Effect of cadmium contamination with sewage sludge and phosphate fertiliser amendments on soil enzyme activities, microbial structure and available cadmium

The effect of Cd pollution (50 mg kg^-1), with and without sewage sludge (Sw) and PO₄^3- fertiliser (P) addition, on soil biochemical activity and available Cd was assessed in a 112-day soil incubation experiment. The availability of Cd decreased with incubation time and was reduced by the Sw and P additions resulting in the following order of treatments: Cd>P+Cd>Sw+Cd. With the exception of urease and N-acetylglucosaminidase activities, all enzyme activities were negatively correlated with available Cd. The total culturable bacterial population was significantly higher with the addition of Sw alone than in the control during the incubation period (P<0.05). The number of fluorescent pseudomonads decreased with time, but was significantly increased by the addition of Sw. The total fungal populations decreased with time in all treatments, whilst the addition of Sw and PO₄^3- fertilisers relatively increased the fungal population. Addition of Sw in the presence of Cd increased the fungal populations in relation to the addition of Cd alone. The results support the view that Cd contamination has a large detrimental effect on nutrient cycling and microbial activity and that the effects of Cd are reduced by P and Sw additions.     

Soil compaction and forest floor removal reduced microbial biomass and enzyme activities in a boreal aspen forest soil

Soil enzymes are linked to microbial functions and nutrient cycling in forest ecosystems and are considered sensitive to soil disturbances. We investigated the effects of severe soil compaction and whole-tree harvesting plus forest floor removal (referred to as FFR below, compared with stem-only harvesting) on available N, microbial biomass C (MBC), microbial biomass N (MBN), and microbial biomass P (MBP), and dehydrogenase, protease, and phosphatase activities in the forest floor and 0–10 cm mineral soil in a boreal aspen (Populus tremuloides Michx.) forest soil near Dawson Creek, British Columbia, Canada. In the forest floor, no soil compaction effects were observed for any of the soil microbial or enzyme activity parameters measured. In the mineral soil, compaction reduced available N, MBP, and acid phosphatase by 53, 47, and 48%, respectively, when forest floor was intact, and protease and alkaline phosphatase activities by 28 and 27%, respectively, regardless of FFR. Forest floor removal reduced available P, MBC, MBN, and protease and alkaline phosphatase activities by 38, 46, 49, 25, and 45%, respectively, regardless of soil compaction, and available N, MBP, and acid phosphatase activity by 52, 50, and 39%, respectively, in the noncompacted soil. Neither soil compaction nor FFR affected dehydrogenase activities. Reductions in microbial biomass and protease and phosphatase activities after compaction and FFR likely led to the reduced N and P availabilities in the soil. Our results indicate that microbial biomass and enzyme activities were sensitive to soil compaction and FFR and that such disturbances had negative consequences for forest soil N and P cycling and fertility.     

The use of a microbial contact toxicity test for evaluating cadmium bioavailability in soil

Background, Aims and Scope

Bioavailability of toxic compounds in soil can be defined as the fraction able to come into contact with biota and to cause toxic effects. The contact toxicity tests may detect the total toxic response of all bioavailable contaminants present in a sample. The objectives of this study were to evaluate the use of microbial contact toxicity tests for cadmium bioavailability assessment and to evaluate the relationship between sorption, soil characteristics and cadmium bioavailability.

Methods

A test soil bacterium,Bacillus cereus, was put in direct contact with the solid sample. Four unpolluted soils were selected to provide solid samples with a variety of physicochemical characteristics. The toxicity and sorption behaviour of cadmium spiked to the soil samples were determined.

Results, Discussion and Conclusions

A significant correlation between contact toxicity test results and partitioning of cadmium in the soil samples (r²= 0.79, p <0.05; n = 26) was found. The results confirm that the bioavailability of cadmium in soil depends on its sorption behaviour. Cadmium sorbed to the cation exchange sites associated with fulvic acids is non-bioavailable in the toxicity test employed in this study. It is concluded that the microbial contact toxicity test is a suitable tool for detecting cadmium bioavailablity in the soils used in this study.

Outlook

The application of microbial contact toxicity tests for bioavailability assessment can be very useful for the risk identification and remediation of soil-associated contaminants.     

Potential soil enzyme activities are decoupled from microbial activity in dry residue-amended soil

Extracellular enzymes play an important role in the microbial acquisition of carbon (C) and organically bound nutrients, such as nitrogen (N). The objective of the present study was to investigate the effect of different soil moisture contents on potential soil enzyme activities (β-glucosidase and protease), microbial biomass and activity. Soil incubations were carried out with gravimetric moisture contents (GMC) ranging from 0.8 (air-dry) to 30%. After 14 days, respiration, net N mineralization and potential enzyme activities were lowest at GMC below 10% in the unamended samples. In the residue-amended soil, however, respiration and net N mineralization were highest at GMC of 20% or more, while potential β-glucosidase and protease activity were highest at GMC of 10% or less. Increasing the moisture content of air-dry soil after 14 days of incubation resulted in significantly reduced β-glucosidase activity, but increased protease activity. With the exception of the high potential β-glucosidase activity in the residue-amended dry soil, enzyme activities were well correlated with microbial biomass and ergosterol, a biomarker for fungal biomass. Therefore, our results suggest that across the different GMC, protease activity was mainly dependent on the continuous production by microorganisms, while β-glucosidase accumulated in the dry soil due to an increased half-life, which was the result of interactions with soil colloids. Shifts in microbial community composition may also have contributed to the observed differences.     

长期不同施肥条件下土壤微生物量及 土壤酶活性的季节变化特征

研究长期不同施肥条件下褐潮土微生物量碳（SMBC）、微生物量氮（SMBN）和土壤酶活性随季节的变化特征。结果表明,长期施肥条件下土壤SMBC、SMBN含量及土壤酶活性均表现出一定的季节变化。SMBC、SMBN含量在各施肥处理中的顺序为:化肥与猪厩肥配施处理（NPKM）化肥配施玉米秸秆处理（NPKS）单施化肥处理（NPK）不施肥处理（CK）,各处理之间差异显著(P0.05);施肥还显著提高了土壤脲酶、转化酶、碱性磷酸酶活性,有机无机配施的高于单施化肥的。除过氧化氢酶活性随季节变化显著下降外,SMBC、SMBN、酶活性的值一般在夏季（6月到8月）较高。通过双因素单变量方差分析表明,不同施肥制度与季节变化对SMBC、SMBN与酶活性的影响分别达极显著水平（P0.01）,不同施肥制度的SMBC、SMBN与酶活性的季节波动有极显著不同（P0.01）。     

菌肥对混播牧草土壤酶活性及微生物的影响

为研究菌肥与混播对土壤酶活性及微生物生物量的影响,本试验以苜蓿和饲用高粱为研究对象,设8个处理,分别为苜蓿单播(N1)、饲用高粱单播(N2)、苜蓿与饲用高粱同行混播(N3)、苜蓿与饲用高粱间行混播(N4)以及分别施入微生物菌肥(T1、T2、T3与T4)。在饲草生长的苗期、旺盛期与收获期分别取0～20、20～40和40～60 cm土样并测定土壤脲酶、蔗糖酶、过氧化氢酶活性以及微生物生物量碳、氮含量。结果表明:菌肥及混播各处理土壤酶活性及微生物生物量均显著高于未施菌肥及饲草单播各处理,且混播配施菌肥效果更优。土壤酶活性随土层深入逐渐降低,随生育期推进,过氧化氢酶和蔗糖酶活性呈现先降低后升高趋势;土壤脲酶活性呈现先升后降趋势,微生物生物量碳、氮的规律与脲酶相同。混播配施菌肥有利于增加有益酶活性,提高土壤微生物生物量,增强土壤生产力的可持续性,从而达到保护和改善土壤环境的效果,为内蒙古地区马铃薯提供倒茬作物,提供充足饲草,对农业与畜牧业发展意义重大。     

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20 mg Cd kg⁻¹), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.     

蚯蚓粪与鼠李糖脂配施对小白菜和生菜产量、生长指标及品质的影响

为了探明蚯蚓粪配施鼠李糖脂对小白菜及生菜品质的影响,基于盆栽试验,研究了蚯蚓粪及其与鼠李糖脂（0.027%、0.054%和0.108%）配施处理对小白菜和生菜产量、生长指标和品质指标的影响。结果表明,蚯蚓粪与鼠李糖脂配施可以不同程度地提高小白菜及生菜品质,相比不施肥处理蚯蚓粪配施鼠李糖脂处理小白菜及生菜的产量、叶面积、可溶性糖、可溶性蛋白和可滴定酸均显著提高。蚯蚓粪配施鼠李糖脂处理小白菜和生菜产量、可溶性糖、可溶性蛋白、可滴定酸及硝酸盐含量与蚯蚓粪处理无显著性差异。随着鼠李糖脂浓度的增大,蚯蚓粪配施鼠李糖脂处理的小白菜产量呈现下降趋势,未达到显著性差异。蚯蚓粪配施鼠李糖脂相比蚯蚓粪处理可显著提高小白菜游离氨基酸含量。综上,蚯蚓粪配施鼠李糖脂具有显著提高蔬菜产量的效果,蚯蚓粪配施鼠李糖脂与蚯蚓粪处理对蔬菜产量及品质方面的影响没有显著性差异,二者配施没有降低蚯蚓粪的肥效,说明蚯蚓粪与鼠李糖脂配施具有药肥开发的可行性。     

生物质炭及过氧化钙对旱地红壤酶活性和微生物群落结构的影响

明确生物质炭等改良剂对土壤酶活性及土壤微生物群落结构的影响,对南方红壤旱地改良剂的合理施用及评价不同改良剂对旱地红壤肥力的影响具有重要意义。针对江西旱地红壤进行室内培养试验,试验设置4个处理,即CK、Ca(过氧化钙,1.72 g/kg)、C(生物质炭,21.46 g/kg)、C+Ca(过氧化钙,1.72 g/kg;生物质炭,21.46 g/kg),利用磷脂脂肪酸方法(PLFA),研究改良剂对土壤微生物量和组成以及土壤酶活性、土壤活性有机碳的影响。结果表明:旱地红壤中添加生物质炭和过氧化钙土壤提高可溶性有机碳(DOC)和微生物量碳(MBC)含量;增加蔗糖酶(INV)、淀粉酶(AMY)及脲酶(URE)活性,特别是配施(C+Ca)显著提高土壤活性碳含量及酶活性。PLFA分析表明,土壤微生物总PLFAs量的大小顺序为:C+CaCCaCK;各处理土壤细菌的相对丰度最大,大约占微生物总含量的80%,放线菌次之,大约占微生物总含量的13%～15%,而真菌和丛枝菌根真菌的相对丰度较低。生物质炭和过氧化钙增加了革兰氏阴性菌(GN)/革兰氏阳性菌(GP)值,尤以C+Ca处理增加幅度最大。主成分分析(PCA)表明,添加生物质炭和过氧化钙能够改善土壤微生物群落结构;计算主成分的综合得分,配施(C+Ca)处理的综合得分最高,对土壤微生物群落结构的影响最大。冗余分析(RDA)表明,土壤MBC、DOC和土壤INV酶活性是影响土壤微生物数量和结构的主要因子。因此,施用生物质炭和过氧化钙能够明显提高旱地红壤微生物生物量,改变红壤微生物群落结构以及激发红壤酶活性,且配施效果最显著。     

Inoculation of Pseudomonas sp. GHD-4 and mushroom residue carrier increased the soil enzyme activities and microbial community diversity in Pb-contaminated soils

Journal of Soils and Sediments - To remedy the heavy metal polluted soils, microbe-assisted phytoextraction was employed to remove Pb from soils. The Pb contents, soil enzyme activities, and...     

红壤丘陵区人工林恢复措施对土壤酶活性和微生物学性质的影响

我国红壤丘陵区水土流失较严重。本文研究人工林对土壤(0～20和20～40 cm)酶活性和微生物学性质的短期(13～14年)影响。土壤转化酶、脲酶、多酚氧化酶活性在次生天然林和湿地松樟树混交林中高于其他林分。次生天然林和湿地松樟树混交林土壤微生物生物量和土壤呼吸值较大、有机碳活性较强、土壤微生物基质利用效率较高。因此,短期影响下,湿地松樟树混交林较之针叶纯林和针叶混交林可改善土壤生化强度和微生物活性。     

湿地土壤质量退化的模糊综合评价

Due to frequent soil Cd contamination and wide use of butachlor in China,there is a need to assess their combined toxicity to soil microorganisms.The combined effects of cadmium (Cd,10 mg kg^-1 soil) and herbicide butachlor (10,50,and 100 mg kg^-1 soil) on enzyme activities and microbial community structure in a paddy soil were assessed using the traditional enzyme assays and random amplified polymorphic DNA (RAPD) analysis.The results showed that urease and phosphatase activities were significantly reduced by high butachlor concentration (100 mg kg^-1 soil).When the concentrations of Cd and butachlor added were at a ratio of 1:10,urease and phosphatase activities were significantly decreased whereas enzyme activities were greatly improved at the ratio of 1:5,which indicated that the combined effects of Cd and butachlor on soil urease and phosphatase activities depended largely on their addition concentration ratios.Random amplified polymorphic DNA (RAPD) analysis showed loss of original bands and appearance of new bands when compared with the control soil.Random amplified polymorphic DNA fingerprints suggested substantial differences between the control and treated soil samples,with apparent changes in the number and size of amplified DNA fragments.The addition of high concentration butachlor and the combined impacts of Cd and butachlor significantly affected the diversity of the microbial community.RAPD analysis in conjunction with other biomarkers such as soil enzyme parameters would prove a powerful ecotoxicological tool.Further investigations should be carried out to understand the clear link between RAPD patterns and enzyme activity.     

不同种植时间菜园土壤微生物生物量和酶活性变化特征

土壤生物学指标能够反映土壤质量在各种自然和人为作用下的微小变化,是敏感的土壤质量指标。本文以太湖地区高强度开发为背景,研究了不同利用年限的菜园土壤微生物生物量C和酶活性的变化特征。研究结果表明,菜园土壤随着利用年限的不断增加,土壤养分逐渐升高,土壤脲酶活性、土壤微生物生物量C与土壤有机质、全N、全P之间具有良好的线性关系,土壤纤维素酶活性随菜地利用时间增加有上升的趋势,它们能较好地区别不同利用年限的菜地土壤,可以作为敏感的土壤生物学指标。但土壤转化酶活性与土壤养分的变化没有明显的相关性。     

Micro-scale distribution of microorganisms and microbial enzyme activities in a soil with long-term organic amendment

Microbial ecology is the key to understanding the function of biodiversity for organic matter cycling in the soil. We have investigated the impacts of farmyard manure added over 120 years on organic matter content, enzyme activities, total microbial biomass and structure of microbial populations in several particle‐size fractions of a Luvic Phaeozem a few kilometres northeast of Halle, Germany. We compared two treatments: no fertilization (control) and 12 t farmyard manure (FYM) ha^?1 year^?1 since 1878. The fine fractions contained most C and N, microbial biomass, total amount of phospholipid fatty acids (PLFAs) and greatest invertase activity. Xylanase activity as well as fungal biomass increased only gradually with diminishing particle size, whereas the relative abundance of fungi decreased with diminishing particle size. The least diversity of the soil microbial community, indicated by the smallest Shannon index based on the abundance and amount of different PLFAs and small number of terminal restriction fragments (T‐RFs) of 16S rRNA genes, was in the sand fractions. The results supported the hypothesis that this microhabitat is colonized by a less complex bacterial community than the silt and clay fractions. Addition of FYM had enhanced the amount of organic matter, total microbial biomass, and xylanase and invertase activity, and induced a shift of the microbial community towards a more bacteria‐dominated community in the coarse sand fraction. Microbial communities in finer fractions were less affected by addition of FYM.     

Evaluation of soil enzyme activities and microbial communities in tomato continuous cropping soil treated with jerusalem artichoke residues

ABSTRACT

Jerusalem artichoke (JY) (Helianthus tuberosus L.) has been reported to have a strong inhibitory effect on weed growth and root knot nematodes, but little information is available on the effects on soil ecosystems, especially soil microorganisms and soil enzyme activities. Understanding the dynamics of soil microbes and soil enzyme activities in cropping systems can help determine how agricultural practices influence soil processes mediated by JY residues. This study used a pot experiment, with five-year continuous cropping soil of tomato plants as the experimental material and 2% (w/w) JY residue as the treatment material in the soil. The treatment was compared to continuously monocropped tomato soil that was not treated with JY residues. The results of 16S high-throughput sequencing showed that both fungal and bacterial community structure and composition varied significantly at each stage of JY treatment. The analysis showed that the major phyla in the soil fungal community included Ascomycota, Zygomycota and Basidiomycota. Chytridiomycota was dominant in only the JY-treated soil. At the genus level, the abundances of Mortierella, Cephaliophora, Cryptococcus and Fusarium notably changed at each stage of JY treatment. In the bacterial community in the JY-treated group, the abundance of Proteobacteria increased significantly, while that of Firmicutes decreased significantly, compared to the control group. JY enhanced the activity of soil sucrase and urease. In addition, the soil sucrase activity showed a strong negative correlation with Fusarium and Bacillus. Overall, our results revealed that JY residues changed both the soil bacterial and fungal community composition and the soil enzyme activities.     

小分子有机物对土壤酶活性及微生物多样性的影响

目前对小分子有机物的研究主要集中在叶面肥方面,较少在土壤肥料的应用方面,而对土壤酶活性以及微生物功能多样性的研究就更少。以分别添加葡萄糖、甘油以及甘氨酸的土壤(25℃培养)为试材,采用酶活性(每15 d取样)测定方法与Biolog-Eco板技术(取培养45 d的土样),研究小分子有机物对土壤微生物及酶活性的影响。结果表明,3种小分子有机物处理土壤的4种酶活性在15～75 d内,变化规律基本一致;在45 d时葡萄糖处理土壤的过氧化氢酶活性显著高于清水对照(CK)、甘油以及甘氨酸,而碱性磷酸酶活性显著低于其它处理。与CK、葡萄糖以及甘氨酸相比,甘油处理土壤微生物平均吸光度值和功能多样性指标(除指数D外)显著提高,而CK、葡萄糖以及甘氨酸处理之间没有显著性差异。葡萄糖、甘油以及甘氨酸处理改变了土壤的微生物功能多样性以及碳源利用比分,其中甘氨酸和葡萄糖处理土壤胺类利用百分比(AM)几乎为零。土壤微生物多样性与酶活性冗余分析表明,碱性磷酸酶与微生物功能多样性指数S、U、H′、碳水化合物利用百分比以及AM呈显著正相关,相关系数分别为0.588、0.669、0.616、0.678及0.603,与指数D及蔗糖酶活性呈显著负相关,相关系数分别为-0.737和-0.741。由此可知,不同种类小分子有机添加物对土壤酶活性以及微生物功能多样性影响不一,其中甘油显著提高了土壤微生物代谢活性以及多样性指数(除指数D外),而土壤酶活性与微生物功能多样性的主成分分析表明甘氨酸与另外两种小分子有机物存在明显差别。     

黄顶菊入侵对土壤微生物、土壤酶活性及土壤养分的影响

通过采样分析,研究了外来植物黄顶菊入侵对非耕地和耕地,以及对玉米根系土壤微生物、土壤酶活性、土壤速效养分的影响,旨在揭示黄顶菊入侵农田和贫瘠荒地的机制。本试验比较了距根系不同距离土壤的微生态变化;分析了根系土壤3大微生物类群结构、5种土壤理化性质以及5种土壤酶活性之间的相关性。结果表明,非耕地黄顶菊根表速效氮、速效磷、速效钾的含量分别为对照的4.44、6.88、2.64倍,耕地中分别为对照的5.31、13.78、7.56倍;非耕地黄顶菊根表土壤细菌、真菌、放线菌数量分别为对照的13.23、6.67、21.40倍,耕地中分别为对照的9.27、2.15、2.24倍,可见黄顶菊对非耕地土壤中可培养的细菌、真菌、放线菌数量的影响更为明显;非耕地中黄顶菊根表土壤碱性磷酸酶、酸性磷酸酶、脲酶、脱氢酶、蔗糖酶的活性分别为对照的19.44、5.39、1.64、1.74、4.62倍,说明细菌非常活跃。耕地中分别为对照的2.26、3.45、1.53、0.95、4.89倍。另外在玉米与黄顶菊互作时,其根表土壤速效氮、磷、钾分别为非互作条件下的63.54%、64.70%、80.71%、,黄顶菊入侵明显降低了玉米根表速效养分。综上,黄顶菊入侵增加了其根系周围可培养土壤微生物数量、土壤酶活性及土壤速效养分含量;降低了附近玉米根表土壤中可培养微生物数量、土壤酶活性和速效养分含量。     

Response of microbial activity and microbial community composition in soils to long-term arsenic and cadmium exposure

Arsenic (As) and cadmium (Cd) in soils can affect soil microbial function and community composition and, therefore, may have effects on soil ecosystem functioning. The aim of our study was to assess the effects of long-term As and Cd contamination on soil microbial community composition and soil enzyme activities. We analyzed soils that have been contaminated 25 years ago and at present still show enhanced levels of either As, 18 and 39 mg kg⁻¹, or Cd, 34 and 134 mg kg⁻¹. Soil without heavy metal addition served as control. Polymerase chain reaction (PCR) followed by denaturing gradient gel electrophoresis (DGGE) showed that bacterial community composition in As and Cd contaminated soils differed from that in the control soil. The same was true for the microbial community composition assessed by analysis of respiratory quinones. Soil fungi and Proteobacteria appeared to be tolerant towards As and Cd, while other groups of bacteria were reduced. The decline in alkaline phosphatase, arylsulphatase, protease and urease activities in the As- and Cd-contaminated soils was correlated with a decrease of respiratory quinones occuring in Actinobacteria and Firmicutes. Xylanase activity was unaffected or elevated in the contaminated soils which was correlated with a higher abundance of fungal quinones, and quinones found in Proteobacteria.     

Spatial variation of soil enzyme activities and microbial functional diversity in temperate alley cropping systems

Spatially dependent patterns in microbial properties may exist in temperate alley cropping systems due to differences in litter quality and microclimate in areas under trees compared to those in the alleys. The effect of tree row location was evaluated for its impact on soil enzyme activities and Biolog substrate use patterns. Soils were sampled to a depth of 30 cm at the tree row and at the middle of the alley at two sites: a 21-year-old pecan (Carya illinoinensis)/bluegrass (Poa trivials) intercrop (Pecan site) and a 12-year-old silver maple (Acer saccharinum)/soybean (Glycine max)–maize (Zea mays) rotation (Maple site). Sampling was done in fall 2001 and summer 2002. β-Glucosidase activities, Biolog patterns expressed as average well color (AWC), substrate richness, and Shannon diversity index, and total Kjeldahl nitrogen (TKN) were significantly higher (P<0.05) in the tree row than at the middle of the alley for surface soils at the Pecan site. Fluorescein diacetate (FDA) hydrolytic activity was also higher at the tree row for soils sampled in the fall, but did not differ significantly for soils sampled in the summer. At the Maple site, AWC and substrate richness were significantly higher at the tree row for soils sampled in 2001. Soil volumetric water content and temperature were generally lower in the tree row at the Maple site. The results of this study suggest that functionally different microbial populations may be present under pecan trees compared to cropped alleys which may promote disparities in nutrient availability necessitating differential long-term nutrient management in such alley cropping systems.