Soil organic matter stabilization in turfgrass ecosystems: Importance of microbial processing

Biochemical modification of plant materials may contribute considerably to the formation and stabilization of soil organic matter, but its significance remains elusive in turfgrass systems. This study aimed to close this knowledge gap by examining the dynamics of soil organic matter in turfgrass systems as well as its stability using delta C-13 and delta N-15 records. Two geographic locations, each containing 3 or 4 turfgrass systems of different ages were used as the study sites because site-associated differences, in particular soil pH (alkaline versus acidic) might cause divergence in microbial processing during organic matter decomposition and resynthesis. We observed that soil C storage was similar to 12% greater in the alkaline site than the acidic one. In addition, accumulation rates of soil organic C and N were about 3-fold higher in the alkaline site. Soil organic matter was physically fractionated into light and heavy fractions. Heavy fraction from the alkaline site mineralized more slowly than the acidic one, indicating that soil organic matter was more stable in the alkaline site. Furthermore, the stability of soil organic matter based upon delta N-15 records and C-to-N ratio of organic matter was again found to be more stable in the alkaline site than the acidic one. While both soil delta C-13 and delta N-15 increased as turfgrass systems aged, rates were greater in the alkaline site than the acidic one. Temporal shifts in Soil delta C-13 and delta N-15 were attributed mainly to isotope fractionation associated with microbial processes rather than selective preservation of C-13- or N-15-enriched chemical compounds of plant materials. Our results suggested that microbial decomposition and resynthesis played an important role in organic matter stabilization in turfgrass systems and this microbial processing could be managed via microbial activity-regulating factors, such as soil pH. (c) 2010 Elsevier Ltd. All rights reserved.