Understanding the influences of climatic factors on hydraulic efficiency and mechanical strength in trees is essential for predicting the processes and services of forest ecosystems. Xylem evolution can be viewed as a ‘trade-off triangle’ among mechanical strength, conductive efficiency and resistance to embolism. However, the evidence for a trade-off between mechanical strength and hydraulic efficiency is ambiguous, and this possible trade-off remains unknown across a wide range of species.
Prof. Cao Kunfang and his team of Xishuangbanna Botanical Garden (XTBG) compiled published data for xylem traits from 316 angiosperm species in 42 families and examined the data set for xylem traits of woody angiosperm species from a diverse array of forest ecosystems within Yunnan Province in south-western China. Their principal objectives were to determine how xylem traits vary over climatic gradients, and to identify any correlations between hydraulic efficiency and mechanical stability.
They tested the following three predictions: (1) species from cold habitats would be hydraulically less efficient because of selection for smaller vessel diameters at a lower temperature; (2) species growing in environments with less precipitation would have greater mechanical strength and lower hydraulic efficiency to facilitate water extraction from drying soils but without creating a rise in the water-potential gradient; and (3) a trade-off would exist between efficiency and strength because of the conflicting structural requirements for xylem design.
Their study found that, over a broad range of angiosperm species, xylem hydraulic traits are influenced by temperature rather than by precipitation. Xylem development in evergreen trees was more sensitive to changes in temperature and moisture when compared with deciduous trees. No trade-off was found between mechanical strength and hydraulic efficiency.
The study entitled “Potential hydraulic efficiency in angiosperm trees increases with growth-site temperature but has no trade-off with mechanical strength” has been published online in Global Ecology and Biogeography, DOI: 10.1111/geb.12056