Plant species richness in a natural Argentinian matorral shrub-land correlates negatively with levels of plant phosphorus

Abstract

The aim of this study was to ascertain whether there is a relationship between plant species richness and plant-available N, P and water in an environment subject to little anthropogenic disturbance. To accomplish this we studied the vegetation in matorral shrub-lands in northern Patagonia, Argentina. Due to the variation in slope, precipitation and aspect between the sites water status was determined using the 12 C/ 13 C fraction, δ 13 C, to investigate whether this was a confounding factor. The numbers of herb, shrub, liana and tree species were determined at 20 sites along an estimated precipitation gradient. Leaf P and N content and the δ 13 C of Berberis buxifolia were determined, as well as the soil P and N content at the different sites. A negative correlation was found between species richness and Berberis buxifolia foliar P concentration (52% of the species richness variation was accounted for), and a positive correlation was found between plant species richness and Berberis buxifolia foliar N: P ratios (54% of the species richness variation was accounted for). The relationship between species richness and foliar P was seen when all layers of vegetation were included (trees, lianas, shrubs and herbs). Foliar N showed no correlation with species richness, while soil extractable NH 4 showed a weak positive correlation with the number of shrub layer species (lianas, shrubs and trees). The species richness of the shrub layer increased with decreasing values of δ 13 C. Low soil P availability thus affects local species richness in the matorral shrub-lands of Patagonia in Argentina although the growth of vegetation in the area has been shown to be limited by N. We suggest that low P levels increase plant species richness because low soil P concentration is associated with a high P partitioning and high potential for niche separation.

Does phosphorus limitation promote species-rich plant communities?

“…Such species pool effects could potentially explain the decreasing or unimodal relationships between local species richness and vegetation N:P ratio in YODFELs, and increasing relationships in OCBILs (see above). The results from the Patagonian site (a YODFEL) of Blanck et al (2011) would fit as part of the upward slope of a unimodal pattern between richness and N:P ratio, which corresponds with the very low range of N: P ratios they observed (2-12 on mass base).…”

“…In this issue of Plant and Soil, Blanck et al (2011) show that total plant species richness in matorral shrub-lands in Patagonia, Argentina, decreases with increasing P availability, as indicated not only by concentrations of P in the soil but also by N:P ratios and P concentrations in the leaves of the common shrub Berberis buxifolia. These correlations with species richness are consistent with data from other studies.…”

“…This mechanism is likely to be more relevant for aquatic ecosystems, where nutrients are well mixed, than for plants growing in soil, where nutrients are distributed heterogeneously (Huston and DeAngelis 1994); however, there is some evidence that it does apply also in terrestrial ecosystems (Harpole and Tilman 2007;Roem et al 2002). In their study, Blanck et al (2011) found that the N:P ratio in leaves of the shrub Berberis buxifolia ranged between 4-25 on molar base which corresponds to c. 2-12 on mass base. Despite this wide range in N:P ratios, they conclude that all their plots were probably N-limited.…”

“…The papers cited above, including (Blanck et al 2011), are examples of studies performed at a local or regional scale. Furthermore, the study site of Blanck et al in Patagonia is an example of a relatively young, often disturbed, fertile landscape (YODFEL; Hopper 2009).…”

“…Finally, we need to understand better how the type of nutrient limitation might interact with species richnessproductivity patterns, and the mechanisms behind these patterns. To start with, more studies like that of Blanck et al (2011) are needed to provide the material for future meta-analyses.…”