Applying Biodiversity And Ecosystem Functioning Theory To Urban Grassland Management
Urban grasslands are rapidly expanding in the United States and around the world. Such landscapes are dominated by turfgrasses and are kept as aesthetic or recreational groundcovers. These systems are less diverse than the natural or agricultural systems they replace, leading to potential losses in ecosystem functioning. Research in prairie grassland ecosystems suggests increasing aboveground diversity may enhance multiple ecosystem services. Biodiversityecosystem functioning (BEF) research has linked species richness to enhanced productivity, resilience, invader resistance, and overall multi-functionality. Therefore, there is potential to improve the ecosystem services of urban landscapes if biodiversity is explicitly considered in their design and maintenance. An urban grassland diversity gradient was studied in greenhouse mesocosms to determine biodiversity effects on productivity and nitrate leaching. Twelve turfgrass components were randomly assigned to four diversity level treatments: monoculture or 3, 6, or 12-part polycultures. Productivity was examined over 17 weeks by measuring total aboveground and belowground yield. Nitrate leaching was assessed by quantifying nitrate-nitrogen (NO3--N) losses recovered from lysimeters. Plant diversity stimulated total and standing productivity between monoculture and 3component polyculture treatments. Positive trends were observed for 6- and 12-component polycultures compared to monocultures for standing aboveground harvest and total biomass. No differences were observed in belowground productivity. Experimental observations presented here match literature trends, generally showing positive productivity responses to aboveground diversity. Highly productive species effects are driving some of the observed productivity trends. Yet, selection of diverse turf assemblages does increase the likelihood of including highly productive species, thus aboveground richness is still a valuable means for enhancing urban grassland productivity. Aboveground diversity reduced NO3--N concentrations in leachate. When a nitrogen (N) fixing legume was included in turf assemblages, NO3- leaching increased, but not significantly more than other assemblages within the same diversity level treatment. Nitrate losses decreased up to four fold in the highest diversity polyculture compared to the monoculture legume treatment. Nitrate leaching trends observed in experimental mesocosms concur with published results in the literature, supporting the conclusion that polycultures retain N more effectively than monocultures. Polycultures also enriched for greater diversity of soil microbiota. The gradient of plant diversity did not show an increasing level of bacterial or fungal diversity. Instead, it mattered whether there was a single plant species versus multiple plant species. A similar pattern held when the structure of the microbial community showed greater variability in monoculture, but similar profiles when multiple plant species were present. This study agrees with previous BEF research, showing biodiversity effects enhance multiple ecosystem services. Future studies should focus on ecosystem processes relevant to urban grasslands such as carbon storage, N retention, and resistance to biological invasions. Furthermore, studies should assess the strengths of biodiversity effects in situ and determine the scales at which diversity enhances multiple ecosystem processes.
biodiversity ecosystem funciton; turfgrass; urban grassland
Kao-Kniffin, Jenny T.
Drinkwater, Laurie E; Rossi, Frank S
M.S. of Horticultural Biology
Master of Science
dissertation or thesis