Drivers of phytoplankton diversity in Patagonian and Antarctic lakes across a latitudinal gradient (2150 km): the importance of spatial and environmental factors

We investigated the phytoplankton structure in 60 lakes across a latitudinal gradient (2150 km), from Austral Patagonia to Antarctica, including environments ranging from oligotrophic to eutrophic. We analysed the latitudinal variation of species richness (local and regional) and evenness, as well as the similarity decay in phytoplankton composition in Patagonia and Antarctica. The following hypotheses were tested: (1) there is a decline of phytoplankton species richness with increasing latitude; (2) phytoplankton structure is influenced by both geographical and environmental factors. (3) The predominant algal trophic strategy (autotrophic vs mixotrophic) is influenced by lake trophic status. Phytoplankton was analysed using a polyphasic approach (morphologically based species diversity, functional diversity, dominant molecular diversity). We found a significant decline in phytoplankton richness with increasing latitude. Multivariate analyses showed that phytoplankton is structured by the lake geographic position (mainly latitude) and variables related with trophic state (nutrients, conductivity and pH). The autotrophs/mixotrophs ratio increased towards higher trophic states. The initial similarity was higher in Antarctica than in Patagonia, whereas the halving distance was lower for Antarctic lakes. The three biodiversity approaches of this meta-analysis evidenced that both geographic and environmental factors influence phytoplankton diversity at large spatial scale, although the local effect was stronger.