Leaf temperature (Tl) is the direct micro-environment governing plant ecophysiological processes. Thermal regulation, thermal tolerance, and thermal avoidance together constitute thermal adaptation strategies of plants. However, the mechanisms underlying leaf thermal regulation strategies across different environmental gradients have not been fully explored.
Some previous studies employed a method called “3-T method” (comparing the temperature of a control leaf, the temperature of a non-transpiring leaf, and air temperature) to quantitatively distinguish thermal effects of transpiration and leaf physical traits in situ.
In a recent study published in Agricultural and Forest Meteorology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and University of Plymouth used 3-T method to study thermal regulation strategies of leaves along a temperature and precipitation gradient.
The researchers selected four vegetation types from the south to the north of Yunnan province, China, including a savanna woodland (SAV), a tropical rain forest (TRF), a subtropical evergreen broad-leaved forest (STF), and a temperate mixed forest (TEF). They studied the thermal regulation strategies of upper canopy species in the four vegetation types.
They found that leaf-air temperature difference decreased with increasing environmental temperature. Plants in the hot environment mainly relied on transpirational cooling to avoid high leaf temperatures. Transpirational cooling was strongest in savanna woodland, and decreased from the hottest site to the coldest site.
They further found that plants under extreme thermal environment can utilize all means to optimize performance and survive. Plants minimized transpirational cooling, facilitated leaf warming in cold forest. There was no trade-off between thermal regulation, thermal tolerance and thermal avoidance. Leaf area and water content played significant roles in physical thermal regulation.
The results suggested that plants presented limited homeothermy at the biome scale, as cooling effects were stronger in hotter environments and warming effects were stronger in colder environments.?
"The present research revealed a relatively comprehensive scenario of leaf regulation strategies under four distinct environments, thereby enhance our understanding of how plants adapt to thermal environments," said LIN Hua of XTBG.

Contact
LIN Hua Ph.D
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
E-mail:lh@xtbg.ac.cn?
First published: 25 October 2023?

 Leaf thermal regulation strategies of canopy species across four vegetation types along a temperature and precipitation gradient.

(Image by ZHOU Yingying)