Dr Yui Osanai1, Dr Oliver Knox1, A/Prof Brian Wilson1,2
1University Of New England, Armidale, Australia, 2NSW Office of Environment and Heritage, Armidale, Australia
Recent studies highlight the importance of dissolved organic carbon (DOC) in soil carbon (C) dynamics through microbial processes. Both the quantity and spatial accessibility of DOC influence the relative importance of microbial processes compared with physical processes. However, the extent to which microbial activity responds to DOC and differences in physical condition through the soil profile remain largely unknown. Here, we conducted a laboratory incubation to quantify microbial respiration responses to DOC in the topsoil (0–30 cm) and the subsoil (30–100 cm) along a simulated soil compaction gradient (disturbed, no adjustment, slightly compacted and compacted), using the soils collected from cotton-based cropping systems under different tillage and rotational managements. Preliminary analysis showed that basal respiration decreased in response to compaction, but increased following disturbance in both topsoil and subsoil. DOC addition increased microbial respiration. However, the response differed between the physical treatments and soil profiles. Both disturbance and compaction resulted in reduced respiration, with a greater reduction observed in the topsoil than the subsoil. When adjusted for field bulk density, the estimated respiration responses to DOC showed much larger responses in the topsoil than the subsoil and in maximum tillage than minimum tillage systems. These results suggest that under field conditions, subsoil respiration will be lower than that of the topsoil due to both physical and substrate constraints. The contrasting effect of disturbance on basal and DOC-induced respiration also suggests that there is a complex interplay between physical and biological processes in regulating C fluxes. Our study demonstrates that soil physical conditions modulate microbial responses to substrate availability, and that agricultural practices that affect physical conditions can have a significant impact on C dynamics and sequestration in agricultural soils.
Yui is a postdoctoral research fellow at University of New England. She is interested in the regulation of the C and N cycles in terrestrial ecosystems in the context of environmental changes. In particular, her research focuses on the interactions and feedback between plants, soil and soil microbial communities and how changes in the environment may directly or indirectly impact the interactions between them to influence soil processes and nutrient availability, and their consequences for plant productivity.