The ability of plants to develop efficient uptake and storage mechanisms when P becomes available may have strong selective advantages. Hawaiian wet forests have previously been shown to contain examples of both N- and P-limitation, as demonstrated by fertilization experiments at a 300-yr-old N- limited site and a 4.1-myr-old P-limited site. Using fertilization plots that exist within these two soil fertility extremes, plants increased both inorganic and organic foliar phosphorus to a much greater degree than foliar nitrogen in either organic or inorganic forms.
Results/Conclusions
This foliar P accumulation was seen across 16 species and occurred at both sites, although it was more pronounced at the P-limited site. The magnitude of foliar P accumulation varied by species, ranging from 73-498% increases relative to unfertilized plants. To determine if this P accumulation may be related to other leaf-level traits, I sampled eight common species at the P-limited site. Photosynthesis, leaf mass per area (LMA), and N and P concentrations were sampled from individuals growing in long-term fertilization plots (control, +N, +P). For species in +P plots, P accumulation was significantly negatively correlated to photosynthesis on a mass and area basis and photosynthetic P-use efficiency, and positively correlated to LMA. In contrast, there were no significant correlations for plants in +N plots; in addition, foliar N accumulation was unrelated to any of the leaf traits measured. These results suggest the species that are best at storing P are those with characteristics related to slower growth. The ability of species to accumulate P in leaves after pulses of P availability may be part of the suite of co-evolved traits related to efficient resource use in low fertility environments.
