Wheat straw biochar amendment suppresses tomato bacterial wilt caused by Ralstonia solanacearum: Potential effects of rhizosphere organic acids and amino acids

Complex interactions based on host plant, rhizosphere microorganisms and soil microenvironment are presumed to be responsible for the suppressive properties of biochar against soil-borne diseases, although the underlying mechanisms are not well understood. This study is designed to evaluate the efficacy of biochar amendment for controlling tomato bacterial wilt caused by Ralstonia solanacearum, and to explore the interactions between biochar-induced changes in rhizosphere compound composition, the pathogen and tomato growth. The results showed that biochar amendment decreased disease incidence by 61–78% and simultaneously improved plant growth. The positive ‘biochar effect' could be associated with enhanced microbial activity and alterations in the rhizosphere organic acid and amino acid composition. Specifically, elevated rhizosphere citric acid and lysine, but reduced salicylic acid, were induced by biochar which improved microbial activity and rendered the rhizosphere unsuitable for the development of R. solanacearum. In addition, nutrients which were either made more available by the stimulated microbial activity or supplied by the biochar could improve plant vigor and potentially enhance tomato resistance to diseases. Our findings highlight that biochar's ability to control tomato bacterial wilt could be associated with the alteration of the rhizosphere organic acid and amino acid composition, however, further research is required to verify these ‘biochar effects' in field conditions.

An effective planting model to decrease cadmium accumulation in rice grains and plants:Intercropping rice with wetland plants

Cadmium(Cd)pollution affects plant growth and poses a serious threat to food safety and human health.Cadmium-contaminated rice is assumed to be the main source of Cd exposure to humans,with grave health risks.Phytoremediation is an efficient,cost-effective,and eco-friendly approach to minimize Cd accumulation in rice.However,research on the effect of rice intercropping with wetland plants that exhibit great capacity for phytoremediation in decreasing Cd concentrations in paddies is limited.A pot experiment in greenhouse was conducted to evaluate the effect of rice intercropping with two wetland plants(Pontederia cordata and Canna indica)under different soil Cd levels(0,1,10,and 25 mg kg^(-1))on rice growth and Cd accumulation and translocation.The results showed that rice intercropping with the two wetland plants significantly improved plant height,tiller,and biomass of rice,but reduced Cd bioconcentration factors(BCFs)and Cd concentrations in rice and wetland plants.Compared with rice monocropping,the BCF in rice grain under 25 mg kg^(-1)soil Cd level significantly decreased by 54.39%and 59.65%in the systems of rice intercropping with C.indica and P.cordata,respectively.In addition,intercropping inhibited the increase in BCFs in rice and wetland plants under increasing soil Cd levels.In conclusion,the systems of rice intercropping with P.cordata and C.indica can be considered two new and effective approaches for ameliorating Cd pollution in paddies,as well as minimizing Cd accumulation in rice and improving food safety.Of the two intercropping systems,rice intercropping with P.cordata performed better than intercropping with C.indica.

Effects of acid deposition on the avoidance behavior of Folsomia candida (Collembola, Isotomidae)

Excessive acid deposition causes soil acidification,and changes the soil microhabitat,thus affecting the survival and reproduction of soil organisms.Folsomia candida(Collembola,Isotomidae),as a model organism,is widely used to assess the chemical toxicity in soil,and its avoidance response can indicate the environmental changes.In this study,we used Folsomia candida to assess the risks of acid deposition on soil ecosystems.Different pH(3.0,3.5,4.0,4.5,5.0,and 5.5)treatments were set up in petri dish experiments,and the avoidance behavior of Folsomia candida was measured after 12,24,and 48 h exposure to the pH conditions.The results indicated that(1)both the exposure duration and pH level influenced avoidance behavior of collembolan.(2)After 12 h exposure,most of the individuals showed avoidance behavior but without significant differences among the treatments.(3)After 24 h exposure,significant avoidance behavior was observed at pH 3.0,3.5,and 4.0.(4)After 48 h exposure,avoidance behavior was found in all treatment conditions except for pH 5.5.This study clarified the direct responses of soil fauna to acid deposition,and indicated that both pH and length of exposure influenced the avoidance behavior of Folsomia candida.During the experimental period,the collembolan reacted negatively and showed consistent avoidance behavior at pH 3.0,3.5,and 4.0.Reversed avoidance behavior was apparent between pH 4.5 and 5.0 and not observed at pH 5.5,indicating that the latter was the preferred pH environment.