Stronger cooling effects of transpiration and leaf physical traits of plants from a hot dry habitat than from a hot wet habitat

Abstract

Leaf temperature exerts an important impact on the microenvironment and physiological processes of leaves. Plants from different habitats have different strategies to regulate leaf temperature. The relative importance of physical traits and transpiration for leaf temperature regulation in the hot habitat is still unclear. We investigated 22 leaf physical traits, transpiration, and thermal properties of 38 canopy species of seedlings in a greenhouse, including 18 dominant species from a hot wet habitat (HW) and 20 dominant species from a hot dry habitat (HD). To separate the impact of transpiration and leaf physical traits on leaf temperature, we measured the diurnal courses of leaf temperatures with and without transpiration. The temperature of a reference leaf beside each individual was measured simultaneously to render temperatures comparable. Generally, the species from HD showed lower leaf temperatures than the species from HW under the same conditions. Both transpiration capacity and cooling effect of leaf physical traits were stronger for the plants from HD. Active transpiration provides a suitable thermal environment for photosynthesis, while xeromorphic leaves can dampen heat stress when transpiration is suppressed. Higher vein density and stomatal pore area index (SPI) facilitated higher transpiration capacity of the plants from HD. Meanwhile, shorter leaves and thinner lower epidermis of the plants from HD were more efficient in heat transfer, although relationships were much weaker than the synergic effect of all the physical traits. Our results confirmed that transpiration and leaf physical traits provided double insurance for avoiding overheating, particularly for plant from HD. We emphasize that transpiration is a more effective way to cool leaves than physical traits when water is sufficient, which may be an important adaptation for plant from HD where rainfall is sporadic. Our results provide further insight into the relationship between physical traits and transpiration for the regulation of leaf temperature, and the co‐evolution of gas exchange and thermal regulation of leaves. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12923/suppinfo is available for this article.

Trees tolerate an extreme heatwave via sustained transpirational cooling and increased leaf thermal tolerance

“…We speculate that trees without groundwater access rely primarily on physical adaptations such as reflective leaves (Curtis, Leigh, & Rayburg, ; Ehleringer & Mooney, ) or biochemical adaptations such as heat‐shock proteins (Feder & Hofmann, ) to cope with extreme heatwaves. The interplay between these adaptations and latent cooling may be an interesting area of further study (e.g., Lin, Chen, Zhang, Fu, & Fan, ).…”

“…Note that some leaves in the heatwave treatment exceeded the T 50 value observed preheatwave (dashed blue line) but did not exceed the T 50 value observed during the heatwave (dashed red line; c) [Colour figure can be viewed at wileyonlinelibrary.com] Rayburg, 2012; Ehleringer & Mooney, 1978) or biochemical adaptations such as heat-shock proteins (Feder & Hofmann, 1999) to cope with extreme heatwaves. The interplay between these adaptations and latent cooling may be an interesting area of further study (e.g., Lin, Chen, Zhang, Fu, & Fan, 2017).…”

A Simple Method for Simulating Drought Effects on Plants

“…Stomatal conductance and transpiration result in evaporative cooling of leaves (Nobel, 1974;Farquhar and Sharkey, 1982), so partial stomatal closure under water deficit can result in higher T leaf (Medina and Gilbert, 2015). Transpiration alone can cool leaves by at least 2°C-3°C (Lin et al, 2017) and up to 8°C for species with high transpiration rates (e.g., M. grandiflora, Figure 6). About half of the species (5 FIGURE 6 | Differences in (A) rates of stomatal conductance (g s , mmol m -2 s -1 ) and (B) leaf temperature (T leaf ,°C) between control and drought plants of 11 selected tree/shrub species.…”

Differences in Leaf Temperature between Lianas and Trees in the Neotropical Canopy

“…We hypothesized that leaves of trees with lianas would experience higher values of T d than leaves of trees without lianas. This is based on the negative effects of lianas on trees associated with the ability of lianas to reduce the water availability around their host trees [25]; a process that could affect the heat dissipation by transpiration of leaves of host trees [26]. Likewise, we expect that leaves of lianas would show lower T d in comparison with host tree leaves; due to their ability to grow in drought environments [16] and their greater competitive advantage on the acquisition, regulation, and efficient use of water in comparison with trees [24,[27][28][29].…”