Spatial and temporal patterns of soil biological activity in a forest and an old field

The spatial distribution of C mineralization, nematode density, organic matter content and soil moisture were determined for a forest and an old field soil in the northeastern U.S.A. over the course of a year. The data were analyzed using univariate, multivariate and geostatistical methods. The forest soil had a higher C mineralization rate, soil moisture content and nematode density than the old field soil throughout the year. High C mineralization rates and nematode density coincided with a brief January thaw in the forest, but not in the old field soil. Multiple regression analysis identified different components as significant for C mineralization depending on sampling date. In the old field, soil moisture and organic matter content were significant regression components for C mineralization at different times of the year. In the forest, organic matter, root mass (> 2 mm) and bulk density were significant regression components on different dates. For nematodes, the multiple regression analysis identified soil moisture and bulk density as significant in both soils at different times of the year. Maps for each property were estimated with block kriging for each sampling date. In the forest, areas of maximal C mineralization and nematode density coincided with areas of high organic matter and moisture content only on some sampling dates. In the old field, maximal C mineralization generally coincided with areas of high moisture and organic matter content. Spatial structure in both forest and old field changed through the year. Our results suggest that dynamics and spatial patterns of C mineralization in the old field may be more susceptible to changes in soil moisture than in the forest soil. By contrast, temporal and spatial patterns of nematode density in both ecosystems appear to be susceptible to soil moisture dynamics. Organic matter appears to be important in controlling the spatial distribution of C mineralization, but not that of nematodes.