Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot.

摘要

Questions: What is the role of nutrient limitation of dominant species in maintaining plant species diversity at small spatial scales, particularly in biodiversity hotspots? Location: Southwest of Western Australia. Methods: The extent of nutrient limitation was determined by measuring variation in the foliar nutrients of dominant plant species and total above-ground biomass in relation to soil N and P across 16 plots. Plant species richness and evenness for the same plots were then regressed against foliar N:P and delta 15N of the dominant species. Results: Foliar N and P content as well as above-ground biomass increased, while foliar N:P decreased with increasing soil N and P, suggesting that dominant species are limited by both N and P in southwest Australia. In contrast, foliar delta 15N values only increased with decreasing soil P, indicating that delta 15N enrichment reflects low P availability. Species richness increased at sites where foliar N:P was higher and delta 15N more enriched, suggesting that a relatively greater number of rare plant species co-exist where the growth of dominant vegetation is more nutrient-limited. Conclusions: The mechanisms that allow an exceptionally high number of plant species to co-exist at small spatial scales in a southwest Australian biodiversity hotspot are linked to the extent to which the dominant plant species are limited in N and P. In addition, on nutrient-impoverished soils, a foliar N:P ratio >16 can reflect N as well as P limitation. While foliar delta 15N also reflects availability of soil P, it is not necessarily a reliable indicator of nutrient limitation in southwest Australia, and perhaps in other environments where plants are highly adapted to low-nutrient conditions.