Functional traits of fringe and dwarf mangroves in Pacific and Caribbean populations

Background/Question/Methods

Functional traits reveal how plants respond to their environments, with traits reflecting climate, soil resources, disturbance, competition, and protection against herbivory. Nutrient limitation is a major factor structuring mangrove forests, with nitrogen (N) and phosphorous (P) limitation causing stunted growth forms around the world. In this study, we examined how functional traits of the rare mangrove Pelliciera rhizophorae vary on the Pacific and Caribbean coasts of Panama and in dwarf trees compared to fringe trees. Mangroves on the Pacific coast of Panama experience increased tidal flushing, more seasonal precipitation, and different geomorphology compared to mangroves on the Caribbean coast of Panama. We predicted that P. rhizophorae on the Caribbean coast would have lower nutrient content and better resorption efficiency than plants on the Pacific coast. We also predicted dwarf trees would dedicate more biomass to wood than leaf tissue and have lower nutrient content than fringe trees.

Results/Conclusions

Phosphorous content was lower in Caribbean fringe trees than Pacific fringe trees (t-test t = -2.24, df = 112.38, p-value = 0.03). P resorption efficiency was higher in Caribbean trees than in Pacific trees (t-test, t = 7.15, df = 138.56, p-value < 0.001), but was not different between fringe and dwarf trees (t-test, t = -0.498, df = 19.22, p-value = 0.624). Nitrogen resorption efficiency was not significantly different between the two coasts (t-test, t = -1.68, df = 137.08, p-value = 0.095). N content did not differ between coasts (t = 0.743, df = 132.827, p-value = 0.46), but N content was significantly different between fringe and dwarf trees (t = 2.37, df = 29.86, p-value = 0.02). Five of six biomass allocation ratios were significantly different in fringe and dwarf trees, but only the ratio of stem length to stem biomass was significantly different between the two coasts.