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

Abstract

Tropical forests contribute significantly to the global carbon cycle, but little is known about the temperature response of photosynthetic carbon uptake in tropical species, and how this varies within and across forests. We determined in situ photosynthetic temperature-response curves for upper canopy leaves of 42 tree and liana species from two tropical forests in Panama with contrasting rainfall regimes. On the basis of seedling studies, we hypothesized that species with high photosynthetic capacity - light-demanding, fast-growing species - would have a higher temperature optimum of photosynthesis (T ) than species with low photosynthetic capacity - shade-tolerant, slow-growing species - and that, therefore, T would scale with the position of a species on the slow-fast continuum of plant functional traits. T was remarkably similar across species, regardless of their photosynthetic capacity and other plant functional traits. Community-average T was almost identical to mean maximum daytime temperature, which was higher in the dry forest. Photosynthesis above T appeared to be more strongly limited by stomatal conductance in the dry forest than in the wet forest. The observation that all species in a community shared similar T values suggests that photosynthetic performance is optimized under current temperature regimes. These results should facilitate the scaling up of photosynthesis in relation to temperature from leaf to stand level in species-rich tropical forests.

High tolerance of tropical sapling growth and gas exchange to moderate warming

“…While in seedlings the optimum and maximum temperature for net photosynthesis is higher in early‐ than in late‐successional species (Slot et al., ), in leaves of canopy trees this difference in temperature‐response traits disappears (Slot & Winter, ). This change probably reflects adaptation to the common ontogenetic trajectories of early‐ and late‐successional canopy trees; while early‐successional species tend to germinate in open areas and maintain high‐light exposure—and thus higher tissue temperatures—throughout their development, late‐successional canopy species start out as seedlings in the shaded understorey—buffered against high leaf temperatures—but experience high light and high temperature conditions as adults in the canopy (e.g.…”

Variations of leaf longevity in tropical moist forests predicted by a trait‐driven carbon optimality model

“…During the calculation, we assumed that (1) ambient temperature and vapour pressure deficit for A sat measurements are equal to long‐term average values at 10:00 AM, (2) leaf temperature for understory leaves is equal to the ambient temperature and (3) leaf temperature for canopy leaves (under direct sunlight) is about 5 °C higher than understory leaves (Rey‐Sánchez et al . ; Slot & Winter ). In total, there are 140 data entries (102 for canopy leaves, 38 for understory leaves) from 105 species in our study (Appendix ).…”

Thermal imaging in plant and ecosystem ecology: applications and challenges

“…A wide variety of trees (broadleaf and coniferous species, from subtropical through boreal biomes) were shown to converge on a common, integrated T leaf , suggesting that tree leaves, particularly in boreal latitudes, deviate substantially from air temperature when weighted for photosynthesis (Helliker and Richter 2008). Slot and Winter (2017) showed that a wide range of tropical tree and liana species, regardless of canopy position, have optimal temperatures for leaf photosynthesis around 30°C, with a high-temperature threshold around 35°C that was also seen in earlier work (Doughty and Goulden 2008). Linking thermal and photosynthetic measurements can offer important insight into how forests, and the diversity of trees within those forests, respond to episodic thermal extremes.…”

“…Examples include photosynthesis and respiration (Slot and Winter 2017), as well as biophysical attributes such as leaf-to-air vapor pressure deficit (VPD), which is critical for estimating evapotranspiration and its influence on biogeochemistry. Temperature is also a fundamental characteristic of climate.…”