The influence of individual plants on soil nutrient dynamics in the central grassland region of the United States.

摘要

The extent to which plant community structure influences ecosystem nutrient cycling is an important but poorly understood element of ecosystem ecology. I studied the effects of two aspects of vegetation structure, plant cover patterns and plant species composition, on nutrient cycling in soils of shortgrass-steppe, mid- and tallgrass prairie, and desert grassland in the Great Plains. My general objective was to identify the importance of plant cover patterns and species composition, especially in the context of other environmental variables, to soil nutrient dynamics in these grasslands.; In the dry shortgrass-steppe and desert grasslands, plant cover patterns were very important in determining patterns of soil nutrient dynamics. Soils under plants had generally higher rates of carbon and nitrogen pool sizes and turnover rates than soils from adjacent bare ground areas between plants. Individual plant characteristics, such as lifespan and growth form, explained the degree of soil heterogeneity in some cases, with the most long-lived, productive species fostering the most plant-interspace soil heterogeneity. Also, abiotic environmental variables explained patterns in plant-induced soil heterogeneity. The desert grassland with the largest proportion of bare ground, and thus possibly the most soil erosion, had the largest plant-interspace soil heterogeneity. The wet grasslands, the mid- and tallgrass prairies, had more continuous plant cover; thus plant cover did not impose strong control over soil nutrient patterns in these ecosystems.; Plant litter quantity and quality of tissue for decomposers differed between species and grassland ecosystems and, in some cases, affected soil nutrient cycling. Kochia scoparia, an introduced species in shortgrass steppe, had high quality tissue (low carbon:nitrogen and lignin:nitrogen) and had relatively high rates of nitrogen and carbon mineralization in its soils. Precipitation affected plant tissue quality, with a general decrease in average quality and increase in inter-species variation in quality from dry to wet grasslands.; Vegetation structure, and its interaction with site-based abiotic variables such as precipitation, had important effects on soil carbon and nitrogen dynamics in these grassland ecosystems. Results indicate that information about plant community structure may be critical to large-scale estimates of ecosystem function.