Functional groups show distinct differences in nitrogen cycling during early stand development: implications for forest management

Abstract

Nutrient acquisition of forest stands is controlled by soil resource availability and belowground production, but tree species are rarely compared in this regard. Here, we examine ecological and management implications of nitrogen (N) dynamics during early forest stand development in productive commercial tree species with narrow (Populus deltoides Bartr. and Platanus occidentalis L.) and broad (Liquidambar styraciflua L. and Pinus taeda L.) site requirements while grown with a range of nutrient and water resources. We constructed N budgets by measuring N concentration ([N]) and N content (N C ) of above- and belowground perennial and ephemeral tissues, determined N uptake (N UP ), and calculated N use efficiency (NUE). Forest stands regulated [N] within species-specific operating ranges without clear temporal or treatment patterns, thus demonstrating equilibrium between tissue [N] and biomass accumulation. Forest stand N C and N UP increased with stand development and paralleled treatment patterns of biomass accumulation, suggesting productivity is tightly linked to N UP . Inclusion of above- and belowground ephemeral tissue turnover in N UP calculations demonstrated that maximum N demand for narrow-sites adapted species exceeded 200 kg N ha−1 year−1 while demand for broad-site adapted species was below this level. NUE was species dependent but not consistently influenced by N availability, suggesting relationships between NUE and resource availability were species dependent. Based on early stand development, species with broad site adaptability are favored for woody cropping systems because they maintain high above- and belowground productivity with minimal fertilization requirements due to higher NUE than narrow site adapted species.