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1.
Elevated atmospheric carbon dioxide (CO2) levels generally stimulate carbon (C) uptake by plants, but the fate of this additional C largely remains unknown. This uncertainty is due in part to the difficulty in detecting small changes in soil carbon pools. We conducted a series of long-term (170-330 days) laboratory incubation experiments to examine changes in soil organic matter pool sizes and turnover rates in soil collected from an open-top chamber (OTC) elevated CO2 study in Colorado shortgrass steppe. We measured concentration and isotopic composition of respired CO2 and applied a two-pool exponential decay model to estimate pool sizes and turnover rates of active and slow C pools. The active and slow C pools of surface soils (5-10 cm depth) were increased by elevated CO2, but turnover rates of these pools were not consistently altered. These findings indicate a potential for C accumulation in near-surface soil C pools under elevated CO2. Stable isotopes provided evidence that elevated CO2 did not alter the decomposition rate of new C inputs. Temporal variations in measured δ13C of respired CO2 during incubation probably resulted mainly from the decomposition of changing mixtures of fresh residue and older organic matter. Lignin decomposition may have contributed to declining δ13C values late in the experiments. Isotopic dynamics during decomposition should be taken into account when interpreting δ13C measurements of soil respiration. Our study provides new understanding of soil C dynamics under elevated CO2 through the use of stable C isotope measurements during microbial organic matter mineralization. 相似文献
2.
Understanding rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha?1 was pulse‐labeled with 13CO2 at tillering, elongation, anthesis, and grain‐filling stages. The 13C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO2 was measured 28 d after each 13C labeling. The proportion of net‐photosynthesized 13C recovered (shoots + roots + soil + soil respired CO2) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the 13C respired CO2 allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of 13C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment. 相似文献
3.
Two processes contribute to changes of the δ13C signature in soil pools: 13C fractionation per se and preferential microbial utilization of various substrates with different δ13C signature. These two processes were disentangled by simultaneously tracking δ13C in three pools - soil organic matter (SOM), microbial biomass, dissolved organic carbon (DOC) - and in CO2 efflux during incubation of 1) soil after C3-C4 vegetation change, and 2) the reference C3 soil.The study was done on the Ap horizon of a loamy Gleyic Cambisol developed under C3 vegetation. Miscanthus giganteus - a perennial C4 plant - was grown for 12 years, and the δ13C signature was used to distinguish between ‘old’ SOM (>12 years) and ‘recent’ Miscanthus-derived C (<12 years). The differences in δ13C signature of the three C pools and of CO2 in the reference C3 soil were less than 1‰, and only δ13C of microbial biomass was significantly different compared to other pools. Nontheless, the neglecting of isotopic fractionation can cause up to 10% of errors in calculations. In contrast to the reference soil, the δ13C of all pools in the soil after C3-C4 vegetation change was significantly different. Old C contributed only 20% to the microbial biomass but 60% to CO2. This indicates that most of the old C was decomposed by microorganisms catabolically, without being utilized for growth. Based on δ13C changes in DOC, CO2 and microbial biomass during 54 days of incubation in Miscanthus and reference soils, we concluded that the main process contributing to changes of the δ13C signature in soil pools was preferential utilization of recent versus old C (causing an up to 9.1‰ shift in δ13C values) and not 13C fractionation per se.Based on the δ13C changes in SOM, we showed that the estimated turnover time of old SOM increased by two years per year in 9 years after the vegetation change. The relative increase in the turnover rate of recent microbial C was 3 times faster than that of old C indicating preferential utilization of available recent C versus the old C.Combining long-term field observations with soil incubation reveals that the turnover time of C in microbial biomass was 200 times faster than in total SOM. Our study clearly showed that estimating the residence time of easily degradable microbial compounds and biomarkers should be done at time scales reflecting microbial turnover times (days) and not those of bulk SOM turnover (years and decades). This is necessary because the absence of C reutilization is a prerequisite for correct estimation of SOM turnover. We conclude that comparing the δ13C signature of linked pools helps calculate the relative turnover of old and recent pools. 相似文献
4.
We propose and successfully applied a new approach for 3-source-partitioning based on a combination of 14C labeling with 13C natural abundance. By adding 14C-labeled glucose to soil after C3 - C4 vegetation change, we partitioned three C sources in three compartments, namely CO2, microbial biomass and dissolved organic C (DOC). This enabled us to estimate mechanisms and sources of priming effects (PE).Glucose application at low and high rate (GL: 100 and GH: 1000 μg C g−1, respectively) caused positive PE both short-term (during 1-3 days) and long-term (3-55 days). Despite a 10-fold difference in the amount of substrate added, the PE observed was larger by a factor of only 1.6 at the high versus low rate of glucose. The real and apparent priming effects were distinguished by partitioning of microbial C for glucose-C and SOM-derived C. As the amount of primed CO2 respired during short-term PE was 40% lower than microbial C, and the contribution of soil C in microbial biomass did not increase, we concluded that such short-term PE was apparent and was mainly caused by accelerated microbial turnover (at GL) and by pool substitution (at GH). Both the amount of primed CO2-C, which was 1.3-2.1 times larger than microbial C, and the increased contribution of soil C in microbial biomass allowed us to consider the long-term PE as being real. The sole source of real PE (GL treatment) was the “recent” soil organic matter, which is younger than 12-year-old C. The real PE-induced by a glucose amount exceeding microbial biomass (GH) was due to the almost equal contribution of ‘recent’ (<12 years) and ‘old’ (>12 years) C. Thus, the decomposition of old recalcitrant SOM was induced only by an amount of primer exceeding microbial C. We conclude that combining 14C labeling with 13C natural abundance helped disentangle three C sources in CO2, microbial biomass and DOC and evaluate mechanisms and sources of PE. 相似文献
5.
In view of the significance of agricultural soils in affecting global C balance, the impact of manipulation of the quality of exogenous inputs on soil CO2–C flux was studied in rice–barley annual rotation tropical dryland agroecosystem. Chemical fertilizer, Sesbania shoot (high quality resources), wheat straw (low quality resource) and Sesbania + wheat straw (high + low quality), all carrying equivalent recommended dose of N, were added to soil. A distinct seasonal variation in CO2–C flux was recorded in all treatments, flux being higher during rice period, and much reduced during barley and summer fallow periods. During rice period the mean CO2–C flux was greater in wheat straw (161% increase over control) and Sesbania + wheat straw (+129%) treatments; however, during barley and summer fallow periods differences among treatments were small. CO2–C flux was more influenced by seasonal variations in water-filled pore space compared to soil temperature. In contrast, the role of microbial biomass and live crop roots in regulating soil CO2–C flux was highly limited. Wheat straw input showed smaller microbial biomass with a tendency of rapid turnover rate resulting in highest cumulative CO2–C flux. The Sesbania input exhibited larger microbial biomass with slower turnover rate, leading to lower cumulative CO2–C flux. Addition of Sesbania to wheat straw showed higher cumulative CO2–C flux yet supported highest microbial biomass with lowest turnover rate indicating stabilization of microbial biomass. Although single application of wheat straw or Sesbania showed comparable net change in soil C (18% and 15% relative to control, respectively) and crop productivity (32% and 38%), yet they differed significantly in soil C balance (374 and −3 g C m−2 y−1 respectively), a response influenced by the recalcitrant and labile nature of the inputs. Combining the two inputs resulted in significant increment in net change in soil C (33% over control) and crop yield (49%) in addition to high C balance (152 g C m−2 y−1). It is suggested that appropriate mixing of high and low quality inputs may contribute to improved crop productivity and soil fertility in terms of soil C sequestration. 相似文献
6.
Addition of soluble organic substrates to soil has been shown to either increase or restrict the rate of microbial CO2–C evolution. This has been attributed to a priming effect resulting from accelerated or decreased turnover of the soil organic
matter including the soil microflora. We investigated microbial responses to small glucose-C additions (10–50 μg C g1 soil) in arable soils either amended or not with cellulose. An immediate CO2–C release between 0 and 69 h (equivalent to 59% of glucose-C applied) was measured. However, only half of the CO2–C respired could be attributed to the utilisation of glucose-C substrate, based on the percentage of 14C–CO2 evolved after the addition of a 14C-labelled glucose tracer. Thus, although no evidence of an immediate release of ‘extra’ C above the rate applied as glucose-C
was observed, the pattern of decomposition for 14C-glucose suggested utilisation of an alternate C source. Based on this, a positive priming effect (1.5 to 4.3 times the amount
CO2–C evolved that was attributed to glucose-C decomposition) was observed for at least 170 h in non-cellulose-amended soil and
612 h in cellulose-amended soil. Two further phases of microbial activity in cellulose-amended soils were attributed to either
activation of different microbial populations or end-product inhibition of cellulase activity after glucose addition. During
these subsequent phases, a negative priming effect of between 0.1 and 1.5 times was observed. Findings indicate that the response
of the microbial community to small additions of soluble organic C substrate is not consistent and support the premise that
microbial response varies in a yet to be predicted manner between soil type and ecosystems. We hypothesise that this is due
to differences in the microbial community structure activated by the addition of organic C and the timing of soluble organic
substrate addition with respect to the current dissolved organic C status of the soil. 相似文献
7.
Tillage practices and straw management can affect soil microbial activities with consequences for soil organic carbon (C) dynamics. Microorganisms metabolize soil organic C and in doing so gain energy and building blocks for biosynthesis, and release CO2 to the atmosphere. Insight into the response of microbial metabolic processes and C use efficiency (CUE; microbial C produced per substrate C utilized) to management practices may therefore help to predict long term changes in soil C stocks. In this study, we assessed the effects of reduced (RT) and conventional tillage (CT) on the microbial central C metabolic network, using soil samples from a 12-year-old field experiment in an Irish winter wheat cropping system. Straw was removed from half of the RT and CT plots after harvest or incorporated into the soil in the other half, resulting in four treatment combinations. We added 1-13C and 2,3-13C pyruvate and 1-13C and U-13C glucose as metabolic tracer isotopomers to composite soil samples taken at two depths (0–15 cm and 15–30 cm) from each of the treatments and used the rate of position-specific respired 13CO2 to parameterize a metabolic model. Model outcomes were then used to calculate CUE of the microbial community. Whereas the composite samples differed in CUE, the changes were small, with values ranging between 0.757 and 0.783 across treatments and soil depth. Increases in CUE were associated with a reduced tricarboxylic acid cycle and reductive pentose phosphate pathway activity and increased consumption of metabolic intermediates for biosynthesis. Our results suggest that RT and straw incorporation do not substantially affect CUE. 相似文献
8.
Influence of soil phosphorus status and nitrogen addition on carbon mineralization from 14C-labelled glucose in pasture soils 总被引:2,自引:0,他引:2
This study examines the effect of soil P status and N addition on the decomposition of 14C-labelled glucose to assess the consequences of reduced fertilizer inputs on the functioning of pastoral systems. A contrast
in soil P fertility was obtained by selecting two hill pasture soils with different fertilizer history. At the two selected
sites, representing low (LF) and high (HF) fertility status, total P concentrations were 640 and 820 mg kg–1 and annual pasture production was 4,868 and 14,120 kg DM ha–1 respectively. Soils were amended with 14C-labelled glucose (2,076 mg C kg–1 soil), with and without the addition of N (207 mg kg–1 soil), and incubated for 168 days. During incubation, the amounts of 14CO2 respired, microbial biomass C and 14C, microbial biomass P, extractable inorganic P (Pi) and net N mineralization were determined periodically. Carbon turnover was greatly influenced by nutrient P availability.
The amount of glucose-derived 14CO2 production was high (72%) in the HF and low (67%) in the LF soil, as were microbial biomass C and P concentrations. The 14C that remained in the microbial biomass at the end of the 6-month incubation was higher in the LF soil (15%) than in the
HF soil (11%). Fluctuations in Pi in the LF soil during incubation were small compared with those in HF soil, suggesting that P was cycling through microbial
biomass. The concentrations of Pi were significantly greater in the HF samples throughout the incubation than in the LF samples. Net N mineralization and nitrification
rates were also low in the LF soils, indicating a slow turnover of microorganisms under limited nutrient supply. Addition
of N had little effect on biomass 14C and glucose utilization. This suggests that, at limiting P fertility, C turnover is retarded because microbial biomass becomes
less efficient in the utilization of substrates.
Received: 18 October 1999 相似文献
9.
Kees-Jan van Groenigen Antonie Gorissen Dave Harris Jan Willem van Groenigen 《Soil biology & biochemistry》2005,37(3):497-506
The net flux of soil C is determined by the balance between soil C input and microbial decomposition, both of which might be altered under prolonged elevated atmospheric CO2. In this study, we determined the effect of elevated CO2 on decomposition of grass root material (Lolium perenne L.). 14C-labeled root material, produced under ambient (35 Pa pCO2) or elevated CO2 (70 Pa pCO2) was incubated in soil for 64 days. The soils were taken from a pasture ecosystem which had been exposed to ambient (35 Pa pCO2) or elevated CO2 (60 Pa pCO2) under FACE-conditions for 10 years and two fertilizer N rates: 140 and 560 kg N ha−1 year−1. In soil exposed to elevated CO2, decomposition rates of root material grown at either ambient or elevated CO2 were always lower than in the control soil exposed to ambient CO2, demonstrating a change in microbial activity. In the soil that received the high rate of N fertilizer, decomposition of root material grown at elevated CO2 decreased by approximately 17% after incubation for 64 days compared to root material grown at ambient CO2. The amount of 14CO2 respired per amount of 14C incorporated in the microbial biomass (q14CO2) was significantly lower when roots were grown under high CO2 compared to roots grown under low CO2. We hypothesize that this decrease is the result of a shift in the microbial community, causing an increase in metabolic efficiency. Soils exposed to elevated CO2 tended to respire more native SOC, both with and without the addition of the root material, probably resulting from a higher C supply to the soil during the 10 years of treatment with elevated CO2. The results show the importance of using soils adapted to elevated CO2 in studies of decomposition of roots grown under elevated CO2. Our results further suggest that negative priming effects may obscure CO2 data in incubation experiments with unlabeled substrates. From the results obtained, we conclude that a slower turnover of root material grown in an ‘elevated-CO2 world’ may result in a limited net increase in C storage in ryegrass swards. 相似文献
10.
Understanding soil organic matter (SOM) decomposition and its interaction with rhizosphere processes is a crucial topic in soil biology and ecology. Using a natural 13C tracer method to separately measure SOM-derived CO2 from root-derived CO2, this study aims to connect the level of rhizosphere-dependent SOM decomposition with the C and N balance of the whole plant–soil system, and to mechanistically link the rhizosphere priming effect to soil microbial turnover and evapotranspiration. Results indicated that the magnitude of the rhizosphere priming effect on SOM decomposition varied widely, from zero to more than 380% of the unplanted control, and was largely influenced by plant species and phenology. Balancing the extra soil C loss from the strong rhizosphere priming effect in the planted treatments with C inputs from rhizodeposits and root biomass, the whole plant–soil system remained with a net carbon gain at the end of the experiment. The increased soil microbial biomass turnover rate and the enhanced evapotranspiration rate in the planted treatments had clear positive relationships with the level of the rhizosphere priming effect. The rhizosphere enhancement of soil carbon mineralization in the planted treatments did not result in a proportional increase in net N mineralization, suggesting a possible de-coupling of C cycling with N cycling in the rhizosphere. 相似文献
11.
Susan E. Crow Elizabeth W. Sulzman Richard D. Bowden 《Soil biology & biochemistry》2006,38(11):3279-3291
A detailed understanding of the processes that contribute to the δ13C value of respired CO2 is necessary to make links between the isotopic signature of CO2 efflux from the soil surface and various sources within the soil profile. We used density fractionation to divide soils from two forested sites that are a part of an ongoing detrital manipulation experiment (the Detrital Input and Removal Treatments, or DIRT project) into two soil organic matter pools, each of which contributes differently to total soil CO2 efflux. In both sites, distinct biological pools resulted from density fractionation; however, our results do not always support the concept that the light fraction is readily decomposable whereas the heavy fraction is recalcitrant. In a laboratory incubation following density fractionation we found that cumulative respiration over the course of the incubation period was greater from the light fraction than from the heavy fraction for the deciduous site, while the opposite was true for the coniferous site.Use of stable isotopes yielded insight as to the nature of the density fractions, with the heavy fraction solids from both forests isotopically enriched relative to those of the light fraction. The isotopic signature of respired CO2, however, was more complicated. During incubation of the fractions there was an initial isotopic depletion of the respired CO2 compared to the substrate for both soil fractions from both forests. Over time for both fractions of both soils the respired δ13C reflected more closely the initial substrate value; however, the transition from depleted to enriched respiration relative to substrate occurs at a different stage of decomposition depending on site and substrate recalcitrance. We found a relationship between cumulative respiration during the incubation period and the duration of the transition from isotopically depleted to enriched respiration in the coniferous site but not the deciduous site. Our results suggest that a shift in microbial community or to dead microbial biomass as a substrate could be responsible for the transition in the isotopic signature of respired CO2 during decomposition. It is likely that a combination of organic matter quality and isotopic discrimination by microbes, in addition to differences in microbial community composition, contribute to the isotopic signature of different organic matter fractions. It is apparent that respired δ13CO2 cannot be assumed to be a direct representation of the substrate δ13C. Detailed knowledge of the soil characteristics at a particular site is necessary to interpret relationships between the isotopic values of a substrate and respired CO2. 相似文献
12.
Natural variations of the 13C/12C ratio have been frequently used over the last three decades to trace C sources and fluxes between plants, microorganisms, and soil. Many of these studies have used the natural-13C-labelling approach, i.e. natural δ13C variation after C3-C4 vegetation changes. In this review, we focus on 13C fractionation in main processes at the interface between roots, microorganisms, and soil: root respiration, microbial respiration, formation of dissolved organic carbon, as well as microbial uptake and utilization of soil organic matter (SOM). Based on literature data and our own studies, we estimated that, on average, the roots of C3 and C4 plants are 13C enriched compared to shoots by +1.2 ± 0.6‰ and +0.3 ± 0.4‰, respectively. The CO2 released by root respiration was 13C depleted by about −2.1 ± 2.2‰ for C3 plants and −1.3 ± 2.4‰ for C4 plants compared to root tissue. However, only a very few studies investigated 13C fractionation by root respiration. This urgently calls for further research. In soils developed under C3 vegetation, the microbial biomass was 13C enriched by +1.2 ± 2.6‰ and microbial CO2 was also 13C enriched by +0.7 ± 2.8‰ compared to SOM. This discrimination pattern suggests preferential utilization of 13C-enriched substances by microorganisms, but a respiration of lighter compounds from this fraction. The δ13C signature of the microbial pool is composed of metabolically active and dormant microorganisms; the respired CO2, however, derives mainly from active organisms. This discrepancy and the preferential substrate utilization explain the δ13C differences between microorganisms and CO2 by an ‘apparent’ 13C discrimination. Preferential consumption of easily decomposable substrates and less negative δ13C values were common for substances with low C/N ratios. Preferential substrate utilization was more important for C3 soils because, in C4 soils, microbial respiration strictly followed kinetics, i.e. microorganisms incorporated heavier C (? = +1.1‰) and respired lighter C (? = −1.1‰) than SOM. Temperature and precipitation had no significant effect on the 13C fractionation in these processes in C3 soils. Increasing temperature and decreasing precipitation led, however, to increasing δ13C of soil C pools.Based on these 13C fractionations we developed a number of consequences for C partitioning studies using 13C natural abundance. In the framework of standard isotope mixing models, we calculated CO2 partitioning using the natural-13C-labelling approach at a vegetation change from C3 to C4 plants assuming a root-derived fraction between 0% and 100% to total soil CO2. Disregarding any 13C fractionation processes, the calculated results deviated by up to 10% from the assumed fractions. Accounting for 13C fractionation in the standard deviations of the C4 source and the mixing pool did not improve the exactness of the partitioning results; rather, it doubled the standard errors of the CO2 pools. Including 13C fractionations directly into the mass balance equations reproduced the assumed CO2 partitioning exactly. At the end, we therefore give recommendations on how to consider 13C fractionations in research on carbon flows between plants, microorganisms, and soil. 相似文献
13.
The initial reaction of microbial transformation and turnover of soil carbon inputs may influence the magnitude of longer-term
net soil C storage. The objective of this study was to test the merit of the hypothesis that the more rapid substrates are
initially utilized, the longer the residual products remain in the soil. We used simple model C compounds to determine their
decomposition rates and persistence over time. Pure 14C compounds of glucose, acetate, arginine, oxalate, phenylalanine, and urea were incubated in soil for 125 days at 24°C. Total
respired CO2 and 14CO2 was quantitatively measured every day for 15 days and residual soil 14C after 125 days. The percent 14C remaining in the soil after 125 days of incubation was positively and significantly correlated with the percent substrate
utilized in the first day of incubation. The 14C in the microbial biomass ranged from 4–15% after 15 days and declined through day 125, contributing significantly to the
14C that evolved over the longer time period. Priming of 12C soil organic matter (SOM) was negative at day 3 but became positive, reaching a maximum on day 12; the total increase in
soil C from added substrates was greater than the primed C. The primed C came from 12C SOM rather than the microbial biomass. This data supports the concept that the more rapidly a substrate is initially mineralized,
the more persistent it will be in the soil over time. 相似文献
14.
The chemical composition and quantity of plant inputs to soil are primary factors controlling the size and structure of the soil microbial community. Little is known about how changes in the composition of the soil microbial community affect decomposition rates and other ecosystem functions. This study examined the degradation of universally 13C-labeled glucose, glutamate, oxalate, and phenol in soil from an old-growth Douglas-fir (Pseudotsuga menziesii)—western hemlock (Tsuga heterophylla) forest in the Oregon Cascades that has experienced 7 y of chronic C input manipulation. The soils used in this experiment were part of a larger Detritus Input and Removal Treatment experiment and have received normal C inputs (control), doubled wood inputs, or root and litter input exclusion (no inputs). Soil from the doubled wood treatment had a higher fungal:bacterial ratio, and soil from the no inputs treatment had a lower fungal:bacterial ratio, than the control soil. Differences in the utilization of the compounds added to the field-manipulated soils were assessed by following the 13C tracer into microbial biomass and respiration. In addition, 13C-phospholipid fatty acids (PLFA) analysis was used to examine differential microbial utilization of the added substrates. Glucose and glutamate were metabolized similarly in soils of all three litter treatments. In contrast, the microbial community in the double wood soil respired more added phenol and oxalate, whereas microbes in the no inputs soil respired less added phenol and oxalate, than the control soil. Phenol was incorporated primarily into fungal PLFA, especially in soil of the double wood treatment. The addition of all four substrates led to enhanced degradation of soil organic matter (priming) in soils of all three litter treatments, and was greater following the addition of phenol and oxalate as compared to glucose and glutamate. Priming was greater in the no inputs soil as compared to the control or doubled wood soils. These results demonstrate that altering plant inputs to soil can lead to changes in microbial utilization of C compounds. It appears that many of these changes are the result of alteration in the size and composition of the microbial community. 相似文献
15.
Oliver Dilly Seth Nii-Annang Thomas Fischer Anatoly Zyakun 《Soil biology & biochemistry》2011,43(9):1808-1811
On the basis of CO2 evolution rate, O2 uptake rate, and 13C isotopic signature of respired CO2, the metabolic response to the addition of 13C labelled n-hexadecane and palmitic acid each with supplementary nitrogen was studied for two topsoils, one under continuous agricultural management and the other under beech forest. The CO2 evolution rate was immediately stimulated in the agricultural soil and the respiratory quotient (RQ) decreased from 0.8 to 0.4 mol CO2 evolution rate per mol O2 uptake rate, which was below the theoretically expected value of 0.65 and 0.70 for the degradation of n-hexadecane and palmitic acid, respectively. The microbial response was delayed in the forest soil, but developed better than in the agricultural soil throughout the subsequent 2-4 weeks. Consequently, the respiration rate returned earlier to the initial level for the beech forest soil and the δ13C of respired CO2 and RQ approached values before hydrocarbon addition. Based on the link among respiration rates, RQ and 13C-CO2 value, the added oil-analogue compounds induced a more rapid response in the agricultural soil and were degraded more completely in the forest soil. We concluded that the resilience, which we defined here as the capacity of the soil microbiota to buffer perturbance and to reorganise in response to change resulting in a more desirable system, was higher in our forest soil than for the agricultural soil. 相似文献
16.
Joshua P. Schimel J.Å. Martin Wetterstedt Susan E. Trumbore 《Soil biology & biochemistry》2011,43(5):1101-1103
We measured the 14C and 13C signatures of CO2 respired from surface and deep soils released through multiple dry/rewetting cycles in laboratory incubations. The C respired from surface soils included components fixed before and after the 1960s. However, that respired from deep soils was derived from organic matter with a mean turnover time estimated in the range of 650-850 years. This reinforces previous research suggesting that a substantial amount of deep soil C is chemically labile but physically inaccessible to microorganisms, but also suggests that substantial amounts of that C may not be so strongly bound to minerals as to be effectively inert, raising the question of why it hasn’t already been metabolized. It also demonstrates the contribution of C fixed before the 1960s to CO2 metabolized in the surface soils at this site. 相似文献
17.
《Applied soil ecology》2011,47(3):436-442
Inputs of fresh organic matter (FOM) are known to affect the rate of soil organic matter (SOM) mineralization. SOM mineralization can be accelerated or decelerated by FOM inputs. This phenomenon, known as the Priming effect (PE), may largely influence the carbon (C) storage capacity of soils. However, the link between PE intensity and FOM inputs is not clearly understood. Indeed, almost all the studies about PE used only one FOM amount which is generally largely below the amount of FOM observed in field conditions. In our study, we incubated soil amended with three levels of 13C-labeled straw as FOM and a control without FOM amendment for 80 days. The three levels used were in the same range as the natural FOM inputs observed on our sampling site. Various levels of mineral nitrogen were added within each level of straw supply so that the final input C:N ratios ranged among 44, 30 and 20. CO2 and δ13C-CO2 were measured during the experiment allowing us to distinguish the FOM respired CO2 from the SOM respired CO2. We observed that PE intensity did not increase linearly with increasing FOM additions. Moreover, decreasing the input C:N ratios did not systematically affect PE intensity probably because of shifts in the microbial characteristics such as their C:N ratio or their assimilation yields. These results suggest that PE is a saturating function of FOM inputs that is only weakly influenced by initial N availability. Our results may be explained (i) by the existence of a limited SOM pool subject to PE (ii) or by the occurrence of two simultaneous and antagonistic mechanisms: an increase of the total active microbial biomass accelerating SOM mineralization (i.e. a positive PE) and a preferential substrate utilization of FOM over SOM decreasing SOM mineralization (i.e. a negative PE). Finally, irrespective of the mechanisms implied, our results suggest that the importance of positive PE relatively to the amount of FOM may decrease when FOM inputs increase, which is favorable to carbon sequestration in soils. Indeed, in the case of the lower amount of FOM, the PE corresponded to 6.25% of the total amount of CO2 mineralized at the end of the experiment while, for the higher amount of FOM, the PE corresponded to 5% of the total amount of CO2 mineralized at the end of the experiment. 相似文献
18.
《Soil biology & biochemistry》1986,18(4):445-449
The growth of wheat plants and the distribution of labelled photosynthate from pulse-labelling with 14CO2 were measured periodically during the growing season in the field. During early growth there was approximately the same proportion of photosynthate translocated below ground and retained in the shoots. Of the 14C below ground about a half was respired and a quarter each was in the soil and roots. This distribution changed exponentially during growth with an increasing proportion of 14C remaining in the shoots and a corresponding decreasing proportion being translated below ground, which was only a few percent by flowering. From this information the total input of carbon to the soil from the crop was calculated to be 1305 kg Cha−1. Comparison of these estimates with those from previous experiments suggest that differences do occur due to the stage of growth of the plant, the environmental conditions, soil type and microbial activity. 相似文献
19.
Radiocarbon analysis of soil CO2 can provide information on the age, source and turnover rate of soil organic C. We developed a new method for passively trapping respired CO2 on molecular sieve, allowing it to be returned to the laboratory and recovered for C isotope analysis. We tested the method on a soil at a grassland site, and using a synthetic soil created to provide a contrasting isotopic signature. As with other passive sampling techniques, a small amount of fractionation of the 13C isotope occurs during sampling, which we have quantified, otherwise the results show that the molecular sieve traps a sufficiently large and representative sample of CO2 for C isotope analysis. Since 14C results are routinely corrected for mass-dependent fractionation, our results show that passive sampling of soil respiration using molecular sieve offers a reliable method to collect soil-respired CO2 for 14C analysis. 相似文献
20.
Amy M. Treonis Nick J. Ostle Ruth Primrose Philip Ineson 《Soil biology & biochemistry》2004,36(3):533-537
We combined microbial community phospholipid fatty acid (PLFA) analyses with an in situ stable isotope 13CO2 labelling approach to identify microbial groups actively involved in assimilation of root-derived C in limed grassland soils. We hypothesized that the application of lime would stimulate more rapid 13C assimilation and turnover in microbial PLFAs. Four and 8 d after label application, 18:1ω9, 18:2ω6,9 (fungal biomarkers) and 16:1ω7, 18:1ω7, 19:0cy (Gram-negative bacterial biomarkers) showed the most 13C enrichment and rapid turnover rates. This suggests that these microorganisms were assimilating recently-photosynthesized root C inputs to soils. Contrary to our hypothesis, liming did not affect assimilation or turnover rates of 13C-labelled C. 13C stable isotope pulse-labelling technique paired with analyses of PLFA microbial biomarkers shows promise for in situ investigations of microbial function in soils. 相似文献