The Rhizosphere Interaction Between Endophytes And Ryegrass,Exophytes And Poplar:Impact On Heavy Metal Uptake,Tolerance,and Soil Biogeochemical Processes

Plant-microbe interaction is an important system in improving the environmental quality and health of all organisms.Plants are known to be involved in the remediation of polluted environments and recycle soil nutrients through a mechanism known as phytoremediation and these processes are usually more effective in collaboration with microbes.Plants and microbes have characteristics that make them great candidates for sustainable soil nutrient cycling and soil heavy metal remediation.Cadmium（Cd）is a major environmental pollutant and one of the most toxic metals in the environment.Cd can be removed from polluted soils with the help of arbuscular mycorrhizal fungi（AMF）,but the role of AMF in Cd accumulation and tolerance remains poorly understood.Here in the first experiment,Lolium perenne plants were inoculated with two different AMF species（Glomus etunicatum and Glomus mosseae）.Mycorrhizal L.perenne and non-mycorrhizal controls were exposed to Cd stress and the effects of AMF my-corrhization on Cd uptake and subsequent tolerance were tested,as well as the underlying mechanisms.Mycorrhizal colonization increased root Cd²⁺uptake and it was observed that net Cd²⁺influx was coupled with net Ca²⁺influx.The inactivation of Ca²⁺transporter channels decreased Cd²⁺uptake in non-inoculated roots to a greater extent than in inoculated roots,in-dicating that AMF activates additional ion transport channels.In consequence,inoculated plants exhibited higher Cd accumulation in both roots and shoots than non-inoculated controls.However,AMF-inoculated plants showed higher chlorophyll concentrations,photosynthesis,and growth under Cd,indicating lower Cd toxicity in AMF-inoculated plants relative to non-inoculated plants,despite the increase in Cd uptake.We observed that AMF-inoculated favored the isolation of Cd within cell walls and vacuoles,and had higher concentrations of superoxide dismutase activity and glutathione concentration in roots than non-inoculated plants,conse-quently experiencing less stress upon Cd exposure.These results highlight the potential and mechanism of AMF for enhancing phytoremediation of L.perenne in heavy metal contami-nated environments.Dioecy may subject female and male individuals to contrasting selective pressures and lead to differences in adaptive traits associated with resource allocation and ecophysiology across genders such as plant-microbe interactions.Such differences may then exert carry-over effects on the surrounding ecosystem.Whether or not gender combinations affect ecosystem biogeochemical cycles via organic matter decomposition has not yet been addressed.Here,in the second experiment female and male Populus cathayana were used to elucidate the carry-over effects of dioecy on organic matter decomposition.900 saplings were grown in field plots in either single-gender or mixed-gender treatments.The teabag index was then used to estimate decomposition rates,and also measured microbial respiration in vitro,and characterize the mi-crobial community.Variations in the influence of different gender combinations on plant growth,assimilation rates,and soil processes under field conditions were observed.Specifi-cally,different plant gender combinations showed significant variations in shoot length,stem diameter,photosynthetic rates,soil microbial respiration rates,litter decomposition rate,the extent of litter stabilization,and the soil microbiome structure.Inter-gender competition（FM）led to higher rates of soil respiration and litter decomposition rate while intra-gender competi-tion（FF and MM）led to higher diversity relative to inter-gender.Changes in plant productivity with gender exerted carry-over effects on soil processes,including soil respiration,litter de-composition rate,and also on soil p H.Respiration,decomposition,and rhizosphere p H were both higher in FM plots,where the highest plant productivity occurred,followed by FF and MM plots.Higher microbial abundance and diversity occurred in FF plots while FM plots swayed both abundance and diversity to levels lower than those in MM plots.These results indicate that gender plays a significant role in soil biogeochemical pro-cesses and provide novel insights relevant to dioecious plantations and biogeochemical mod-eling.