Study On Characteristics And Physiological Mechanism Of Phosphorus Efficient Utilization Of Switchgrass In Saline-alkali Soil

The deficiency of soil phosphorus is one of the main reasons that restrict the growth and development of crops.The energy crop switchgrass has strong stress resistance and high phosphorus utilization rate.Analyzing the response and adaptation of switchgrass to low phosphorus is helpful to understand the mechanism of efficient utilization of phosphorus and optimize the acquisition and utilization of phosphorus by crops.It is one of the effective ways to improve the utilization efficiency of phosphate fertilizer and achieve sustainable production.Studying the response mechanism of switchgrass to low phosphorus stress in saline-alkali land is of great significance for high-yield and efficient cultivation of switchgrass and sustainable utilization of saline-alkali land.In this study,pot and field experiments were conducted to investigate the effects of different phosphorus levels on the growth,physiological characteristics,metabolomics,rhizosphere soil characteristics and microbial diversity of switchgrass(Panicum virgatum L.)using two varieties(Alamo and Pathfinder)as materials.The main research results are as follows:(1)Under severe(20μM),moderate(100μM),mild(200μM)phosphorus deficiency and sufficient phosphorus(500μM)treatments,the plant height,leaf area and biomass of switchgrass increased with the increase of phosphorus level.Low phosphorus had greater effects on roots than on stems and leaves,and moderate phosphorus deficiency stress significantly promoted the growth of total root length,total root surface area,average root diameter and root volume of switchgrass.With the increase of phosphorus level,the root activity of switchgrass was gradually increased,and the root acid phosphatase activity was gradually decreased.The secretion of root organic acids was increased under severe and mild phosphorus deficiency stresses.Citric acid,malic acid,malonic acid and lactic acid were the main components of organic acids in switchgrass roots.According to correlation analysis and comprehensive evaluation,the biomass of switchgrass was positively correlated with phosphorus concentration and negatively correlated with phosphorus utilization efficiency.The two switchgrass varieties had the highest phosphorus utilization efficiency under mild phosphorus deficiency stress.Root volume,biomass,total root area and root activity were the main factors affecting phosphorus absorption.Biomass and plant height were the main performance results of phosphorus utilization efficiency.The chlorophyll content,net photosynthetic rate,stomatal conductance,transpiration rate and relative conductivity of switchgrass leaves increased with the increase of phosphorus level,while the intercellular CO2 concentration,MDA,Pro,SS content,SOD,POD,CAT enzyme activity decreased with the increase of phosphorus level.(2)Based on the metabolic analysis of LC-MS non-targeted metabolomics technology,650 secondary specific differential metabolites were detected from four phosphorus levels of two switchgrass varieties.The number of differential metabolites between Alamo phosphorus levels and sufficient phosphorus supply P500 treatment increased first and then decreased with the increase of phosphorus level.The number of differential metabolites between Pathfinder phosphorus levels and sufficient phosphorus supply P500 treatment gradually decreased with the increase of phosphorus level.The two switchgrass varieties showed the minimum value under mild phosphorus deficiency treatment.The number of differential metabolites in Biosynthesis of secondary metabolites and Microbial metabolism in diverse environments was the highest in the two varieties under mild phosphorus deficiency.Organic acids,amino acids,sugars,flavonoids,vitamins,alkaloids and derivatives were accumulated,but the accumulation degree between the two varieties was different.The response of the two varieties to mild phosphorus deficiency was mainly regulated by metabolic pathways such as Biosynthesis of plant secondary metabolites,Biosynthesis of alkaloids derived from histidine and purine,Citrate cycle(TCA cycle),Carbon metabolism,Carbon fixation pathways in prokaryotes.(3)Under the treatments of no phosphorus(0kg/ha),low phosphorus(30kg/ha)and high phosphorus(90kg/ha),the rhizosphere/non-rhizosphere soil pH and total salt content of the two switchgrass varieties gradually decreased with the advancement of growth period and the increase of phosphorus supply level,while the total phosphorus,available phosphorus content and phosphorus activation coefficient gradually increased.The contents of Ca10-P,Ca8-P and Al-P in rhizosphere/non-rhizosphere soil were higher,while the contents of Ca2-P,Fe-P and O-P were lower.The contents of Ca10-P,Ca8-P and Al-P in rhizosphere/non-rhizosphere soil increased with the increase of phosphorus level and the advancement of growth period,and the contents in non-rhizosphere were higher than those in rhizosphere.Canonical correlation analysis showed that phosphorus utilization efficiency,acid phosphatase activity and organic acid content in rhizosphere soil were positively correlated with pH,total salt,total phosphorus,Ca10-P and Ca8-P content in rhizosphere and non-rhizosphere soil of switchgrass at different growth stages.Alkaline phosphatase activity,biomass,mycorrhizal infection rate and phosphorus uptake in rhizosphere soil were positively correlated with available phosphorus,Ca2-P,Al-P and Fe-P content.Lactic acid,succinic acid,malic acid and malonic acid are the main organic acids secreted by switchgrass roots in saline-alkali land.Phosphorus application significantly affects the secretion of organic acids in roots,thus affecting the soil environment of switchgrass roots in saline-alkali land.(4)Phosphorus supply level affected the number of microbial groups and bacterial diversity in the rhizosphere soil of switchgrass.Low phosphorus decreased the bacterial richness and increased the diversity in the rhizosphere soil of Alamo,while high phosphorus increased the bacterial richness and decreased the diversity in the rhizosphere soil of Pathfinder.The application of phosphorus changed the microbial community structure of saline-alkali low-phosphorus soil.Under low phosphorus and high phosphorus treatments,the rhizosphere bacterial community structure of Alamo and Pathfinder tended to be consistent.Proteobacteria,Bacteroidetes,Actinobacteria,Chloroflexi,Acidobacteria,Planctomycetes,Verrucomicrobia and Firmicutes were the dominant flora.Bacterial community bacteria were related to alkaline phosphatase,non-rhizosphere/rhizosphere total salt content,pH,available phosphorus and total phosphorus content in soil.Total salt,pH,available phosphorus and total phosphorus were the key factors to change the microbial changes in rhizosphere and non-rhizosphere soil.