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PremiseBelowground functional traits play a significant role in determining plant water‐use strategies and plant performance, but we lack data on root traits across communities, particularly in the tropical savanna biome, where vegetation dynamics are hypothesized to be strongly driven by tree–grass functional differences in water use. MethodsWe grew seedlings of 21 tree and 18 grass species (N= 5 individuals per species) from the southern African savanna biome under greenhouse conditions and collected fine‐root segments from plants for histological analysis. We identified and measured xylem vessels in 539 individual root cross sections. We then quantified six root vascular anatomy traits and tested them for phylogenetic signals and tree–grass differences in trait values associated with vessel size, number, and hydraulic conductivity. ResultsGrass roots had larger root xylem vessels than trees, a higher proportion of their root cross‐sectional area comprised vessels, and they had higher estimated axial conductivities than trees, while trees had a higher number of vessels per root cross‐sectional area than grasses did. We found evidence of associations between trait values and phylogenetic relatedness in most of these traits across tree species, but not grasses. ConclusionsOur findings support the hypothesis that grass roots have higher water transport capacity than tree roots in terms of maximum axial conductivity, consistent with the observation that grasses are more “aggressive” water users than trees under conditions of high soil moisture availability. Our study identifies root functional traits that may drive differential responses of trees and grasses to soil moisture availability.
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Root vascular anatomy predicts maximum growth rates in savanna trees and grasses
Abstract Root‐based functional traits are relatively overlooked as drivers of savanna plant community dynamics, an important gap in water‐limited ecosystems. Recent work has shed light on patterns of trait coordination in roots, but less is known about the relationship between root functional traits, water acquisition, and plant demographic rates. Here, we investigated how fine‐root vascular and morphological traits are related in two dominant PFTs (C3trees and C4grasses from the savanna biome), whether root traits can predict plant relative growth rate (RGR), and whether root trait multivariate relationships differ in trees and grasses. We used root data from 21 tree and 18 grass species grown under greenhouse conditions, and quantified a suite of vascular and morphological root traits. We used a principal components analysis (PCA) to identify common axes of trait variation, compared trait correlation matrices between the two PFTs, and investigated the relationship between PCA axes and individual traits and RGR. We found that there was no clear single axis integrating vascular and morphological traits, but found that vascular anatomy predicted RGR in both trees and grasses. Trait correlation matrices differed in trees and grasses, suggesting potentially divergent patterns of trait coordination between the two functional types. Our results suggested that, despite differences in trait relationships between trees and grasses, root conductivity may constrain maximum growth rate in both PFTs, highlighting the critical role that water relations play in savanna vegetation dynamics and suggesting that root water transport capacity is an important predictor of plant performance in the savanna biome.
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- Award ID(s):
- 1928860
- PAR ID:
- 10464516
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Biotropica
- Volume:
- 55
- Issue:
- 6
- ISSN:
- 0006-3606
- Format(s):
- Medium: X Size: p. 1159-1164
- Size(s):
- p. 1159-1164
- Sponsoring Org:
- National Science Foundation
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