Rhizosphere bacterial communities and soil nutrient conditions reveal sexual dimorphism of Populus deltoides

Sexual dimorphism of plants shapes the diff erent morphology and physiology between males and females.However,it is still unclear whether it infl uences belowground ecological processes.In this study,rhizosphere soil of male and female Populus deltoides and bulk soil were collected from an 18-year plantation(male and female trees mix-planted)and grouped into three soil compartments.Soil carbon(C),nitrogen(N)and phosphorus(P)levels were determined,and soil bacterial communities were analyzed by high-throughput sequencing.The results showed the less total carbon and total organic carbon,the more nutrients(available phosphorus,nitrate nitrogen and ammonium nitrogen)available in the rhizosphere soils of female poplars than soils of males.However,α-diversity indices of the rhizosphere bacterial communities under male plants were signifi-cantly higher.Principal component analysis showed that the bacterial communities were signifi cantly diff erent between the male and female soil compartments.Further,the bacterial co-occurrence network in soil under male trees had more nodes and edges than under females.BugBase analysis showed the more functional bacteria taxa related to biofi lm formation and antioxidation under males.The results indicate that soils under male poplars had more diverse and more complex co-occurrence networks of the rhizosphere bacterial community than soils under female trees,implying that male poplars might have better environmental adaptability.The study provides insight into the diff erent soil-microbe interactions of dioecious plants.More details about the infl uencing mechanism of sexual dimorphism on rhizosphere soil bacterial communities need to be further studied.

Comparison of rhizosphere and endophytic microbial communities of Chinese leek through high-throughput 16S rRNA gene Illumina sequencing

Chinese leek（Allium tuberosum Rottler ex Sprengel） is a common vegetable in China. In our previous study, Chinese leek in rotation was found to have significant antifungal and nematicidal activity. This study＇s aim was to investigate the potential antifungal and nematicidal activity associated with rhizosphere or endophytic microbes of Chinese leek. Thus, a total of 79 261 high-quality sequences were obtained from Chinese leek rhizosphere soil, leaf and root samples. In the rhizosphere soil, the bacterial community comprised five dominant phyla： Proteobacteria（37.85%）, Acidobacteria（10.99%）, Bacteroidetes（8.24%）, Cyanobacteria（7.79%） and Planctomycetes（7.1%）. The leaf and root bacterial communities comprised two dominant phyla： Cyanobacteria（83.42% in leaf and 75.44% in root） and Proteobacteria（14.75% in leaf and 21.04% in root）. Microbial diversity, richness and evenness in the rhizosphere soil bacterial community were higher than that in the endophytic bacterial communities. The rhizosphere bacterial community was significantly different from the endophytic bacterial communities. The endophytic bacterial communities from the leaf and the root were slightly, but not significantly different from each other. This study＇s findings would contribute to the isolation and identification of nematicidal and antifungal bacterial communities in Chinese leek.

Wheat, maize and sunflower cropping systems selectively influence bacteria community structure and diversity in their and succeeding crop's rhizosphere

supported by the Special Fund for Agro-scientific Research in the Public Interest in China （201103001）

Rhizosphere microbes influence wogonoside accumulation in perennial Scutellaria baicalensis

Dried roots of Scutellaria baicalensis Georgi are an acclaimed traditional Chinese medicine,and wogonoside content is a key indicator used to evaluate S.baicalensis quality.Rather than rising linearly with cultivation years,S.baicalensis quality initially increases and then declines.However,little is known regarding the dynamic variations in S.baicalensis rhizosphere microorganisms under long-term cultivation and underlying mechanisms of their effects on wogonoside formation and accumulation.The aim of this study was to investigate the roles of soil nutrients and rhizosphere microbes on S.baicalensis quality across different cultivation years(1-4 years).The wogonoside content(25.14 mg g^(-1))was highest in the biennial S.baicalensis and then decreased following long-term cultivation.Most soil nutrients(available nitrogen,available phosphorus,available iron,available manganese,and available zinc)were reduced significantly as cultivation years increased.Time also affected rhizosphere bacterial community structure significantly,driving it toward deterministic process(i.e.,β-nearest taxon index<-2).Available manganese and exchangeable calcium indirectly affected wogonoside formation and accumulation.Wogonoside inhibition was driven by the reduction in rhizosphere bacterial diversity,which significantly increased the relative abundance of beta-glucosidase and decreased the relative abundance of phenylalanine ammonialyase.The rhizosphere microenvironment was altered under long-term cultivation,thereby shaping rhizosphere bacterial community,reducing the community diversity,and ultimately inhibiting wogonoside formation and accumulation.Our findings may aid in understanding of the mechanisms and reasons for the reduction in S.baicalensis quality under long-term cultivation from the perspective of soil nutrients and microorganisms,which may theoretically support the future artificial cultivation and management of Chinese medicinal plants.

The relative importance of soil moisture in predicting bacterial wilt disease occurrence

Soil-borne plant diseases cause major economic losses globally.This is partly because their epidemiology is difficult to predict in agricultural fields,where multiple environmental factors could determine disease outcomes.Here we used a combination of field sampling and direct experimentation to identify key abiotic and biotic soil properties that can predict the occurrence of bacterial wilt caused by pathogenic Ralstonia solanacearum.By analyzing 139 tomato rhizosphere soils samples isolated from six provinces in China,we first show a clear link between soil properties,pathogen density and plant health.Specifically,disease outcomes were positively associated with soil moisture,bacterial abundance and bacterial community composition.Based on soil properties alone,random forest machine learning algorithm could predict disease outcomes correctly in 75%of cases with soil moisture being the most significant predictor.The importance of soil moisture was validated causally in a controlled greenhouse experiment,where the highest disease incidence was observed at 60%of maximum water holding capacity.Together,our results show that local soil properties can predict disease occurrence across a wider agricultural landscape,and that management of soil moisture could potentially offer a straightforward method for reducing crop losses to R.solanacearum.