Chemical quality impacts of tropical forest tree leaf litters on the growth and fecundity of soil Collembola

The growth performances of a soil microarthropod, Cyphoderus javanus Börner (Collembola: Hexapoda), were tested in microcosms on leaf litter of different tropical forest trees to compare their nutritional quality to detritivores. The macronutrient profile was more or less similar between the litter types, but the quantities of non-nutrients like polyphenols, tannins and lignins were notably higher in the litter of Acacia auriculiformis and Shorea robusta trees than in the litter of Cassia siamea and Dalbergia sissoo trees. A choice experiment showed persistently higher colonisation of Collembola on litter of Cassia and Dalbergia, which differed significantly from a trend of lower occurrence in Acacia and Shorea. The nutritional benefit of the litter types was compared by measuring levels of tissue carbohydrates, proteins and lipids in C. javanus. Analysis of data by t test showed that animals reared on Cassia and Dalbergia litters contained statistically significant higher concentrations of tissue carbohydrates and proteins than those fed on Acacia. But the differences with the animals fed on Shorea were not significant. In contrast, C. javanus registered significantly low levels of tissue lipids in Cassia and Dalbergia litters when compared to animals reared on Acacia and Shorea litters. The 2-way RM-ANOVA test revealed highly significant main effect of time intervals for tissue carbohydrates and proteins and highly significant main effect of litter types for tissue lipids. Benefits derived from litter quality on growth were seen from enhanced fecundity and higher rate of moulting of C. javanus reared on Dalbergia followed by Cassia, Acacia and Shorea in descending order. The higher reproductive rate on Dalbergia and Cassia probably resulted in decreased level of tissue lipids in animals. Growth parameters, namely tissue nutrients, fecundity and moulting were influenced by the chemical constituents of different litter types, and these qualities are potential indicators of the nutritional quality of litter to detritivores, and the ecological suitability of tree species for enhancing the biological activity in soil system.     

Soil enzyme activities in dependence on tree litter and season of a social forest,Burdwan, India

The study was done to evaluate enzyme activities (amylase, cellulase and invertase) from the soils of different vegetation sites, with seasonal variation, of social forest, Burdwan, India. Study results showed significant lower enzymatic activities in the subsoil compared to those of the topsoil. The seasonal variations indicated that amylase, cellulase and invertase enzyme activities had reached peaks during the rainy seasons in different soil depths. Amylase activity was highest in Tectona litter containing soil in all seasons in both the soil layers. All the three enzyme activities have shown significant positive correlation with available nitrogen (p < 0.05) and available phosphorous (p < 0.05) during rainy season in both the soil depths. Correlation study revealed that soil organic carbon was positively correlated with cellulase and invertase activities except in the Anacardium vegetation site in the topsoil during rainy season. Irrespective of the seasons and the depths of soil, control site without vegetation showed much lower levels of organic carbon and enzyme activity compared to those of the experimental sites. Therefore, it is concluded that carbon transformation will be higher during rainy season in the vegetation sites of forest soil under such agroclimatic conditions.     

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.     

Microbial function in adjacent subtropical forest and agricultural soil

Soil microbial communities and their activities are altered by land use change; however impacts and extent of these alterations are often unclear. We investigated the functional responses of soil microbes in agricultural soil under sugarcane and corresponding native soil under Eucalyptus forest to additions of contrasting plant litter derived from soybean, sugarcane and Eucalyptus in a microcosm system, using a suite of complimentary techniques including enzyme assays and community level physiological profiles (CLPP). Initially agricultural soil had 50% less microbial biomass and lower enzyme activities than forest soil, but significantly higher nitrification rates. In response to litter addition, microbial biomass increased up to 11-fold in agricultural soil, but only 1.8-fold in forest soil, suggesting a prevalence of rapidly proliferating ‘r’ and slower growing ‘K’ strategists in the respective soils. Litter-driven change in microbial biomass and activities were short lived, largely returning to pre-litter addition levels by day 150. Decomposition rates of sugarcane and soybean litter as estimated via CO₂ production were lower in agricultural than in forest soil, but decomposition of more recalcitrant Eucalyptus litter was similar in both soils, contradicting the notion that microbial communities specialise in decomposing litter of the dominant local plant species. Enzyme activities and community level physiological profiles (CLPP) were closely correlated to microbial biomass and overall CO₂ production in the agricultural soil but not the forest soil, suggesting contrasting relationships between microbial population dynamics and activity in the two soils. Activities of enzymes that break down complex biopolymers, such as protease, cellulase and phenol oxidase were similar or higher in the agricultural soil, which suggests that the production of extracellular biopolymer-degrading enzymes was not a factor limiting litter decomposition. Enzyme and CLPP analyses produced contrasting profiles of microbial activity in the two soils; however the combination of both analyses offers additional insights into the changes in microbial function and community dynamics that occur after conversion of forest to agricultural land.     

High specific activity in low microbial biomass soils across a no-till evapotranspiration gradient in Colorado

The need to identify microbial community parameters that predict microbial activity is becoming more urgent, due to the desire to manage microbial communities for ecosystem services as well as the desire to incorporate microbial community parameters within ecosystem models. In dryland agroecosystems, microbial biomass C (MBC) can be increased by adopting alternative management strategies that increase crop residue retention, nutrient reserves, improve soil structure and result in greater water retention. Changes in MBC could subsequently affect microbial activities related to decomposition, C stabilization and sequestration. We hypothesized that MBC and potential microbial activities that broadly relate to decomposition (basal and substrate-induced respiration, N mineralization, and β-glucosidase and arylsulfatase enzyme activities) would be similarly affected by no-till, dryland winter wheat rotations distributed along a potential evapotranspiration (PET) gradient in eastern Colorado. Microbial biomass was smaller in March 2004 than in November 2003 (417 vs. 231 μg g⁻¹ soil), and consistently smaller in soils from the high PET soil (191 μg g⁻¹) than in the medium and low PET soils (379 and 398 μg g⁻¹, respectively). Among treatments, MBC was largest under perennial grass (398 μg g⁻¹). Potential microbial activities did not consistently follow the same trends as MBC, and the only activities significantly correlated with MBC were β-glucosidase (r = 0.61) and substrate-induced respiration (r = 0.27). In contrast to MBC, specific microbial activities (expressed on a per MBC basis) were greatest in the high PET soils. Specific but not total activities were correlated with microbial community structure, which was determined in a previous study. High specific activity in low biomass, high PET soils may be due to higher microbial maintenance requirements, as well as to the unique microbial community structure (lower bacterial-to-fungal fatty acid ratio and lower 17:0 cy-to-16:1ω7c stress ratio) associated with these soils. In conclusion, microbial biomass should not be utilized as the sole predictor of microbial activity when comparing soils with different community structures and levels of physiological stress, due to the influence of these factors on specific activity.     

荒漠盐生植物根际土壤酶活性的变化

利用根袋法研究了荒漠盐土和灌耕灰漠土中6种不同荒漠盐生植物根际养分和酶活性特征.结果表明:两种土壤中,根际土全氮含量比非根际土高,但全磷却比非根际土低.根际土有效态养分的变化则与全态相反,6种植物的根际土有效氮含量均显著低于非根际土,除芦苇外,根际土有效磷含量均高于非根际土.6种植物中,钠猪毛菜根际土有效氮亏缺最高,有效磷富集也最少.分析测定了根际土和非根际土转化酶、蛋白酶、过氧化氢酶、脲酶、中性磷酸酶和碱性磷酸酶活性及其与土壤养分的关系.结果表明:过氧化氢酶、脲酶和蛋白酶在两种土壤的植物根际表现出相反的变化,荒漠盐土中,根际土3种酶的活性均高于非根际土;而灌耕灰漠土的根际土3种酶活性均低于非根际土.荒漠盐土碱性磷酸酶、过氧化氢酶和转化酶与几种主要养分含量有很强的相关性,较好地体现了荒漠盐土根际的养分状况,也说明盐生植物对荒漠盐土酶活性有较大的影响.     

不同耕作方式对土壤有机碳、微生物量及酶活性的影响

【目的】依托8年长期(2005~2012)固定道定位试验,研究不同耕作方式对土壤有机碳、土壤微生物量、土壤酶活性在0—90 cm土层的分布特征,为优化中国西北干旱区的耕作方式提供理论依据。【方法】试验包括固定道垄作(PRB)、固定道平作(PFT)与传统耕作(CT)三种耕作模式下的土壤有机碳土壤总有机碳(TOC)、颗粒有机碳(POC)、土壤微生物量碳(MBC)、土壤微生物量氮(MBN)、土壤微生物量磷(MBP)、蔗糖酶、过氧化氢酶、脲酶及小麦产量进行了测定和分析。【结果】在0—90 cm土层,不同耕作方式下的TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性均随着土层的增加呈下降趋势,过氧化氢酶活性呈先下降后增大的分布特征;在0—60 cm,固定道保护性耕作能够显著增加心土层作物生长带土壤有机碳储量,有机碳储量大小为PRBPFTCT;PRB、PFT较CT可以显著增加0—10 cm作物生长带TOC、POC、MBC、MBN、MBP含量、蔗糖酶、脲酶活性,其大小为PRBPFTCT;耕作方式对过氧化氢酶活性影响不显著;TOC、POC、MBC、MBN、MBP、蔗糖酶活性、脲酶活性、过氧化氢酶活性之间均达到了显著或极显著相关。【结论】PRB较PFT、CT能够提高耕作层(0—10 cm)土壤有机碳含量、土壤微生物量、土壤酶活性, 增加作物产量, 增大0—60 cm土层有机碳储量,耕作方式(PRB、PFT及CT)对10 cm以下土层土壤环境改善作用不明显。     

沙漠腹地咸水滴灌林地土壤养分、微生物量和酶活性的典型相关关系

鉴于塔里木沙漠公路防护林所处环境条件和管理模式的特殊性及在南疆社会、经济发展中的重要性,试验选择四种不同矿化度(2.58、5.75、8.90、13.99 g L-1)水滴灌的防护林地,采集0~5 cm、5~15cm、15~30 cm、30~50 cm四层土样为研究材料,主要采用典型相关分析法,对防护林地土壤养分因子、微生物量因子和酶活性因子中每两组变量间的相关性进行了分析。结果表明:三组变量土壤养分、微生物量、酶活性中,每两者之间均有显著的典型相关变量存在,而且基本能够代表变量总体相关信息;土壤养分与土壤微生物量的相关性主要由养分中的全氮、速效氮、有机质、全磷含量和土壤微生物量中的放线菌数量、微生物量碳和微生物量磷引起的;土壤养分与土壤酶活性的相关性主要由土壤有机碳、速效钾含量与土壤过氧化氢酶、磷酸酶活性的相关性引起;土壤微生物量与土壤酶活性的相关性主要由土壤微生物量磷、微生物量氮与土壤蔗糖酶、磷酸酶活性的相关性引起;滴灌水矿化度对塔里木沙漠公路防护林地土壤养分和微生物量的效应明显,高矿化度水不利于土壤养分积累和微生物生存。     

The relationships among microbial parameters and the rate of organic matter mineralization in forest soils,as influenced by forest type

Vegetation type influences the rate of accumulation and mineralization of organic matter in forest soil, mainly through its effect on soil microorganisms. We investigated the relationships among forest types and microbial biomass C (MBC), basal respiration (R_B), substrate-induced respiration (R_S), N mineralization (N_min), specific growth rate μ, microbial eco-physiology and activities of seven hydrolytic enzymes, in samples taken from 25 stands on acidic soils and one stand on limestone, covering typical types of coniferous and deciduous forests in Central Europe. Soils under deciduous trees were less acidic than soils of coniferous forests, which led to increased mineralizing activities R_B and N_min, and a higher proportion of active microbial biomass (R_S/MBC) in the Of horizon. This resulted in more extractable organic C (0.5 M K₂SO₄) in soils of deciduous forests and a higher accumulation of soil organic matter (SOM) in coniferous forest soil. No effect of forest type on the microbial properties was detected in the Oh horizon and in the 0–10 cm layer. The microbial quotient (MBC/C_org), reflecting the quality of organic matter used for microbial growth, was higher in deciduous forests in all three layers. The metabolic quotient qCO₂ (R_B/MBC) and the specific growth rate μ, estimated using respiration growth curves, did not differ in soils of both forest types. Our results showed that the quality of SOM in coniferous forests supported microorganisms with higher activities of β-glucosidase, cellobiosidase and β-xylosidase, which suggested the key importance of fungi in these soils. Processes mediated by bacteria were probably more important in deciduous forest soils with higher activities of arylsulphatase and urease. The results from the stand on limestone showed that pH had a positive effect on microbial biomass and SOM mineralization.     

东北农田黑土土壤酶活性与理化性质的关系研究

黑土是保证我国粮食安全的最重要的土壤资源之一,主要分布在我国的东北地区。为了调查我国黑土区土壤理化性状、土壤酶活性及两者间相互关系,我们从黑土区不同纬度农田采集了26个土壤样品,分析其土壤酶活性与微生物量碳（SMBC）及其它土壤理化性状的关系。结果发现,黑龙江北安黑土土壤全碳、全氮、全磷、碱解氮、SMBC、过氧化氢酶、脲酶及转化酶活性最大;简单相关分析发现,过氧化氢酶、脲酶、磷酸酶及转化酶均与土壤全氮、全碳及SMBC呈极显著正相关;通径分析表明,全氮是影响该土壤区土壤酶活性的主导因子,pH值是通过直接作用或间接作用影响过氧化氢酶活性的另一主导理化因子,全氮是脲酶活性的主导因子,碱解氮、全碳、全氮是磷酸酶活性的主导因子,全氮和pH值是影响转化酶的两大主导理化因子。     

Changes in enzyme activities and microbial biomass after “in situ” remediation of a heavy metal-contaminated soil

Microbial properties such as microbial biomass carbon (MBC), arylsulfatase, β-glucosidase and dehydrogenase activities, and microbial heterotrophic potential, together with several chemical properties such as pH, CaCl₂ soluble heavy metal concentrations, total organic carbon and hydrosoluble carbon were measured to evaluate changes in soil quality, after “in situ” remediation of a heavy metal-contaminated soil from the Aznalcóllar mine accident (Southern Spain, 1998). The experiment was carried out using containers, filled with soil from the affected area. Four organic amendments (a municipal waste compost, a biosolid compost, a leonardite and a litter) and an inorganic amendment (sugarbeet lime) were mixed with the top soil at the rate of 100 Mg ha⁻¹. Unamended soil was used as control. Agrostis stolonifera L. was sown in the containers. The soil was sampled twice: one month and six months after amendment application. In general, these amendments improved the soil chemical properties: soil pH, total organic carbon and hydrosoluble carbon increased in the amended soils, while soluble heavy metal concentrations diminished. At the same time, higher MBC, enzyme activities and maximum rate of glucose mineralization values were found in the organically amended soils. Plant cover was also important in restoring the soil chemical and microbial properties in all the soils, but mainly in those that were not amended organically. As a rule, remediation measures improved soil quality in the contaminated soils.     

A soil quality index based on the equilibrium between soil organic matter and biochemical properties of undisturbed coniferous forest soils of the Pacific Northwest

Recent studies have suggested that the organic matter contents of undisturbed soils (under natural vegetation) are in equilibrium with biological and biochemical properties. Accordingly, we hypothesised that such equilibria should be disrupted when soils are subjected to disturbance or stress, and that measurement of this disruption can be expressed mathematically and used as a soil quality index. In this study, we evaluated these hypotheses in soils from the H.J. Andrews Experimental Forest in Oregon. Both O and A horizons were sampled from nine sites in Spring 2005 and Fall 2006. Soil samples were analyzed for enzyme activities (phosphatase, β-glucosidase, laccase, N-acetyl-glucosaminidase, protease and urease), and other biological and chemical properties including N-mineralization, respiration, microbial biomass C (MBC), soil organic carbon (SOC) and total nitrogen content. In addition, soil samples from one old-growth site were manipulated in the laboratory to either simulate chemical stresses (Cu addition or pH alteration) or physical disturbances (wet-dry or freeze-thaw cycles). The results showed variation in biological and biochemical soil properties that were closely correlated with SOC. Multiple regression analysis of SOC levels against all soil properties showed that a model containing only MBC and phosphatase activity could account for 97% of the SOC variation among the sites. The model fit was independent of spatial and temporal variations because covariates such as site, stand age, sampling date, and soil horizon were found to be not statistically significant. Although the application of stress/disturbance treatments inconsistently affected most of the individual biochemical properties, in contrast, the ratio of soil C predicted by the model (C_p), and soil C measured (C_m) was consistently reduced in soils submitted to at least one level of stress and disturbance treatments. In addition, C_p/C_m was more affected in soils submitted to wet-dry cycles and Cu contamination than to freeze-thaw cycles or shifts in soil pH. Our results confirm previous evidence of a biochemical balance in high quality undisturbed soils, and that this balance is disrupted when the soil is submitted to disturbances or placed under stress conditions. The C_p/C_m ratio provides a simple reference value against which the degrading effects of pollutants or management practices on soil quality can be assessed.     

Relationships of soil respiration to microbial biomass, substrate availability and clay content

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

连续3年施用生物有机肥对土壤养分、微生物生物量及酶活性的影响

通过温室盆栽试验,研究了连续3年在不同土壤中施用不同量的生物有机肥的土壤养分、微生物生物量、酶活性及棉花各器官干物质量的变化。结果表明:连续3年施用生物有机肥,3种土壤的养分、酶活性、微生物量和各器官干物质量均有不同程度的提高。随着其用量的增加,土壤养分、微生物量及脲酶活性也在增加,土壤pH则相反,土壤蔗糖酶、多酚氧化酶、蛋白酶活性表现先上升后下降的趋势,且在不同土壤施用生物有机肥10~30 g/kg时基本达到最高,过氧化氢酶活性无显著变化。高、中、低有机质含量的土壤的棉花各器官干物质量分别在施用生物有机肥10~20、20~30、40 g/kg时基本达到最高。随着施肥年限的延长,3种土壤微生物生物量碳、氮均表现为先降低后升高的趋势,土壤酶活性则变化差异较大。通过在不同有机质含量土壤中施肥与不施肥比较发现,本底有机质含量越低的土壤,施肥较不施肥的土壤养分、脲酶、蔗糖酶、蛋白酶活性及微生物量增加幅度越大。     

紫色丘陵区土壤侵蚀对土壤生物学肥力的影响

为更好地理解侵蚀土壤质量变化,该文利用137Cs技术探讨了川中丘陵区紫色土陡坡耕地土壤侵蚀对土壤生物学肥力的影响。结果表明,与无侵蚀的坡地相比,陡坡耕地土壤微生物量碳含量及碱性磷酸酶、蔗糖酶活性分别显著降低41%、44%、17%,土壤生物学肥力退化指数MFDI达-35%。陡坡耕地土壤蔗糖酶活性与137Cs浓度显著正相关（r=0.643,p=0.024）,表明蔗糖酶活性随土壤侵蚀强度增大而降低。耕作侵蚀造成的陡坡耕地上坡土壤损失导致土壤微生物量碳含量、碱性磷酸酶、脲酶及蔗糖酶活性最低,而耕作侵蚀造成的陡坡耕地坡底土壤堆积导致这4个微生物特性最高,结果陡坡耕地这些微生物特性的空间变异分别增大2.8、0.8、1.4、4.5倍。紫色土陡坡耕地土壤生物学肥力退化与空间变异性增大在今后的土地管理中应引起关注。     

Decomposition and mineralization of energy crop residues governed by earthworms

Energy crops are increasingly cultivated in agricultural management systems world-wide. A substitution of food crops (e.g. cereals) by energy crops may generally alter the biological activity and litter decomposition in soil due to their varying structural and chemical composition and subsequently modify soil functioning. A soil microcosm experiment was performed to assess the decomposition and microbial mineralization of different energy crop residues in soil compared to a food crop, with or without earthworms. Residues of the energy crops winter rape (Brassica napus), maize (Zea mays), miscanthus (Miscanthus giganteus) and the food crop oat (Avena sativa) were each provided as food source for a mixed earthworm population, each consisting of one individual of Lumbricus terrestris, Aporrectodea caliginosa, and Octolasion tyrtaeum. After 6 weeks, the rate of litter loss from the soil surface, earthworm biomass, microbial biomass-C and -N, microbial activity, and enzyme activities were determined. The results emphasized, that litter loss and microbial parameters were predominantly promoted by earthworms and were additionally influenced by the varying structural and chemical composition of the different litter. Litter decay by earthworms was highest in N-rich maize litter treatment (C-N ratio 34.8) and lowest in the case of miscanthus litter (C-N ratio 134.4). As a consequence, the microbial biomass and basal respiration in soils with maize litter were higher, relative to other litter types. MBC-MBN ratio in soil increased when earthworms were present, indicating N competition between earthworms and microorganisms. Furthermore, enzyme activities responded in different ways on the varying types of litter and earthworm activity. Enzymes involved in the N-cycle decreased and those involved in the C-cycle tended to increase in the presence of earthworms, when litter with high C-N ratio was provided as a food source. Especially in the miscanthus treatments, less N might remain for enzymatic degradation, indicating that N competition between earthworms and microorganisms may vary between different litter types. Especially, an expansion of miscanthus in agricultural management systems might result in a reduced microbial activity and a higher N deficit for microorganisms in soil.     

北松辽平原沿纬度梯度农田土壤酶活性与微生物量分布研究

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.     

Effects of the ecological restoration practices of prescribed burning and mechanical thinning on soil microbial enzyme activities and leaf litter decomposition

The effects of ecological restoration on belowground processes such as decomposition are generally unknown. To assess the immediate effects of prescribed fire and mechanical thinning on belowground processes, we measured the activities of five extracellular enzymes (phosphatase, β-glucosidase, β-N-acetylglucosaminidase, phenol oxidase, and lignin-peroxidase) in soils and on decomposing Quercus falcata leaf litter in unburned, burned, and burned and thinned plots in a mesic forest in northern Mississippi. Decomposition rates of Q. falcata leaf litter were also assessed at each plot. Soil phosphatase activity decreased after a prescribed burn and was related to an increase in soil organic matter in plots that had been burned. Soil β-N-acetylglucosaminidase activity increased after a burn, and was related to a decrease in leaf litter. Leaf litter enzyme activity showed no consistent patterns amongst treatments, or between individual enzymes, while decomposition rates of leaf litter were slightly accelerated in the treatment plots, but not significantly so. Decomposition rates were related to cumulative enzyme activity, with phenol oxidase and lignin-peroxidase having the highest apparent efficiencies in degrading the leaf material. Overall, the microbial degradation of Q. falcata leaf litter was more efficient in plots that were burned and thinned than in the other plots. Increases in the efficiency of litter decomposition coupled with reductions in litter inputs due to canopy thinning likely allows for increased solar penetration to the soil, and could promote the restoration of the shade-intolerant species that once dominated the understory. Post-burn increases in β-N-acetylglucosaminidase activity and decreases in phosphatase activity also suggest a potential shift in the soil community from phosphorus limitation to nitrogen limitation following a fire.     

The adverse effects of soil salinization on the growth of Trifolium alexandrinum L. and associated microbial and biochemical properties in a soil from Iran

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.     

Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition

In a field study, long-term application of compost to a tropical Aeric Endoaquept under continuous rice growing in a rice-rice-fallow sequence resulted in the stimulation of microbial biomass and select soil enzyme activities. Mean seasonal soil microbial biomass-C (C_mic) increased by 42%, 39% and 89% in inorganic fertilizer, compost and compost+inorganic fertilizer treatments, respectively, over the unamended control. C_mic content was also influenced by the rice crop growth stage and was highest at maximum tillering stage irrespective of treatments and declined thereafter. Soil organic C (C_org) content showed highly significant positive correlation with dehydrogenase, urease, cellulase, β-glucosidase and fluorescein di-acetate (FDA) hydrolysis activity, and a positive but not significant correlation with invertase and amidase activity. C/N ratio which was lowest in unamended control plots showed a significant positive relationship with only the enzymes involved in C cycle. Stepwise regression analysis revealed that for prediction of both total organic C and total N, FDA hydrolysis activity contributed significantly for the variance and explained up to 85-96% variability. Results demonstrated that microbial biomass and soil enzyme activity is sensitive in discriminating between long-term organic residue amendment practices.