Variation in leaf temperatures of tropical and subtropical trees are related to leaf thermoregulatory traits and not geographic distributions

Abstract

To help predict the effects of global warming on plants, previous studies have investigated how the distributions and physiological performances of plants relate to environmental temperatures. This approach implicitly assumes that leaf temperatures are tightly linked to regional air temperatures. However, the thermoregulatory behaviors and physical properties of leaves can differ greatly between species, leading to different plants having different leaf temperatures even when they occur under similar conditions. It is important to understand this variation in leaf thermoregulatory traits and temperatures in order to predict how individual species will be impacted by global warming. We measured the thermal properties of leaves from >50 tropical and subtropical tree species grown at the Gifford Arboretum (Florida, USA). For each species, we measured maximum leaf temperature and rate of leaf warming using a new standardized protocol to control for both environmental variation and select plant thermoregulatory behaviors. We tested the relationships between the two thermal variables and several leaf functional traits. Even under laboratory-controlled conditions, leaf temperatures varied by over 8.5°C among species. Maximum leaf temperature was positively correlated with leaf area, and rate of leaf warming was negatively correlated with water content per leaf area. This suggests that some species may be able to offset rising air temperatures through acclimation or adaptation of these leaf properties. Next, we tested the relationships between the species' leaf thermal properties and their climatic niches/distributions, but we found no significant associations.These results call into question the use of regional air temperatures to model plant physiological and demographic performance.

Leaf heat tolerance of 147 tropical forest species varies with elevation and leaf functional traits, but not with phylogeny

“…Tropical forest trees routinely experience high temperatures when exposed to direct irradiance, especially during moments of low wind speed, with leaf temperatures exceeding air temperature by as much as 10°C–18°C (Doughty & Goulden, 2008; Fauset et al, 2018; Rey‐Sanchez, Slot, Posada, & Kitajima, 2016). Leaf traits can influence both the magnitude and rate of leaf heating (Jones, 2013; Tserej & Feeley, 2021). For example, greater leaf width and leaf size are generally associated with a thicker leaf boundary layer and greater decoupling of leaf and air temperatures (Jones, 2013).…”

“…The short τ of relatively small and thin leaves indicates that they heat up and cool down quickly, so that leaf temperatures essentially track changes in microclimate variables, including very high temperatures when in full sun. By contrast, leaves with a comparatively large thermal mass and a long τ are buffered against fluctuations in microclimate, so that leaf temperatures lag behind changes in microclimate variables (Michaletz et al, 2015(Michaletz et al, , 2016Tserej & Feeley, 2021). Leaf temperature can also be affected by transpirational cooling, especially in hot and dry environments (Lin et al, 2017), and thus stomatal conductance is another potentially relevant leaf trait.…”

Warming Responses of Leaf Morphology Are Highly Variable among Tropical Tree Species

“…Leaf size and shape influences leaf energy balance, and size correlates with stomatal conductance [8,38], carbon assimilation rates and productivity [3,39]. Small and narrow leaves have thinner leaf boundary layers, and thus, more efficient heat dissipation, leading to lower leaf temperatures and heat stress under sunny and hot conditions [40][41][42][43].…”

Correlations between photosynthetic heat tolerance and leaf anatomy and climatic niche in Asian mangrove trees

“…When diverse plant lineages grown in a common garden were examined, both phylogeny and climate niche were weak predictors of P HT , pointing to the potential role of microenvironment, thermoregulatory traits and leaf temperatures in determining heat tolerance (Perez & Feeley 2021). In general, wider leaves and a larger leaf area are connected to higher leaf temperatures (Tserej & Feeley 2021) due to reduced transpirational cooling (Fauset et al . 2018), which, in turn, scale with heat tolerance (Perez & Feeley 2020).…”