COS 40-1 - Root anatomy helps to reconcile observed root trait syndromes in tropical and temperate trees

Tuesday, August 13, 2019: 1:30 PM
L005/009, Kentucky International Convention Center
Louise Authier, UMR EcoFoG, University of Montpelier, Korou, French Guiana, Christopher Baraloto, INRA, UMR EcoFOG, Kourou, FL, French Guiana, Heidy Schimann, INRA-UMR ECOFOG, Kourou, French Guiana and Oscar J. Valverde-Barrantes, International Center of Tropical Botany, Florida International University, Miami, FL
Background/Question/Methods

Efforts to understand the organization of functional traits in leaves and stems of plants have revealed notable patterns, however evidence of similarly robust organization among root tissues (root economic spectrum, RES hypothesis) remain controversial. Previous studies have demonstrated that root diameter is the main factor influencing root trait variation across species and historically along lineages. Root diameter is anatomically composed by the stele and the tissue outside the stele (ToS), then due to their geometry, we hypothesize that variation in the two concentrically organized tissues conforming the root must related in a non-linear fashion to other morphological and architectural traits (Rhizo-centric hypothesis). We also predicted that the investment in ToS must generate constraints between the extension of habitat for biotic interactions and the branching pattern in root systems. Finally, based on the differences in tissue makeup and the dominant role of cortical tissue determining root diameter, we predicted negative relationships between diameter and root tissue density (RTD). We studied 25 tropical tree species in French Guiana, including the analysis of anatomical traits via microscopy on first order roots, and functional trait description for the entire root systems (3-4 root orders of absorptive roots, sensu Valverde-Barrrantes et al. 2017).

Results/Conclusions

Our results supported the predicted non-linear relationships between root traits and anatomy, with cortical size being more important that stele size to explain morphological and architectural patterns. Moreover, we confirmed that the predicted negative relationship between RTD and diameter holds not only in our study but also at global scales, suggesting similar anatomical constraints in root systems of all woody plants. Nonetheless, the importance of diameter and RTD affecting specific root length (SRL), another key root functional trait, varied across biomes, with diameter having a stronger importance on SRL variation in temperate than subtropical or tropical forests. Our findings imply that the Rhizo-centric hypothesis may help to reconcile some of the previous weak support reported for the RES hypothesis. Additional anatomical and functional trait studies at species and community levels are necessary to fully understand how plants modulate root acquisition traits and how climatic and soil conditions shape these relationships at global scales.