Leaf temperature influences enzyme activity and the metabolic processes of leaves. It may be very different from the air temperature, and varies between species owing to the physical and physiological differences of plant leaves. However, the relative importance of physical traits and transpiration for leaf temperature regulation in the hot habitat remains unclear. 

Dr. LIN Hua and her colleagues of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to assess the temperature differences between plants from hot dry habitat (HW) and hot wet habitat (HD).

They also assessed the relative importance of transpiration and leafphysical traits in leaf temperature regulation. Moreover, they further wanted to determine leaf temperature regulation strategies for the plants from hot wet and hot dry habitats.

The researchers planted seedlings of 38 canopy species originating from contrasting hydrothermal habitats in a greenhouse, including 18 dominant species from tropical seasonal rain forest (HW) and 20 dominant species from a hot dry valley (HD) in southwestern China.   

They measured 22 leaf physical traits, transpiration, and the thermal properties of all the species. They monitored the diurnal temperatures of controlled leaves and vaselined leaves (transpiration prohibited) using a thermal camera, and simultaneously measured the temperature of the reference leaf beside each individual. 

They found that the plants from hot dry habitat showed lower leaf temperatures than the plants from hot wet habitat under identical environmental conditions. Moreover, transpiration contributed more to leaf cooling than morphology when there was no water limitation. 

There was an increase in transpiration capacity and allied traits including vein density, stomatal pore area index (SPI), and maximum stomatal conductances in the plants from HD.  

HD plants performed a wider range of stomatal regulation and were more efficient in water transport than HW plants. The hot and dry environment can improve the vigour of water transferring structures of leaves. 

Their results confirmed that transpiration and leaf morphology provided double insurance for avoiding overheating, particularly for plant from HD. Transpiration was a more effective way to cool leaves than morphology when water is sufficient, which may be an important adaptation for plant from HD where rainfall is sporadic. 

The study entitled "Stronger cooling effects of transpiration and leaf physical traits of the plants from a hot dry habitat than from a hot wet habitat" has been published online in Functional Ecology.