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1.
Soil enzymes activities and microbial biomass have an important influence on nutrient cycling. The spatial distribution of soil enzymes activities and microbial biomass were examined along a latitudinal gradient in farmlands of Songliao Plain, Northeast China to assess the impact of climatic changes along the latitudinal transect on nutrient cycling in agroecosystems. Top soils （0-20 cm depth） were sampled in fields at 7 locations from north （Hallun） to south （Dashiqiao） in the end of October 2005 after maize harvest. The contents of total C, N, and P, C/N, available N, and available P increased with the latitude. The activities of invertase and acid phosphatase, microbial biomass （MB） C and N, and MBC/MBN were significantly correlated with latitude （P 〈 0.05, r^2 = 0.198, 0.635, 0.558, 0.211 and 0.317, respectively）, that is, increasing with the latitude. Significant positive correlations （P 〈 0.05） were observed between invertase activity and the total N and available P, and between acid phosphatase activity and the total C, C/N, available N, total P and available P. The urease, acid phosphatase, and dehydrogenase activities were significantly correlated with the soil pH and electrical conductivity （EC） （P 〈 0.05）. MBC and MBN were positively correlated with the total C, C/N, and available P （P 〈 0.05）. The MBC/MBN ratio was positively correlated with the total C, total N, C/N, and available N （P 〈 0.05）. The spatial distribution of soil enzyme activities and microbial biomass resulted from the changes in soil properties such as soil organic matter, soil pH, and EC, partially owing to variations in temperature and rainfall along the latitudinal gradient.  相似文献   

2.
Using a scheme of agricultural fields with progressively less intensive management （deintensification）, different management practices in six agroecosystems located near Goldsboro, NC, USA were tested in a large-scale experiment, including two cash-grain cropping systems employing either tillage （CT） or no-tillage （NT）, an organic farming system （OR）, an integrated cropping system with animals （IN）, a successional field （SU）, and a plantation woodlot （WO）. Microbial phospholipid fatty acid （PLFA） profiles and substrate utilization patterns （BIOLOG ECO plates） were measured to examine the effects of deintensification on the structure and diversity of soil microbial communities. Principle component analyses of PLFA and BIOLOG data showed that the microbial community structure diverged among the soils of the six systems.Lower microbial diversity was found in lowly managed ecosystem than that in intensive and moderately managed agroecosystems, and both fungal contribution to the total identified PLFAs and the ratio of microbial biomass C/N increased along with agricultural deintensification. Significantly higher ratios of C/N （P 〈 0.05） were found in the WO and SU systems, and for fungal/bacterial PLFAs in the WO system （P 〈 0.05）. There were also significant decreases （P 〈 0.05） along with agricultural deintensification for contributions of total bacterial and gram positive （G＋） bacterial PLFAs.Agricultural deintensification could facilitate the development of microbial communities that favor soil fungi over bacteria.  相似文献   

3.
Land degradation causes great changes in the soil biological properties.The process of degradation may decrease soil microbial biomass and consequently decrease soil microbial activity.The study was conducted out during 2009 and 2010 at the four sites of land under native vegetation(NV),moderately degraded land(LDL),highly degraded land(HDL) and land under restoration for four years(RL) to evaluate changes in soil microbial biomass and activity in lands with different degradation levels in comparison with both land under native vegetation and land under restoration in Northeast Brazil.Soil samples were collected at 0-10 cm depth.Soil organic carbon(SOC),soil microbial biomass C(MBC) and N(MBN),soil respiration(SR),and hydrolysis of fluorescein diacetate(FDA) and dehydrogenase(DHA) activities were analyzed.After two years of evaluation,soil MBC,MBN,FDA and DHA had higher values in the NV,followed by the RL.The decreases of soil microbial biomass and enzyme activities in the degraded lands were approximately 8-10 times as large as those found in the NV.However,after land restoration,the MBC and MBN increased approximately 5-fold and 2-fold,respectively,compared with the HDL.The results showed that land degradation produced a strong decrease in soil microbial biomass.However,land restoration may promote short-and long-term increases in soil microbial biomass.  相似文献   

4.
To show the vegetation succession interaction with soil properties, microbial biomass, basal respiration, and enzyme activities in different soil layers (0--60 cm) were determined in six lands, i.e., 2-, 7-, 11-, 20-, 43-year-old abandoned lands and one native grassland, in a semiarid hilly area of the Loess Plateau. The results indicated that the successional time and soil depths affected soil microbiological parameters significantly. In 20-cm soil layer, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), MBC/MBN, MBC to soil organic carbon ratio (MBC/SOC), and soil basal respiration tended to increase with successional stages but decrease with soil depths. In contrast, metabolic quotient (qCO2) tended to decrease with successional stages but increase with soil depths. In addition, the activities of urease, catalase, neutral phosphatase, β-fructofuranosidase, and carboxymethyl cellulose (CMC) enzyme increased with successional stages and soil depths. They were significantly positively correlated with microbial biomass and SOC (P < 0.05), whereas no obvious trend was observed for the polyphenoloxidase activity. The results indicated that natural vegetation succession could improve soil quality and promote ecosystem restoration, but it needed a long time under local climate conditions.  相似文献   

5.
The responses of soil microbes to global warming and nitrogen enrichment can profoundly affect terrestrial ecosystem functions and the ecosystem feedbacks to climate change. However, the interactive effect of warming and nitrogen enrichment on soil microbial community is unclear. In this study, individual and interactive effects of experimental warming and nitrogen addition on the soil microbial community were investigated in a long-term field experiment in a temperate steppe of northern China. The field experiment started in 2006 and soils were sampled in 2010 and analyzed for phospholipid fatty acids to characterize the soil microbial communities. Some soil chemical properties were also determined. Five-year experimental warming significantly increased soil total microbial biomass and the proportion of Gram-negative bacteria in the soils. Long-term nitrogen addition decreased soil microbial biomass at the 0-10 cm soil depth and the relative abundance of arbuscular mycorrhizal fungi in the soils. Little interactive effect on soil microbes was detected when experimental warming and nitrogen addition were combined. Soil microbial biomass positively correlated with soil total C and N, but basically did not relate to the soil C/N ratio and pH. Our results suggest that future global warming or nitrogen enrichment may significantly change the soil microbial communities in the temperate steppes in northern China.  相似文献   

6.
不同肥力水平和利用历史的红壤磷脂脂肪酸图谱   总被引：4，自引：0，他引：4  
Analysis of phospholipid fatty acids(PLFAs) was used to estimate the microbial community structures of eight Chinese red soils with different fertility levels and land use histories.The total amounts of PLFAs in the soils were significantly correltaed with soil organic carbon, total nitrogen,microbial biomass C and basal respiration,indicating that total PLFA was closely related to fertility and sustainbility in these highly weathered soils.Soils of the eroded wastelan were rich in Gram-positive species .When the eroded soils were planted with citrus trees,the soil microbial population had changed little in 4 years but took up to 8-12 yearss before it reached a significantly different population,Multivariate analysis of PLFAs demonstrated that land use history and plant cover type had a significant impact on microbial community structure.Howver,the difference of soil microbial community structure in the paddy field compared to other land uses was not larger than expected in this experiment.  相似文献   

7.
Soil microbial biomass and community structures are commonly used as indicators for soil quality and fertility. A investigation was performed to study the effects of long-term natural restoration, cropping, and bare fallow managements on the soil microbial biomass and bacterial community structures in depths of 0--10, 20--30, and 40--50 cm in a black soil (Mollisol). Microbial biomass was estimated from chloroform fumigation-extraction, and bacterial community structures were determined by analysis of 16S rDNA using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Experimental results showed that microbial biomass significantly declined with soil depth in the managements of restoration and cropping, but not in the bare fallow. DGGE profiles indicated that the band number in top 0--10 cm soils was less than that in depth of 20--30 or 40--50 cm. These suggested that the microbial population was high but the bacterial community structure was simple in the topsoil. Cluster and principle component analysis based on DGGE banding patterns showed that the bacterial community structure was affected by soil depth more primarily than by managements, and the succession of bacterial community as increase of soil depth has a similar tendency in the three managements. Fourteen predominating DGGE bands were excised and sequenced, in which 6 bands were identified as the taxa of Verrucomicrobia, 2 bands as Actinobacteria, 2 bands as α-Proteobacteria, and the other 4 bands as δ-Proteobacteria, Acidobacteria, Nitrospira, and unclassified bacteria. In addition, the sequences of 11 DGGE bands were closely related to uncultured bacteria. Thus, the bacterial community structure in black soil was stable, and the predominating bacterial groups were uncultured.  相似文献   

8.
Alpine grasslands with a high soil organic carbon(SOC)storage on the Tibetan Plateau are experiencing rapid climate warming and anthropogenic nitrogen(N)deposition;this is expected to substantially increase the soil N availability,which may impact carbon(C)cycling.However,little is known regarding how N enrichment influences soil microbial communities and functions relative to C cycling in this region.We conducted a 4-year field experiment on an alpine grassland to evaluate the effects of four different rates of N addition(0,25,50,and 100 kg N ha^-1 year^-1)on the abundance and community structure(phospholipid fatty acids,PLFAs)of microbes,enzyme activities,and community level physiological profiles(CLPP)in soil.We found that N addition increased the microbial biomass C(MBC)and N(MBN),along with an increased abundance of bacterial PLFAs,especially Gram-negative bacterial PLFAs,with a decreasing ratio of Gram-positive to Gram-negative bacteria.The N addition also stimulated the growth of fungi,especially arbuscular mycorrhizal fungi,reducing the ratio of fungi to bacteria.Microbial functional diversity and activity of enzymes involved in C cycling(β-1,4-glucosidase and phenol oxidase)and N cycling(β-1,4-N-acetyl-glucosaminidase and leucine aminopeptidase)increased after N addition,resulting in a loss of SOC.A meta-analysis showed that the soil C/N ratio was a key factor in the response of oxidase activity to N amendment,suggesting that the responses of soil microbial functions,which are linked to C turnover relative to N input,primarily depended upon the soil C/N ratio.Overall,our findings highlight that N addition has a positive influence on microbial communities and their associated functions,which may reduce soil C storage in alpine grasslands under global change scenarios.  相似文献   

9.
The effects of fertilization on activity and composition of soil microbial community depend on nutrient and water availability;however,the combination of these factors on the response of microorganisms was seldom studied.This study investigated the responses of soil microbial community and enzyme activities to changes in moisture along a gradient of soil fertility formed within a long-term(24 years)field experiment.Soils(0–20 cm)were sampled from the plots under four fertilizer treatments:i)unfertilized control(CK),ii)organic manure(M),iii)nitrogen,phosphorus,and potassium fertilizers(NPK),and iv)NPK plus M(NPK+M).The soils were incubated at three moisture levels:constant submergence,five submerging-draining cycles(S-D cycles),and constant moisture content at 40%water-holding capacity(low moisture).Compared with CK,fertilization increased soil organic carbon(SOC) by 30.1%–36.3%,total N by 27.3%–38.4%,available N by 35.9%–56.4%,available P by 61.4%–440.9%,and total P by 28.6%–102.9%.Soil fertility buffered the negative effects of moisture on enzyme activities and microbial community composition.Enzyme activities decreased in response to submergence and S-D cycles versus low moisture.Compared with low moisture,S-D cycles increased total phospholipid fatty acids(PLFAs)and actinomycete,fungal,and bacterial PLFAs.The increased level of PLFAs in the unfertilized soil after five S-D cycles was greater than that in the fertilized soil.Variations in soil microbial properties responding to moisture separated CK from the long-term fertilization treatments.The coefficients of variation of microbial properties were negatively correlated with SOC,total P,and available N.Soils with higher fertility maintained the original microbial properties more stable in response to changes in moisture compared to low-fertility soil.  相似文献   

10.
印度热带森林干旱扰动土壤的微生物碳, 氮, 磷的研究   总被引：1，自引：0，他引：1  
Variations in microbial biomass C (MB-C),N (MB-N) and P (MB-P) along a gradient of different dominant vegeta- tion covers (natural forest,mixed deciduous forest,disturbed savanna and grassland ecosystems) in dry tropical soils of Vindhyan Plateau,India were studied from January 2005 to December 2005.The water holding capacity,organic C,total N,total P and soil moisture content were comparatively higher in forest soils than in the savanna and grassland sites.Across different study sites the mean annual MB-C,MB-N and MB-P at 0-15 cm soil depth varied from 312.05 ± 4.22 to 653.40 ± 3.17,32.16 ± 6.25 to 75.66 ± 7.21 and 18.94 ± 2.94 to 30.83 ± 23.08 μg g ?1 dry soil,respectively.At all the investigated sites,the maximum MB-C,MB-N and MB-P occurred during the dry period (summer season) and the minimum in wet period (rainy season).In the present study,soil MB-C,MB-N and MB-P were higher at the forest sites compared to savanna and grassland sites.The differences in MB-C,MB-N and MB-P were significant (P 0.001) among sites and seasons.The MB-C (P 0.0001),MB-N (P 0.001) and MB-P (P 0.0001) were positively correlated with organic C,while the relationship between soil moisture and MB-C,MB-N and MB-P (P 0.001,P 0.01 and P 0.0001,respectively) was negative.The decreasing order of MB-C,MB-N and MB-P along study ecosystems was natural forest mixed deciduous forest savanna grassland.The results suggested that deforestation and land use practices (conversion of forest into savanna and grassland) caused the alterations in soil properties,which as a consequence,led to reduction in soil nutrients and MB-C,MB-N and MB-P in the soil of disturbed sites (grassland and savanna) compared to undisturbed forest ecosystems.  相似文献   

11.
Loss of soil organic matter under cropping systems is often considered one of the most serious forms of agriculturally induced soil degradation. Therefore, understanding how to improve or maintain soil fertility is of importance for sustainable systems of agriculture. This study deals with the effects of succession fallow and fertilization combined with crop rotation on the chemical properties and microbial biomass of soil in the central Loess Plateau, China. In order to create a more uniform experimental environment and avoid the influence of different crop residues, wheat/potato (W/P) rotation was selected as a fertilization treatment. The results showed that with increasing fallow time organic carbon (Corg) and total nitrogen (TN) slightly increased, microbial biomass carbon (MBC) and MBC/Corg gradually decreased, and microbial biomass nitrogen (MBN) remained unchanged. However, only MBC/Corg among all the microbial parameters measured showed significant differences at various stages of fallow. Although there was a decrease in organic carbon and total nitrogen in the fertilized plots, MBC was not significantly different in the various fallow and fertilized plots except for one‐year‐old fallows, which had the highest MBC. MBN, MBC/Corg and MBN/TN in fertilized plots were higher than for plots at different stages of fallow. Fertilization can increase organic carbon, total nitrogen, MBC and MBN content (compared to the control). It was concluded that appropriate land management, such as fertilization combined with crop rotation and reducing one‐year‐old fallow, would be useful ways to improve or maintain soil fertility. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

12.
Soil microbial communities are very sensitive to changes in land use and are often used as indicators of soil fertility. We evaluated the microbial communities in the soils of four types of vegetation (cropland (CP), natural grassland (NG), broadleaf forest (BF) and coniferous forest (CF)) at depths of 0–10 and 10–20 cm on the Loess Plateau in China using phospholipid fatty acid (PLFA) profiling and denaturing gradient gel electrophoresis (DGGE) of DNA amplicons from polymerase chain reactions. The soil microbial communities were affected more by vegetation type than by soil depth. Total organic carbon, total nitrogen, soil-water content, pH, bulk density (BD) and C:N ratio were all significantly associated with the composition of the communities. Total PLFA, bacterial PLFA and fungal PLFA were significantly higher in the BF than the CP. The DGGE analyses showed that NG had the most diverse bacterial and fungal communities. These results confirmed the significant effect of vegetation type on soil microbial communities. BFs and natural grass were better than the CFs for the restoration of vegetation on the Loess Plateau.  相似文献   

13.
Soil carbon (C) and nitrogen (N) are important for maintaining soil fertility, and they are considerably affected by soil use and management. In the present study, we conducted an 8-year ?eld experiment on loessial dryland soil (Eum-Orthic Anthrosol, Food and Agriculture Organization of the United Nations (FAO)) in the southern Loess Plateau, China. We tested four soil management regimes—i.e., winter wheat (Triticum aestivum L.) cultivation with phosphorus (P) fertilization (WP), winter wheat cultivation with N and P fertilization (WNP), natural fallow (NF) and bare fallow (BF)—to evaluate their effects on soil C and N fractions. After 8 years, compared with the WNP treatment, the total soil organic nitrogen (SON) in the WP treatment decreased by 14.6% and 36.8%, and microbial biomass nitrogen (MBN) by 35.6% and 61.1%, at 0–20 and 20–40 cm soil depths, respectively. The soil heavy fraction nitrogen (HFN) and light fraction nitrogen (LFN) in the WP treatment also decreased by 36.6% and 39.4%, respectively. Furthermore, BF treatment decreased total soil organic carbon (SOC), heavy fraction carbon (HFC), LFN and MBN at both soil depths with average reductions of 43.4%. The NF treatment decreased light fraction carbon (LFC) by 17.0% at 0–20 cm soil depth, as well as MBN by 24.8% and 71.2%, and inorganic C by 29.1% and 23.8%, at 0–20 and 20–40 cm soil depths, respectively. There was no significant difference of microbial biomass C concentration among the WP, NF and BF treatments. These results confirmed that a lack of N fertilization decreased SON, BF reduced both SOC and SON, and NF decreased soil inorganic C. Therefore, the managements of a recommended rate of N fertilizer application and shortened time of bare fallow are critical for maintaining or increasing SON fraction sequestration, and natural fallow management is not a useful method for maintaining soil fertility in dryland in the Loess Plateau in China.

Abbreviations: HFC: heavy fraction carbon; HFN: heavy fraction nitrogen; LFC: light fraction carbon; LFN: light fraction nitrogen; MBC: microbial biomass carbon; MBN: microbial biomass nitrogen; SOC: soil organic carbon; SON: soil organic nitrogen  相似文献   

14.
Soil erosion is the main process leading to soil degradation on the Loess Plateau of China. The effects of soil‐erosion intensity (sheet, rill, and gully erosion) and different land use (140 y–old secondary forest site, 16 y–old bare site, 6 y–old succession site, and 43 y–old arable site) on gross and net N mineralization, soil organic‐carbon (SOC) turnover, the size and structure of the soil microbial community (phospholipid fatty acid analysis) were assessed. Erosion intensity in the bare plot increased from top slope (sheet erosion) to down slope (gully erosion). The more severe the soil erosion the stronger was the decline of SOC, total N, and microbial biomass (MB). The MBC/SOC ratio decreased whereas the metabolic quotient (qCO2) increased. Differences in nutrient turnover in the different erosion zones of the bare plot were not significant. The microbial community changed towards less Gram negative bacteria and relative more fungi in the gully‐erosion zone. In forest soils, qCO2 and the MBC/SOC ratio demonstrate a higher substrate‐use efficiency of the microbial biomass than in bare soils. Gross N mineralization and gross NH consumption clearly indicated a higher microbial activity in forest than in bare soils. Arable land use shifted the soil microbial community towards a higher relative abundance of fungi and a lower one of actinomycetes. During 6 y of natural succession on former bare plots, soil nutrient content and turnover as well as microbial biomass and structure developed towards forest conditions.  相似文献   

15.
以渭北黄土高原苹果园土壤为研究对象,设置传统苹果（Malus domestica Borkh.）园清耕及间作白三叶（Trifolium repens L.）两个处理,测定和分析了不同土层（0—5 cm,5—10 cm,10—20 cm及20—40 cm）的土壤微生物量碳（SMBC）、氮（SMBN）、4种土壤酶活性、有机碳（SOC）和全氮（TN）等指标,从土壤微生物碳、氮及酶活性的角度探讨间作白三叶对苹果/白三叶复合系统土壤的影响。结果表明:间作白三叶能够显著提高土壤微生物量碳、氮的含量和土壤酶活性,提高土壤微生物对有机碳和全氮的利用效率,其作用随着土层深度的增加而降低,在表层土壤效果更为显著。土壤微生物量碳、氮及土壤酶活性与土壤有机碳、全氮呈极显著相关或显著性相关。苹果园土壤微生物量碳、氮及土壤酶活性能敏感响应生草间作,可以作为评价果园生草对果园土壤影响的良好指标。  相似文献   

16.
长期施氮肥对黄棕壤微生物生物性状的影响及其调控因素   总被引：2，自引：0，他引：2  
基于黄棕壤小麦-甘薯轮作的长期定位试验,探究不同施氮处理土壤微生物生物量碳(MBC)、氮(MBN)含量和酶活性的变化及其潜在调控因子,为科学施氮提高土壤质量和改善土壤生态功能提供依据。试验选取始于2011年4个施氮处理:不施肥(CK)、不施氮肥(PK)、施化学氮肥(NPK)和化学氮肥配施有机肥(NPKM),调查两季作物收获后土壤MBC和MBN含量、酶活性及微生物碳氮利用效率的变化,并通过冗余分析(RDA)和结构方程模型(SEM)明确调控弱酸性黄棕壤中MBC和MBN变化的潜在因素。小麦和甘薯两季的结果表明:施氮肥降低了土壤MBC、MBN含量和蔗糖酶(SSC)、脲酶(SUE)活性,与NPK处理相比, NPKM处理增加了MBC、MBN含量和SSC、SUE活性。长期施用氮肥提高了土壤有机碳(SOC)和土壤养分[全氮(TN)和矿质态氮(MN)]含量,但施氮肥显著降低土壤p H以及微生物的碳氮利用效率。与小麦季相比,甘薯季土壤SOC和MN含量有所下降,而MBN含量和SSC活性有所升高。RDA和SEM结果表明,氮肥的施用强化了MBC与MBN、SSC与MBC以及SUE与MBC之间的关联性;不同施氮处理下土壤p H、有机碳、氮含量以及微生物的碳氮利用效率的变化直接或间接地影响土壤MBC、MBN含量和SSC、SUE活性,其中p H是调控土壤MBC变化的直接因素,而土壤SSC和SUE活性与MBC、MBN含量相互影响。长期施用氮肥降低了黄棕壤MBC、MBN含量和酶活性,化学氮肥配施有机肥有利于缓解生物性状的下降,土壤p H是影响MBC变化的主要因素,小麦-甘薯轮作中土壤微生物强烈的碳代谢过程利于增加MBN。  相似文献   

17.
有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮   总被引：27，自引：6，他引：27  
土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。  相似文献   

18.
The leguminous cover crops Atylosia scarabaeoides (L.) Benth., Centrosema pubescens Benth., and Pueraria phaseoloides (Roxb.) Benth., were grown in the interspaces of a 19 y–old coconut plantation and incorporated into the soil at the end of the monsoon season every year. At the end of the 12th year, soils from different depths were collected and analyzed for various microbial indices and their interrelationships. The objectives were to assess the effects of long‐term cover cropping on microbial biomass and microbial‐community structure successively down the soil profile. In general, total N (TN), organic C (OC), inorganic N, extractable P, and the levels of biological substrates viz., dissolved organic C (DOC) and N (DON), labile organic N (LON), and light‐fraction organic matter (LFOM) C and N decreased with depth at all the sites. Among sites, the cover‐cropped (CC) sites possessed significantly greater levels of TN, OC, DOC, DON, and LON compared to the control. Consequently, microbial biomass C (MBC), N (MBN), and P (MBP), CO2 evolution, and ATP levels, in general, decreased with depth at all sites and were also significantly higher in the CC sites. Among the ratios of various microbial indices, the ratio of MBC to OC and metabolic quotient (qCO2) declined with depth. Higher MBC‐to‐OC ratios and large qCO2 levels in the surface soils could be ascribed to greater levels of readily degradable C content and indicated short turnover times of the microbial biomass. In contrast, the ratios of MBC to MBN and MBC to MBP increased with depth due to low N/P availability and relatively higher C availability in the subsoils. Cover cropping tended to enhance the ratios of MBC to OC, MBC to MBN, MBC to MBP, and ergosterol to MBC and decreased the ATP‐to‐MBC ratio at all depths. The relatively lower ATP‐to‐MBC ratios in the CC site, especially in the subsoil indicated microbial‐community structure possibly dominated by fungi. By converting the ergosterol content to fungal biomass, it was observed that fungi constituted 52%–63% of total biomass C at the CC site, but only 33%–40% of total biomass C at the control site. Overall, the study indicated that leguminous cover crops like P. phaseoloides or A. scarabaeoides significantly enhanced the levels of OC, N and microbial activity in the soils, even down to 50 cm soil depth.  相似文献   

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