Soil pore effects on spatial patterns of extracellular enzymes: combined X-ray computed tomography and 2D zymography

Extracellular enzymes play an important role in soil biochemical processes as they are the key regulators of litter and soil organic matter degradation. However, understanding of the factors influencing their activity and fate in soil is still limited. In this study, we examined the relationship between soil pores and spatial patterns of extracellular enzyme activity in soils from two bioenergy cropping systems: monoculture switchgrass (Panicum virgatum L.) and restored prairie. Intact soil cores (5 cm Ø x 5 cm height) were collected at two contrasting topographical positions (depression and slope) within large topographically diverse fields where the switchgrass and prairie were grown since 2008. The cores were subjected to X-ray computed tomography scanning at 18 µm resolution. After the scanning, a switchgrass seedling was planted in these cores and allowed to grow for three months. Then the plants were terminated and the cores were rescanned. Pore characteristics were assessed using the image information, and b-glucosidase activity was characterized via 2D zymography. Preliminary results showed that soil of the prairie system had greater volumes of 60-180 mm Ø size pores compared to monoculture switchgrass system. However, enzyme activity was higher in the soil of monoculture switchgrass. Our preliminary results indicate that the soil pore size distribution and enzyme activity differ depending on the type of the bioenergy cropping system. Further analysis is conducted to determine microbial abundance, total C in soil and microbial biomass in these cropping systems to understand the effect of pores on microbial activity associated with C processes in soil.