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1.
Soil heterotrophic respiration and its temperature sensitivity are affected by various climatic and environmental factors.However,little is known about the combined effects of concurrent climatic and environmental changes,such as climatic warming,changing precipitation regimes,and increasing nitrogen(N)deposition.Therefore,in this study,we investigated the individual and combined effects of warming,wetting,and N addition on soil heterotrophic respiration and temperature sensitivity.We incubated soils collected from a temperate forest in South Korea for 60 d at two temperature levels(15 and 20℃,representing the annual mean temperature of the study site and 5℃warming,respectively),three moisture levels(10%,28%,and 50%water-filled pore space(WFPS),representing dry,moist,and wet conditions,respectively),and two N levels(without N and with N addition equivalent to 50 kg N ha-1year-1).On day 30,soils were distributed across five different temperatures(10,15,20,25,and 30℃)for 24 h to determine short-term changes in temperature sensitivity(Q10,change in respiration with 10℃increase in temperature)of soil heterotrophic respiration.After completing the incubation on day 60,we measured substrate-induced respiration(SIR)by adding six labile substrates to the three types of treatments.Wetting treatment(increase from 28%to 50%WFPS)reduced SIR by 40.8%(3.77 to 2.23μg CO2-C g-1h-1),but warming(increase from 15 to 20℃)and N addition increased SIR by 47.7%(3.77 to 5.57μg CO2-C g-1h-1)and 42.0%(3.77 to 5.35μg CO2-C g-1h-1),respectively.A combination of any two treatments did not affect SIR,but the combination of three treatments reduced SIR by 42.4%(3.70 to 2.20μg CO2-C g-1h-1).Wetting treatment increased Q10by 25.0%(2.4 to 3.0).However,warming and N addition reduced Q10by 37.5%(2.4 to 1.5)and 16.7%(2.4 to 2.0),respectively.Warming coupled with wetting did not significantly change Q10,while warming coupled with N addition reduced Q10by 33.3%(2.4 to 1.6).The combination of three treatments increased Q10by 12.5%(2.4 to 2.7).Our results demonstrated that among the three factors,soil moisture is the most important one controlling SIR and Q10.The results suggest that the effect of warming on SIR and Q10can be modified significantly by rainfall variability and elevated N availability.Therefore,this study emphasizes that concurrent climatic and environmental changes,such as increasing rainfall variability and N deposition,should be considered when predicting changes induced by warming in soil respiration and its temperature sensitivity.  相似文献   

2.
The increase in microbial C content, cumulative respiration and changes in ”︁available” C were determined after adding glucose (2 mg glucose-C (g soil)—1, ”︁C”), glucose + nitrogen (”︁C+N”) or glucose + nitrogen + phosphorus (”︁C+N+P”) to four soils. In two sandy soils, one agricultural and the other from a beech forest in Germany, available C was still present approximately 7 days after C addition. The supplement N and N+P decreased the content of available C and stimulated respiration rate and microbial growth. In two loamy forest soils from Italy, which had a high native content of microbial C, available C was present in the beech soil but not in a silver fir soil treated with C+N. In the Italian beech and fir soil, microbial growth was highest with C+N+P and C+N addition respectively. Available C remaining in the soil was related to some extent to the native microbial C content. However, microbial growth and respiration response varied between soil and treatment. The respiratory coefficient, that is the ratio of assimilated to respired C, varied between 0.0 and 1.45 μg Cmic (μg CO2-C)—1 and was generally higher when a large amount of native biomass was present. The eco-physiological strategy of the soil microbiota in using C seemed to shift according to the biomass content, the added concentration and composition of available substrates, and emergent system properties.  相似文献   

3.
The Antarctic dry valleys are characterized by extremely low temperatures, dry conditions and lack of conspicuous terrestrial autotrophs, but the soils contain organic C, emit CO2 and support communities of heterotrophic soil organisms. We have examined the role of modern lacustrine detritus as a driver of soil respiration in the Garwood Valley, Antarctica, by characterizing the composition and mineralization of both lacustrine detritus and soil organic matter, and relating these properties to soil respiration and the abiotic controls on soil respiration. Laboratory mineralization of organic C in soils from different, geomorphically defined, landscape elements at 10 °C was comparable with decomposition of lacustrine detritus (mean residence times between 115 and 345 d for the detritus and 410 and 1670 d for soil organic matter). The chemical composition of the detritus (C-to-N ratio=9:1-12:1 and low alkyl-C-to-O-alkyl-C ratio in solid-state 13C nuclear magnetic resonance spectroscopy) indicated that it was a labile, high quality resource for micro-organisms. Initial (0-6 d at 10 °C) respiratory responses to glucose, glycine and NH4Cl addition were positive in all the soils tested, indicating both C and N limitations on soil respiration. However, over the longer term (up to 48 d at 10 °C) differential responses occurred. Glucose addition led to net C mineralization in most of the soils. In the lake shore soils, which contained accumulated lacustrine organic matter, glucose led to substantial priming of the decomposition of the indigenous organic matter, indicating a C or energetic limitation to mineralization in that soil. By contrast, over 48 d, glycine addition led to no net C mineralization in all soils except stream edge and lake shore soils, indicating either substantial assimilation of the added C (and N), or no detectable utilization of the glycine. The Q10 values for basal respiration over the −0.5-20 °C temperature range were between 1.4 and 3.3 for the different soils, increasing to between 3.4 and 6.9 for glucose-induced respiration, and showed a temperature dependence with Q10 increasing with declining temperature. Taken together, our results strongly support contemporaneous lacustrine detritus, blown from the lake shore, as an important driver of soil respiration in the Antarctic dry valley soils.  相似文献   

4.
Respiration rate of soils manured by seabirds and seals on sub-Antarctic Marion Island (47°S, 38°′E) is considerably higher than that of unmanured soils, and the main objective of this study was to determine whether this is caused by an enhanced supply of inorganic nutrients (N and P) or organic C substrates, or both. The effect of soil moisture content was also investigated. Soils from five habitats were studied: Mesic fellfield, Dry mire, Closed fernbrake, Coastal herbfield and Cotula herbfield. The latter two are strongly influenced by manuring. Respiration rate increased with soil moisture content up to full water holding capacity, and the response of respiration to moisture increased strongly with temperature (especially above 10 °C). Respiration Q10 increased with soil moisture content. Glucose addition markedly stimulated soil respiration rate in all the soils, despite the fact that they all possessed substantial concentrations of organic C, a wide range of N and P concentrations and a 2-fold variation in C:N ratio. This suggests that the primary factor limiting soil respiration on the island is the supply of labile carbon substrate. Soil N and P status is also important, since adding glucose with N and/or P to soils with low N and P concentrations resulted in a significantly greater stimulation of respiration rate than adding glucose alone. In fact, for the Mesic fellfield and Dry mire soils (especially poor in N and P) adding N and P stimulated respiration rate even without added glucose. For soils with adequate endogenous concentrations of N and P (the Coastal herbfield and Cotula herbfield soils), adding further N and P did not stimulate respiration, and adding N and P with glucose did not enhance respiration more than adding glucose alone. It is proposed that manuring results in a whole syndrome of consequences for soil respiration rate, including increased litter input and root exudation due to higher primary production, higher quality of litter and soil organic matter, larger, more active and more diverse soil microbial populations and larger numbers of microbivores that stimulate microbial activity and turnover.  相似文献   

5.
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   

6.
Biogeochemical mechanisms at microscale regions within soil macroaggregates strengthen aggregates during repeated DW cycles. Knowledge of additional biogeochemical processes that promote the movement of dissolved organic carbon (DOC) into and throughout soil aggregates and soil aggregate stabilization are essential before we can more accurately predict maximum carbon (C) sequestration by soils subjected to best management practices. We investigated the spatial distribution of 13C-glucose supplied to individual soil macroaggregate surfaces and subjected to multiple drying and wetting (DW) cycles. Subsequent distribution of added glucose-C, CO2 respiration, increased microbial community activity and concomitant changes in soil aggregate stabilization were monitored. Moist macroaggregates were treated with no DW cycles and zero glucose C (Control), 5 DW cycles and zero glucose (DW0G), and 5 DW cycles with additions of 250 μg glucose-13C/g soil during each cycle (DW+G). Repeated additions of glucose-C to aggregate surfaces reduced the mineralization of pre-existing soil C by an average of 45% and established concentric gradients of glucose-derived C. It is concluded these increasing gradients promoted the diffusion of soluble C into interior regions and became less available to microbial respiration. Spatial gradients of glucose-derived C within aggregates influenced a shift in the abundance of unique ribotypes spatially distributed within aggregates. Rapid decreases in the mineralization rates of glucose-C during repeated DW cycles suggested greater C sequestration by either physical restriction of microbes or chemical sorption of new C that diffused into aggregates. Aggregate stability decreased significantly following 2-3 DW cycles, when glucose-C was not added. Additions of glucose-C with each DW cycle maintained soil aggregate stability equal to the moist but not cycled control throughout the 5 DW cycles of this study. These data simulate the strengthening of soil aggregates in no tillage agroecosystems which provides continuous additions of DOC compounds generated by decomposing plant residues on the soil surface, and root exudates and decomposition, as well as the mineralization of POM materials within nondisturbed soil profiles.  相似文献   

7.
Tea (Camellia sinensis) is a globally important crop and is unusual because it both requires an acid soil and acidifies soil. Tea stands tend to be extremely heavily fertilized in order to improve yield and quality, resulting in a great potential for diffuse pollution. The microbial ecology of tea soils remains poorly understood; an improved understanding is necessary as processes affecting nutrient availability and loss pathways are microbially mediated. We therefore examined the relationships between soil characteristics (pH, organic C, total N, total P, available P, exchangeable Al), the soil microbial biomass (biomass C, biomass ninhydrin-N, ATP, phospholipid fatty acids—PLFAs) and its activities (respiration, net mineralization and nitrification). At the Tea Research Institute, Hangzhou (TRI), we compared fields of different productivity levels (low, medium and high) and at Hongjiashan village (HJS) we compared fields of different stand age (9, 50 and 90 years). At both sites tea soils were compared with adjacent forest soils. At both sites, soil pH was highest in the forest soil and decreased with increasing productivity and age of the tea stand. Soil microbial biomass C and biomass ninhydrin-N were significantly affected by tea production. At TRI, microbial biomass C declined in the order forest>low>high>middle production and at HJS in the order stand age 50>age 9>forest>age 90. Soil pH had a strong influence on the microbial biomass, demonstrated by positive linear correlations with: microbial biomass C, microbial biomass ninhydrin-N, the microbial biomass C:organic C ratio, the microbial biomass ninhydrin-N:total N ratio, the respiration rate and specific respiration rate. Above pH(KCl) 3.5 there was net N mineralization and nitrification, and below this threshold some samples showed net immobilization of N. A principal component (PC) analysis of PLFA data showed a consistent shift in the community composition with productivity level and stand age. The ratio of fungal:bacterial PLFA biomarkers was negatively and linearly correlated with specific respiration in the soils from HJS (r2=0.93, p=0.03). Our results demonstrate that tea cultivation intensity and duration have a strong impact on the microbial community structure, biomass and its functioning, likely through soil acidification and fertilizer addition.  相似文献   

8.
A method for determining microbially available N and P in an organic soil   总被引：3，自引：0，他引：3  
Summary A bioassay of microbially available soil N and P is described. It is based on the addition of glucose together with N or P to soil, followed by monitoring of the respiration rate. The addition of glucose + N resulted in an immediate increase in the soil respiration rate followed by a short period of exponential increase, reflecting the growth of microorganisms on the added substrate. The exponential phase levelled off, when lack of P prevented further growth of the soil microorganisms. The soil respiration rate then remained constant for several hours before decreasing, when glucose became limiting. The addition of glucose + P resulted in a lower plateau of the soil respiration rate, indicating that microbial growth was more limited by N than P in this forest soil (0.28 and 0.79 mg CO2 g-1 organic matter h-1, respectively). Additions of the limiting nutrient resulted in a proportional increase in the constant level of the soil respiration rate. This was used to calculated the increase in the soil respiration rate per mg N (0.71 mg CO2 h-1) or mg P (4.6 mg CO2 h-1) added to this particular soil. Microbially available N was then calculated in two ways from the regression equation (0.15 or 0.40 mg g-1 organic matter) and P (0.13 or 0.17 mg g-1 organic matter). A comparison with 2 M KCl extraction showed that in nutrient-poor forest soils the microbially available N was 6.3 or 18.5 times higher than the KCl extractable N.  相似文献   

9.
In the long term, all CO2 produced in the soil must be emitted by the surface and soil CO2 efflux (FCO2) must correspond to soil respiration (Rsoil). In the short term, however, the efflux can deviate from the instantaneous soil respiration, if the amount of CO2 stored in the soil pore-space (SCO2) is changing. We measured FCO2 continuously for one year using an automated chamber system. Simultaneously, vertical soil profiles of CO2 concentration, moisture, and temperature were measured in order to assess the changes in the amount of CO2 stored in the soil. Rsoil was calculated as the sum of the rate of change of the CO2 storage over time and FCO2. The experiment was split into a warm and a cold season. The dependency of soil respiration and soil efflux on soil temperature and on soil moisture was analyzed separately. Only the moisture-driven model of the warm season was significantly different for FCO2 and Rsoil. At our site, a moisture-driven soil-respiration model derived from CO2 efflux data would underestimate the importance of soil moisture. This effect can be attributed to a temporary storage of CO2 in the soil pore-space after rainfalls where up to 40% of the respired CO2 were stored.  相似文献   

10.
A reliable determination of the response of soil organic carbon decomposition to temperature is critical in the context of global warming. However, uncertainties remain in estimated temperature sensitivity of soil respiration, which may be partly due to different experimental conditions. To investigate the possible effects of laboratory incubation procedures on estimated Q10 value, soil samples taken from various ecosystems were incubated under changing temperature with different experimental conditions or procedures: 1) different rate of temperature change; 2) different intervals of temperature change; 3) equilibration time after temperature change; 4) the duration of chamber closure and 5) the size of incubated soil sample. The results indicated that respiration rate was affected by experimental procedures. The respiration rate of soil samples containing high concentration of organic carbon decreased quickly if the soil container sealed longer than 2 h. Estimated Q10 values across all soils ranged from 1.56 to 2.70, with respect to the effects of incubation procedures. Temperature rate change, equilibration time, the duration of chamber closure and soil sample size had no effect on estimated Q10 values of soil respiration. However, Q10 values derived from temperature changing intervals of 2 and 7 °C were significantly different, despite the fact that the exponential function fitted well for the relationship between respiration rate and temperature for both intervals. The results of these experiments suggested that incubation procedures have different effects on measured soil respiration and estimated Q10 values. For soil incubations of short-duration, the effects of incubation procedures on soil respiration and estimated Q10 values based on respiration rate should be appropriately tested with experimental setting-up, and estimating Q10 values with few temperatures should be avoided.  相似文献   

11.
Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. Responses of soil respiration to temperature fluctuations were investigated in a root-free soil of a mid-European beech-oak forest. First, in laboratory we analysed the efflux of CO2 from soil microcosms exposed to seasonal (±5 °C of the annual mean) and diurnal fluctuations (±5 °C of the seasonal levels) in a two-factorial design. Second, in field microcosms we investigated effects of smoothing diurnal temperature fluctuations in soil (simulating a possible global trend) on CO2 efflux. Third, the natural temperature regime was simulated in laboratory microcosms and their CO2 efflux was compared to the one in the field. The experiments lasted for 1 year to differentiate seasonal and annual responses.Dynamics of CO2 efflux, microbial basal respiration, biomass and qO2 varied with seasonal temperature regime. However, in the laboratory the annual cumulative CO2-C production did not differ between treatments and varied between 10.9% and 11.7% of the total microcosm C, disregarding seasonal and/or diurnal fluctuations. The similarity of cumulative C production suggests that the availability of microbially mobilisable carbon pools rather than the temperature regime limited soil respiration. Diurnal fluctuations generally did not affect CO2 efflux and microbial activity, though winter Q10 values were increased in their absence. Simulation of the natural temperature regime in the laboratory resulted in CO2 efflux similar to field microcosms. In the field, rates of CO2 efflux and microbial activity, seasonal and annual cumulative CO2-C production were significantly higher at smoothed than at natural temperature conditions (annually 13.1% and 11.0% of total C was respired, respectively). Facing global climate changes the mechanisms regulating responses of soil respiration to temperature fluctuations need further investigation.  相似文献   

12.
Soil respiration is the largest terrestrial source of CO2 to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO2 concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO2 emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO2 emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO2 effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO2-C m−2 h−1). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the Oi - and Oe horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO2 efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.  相似文献   

13.
A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO2 emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios (δ13C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in δ13C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation-extraction method (Cmic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in Cmic and substrate-induced respiration (SIR) were large. In woodland and woodland-wooded grassland Cmic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands Cmic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor Cmic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.  相似文献   

14.
Heterotrophic soil respiration (R H) and autotrophic soil respiration (R A) by a trenching method were monitored in four vegetation types in subtropical China from November 2011 to October 2012. The four vegetation types included a shrubland, a mixed-conifer, a mixed-legume, and a mixed-native species. The average R H was significantly greater in soils under the mixed-legume and the mixed-native species than in the shrubland and the mixed-conifer soils, and it affected the pattern of soil total respiration (R S) of the four soils. The change in R H was closely related to the variations of soil organic C, total N and P content, and microbial biomass C. The R A and the percentage of R S respired as R A were only significantly increased by the mixed-native species after reforestation. Probably, this depended on the highest fine root biomass of mixed-native species than the other vegetation types. Soil respiration sources were differently influenced by the reforestation due to different changes in soil chemical and biological properties and root biomass.  相似文献   

15.
Soil heterotrophic respiration during decomposition of carbon (C)-rich organic matter plays a vital role in sustaining soil fertility. However, it remains poorly understood whether dinitrogen (N2) fixation occurs in support of soil heterotrophic respiration. In this study, 15N2-tracing indicated that strong N2 fixation occurred during heterotrophic respiration of carbon-rich glucose. Soil organic 15N increased from 0.37 atom% to 2.50 atom% under aerobic conditions and to 4.23 atom% under anaerobic conditions, while the concomitant CO2 flux increased by 12.0-fold under aerobic conditions and 5.18-fold under anaerobic conditions. Soil N2 fixation was completely absent in soils replete with inorganic N, although soil N bioavailability did not alter soil respiration. High-throughput sequencing of the 16S rRNA gene further indicated that: i) under aerobic conditions, only 15.2% of soil microbiome responded positively to glucose addition, and these responses were significantly associated with soil respiration and N2 fixation and ii) under anaerobic conditions, the percentage of responses was even lower at 5.70%. Intriguingly, more than 95% of these responses were originally rare with < 0.5% relative abundance in background soils, including typical N2-fixing heterotrophs such as Azotobacter and Clostridium and well-recognized non-N2-fixing heterotrophs such as Sporosarcina, Agromyces, and Sedimentibacter. These results suggest that only a small portion of the soil microbiome could respond quickly to the amendment of readily accessible organic C in a fluvo-aquic soil and highlighted that rare phylotypes might have played more important roles than previously appreciated in catalyzing soil C and nitrogen turnovers. Our study indicates that N2 fixation could be closely associated with microbial turnover of soil organic C when available in excess.  相似文献   

16.
We studied nutrient limitation and availability for soil microbial respiration after additions of glucose (C), in combination with nitrogen (N) and phosphorus (P) in soil samples taken from parklands of Vitellaria paradoxa and Faidherbia albida. We hypothesized that in these P-fixing soils: (i) after C addition, respiration will be limited by P, but P-limitation will be lower under tree canopies; and (ii) the maximum respiration rates after adding C will be higher with than without applications of inorganic fertilizer (NPK) in the field. The study site was located in the south-Sudanese zone of Burkina Faso. Microbial respiration was measured as CO2 evolution from soil samples incubated under laboratory conditions. Two microbial growth peaks were observed after addition of C plus P to the soil samples. When P was added together with C, the initial increase in the microbial respiration rate was higher than when N and C were added, and the maximum respiration rate was also reached earlier. We conclude that P limited the initial rate of respiration. Under the tree canopy the P and N availability, was higher under both F. albida and V. paradoxa trees, than in areas beyond their canopies. NPK fertilization in the field resulted in higher soil reserves of N and P, but these nutrients had low availability in the short term. Results indicated that more P is available in forms that are immediately accessible to microorganisms under tree canopies, than outside the cover of their canopies.  相似文献   

17.
The measurement of soil carbon dioxide (CO2) respiration is a means to gauge biological soil fertility. Test methods for respiration employed in the laboratory vary somewhat, and to date the equipment and labor required have limited more widespread adoption of such methodologies. A new method to measure soil respiration was tested along with the traditional alkali trap and titration method. The new method involves the Solvita gel system, which was originally designed for CO2 respiration from compost but has been applied in this research to soils with treatments of increasing dairy manure compost. The objectives of this research are to (1) examine the relationship between the CO2 release after 1 day of incubation from soils amended with dairy manure compost that have been dried and rewetted as determined using the titration method and the Solvita gel system, and (2) compare water‐soluble organic nitrogen (N), as well as carbon (C), N, and phosphorus (P) mineralization after 28 days of incubation with 1‐day CO2 release from the titration method and Solvita gel system. One‐day CO2 from both titration and the Solvita gel system were highly correlated with cumulative 28‐day CO2 as well as the basal rate from 7–28 days of incubation. Both methods were also highly correlated with 28‐day N and P mineralization as well as the initial water‐extractable organic N and C concentration.

The data suggest that the Solvita gel system for soil CO2 analysis could be a simple and easily used method to quantify soil microbial activity and possibly provide an estimate of potential mineralizable N and P. Once standardized soil sampling and laboratory analysis protocols are established, the Solvita method could be easily adapted to commercial soil testing laboratories as an index of soil microbial activity.  相似文献   

18.
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   

19.
The aim of this study was to evaluate a set of microbial soil tests for their ability to discriminate between different agricultural practices. For this purpose three sites included in the Swedish Long-Term Soil Fertility Experiments were chosen. The fertility experiments were designed to compare different cropping systems (simulating farming with and without livestock), PK-fertiliser and N-fertiliser regimes. Six different microbial tests were used to derive nine variables describing: (1) basal microbial activity (B-res), (2) potential microbial activities (substrate induced respiration, SIR; potential NH4 + oxidation, PAO; potential denitrification activity, PDA; and alkaline phosphatase activity, Alk-P), (3) specific microbial growth rates (μ res and μ PDA) and (4) nutrient-limited respiration rates (maximal P-limited respiration, Max-P; and maximal N-limited respiration, Max-N?). Among the individual microbial variables B-res, SIR, μ res and μ PDA were the best discriminators of the two different cropping systems. All of them, except μ PDA, showed some degree of interaction between different treatments. However, the best discriminators between cropping systems were the components [principal component (PC)?1 and 2] from a PC analysis (PCA). In all three soils PC?1 discriminated well between the two cropping systems. In addition, PC?1 and PC?2 reflected the P-fertilisation rate. Max-P alone had the best potential to reflect the microbially available P in the soil and thereby indirectly the plant-available P. The μ res was also useful when assessing available P in the soil. The N-fertilisation rate seemed to be the most difficult treatment to assess with the microbial activity variables. In addition, PCA revealed a consistent functional relationship in all three soils between the potential activity variables (SIR, PAO, PDA, and Alk-P).  相似文献   

20.
Field pea (Pisum sativum L.) is widely grown in South Australia (SA), often without inoculation with commercial rhizobia. To establish if symbiotic factors are limiting the growth of field pea we examined the size, symbiotic effectiveness and diversity of populations of field pea rhizobia (Rhizobium leguminosarum bv. viciae) that have become naturalised in South Australian soils and nodulate many pea crops. Most probable number plant infection tests on 33 soils showed that R. l. bv. viciae populations ranged from undetectable (six soils) to 32×103 rhizobia g−1 of dry soil. Twenty-four of the 33 soils contained more than 100 rhizobia g−1 soil. Three of the six soils in which no R. l. bv. viciae were detected had not grown a host legume (field pea, faba bean, vetch or lentil). For soils that had grown a host legume, there was no correlation between the size of R. l. bv. viciae populations and either the time since a host legume had been grown or any measured soil factor (pH, inorganic N and organic C). In glasshouse experiments, inoculation of the field pea cultivar Parafield with the commercial Rhizobium strain SU303 resulted in a highly effective symbiosis. The SU303 treatment produced as much shoot dry weight as the mineral N treatment and more than 2.9 times the shoot dry weight of the uninoculated treatment. Twenty-two of the 33 naturalised populations of rhizobia (applied to pea plants as soil suspensions) produced prompt and abundant nodulation. These symbioses were generally effective at N2 fixation, with shoot dry weight ranging from 98% (soil 21) down to 61% (soil 30) of the SU303 treatment, the least effective population of rhizobia still producing nearly double the growth of the uninoculated treatment. Low shoot dry weights resulting from most of the remaining soil treatments were associated with delayed or erratic nodulation caused by low numbers of rhizobia. Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) fingerprinting of 70 rhizobial isolates recovered from five of the 33 soils (14 isolates from each soil) showed that naturalised populations were composed of multiple (5-9) strain types. There was little evidence of strain dominance, with a single strain type occupying more than 30% of trap host nodules in only two of the five populations. Cluster analysis of RAPD PCR banding patterns showed that strain types in naturalised populations were not closely related to the current commercial inoculant strain for field pea (SU303, ≥75% dissimilarity), six previous field pea inoculant strains (≥55% dissimilarity) or a former commercial inoculant strain for faba bean (WSM1274, ≥66% dissimilarity). Two of the most closely related strain types (≤15% dissimilarity) were found at widely separate locations in SA and may have potential as commercial inoculant strains. Given the size and diversity of the naturalised pea rhizobia populations in SA soils and their relative effectiveness, it is unlikely that inoculation with a commercial strain of rhizobia will improve N2 fixation in field pea crops, unless the number of rhizobia in the soil is very low or absent (e.g. where a legume host has not been previously grown and for three soils from western Eyre Peninsula). The general effectiveness of the pea rhizobia populations also indicates that reduced N2 fixation is unlikely to be the major cause of the declining field pea yields observed in recent times.  相似文献   

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