δ 15 N and δ 13 C Patterns in Savanna Vegetation: Dependence on Water Availability and Disturbance

Plant leaves were collected from four sites in Kenya, East Africa and analysed for %N, δ 15 N and δ 13 C. Each site had different kinds and amounts of water supply and physical disturbance. There were no uniform relationships among δ 15 N, δ 13 C, % leaf N and plant growth forms. These data indicate that many of the previously published relationships for these variables were peculiar to the ecosystems investigated and should not be assumed as general models. At all sites, δ 15 N variability was large and extreme values were clustered into definable categories, suggesting different N sources. Plant-available soil N could not be treated as a single source at any site and no model for estimation of in situ N 2 fixation could be applied (...)