RANGELANDS CONTAINING MIXTURES OF MANY PLANT SPECIES GENERALLY PRODUCE MORE BIOMASS AND GENERATE SOILS WITH GREATER FERTILITY AND HIGHER ORGANIC MATTER. THE BENEFITS OF PLANT DIVERSITY IN RANGELANDS MAY EXTEND TO CLEANER WATERWAYS AND IMPROVED DRINKING WATER, BUT THIS RELATIONSHIP LIKELY DEPENDS UPON THE DETAILS OF THE SOIL MICROBIOLOGY, WHICH WILL AFFECT SOIL NUTRIENT RETENTION. HOWEVER, TO DATE, PLANT DIVERSITY REPRESENTS AN UNDEREXPLORED, BUT POTENTIALLY CRITICAL, MEDIATOR OF HUMAN IMPACTS ON LAND-WATER CONNECTIVITY. OUR RESEARCH WILL TEST COMPETING HYPOTHESES DESCRIBING HOW THE DIVERSITY OF PLANT COMMUNITIES DRIVES BOTH PLANT GROWTH AND SOIL NUTRIENT RETENTION. BROADENING OUR UNDERSTANDING OF THE POTENTIAL BENEFITS OF PLANT DIVERSITY BEYOND PLANT PRODUCTIVITY WILL INCREASE OUR ABILITY TO PREDICT WHERE AND WHEN LOSS OF PLANT DIVERSITY MIGHT CHANGE IMPORTANT ECOSYSTEM ATTRIBUTES LIKE SOIL FERTILITY AND WATER QUALITY. IT ALSO MIGHT IMPROVE OUR ABILITY TO MANAGE OUR RANGELANDS TO OPTIMIZE THEIR LONG-TERM HEALTH, PRODUCTIVITY, AND DOWNSTREAM WATER QUALITY.