The energetic and carbon economic origins of leaf thermoregulation

Abstract

Leaf thermoregulation has been documented in a handful of studies, but the generality and origins of this pattern are unclear. We suggest that leaf thermoregulation is widespread in both space and time, and originates from the optimization of leaf traits to maximize leaf carbon gain across and within variable environments. Here we use global data for leaf temperatures, traits and photosynthesis to evaluate predictions from a novel theory of thermoregulation that synthesizes energy budget and carbon economics theories. Our results reveal that variation in leaf temperatures and physiological performance are tightly linked to leaf traits and carbon economics. The theory, parameterized with global averaged leaf traits and microclimate, predicts a moderate level of leaf thermoregulation across a broad air temperature gradient. These predictions are supported by independent data for diverse taxa spanning a global air temperature range of ∼60 °C. Moreover, our theory predicts that net carbon assimilation can be maximized by means of a trade-off between leaf thermal stability and photosynthetic stability. This prediction is supported by globally distributed data for leaf thermal and photosynthetic traits. Our results demonstrate that the temperatures of plant tissues, and not just air, are vital to developing more accurate Earth system models.

Spatial patterns and climate relationships of major plant traits in the New World differ between woody and herbaceous species

“…This corresponds to the trade‐off between slow photosynthetic rate and long leaf lifespan under stressful conditions versus fast tissue turnover and high potential for resource capture under more favourable conditions (Reich, ). It is also consistent with a recent hypothesis that lower specific leaf area in colder environments helps modulate leaf temperatures (Michaletz et al., ). Interestingly, specific leaf area of both growth form groups increased with increasing temperature seasonality after accounting for the effect of temperature and precipitation.…”

In situ temperature response of photosynthesis of 42 tree and liana species in the canopy of two Panamanian lowland tropical forests with contrasting rainfall regimes

“…(c) – no change in curve width – albeit that the curves with higher T Opt did not exclusively represent ‘fast’ species. We did not find evidence that ‘fast’ species have wider curves than ‘slow’ species, as is the case in temperate species (Michaletz et al ., ).…”

“…Curves could widen or narrow with increasing T Opt , depending on whether higher T Opt is associated with higher or lower physiological plasticity. A recent theory linking carbon economics and leaf temperature regulation proposes that ‘fast’ species have wider temperature–response curves, and thus greater plasticity, than ‘slow’ species, and data on a mix of forbs, grasses and trees from thermally dynamic temperate environments support this theory (Michaletz et al ., ). This would be consistent with scenario I in Fig.…”

Plasticity of photosynthetic heat tolerance in plants adapted to thermally contrasting biomes

“…However, we do not totally exclude the possibility of adaptation to water limitations because water availability may also play an important role in influencing P HT in some species (Curtis et al, ; Ghouil et al, ). Species might vary in T crit in the cooling ability of leaves that can be influenced by factors such as leaf thickness, shape, and size (Leigh et al, ; Michaletz et al ; Michaletz et al ; Vogel, ).…”