Plant stoichiometry has been used to diagnose phosphorus (P) limitation caused by increased atmospheric nitrogen (N) deposition. Spatial variability of N/P stoichiometry within a forested watershed has not yet been evaluated. This study conducted synoptic sampling of leaf matter in 27 plots within a temperate forested watershed on low P availability rock (serpentine bedrock) with a moderately high atmospheric N deposition (16 kg N ha-1 year-1) to assess the effects of spatial topographic variation on N/P stoichiometry. Leaf N and P concentrations and N/P ratios of Japanese cypress were assessed, and their spatial variations were evaluated across a catchment. Average leaf P concentration was low (0.66 ± 0.16 mg g-1) across the sites, while leaf N concentration was high (13.0 ± 1.5 mg g-1); subsequently, N/P ratios were high (21 ± 5). In addition, the aboveground biomass growth of Japanese cypress positively correlated with litter P, implying the P limitation of Japanese cypress at the study site. Leaf P concentrations responded to the index of convexity (IC) values more than those of N. Subsequently, the N/P ratio correlated with IC, suggesting that N/P ratios are susceptible to topographic features. This could be partly caused by smaller spatial variability of N availability compared with P, owing to increased atmospheric N deposition. Thus, topography should be taken into consideration when diagnosing P limitation caused by N deposition.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Environmental Chemistry
- Ecological Modelling
- Water Science and Technology