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1.
In this study, the effects of different management practices on soil biochemical properties were evaluated in three pairs of grassland soils (unmanaged and managed) located in three areas of Galicia (NW Spain) where different types of climate prevail. Variations in soil biochemical properties were monitored throughout 1 year. Changes in soil temperature, soil moisture content, and particularly soil location and soil management affected the values of the biochemical properties. Comparatively higher levels of enzyme activity were observed in the unmanaged grasslands than in the managed grasslands, especially for β-glucosidase activity and the enzymes involved in the P and S cycles (phosphodiesterase, phosphomonoesterase, and arylsulphatase activities). A biochemical equilibrium index was used to evaluate soil quality. Although variations in the index were observed throughout the year, the values mainly depended on soil management and revealed that unmanaged grasslands were in a situation of biochemical equilibrium throughout the study period, while no such equilibrium was observed in managed grasslands for most of the studied period.  相似文献   

2.
Biochemical properties are considered to be the best indicators available at present for assessing soil quality. However, there are still many gaps in our knowledge about how these properties are affected by abiotic factors and how these factors interact with soil management. With the aim of understanding how climate and soil management affect soil biochemical properties in grasslands soils from a temperate-humid area (Galicia, NW Spain), a total of 60 soils were analyzed for several microbial and biochemical properties. Grasslands were divided into groups according to the type of management applied (native compared with intensive) and to the climate in the area where they were sampled (Mediterranean subhumid with centroeuropean drift climate compared with Atlantic climate). We found that management had a greater influence on soil biochemical properties than climate. Altitude, which strongly influences climate in the region where the soils were analyzed, was found to be a significant factor that affected most soil biochemical properties. In conclusion, the results show that microbially-mediated processes are greatly affected by both, management and abiotic factors and that, for some properties (like net N mineralization and cellulase and casein-protease activities), abiotic factors can have an important influence on soil biochemical properties.  相似文献   

3.
Woody plant proliferation in grasslands and savannas has been documented worldwide in recent history. To better understand the consequences of this vegetation change for the C-cycle, we measured soil microbial biomass carbon (Cmic) in remnant grasslands (time 0) and woody plant stands ranging in age from 10 to 130 years in a subtropical ecosystem undergoing succession from grassland to woodlands dominated by N-fixing trees. We also determined the ratio of SMB-C to soil organic carbon (Cmic/Corg) as an indicator of soil organic matter quality or availability, and the metabolic quotient (qCO2) as a measure of microbial efficiency. Soil organic carbon (Corg) and soil total nitrogen (STN) increased up to 200% in the 0–15 cm depth increment following woody plant invasion of grassland, but changed little at 15–30 cm. Cmic at 0–15 cm increased linearly with time following woody plant encroachment and ranged from 400 mg C kg−1 soil in remnant grasslands up to 600–1000 mg C kg−1 soil in older (>60 years) woody plant stands. Cmic at 15–30 cm also increased linearly with time, ranging from 100 mg C kg−1 soil in remnant grasslands to 400–700 mg C kg−1 soil in older wooded areas. These changes in Cmic in wooded areas were correlated with concurrent changes in stores of C and N in soils, roots, and litter. The Cmic/Corg ratio at 0–15 cm decreased with increasing woody plant stand age from 6% in grasslands to <4% in older woodlands suggesting that woody litter may be less suitable as a microbial substrate compared with grassland litter. In addition, higher qCO2 values in woodlands (0.8 mg CO2-C g−1 Cmic h−1) relative to remnant grasslands (0.4 mg CO2-C g−1 Cmic h−1) indicated that more respiration was required per unit of Cmic in wooded areas than in grasslands. Observed increases in Corg and STN following woody plant encroachment in this ecosystem may be a function of both greater inputs of poor quality C that is relatively resistant to decay, and the decreased ability of soil microbes to decompose this organic matter. We suggest that increases in the size and activity of Cmic following woody plant encroachment may result in: (a) alterations in competitive interactions and successional processes due to changes in nutrient dynamics, (b) enhanced formation and maintenance of soil physical structures that promote Corg sequestration, and/or (c) increased trace gas fluxes that have the potential to influence atmospheric chemistry and the climate system at regional to global scales.  相似文献   

4.
Soil microbial properties are widely used as indicators of soil quality. The interpretation of soil microbial processes, however, is difficult because of their regional and seasonal heterogeneity as well as the lack of reference values. One possibility to overcome these limitations to apply the fuzzy set theory. This approach more realistically describes ecological systems because it considers natural ambiguity and complexity. The present study applies a fuzzy rule-based classification model to define soil quality based on soil microbial biomass, N-mineralisation, enzyme activity data (urease, xylanase, phosphatase, arylsulfatase) and soil organic matter. The data have been collected from different grassland sites in the European Union over a period of 20 years. The fuzzy model is based on a rule system derived from a training set using simulated annealing as an optimisation algorithm. For each variable, nine triangular fuzzy sets were defined for consideration as possible rule arguments. The model uses the t-norm for combination of arguments, product inference, the weighted sum as rule combination and the maximum method for defuzzification. The output is the assignment of membership of the object to a given soil quality class. The soil quality classes (very poor, poor, medium, high, very high) were defined by five heavy metal contamination levels (very high, high, medium, low, no). A predefined number of fuzzy rules were assessed using a simulated annealing algorithm. The fuzzy model was validated by a test file by assigning the soils to the quality class with the highest response value. The fuzzy model yielded an overall coincidence of 88.8% between observed and simulated results. The most sensitive index of soil quality was microbial biomass. N-mineralisation was a good indicator for the high-quality soils, while urease and arylsulfatase were important indicators for heavily contaminated, poor soil quality. Xylanase and phosphatase behaved ambivalently. Including soil organic carbon in the model decreased its effectiveness by 6.5%. We suggest that the presented fuzzy model based on soil microbial properties could be applied not only to soil degradation, upscaling and prediction, but also to judge the response of soils to environmental changes.  相似文献   

5.
Intensive agriculture has resulted in the loss of biodiversity and the specialist flora and fauna associated with the semi-natural grasslands of low-intensity pastoral systems throughout northwest Europe. Techniques employed to restore and re-create these grasslands on agricultural land in the UK are reviewed. Extensive cutting and grazing management have been shown to diversify improved swards and facilitate re-colonisation on ex-arable soils, although rates of re-assembly of plant communities with affinity to existing semi-natural grasslands have generally been slow. On former agriculturally improved swards, nutrient depletion has accelerated this process, especially where “gaps” for establishment have been created. Similarly, on ex-arable soils “nutrient stripping” and sowing with diverse seed mixtures has led to the rapid development of species-rich swards. On free draining brown earths such an approach may be required to restore grassland communities where soil phosphorous concentrations exceed semi-natural levels by more than 10 mg/l (using Olsen's bicarbonate extractant). However, the appropriateness of this threshold for other soil types requires further sampling. Although restored grasslands are likely to contribute to national biodiversity targets success will ultimately depend on the reinstatement of the communities and ecological functions of semi-natural references. Although this is technically feasible for a few plant assemblages, less is known about the re-assembly of microbial and faunal communities, or the importance of trophic interactions during grassland succession. As a consequence, more research is required on the functional attributes of semi-natural grasslands, as well as the methods required to restore localised types, novel nutrient depletion techniques, the “phased” introduction of desirable but poor-performing species and the performance of different genotypes during grassland restoration.  相似文献   

6.
Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.  相似文献   

7.
Rainfall in Mediterranean climates may affect soil microbial processes and communities differently in agricultural vs. grassland soils. We explored the hypothesis that land use intensification decreases the resistance of microbial community composition and activity to perturbation. Soil carbon (C) and nitrogen (N) dynamics and microbial responses to a simulated Spring rainfall were measured in grassland and agricultural ecosystems. The California ecosystems consisted of two paired sets: annual vegetable crops and annual grassland in Salinas Valley, and perennial grass agriculture and native perennial grassland in Carmel Valley. Soil types of the respective ecosystem pairs were derived from granitic parent material and had sandy loam textures. Intact cores (30 cm deep) were collected in March 1999. After equilibration, dry soil cores (approx. −1 to −2 MPa) were exposed to a simulated Spring rainfall of 2.4 cm, and then were measured at 0, 6, 24, and 120 h after rewetting. Microbial biomass C (MBC) and inorganic N did not respond to rewetting. N2O and CO2 efflux and respiration increased after rewetting in all soils, with larger responses in the grassland than in the agricultural soils. Phospholipid fatty acid (PLFA) profiles indicated that changes in microbial community composition after rewetting were most pronounced in intensive vegetable production, followed by the relict perennial grassland. Changes in specific PLFA markers were not consistent across all sites. There were more similarities among microbial groups associated with PLFA markers in agricultural ecosystems than grassland ecosystems. Differences in responses of microbial communities may be related to the different plant species composition of the grasslands. Agricultural intensification appeared to decrease microbial diversity, as estimated from numbers of individual PLFA identified for each ecosystem, and reduce resistance to change in microbial community composition after rewetting. In the agricultural systems, reductions in both the measures of microbial diversity and the resistance of the microbial community composition to change after a perturbation were associated with lower ecosystem function, i.e. lower microbial responses to increased moisture availability.  相似文献   

8.
Soil biological and biochemical properties are highly sensitive to environmental stress and thus can be used to assess quality. Any soil quality index should include several biological and biochemical variables so as to reflect better the complex processes affecting soil quality and to compensate for the wide variations occurring in individual properties. Many authors recommend the use of a native soil supporting climax vegetation that has undergone minimal anthropogenic disturbance as a high quality reference soil. In this study which examined three such native soils of Galicia (N.W. Spain) bearing Atlantic oakwood as the climax vegetation, biological and biochemical properties were found to vary widely seasonally and with sampling site and depth. These variations were closely correlated with the total carbon (C) and/or total nitrogen (N) contents of the soils. The following equation: Total N= (0.38×10–3) microbial biomass C +(1.4×10–3) mineralized N +(13.6×10–3) phosphomonoesterase +(8.9×10–3) β-glucosidase+(1.6×10–3) urease explained 97% of the variance in total N for the soils studied, suggesting that a balance exists between the organic matter content of a soil and its biological and biochemical properties. A simplified expression of the above equation may be useful as a biochemical quality index for soils. Received: 5 March 1997  相似文献   

9.
川西北退化草地土壤微生物生化活性的初步研究   总被引：10，自引：0，他引：10       下载免费PDF全文
龙章富  刘世贵 《土壤学报》1995,32(2):221-227
通过对川西北三种不同退化程度的几种土壤的生化活性大小及其相关性进行研究，结果表明，草地退化后其土壤生化活性受到不同程度的影响，其影响明显地与退化程度有关；土壤生化活性大小有随退化程度增高而减小的趋势，但差异并非都达到统计学上的显著性，而土壤生化活性间地的相关性则显著地与草地退经程度有关，说明退化草地其土壤微生物间的协同作用受到显著影响，从而影响其土壤碳氮循环代途径，降低土壤肥力水平。  相似文献   

10.
Agricultural practices have strong impacts on soil microbes including both the indices related to biomass and activity as well as those related to community composition. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Three treatments were compared: annual grassland, bare soil fallow, and restored perennial grassland. Soil profiles down to 80 cm in depth were investigated in four separate layers (0-15, 15-30, 30-60, and 60-80 cm) using both phospholipid ester-linked fatty acid (PLFAs) and ergosterol as biomarkers in addition to microbial biomass C by fumigation extraction. PLFA fingerprinting showed much stronger differences between the tilled bare fallow treatment vs. grasslands, compared to fewer differences between restored perennial grassland and annual grassland. The presence or absence of plants over several years clearly distinguished microbial communities. Microbial communities in lower soil layers were little affected by management practices. Regardless of treatment, soil depth caused a strong gradient of changing habitat conditions, which was reflected in Canonical Correspondence Analysis of PLFAs. Fungal organisms were associated with the presence of plants and/or litter since the total amount and the relative proportion of fungal markers were reduced in the tilled bare fallow and in lower layers of the grassland treatments. Total PLFA and soil microbial biomass were highly correlated, and fungal PLFA biomarkers showed strong correlations to ergosterol content. In conclusion, microbial communities are resilient to the grassland restoration process, but do not reflect the change in plant species composition that occurred after planting native bunchgrasses.  相似文献   

11.
The effects of a dry-rewetting event (D/RW) on soil microbial properties and nutrient release by leaching from two soils taken from adjacent grasslands with different histories of management intensity were studied. These were a low-productivity grassland, with no history of fertilizer application and a high-productivity grassland with a history of high fertilizer application, referred to as unimproved and improved grassland, respectively. The use of phospholipid fatty acid analysis (PLFA) revealed that the soil of the unimproved grassland had a significantly greater microbial biomass, and a greater abundance of fungi relative to bacteria than did the improved grassland. Soils from both grasslands were maintained at 55% water holding capacity (WHC) or dried to 10% WHC and rewetted to 55% WHC, and then sampled on days 1, 3, 9, 16, 30 and 50 after rewetting. The D/RW stress significantly reduced microbial biomass carbon (C), fungal PLFA and the ratio of fungal-to-bacterial PLFA in both soils. In contrast, D/RW increased microbial activity, but had no effect on total PLFA and bacterial PLFA in either soil. Microbial biomass nitrogen (N) was reduced significantly by D/RW in both soils, but especially in those of the improved grassland. In terms of nutrient leaching, the D/RW stress significantly increased concentrations of dissolved organic C and dissolved organic N in leachates taken from the improved soil only. This treatment increased the concentration of dissolved inorganic N in leachate of both soils, but this effect was most pronounced in the improved soil. Overall, our data show that D/RW stress leads to greater nutrient leaching from improved than from unimproved grassland soils, which have a greater microbial biomass and abundance of fungi relative to bacteria. This finding supports the notion that soils with more fungal-rich communities are better able to retain nutrients under D/RW than are their intensively managed counterparts with lower fungal to bacterial ratios, and that D/RW can enhance nutrient leaching with potential implications for water quality.  相似文献   

12.
Phospholipid ester-linked fatty acid (PLFA) profiles were used to evaluate soil microbial community composition for 9 land use types in two coastal valleys in California. These included irrigated and non-irrigated agricultural sites, non-native annual grasslands and relict, never-tilled or old field perennial grasslands. All 42 sites were on loams or sandy loams of similar soil taxa derived from granitic and alluvial material. We hypothesized that land use history and its associated management inputs and practices may produce a unique soil environment, for which microbes with specific environmental requirements may be selected and supported. We investigated the relationship between soil physical and chemical characteristics, management factors, and vegetation type with microbial community composition. Higher values of total soil C, N, and microbial biomass (total PLFA) and lower values of soil pH occurred in the grassland than cultivated soils. The correspondence analysis (CA) of the PLFA profiles and the canonical correspondence analysis (CCA) of PLFA profiles, soil characteristics, and site and management factors showed distinct groupings for land use types. A given land use type could thus be identified by soil microbial community composition as well as similar soil characteristics and management factors. Differences in soil microbial community composition were highly associated with total PLFA, a measure of soil microbial biomass, suggesting that labile soil organic matter affects microbial composition. Management inputs, such as fertilizer, herbicide, and irrigation, also were associated with the distinctive microbial community composition of the different cultivated land use types.  相似文献   

13.
The functional potential of soil ecosystems can be predicted from the activity and abundance of the microbial community in relation to key soil properties. When describing microbial community dynamics, soil physicochemical properties have traditionally been used. The extent of correlations between properties, however, differs between studies, especially across larger spatial scales. In this research we analysed soil microbial biomass and substrate‐induced respiration of 156 samples from Irish grasslands. In addition to the standard physicochemical, soil type and land management variables, soil diagnostic properties were included to identify if these important soil–landscape genesis classes affected microbial biomass and respiration dynamics in Irish soil. Apart from physicochemical properties, soil drainage class was identified as having an important effect on microbial properties. In particular, biomass‐specific basal (qCO2) and substrate‐induced respiration (SIR:CFE) were explained best by the soil drainage. Poorly drained soil had smaller values of these respiration measures than well‐drained soil. We concluded that this resulted from different groups within the microbial community that could use readily available carbon sources, which suggests a change in microbial community dynamics associated with soil texture and periods of water stress. Overall, our results indicate that soil quality assessments should include both physicochemical properties and diagnostic classes, to provide a better understanding of the behaviour of soil microbial communities.

Highlights

  • Assessing the effect of soil diagnostic features and properties on microbial biomass and respiration
  • A soil biological survey from 156 grassland sites in Ireland
  • Soil drainage class has an important effect on microbial properties
  • Soil quality assessments should include both physicochemical properties and diagnostic classes
  相似文献   

14.
Defining the validity of a biochemical index of soil quality   总被引：2，自引：0，他引：2  
 The native soils of Galicia (NW Spain) exhibit a biochemical equilibrium such that total soil N is a function of five biochemical and microbiological parameters: microbial biomass C, mineralized N, phosphomonoesterase, β-glucosidase and urease activities. To investigate whether the ratio of the total N calculated from biochemical soil properties (Nc) and the total N as measured by the Kjeldahl method (Nk; Nc/Nk) can be used as an index of soil quality, we determined these variables and consequently the ratio in three kinds of disturbed soils: an artificially Cu-contaminated soil, two lignite mine soils, and a number of arable soils. In none of the studied soils did the individual biochemical parameters respond consistently to the factors influencing soil quality, but in all cases soil degradation was reflected by the Nc/Nk value, which differed more or less markedly from 100%. Nc/Nk can therefore be used for the rapid evaluation of soil degradation, since it distinguishes among biochemically balanced soils, soils in a transient state of high microbiological and biochemical activity and degraded soils. It can also serve as a reliable basis for the rapid calculation of the "ecological dose" (ED50) of soil pollutants. The use of Nc/Nk as an objective index of the biochemical quality of soils is recommended. Received: 20 December 1998  相似文献   

15.
Biotic soil parameters have so far seldom played a role in practical soil assessment and management of grasslands. However, the ongoing reduction of external inputs in agriculture would imply an increasing reliance on ecosystem self-regulating processes. Since soil biota play an important role in these processes and in the provision of ecosystem services, biological soil parameters should be an integral part of soil assessment. The general objective of the current study is to investigate to what extent biotic soil parameters provide additional value in soil quality assessment of grassland on sandy soils. We measured abiotic and biotic soil parameters together with process parameters underlying ecosystem services in 20 permanent production grasslands. Cross-validated stepwise regression was used to identify abiotic and biotic soil parameters that explained the soil ecosystem services soil structure maintenance, water regulation, supply of nutrients, and grassland production, respectively.Process parameters underlying the ecosystem service soil structure maintenance such as bulk density and the percentage of sub-angular blocky elements were mainly influenced by SOM and its qualities. The correlations between penetration resistance at 0-10 cm and the percentage of soil crumbs with earthworms suggested a relationship to earthworm activity. Parameters underlying the service of water regulation showed no clear relationship to biotic soil parameters. Water infiltration rate in the field was explained by the penetration resistance at 10-20 cm. Process parameters underlying the service of nutrients’ supply such as the potentially mineralizable C and N were mainly determined by soil total N. The potential C and N mineralization were more related to biotic soil parameters, whereby each parameter was the other’s antithesis. The grassland production without N fertilization viz. the nitrogen supply capacity of the soil measured as N yield, was mainly explained by soil organic matter (SOM) and soil moisture, and to a lesser extent by soil total N. One gram of SOM per kg of dry soil corresponded to 3.21 kg N yield ha−1, on top of a constant of 15.4 kg N ha−1. The currently applied calculations in the Dutch grassland fertilization recommendation, underestimated in 85% of the production grasslands, the measured nitrogen supply capacity of the soil by on average 42 kg N ha−1 (31%). This legitimizes additional research to improve the currently applied recommendations for sandy soils. The response of N yield to N fertilization ranged from 35 to 102%. This wide range emphasizes the importance of a better recommendation base to target N fertilizer. The response of N yield to N fertilization was predicted by the total number of enchytraeids, the underlying mechanism of which needs further investigation on different soil types. This knowledge can be important for the optimal use of fertilizer and its consequences for environmental quality.  相似文献   

16.
In the last century, conversion of native North American grasslands to Juniperus virginiana forests or woodlands has dramatically altered ecosystem structure and significantly increased ecosystem carbon (C) stocks. We compared soils under recently established J. virginiana forests and adjacent native C4-dominated grassland to assess changes in potential soil nitrogen (N) transformations and plant available N. Over a 2-year period, concentrations of extractable inorganic N were measured in soils from forest and grassland sites. Potential gross N ammonification, nitrification, and consumption rates were determined using 15N isotope-dilution under laboratory conditions, controlling for soil temperature and moisture content. Potential nitrification rates (Vmax) and microbial biomass, as well as soil physical and chemical properties were also assessed. Extractable NH4+ concentrations were significantly greater in grassland soils across the study period (P ≤ 0.01), but analysis by date indicated that differences in extractable inorganic N occurred more frequently in fall and winter, when grasses were senescent but J. virginiana was still active. Laboratory-based rates of gross N mineralization (ammonification) and nitrification were greater in grassland soils (P ≤ 0.05), but only on one of four dates. Potential nitrification rates (Vmax) were an order of magnitude greater than gross nitrification rates in both ecosystems, suggesting that nitrification is highly constrained by NH4+ availability. Differences in plant uptake of N, C inputs, and soil microclimate as forests replace grasslands may influence plant available N in the field, as evidenced by seasonal differences in soil extractable NH4+, and total soil C and N accumulation. However, we found few differences in potential soil N transformations under laboratory conditions, suggesting that this grassland-to-forest conversion caused little change in mineralizable organic N pools or potential microbial activity.  相似文献   

17.
已有许多研究证明,中国北方草地生态系统的植物群落结构和组成对气候变化和氮沉降较为敏感,但是关于草原土壤微生物群落响应多重环境因子变化方面的研究较薄弱。水和氮是陆地生态系统生产力的两大限制性因子。本研究在内蒙古多伦半干旱草原地区进行增雨和施氮的野外控制试验,以模拟未来该地区的降水变化和氮沉降,使用微生物群落水平生理图谱法,监测样地土壤理化指标和土壤微生物群落碳源利用潜力的变化。3年的跟踪监测结果显示:增雨显著提高了半干旱草原地区土壤含水量和有机质含量;施氮和增雨同时施氮则显著提高了土壤可溶性氮含量,降低了土壤pH;施氮和增雨都没有单独引起土壤微生物群落碳源利用潜力的显著变化,而在同时增雨和施氮试验处理下,微生物群落碳源利用潜力得到提高,说明在水和氮都充足的条件下,土壤微生物碳源利用潜力才会显著提高。以上研究结果预示着在未来降雨增加和氮沉降的全球变化背景下,中国北方半干旱草地生态系统的碳循环速率可能会加快。  相似文献   

18.
Surface (0–15 cm) soil samples were collected from a semi-arid, sandy grassland in Keerqin Sandy Lands, Northeast China to study changes in soil microbial and chemical properties after five consecutive years of nitrogen (N) and phosphorus (P) additions. Nitrogen and P additions and their interactions negligibly affected soil organic carbon and total N contents, while P addition significantly increased soil total P content. Soil pH was significantly decreased by N addition, which significantly increased net nitrification rate, whereas it did not affect net N mineralization rate. No significant effects of N and P additions and their interactions on basal respiration were detected. In addition, N addition significantly decreased microbial biomass C (MBC) and N, and thus microbial quotient, but increased dissolved organic C and microbial metabolic quotient due to the significant decrease of MBC. Our results suggest that in the mid-term the addition of N, but not P, can change soil microbial properties, with a possible decline in soil quality of semi-arid, sandy grasslands.  相似文献   

19.
Management intensity modifies soil properties, e.g., organic carbon (Corg) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (Pmic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling Pmic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on Pmic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (Cmic), Pmic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, Pmic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil Corg is the profound driver of plant diversity effects on Pmic in grasslands. For both forest and grassland, we found regional differences in Pmic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on Pmic due to a lack of effects on controlling variables (e.g., Corg). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling Pmic or Cmic in soil differ in part and that regional differences in controlling variables are more important for Pmic in soil than those induced by management.  相似文献   

20.
退化草地土壤农化性状与微生物区系研究   总被引：17，自引：0，他引：17  
龙章富  刘世贵 《土壤学报》1996,33(2):192-200
通过对三种退化程度不同的草地土壤农化性状与微生物区系进行研究，结果表明，草地退化后，其土壤肥力水平、土壤微生物数量和微生物种类有随退化程度增高而下降的趋势；退化草地存在不同的程度的营养元素比例失调，表现为少氮、缺磷、富钾和高有机质含量，且退化程度接近的草地间，在土壤微生物区系和农化性状有部分类似的特征。  相似文献   

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