Foliar nitrogen and phosphorus accumulation responses after fertilization: an example from nutrient-limited Hawaiian forests

How plants respond to long-term nutrient enrichment can provide insights into physiological and evolutionary constraints in various ecosystems. The present study examined foliar concentrations after fertilization-to determine if nutrient accumulation responses of the most abundant species in a plant community reflect differences in N and P uptake and storage. Using a chronosequence in the Hawaiian Islands that differs in N and P availability, it was shown that after fertilization, plants increase foliar P to a much greater degree than foliar N, as indicated by response ratios. In addition, foliar P responses after fertilization were more variable and largely driving the observed changes in N:P values. Across species, both inorganic and organic P increased but neither form of N increased significantly. This pattern of P accumulation was consistent across 13 species of varying life forms and occurred at both the N-limited and P-limited site, although its magnitude was larger at the P-limited site. Foliar P accumulation after nutrient enrichment may indicate nutrient storage and may have evolved to be a general strategy to deal with uncertainties in P availability. Storage of P complicates interpretations of N:P values and the determination of nutrient limitation.