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1.
Soil organic carbon (SOC), microbial biomass carbon (MBC), their ratio (MBC/SOC) which is also known as microbial quotient, soil respiration, dehydrogenase and phosphatase activities were evaluated in a long-term (31 years) field experiment involving fertility treatments (manure and inorganic fertilizers) and a maize (Zea mays L.)-wheat (Triticum aestivum L.)-cowpea (Vigna unguiculata L.) rotation at the Indian Agricultural Research Institute near New Delhi, India. Applying farmyard manure (FYM) plus NPK fertilizer significantly increased SOC (4.5-7.5 g kg−1), microbial biomass (124-291 mg kg−1) and microbial quotient from 2.88 to 3.87. Soil respiration, dehydrogenase and phosphatase activities were also increased by FYM applications. The MBC response to FYM+100% NPK compared to 100% NPK (193 vs. 291 mg kg−1) was much greater than that for soil respiration (6.24 vs. 6.93 μl O2 g−1 h−1) indicating a considerable portion of MBC in FYM plots was inactive. Dehydrogenase activity increased slightly as NPK rates were increased from 50% to 100%, but excessive fertilization (150% NPK) decreased it. Acid phosphatase activity (31.1 vs. 51.8 μg PNP g−1 h−1) was much lower than alkali phosphatase activity (289 vs. 366 μg PNP g−1 h−1) in all treatments. Phosphatase activity was influenced more by season or crop (e.g. tilling wheat residue) than fertilizer treatment, although both MBC and phosphatase activity were increased with optimum or balanced fertilization. SOC, MBC, soil respiration and acid phosphatase activity in control (no NPK, no manure) treatment was lower than uncultivated reference soil, and soil respiration was limiting at N alone or NP alone treatments.  相似文献   

2.
The main energy sources of soil microorganisms are litter fall, root litter and exudation. The amount on these carbon inputs vary according to basal area of the forest stand. We hypothesized that soil microbes utilizing these soil carbon sources relate to the basal area of trees. We measured the amount of soil microbial biomass, soil respiration and microbial community structure as determined by phospholipid fatty acid (PLFA) profiles in the humus layer (FH) of an even-aged stand of Scots pine (Pinus sylvestris L.) with four different basal area levels ranging from 19.9 m2 ha−1 in the study plot Kasper 1 to 35.7 m2 ha−1 in Kasper 4. Increasing trend in basal respiration, total PLFAs and fungal-to-bacterial ratio was observed from Kasper 1 to Kasper 3 (basal area 29.2 m2 ha−1). The soil microbial community structure in Kasper 3 differed from that of the other study plots.  相似文献   

3.
Forest ecosystems on the Loess Plateau are receiving increasing attention for their special importance in carbon fixation and conservation of soil and water in the region. Soil respiration was investigated in two typical forest stands of the forest-grassland transition zone in the region, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest, in response to rain events (27.7 mm in May 2009 and 19 mm in May 2010) during the early summer dry season. In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4 μmol CO2 m−2 s−1 in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, being consistent with the differences in C, N contents and fine root mass on the forest floor and in soil between the two stands. However, root respiration (Rr) per unit fine root mass and microbial respiration (Rm) per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Respiration by root rhizosphere in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.  相似文献   

4.
Soil respiration was measured with the enclosed chamber method in an ungrazed Leymus chinensis steppe during the growing seasons of 2001 and 2002. Soil respiration rate (RS) was significantly influenced by air temperature (T) at the diurnal scale, and could be described by Van't Hoff's equation (RS = R10 exp(β(T − 10))). At the seasonal scale, the normalized soil respiration rate at 10 °C (R10) was mainly controlled by soil water content (R2 = 0.717, P < 0.001), while the sensitivity of soil respiration to temperature (Q10) was partially affected by absolute growth rate (R2 = 0.482, P = 0.004). Thus, soil respiration could be described as RS = (20.015W − 84.085) (0.103AGR + 1.786)(T−10)/10 during the growing seasons, integrating soil water content (W) and absolute growth rate (AGR) into the temperature-dependent soil respiration equation. It was validated by the observed soil respiration rates in this study (R2 = 0.890, P < 0.001) and observations from near-field experiment (R2 = 0.687, P = 0.011). It implied that accurately evaluating annual soil respiration should include the effects of plant biomass production and other abiotic factors besides air temperature.  相似文献   

5.
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6.
Soil respiration is an important process for carbon geochemical cycling. Based on our five long‐term fertilizer experiments, soil respiration was measured using pot experiments with or without planting soybean. Soil respiration rates and soybean root biomass were determined at different observation times. Soil respiration rates due to soil microbial activity could be estimated by extrapolating a newly derived regressive equation at zero root biomass. Soil microbial respiration rates in the control were also observed directly, ranging from 16.0 to 42.7 mg carbon (C) m?2 h?1. Average soil microbial respiration rates from the regression analyses and direct observations were 32.9 and 27.8 mg C m?2 h?1, respectively. The average proportions of soil respiration rates due to the soybean growth were 63.0% using the regressive equation and 69.8% from direct observation. Therefore, the application of these two methods could provide new insight for separating plant root respiration from soil microbial respiration, which is important for estimating their individual contributions to atmospheric carbon dioxide.  相似文献   

7.
The aim of this study was to determine the effects of increasing concentrations of salt solutions (including 0.12, 2, 6, and 10 dS m−1) on the growth of berseem clover (Trifolium alexandrinum L.) and related soil microbial activity, biomass and enzyme activities. Results showed that the dry weights of root and shoot decreased with an increase in the concentrations of salt solutions. Soil salinization depressed the microbiological activities including soil respiration and enzyme activities. Substrate-induced respiration was consistently lower in salinized soils, whereas microbial biomass C did not vary among salinity levels. Higher metabolic quotients (qCO2) and unaffected microbial biomass C at high EC values may indicate that salinity is a stressful factor, inducing either a shift in the microbial community with less catabolic activity or reduced efficiency of substrate utilization. Acid phosphatase and alkaline phosphatase activities decreased with increasing soil salinity. We found significant, positive correlations between the activities of phosphatase enzymes and plant's root mass, suggesting that any decrease in the activities of the two enzymes could be attributed to the reduced root biomass under saline conditions.  相似文献   

8.
The accumulation and transformation of organic matter during soil development is rarely investigated although such processes are relevant when discussing about carbon sequestration in soil. Here, we investigated soils under grassland and forest close to the North Sea that began its genesis under terrestrial conditions 30 years ago after dikes were closed. Organic C contents of up to 99 mg g−1 soil were found until 6 cm soil depth. The humus consisted mainly of the fraction lighter than 1.6 g cm−3 which refers to poorly degraded organic carbon. High microbial respiratory activity was determined with values between 1.57 and 1.17 μg CO2-C g−1 soil h−1 at 22 °C and 40 to 70% water-holding capacity for the grassland and forest topsoils, respectively. The microbial C to organic C ratio showed values up to 20 mg Cmic g−1 Corg. Although up to 2.69 kg C m−2 were estimated to be sequestered during 30 years, the microbial indicators showed intensive colonisation and high transformation rates under both forest and grassland which were higher than those determined in agricultural and forest topsoils in Northern Germany.  相似文献   

9.
Small changes in C cycling in boreal forests can change the sign of their C balance, so it is important to gain an understanding of the factors controlling small exports like water-soluble organic carbon (WSOC) fluxes from the soils in these systems. To examine this, we estimated WSOC fluxes based on measured concentrations along four replicate gradients in upland black spruce (Picea mariana [Mill.] BSP) productivity and soil temperature in interior Alaska and compared them to concurrent rates of soil CO2 efflux. Concentrations of WSOC in organic and mineral horizons ranged from 4.9 to 22.7 g C m−2 and from 1.4 to 8.4 g C m−2, respectively. Annual WSOC fluxes (4.5-12.0 g C m−2 y−1) increased with annual soil CO2 effluxes (365-739 g C m−2 y−1) across all sites (R2=0.55, p=0.02), with higher fluxes occurring in warmer, more productive stands. Although annual WSOC flux was relatively small compared to total soil CO2 efflux across all sites (<3%), its relative contribution was highest in warmer, more productive stands which harbored less soil organic carbon. The proportions of relatively bioavailable organic fractions (hydrophilic organic matter and low molecular weight acids) were highest in WSOC in colder, low-productivity stands whereas the more degraded products of microbial activity (fulvic acids) were highest in warmer, more productive stands. These data suggest that WSOC mineralization may be a mechanism for increased soil C loss if the climate warms and therefore should be accounted for in order to accurately determine the sensitivity of boreal soil organic C balance to climate change.  相似文献   

10.
Nitrogen (N) deposition to semiarid ecosystems is increasing globally, yet few studies have investigated the ecological consequences of N enrichment in these ecosystems. Furthermore, soil CO2 flux – including plant root and microbial respiration – is a key feedback to ecosystem carbon (C) cycling that links ecosystem processes to climate, yet few studies have investigated the effects of N enrichment on belowground processes in water-limited ecosystems. In this study, we conducted two-level N addition experiments to investigate the effects of N enrichment on microbial and root respiration in a grassland ecosystem on the Loess Plateau in northwestern China. Two years of high N additions (9.2 g N m−2 y−1) significantly increased soil CO2 flux, including both microbial and root respiration, particularly during the warm growing season. Low N additions (2.3 g N m−2 y−1) increased microbial respiration during the growing season only, but had no significant effects on root respiration. The annual temperature coefficients (Q10) of soil respiration and microbial respiration ranged from 1.86 to 3.00 and 1.86 to 2.72 respectively, and there was a significant decrease in Q10 between the control and the N treatments during the non-growing season but no difference was found during the growing season. Following nitrogen additions, elevated rates of root respiration were significantly and positively related to root N concentrations and biomass, while elevated rates of microbial respiration were related to soil microbial biomass C (SMBC). The microbial respiration tended to respond more sensitively to N addition, while the root respiration did not have similar response. The different mechanisms of N addition impacts on soil respiration and its components and their sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling and storage in semiarid grasslands under future scenarios of global change.  相似文献   

11.
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   

12.
Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration (Rh). In comparisons of Rh determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO2 efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO2 flux in trenched plots (Rh-t) was significantly lower than in tree-girdled plots (Rh-g) in both plantations. The estimates of Rh-t and Rh-g, expressed as a percentage of total soil respiration, were 58 ± 4% and 74 ± 6%, respectively, for A. crassicarpa, and 64 ± 3% and 78 ± 5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO2 efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual Rh (mean of the annual Rh-t and Rh-g) and net primary production (NPP) were 470 ± 25 and 800 ± 118 g C m−2 yr−1, respectively, for A. crassicarpa, and 420 ± 35 and 2380 ± 187 g C m−2 yr−2, respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330 ± 76 C m−2 yr−1 for A. crassicarpa and 1960 ± 178 g C m−2 yr−1 for E. urophylla.  相似文献   

13.
Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha−1, while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha−1, was approximately twice that of the LG site. Soil respiration measurements showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q10 value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m−2 y−1 to the atmosphere, which was about one third more than the 1530 g CO2 m−2 y−1 released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem.  相似文献   

14.
This paper reports the results of soil respiration (SR, including heterotrophic and autotrophic respiration), in a presumably successional series (early, middle and advanced) of subtropical forests in Dinghushan Biosphere Reserve in Guangdong Province, China. A static chamber method was used to characterize SR in dynamics of diurnal and seasonal patterns. The relationships of SR with soil temperature (ST) at 5 cm depth and with soil moisture (SM) at 0-10 cm depth were studied in order to estimate the annual SR of each of the forests. The annual SR in a climax forest community, monsoon evergreen broad-leaved forest (MEBF) was estimated as 1163.0 g C m−2 year−1 and in its successional communities, coniferous and broad-leaved mixed forest (MF) and the Masson pine forest (MPF) were 592.1 g C m−2 year−1, 1023.7 g C m−2 year−1, respectively. In addition, removal of surface litter led to the reduction of annual SR by 27-45% in those three forests. Analysis of the results indicated that the annual SR was highly correlated with both ST and SM. Furthermore, ST and SM themselves were highly correlated with each other across season in this study area. Thus for seasonal predictive SR model, either ST or SM could be integrated. However, for SR daily change prediction, both ST and SM were required because of confounding effects of ST and SM on a diurnal time scale. The Q10 values of SR derived from ST dependence function were 2.37, 2.31 and 2.25 in the three forests: MPF, MF and MEBF, respectively, suggesting a decreasing trend of the Q10 with the degree of forest succession.  相似文献   

15.
Our objectives were to determine both spatial and temporal variations in soil respiration of a mixed deciduous forest, with soils exhibiting contrasting levels of hydromorphy. Soil respiration (RS) showed a clear seasonal trend that reflected those of soil temperature (TS) and soil water content (WS), especially during summer drought. Using a bivariate model (RMSE=1.03), both optimal soil water content for soil respiration (WSO) and soil respiration at both 10 °C and optimal soil water content (RS10) varied among plots, ranging, respectively, from 0.25 to 0.40 and from 2.30 to 3.60 μmol m−2 s−1. Spatial variation in WSO was related to bulk density and to topsoil N content, while spatial variation in RS10 was related to basal area and the difference in pH measured in water or KCl suspensions. These results offer promising perspectives for spatializing ecosystem carbon budget at the regional scale.  相似文献   

16.
Although information regarding the spatial variability of soil respiration is important for understanding carbon cycling and developing a suitable sampling design for estimating average soil respiration, it remains relatively understudied compared to temporal changes. In this study, soil respiration was measured at 35 locations by season on a slope of Japanese cedar forest in order to examine temporal changes in the spatial distribution of soil respiration. Spatial variability of soil respiration varied between seasons, with the highest coefficient variation in winter (42%) and lowest in summer (26%). Semivariogram analysis and kriged maps revealed different patterns of spatial distribution in each season. Factors affecting the spatial variability were relief index (autumn), soil hardness of the A layer (winter), soil hardness at 50 cm depth (spring) and the altitude and relief index (summer). Annual soil respiration (average: 39 mol m−2 y−1) varied from 26 mol m−2 y−1 to 55 mol m−2 y−1 between the 35 locations and was higher in the upper part of the slope and lower in the lower part. The average Q10 value was 2.3, varying from 1.3 to 3.0 among the locations. These findings suggest that insufficient information on the spatial variability of soil respiration and imbalanced sampling could bias estimates of current and future carbon budgets.  相似文献   

17.
A long-term field experiment was conducted to examine the influence of mineral fertilizer and organic manure on the equilibrium dynamics of soil organic C in an intensively cultivated fluvo-aquic soil in the Fengqiu State Key Agro-Ecological Experimental Station (Fengqiu county, Henan province, China) since September 1989. Soil CO2 flux was measured during the maize and wheat growing seasons in 2002-2003 and 2004 to evaluate the response of soil respiration to additions and/or alterations in mineral fertilizer, organic manure and various environmental factors. The study included seven treatments: organic manure (OM), half-organic manure plus half-fertilizer N (NOM), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). Organic C in soil and the soil heavy fraction (organo-mineral complex) was increased from 4.47 to 8.61 mg C g−1 and from 3.32 to 5.68 mg C g−1, respectively, after the 13 yr application of organic manure. In contrast, organic C and the soil heavy fraction increased in NPK soil to only 5.41 and 4.38 mg C g−1, respectively. In the CK treatment, these parameters actually decreased from the initial C concentrations (4.47 and 3.32 mg C g−1) to 3.77 and 3.11 mg C g−1, respectively. Therefore, organic manure efficiently elevated soil organic C. However, only 66% of the increased soil organic C was combined with clay minerals in the OM treatment. Cumulative soil CO2 emissions from inter-row soil in the OM and NPK treatments were 228 and 188 g C m−2 during the 2002 maize growing season, 132 and 123 g C m−2 during the 2002/2003 wheat growing season, and 401 and 346 g C m−2 yr−1 in 2002-2003, respectively. However, during the 2004 maize growing season, cumulative soil CO2 emissions were as high as 617 and 556 g C m−2, respectively, due to the contribution of rhizosphere respiration. The addition of organic manure contributed to a 16% increase in soil CO2 emission in 2002-2003 (compared to NPK), where only 27%, 36% and 24% of applied organic C was released as CO2 during the 2002 and 2004 maize growing seasons and in 2002-2003, respectively. During the 2002/2003 wheat growing season, soil CO2 flux was significantly affected by soil temperature below 20 °C, but by soil moisture (WFPS) during the 2004 maize growing season at soil temperatures above 18 °C. Optimum soil WFPS for soil CO2 flux was approximately 70%. When WFPS was below 50%, it no longer had a significant impact on soil CO2 flux during the 2002 maize growing season. This study indicates the application of organic manure composted with wheat straw may be a preferred strategy for increasing soil organic C and sequestering C in soil.  相似文献   

18.
Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km2 digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO2 m−2 s−1, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km2 region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.  相似文献   

19.
Afforestation and reforestation of pastures are key land-use changes in New Zealand that help sequester carbon (C) to offset its carbon dioxide (CO2) emissions under the Kyoto Protocol. However, relatively little attention has been given so far to associated changes in trace gas fluxes. Here, we measure methane (CH4) fluxes and CO2 production, as well as microbial C, nitrogen (N) and mineral-N, in intact, gradually dried (ca. 2 months at 20 °C) cores of a volcanic soil and a heavier textured, non-volcanic soil collected within plantations of Pinus radiata D. Don (pine) and adjacent permanent pastures. CH4 fluxes and CO2 production were also measured in cores of another volcanic soil under reverting shrubland (mainly Kunzea var. ericoides (A. Rich) J. Thompson) and an adjacent pasture. CH4 uptake in the pine and shrubland cores of the volcanic soils at field capacity averaged about 35 and 14 μg CH4-C m−2 h−1, respectively, and was significantly higher than in the pasture cores (about 21 and 6 μg CH4-C m−2 h−1, respectively). In the non-volcanic soil, however, CH4-C uptake was similar in most cores of the pine and pasture soils, averaging about 7-9 μg m−2 h−1, except in very wet samples. In contrast, rates of CO2 production and microbial C and N concentrations were significantly lower under pine than under pasture. In the air-dry cores, microbial C and N had declined in the volcanic soil, but not in the non-volcanic soil; ammonium-N, and especially nitrate-N, had increased significantly in all samples. CH4 uptake was, with few exceptions, not significantly influenced by initial concentrations of ammonium-N or nitrate-N, nor by their changes on air-drying. A combination of phospholipid fatty acid (PLFA) and stable isotope probing (SIP) analyses of only the pine and pasture soils showed that different methanotrophic communities were probably active in soils under the different vegetations. The C18 PLFAs (type II methanotrophs) predominated under pine and C16 PLFAs (type I methanotrophs) predominated under pasture. Overall, vegetation, soil texture, and water-filled pore space influenced CH4-C uptake more than did soil mineral-N concentrations.  相似文献   

20.
The effects of tillage on the interaction between soil structure and microbial biomass vary spatially and temporally for different soil types and cropping systems. We assessed the relationship between soil structure induced by tillage and soil microbial activity at the level of soil aggregates. To this aim, organic C (OC), microbial biomass C (MBC) and soil respiration were measured in water-stable aggregates (WSA) of different sizes from a subtropical rice soil under two tillage systems: conventional tillage (CT) and a combination of ridge with no-tillage (RNT). Soil (0–20 cm) was fractionated into six different aggregate sizes (> 4.76, 4.76–2.0, 2.0–1.0, 1.0–0.25, 0.25–0.053, and < 0.053 mm in diameter). Soil OC, MBC, respiration rate, and metabolic quotient were heterogeneously distributed among soil aggregates while the patterns of aggregate-size distribution were similar among properties, regardless of tillage system. The content of OC within WSA followed the sequence: medium-aggregates (1.0–0.25 mm and 1.0–2.0 mm) > macro-aggregates (4.76–2.0 mm) > micro-aggregates (0.25–0.053 mm) > large aggregates (> 4.76 mm) > silt + clay fractions (< 0.053 mm). The highest levels of MBC were associated with the 1.0–2.0 mm aggregate size class. Significant differences in respiration rates were also observed among different sizes of WSA, and the highest respiration rate was associated with 1.0–2.0 mm aggregates. The Cmic/Corg was greatest for the large-macroaggregates regardless of tillage regimes. This ratio decreased with aggregate size to 1.0–0.25 mm. Soil metabolic quotient (qCO2) ranged from 3.6 to 17.7 mg CO2 g− 1 MBC h− 1. The distribution pattern of soil microbial biomass and activity was governed by aggregate size, whereas the tillage effect was not significant at the aggregate scale. Tillage regimes that contribute to greater aggregation, such as RNT, also improved soil microbial activity. Soil OC, MBC and respiration rate were at their highest levels for 1.0–2.0 mm aggregates, suggesting a higher biological activity at this aggregate size for the present ecosystem.  相似文献   

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