**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FUTURE CLIMATE VARIABILITY THREATENS THE RESILIENCE OF GRAIN AGROECOSYSTEMS, WHILE FARMERS ALSO FACE INCREASING PRESSURE TO REDUCE AGRICULTURE'S CONTRIBUTION TO GREENHOUSE GAS EMISSIONS AND NUTRIENT POLLUTION OF WATERWAYS. INTEGRATING PERENNIAL SPECIES INTO AGROECOSYSTEMS IS CENTRAL TO AN ECOLOGICAL MANAGEMENT APPROACH THAT CAN AVOID SURPASSING CRITICAL PLANETARY THRESHOLDS FOR SUSTAINABILITY. THE GREATER VULNERABILITY OF ANNUAL CROPPING SYSTEMS IN A CHANGING CLIMATE MAKE PERENNIAL CROPS INCREASINGLY APPEALING TO FARMERS. INTERMEDIATE WHEATGRASS (IWG) IS THE MOST ADVANCED PERENNIAL GRAIN CROP, WHICH HAS BEEN SELECTED FOR INCREASED GRAIN YIELD. A PARTICULARLY PROMISING, AND NOVEL, SYSTEM FOR INCREASING ECOSYSTEM SERVICES IS INTERCROPPING PERENNIAL GRAINS WITH LEGUMES TO SUPPLY AN ORGANIC NITROGEN SOURCE. HOWEVER, THERE REMAINS A NEED TO OPTIMIZE THESE INTERCROPS FOR RESOURCE USE EFFICIENCY AND PRODUCTIVITY, WHICH REQUIRES UNDERSTANDING THEIR ECOLOGICAL MECHANISMS AND INTERACTIONS. THIS PROJECT WILL ADDRESS THREE RESEARCH GAPS RELATED TO PERENNIAL GRAIN-LEGUME INTERCROPS THROUGH THE FOLLOWING OBJECTIVES: (I) UNDERSTAND HOW TWO PERENNIAL FORAGE LEGUMES - ALFALFA AND WHITE CLOVER - IMPACT IWG YIELD, GRAIN QUALITY, AND SOIL HEALTH; (II) DETERMINE THE RELATIVE CONTRIBUTION OF ABOVE- AND BELOW-GROUND ALFALFA BIOMASS TO INPUTS OF BIOLOGICALLY-FIXED N AND SOIL N CYCLING CAPACITY BY SIMULATING FORAGE REMOVAL; AND (III) IMPROVE MECHANISTIC UNDERSTANDING OF INTERACTIONS BETWEEN INTERCROPPED SPECIES - INCLUDING N FIXATION RATES, TRANSFER OF FIXED N TO IWG, AND CHANGES IN ROOT FUNCTIONAL TRAITS - THAT INCREASE ECOSYSTEM SERVICES. THIS PROJECT WILL ESTABLISH THE FOUNDATION FOR FUTURE LONG-TERM, INTERDISCIPLINARY RESEARCH ON PERENNIAL GRAIN AGROECOSYSTEMS THAT INCLUDES OUTREACH AND ENGAGEMENT WITH THE LOCAL FARMING COMMUNITY AND OTHER FOOD SYSTEM ACTORS. ULTIMATELY, THIS WORK WILL EXTEND THE LIMITED BODY OF RESEARCH ON PERENNIAL GRAINS BY APPLYING ECOLOGICAL SCIENCE TO IDENTIFY GENERALIZABLE MECHANISMS THAT CAN INFORM MORE SUSTAINABLE CROP PRODUCTION.