森林次生演替和土壤层次对微生物群落结构的影响

森林次生演替与生态系统结构和功能的动态变化密切相关。大多数研究主要关注植物群落以及土壤有机碳(SOC)的变化,然而土壤微生物群落如何响应森林次生演替还需要进一步探究。本研究以长白山森林次生演替序列(20、80、120、200和≥300年)和两个土壤层次为对象,采用磷脂脂肪酸微生物标志物,探究温带森林次生演替过程中地下微生物群落结构变化。森林次生演替改变了土壤微生物群落结构,主要归因于某些特定微生物类群的变化,演替前期革兰氏阴性菌和腐生真菌占主导,而在演替后期革兰氏阳性菌和丛枝菌根真菌占主导。另外,土壤有机质数量和质量差异是影响微生物群落结构和生物量的主要环境因素。森林演替前期和中期增加的SOC含量促进了微生物生物量,而演替后期增加的难分解芳香族有机组分抑制了微生物生物量合成。土壤层次间理化性质的差异导致微生物群落变化,有机质层高的SOC以及氮含量导致更多微生物生物量的合成。微生物群落在时间和空间尺度的变化及其驱动因素反映了生态系统结构和功能对环境变化的响应。     

小麦根系分泌物对黄瓜生长及土壤真菌群落结构的影响

以黄瓜为受体,以不同化感效应(促进/抑制)小麦品种为供体,采用PCR-DGGE技术,研究了小麦根系分泌物及伴生小麦对黄瓜生长及土壤真菌群落结构的影响.结果表明： 在处理第6天和第12天,化感促进效应小麦根系分泌物分别显著提高了黄瓜幼苗株高和茎粗;在处理第18天,化感促进和抑制效应小麦根系分泌物均显著提高了黄瓜幼苗株高;在处理第6天,不同化感效应小麦根系分泌物均显著降低了黄瓜幼苗根际土壤真菌群落条带数、Shannon指数及均匀度指数,有苗对照(W)显著高于无苗对照(Wn);在处理第18天,各处理的真菌群落结构条带数、Shannon指数及均匀度指数均显著高于无苗对照(Wn).伴生化感抑制效应小麦显著降低了黄瓜根际土壤真菌群落Shannon指数和均匀度指数,说明小麦根系分泌物及伴生小麦改变了土壤真菌群落结构.DGGE图谱及其主成分分析结果表明,伴生不同化感效应小麦对土壤真菌群落结构影响较大.     

氮添加对亚热带毛竹林土壤微生物群落结构的影响

氮沉降会影响森林生态系统地上(如植物生产力和组成)和地下特性(如土壤养分循环),进而影响土壤微生物群落结构和功能。本研究以亚热带戴云山毛竹林为对象,设置N0(0 kg N·hm^-2·a^-1)、N20(20 kg N·hm^-2·a^-1)、N80(80 kg N·hm^-2·a^-1) 3个施氮水平,进行3年的氮沉降模拟实验。通过测定土壤基本理化性质、腐殖化指数和微生物磷脂脂肪酸等指标,研究氮添加对毛竹林土壤养分、腐殖化指数和微生物群落结构的影响。结果显示,N20显著增加土壤腐殖化指数,降低土壤中碱性阳离子总量(K⁺,Na⁺,Ca²⁺,Mg²⁺)、革兰氏阳性菌(G⁺)、革兰氏阴性菌(G^-)、总磷脂脂肪酸含量和G⁺/G^-。与N20相比,N80处理土壤NO₃^-     

乙草胺和甲胺磷对农田黑土可培养真菌数量及种群结构的影响

应用传统及PCR-DGGE方法(denaturing gradient gel electrophoresis),分别对不同浓度乙草胺、甲胺磷胁迫下黑土中可培养真菌CFU(colony forming units)、种群丰富度(richness)及种群结构动态变化规律进行了研究.结果表明,在实验室微域条件下,乙草胺对黑土可培养真菌CFU的影响随处理浓度的增加而抑制作用增强,表现出由低浓度(50 mg·kg^-1)时的刺激生长到高浓度(250 mg·kg^-1)时的长期抑制效应;250 mg·kg^-1甲胺磷在8周处理过程中对土壤可培养真菌生长具有显著的刺激效应,使可培养真菌CFU比对照增加10倍,但50和150 mg·kg^-1甲胺磷处理对土壤可培养真菌CFU无显著影响.种群丰富度系数分析结果表明,高、中浓度乙草胺处理可使土壤可培养真菌种群丰富度不可逆地降低.土壤真菌rDNA特异PCR-DGGE聚类分析结果表明,不同浓度乙草胺、甲胺磷处理均不同程度地对土壤可培养真菌的种群组成和结构造成影响,其中甲胺磷尤为显著.     

降水变化驱动下红松阔叶林土壤真菌多样性的分布格局

红松阔叶林生态系统是中国东北地区地带性顶极植被,具有重要的生态学意义,长白山是研究温带森林对大气降水变化正负反馈的理想地带.本文以长白山原始红松阔叶林为研究对象,基于末端限制性片段长度多态性分析技术,分析了降水控制样地(增、减30％)和对照样地的0 ～5 cm和5～ 10 cm表层土和红松根际土真菌多样性的空间异质性.结果表明:降水的增加和减少均能提高土壤真菌的多样性,但优势种群有所变化.表层土中,片段长度超过500 bp的T-RFs丰度随降水增加而提高,根际土中对降水变化响应的T-RFs分别为380、455和487 bp,且根际土的响应模式较表层土复杂.典范对应分析结果表明,土壤pH、有机碳含量、总氮和有效磷等对真菌群落组成影响显著.     

毛竹种植对土壤细菌和真菌群落结构及多样性的影响

为揭示天然林改为毛竹林过程中土壤微生物变化规律,在浙江省湖州市安吉县和长兴县两地选择不同种植历史的粗放经营毛竹林,分层采集0～20和20～40 cm的混合土壤样品,应用PCR-DGGE技术分析土壤细菌和真菌群落结构及多样性变化.结果表明: 在马尾松林改种毛竹林或毛竹林入侵杂灌阔叶林形成毛竹纯林过程中,土壤细菌和真菌的群落结构均发生明显变化,且细菌结构对毛竹种植的响应更敏感;随着毛竹生长时间的延长,表层土壤细菌群落表现出抵抗干扰、最后向改种毛竹之前状态恢复的趋势.毛竹种植时间、样地和土层均对土壤细菌和真菌多样性产生显著影响,其中样地和土层的影响明显大于种植时间.土壤性质和细菌、真菌结构的冗余分析结果表明,不同地点、不同土层驱动土壤微生物结构随时间变化的主要因子没有一致规律,且第1、2轴对样地变化的解释率大多低于65.0%,说明除本研究分析的5个土壤化学指标外,可能还有其他土壤理化性质共同驱动微生物结构的变化.     

Effects of defoliation intensity on soil food-web properties in an experimental grassland community

We established a greenhouse experiment based on replicated mini‐ecosystems to evaluate the effects of defoliation intensity on soil food‐web properties in grasslands. Plant communities, composed of white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) with well‐established root and shoot systems, were subjected to five defoliation intensity treatments: no trimming (defoliation intensity 0, or DI 0), and trimming of all plant material to 35 cm (DI 1), 25 cm (DI 2), 15 cm (DI 3) and 10 cm (DI 4) above soil surface every second week for 14 weeks. Intensification of defoliation reduced shoot production and standing shoot and root mass of plant communities but increased their root to shoot ratio. Soil microbial activity and biomass decreased with intensification of defoliation. Concentrations of NO₃–N in soil steadily increased with intensifying defoliation, whereas NH₄–N concentrations did not vary between treatments. Numbers of microbi‐detritivorous enchytraeids, bacterial‐feeding rotifers and bacterial‐feeding nematodes steadily increased with intensifying defoliation, while the abundance of fungal‐feeding nematodes was significantly enhanced only in DI 3 and DI 4 relative to DI 0. The abundance of herbivorous nematodes per unit soil mass was lower in DI 3 and DI 4 than in DI 0, DI 1 and DI 2, but when calculated per unit root mass, their abundance tended to increase with defoliation intensity. The abundance of omnivorous and predatory nematodes appeared to be highest in the most intensely defoliated systems. The ratio of abundance of fungal‐feeding nematodes to that of bacterial‐feeding nematodes was not significantly affected by defoliation intensity. The results infer that defoliation intensity may significantly alter the structure of soil food webs in grasslands, and that defoliation per se is able to induce patterns observed in grazing studies in the field. The results did not support hypotheses that defoliation per se would cause a shift between the bacterial‐based and fungal‐based energy channels in the decomposer food web, or that herbivore and detritivore densities in soil would be highest under intermediate defoliation. Furthermore, our data for microbes and microbial feeders implies that the effects of defoliation intensity on soil food‐web structure may depend on the duration of defoliation and are therefore likely to be dynamic rather than constant in nature.     

土地利用变化对土壤真菌群落结构的影响

应用PCR-RFLP和测序分析对川西亚高山米亚罗林区不同土地利用类型的土壤真菌18S rDNA基因进行了多样性和系统发育研究,探讨了土地利用变化对土壤真菌群落结构的影响。在20a龄云杉(Picea likiandensis var balfourianan)人工林和菜地两种类型土壤中,共得到238个阳性克隆,限制性内切酶MspI和RsaI进行RFLP分析后得到56个不同的分类操作单元(OTUs),其中20a龄云杉人工林样地获得137个阳性克隆和37个OTUs,而菜地样地获得101个阳性克隆和19个OTUs。在两类样地中具有不同的优势种群,其中20a龄云杉人工林样地有1个明显优势种群,占总克隆数的20.4%;菜地样地有2个明显优势种群,分别占总克隆数的25.7%和21.8%。对14个克隆进行了序列测定,序列的相似性在86%~99%之间,与GenBank数据库中的序列进行比对,与已知序列的相似性在92%~100%之间。系统发育分析表明,所有的18SrDNA基因被分为3个主要的簇,其中20a龄云杉人工林样地的克隆都聚集在第一和第三簇中,而菜地样地的克隆都聚集在第二簇中。结果说明,两类土壤中具有较为丰富的真菌多样性,而土地利用变化引起了土壤真菌群落结构的明显变化。     

Detection of the horizontal spatial structure of soil fungal communities in a natural forest

Soil microbes are considered to be a key determinant of the aboveground plant community. They are not distributed uniformly in the environment, and their activity, abundance, and ecosystem functioning could vary across localities, characterized by high β-diversity. Investigating factors that contribute to high β-diversity can help infer the possible mechanisms of microbial community assembly, and predict the scale and extent of impacts that soil microbes have on the plant community. Because soil systems consist of multiple horizons (i.e., vertical stratification) associated with different soil properties, complete understanding of high β-diversity requires consideration of both horizontal and vertical spatial structures of soil microbial communities. We studied the community composition of soil fungi from the O- and A-horizons in a Castanopsis-dominated temperate forest, and compared horizontal spatial autocorrelation in species composition between the two soil horizons (O- versus A-horizons). Pyrosequencing analysis yielded 67,129 sequencing reads, summed across all the 48 forest soil samples. Clustering analysis resulted in 597 molecular operational taxonomic units (OTUs), 68 % of which were identified as fungi, represented by four phyla. The Mantel test revealed that the O-horizon communities are spatially clustered, and the observed high β-diversity was driven not only by changes in OTUs present, but also by high turnover in identities of OTUs in soil samples. Furthermore, Mantel correlogram analysis showed that the O-horizon communities resembled each other in composition within the range of 50 m, whereas the A-horizon communities lacked such horizontal autocorrelation. These differences in the scale patchiness could arise from two processes: (1) that environmental conditions could show higher heterogeneity in finer scale at the A-horizon than at the O-horizon; and/or (2) dispersal could be more frequent at the O-horizon than the A-horizon. The present study suggests that either environmental filtering (i.e., the niche-based process) or dispersal limitation (i.e., neutral process) could characterize the observed patterns of spatial clustering in the soil fungal community.     

The effect of shade on leaf structure and physiology of tree seedlings from a mixed dipterocarp forest

This study builds upon past work investigating seedling leaf physiology and structure among tropical trees. We seek to explain how related and unrelated species and genera co‐occur in relation to varying amounts of shade. Seedlings of eight Sri Lankan rain forest tree species in three genera (Dipterocarpus, Mesua, Shorea section Doona) were grown for 2 years in four treatments that simulated a variety of shade environments across the understorey of a rain forest. All three genera comprise major canopy tree species of mixed dipterocarp forest, a widespread and important Asian tropical forest type. Compared with the other genera, Dipterocarpus spp. had the largest leaves, the thinnest leaf blades and relatively high rates of stomatal conductivity across all shade treatments, making them water‐loving species sensitive to droughty soils. Mesua spp. had intermediate sized leaves, with the thickest leaf blades and palisade mesophyll layers, the highest stomatal densities, the smallest aperture sizes and the lowest rates of stomatal conductance, making them the most water conservative. Shorea spp. were generally intermediate in blade and palisade mesophyll dimensions between Dipterocarpus spp. and Mesua spp., but they had the smallest leaves. Greater differences among genera than among species within genera were apparent, but species differences within genera were also apparent. Differences among genera and species conform to their known successional status and topographical affinities and provide a more comprehensive understanding of species site adaptation. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167 , 332–343.     

Root controls on soil microbial community structure in forest soils

We assessed microbial community composition as a function of altered above- and belowground inputs to soil in forest ecosystems of Oregon, Pennsylvania, and Hungary as part of a larger Detritus Input and Removal Treatment (DIRT) experiment. DIRT plots, which include root trenching, aboveground litter exclusion, and doubling of litter inputs, have been established in forested ecosystems in the US and Europe that vary with respect to dominant tree species, soil C content, N deposition rate, and soil type. This study used phospholipid fatty-acid (PLFA) analysis to examine changes in the soil microbial community size and composition in the mineral soil (0–10 cm) as a result of the DIRT treatments. At all sites, the PLFA profiles from the plots without roots were significantly different from all other treatments. PLFA analysis showed that the rootless plots generally contained larger quantities of actinomycete biomarkers and lower amounts of fungal biomarkers. At one of the sites in an old-growth coniferous forest, seasonal changes in PLFA profiles were also examined. Seasonal differences in soil microbial community composition were greater than treatment differences. Throughout the year, treatments without roots continued to have a different microbial community composition than the treatments with roots, although the specific PLFA biomarkers responsible for these differences varied by season. These data provide direct evidence that root C inputs exert a large control on microbial community composition in the three forested ecosystems studied.     

Effects of long-term fertilization on AM fungal community structure and Glomalin-related soil protein in the Loess Plateau of China

Arbuscular mycorrhizal fungi (AMF) are crucial for ecosystem functioning, and thus have potential use for sustainable agriculture. In this study, we investigated the impact of organic and mineral fertilizers on the AMF community composition and content of Glomalin-related soil protein (GRSP) in a field experimental station which was established in 1979, in the Loess Plateau of China. Roots and soils were sampled three times during the growing period of winter wheat in 2008. The treatments including: N (inorganic N), NP (inorganic N and P), SNP (straw, inorganic N and P), M (farmyard manure), MNP (farmyard manure, inorganic N and P), and CK (no fertilization). AMF communities of root and soil samples were analyzed using PCR-DGGE, cloning and sequencing techniques; and GRSP content was determined by Bradford assay. Our results indicated that spore density, GRSP, and AMF community varied significantly in soils of long-term fertilization plots at three different wheat growing stages. The effects of wheat growing period on AMF community in roots were much more evident than fertilization regimes. However, the diversity of AMF was low in our study field. Up to five AMF phylotypes appeared in each sample, with the overwhelming dominance of a Glomus-like phylotype affiliated to G. mosseae. GRSP content was correlated positively with organic carbon, total phosphorus, available phosphorus, soil pH, and spore densities, but correlated negatively with soil C/N (P?<?0.05). The results of our study highlight that the richness of AMF in Loess Plateau agricultural region is low, and long-term fertilization, especially amendments with manure and straw, has beneficial effects on accumulation of soil organic carbon, spore density, GRSP content, and AMF diversity. Host phenology, edaphic factors (influenced by long-term fertilization), and habitats interacted to affect the AMF community and agoecosystem functioning. Additionally, soil moisture and pH make a greater contribution than other determined soil parameters to the AMF community dynamics in such a special semi-arid agroecosystem where crops rely greatly on rainfall.     

Analysis of fungal community structure in the soil of Zoige Alpine Wetland

To understand the soil fungal community diversity in different zones of the Zoige Alpine Wetland, BIOLOG analysis and traditional culture method were employed in our research. Three sample sites namely the Conservatory Station up-hill slope (CSUS), the Flower Lake side (FLS) and the Conservatory Station down slope (CSDS) with increasing by water content were investigated. The results of BIOLOG showed that fungal catabolic richness index (S) and Shannon diversity index (H) increasingly rose with water content augmented from CSUS to CSDS, while different from the former tendency, the fungal catabolic activity was highest at CSDS and lowest at FLS. Principal component analysis (PCA) results demonstrated the functional diversity of fungal community varied among the three sample sites, showing us more similarity between CSDS and FLS, and considerable difference between CSUS and the former two sites. The outcome of traditional culture method illustrated the number of soil fungi increased from CSUS to CSDS, while the sort of fungal species that could be cultured did not show much difference among the three sample sites.     

Analysis of fungal community structure in the soil of Zoige Alpine Wetland

To understand the soil fungal community diversity in different zones of the Zoige Alpine Wetland, BIOLOG analysis and traditional culture method were employed in our research. Three sample sites namely the Conservatory Station up-hill slope (CSUS), the Flower Lake side (FLS) and the Conservatory Station down slope (CSDS) with increasing by water content were investigated. The results of BIOLOG showed that fungal catabolic richness index (S) and Shannon diversity index (H) increasingly rose with water content augmented from CSUS to CSDS, while different from the former tendency, the fungal catabolic activity was highest at CSDS and lowest at FLS. Principal component analysis (PCA) results demonstrated the functional diversity of fungal community varied among the three sample sites, showing us more similarity between CSDS and FLS, and considerable difference between CSUS and the former two sites. The outcome of traditional culture method illustrated the number of soil fungi increased from CSUS to CSDS, while the sort of fungal species that could be cultured did not show much difference among the three sample sites.     

Bamboo forest expansion increases soil organic carbon through its effect on soil arbuscular mycorrhizal fungal community and abundance

Plant and Soil - There is an urgent need to develop new high throughput approaches to phenotype roots in the field. Excavating roots to make direct measurements is labour intensive. An alternative...     

降水、土壤水分和结皮对人工梭梭(Haloxylonammodendron)林的影响

通过对石羊河下游沙井子地区不同立地类型、不同林龄人工梭梭林的大范围调查和定位观测研究，分析了主要生态因子降水、土壤水分和结皮对人工梭梭种群及其群落的影响。结果表明，梭梭对降水下限要求不严，但对降水上限有较为严格的要求，180mm降水量是建立人工梭梭林的上限；石羊河流域现存人工梭梭林基本依靠降水生存，但非连续同向的年际降水波动变化，对人工梭梭种群无明显影响，却显著影响梭梭林中草本植物物种组成、种群数量和生物产量。土壤水分是影响人工梭梭林最关键、最直接的生态因子，风沙土土壤含水率低于0．824％，梭梭死亡，介于0．824％-1．30％之间，处于退化状态，高于1．30％，生长正常；土壤水分限制梭梭生长，而梭梭生长又会进一步加剧土壤水分下降，梭梭造林8a后土壤含水率降低到1．30％，14a后降至土壤调萎系数之下，30a后又恢复到1．30％并保持稳定，残存梭梭种群生长趋于正常。结皮在起到固沙和保护梭梭免遭风蚀的同时，明显限制水分下渗并引起土壤干旱，加速了人工梭梭林的退化，破坏结皮后土壤含水率逐渐增加；同时，结皮还改变了1年生植物的种类组成及其数量。