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**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FARMERS CHOOSE WHICH COVER CROPS TO USE BECAUSE OF THE SPECIFIC AGROECOSYSTEM SERVICES THEY PROVIDE (E.G., NITROGEN MANAGEMENT, NUTRIENT SCAVENGING, WEED SUPPRESSION, AND PEST REDUCTION). LEGUMES ARE USED AS COVER CROPS BECAUSE THEY INCREASE SOIL NITROGEN LEVELS FOR FUTURE CROPS. LEGUMES ACCOMPLISH THIS FEAT BY ESTABLISHING BENEFICIAL ASSOCIATIONS WITH RHIZOBIAL BACTERIA WHO PERFORM BIOLOGICAL NITROGEN FIXATION AND THUS PROVIDE NITROGEN (N) FERTILIZATION WITHOUT THE ECONOMIC AND GREENHOUSE GAS EMISSION COSTS OF CHEMICAL N INPUTS. IN ADDITION TO THIS DIRECT EFFECT, GROWING LEGUME COVER CROPS CHANGES SOIL MICROBIOMES VIA ENRICHMENT OF SPECIFIC STRAINS, SPECIES, OR GENERA OF RHIZOBIA. SOME LEGUME COVER CROP SPECIES ARE PARTICULAR ABOUT WHICH RHIZOBIA THEY ASSOCIATE WITH, WHILE OTHERS ARE GENERALISTS. FURTHER, SOME COVER CROP SPECIES SHARE RHIZOBIAL PARTNERS WITH FUTURE LEGUME CASH CROPS IN ROTATIONAL CONTEXTS, WHILE OTHERS DO NOT. HERE FIELD AND GREENHOUSE EXPERIMENTS WILL BE USED TO TEST THE HYPOTHESIS THAT RHIZOBIAL CYCLING AND EFFECTIVE N- FIXATION DEPENDS ON THE SPECIFICITY AND DEGREE OF SYMBIOTIC PARTNER OVERLAP BETWEEN COVER CROP AND FOCAL CROP HOSTS. SEQUENCING DATA WILL BE USED TO TEST METHODS THAT SIMULTANEOUSLY EXAMINE SPECIES COMPOSITION AND STRAIN-LEVEL VARIATION AND THUS ENABLE THE EXAMINATION OF AGRICULTURAL MICROBIOME STRUCTURE AND FUNCTIONING ACROSS SCALES. ULTIMATELY, LEVERAGING THE POWER OF HOST-MICROBIOME MANIPULATION TO ENRICH SPECIFIC POPULATIONS REPRESENTS A NOVEL, COST-EFFECTIVE AVENUE TO PROMOTE EFFICIENT N-FIXATION, THEREBY SUPPORTING ROBUST YIELDS, IMPROVING SOIL HEALTH, AND DECREASING CHEMICAL N-INPUTS AND GREENHOUSE GAS EMISSIONS.

$300,000FY2022National Institute of Food and AgricultureUSDA

The Pennsylvania State University

Investigators

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**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FARMERS CHOOSE WHICH COVER CROPS TO USE BECAUSE OF THE SPECIFIC AGROECOSYSTEM SERVICES THEY PROVIDE (E.G., NITROGEN MANAGEMENT, NUTRIENT SCAVENGING, WEED SUPPRESSION, AND PEST REDUCTION). LEGUMES ARE USED AS COVER CROPS BECAUSE THEY INCREASE SOIL NITROGEN LEVELS FOR FUTURE CROPS. LEGUMES ACCOMPLISH THIS FEAT BY ESTABLISHING BENEFICIAL ASSOCIATIONS WITH RHIZOBIAL BACTERIA WHO PERFORM BIOLOGICAL NITROGEN FIXATION AND THUS PROVIDE NITROGEN (N) FERTILIZATION WITHOUT THE ECONOMIC AND GREENHOUSE GAS EMISSION COSTS OF CHEMICAL N INPUTS. IN ADDITION TO THIS DIRECT EFFECT, GROWING LEGUME COVER CROPS CHANGES SOIL MICROBIOMES VIA ENRICHMENT OF SPECIFIC STRAINS, SPECIES, OR GENERA OF RHIZOBIA. SOME LEGUME COVER CROP SPECIES ARE PARTICULAR ABOUT WHICH RHIZOBIA THEY ASSOCIATE WITH, WHILE OTHERS ARE GENERALISTS. FURTHER, SOME COVER CROP SPECIES SHARE RHIZOBIAL PARTNERS WITH FUTURE LEGUME CASH CROPS IN ROTATIONAL CONTEXTS, WHILE OTHERS DO NOT. HERE FIELD AND GREENHOUSE EXPERIMENTS WILL BE USED TO TEST THE HYPOTHESIS THAT RHIZOBIAL CYCLING AND EFFECTIVE N- FIXATION DEPENDS ON THE SPECIFICITY AND DEGREE OF SYMBIOTIC PARTNER OVERLAP BETWEEN COVER CROP AND FOCAL CROP HOSTS. SEQUENCING DATA WILL BE USED TO TEST METHODS THAT SIMULTANEOUSLY EXAMINE SPECIES COMPOSITION AND STRAIN-LEVEL VARIATION AND THUS ENABLE THE EXAMINATION OF AGRICULTURAL MICROBIOME STRUCTURE AND FUNCTIONING ACROSS SCALES. ULTIMATELY, LEVERAGING THE POWER OF HOST-MICROBIOME MANIPULATION TO ENRICH SPECIFIC POPULATIONS REPRESENTS A NOVEL, COST-EFFECTIVE AVENUE TO PROMOTE EFFICIENT N-FIXATION, THEREBY SUPPORTING ROBUST YIELDS, IMPROVING SOIL HEALTH, AND DECREASING CHEMICAL N-INPUTS AND GREENHOUSE GAS EMISSIONS. · GrantIndex