Microbial Leaf Decomposition in Adirondack Streams Exhibiting pH Gradients

Abstract

The effects of water pH and related water chemistry parameters on microbial decomposition processes were studied in three small, low-order woodland streams located in the Adirondack region of New York State. These streams exhibited spatial and seasonal gradients in water pH ranging from pH values of 4.5 to 7.0. Measurements of microbial biomass (ATP), bacterial numbers, and bacterial production (thymidine incorporation) on leaves of Acer saccharum were made over a 9-mo period (fall to spring). Decomposition of A. saccharum leaves was significantly decreased at lower pH. The developing epiphytic microbial community was affected in a very specific way. Bacterial numbers were not related to water pH values, nor were ATP measurements significantly correlated with pH or any pH-related water chemistry variable. However, thymidine incorporation by bacteria on leaf material (used as a measure of bacterial productivity) was significantly decreased at lower pH. This was the only consistent indicator of reduced microbial activity in response to acidification of these streams.