Diversity of carbon cycle-linked phyllosphere microorganisms: A key driver of CO_(2) flux in macrophyte-dominated aquatic systems

Planktonic microorganisms have been recognized as important components in biogeochemical cycling in lakes.However,research into the impact of phyllosphere microorganisms,particularly those involved in carbon cycling,on CO_(2) fluxes in macrophyte-dominated lakes within the context of global environmental changes remains scarce.Here,by employing high-throughput sequencing techniques,we experimentally tested how nutrient enrichment,top-down effects of fish and increases in dissolved organic carbon(DOC)affect CO_(2) exchange flux at the water-air interface by altering the community structure and functioning of phyllosphere bacteria on macrophytes.We found that our mesocosm ecosystems exhibited a net absorption of CO_(2),but nutrient enrichment significantly decreased the absorption ability.Mantel tests and multiple regression modeling also showed that eutrophication-associated parameters(total nitrogen,total phosphorus and ammonium nitrogen),pH,and extinction coefficient were the key drivers influencing abundance of phyllosphere functional microorganisms.In addition,these experimental treatments significantly altered the composition,diversity and co-occurrence networks of carbon cyclingassociated phyllosphere microorganisms,which impacted the CO_(2) flux.Structural equation models and linear regression further showed that the Shannon Index of phyllosphere functional microorganisms related to carbon cycling(rather than plant volume inhabited-PVI)had a significant positive impact on CO_(2) fixation.This means that environmental changes—especially eutrophication—may hinder carbon sequestration by decreasing the diversity of phyllosphere microorganisms rather than reducing the abundance of submerged macrophytes.This study increases our understanding of carbon cycling processes in aquatic environments from a management perspective by emphasizing the importance of protecting the diversity of phyllosphere microorganisms in macrophyte-dominated lakes.

Enantioselective effects of imazethapyr residues on Arabidopsis thaliana metabolic profile and phyllosphere microbial communities

Imazethapyr(IM)is a widely used acetolactate synthase-inhibiting chiral herbicide.It has long-term residuals that may be absorbed by the human body through the edible parts of plants,such as vegetable leaves or fruits.Here,we selected a model plant,Arabidopsis thaliana,to determine the effects of R-IM and S-IM on its leaf structure,photosynthetic efficiency,and metabolites,as well as the structures of microorganisms in the phyllosphere,after 7 days of exposure.Our results indicated enantiomeric differences in plant growth between R-IM and S-IM;133μg/kg R-IM showed heavier inhibition of photosynthetic efficiency and greater changes to subcellular structure than S-IM.R-IM and S-IM also had different effects on metabolism and leaf microorganisms.S-IM mainly increased lipid compounds and decreased amino acids,while R-IM increased sugar accumulation.The relative abundance of Moraxellaceae human pathogenic bacteria was increased by R-IM treatment,indicating that R-IM treatment may increase leaf surface pathogenic bacteria.Our research provides a new perspective for evaluating the harmfulness of pesticide residues in soil,phyllosphere microbiome changes via the regulation of plant metabolism,and induced pathogenic bacterial accumulation risks.

Halotolerant Bacillus sp.strain RA coordinates myo-inositol metabolism to confer salt tolerance to tomato

Soil salinity is a worldwide problem threatening crop yields.Some plant growth-promoting rhizobacteria(PGPR)could survive in high salt environment and assist plant adaptation to stress.Nevertheless,the genomic and metabolic features,as well as the regulatory mechanisms promoting salt tolerance in plants by these bacteria remain largely unknown.In the current work,a novel halotolerant PGPR strain,namely,Bacillus sp.strain RA can enhance tomato tolerance to salt stress.Comparative genomic analysis of strain RA with its closely related species indicated a high level of evolutionary plasticity exhibited by strain-specific genes and evolutionary constraints driven by purifying selection,which facilitated its genomic adaptation to salt-affected soils.The transcriptome further showed that strain RA could tolerate salt stress by balancing energy metabolism via the reprogramming of biosynthetic pathways.Plants exude a plethora of metabolites that can strongly influence plant fitness.The accumulation of myo-inositol in leaves under salt stress was observed,leading to the promotion of plant growth triggered by Bacillus sp.strain RA.Importantly,myo-inositol serves as a selective force in the assembly of the phyllosphere microbiome and the recruitment of plant-beneficial species.It promotes destabilizing properties in phyllosphere bacterial co-occurrence networks,but not in fungal networks.Furthermore,interdomain interactions between bacteria and fungi were strengthened by myo-inositol in response to salt stress.This work highlights the genetic adaptation of RA to salt-affected soils and its ability to impact phyllosphere microorganisms through the adjustment of myo-inositol metabolites,thereby imparting enduring resistance against salt stress in tomato.