Distribution of two C cycle enzymes in soil aggregates of a prairie chronosequence

Knowledge of the cycling and compartmentalization of soil C that influence C storage may lead to the development of strategies to increase soil C storage potentials. The objective of this study was to use soil hydrolases and soil aggregate fractionation to explore the relationship between C cycling activity and soil aggregate structure. The prairie chronosequence soils were native prairie (NP) and agricultural (AG) and tallgrass prairies restored from agriculture in 1979 (RP-79) and 1993 (RP-93). Assays for beta-glucosidase ( E. C. 3.2.1.21) and N-acetyl-beta-glucosaminidase (NAGase, EC 3.2.1.30) activities were conducted on four aggregate size fractions (> 2 mm, 1 - 2 mm, 250 mu m - 1 mm, and 2 - 250 mu m) from each soil. There were significantly greater amounts of > 2- mm aggregates in the RP-79 and RP-93 soils compared to the NP and AG soils due to rapid C accumulation from native plant establishment. Activities for both enzymes (mu g PNP g(-1) soil h(-1)) were greatest in the microaggregate ( 2 - 250 mu m) compared to the macroaggregate (> 2 mm) fraction; however, microaggregates are a small proportion of each soil (< 12%) compared to the macroaggregates (similar to 75%). The RP soils have a hierarchical aggregate system with most of the enzyme activity in the largest aggregate fractions. The NP and AG soils show no hierarchical structure based on aggregate C accretion and significant C enzyme activity in smaller aggregates. The distribution of enzyme activity may play a role in the storage of C whereby the aggrading restored soils may be more susceptible to C loss during turnover of macroaggregates compared to the AG and NP soils with less macroaggregates.