** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** KEYSTONE TAXA ARE HIGHLY CONNECTED TAXA IN THE MICROBIOME THAT, THROUGH THEIR CONNECTIVITY, CAN ENHANCE MICROBIOME RESILIENCE TO ENVIRONMENTAL STRESS. HARNESSING SUCH TAXA WILL CREATE OPPORTUNITIES FOR MANIPULATING MICROBIOMES TO ENHANCE CROP RESILIENCE TO STRESS IN A RAPIDLY CHANGING CLIMATE. MOST STUDIES HAVE USED NETWORK-BASED SCORES TO IDENTIFY KEYSTONE TAXA, BUT THE EMPIRICAL VALIDATION OF SUCH TAXA HAS REMAINED ELUSIVE. THE FEW ATTEMPTS TO PERFORM VALIDATION USED THE 'ADD-IN OR EXCLUSION' APPROACH WHEREIN A PUTATIVE TAXON IS ADDED OR EXCLUDED TO ASSESS ITS IMPACT. HOWEVER, TO ASSESS THE 'TRUE' IMPACT OF A KEYSTONE, IT MUST BE ELIMINATED FROM AN ALREADY ASSEMBLED COMMUNITY TO EVALUATE THE EFFECT OF ITS REMOVAL AND THEN REINTRODUCED TO ASSESS IF IT CAN RESTORE ITS EFFECT. THE USE OF BACTERIOPHAGE IS AN INNOVATIVE WAY TO ADDRESS THIS. THE PROPOSED STUDY AIMS TO USE SALINITY AS A MODEL FOR ENVIRONMENTAL STRESS AND BACTERIOPHAGE AS A TOOL TO VALIDATE THE ROLE OF KEYSTONE TAXA IN MICROBIOME RESILIENCE TO SALINE STRESS. WE WILL ACHIEVE THIS BY 1) ASSESSING THE IMPACT OF KEYSTONE TAXA ON MICROBIOME CONNECTIVITY, 2) EMPLOYING BACTERIOPHAGE TO ELIMINATE KEYSTONE TAXA AND EVALUATE THE IMPACT OF THEIR ABSENCE, AND 3) ASCERTAINING IF KEYSTONE TAXA CAN REPRODUCE THEIR EFFECTS ON MICROBIOMES UPON RE-INTRODUCTION. OVERALL, THIS STUDY WILL ELUCIDATE HOW KEY MICROBIAL GROUPS CAN BE HARNESSED TO IMPROVE RESILIENCE TO ENVIRONMENTAL STRESS. THE STUDY ADDRESSES PRIORITIES OUTLINED IN THE AGRICULTURAL MICROBIOMES PROGRAM BY INVESTIGATING MICROBIOME ASSEMBLY AND INTERACTIONS IN VARIOUS ENVIRONMENTS OR PHYSIOLOGICAL STATES SUCH AS STRESS.