Patterns of phosphorus, nitrogen and δ15N along a peat development gradient in a coastal mire, Panama

Differentiation of limiting nutrients within small spatial scales has been observed in coastal mangrove forests, but research on other tropical peatlands suggests it is a more widespread phenomenon. In the Changuinola mire of coastal Panama, oligotrophy was hypothesized to increase along a gradient of peat development (peat doming). Nutrient and carbon concentration of leaf tissue, soil, and soil porewater were characterised over a successive sequence of plant communities along the gradient. Soil phosphorus (P) and nitrogen (N) concentrations decreased from 1200 mu g P g(-1) and 27 mg N g(-1) to 3 77 mu g P g(-1) and 22 mg N g(-1) within 2.7 km into the mire interior. These changes coincided with an increase in soil and average leaf N:P molar ratios from 52-128 and 24-41, respectively. Soil P was strongly related to leaf P and soil N:P to foliar N:P. There was a wide range in delta N-15 values for canopy (4.0 to -9.4%), Campnosperma panamense (4.0 to -7.8 parts per thousand) and understorey (4.8 to -3.1 parts per thousand) species. Foliar delta N-15 values of canopy species were strongly related to soil N:P, soil P and leaf P. The depleted foliar delta N-15 values appeared to be an effect of both the N atmospheric source and P limitation. Here, P limitation is likely associated with ombrotrophic conditions that developed as hydrologic inputs became dominated by precipitation.