Community assemblage of free-living diazotrophs along the elevational gradient of Mount Gongga

Mountain systems are unique for studying the responses of species distribution and diversity to environmental changes along elevational gradients.It is well known that free-living diazotrophic microorganisms are important to nitrogen cycling in mountain systems.However,the elevational patterns of free-living diazotrophs and the underlying ecological processes in controlling their turnover along broader gradients are less well documented.Here,we investigated the pattern of diazotrophic diversity along the elevational gradient(1800 m-4100 m)in Mount Gongga of China.The results showed that the α-diversity of diazotrophs did not change with the elevation from 1800 m to 2800 m,but decreased at elevations above 3000 m.Such diversity pattern was driven mainly by soil total carbon,nitrogen,and plant richness.Various diazotrophic taxa showed differential abundance-elevation relationships.Ecological processes determining diazotrophic community assemblage shift along the elevations.Deterministic processes were relatively stronger at both low and high elevations,whereas stochastic processes were stronger at the middle elevation.This study also suggested a strong relationship among aboveground plants and diazotrophs,highlighting their potential interactions,even for free-living diazotrophs.

Ambient temperature alters body size and gut microbiota of Xenopus tropicalis

Temperature is important to determine physiological status of ectotherms. However, it is still not fully understood how amphibians and their symbiotic microbiota acclimate to ambient temperature. In this study, we investigated the changes of gut microbiota of Xenopus tropicalis at different temperatures under controlled laboratory conditions. The results showed that microbial communities were distinct and shared only a small overlap among froglet guts, culture water and food samples.Furthermore, the dominant taxa harbored in the gut exhibited low relative abundance in water and food. It indicates that bacterial taxa selected by amphibian gut were generally of low abundance in the external environment. Temperature could affect betadiversity of gut microbiota in terms of phylogenetic distance, but it did not affect alpha diversity. The composition of gut microbiota was similar in warm and cool treatments. However, signature taxa in different temperature environments were identified. The relationships between temperature, gut microbiota and morphology traits of X. tropicalis revealed in this study help us to predict the consequences of environmental changes on ectothermic animals.

植物根际微生物群落构建的研究进展

植物根际是指植物根系与土壤的交界面,是根系自身生命活动和代谢对土壤影响最直接、最强烈的区域,其物理、化学和生物性质不同于土体土壤。在这个区域里,与植物发生相互作用的大量微生物,被称为根际微生物。根际微生物在植物的生长发育和植物病虫害的生物防治等方面都具有十分重要的意义。本文总结了根际微生物群落构建的研究现状,介绍了根际微生物的经典和最新的研究方法,包括根箱法、同位素技术以及高通量测序、菌群定量分析、高通量分离培养等方法在根际微生物研究中的应用,讨论了植物根系分泌物(碳水化物、氨基酸、黄酮类、酚类、激素及其信号物质)和土壤物理化学性质对根际微生物群落的影响,概述了根际微生物-植物的互作机制,以及根际微生物群落对植物的促生作用、提高植物抗逆性和抑制作用,并对根际微生物群落研究中存在的问题和未来发展方向进行了展望。

Soil total organic carbon/total nitrogen ratio as a key driver deterministically shapes diazotrophic community assemblages during the succession of biological soil crusts

The diazotrophic community in biological soil crusts(biocrusts)is the key supplier of nitrogen in dryland.To date,there is still limited information on how biocrust development influences the succession of diazotrophic community,and what are the most important factors mediating diazotrophic communities during biocrust succession.Using the high throughput nifH amplicon sequencing,the diazotrophs in soils at different developmental stages of biocrust were comparatively studied.The results evidenced the decreases of TOC/TN ratio and pH value with biocrust development.Nostoc and Scytonema were the most dominant diazotrophic genera at all biocrust stages,while Azospirillum and Bradyrhizobium were abundant only in bare soil.Diazotrophic co-occurrence networks tended to be less complex and less connected with biocrust succession.The soil TOC/TN ratio was the most dominant factor mediating diazotrophic diversity,community composition and assembly processes,while diazotrophic-diversity and NO3–-N/NH4+-N ratio were positively correlated with the nitrogenase activity during biocrust succession.This study provided novel understandings of nitrogen fixation and succession patterns of diazotrophic community,by showing the effects of biocrust succession on diazotrophic diversity,community composition,community assembly and co-occurrence networks,and recognizing TOC/TN ratio as the most dominant factor mediating diazotrophs during biocrust succession.

Effects of Cu^(2+)and humic acids on degradation and fate of TBBPA in pure culture of Pseudomonas sp.strain CDT

Soil contamination with tetrabromobisphenol A（TBBPA） has caused great concerns;however, the presence of heavy metals and soil organic matter on the biodegradation of TBBPA is still unclear. We isolated Pseudomonas sp. strain CDT, a TBBPA-degrading bacterium, from activated sludge and incubated it with ^（14）C-labeled TBBPA for 87 days in the absence and presence of Cu^（2＋）and humic acids（HA）. TBBPA was degraded to organic-solvent extractable（59.4% ± 2.2%） and non-extractable（25.1% ± 1.3%） metabolites,mineralized to CO_2（4.8% ± 0.8%）, and assimilated into cells（10.6% ± 0.9%） at the end of incubation. When Cu^（2＋）was present, the transformation of extractable metabolites into non-extractable metabolites and mineralization were inhibited, possibly due to the toxicity of Cu^（2＋）to cells. HA significantly inhibited both dissipation and mineralization of TBBPA and altered the fate of TBBPA in the culture by formation of HA-bound residues that amounted to 22.1% ± 3.7% of the transformed TBBPA. The inhibition from HA was attributed to adsorption of TBBPA and formation of bound residues with HA via reaction of reactive metabolites with HA molecules, which decreased bioavailability of TBBPA and metabolites in the culture. When Cu^（2＋）and HA were both present, Cu^（2＋）significantly promoted the HA inhibition on TBBPA dissipation but not on metabolite degradation. The results provide insights into individual and interactive effects of Cu^（2＋）and soil organic matter on the biotransformation of TBBPA and indicate that soil organic matter plays an essential role in determining the fate of organic pollutants in soil and mitigating heavy metal toxicity.