黄淮地区部分土壤中几丁质降解微生物及土壤几丁质酶活性

分析了采自黄淮部分地区２６个土样口的几丁质降解微生物的数量，种类和土壤几丁质酶活性，这些土壤中普遍存在大量的几丁质降解微生物，并可检测出几丁质酶活性，几丁质酶应是土壤累积的酶的一种，属于水解酶类。     

山冈单胞菌ZL261几丁质酶基因的克隆及原核表达

分离自西藏色季拉山海拔4 530 m高山草甸土壤的山冈单胞菌(Collimonas pratensis)ZL261具有很高的几丁质酶活性,为了明确其几丁质酶种类及作用特点,依据已报道的食真菌山冈单胞菌(Collimonas fungivorans)Ter331胞外内切几丁质酶基因chiI相关序列设计引物,利用分段扩增的方法得到了菌株ZL261几丁质酶基因,并对其序列和编码蛋白的氨基酸进行分析。结果表明,全长1 338 bp的chiIQ基因编码的几丁质酶ChiIQ由445个氨基酸组成,分子量为46.04 kDa,等电点为5.67。序列比对和同源性分析发现,该基因与食真菌山冈单胞菌Ter331几丁质酶基因chiI序列相似性最高(92%),其氨基酸序列含有几丁质酶GH18家族高度保守序列SXGG和GXDXDXE,因此,ChiIQ属GH18家族。利用双酶切法构建了ZL261几丁质酶基因原核表达载体,并在大肠杆菌BL21中成功诱导表达。本试验结果为后期研究几丁质酶在山冈单胞菌生防应用中的功能以及生防菌ZL261的开发和应用奠定了基础。     

生物信息学在几丁质酶研究中的应用

几丁质酶在防治病原真菌,抵御农业害虫,参与共生固氮及植物的生长调控等方面都有重要作用。几丁质酶种类较多,在大小、三维结构、理化性质和酶学性质等方面差异较大,因而,采用生物信息学方法快速有效地分析几丁质酶是十分有必要的。对将生物信息学应用到新型几丁质酶基因的发现、几丁质酶的结构分析、几丁质酶的后基因组分析以及在几丁质酶分析中出现的问题等几方面进行了综述。     

昆虫几丁质酶的分类、功能分析、重组表达及酶学性质的研究进展

昆虫几丁质酶及其类似蛋白在昆虫生长和发育阶段起到重要调节作用。最近几年,运用新的生物技术对昆虫几丁质酶的结构,时空表达,和组织特异性表达以及生物学功能进行了深入研究,取得了许多新的成果。本文就昆虫几丁质酶基因的结构特征,几丁质酶生理功能、重组表达特点、酶活测定方法及影响酶活性因素等方面进行讨论与综述。     

北京低山区栓皮栎林和油松林土壤酶活性研究

为探讨不同林分对土壤有机质分解过程的影响,以北京低山区栓皮栎林、油松林以及栓皮栎油松混交林土壤为研究对象,基于目前国际通用的土壤酶测试方法,对与土壤有机碳、氮和磷转化相关的酶活性及土壤pH、有机碳、有机氮等影响因素进行了研究.结果表明:在0～5cm土层中,栓皮栎林土壤纤维二糖酶、α-葡萄糖苷酶、β-葡萄糖苷酶、蛋白酶、脲酶的活性显著高于油松林,而油松林土壤过氧化物酶和磷酸酶的活性则显著高于混交林和栓皮栎林;在5～10cm土层中,除土壤脲酶外,不同林分类型的土壤酶活性无显著差异.相关分析表明,土壤pH与过氧化物酶和磷酸酶的活性呈显著性负相关,而土壤纤维二糖酶、α-葡萄糖苷酶、β-葡萄糖苷酶、酚氧化酶、几丁质酶、蛋白酶、脲酶的活性与土壤有机碳、溶解性有机碳、土壤全氮以及溶解性有机氮含量之间存在极显著或显著的正相关关系.研究认为,栓皮栎林与油松林的混交,有利于土壤酶活性以及有机物质分解过程的调节.     

沙化对高寒草地土壤碳、氮、酶活性及细菌多样性的影响

高寒草地沙化是青藏高原生态安全的严峻威胁,研究沙化过程中土壤碳氮和微生物变化有助于揭示驱动高寒草地沙化演替的生物学机制。以川西北沙化高寒草地为研究对象,分析了未沙化、轻度沙化、中度沙化和重度沙化程度下土壤碳氮、酶活性以及细菌多样性的变化。结果表明:中度和重度沙化显著降低了土壤有机碳、溶解性有机碳、微生物量碳、全氮、可溶解性总氮、可溶解性有机氮、微生物量氮、硝态氮和铵态氮含量(P0.05),但轻度沙化下的土壤有机碳、微生物量碳、硝态氮和铵态氮含量没有显著变化;土壤β-葡萄糖苷酶、蔗糖酶、几丁质酶、脲酶和过氧化物酶活性通常随沙化的加剧而降低,下降速率最大的阶段出现在轻度沙化向中度沙化过渡的阶段;土壤细菌多样性随着沙化的加剧先增加后降低,最高细菌多样性出现在轻度沙化阶段,但不同沙化程度下土壤细菌群落结构并无显著差异。冗余分析表明,土壤碳、氮、酶活性与细菌多样性呈正相关关系;主成分分析表明,土壤有机碳、微生物量氮、过氧化物酶和几丁质酶对土壤优势菌的影响最大。因此,在轻度沙化阶段及时采取治理措施更能有效阻止土壤性质的恶化,在沙化土壤恢复过程中还需要关注少数菌群的重建作用。     

种植转双价抗真菌基因水稻对根际微生物群落及酶活性的影响

对转几丁质酶和葡聚糖酶双价抗真菌基因抗病水稻七转39种植后的根际土壤微生物群落和酶活性进行了分析。研究结果表明,七转39根内生真菌和细菌数量显著低于非转基因阴性对照七丝软粘和常规水稻竹籼B,根际土壤中真菌和细菌数量也少于七丝软粘,与竹籼B数量接近。在水稻抽穗期测定,转基因水稻根际土壤过氧化氢酶、多酚氧化酶、蔗糖酶和脲酶活性以及可溶性有机质、氮、磷含量均与对照无显著差异。转基因水稻残体腐解过程中土壤腐殖酸含量变化与七丝软粘一致。与对照相比, 种植七转39未对下茬水稻的生长产生显著影响。     

硅对水稻几丁质酶和β-1,3-葡聚糖酶活性的影响及其与抗纹枯病的关系

在溶液培养条件下,以水稻抗病品种91SP和感病品种Lemont为材料,研究施硅和接种纹枯病菌对水稻纹枯病发生情况、外切几丁质酶、内切几丁质酶和β-1,3-葡聚糖酶活性的影响。结果表明,施硅能降低抗病品种91SP的纹枯病病级和病情指数,显著降低感病品种Lemont的病级和病情指数。在未接种纹枯病菌条件下,施硅增加了抗病品种几丁质酶活性,增加了感病品种的几丁质酶活性,但对β-1,3-葡聚糖酶活性影响不大。接种纹枯病菌后,水稻几丁质酶活性被迅速激活后又下降,施硅通过提高抗病品种91SP几丁质酶和β-1,3-葡聚糖酶活性,以及通过提高感病品种Lemont几丁质酶活性来增强对纹枯病的抗性,但感病品种Lemont施硅处理的几丁质酶活性降低幅度小于抗病品种91SP。     

微生物几丁质酶的分子生物学研究及其应用*

几丁质酶是广泛存在于植物、真菌以及细菌等生物体内的一种分解几丁质的蛋白质。综述重点介绍了微生物几丁质酶基因克隆、功能分析以及将几丁质酶作为生物靶标进行杀虫和抗病的应用前景。     

长期无机有机肥配施对红壤性水稻土微生物群落多样性及酶活性的影响

【目的】长期有机与无机肥配合施用是促进农田生产力和土壤有机碳固定的重要技术途径。本文以江西省红壤研究所长期不同施肥试验田的表土(0—15 cm)为对象,探讨不同施肥措施对土壤微生物群落多样性和酶活性的影响。【方法】在水稻收获后,采集表土壤样品,提取土壤总DNA。采用聚合酶链反应结合变性梯度凝胶电泳(PCR-DGGE)的方法研究土壤微生物的群落结构多样性,并结合克隆测序研究土壤微生物的群落组成;用实时荧光定量PCR(q PCR)的方法研究土壤微生物的丰度。土壤细菌定量和群落结构分析的分子标靶基因分别为16S rRNA基因V3区和V6区片段,土壤真菌定量和群落结构分析的标靶基因均为18S rRNA基因。DGGE分析采用8%的聚丙烯酰胺凝胶分离细菌和真菌,所用变性梯度分别为35%65%和20%40%。同时采用荧光微孔板检测技术测定土壤几丁质酶、α-葡萄糖苷酶、β-葡萄糖苷酶、纤维素酶、酸性磷酸单脂酶和木聚糖酶活性;用紫外分光光度计法测定土壤过氧化物酶活性。【结果】PCR-DGGE分析表明,与不施肥对照(CK)相比,有机无机肥配施(NPKM),土壤细菌的香农指数和丰富度指数显著增大,而土壤真菌的香农指数和丰富度指数在不同施肥处理间无显著差异。DGGE图谱聚类分析显示,NPKM处理的土壤细菌和真菌的群落结构显著区别于其他3个处理。后续的切胶测序得出,土壤细菌分属于Chloroflexi(绿弯菌门),Proteobacteria(变形菌门)和Firmicutes(厚壁菌门);NPKM处理下隶属于Clostridum(梭菌属)和Anaerolineaceae(厌氧绳菌科)的两类细菌显著增加。土壤真菌主要分属于Basidiomycota(担子菌门)和Ascomycota(子囊菌门),这些真菌条带在DGGE图谱上的分布不同处理间均无明显的规律性,因而不同处理间真菌的群落分布未出现较清晰的变化。q PCR的结果显示,土壤细菌和真菌拷贝数在不同处理间无显著差异。土壤酶的检测结果表明,与CK相比,单施氮肥(N)处理的土壤几丁质酶活性显著提高,常规氮磷钾处理(NPK)处理的几丁质酶和α-葡萄糖苷酶活性显著增强,NPKM处理提高了土壤几丁质酶、纤维素酶和过氧化物酶活性;酸性磷酸单酯酶和木聚糖酶活性在各处理间无显著差异。归一化酶活性值,NPKM处理显著高于CK和其他施肥处理。【结论】长期有机无机肥配施可显著提高土壤细菌多样性,并改变土壤细菌和真菌的群落结构,提高土壤酶活性,因而提高了农田生态系统的生产力并对生态系统健康有改善作用。     

Do general spatial relationships for microbial biomass and soil enzyme activities exist in temperate grassland soils?

In heterogeneous environments such as soil it is imperative to understand the spatial relationships between microbial communities, microbial functioning and microbial habitats in order to predict microbial services in managed grasslands. Grassland land-use intensity has been shown to affect the spatial distribution of soil microorganisms, but so far it is unknown whether this is transferable from one geographic region to another. This study evaluated the spatial distribution of soil microbial biomass and enzyme activities involved in C-, N- and P-cycling, together with physico-chemical soil properties in 18 grassland sites differing in their land-use intensity in two geographic regions: the Hainich National Park in the middle of Germany and the Swabian Alb in south-west Germany. Enzyme activities associated with the C- and N-cycles, namely β-glucosidase, xylosidase and chitinase, organic carbon (C_org), total nitrogen (N_t), extractable organic carbon, and mineral nitrogen (N_min) were higher in the Swabian Alb (Leptosols) than in the Hainich National Park (primarily Stagnosols). There was a negative relationship between bulk density and soil properties such as microbial biomass (C_mic, N_mic), urease, C_org, and N_t. The drivers (local abiotic soil properties, spatial separation) of the enzyme profiles (β-glucosidase, chitinase, xylosidase, phosphatase, and urease) were determined through a spatial analysis of the within site variation of enzyme profiles and abiotic properties, using the Procrustes rotation test. The test revealed that physical and chemical properties showed more spatial pattern than the enzyme profiles. β-glucosidase, chitinase, xylosidase, phosphatase, and urease activities were related to local abiotic soil properties, but showed little spatial correlation. Semivariogram modeling revealed that the ranges of spatial autocorrelation of all measured variables were site specific and not related to region or to land-use intensity. Nevertheless, land-use intensity changed the occurrence of spatial patterns measurable at the plot scale: increasing land-use intensity led to an increase in detectable spatial patterns for abiotic soil properties on Leptosols. The conclusion of this study is that microbial biomass and functions in grassland soils do not follow general spatial distribution patterns, but that the spatial distribution is site-specific and mainly related to the abiotic properties of the soils.     

不同土地利用和施肥方式对土壤酶活性及相关肥力因子的影响

以中国科学院海伦农业生态实验站长期定位试验为平台,研究了不同土地利用和施肥方式对土壤酶活性和相关肥力因子的影响,结果表明,种植苜蓿和土地休闲两种方式与裸地相比脲酶、转化酶、磷酸酶、过氧化氢酶活性、土壤全碳、全氮含量和碱解氮、速效磷、速效钾含量均显著增加。其中,脲酶活性增加了24.5%和25.0%,转化酶活性增加了18.4%和18.9%,磷酸酶活性增加了54.6%和50.4%,过氧化氢酶活性增加了8.52%和59.3%,土壤全碳、全氮含量分别增加了13.8%、13.0%和36.8%、33.7%,但苜蓿和休闲两种方式间无显著差异。不同施肥方式相比,土壤酶活性、土壤全碳、全氮含量及土壤养分含量相差显著,其高低顺序为:NPKOM （氮磷钾肥＋有机肥）＞NPKST （氮磷钾肥＋秸秆）＞NPK（氮磷钾肥）＞CK （无肥）;施肥,特别是有机肥,显著提高了土壤酶活性,使土壤全碳、全氮、有效养分含量显著增加。表明黑土经自然恢复和人工恢复及施肥后土壤肥力提高,土壤质量得到改善。     

不同施肥模式对设施秋冬茬芹菜生育期间土壤酶活性的影响

【目的】利用在天津的日光温室蔬菜不同施肥模式定位试验,研究了不同施肥模式对设施菜田土壤酶活性的影响,为设施蔬菜高效施肥和菜田土壤可持续利用提供依据。【方法】取样调查在第9茬蔬菜(秋冬茬芹菜)进行。定位试验设6个处理,在等氮磷钾条件下,分别为1)全部施用化肥氮(4/4CN),2)3/4化肥氮+1/4猪粪氮(3/4CN+1/4PN),3)2/4化肥氮+2/4猪粪氮(2/4CN+2/4PN),4)1/4化肥氮+3/4猪粪氮(1/4CN+3/4PN),5)2/4化肥氮+1/4猪粪氮+1/4秸秆氮(2/4CN+1/4PN+1/4SN),6)2/4化肥氮+2/4秸秆氮(2/4CN+2/4SN)。在芹菜基肥施用前和定植后30、60、90、110天,采取0—20 cm土壤样品,测定土壤α-葡萄苷酶、β-木糖苷酶、β-葡萄苷酶、β-纤维二糖苷酶、几丁质酶、磷酸酶和脲酶的活性,分析其与土壤微生物量碳氮及土壤可溶性有机碳氮含量之间的关系。【结果】芹菜生育期间不同施肥模式土壤α-葡萄苷酶、β-木糖苷酶、β-葡萄苷酶、β-纤维二糖苷酶、几丁质酶和磷酸酶的活性总体上先增后降,较高土壤酶活性均出现在芹菜定植后60~90 d; 土壤脲酶活性总体上呈逐渐升高的趋势。芹菜季有机无机肥料配施模式土壤α-葡萄苷酶、β-木糖苷酶、β-葡萄苷酶、β-纤维二糖苷酶、几丁质酶、磷酸酶和脲酶的活性较4/4CN模式平均分别增加22.9%~92.0%、20.1%~152.4%、23.1%~145.1%、28.7%~273.8%、9.2%~207.8%、13.7%~86.8%和6.5%~56.5%,其中以配施秸秆模式土壤酶活性相对较高,较4/4CN模式平均分别增加59.9%~92.0%、98.9%~152.4%、90.3%~145.1%、171.6%~273.8%、106.4%~207.8%、68.8%~86.8%和30.7%~56.5%。土壤酶活性与土壤微生物量碳氮、可溶性有机碳氮含量及芹菜产量之间总体上呈显著或极显著正相关关系。【结论】同等养分投入量下,设施菜田土壤酶活性表现为有机无机肥料配合显著高于单施化肥,又以配施秸秆效果更佳; 土壤酶活性与土壤微生物量碳氮、可溶性有机碳氮含量和蔬菜产量之间密切相关。说明有机无机肥配施,特别是配施一定的秸秆可有效提高土壤酶活性,维持较高的菜田土壤肥力,有利于设施蔬菜的可持续和高效生产。     

Induction of systemic resistance in rice against sheath blight disease by Pseudomonas fluorescens

Two Pseudomonas fluorescens strains viz., PF1 and FP7 which inhibited the mycelial growth of sheath blight fungus Rhizoctonia solani and increased the seedling vigour of rice plants in vitro were selected for assessing induced systemic resistance (ISR) against R. solani in rice. The Pseudomonas application as a bacterial suspension or a talc-based formulation through seed, root, soil and foliar application either alone or in combination (seed+root+soil+foliar) effectively reduced sheath blight disease incidence, promoted plant growth and ultimately increased yields under glasshouse or field conditions. Efficacy of Pseudomonas strains against R. solani was comparable to that of the fungicide carbendazim, which is normally used in the field to manage the disease. Pseudomonas treatment of rice cv IR50 led to induction of systemic resistance against R. solani, as a result of increase in chitinase and peroxidase activity. However, the extent of increase varied between treatments, Pseudomonas strains used and their duration. Though two chitinase isoforms (35 and 28 kDa) and five peroxidase isozymes (PO1–PO5) were found to be associated with the ISR, 35 kDa chitinase and three peroxidase isozymes (PO3–PO5) were established as the major determinants of ISR. Although a single application of a Pseudomonas strain resulted in ISR, the combined application through all of the four (seed, root, soil and foliar) methods increased the durability of ISR in rice plants. In addition, the Pseudomonas strains produced chitinase in the culture medium. It is presumed that the induced chitinase, peroxidase and bacterial chitinase may be either directly or indirectly involved in the reduction of sheath blight disease development in rice.     

Soil fungi influence the distribution of microbial functional groups that mediate forest greenhouse gas emissions

The distribution of microbial functional groups in soil may be governed by the interaction between the soil environment and the presence of other microbial competitors or facilitators. In forest soils, one of the most important groups of organisms are fungi, which are vital to many ecosystem processes such as nutrient cycling and decomposition, and can form direct connections to primary producers. Nevertheless, the overall effect of soil fungi on the structure and distribution of the other soil microbial functional groups has not been thoroughly investigated. We hypothesized that by altering the soil environment, fungi create favorable conditions for Archaea, methane oxidizing bacteria (MOB) and denitrifying bacteria (DNB), thereby potentially influencing the ability of forest soils to produce or consume greenhouse gases. To test these hypotheses, we studied the distribution of microbial functional groups and fungi in forest soil using molecular methods and related that distribution to soil environment and extracellular enzyme activity as a measure of microbial activity and metabolic effort. Non-metric multidimensional scaling of terminal restriction fragment length (TRFLP) profiles found that DNB and MOB largely separated within ordination space, suggesting little overlap of these bacteria in soil cores. In addition, DNB were significantly positively correlated with fungal biomass and with chitinase activity while MOB were negatively correlated with both. Most archaeal TRFs were also negatively correlated with fungal biomass, suggesting that forest Archaea and MOB have similar relationships to fungal biomass. Soil chemistry including soil carbon (C), nitrogen (N) and bicarbonate extractable phosphorus (P) were not significantly correlated with DNB, MOB or Archaea. Our results suggest that soil fungi might influence the spatial distribution of important prokaryotic groups in forests, including some groups that mediate the production and consumption of important greenhouse gases.     

Decomposition of leaf litter from chitinase transgenic silver birch (Betula pendula) and effects on decomposer populations in a field trial

Although the area under cultivation of genetically modified plants (GMPs) has substantially increased during the last decade, the effects of transgenic organisms on ecosystem processes (such as litter decomposition and nutrient cycling) largely remain unknown. In this study, the decomposition of leaf litter from transgenic birch trees (Betula pendula) expressing sugar beet chitinase IV gene was studied in a field experiment. Eight chitinase transgenic lines and a non-transgenic control were included in the study. The decomposition of these litters was investigated by studying: (i) litter mass loss, (ii) fungal (litter ergosterol content) and total microbial biomass (SIR) and their activity (basal respiration), and (iii) the effects of transgenic litter on microbial-feeding soil fauna (number of nematodes and abundance of different functional groups). At the end of the study (8 and 11 months after establishment) mass loss of chitinase transgenic leaf litter did not differ from that of non-transgenic control trees. Similarly, no differences in either the fungal or total microbial biomass between the treatments were recorded. A single transgenic line showing high chitinase IV expression differed significantly from the controls in the mean number of nematodes. The nematode populations in this litter showed distinct temporal dynamics compared to the controls, thus indirectly indicating microbial differences in the litter. The results of this study indicate that conceivable changes, possibly derived from pleiotropic effects due to gene modification, in the litter quality due to gene transformation are either absent or too weak to affect the decomposability of the litter in the soil.     

Monoterpenes and higher terpenes may inhibit enzyme activities in boreal forest soil

Plant secondary compounds, including terpenes, potentially play an important role in controlling the decomposition process in boreal forest soil. However, the role of terpenes is not well understood, and their direct influence on enzyme activity is not well-known. The aim of this study was to examine the possible effects of common monoterpenes and higher terpenes on the activity of enzymes crucial in C, N, P, S cycling, i.e. β-glucosidase, chitinase, protease, acid phosphatase and arylsulfatase. Monoterpenes (α-pinene, carene, myrcene), diterpenes (abietic acid and colophony), and triterpene (β-sitosterol) were used. Studies were done in two environments, in vitro (studies without soil) and in vivo (studies with soil). Soil experiments were conducted using humus layers of two different birch stands, the first N-poor with high organic matter content and the second N-rich with a lower organic matter content. In general, all the terpenes studied showed inhibitory potential against enzymes in in vitro studies. In the soil incubation studies, both of the measured enzymes, chitinase and β-glucosidase, showed some decrease in activity when exposed to different terpenes. Our study suggests that terpenes modify the enzyme machinery in boreal forest soil.     

Actinobacteria-enhanced plant growth, nutrient acquisition, and crop protection: Advances in soil, plant, and microbial multifactorial interactions

Agricultural areas of land are deteriorating every day owing to population increase, rapid urbanization, and industrialization. To feed today’s huge populations, increased crop production is required from smaller areas, which warrants the continuous application of high doses of inorganic fertilizers to agricultural land. These cause damage to soil health and, therefore, nutrient imbalance conditions in arable soils. Under these conditions, the benefits of microbial inoculants (such as Actinobacteria) as replacements for harmful chemicals and promoting ecofriendly sustainable farming practices have been made clear through recent technological advances. There are multifunctional traits involved in the production of different types of bioactive compounds responsible for plant growth promotion, and the biocontrol of phytopathogens has reduced the use of chemical fertilizers and pesticides. There are some well-known groups of nitrogen-fixing Actinobacteria, such as Frankia, which undergo mutualism with plants and offer enhanced symbiotic trade-offs.In addition to nitrogen fixation, increasing availability of major plant nutrients in soil due to the solubilization of immobilized forms of phosphorus and potassium compounds, production of phytohormones, such as indole-3-acetic acid, indole-3-pyruvic acid, gibberellins, and cytokinins, improving organic matter decomposition by releasing cellulases, xylanase, glucanases, lipases, and proteases, and suppression of soil-borne pathogens by the production of siderophores, ammonia, hydrogen cyanide, and chitinase are important features of Actinobacteria useful for combating biotic and abiotic stresses in plants.The positive influence of Actinobacteria on soil fertility and plant health has motivated us to compile this review of important findings associated with sustaining plant productivity in the long run.     

秸秆与地膜覆盖条件下旱作玉米田土壤氮组分生长季动态

研究不同覆盖措施下农田土壤全氮及其活性和半活性组分在作物生长季的动态变化,有助于深入理解农田土壤氮循环过程。基于黄土高原8年春玉米覆盖定位试验,系统分析了土壤全氮、矿质氮、微生物量氮、潜在可矿化氮以及颗粒有机氮在玉米不同生育期的动态特征。试验包括全生育期9 000kg/hm2秸秆覆盖、全生育期地膜覆盖和不覆盖对照3个处理。结果表明:(1)除硝态氮和铵态氮在苗期上升外,秸秆和地膜覆盖下土壤全氮及其组分含量在春玉米生育期基本呈苗期下降、拔节期上升、大喇叭口—抽雄期下降、灌浆和收获期回升的变化趋势;(2)与对照相比,秸秆覆盖提高了大多数生育时期0—40cm土层全氮和硝态氮含量及0—20cm土层铵态氮含量,提高各生育时期0—40cm土层微生物量氮、潜在可矿化氮以及颗粒有机氮含量;(3)地膜覆盖较对照提高大多数生育时期0—40cm土层硝态氮和0—20cm土层铵态氮含量,降低作物生育后期0—20cm土层全氮和0—40cm土层颗粒有机氮含量,降低大多数时期0—40cm土层微生物量氮和10—20cm土层潜在可矿化氮含量;(4)除了地膜覆盖下20—40cm土层颗粒有机氮相对含量在作物不同生育期差异不显著外,秸秆和地膜覆盖下0—40cm土层微生物量氮、潜在可矿化氮、颗粒有机氮对土壤全氮的动态均有重要贡献。总之,黄土高原的春玉米田秸秆覆盖具有明显的提升土壤全氮及其组分含量的作用,有助于培肥地力和土壤固氮;地膜覆盖则降低了作物生育后期土壤全氮及其组分含量,同时显著提高了土壤硝态氮水平,导致农田土壤氮素淋溶风险提高。     

Soil enzyme activity in an old-growth northern hardwood forest: Interactions between soil environment,ectomycorrhizal fungi and plant distribution

Plants and soil microbes produce extracellular enzymes (EE) that catalyze the hydrolysis of nitrogen (N) and phosphorus (P) containing compounds in soil and other enzymes involved in degradation of lignin and cellulose. We explored whether soil enzyme activity involved in carbon (C), N and P cycling were correlated with plant distribution, soil chemical conditions and the identity of fungi colonizing tree roots in an old growth forest remnant. Terminal restriction fragment length polymorphism (TRFLP) was used to determine the presence of root fungi and standard fluorometric analysis was used to determine soil enzyme activities. Soil enzymes were consistently positively correlated with soil C and N, but not CN ratio. Soil P was also correlated with enzyme activity during both June and September sampling. We saw no significant relationships between herbaceous plant cover and enzyme activity in June, but there were significant positive correlations between α-glucosidase and herbaceous plant coverage in September. We also found that some enzymes were significantly correlated with the identity of fungi colonizing tree roots separated from the soil cores. Chitinase and β-glucosidase were positively correlated with the genera Russula and Piloderma while chitinase was negatively correlated with Amanita and Entoloma. In addition, phosphatase was positively correlated with Russula, Meliniomyces and Solenopezia. Our results suggest that enzyme activity in old growth forest soils are affected by a variety of environmental factors, and that herbaceous plants and some root fungi may be associated with sites of elevated or decreased decomposition potential and nutrient cycling.