** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** CLIMATE CHANGE IS EXPECTED TO INCREASE THE FREQUENCY OF AGRICULTURAL AND ECOLOGICAL DROUGHT IN WESTERN NORTH AMERICA DURING THE 21ST CENTURY. TREE PLANTATIONS IN THE PACIFIC NORTHWEST WILL UNDOUBTEDLY BE CHALLENGED BY SEVERE DROUGHT EVENTS, MAKING IT A PRIORITY TO DETERMINE HOW BEST TO FOSTER CLIMATE-CHANGE RESILIENT CROPS. FOLIAR ENDOPHYTIC FUNGI (FEF) ARE THE COLLECTION OF NON-PATHOGENIC FUNGAL MICROBES THAT COLONIZE THE INTERIOR OF PLANT LEAF TISSUE. ALTHOUGH THIS PLANT-FUNGAL SYMBIOSIS IS UBIQUITOUS FOR ALL LAND PLANTS, IT IS UNDERSTUDIED. PAST RESEARCH HAS DEMONSTRATED FEF TO FACILITATE PLANT DROUGHT-TOLERANCE, YET THE MECHANISMS THROUGH WHICH THESE SYMBIONTS REGULATE STRESS-TOLERANCE AND THE DEGREE TO WHICH THIS PHENOMENON CAN BE GENERALIZED ACROSS PLANT SPECIES IS STILL UNCLEAR. EXAMINING HOW FEF COMMUNITIES SUPPORT THEIR HOST PLANTS, AND LIKEWISE THE PLANT PHYSIOLOGICAL TRADE-OFFS ASSOCIATED WITH SUPPORTING THESE SYMBIONTS, WILL PROVIDE INSIGHT INTO THE CONTEXT IN WHICH PLANTS MAY RELY ON FEF MICROBIOTA FOR SURVIVAL.THE GOAL OF THIS PROJECT IS TO DETERMINE THE EXTENT TO WHICH FOLIAR ENDOPHYTIC FUNGI CONFER DROUGHT STRESS-TOLERANCE FOR TWO TREE SPECIES NATIVE TO THE PACIFIC NORTHWEST, DOUGLAS-FIR (PSEUDOTSUGA MENZIESII) AND THE BLACK COTTONWOOD (POPULUS TRICHOCARPA). IN ADDITION TO THEIR ROLE AS FOCAL TREE SPECIES FOR THE TIMBER OR FEEDSTOCK INDUSTRIES,P. MENZIESII AND P. TRICHOCARPA STUDY SYSTEMS ARE UNIQUE IN THAT THE TREES USED FOR AGRICULTURE CLOSELY RESEMBLE THOSE TREES FOUND IN WILD POPULATIONS. HERE WE WILL INVESTIGATE HOW MICROBIAL SYMBIONTS FACILITATE THE SURVIVAL OF P. MENZIESIIAND P. TRICHOCARPAIN NATURALLY STRESSFUL ECOSYSTEMS TO INFORM A POTENTIAL ROLE OF MICROBES IN SUPPORTING RESILIENT AGROECOSYSTEMS DURING PERIODS OF ENVIRONMENTAL STRESS, SUCH AS DROUGHT.