Does β diversity predict ecosystem productivity better than species diversity?

Abstract

There is consensus that greater biodiversity is essential to maintain the ecosystem function and stability. Variation in spatial plant community heterogeneity (β diversity) affects productivity and ecosystems function; however, relatively few studies have addressed how β diversity and its components (i.e. species turnover and nestedness) may relate to ecosystems function. In this study, we assessed plant community diversity (richness and evenness) and spatial heterogeneity along a productivity gradient in different bioclimatic regions including desert-steppe, steppe, semi-steppe and Mediterranean rangelands in south west of Iran, and tested (1): how and to what extent the different components of plant diversity affect aboveground biomass (AGB; as ecosystem productivity) and (2): the mechanisms underlying the relationship between β diversity and ecosystem productivity; i.e. niche complementary and selection effects. Sampling was executed in each bioclimatic region by choosing eight sites and estimating AGB of plant species in 2 × 2 m plots nested within 3 macro plots of 30 × 30 m.The results showed that AGB was significantly predicted by species richness; positively in desert-steppe, steppe and semi-steppe rangelands and negatively in Mediterranean rangeland. Furthermore, AGB was negatively predicted by evenness in desert-steppe and semi-steppe rangelands. There were significantly negative relationships between β diversity and AGB in desert-steppe, steppe and semi-steppe rangelands, while, the significantly positive relationship was found for Mediterranean rangeland. The AGB was significantly and positively related to the turnover and nestedness components of β diversity in Mediterranean rangeland. However, a negative relationship was found with turnover in desert-steppe and semi-steppe rangelands.Our results indicate that niche complementarity may play a critical role in providing and provision ecosystems productivity in steppe and Mediterranean rangelands, while, both selection effects and niche complementarity hypotheses could be verified in low-productive regions (desert-steppe and semi-steppe rangelands). Comparing the strength of species diversity with β diversity in predicting ecosystems productivity across different bioclimatic regions, our results revealed that β diversity predict ecosystems productivity more effectively and provide support for biodiversity-ecosystems function theories.