IN RECENT YEARS, CONSIDERABLE EMPHASIS HAS BEEN PLACED ON IMPROVING SOIL HEALTH IN AGRICULTURAL SYSTEMS VIA INCREASED INPUTS OF ORGANIC NUTRIENTS (E.G., COMPOST, COVER CROPS). THERE IS EVIDENCE TO SUGGEST THAT CROPS BRED UNDER CONDITIONS OF HIGH FERTILIZER INPUTS AND RELATIVELY DEGRADED SOILS MAY NOT BE ABLE TO TAKE ADVANTAGE OF, OR SUPPORT, IMPROVEMENTS TO SOIL HEALTH (AND INCREASED ORGANIC N) DUE TO A DISCONNECT BETWEEN PLANTS ROOTS ASSOCIATED INPUTS AND BIOLOGICALLY-MEDIATED NUTRIENT PROCESSES IN SOILS (E.G. DECOMPOSITION AND NUTRIENT RELEASE). BASED ON THESE IDEAS, THE RESEARCH PROPOSED HERE SEEKS TO: 1) EVALUATE HOW CROP VARIETIES AFFECT SOIL MICROBIAL COMMUNITIES AND, IN TURN, IMPACTS N CYCLING; AND 2) INVESTIGATE HOW DIFFERENT VARIETIES RESPOND TO INHERENT DIFFERENCES IN SOIL BIOLOGICAL ACTIVITY AND DIVERSITY. WE WILL EXPLORE EXISTING VARIATION IN WINTER WHEAT (TRITICUM AESTIVUM), FOCUSING SPECIFICALLY ON TRAITS RELATED TO BELOWGROUND ALLOCATION, AND THEN EXPLORE CROP VARIETY RESPONSES TO AN IMPOSED GRADIENT OF SOIL BIOLOGICAL ACTIVITY AND DIVERSITY. A SET OF EXPERIMENTS WILL: 1) QUANTIFY BELOWGROUND C INPUT (FROM ROOTS AND EXUDATES) FROM DIVERSE WHEAT VARIETIES USING 13C ISOTOPIC LABELING IN THE GREENHOUSE; 2) ASSESS IMPACTS OF THESE VARIETIES ON SOIL MICROBIAL COMMUNITIES AND THEIR N CYCLING ACTIVITIES; 3) EXPLORE HOW PRE-EXISTING DIFFERENCES IN SOIL BIOLOGY/HEALTH INTERACT WITH WHEAT GENOTYPES TO AFFECT OVERALL CROP PERFORMANCE; AND 4) EVALUATE HOW VARIETIES AND SOIL MANAGEMENT CHANGES TO N CYCLING AFFECT THE AVAILABILITY OF N AND UPTAKE BY PLANTS. BY EXPLORING RELATIONSHIPS BETWEEN CROP VARIETIES AND THEIR ASSOCIATED MICROBIOMES AND HOW SUCH INTERACTIONS RESPOND TO CHANGES IN SOIL HEALTH, THIS RESEARCH ADDRESSES MULTIPLE PRIORITIES OF THE PROGRAM AREA ON FOUNDATIONAL KNOWLEDGE OF AGRICULTURAL PRODUCTION SYSTEMS.