Response Mechanism Of Peanut And Rhizosphere Microenvironment To Salt Stress Under Sorghum/Peanut Intercropping

Soil salinization has become one of the important global ecological and environmental problem,and seriously threatens sustainable agricultural development and food security.The higher biodiversity of farmland(intercropping)has the capability to increase soil fertility and improve the environmental adaptability of crops,in which rhizosphere microbes playing a particularly vital role in soil biogeochemical cycling in agricultural systems.In this study,peanut cultivar“Huayu 25”and sorghum cultivar“Liaoza 15,”with characteristics of salt tolerance and a high yield potential,were selected to carry out the planting box experiment and the field experiment for two consecutive years.Sole-cropped peanut(SP)and intercropped peanut(IP)experiments were then performed under normal(N)and salt stress(S)soil conditions,respectively.The experiment was comprised of four treatments:sole-cropped peanut under normal condition(N-SP),intercropped peanut under normal condition(N-IP),sole cropped peanut under salt stress condition(S-SP),and intercropped peanut under salt stress condition(S-IP).In addition,morpho-physiological traits,three generation microbial diversity sequencing,metagenomics sequencing and nontarget metabolomics were undertaken to evaluate the specific response of the peanut and rhizosphere microenvironment to salt stress.The main findings are as follows:1.In the sorghum/peanut intercropping system,the relative interaction index(RII)of peanut were negative.However,the negative RII was decreased significantly(66.78%)and the salt tolerance index(STI)was increased significantly in S-IP under salt stress(27.43%),especially after continuously being planted for two years.Sorghum/peanut intercropping has been found to change the overall root distribution and architecture by favoring the development of different types of roots,and also affects rhizosphere nutrients of peanut.Under salt stress,the content of soil potassium increased significantly compared with normal soil conditions,this may be the initial defensive response utilized by plants to maintain Na~+/K~+homeostasis in rhizosphere soil,which regulate Na~+/K~+homeostasis in peanut by influencing the Na~+and K~+selective absorption and transportation.The reduction of Na~+/K~+in intercropped peanut leaves under salt stress reduced the leaf salinity hazard coefficient(LSHC),and the photosynthetic potential and light energy conversion efficiency were significantly improved.Ultimately the dry matter accumulation capacity and yield potential were improved.Therefore,continuous peanut intercropped with sorghum under salt stress could be an effective technique to alleviate peanut negative interactions,which significantly improve STI and alleviate salt stress of peanut by improving soil nutrient status and regulating peanut Na~+/K~+homeostasis,which ultimately maintained the dry matter accumulation capacity and increased yield potential.2.Proteobacteria,Bacteroidota,and Acidobacteriota were the dominant bacterial phyla in intercropped peanut(IP),interspecific interaction zone(II)and intercropped sorghum(IS)rhizosphere soil,whereas Ascomycota,Basidiomycota,and Mucoromycota were the dominant fungal phyla.Under salt stress,the plants-specific response altered the composition of the microbial community(diversity and abundance).Additionally,the interspecific interactions were also helpful for maintaining the stability and ecological functions of microbial communities by restructuring the otherwise stable core microbiome.The phylogenetic structure of the bacterial community was greatly similar between IP and II while that of the fungal community was greatly similar between IP and IS;however,the phylogenetic distance between IP and IS increased remarkably upon salt stress.Overall,salinity was a dominant factor shaping the microbial community structure,although plants could also shape the rhizosphere microenvironment by host specificity when subjected to environmental stresses.In particular,peanut still exerted a greater influence on the microbial community of the interaction zone than sorghum.3.Soil salinity negatively affects soil nutrient availability and enzymatic activities.This change in soil properties triggers changes in the microbial community structure and predicted function.Compared to SP,IP were more effective for maintaining the soil nutrient status and enzymatic activities.Microbial community analysis revealed that S-IP effectively preserves beneficial microbial diversity in peanut rhizosphere soil(e.g.Glomeromycetes,Bacillus,Conocybe,Massilia,Funneliformis,and Talaromyces),which plays a prominent role in the maintenance of the rhizosphere microbial community structure and functional potential.Compared with S-SP,S-IP also demonstrates stronger nutrients recycling and pathogen defense capacity by remodeling the microbial community and optimizing community function(i.e.,saprotrophs and chitinolytic enzymes).Thus,intercropping has a favorable effect on environmental adaptability and yield of peanut under salt-treated conditions.4.A total of 124 putative compounds were detected based on gas chromatography-mass spectrometry(GC-MS)metabolomics and were grouped into 11 classes,of which carbohydrate were the most predominant.Pathway enrichment analysis indicated that the most differentially expressed metabolic pathway was“Carbohydrate metabolism”,where D-Allose 2、Sucrose、Sorbitol 1 and Fructose 1 had higher enrichment.Compared with S-SP,the relative contents of D-Allose 2、Sucrose、Sorbitol 1 and Fructose 1 were significantly increased in S-IP treatment.In addition,the relative abundance of Actinobacteria,Nitrospira,Massilia and other microbial taxa in S-IP was significantly higher than that in S-SP,and there was a significant positive correlation with carbohydrate metabolites such as Sucrose and Sorbitol 1.Therefore,intercropping under salt stress affected the recruitment of beneficial microbial communities indirectly by altering the composition and content of metabolites,and ultimately by mediating microbe participates in plant metabolic pathways to improve the growth and environmental adaptability of target crops.