Impact of soil water deficits in a mature sugar maple forest: stand biogeochemistry

Computer simulations of moisture relationships in an uneven-aged, tolerant hardwood forest at the Turkey Lakes Watershed suggest that soil water deficits during 1982–1983 and 1988–1989 were among the most severe of the past 40 years. Examination of radial growth indices for sugar maple (Acersaccharum Marsh.) trees suggested that reductions in growth coincided with low volumetric soil water contents and with low NO3− concentrations in soil solution. The lowest mean monthly NO3− concentrations in soil percolate were observed during severe summer droughts. Nitrate concentrations were negatively correlated (r2 = −0.803) with SO42− levels in solution and positively correlated (r2 = 0.761) with Ca2+ levels. Nitrification, by stimulating adsorption of SO42− by the soil, may lead to temporary retention of atmospheric SO42− in soils that otherwise exhibit only limited capacity to retain SO42−. If warmer, drier summers become more frequent, nitrogen cycling will become more closed as the supply of nitrogen to the v...