CONTRIBUTIONS OF INTERACTING BIOLOGICAL MECHANISMS TO SOIL AGGREGATE STABILIZATION IN RESTORED PRAIRIE

A better understanding of the soil aggregation process is needed to ad dress a variety of concerns, including soil quality and erosion, agric ultural sustainability, soil C sequestration, the mobility of hazardou s chemicals and remediation of contaminated sites. We used data from a chronosequence of tallgrass prairie restorations and a path analysis approach to evaluate how the lengths of two dia size classes of fibrou s roots, the length of external mycorrhizal hyphae, microbial biomass C, hut-water soluble carbohydrate C and soil organic C interact to pro mote the stabilization of soil aggregates. The measured binding agents accounted for 88% of the variation in macroaggregates >212 mu m diame ter and goodness-of-fit indexes indicated a good practical fit of the path model to the data. The restoration of macroaggregate structure in this system was apparently driven by the direct and indirect effects of roots and external hyphae, with lesser relative contributions by th e three measured C pools. Although the two root size classes had simil ar direct effects on the percentage of macroaggregates, their indirect contributions differed substantially. Fine roots (0.2-1 mm diameter) exerted considerable indirect effects via their strong influences on e xternal hyphae and microbial biomass C. Very fine roots ( < O.2 mm dia ) made a stronger contribution to soil organic C than fine roots, but their overall indirect contribution to aggregation was minimal. In add ition, the relative importance of each binding agent varied for differ ent size fractions of macroaggregates and generally supported the hypo thesis that the effectiveness of various binding mechanisms depends oi l the physical dimensions of the binding agents relative to the spatia l scales of the aggregate planes of weakness being bridged. Published by Elsevier Science Ltd.