Interactive influences of silvicultural management and soil chemistry upon soil microbial abundance and nitrogen mineralization.

摘要

An investigation was made possible interactive effects between soil acidification (a widespread, chronic mode of disturbance) and forest thinning (a site specific acute disturbance) to determine whether such a mechanism was capable of producing changes in more general ecosystem properties and processes. Two experimental forest sites (mixed broadleaved forest dominated by Quercus spp.) in the Daniel Boone National Forest, Kentucky, USA, with similar history, management, and parent material, but differing soil acidity (soil pH 4.4 and 5.1) were selected for the study. An analysis of NO3 and NH4 deposition at the 2 sites from 1984 to 1995, showed that they had similar N deposition histories. At each forest site 2 plots that were experimentally thinned in the 1960s, and 2 adjacent unmanaged plots, were sampled for soil chemical characteristics, microbial abundance, N mineralization and nitrification. There were significant differences between forest sites and significant effects of management for allsoil chemical parameters, fungal biomass, N mineralization and nitrification. Soils from managed plots were generally higher in pH, nutrient availability and nitrification rates. There were significant interactions between site and management for NO3, pH, Ca, Ca:Al ratio and nitrification, resulting from the greater magnitude of the management effect at the less acidified site. Additionally, there were interactive effects of site and management in organic C, NH4 and fungal hyphal length, because plotsat the 2 sites showed dissimilar effects of management. Modelling using path analysis determined that N mineralization was most strongly predicted by combinations of organic C, Al, Ca:Al ratio, and fungal:bacterial ratio, while inorganic N availability and Ca:Al ratio were the main factors for nitrification. Fungal hyphal length was most strongly predicted by Al and pH; in contrast, path analysis failed to produce a model for bacterial abundance. These results suggest (1) that acute and chronic modes ofdisturbance have the potential to interact in a significant and ecologically meaningful manner and (2) that research to assess forest health should be based on key ecosystem processes, such as N mineralization and nitrification.