INFLUENCES OF MYCELIAL FUNGI ON SOIL AGGREGATION AND ORGANIC-MATTER STORAGE IN CONVENTIONAL AND NO-TILLAGE SOILS

Soil microbial community composition, aggregation and organic matter ( SOM) content can be markedly influenced by tillage and crop management practices. This study was undertaken to determine to what extent diff erences in populations of mycelial fungi in conventional (CT) and no-t illage (NT) soils contribute to soil aggregation and soil organic matt er storage. Fungicide (Captan) and control treatments were established in long-term CT and NT plots on a well-drained Hiwassee sandy clay lo am soil (clayey kaolinitc thermic Rhodic Kanhapludult). The effects of these treatments on total and FDA-active fungal hyphal lengths, total bacteria (0-15 cm) and in situ soil respiration rates were measured a t approximately monthly intervals. Soil carbohydrates and water-stable aggregate (WSA) distributions were quantified on the final sample dat e. Surface soil (0-5 cm) of NT had more macroaggregates (> 250 mu m di am) and 1.30 to 1.46 times higher densities of fungal mycelia as compa red to CT soils. The higher populations of fungal mycelia corresponded to a nearly two-fold higher concentration of acid-hydrolysable carboh ydrates, which were composed of proportionally more microbial- than pl ant-derived sugars. Treatment with the fungicide resulted in a 40% red uction in > 2000 mu m WSA and lower concentrations of carbohydrates in NT surface soils, but had no significant effects in CT soils. The con tributions of fungi to aggregate stability may represent an important biotically-regulated mechanism for the protection of soil organic matt er and may help to explain the greater retention of soil organic carbo n in NT than in CT soils.