SS 14-1
New frontiers in trait-based ecology: Testing theory by comparing functional diversity of forest trees and soil microbes across latitude
The processes causing the latitudinal gradient in species richness remain elusive. Ecological theories for the origin of biodiversity gradients such as competitive exclusion, neutral dynamics, and environmental filtering make predictions for how functional diversity should vary at different spatial scales and across broad diversity gradients. In an effort to assess the generality of latitude and temperature and to assess several prominent theories generating diversity patterns, we examined soil microbial and plant taxonomic and functional diversity along a latitudinal gradient.
Comparisons of patterns of diversity across such disparate groups of organisms are rare. Both Plants and Micro-organisms play critical roles in many important biogeochemical processes in the Earth's biosphere. However, understanding and characterizing the functional capacity of plants, but especially microbial communities, are still difficult. This is due to the importance of pairing reliable local surveys with taxon abundance and within site trait measures and functional measures from extremely diverse and often uncultivable nature of most micro-organisms. We test predictions by quantifying differing measures of diversity via functional traits. Measures of functional diversity were based on plant and microbial functional traits that representing major axes of plant strategy variation as well as microbial resource use and functioning. We utilized high throughput sequencing and functional gene array, to analyze microbial functional diversity, composition, structure, metabolic potential/activity and dynamics of microbial communities. We assessed functional gene families related to microbial carbon (C), nitrogen (N), sulphur (S), and phosphorus (P) cycling and energy metabolism. We ask, are shifts in taxonomic diversity best explained by trait shifts and patterns of functional trait diversity. We assess both soil and tree assemblages within sites that span temperate and tropical New World.
Results/Conclusions
Our results enable one of the first comparison of functional diversity within and across microbial and plant species communities across latitude. In contrast to recent studies that have shown that climate only has a relative weak signal in patterns of single trait shifts across climate gradients, we show that when differences in species abundances are taken into account that multivariate shifts in trait composition is largely explained by climate (~ 80 – 98%). We find that soil temperature, in particular, appears to have the strongest effect in shifts in community trait diversity. Overall, our results show that shifts in taxonomic diversity are best explained and viewed by shifts in community trait composition. While we highlight several challenges that remain in fully comparing patterns of diversity across differing taxonomic groups, nevertheless, our findings have important implications for assessing biodiversity theory and for the main drivers that structure diversity gradients.