Multidimensional trait space outlines the effects of changes in abiotic filtering on aquatic plant community from sub-Antarctic ponds

In the current context of climate changes, which causes strong habitat variation, an understanding of the mechanisms underlying plant community dynamics is crucial to predict species fates. The taking of inter- and intraspecific trait variability into account would aid the identification of these mechanisms. Recently, a method involving the calculation of hypervolumes (n-dimensional spaces of trait values) was developed for the study of plant responses to their environments. Through hypervolume comparison, we examined the effects of interannual variations in abiotic conditions on aquatic plant communities in ponds of the sub-Antarctic Iles Kerguelen. This model system is particularly relevant for the examination of the consequences of climate changes–related habitat variation, as aquatic plant communities are adapted to cold and overall stable habitat conditions and the sub-Antarctic climate is changing rapidly. We conducted field sampling over four years at three sites. For all aquatic species, we measured five foliar, shoot, and clonal traits characterizing individual growth strategies that are likely to respond to variations in abiotic conditions on 1565 ramets over the four years. We measured 10 abiotic variables to characterize the plants’ habitats every three months during the survey period. Hypervolumes were calculated for each site and year to assess variation in aquatic plant strategies at the community level. We demonstrated (i) the importance of spatiotemporal gradients of trophic status, temperature, and pH and dissolved oxygen concentration for the functional structure of aquatic plant communities; (ii) that the shape of the mean response was trait dependent, with traits related to plant metabolism (specific leaf area and specific internode mass) and three-dimensional space exploration (height and internode length) responding to the three spatiotemporal abiotic gradients; (iii) that selection pressures were especially high on aerial traits relative to clonal traits; and (iv) that given the community response to interannual variations of abiotic conditions, environmental changes should impact macrophyte community productivity. Synthesis. We conclude that the examination of interannual abiotic variation over four years is sufficient to detect rapid responses of macrophyte communities, with likely reliance on phenotypic plasticity. Our findings may inform the characterization of future functional changes in aquatic plant communities of the sub-Antarctic region, where similar species are found.