Park, E.J. (Michigan State University, Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824, Phone: 517-355-0271, ext. 247; Fax: 517-355-0270; Email: parkeun2@msu.edu)

Increasing the stabilization of soil aggregates and intra-aggregate C dynamics during multiple D/W cycles with glucose

E. J. Park *, Alvin J.M. Smucker

Increasing the recalcitrant C pool in soils requires the expansion of sorptive surface areas that promote organo-mineral complexes within soil aggregates. Additional intra-aggregate pore networks connectivity, formed during repeated soil drying and rapid rewetting (D/W), provides additional pathways for the diffusion of DOC compounds onto new sorptive surface areas. We investigated the spatial distribution and dynamics of DOC (¹³C-glucose) supplied to individual aggregates and its contribution to aggregate stabilization during multiple D/W cycles. Moist macroaggregates were treated with no glucose and no D/W cycles (Control), no glucose and 5 D/W cycles (D/W), and additions of 250 mg glucose-C/g soil with each of the 5 D/W cycles (G+D/W). Aggregate stability decreased significantly during D/W cycles with no C additions, Figure. 1. Additions of glucose-C during the rewetting stage of each D/W cycle maintained soil aggregate stability throughout the 35-day incubation and increased C flux into aggregate interiors (Figure 2). Respiration of C was greater from exterior regions of aggregates than from interior regions of aggregates. Consequently, G+D/W treatments increased C contents within soil macroaggregate interiors and strengthened macroaggregates. These results identify additional mechanisms that explain how plant residues, associated with no tillage agriculture, increase C sequestration by supplying constant sources of DOC that move into interior regions of stable aggregates during natural D/W cycles at the soil surface.