment was conducted in an alpine meadow on the Tibetan Plateau to determine how plant productivity and ecosystem respiration (RE) respond to the timing and amount of N application. In this study, half of the N was added either in the early spring (ES), before the growing season, or in the late fall (LF), after the growing season. All treatments received the other half of the N in mid-July. Three N levels (10, 20, 40 kg N hm−2 yr−1) were used for each of two N treatments, with no N addition used as a control. Plant aboveground biomass, ecosystem respiration (RE) and soil respiration (RS) were measured for the 2011 and 2012 growing seasons. The LF treatment enhanced ecosystem CO2 efflux compared with the ES treatment at high N addition levels, resulting from an increase of soil dissolved organic C (DOC) and soil microbial activity. The ES treatment resulted in increased plant aboveground biomass when compared with LF during both growing seasons, although this increase accounted for little variation in ecosystem and soil respiration. Overall, the ES treatment is likely to increase the ecosystem C pool, while the LF treatment could accelerate ecosystem C cycling, especially for the high N treatment. Our results suggest that supplying N during the early stage of the growing season benefits both forage production and soil C sequestration in this alpine ecosystem.  相似文献   

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