Trophic interactions and microbial-derived carbon in porosphere of arable fields

Abstract

Soil physical properties, such as porosity, are recognized to play an important role in the formation of soil organism communities and may regulate carbon sequestration in the soil ecosystem. However, despite their eminent importance, the relation between the abundance of soil animals, microbial necromass and pore space has been rarely demonstrated empirically. In this study, soil visible macroporosity (measured using X-ray computed tomography), microbial necromass (a pool of soil organic carbon), and densities of nematode groups were measured in the topsoil layer at a depth of 10 cm in four arable fields in southern Finland (clay and loam soils). Bacterial necromass was positively correlated with visible macroporosity smaller than 428 μm in size. Fungal necromass was marginally correlated (p = 0.059) with pores <233 μm in size. The abundance of bacterial feeding nematodes (and unknown juveniles) scaled positively with microbial necromasses, visible macropores smaller than 700 μm and the total visible macroporosity. The abundance of other feeding groups was independent of soil visible macroporosity. However, trophic interactions between feeding groups of nematodes appeared to be weak in this soil layer. Results indicate strong bottom-up regulation between microbes and microbial feeding nematodes. Microbial necromass, as an important organic fraction in soil, was clearly related to small soil macropores (<428 μm). These findings provide novel insights into how soil architecture, particularly macroporosity below 700 μm, influences the spatial ecology of soil organisms - an aspect that has received limited attention in boreal agroecosystems.