Influence of soil pore characteristics on the spatial distribution pattern of added carbon: X-ray micro-tomography and isotopic labelling approach

Abstract:

Soil pore network regulates the flow of water, gas diffusion and nutrient availability in soil. This in turn affects the microbial processes that are involved in processing of new carbon. In this study, we examined the influence of soil pore characteristics, such as pore size distributions and soil pore volumes, on the distribution pattern of added carbon at micro-scale. Intact soil cores were collected from two bioenergy cropping systems: monoculture switchgrass (Panicum virgatum L.) and restored prairie, at different topographical positions (depression and slope). Then switchgrass was planted within the cores and pulse labelled with ¹³C in a greenhouse. Pore characteristics of the cores were assessed via X-ray CT imaging. Soil C processes were quantified by measuring soil respiration, total C and N concentrations, and microbial biomass, and by 2D zymography mapping of enzyme activities. Preliminary results showed that soil of the prairie system had greater volumes of 30-90 um radius pores compared to monoculture switchgrass system. However, soil of monoculture switchgrass system resulted in higher CO2 emissions during incubation. Further analysis of soil ¹³C and total C levels in relation to enzyme activity and microbial biomass will help in understating the effect of different size pores on microbial activity associated with C processes at micro-scale.