Incorporating Diversity Into Grass Polycultures To Enhance Ecosystem Functions.

Biodiversity is known to have positive impacts on a range of ecosystem services, including community productivity and stability in native grasslands. To date, biodiversity effects have not been well studied using turfgrass assemblages, which impact vast areas of urban and agroecosystems. We examined the effects of increasing diversity on plant productivity, soil microbial diversity, and nitrogen retention using grassland mesocosms grown in a controlled environment facility. The diversity gradient consisted of 13 randomized assemblages with five replicates of each of the following assemblages:  six monocultures, three 3-way polycultures, three 6-way polycultures, and one 12-way polyculture. Aboveground biomass was collected for 17 weeks, and added to the total standing above-and below-ground biomass to assess total plant productivity.  Water samples collected from lysimeters were used to measure nitrate losses from the grassland assemblages. Terminal restriction fragment length polymorphism (T-RFLP) was used to assess soil bacterial and fungal diversity. Analysis of variance revealed a positive relationship between diversity level and weekly productivity (p=0.009), standing above-ground biomass (p=0.0178), and nitrogen retention (p=0.0011). Below-ground biomass results did not change with increasing plant diversity. Microbial community profiling (T-RFLP) is currently under analysis to assess linkages between above- and below-ground diversity; the results will be presented at the meeting. A greater understanding of how grassland diversity impacts ecosystem functions will aid land managers in selecting plant assemblages for enhanced productivity and nitrogen management.