Is Photosynthesis Nutrient Limited in Tropical Trees?

Abstract

Tropical forests play an enormously important role in the global cycling of carbon. However, the extent to which nutrients limit the potential for tropical trees to increase carbon gain as atmospheric carbon dioxide rises, a phenomenon known as the carbon-concentration feedback, is uncertain. This chapter addresses our current state of knowledge on nutrient limitation of photosynthesis in tropical trees, summarizing and synthesizing the results of over 20 studies on photosynthetic responses to nutrient manipulation experiments. Our results indicate that nutrient limitation of photosynthesis is widespread, but that contrasting species and ecosystems vary in their responses, with savannah trees showing the least response at the leaf scale. Second, although photosynthesis is strongly limited by N in particular species, N limitation of photosynthesis is modest compared to P limitation of photosynthesis when considering all of the available literature. Finally, alleviation of nutrient limitation through addition of combined nutrient treatments produces the strongest photosynthetic responses, highlighting the potentially complex stroichiometric interactions among elements. The authors discuss several ways forward for resolving questions regarding the potential and limits of tropical trees to influence key carbon cycling processes and thus improve our ability to forecast global responses and feedbacks to climate change.