Author
 |
Tracy, Benjamin |
|
Sanderson, Matt |
|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/18/2004 Publication Date: 12/20/2005 Citation: Tracy, B.F., Sanderson, M.A. 2005. Productivity and stability relationships in mowed pasture communities of varying species composition. Crop Science. 44(6):2180-2186. Interpretive Summary: We know little about the relationship between plant diversity and ecosystem function in managed grasslands like pasture. Recently, some studies have linked increased productivity, stability, and nutrient retention to high plant diversity in grasslands. If such effects apply to northeast pastures, managing pastures for high plant diversity might benefit producers. In May, 1998, we initiated a field experiment to address questions about the relationship between plant diversity and ecosystem function in pasture communities that were frequently clipped to simulate rotational grazing. The experiment consisted of 15 different cool season (C3), grassland forages divided into eight mixtures of 1, 2, 3, 4, 6, 8, 10, and 15 different species, respectively. The eight mixtures were seeded into small plots (1.5 m x 1.5 m) and clipped at four week intervals. In 1999, we measured aboveground production, aboveground C and N concentrations, changes in species composition during drought conditions, root biomass, microbial respiration, and soil nitrate concentrations. Plant production increased with increasing diversity. But beyond three species in a mix, there was little increase in production. Production was controlled mostly by the number of functional groups in a mixture (legumes, grasses). The number of species within each functional group was not as important. Belowground variables were unrelated to plant diversity. Plant diversity also had little effect on the resistance of these swards to drought. The presence of functional groups in mixtures was more important for conferring stability during drought conditions. Overall, our study suggests that only a few species (3-4) from different functional groups may be needed to attain high sustainability in pastures. Technical Abstract: The relationship between biodiversity and ecosystem function has received much attention recently. Few studies, however, have evaluated these relationships under grazing or simulated grazing (i.e., clipping). In May, 1998, we initiated a field experiment to address questions about the relationship between plant diversity and ecosystem function in pasture communities that were frequently clipped. The experiment consisted of 15 different cool season (C3), grassland forages divided into eight mixtures of 1, 2, 3, 4, 6, 8, 10, and 15 different species, respectively. The eight mixtures were seeded into small plots (1.5 m x 1.5 m) and clipped at four week intervals. In 1999, we measured changes in aboveground production, tissue C and N concentration, and species composition from May to October. Root biomass, microbial respiration, and nitrate concentrations were also measured. The simplest communities (1 and 2 species) were consistently less productive aboveground (50-80% less) than other mixtures primarily because they contained only grasses and no legume functional group. Functional group diversity of the mixtures explained ~ 45% of the variation in aboveground production during the growing season, while species diversity explained less than 1%. Root biomass, rates of microbial respiration and, soil nitrate concentrations were unrelated to plant diversity. Plant diversity also had little effect on the stability of biomass and species composition during drought conditions of 1999. Stability, instead, depended on whether stress tolerant species were present in mixtures and how certain functional groups interacted during the drought. Overall, our results provide additional support for the need to preserve and maintain functional group diversity in grassland ecosystems. |
