Does phosphorus limitation promote species-rich plant communities?
It is known that the number of limiting nutrients may affect the species richness of plant communities, but it is unclear whether the type of nutrient limitation is also important. I place the results from a study in Patagonia (elsewhere in this issue) in the context of the number and types of nutrients that are limiting. I present four mechanisms through which N or P limitation may potentially influence species richness. These mechanisms are related to: (i) the number of forms in which P or N are present in soil and the plant traits needed to acquire them, (ii) the mechanisms and traits that control species competition and coexistence under N or P limitation, (iii) the regional species pools of plants capable of growing under N- and P-limited conditions, and (iv) the interaction between the type of nutrient limitation and community productivity. It appears likely that P limitation can favour a higher species richness than N limitation, in at least in a variety of low productive plant communities, but evidence to support this conclusion is so far lacking. The four mechanisms proposed here offer a framework for exploring whether the type of nutrient limitation per se, or an interaction with productivity, is a potential driver for variation in species diversity.
KeywordsN:P stoichiometry Nutrient limitation Diversity-productivity Species competition Species pool Biodiversity N:P ratio Nitrogen Phosphorus Resource balance hypothesis Growth rate hypothesis
I thank Luciola Lannes, Etienne Laliberté, Hans Göransson, Hans Lambers, Peter Edwards, and three reviewers for their discussions and suggestions to improve the manuscript, Kristel Perreijn for drawing Fig. 3, and Luciola Lannes and Etienne Laliberté for allowing to use their photographs (Fig. 1a, b). This paper was written in the context of project 31003A_122563 funded by the Swiss National Science Foundation.
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