Potential hydraulic efficiency in angiosperm trees increases with growth-site temperature but has no trade-off with mechanical strength

Authors

  • Shi-Bao Zhang,

    1. Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, China
    2. Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan, China
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    • These authors contributed equally to the manuscript.
  • Kun-Fang Cao,

    Corresponding author
    1. Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan, China
    • State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, College of Forestry, Guangxi University, Nanning, Guangxi, China
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    • These authors contributed equally to the manuscript.
  • Ze-Xin Fan,

    1. Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan, China
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  • Jiao-Lin Zhang

    1. Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming, Yunnan, China
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  • Editor: Bill Shipley

Correspondence: Kun-Fang Cao, State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Forestry, Guangxi University, Nanning, Guangxi 530004, China.

E-mail: caokf@xtbg.ac.cn

Abstract

Aim

Xylem structures are closely related to a tree's hydraulic efficiency and mechanical stability, both of which affect the life history and ecological strategy of a species. Although mechanical strength and hydraulic capacity can be shaped by the environment, no such associations between hydraulic efficiency and climatic variables have been reported across a wide range of tree species.

Location

Yunnan, south-west China.

Methods

We compiled a data set for vessel density, vessel diameter (D), potential hydraulic conductivity (Kp), wood density (WD), modulus of rupture (MOR) and modulus of elasticity (MOE) from 316 angiosperm tree species. Our objective was to examine the correlations among xylem traits and climatic variables. We hypothesized that both hydraulic efficiency and mechanical strength would vary along climatic gradients, but that a trade-off would occur between them.

Results

All xylem traits varied significantly across species, but the magnitudes of variation were greater for vessel traits than for mechanical properties. Values for Kp and D increased with mean annual temperature (MAT) in both evergreen and deciduous trees, but they were significantly correlated with aridity index (AI) in evergreen species only. Both WD and MOR were significantly correlated with MAT only in evergreen trees. MOR decreased with increasing AI in the evergreens, but not in deciduous trees. These findings indicated that xylem development in evergreens is more sensitive to environmental changes than in deciduous trees. However, stem hydraulic traits are independent of mechanical properties.

Main conclusions

Consistent with our hypothesis, both hydraulic efficiency and mechanical strength of angiosperm trees are influenced by the environment, with temperature having a more important effect on hydraulic efficiency than precipitation. However, no trade-off exists between efficiency and strength. This absence of a link is explained because angiosperms have xylem tissue that specifically functions in either mechanical strength or water transport.

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