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1.
Drying and rewetting cycles are known to be important for the turnover of carbon (C) in soil, but less is known about the turnover of phosphorus (P) and its relation to C cycling. In this study the effects of repeated drying-rewetting (DRW) cycles on phosphorus (P) and carbon (C) pulses and microbial biomass were investigated. Soil (Chromic Luvisol) was amended with different C substrates (glucose, cellulose, starch; 2.5 g C kg−1) to manipulate the size and community composition of the microbial biomass, thereby altering P mineralisation and immobilisation and the forms and availability of P. Subsequently, soils were either subjected to three DRW cycles (1 week dry/1 week moist) or incubated at constant water content (70% water filled pore space). Rewetting dry soil always produced an immediate pulse in respiration, between 2 and 10 times the basal rates of the moist incubated controls, but respiration pulses decreased with consecutive DRW cycles. DRW increased total CO2 production in glucose and starch amended and non-amended soils, but decreased it in cellulose amended soil. Large differences between the soils persisted when respiration was expressed per unit of microbial biomass. In all soils, a large reduction in microbial biomass (C and P) occurred after the first DRW event, and microbial C and P remained lower than in the moist control. Pulses in extractable organic C (EOC) after rewetting were related to changes in microbial C only during the first DRW cycle; EOC concentrations were similar in all soils despite large differences in microbial C and respiration rates. Up to 7 mg kg−1 of resin extractable P (Presin) was released after rewetting, representing a 35-40% increase in P availability. However, the pulse in Presin had disappeared after 7 d of moist incubation. Unlike respiration and reductions in microbial P due to DRW, pulses in Presin increased during subsequent DRW cycles, indicating that the source of the P pulse was probably not the microbial biomass. Microbial community composition as indicated by fatty acid methyl ester (FAME) analysis showed that in amended soils, DRW resulted in a reduction in fungi and an increase in Gram-positive bacteria. In contrast, the microbial community in the non-amended soil was not altered by DRW. The non-selective reduction in the microbial community in the non-amended soil suggests that indigenous microbial communities may be more resilient to DRW. In conclusion, DRW cycles result in C and P pulses and alter the microbial community composition. Carbon pulses but not phosphorus pulses are related to changes in microbial biomass. The transient pulses in available P could be important for P availability in soils under Mediterranean climates.  相似文献   

2.
The effect of drying and rewetting (DRW) on C mineralization has been studied extensively but mostly in absence of freshly added residues. But in agricultural soils large amounts of residues can be present after harvest; therefore, the impact of DRW in soil after residue addition is of interest. Further, sandy soils may be ameliorated by adding clay‐rich subsoil which could change the response of microbes to DRW. The aim of this study was to investigate the effect of DRW on microbial activity and growth in soils that were modified by mixing clay subsoil into sandy top soil and wheat residues were added. We conducted an incubation experiment by mixing finely ground wheat residue (20 g kg–1) into top loamy sand soil with clay‐rich subsoil at 0, 5, 10, 20, 30, and 40% (w/w). At each clay addition rate, two moisture treatments were imposed: constantly moist control (CM) at 75% WHC or dry and rewet. Soil respiration was measured continuously, and microbial biomass C (MBC) was determined on day 5 (before drying), when the soil was dried, after 5 d dry, and 5 d after rewetting. In the constantly moist treatment, increasing addition rate of clay subsoil decreased cumulative respiration per g soil, but had no effect on cumulative respiration per g total organic C (TOC), indicating that the lower respiration with clay subsoil was due to the low TOC content of the sand‐clay mixes. Clay subsoil addition did not affect the MBC concentration per g TOC but reduced the concentration of K2SO4 extractable C per g TOC. In the DRW treatment, cumulative respiration per g TOC during the dry phase increased with increasing clay subsoil addition rate. Rewetting of dry soil caused a flush of respiration in all soils but cumulative respiration at the end of the experiment remained lower than in the constantly moist soils. Respiration rates after rewetting were higher than at the corresponding days in constantly moist soils only at clay subsoil addition rates of 20 to 40%. We conclude that in presence of residues, addition of clay subsoil to a sandy top soil improves microbial activity during the dry phase and upon rewetting but has little effect on microbial biomass.  相似文献   

3.
Drying and rewetting cycles are known to be important for the dynamics of carbon (C), phosphorus (P), and nitrogen (N) in soils. This study reports the short‐term responses of these nutrients to consecutive drying and rewetting cycles and how varying soil moisture content affects microbial biomass C and P (MBC and MBP), as well as associated carbon dioxide (CO2) and nitrous oxide (N2O) emissions. The soil was incubated for 14 d during which two successive drying–rewetting episodes were imposed on the soils. Soils subjected to drying (DRW) were rewetted on the seventh day of each drying period to return them to 60% water holding capacity, whilst continually moist samples (M), with soil maintained at 60% water holding capacity, were used as control samples. During the first seven days, the DRW samples showed significant increases in extractable ammonium, total oxidized nitrogen, and bicarbonate extractable P concentrations. Rewetting after the first drying event produced significant increases only in CO2 flux (55.4 µg C g?1 d?1). The MBC and MBP concentrations fluctuated throughout the incubation in both treatments and only the second drying–rewetting event resulted in a significantly MBC decrease (416.2 and 366.8 mg kg?1 in M and DRW soils, respectively). The two drying–rewetting events impacted the microbial biomass, but distinguishing the different impacts of microbial versus physical impacts of the perturbation is difficult. However, this study, having a combined approach (C, N, and P), indicates the importance of understanding how soils will react to changing patterns of drying–rewetting under future climate change.  相似文献   

4.
An incubation study determined the effect of one dry–rewetting (DRW) event on the turnover of carbon (C), phosphorus (P) and nitrogen (N). Thirty-two soils were collected from different climatic regions of southern Australia, varying in soil type, land use and agronomic management history. We hypothesised that respiration and nutrient pulses are related to soil physio-chemical properties. Respiration (CO2 release) was measured intensively for 90 h after rewetting. C mineralisation (C min) model fitting was used to describe the amount of mineralisable C (Co90 h) and the proportional mineralisation rate (k). Compared to constantly moist soils, 13 soils showed increases in both Co90 h and k, indicating that DRW increased the amount of mineralisable C and the rate at which C was mineralised over the 90-h period. In 17 soils, k was increased but not Co90 h, showing an increase in C mineralisation rate but no change in the amount of mineralisable C. Two soils showed a reduction in k with no change in Co90 h, possibly due to low C contents and small microbial biomass. Only one soil exhibited no change in either Co90 h or k. Multiple linear regression analysis indicated that the magnitude of the increase in mineralisable C in response to the DRW event (∆Co90 h = Co90 h DRW − Co90 h moist) was primarily explained by clay content (39%); however, inclusion of nine soil physio-chemical properties explained more of the variation in ∆Co90 h than any of the properties alone. Five of the nine physio-chemical variables present in the multiple-regression model were related to C content or composition. Pulses in available N and P were not related to ∆Co90 h.  相似文献   

5.
The effects of repeated drying-rewetting (DRW) cycles on the microbial biomass and activity in soils taken from long-term field experiment plots with different fertilization (FERT) management practice histories were studied. We investigated the hypothesis that soil response to DRW cycles differs with soil fertility gradient modified by FERT management practices. The soils were incubated for 51 days, after exposure to either nine or three DRW cycles, or remaining at constant moisture content (CMC) at field capacity. We found that both DRW and FERT significantly affected soil properties including NH4-N, NO3-N, dissolved organic C (DOC), microbial biomass C (Cmic), basal soil respiration rate (BSR), urease activity (URE) and dehydrogenase activity (DHD). Except for NH4-N and BSR, variation in the properties was largely explained by FERT, followed by DRW, and then their interaction. Irrespective of the soils' FERT treatment, repeated DRW cycles significantly raised the DOC and Cmic levels compared with CMC, and the DRW cycles also resulted in a significant decline in BSR and URE and increase in DHD, probably because the organisms were better-adapted to the drying and rewetting stresses. The variations in soil biological properties caused by DRW cycles showed a significantly negative relationship with the soil organic C content measured prior to the start of the DRW experiments, suggesting that soils with higher fertility are better able to maintain their original biological functions (i.e., have a higher functional stability) in response to DRW cycles.  相似文献   

6.
The magnitude of CO2 efflux pulses after rewetting a dry soil is highly variable and the factors regulating these pulses are poorly understood. In this field experiment, we aimed to study the C dynamics after simulated summer rainstorms in a Mediterranean open holm oak woodland (dehesa). We hypothesized that because the herbaceous cover is mostly dead during the summer in this ecosystem, the short-term CO2 efflux (SR) after rewetting could mainly be explained by different measurable soil C fractions: i) K2SO4-extracted soil C (EOC); ii) microbial biomass C (MBC); or iii) chloroform-fumigated extracted C (CFE). On both grazed and abandoned dehesa sites, we simulated three summer rain events at two-week intervals and we measured SR discontinuously in three plots under tree canopy and in another three plots in open grassland. In each plot, C fractions and water content were estimated before (2 h) and after (36 h) each irrigation event. Following rewettings, SR increased up to ten times compared with non-irrigated plots. The CFE actually increased after rewetting in the first two irrigations but not in the third event, suggesting that the capacity of the soil to release labile organic C from soil aggregates or litter was reduced after each irrigation event. Overall, the C released as CO2 in the first 24 h was related to the CFE existing before rewetting, which may help to explain the spatial variability in SR. However, the explained variability decreased after each irrigation, suggesting a change to a less labile composition of the CFE fraction as a consequence of multiple drying-rewetting cycles.  相似文献   

7.
Drying–rewetting cycles (D/W) occur frequently in topsoils and may mobilize phosphorus (P). We investigated the effect of repeated D/W on the release of dissolved inorganic (DIP) and organic P (DOP) from forest floors and A horizons. Samples were taken from 3 European beech sites and from 3 Norway spruce sites. Soils were desiccated up to pF 6 (–100 MPa) in three D/W cycles in the laboratory, while the controls were kept permanently at 50% water holding capacity. After each drying, P was extracted from the soils in water. D/W caused the release of DIP and DOP especially from O layers. There was no general difference in response to D/W between samples from beech and spruce. The net release of DIP after D/W was largest from the Oe horizons (average 50–60 mg P kg?1) for both beech and spruce forest soils. The net release of DIP from Oi layers was on average 7.8 mg P kg?1 and from spruce Oa layers 21.1 mg P kg?1. In the A horizons, net DIP release was similar in beech and spruce soils with 0.4 mg P kg?1. The release of DOP was less than the release of DIP except for the A horizons. Repeated cycles did not increase the release of DIP and DOP. The release of DIP and DOP was positively correlated with the microbial biomass in Oe and Oa layers but not in Oi layers. Our results suggest that D/W may significantly influence the short term availability of dissolved P in both beech and spruce forest soils.  相似文献   

8.
Many surface soils in Japan may experience more frequent and intense drying–rewetting (DRW) events due to future climate changes. Such DRW events negatively and positively affect microbial biomass carbon (MBC) through microbial stress and substrate supply mechanisms, respectively. To assess the MBC immediately after DRW and during the incubation with repeated DRW cycles, two laboratory experiments were conducted for a paddy soil. In the first experiment, we exposed the soil to different drying treatments and examined the MBC and hourly respiration rates immediately after the rewetting to evaluate the microbial stress. In the second experiment, we compared microbial growth rates during the incubation of the partially sterilized soil with a continuously moist condition and repeated DRW cycles to evaluate the contribution of the substrate supply from non-biomass soil organic C on MBC. First, all drying treatments caused a reduction in MBC immediately after the rewetting, and higher drying intensities induced higher reduction rates in MBC. A reduction of more than 20% in MBC induced the C-saturated conditions for surviving microbes because sufficient concentrations of labile substrate C were released from the dead MBC. Second, repeated DRW cycles caused increases in the microbial growth rates because substrate C was supplied from non-biomass organic C. In conclusion, MBC decreased immediately after DRW due to microbial stress, whereas MBC increased during repeated DRW cycles due to substrate C supplied from non-biomass organic C.  相似文献   

9.
The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K2SO4-extractable organic C and 33.3 mM KMnO4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation-extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation-incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO2 production rate, relative C mineralization rate (CO2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.  相似文献   

10.
Little is known about the effect of drying and rewetting (DRW) on phosphorus (P) pools in the detritusphere, the soil adjacent to plant residues. Two plant residues differing in their potential to release P during decomposition were used: mature barley straw, C/P 255 or young faba bean, C/P 38. Residues were placed between two PVC caps filled with soil at 50% water-holding capacity with open ends covered by fine mesh onto which the residues were placed. The open ends of the two PVC caps were pressed together with residues in between. For the unamended controls, no residues were placed between the meshes. After 2 weeks incubation, the soil was separated from the residues and then either dried and kept dry for 2 weeks followed by rapid rewetting to 50% water-holding capacity (WHC) rewetting (RW) or maintained at 50% of WHC constantly moist (CM). Bioavailable P pools (readily available P pools: CaCl2- and anion exchange-P; P bound to soil particles: citrate- and HCl-P; acid phosphomonoesterase- and microbial-P) were measured in dry soil and 1, 7, and 14 days after rewetting. Rewetting of dry soils induced a respiration flush on the first day after which respiration rates declined to those in CM. Compared to the unamended soil, the flush was about 75% higher with barley and more than twofold higher with faba bean. P pools were 3–20-fold higher with faba bean than with barley or in the control. At the end of the dry period, most P pools were higher in dry soil compared to CM. Rewetting had little effect on P pools 1, 7, and 14 days after rewetting compared to CM. To investigate if rewetting induced a short pulse of available P, a second experiment was carried out. As in the first experiment, faba bean detritusphere soil and control were generated and then dried or kept at 50% WHC for 2 weeks. Before rewetting, anion exchange membranes (AEM) were placed in the soil which were removed one, 2 or 4 days after rewetting. The P concentration on the AEM was more than threefold higher with faba bean than the control. One day after rewetting, the P concentration on the AEM with faba bean was about threefold higher in RW than in CM, but did not differ between RW and CM in the control. Four days after rewetting, nearly all P pools with faba bean were 10–30% lower in RW than in CM, except citrate-P which was about 5% higher in RW. We conclude that rewetting induces a short pulse of available P if the P pool concentration is high as in the detritusphere of faba bean. If P is removed from the soil (by binding to AEM or uptake by plants), rewetting can induce depletion of P pools compared to CM.  相似文献   

11.
Although metabolic activity of soil organisms is determined by water accessibility, little attention was given to rewetting with different water potentials. Rapid water potential increase induced a respiration pulse in organic layers in laboratory experiments and significant effects could be observed when soil below −6300 hPa was rewetted.  相似文献   

12.
Global warming in the Arctic may alter decomposition rates in Arctic soils and therefore nutrient availability. In addition, changes in the length of the growing season may increase plant productivity and the rate of labile C input below ground. We carried out an experiment in which inorganic nutrients (NH4NO3 and NaPO4) and organic substrates (glucose and glycine) were added to soils sampled from across the mountain birch forest-tundra heath ecotone in northern Sweden (organic and mineral soils from the forest, and organic soil only from the heath). Carbon dioxide production was then monitored continuously over the following 19 days. Neither inorganic N nor P additions substantially affected soil respiration rates when added separately. However, combined N and P additions stimulated microbial activity, with the response being greatest in the birch forest mineral soil (57% increase in CO2 production compared with 26% in the heath soil and 8% in the birch forest organic soil). Therefore, mineralisation rates in these soils may be stimulated if the overall nutrient availability to microbes increases in response to global change, but N deposition alone is unlikely to enhance decomposition. Adding either, or both, glucose and glycine increased microbial respiration. Isotopic separation indicated that the mineralisation of native soil organic matter (SOM) was stimulated by glucose addition in the heath soil and the forest mineral soil, but not in the forest organic soil. These positive ‘priming’ effects were lost following N addition in forest mineral soil, and following both N and P additions in the heath soil. In order to meet enhanced microbial nutrient demand, increased inputs of labile C from plants could stimulate the mineralisation of SOM, with the soil C stocks in the tundra-heath potentially most vulnerable.  相似文献   

13.
Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (Rs), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of Rs. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO2 efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO2 efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m−2 s−1 in the forest, abandoned field and olive grove, respectively. Rs was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds Rs was controlled by soil moisture. Exponential and linear models adequately described Rs responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of Rs in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO2 efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO2 efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.  相似文献   

14.
During the first few days after rewetting of an air-dried soil (AD-RW), microbial activity increases compared to that in the original moist soil, causing increased mineralisation (a flush) of soil organic carbon (C) and other nutrients. The AD-RW flush is believed to be derived from the enhanced mineralisation of both non-biomass soil organic matter (due to its physical release and enhanced availability) and microbial biomass killed during drying and rewetting. Our aim was to determine the effects of AD-RW on the mineralisation of soil organic matter and microbial biomass during and after repeated AD-RW cycles and to quantify their proportions in the CO2-C flushes that resulted. To do this, a UK grassland soil was amended with 14C-labelled glucose to label the biomass and then given five AD-RW cycles, each followed by 7 d incubation at 25 °C and 50% water holding capacity. Each AD-RW cycle increased the amount of CO2-C evolved (varying from 83 to 240 μg g−1 soil), compared to the control with, overall, less CO2-C being evolved as the number of AD-RW cycles increased. In the first cycle, the amount of biomass C decreased by 44% and microbial ATP by 70% while concentrations of extractable C nearly doubled. However, all rapidly recovered and within 1.3 d after rewetting, biomass C was 87% and ATP was 78% of the initial concentrations measured prior to air-drying. Similarly, by 2 d, extractable organic C had decreased to a similar concentration to the original. After the five AD-RW cycles, the amounts of total and 14C-labelled biomass C remaining in the soil accounted for 60 and 40% of those in the similarly incubated control soil, respectively. Soil biomass ATP concentrations following the first AD-RW cycle remained remarkably constant (ranging from about 10 to 14 μmol ATP g−1 biomass C) and very similar to the concentration in the fresh soil prior to air-drying. We developed a simple mathematical procedure to estimate the proportion of CO2-C derived from biomass C and non-biomass C during AD-RW. From it, we estimate that, over the five AD-RW cycles, about 60% of the CO2-C evolved came from mineralisation of non-biomass organic C and the remainder from the biomass C itself.  相似文献   

15.
To examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5‐yr cultivation in the 0‐ to 20‐cm layer. Significant increases in extractable organic C (EOC), KMnO4‐oxidizable C (KMnO4‐C) and C management index (CMI) in the 0‐ to 20‐cm layer, and light fraction organic C and EOC in the 20‐ to 40‐cm layer were observed in response to plastic film removal after the 1‐yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO4‐C and CMI were also observed after five years in the 20‐ to 40‐cm layer. Moreover, KMnO4‐C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages.  相似文献   

16.
Rewetting events after a drought produce a pulse of soil respiration (the “Birch Effect”) that leads to a loss of carbon from soil, especially in Mediterranean ecosystems. Two main hypotheses have developed to explain the Birch effect: the “metabolic explanation”, based on the rapid consumption of intracellular osmolytes previously accumulated to survive to dry conditions, and the “physical explanation”, based on the consumption of carbon made accessible by physical destruction of internal structures of the soil.Here, we compared the respiration response of intact and crushed 9–4 mm aggregates from a California grassland soil under two different rewetting schemes: (1) successive short dry/wet events and (2) increased drought periods followed by a single rewetting. In intact aggregates, both microbial biomass and respiration rates were relatively stable through both experimental treatments. In crushed aggregates, through multiple short dry/wet cycles, both respiration rate and microbial biomass increased, while as drought length increased, biomass was unaffected but the magnitude of the following rewetting pulse increased. A mechanism that explains both these results is that crushing aggregates exposes occluded particular material that must be degraded into an immediately bioavailable form for microbes to take it up and metabolize it. Nitrification was generally higher in intact than crushed aggregates, suggesting the importance of physical association between nitrifiers and resources in regulating overall soil nitrification.This work suggests that physical processes are most important in driving respiration pulses through multiple rewetting cycles and that the physical association of organisms, substrates, and mineral particles are critical in controlling the functioning of the “microbial landscape”.  相似文献   

17.
Changes in soil caused by drought and wildfire in a Dipterocarp rainforest in Sabah, Malaysia were assessed by phosphorus fractionation, extractable nitrogen and nutrient limited respiration kinetics (after addition of glucose+N or P). Fire increased the concentration of total phosphorus (P) in the litter layer (per ha and per dry soil) by raising the 0.2 M NaOH extractable-P. In the soil organic layer, membrane exchangeable P was reduced by fire while 1.0 M HCl extractable-P, and 0.5 M NaHCO3 extractable-P increased. Microbially available P increased after the fire and was most closely related to NaOH extractable-P that has been considered available to plants only over long time-scales. Total nitrogen (N) increased in the litter layer (per ha and per dry soil) due to post-fire litter fall, while the NO3− increased up to 10-fold down to the 10 cm mineral soil. In contrast, the microbially available N decreased by 50%. Basal respiration and substrate-induced respiration increased in the litter layer and decreased in the organic horizon (per dry soil and per organic matter). P limited microbial growth resulted in a slow and non-exponential increase in respiration, presumably reflecting the P-fixing nature of the soils, while N limitation resulted in a fast exponential increase. However, higher respiration rates were eventually achieved under P limitation than under N limitation.  相似文献   

18.
鄂尔多斯高原脉冲降雨对油蒿灌丛群落土壤碳排放的影响   总被引：1，自引：1，他引：0  
Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such water-limited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO2 efflux, an artificial precipitation event (3 mm) was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8-4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO2 production was between 2 047.0 and 7 383.0 mg m-2. In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO2 loss in desert ecosystems.  相似文献   

19.
Limestone quarrying reduces the land's capacity to support a complete functional ecosystem. Adding sewage sludge to mining residues facilitates the establishment of a vegetation cover and can stimulate C and N cycling.We aimed to evaluate the effects of three composted and three thermally dried sewage sludges, on some biological properties of two types of debris (extraction soil and trituration soil) from a limestone quarry. Lysimeters filled with debris-sludge mixtures and control soils were sampled immediately after preparation and after being left in the open for 13 months. Total carbohydrates (TCH), 0.5 M K2SO4 extractable (ECH) carbohydrates, 0.5 M K2SO4 extractable organic C (EOC), microbial biomass carbon (MBC), microbial respiration (MR), β-glucosidase activity and β-galactosidase activity were determined immediately after sampling. The treated soils were also analyzed for their more general physicochemical characteristics. Adding sewage sludge clearly improved the physicochemical and biological properties of the residual soil and the effect of the type of sludge was greater than that of the type of soil. The sludge effect was generally more durable over the trituration soil. The sludge effect decreased the most in MR and EOC followed by MBC and ECH. Total carbohydrates showed the least enhancement but the sludge effect on this endpoint had the smaller decrease with time. Root exudates and plant debris contributed to β-glucosidase and β-galactosidase activities in the treated soils. Activities present in mixtures partly corresponded to enzymes free in the soil aqueous face. β-Glucosidase was also partly associated with humified organic matter. Thirteen months after sludge addition a fraction of the organic matter present in soils was still moderately labile. Results observed in BMC and MR suggests the sludge did not cause major toxic effects on residual soils. The sludge effect differed with the pre and post treatments of the sludges; thermal drying made the sludge organic matter more easily decomposable.  相似文献   

20.
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   

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