轮作休耕模式对土壤细菌群落的影响

以黄土高原半干旱区9种轮作休耕模式土壤为研究对象,分别设残膜覆盖(T₁)、伏天深耕(T₂)、施牛羊粪(7 500 kg·hm^-2)+深翻耕(30 cm)+连续休耕3 a(T₃)、施牛羊粪(7 500 kg·hm^-2)+深翻耕(30 cm)+连续种植豌豆3 a并在盛花期翻压还田(T₄)、施牛羊粪(7 500 kg·hm^-2)+深翻耕(30 cm)+连续3 a种植豌豆(每kg豌豆种子拌根瘤菌粉8.5 g)并在盛花期翻压还田(T₅)、玉米秸秆粉碎(还田量7 500 kg·hm^-2)+施牛羊粪(7 500 kg·hm^-2)+深翻耕(30 cm)+连续休耕3 a(T₆)、玉米秸秆粉碎(还田量7 500 kg·hm^-2)+施牛羊粪(7 500 kg·hm^-2)+深翻耕(30 cm)+连续3 a种植毛苕子并在盛花期翻压...     

亚热带常绿阔叶林锥和木荷枯立木点格局分析

在广东省康禾自然保护区10 hm²常绿阔叶林样地中,设置1 000个样方调查枯立木,选取主要树种锥及木荷运用单变量成对相关函数g(r)函数进行个体点格局分析,采用标记相关函数k_mm(r)以枯立木胸高断面积为标记进行标记点格局分析,探究枯立木空间分布格局的形成原因。结果表明：锥和木荷枯立木个体径级结构均表现为“L”型,小径级个体死亡多,随着径级的增大,死亡个体数减少。锥枯立木个体空间分布格局在0～50 m尺度下表现为聚集分布,随着尺度的增大,聚集程度降低;木荷枯立木个体空间分布格局在0～4.3 m以及8.7～14.0 m时表现为聚集分布,4.4～8.6 m以及14.1 m后均表现为随机分布。锥及木荷枯立木同种个体间无显著相关性,表明同种枯立木在死亡前个体间无竞争作用。枯立木个体在生长发育早期死亡较多,其空间分布格局的形成可能主要是受活立木种子的扩散限制、密度制约和生境过滤的多重影响,而大径级枯立木主要是由于自然衰老导致其死亡。     

干热处理甜瓜、籽瓜细菌性果斑病种子对幼苗发病的影响

为了筛选出对防治甜瓜、籽瓜细菌性果斑病有效、安全的干热处理方式,对人工接种细菌性果斑病的甜瓜、籽用西瓜种子进行不同温度及不同时间的干热处理,经种植鉴定,观测比较了不同处理的出苗率、果斑病病情指数及防治效果。结果显示:对甜瓜带菌种子有较好的防治效果的处理是60℃处理6、8 d,防治效果为85.6%;65℃处理6 d,防治效果为85.0%。对籽用西瓜带菌种子防治效果较好的处理是60℃处理12 d,防治效果为86.5%;65℃处理12 d,防治效果为83.0%。     

Effects of life‐history traits on stream fish abundances across spatial scales

Identifying cross‐scale patterns of ecological processes is imperative, especially in hierarchically structured riverine ecosystems. The role of abiotic factors in determining cross‐scale spatial structure of stream fish populations and communities is well studied, but less is known about how species traits drive cross‐scale patterns. We investigated the role of species traits for explaining autocorrelation of stream fish abundance at spatial scales ranging from local stream reaches to major basins. We calculated intraclass correlation coefficients (ICCs) representing abundance autocorrelation within species (N = 47) at each of five spatial scales. A hierarchical Bayesian regression then modelled ICCs against spatial scale with the resulting regression coefficients modelled as functions of species traits. Finally, we ordinated the scale‐by‐species ICC matrix to calculate an overall metric describing species whose abundances were autocorrelated along a gradient of large to small scales, and modelled this metric as a function of species traits. Abundances of most species were autocorrelated at smaller spatial scales. Maximum fecundity had a significant positive relationship with abundance patterns across spatial scales. Species habitat affinities and body forms were significantly associated with overall abundance patterns across spatial scales: populations of upland/lotic‐affiliated species adapted to streams with high flow correlated at small (≤10 km²) spatial scales. Lowland/lacustrine species with laterally compressed bodies showed little correlation across scales. The appropriate spatial scale for modelling abundance is determined not only by exogenous (e.g. environmental) factors, but also endogenous factors, like traits. Careful consideration of traits and life history will aid researchers in designing more effective and efficient surveys and analyses.     

Pseudomonas aeruginosa produces secondary metabolites that have biological activity against plant pathogenic Xanthomonas species

The bioactivity of compounds produced by Pseudomonas aeruginosa (LN strain), against three Xanthomonas species was investigated under greenhouse conditions and using electron microscopy. Chromatographic fractions EAP, VLC3, VLC4, VLC3d and VLC4f were tested against Xanthomonas axonopodis pv. malvacearum, X. axonopodis pv. phaseoli and X. axonopodis pv. citri by disc diffusion. Fractions with antibiotic activity were tested in vivo under greenhouse conditions and their bioactivity was evaluated. Scanning electron microscopy showed that VLC4f affects biofilm formation while VLC4f and VLC3d both affect cell morphology. The semi-purified fractions controlled bacterial diseases caused by Xanthomonas spp. when sprayed on plants under greenhouse conditions. The VLC4f fraction showed superior results in disease management, reducing the number of lesions on cotton and orange leaves by 94%, and reducing disease severity in bean leaves by 73%. The data suggest that the fractions were effective and have potential as an alternative to conventional bactericides in the control of plant diseases caused by Xanthomonas sp under greenhouse conditions.     

Bacterial community shifts associated with high abundance of Rhizobium spp. in potato roots under macronutrient-deficient conditions

We evaluated the impacts of a macronutrient deficiency on the community structure of root-associated bacteria in potato (Solanum tuberosum) cultivation. Potato plants were cultivated in a long-term experimental field under a nitrogen, phosphorus, or potassium deficiency, and roots were sampled at the early flowering stage. Amplicon libraries of 16S rRNA gene were constructed for root-associated bacteria, and bacterial diversity was analyzed by means of pyrosequencing. Statistical analyses showed significantly lower species evenness in the nutrient-deficient plots compared with the value in a plot with standard fertilization. Phylogenetic analyses revealed that the abundance of Rhizobium spp. increased dramatically in all plots under a macronutrient deficiency.     

Unearthing the role of biological diversity in soil health

The soil provides a great variety of microhabitats for myriad organisms of different size, physiological activity, behavior and ecosystem function. Besides abundance of participating soil organisms, their species diversity facilitates maximum exploitation of the resources available in the different habitats. At various levels of resolution, species can be categorized into classes performing ecosystem functions and, within each functional class, into guilds of species with similar life course characteristics. Measurement of the diversity and abundance of species within a functional class provides insights into the nature of ecosystem functions and services and to the health of the soil. At higher resolution, species diversity within guilds of a functional class may infer the degree of exploitation of available resources and the complementarity of an ecosystem service; diversity among the guilds of a functional class may indicate successional complementarity of the services. A diversity of guilds within a functional class expands the range of conditions over which ecosystem services are performed while species diversity within a functional class and its guilds contributes to the magnitude of the services. Consequently, diversity of species within functional classes is a key element of the biological component of soil health. In the context of ecosystem services and soil health, the biomass or metabolic activity of species are more useful measures of their abundance than numbers of individuals. Thus, understanding of soil health and ecosystem function requires, besides knowledge of species diversity within functional classes, assessment of the range of functions currently performed in the system and the abundances of organisms by which they are performed. We propose a diversity-weighted abundance product for comparison of the functional magnitude of different assemblages of like organisms.     

Effect of rice-rice-rape rotation on physicochemical property and bacterial community of rhizosphere soil

Through collecting rhizosphere soil sample from a 30-year long-term fixed location test site that use “rice-rice-rape” crop rotation (RRR) and “rice-rice-fallow” continuous cropping systems (RRF), this paper investigated effects of long-term crop rotation on physicochemical property and bacterial community of rhizosphere soil. Results showed that total nitrogen (TN), total phosphorus (TP) and available potassium (AK) contents in rhizosphere soil under long-term RRR were decreased by 28.09%, 15.69% and 6.25% respectively. Alkali-hydrolyzable nitrogen (AN) and available phosphorus (AP) contents were 10.59% and 13.25% higher than those of soil in RRF respectively. Three soil samples collected during different periods also showed that RRR resulted in a lower rhizosphere soil pH than RRF. Clone library analysis revealed that significant difference in rhizosphere soil bacterial community was observed between RRR and RRF continuous cropping. Abundance of α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria were higher in rhizosphere soil of RRR compared to RRF. pH of rhizosphere soil was significantly correlated with Acidobacteria level, while total organic carbon (TOC) content was significantly correlated with Proteobacteria level. Long-term RRR enhanced conversion of N and P in rhizosphere soil, increased bio-availability to crop, and promoted diversity of soil bacterial community. Bacterial diversity in RRR could be ecological significance in maintaining soil fertility and functionality.     

水稻灌浆结实期青枯原因分析及防御措施

近5年来,水稻生理性青枯在江苏省稻麦连作区连续发生,在水稻灌浆期对水稻的危害较大,进而影响水稻产量。通过对宿迁市近几年气象资料及相关资料综合分析,认为导致水稻生理性青枯的重要因子为寒流突至致使气温骤降,其次是植株抗逆性差。因而提出防御水稻生理性青枯应加强栽培管理,促进水稻根系活力,并关注气温变化,适时灌水保温、喷施叶面肥保根促灌浆、完善农业保险等措施。