PS 14-140 - Root Functional Traits of Savanna Trees and Grasses

Background/Question/Methods

Water is the key limiting resource for trees and grasses in many savannas. Therefore, root-based functional traits responsible for water uptake and use are key to understanding the tree-grass dynamics in the savanna biome. We quantified root functional traits and their relationship with growth rates in ~ 40 greenhouse-grown tree and grass species from a Lowveld savanna ecosystem.

Results/Conclusions

We found that trees and grasses differ in terms of their vascular anatomy and water use strategies. Tree roots had a greater number of xylem vessels per root cross-sectional area, while grass roots had larger, but fewer xylem vessels than trees. Additionally, grasses had a higher proportion of their root cross-sectional area comprised of vessels and a greater estimated axial conductivity than trees. These findings support our hypothesis that grasses have greater water transport capacity than trees, yet grass vessel are at higher risk for cavitation under water stress. We also examined how these root functional traits related to plant performance and found a significant relationship between the relative growth rate and vascular anatomy traits for both trees and grasses. These results suggest root water transport plays an important role in the growth of savanna trees and grasses. Understanding how the water use strategies influence the growth rates of these two functional types, will prove to be vital in predicting how future changes in climate and precipitation patterns will affect savanna plant communities.