Root trait variation at the plant community level: Linking belowground trait diversity to vegetation dynamics and ecosystem functioning
Ultimately, both inter- and intraspecific variation in root traits characterize belowground strategies at the community level. In this Special Issue, root trait patterns within plant communities (Table 1) reiterate what is observed within and across species, namely, that plants can display a wide variety of root trait strategies to carry out their belowground functions. Pierick and collaborators (2022) study the variation in root traits in tropical montane forests along an altitudinal gradient in the Andes. In their case, although there were weak trends towards more conservative root trait syndromes on high altitudes with deteriorating soil conditions, all tropical forest communities showed high within-community variance in root traits at each altitude, confirming the importance of multiple strategies for resource capture in tropical forests. In addition, Kotowska et al. (2022) present compelling evidence that expected ecological trends in trait syndromes, like the dominance of “acquisitive traits” in secondary succession, were not supported after comparing mature and secondary forests in Indonesia, despite the large productivity of the secondary forests. Finally, Erktan and colleagues (2022) provide an in-depth view of root diameter distributions, where most of the temperate plant communities (including woody and non-woody species) they studied, showed a multimodal distribution of root diameter reflecting the distinct belowground strategies to exploit soil resources that exist within plant communities.
Such belowground trait diversity may in turn explain vegetation dynamics. Using a novel deep-learning approach to detect roots and analyze root growth images from a rhizobox, Alonso-Crespo et al. (2022) show that the vertical distribution of roots depended on which functional group was arrived first within a plant community. This may in turn determine competitive outcomes among plant species, and thus determine the overall coexistence and exclusion of species within plant communities. Furthermore, Schuster and co-workers (2022) find evidence for belowground overyielding (i.e., greater root standing biomass and root productivity in species’ mixtures compared to monocultures) in temperate forest communities, especially among angiosperm trees. The authors argue that such differences in belowground productivity may occur due to the greater diversity in root systems in angiosperms compared to gymnosperms, reflecting belowground resource partitioning, and thereby link diversity in belowground strategies to an important ecosystem function.