Herb hydraulics: Variation and correlation for traits governing drought tolerance and efficiency of water transport
Hydraulic traits dictate plant response to drought, thus enabling better understanding of community dynamics under global climate change. Despite being intensively documented in woody species, herbaceous species (graminoids and forbs) are largely understudied, hence the distribution and correlation of hydraulic traits in herbaceous species remains unclear. Here, we collected key hydraulic traits for 436 herbaceous species from published literature, including leaf hydraulic conductivity (K), water potential inducing 50 % loss of hydraulic conductivity (P), stomatal closure (P) and turgor loss (P). Trait variation of herbs was analyzed and contrasted with angiosperm woody species within the existing global hydraulic traits database, as well as between different growth forms within herbs. Furthermore, hydraulic traits coordination was also assessed for herbaceous species. We found that herbs showed overall more negative P but less negative P compared with angiosperm woody species, while P did not differ between functional types, regardless of the organ (leaf and stem). In addition, correlations were found between K and P of leaf (P), as well as between P, P and K. Within herbs, graminoids generally exhibited more negative P and P, but lower K, relative to forbs. Within herbs, no clear pattern regarding hydraulic traits-climate relationship was found. Our analysis provided insights into herb hydraulic, and highlighted the knowledge gaps need to be filled regarding the response of herbs to drought.
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