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

Abstract

Exceeding thermal thresholds causes irreversible damage and ultimately loss of leaves. The lowland tropics are among the warmest forested biomes, but little is known about heat tolerance of tropical forest plants. We surveyed leaf heat tolerance of sun‐exposed leaves from 147 tropical lowland and pre‐montane forest species by determining the temperatures at which potential photosystem II efficiency based on chlorophyll a fluorescence started to decrease (TCrit) and had decreased by 50% (T50). TCrit averaged 46.7°C (5th–95th percentile: 43.5°C–49.7°C) and T50 averaged 49.9°C (47.8°C–52.5°C). Heat tolerance partially adjusted to site temperature; TCrit and T50 decreased with elevation by 0.40°C and 0.26°C per 100 m, respectively, while mean annual temperature decreased by 0.63°C per 100 m. The phylogenetic signal in heat tolerance was weak, suggesting that heat tolerance is more strongly controlled by environment than by evolutionary legacies. TCrit increased with the estimated thermal time constant of the leaves, indicating that species with thermally buffered leaves maintain higher heat tolerance. Among lowland species, T50 increased with leaf mass per area, suggesting that in species with structurally more costly leaves the risk of leaf loss during hot spells is reduced. These results provide insight in variation in heat tolerance at local and regional scales.

Handling the heat – photosynthetic thermal stress in tropical trees

“…We note that the PHT thresholds observed in the current study are in the lower end of the range reported for tropical tree species: for T crit from c. 46-50°C, and for T 50 from c. 44.5-53°C (e.g. Sastry & Barua, 2017;Zhu et al, 2018;Feeley et al, 2020;Tiwari et al, 2021;Slot et al, 2021). Given that our laboratory-based measurements on Hmo also yielded higher threshold values in the higher temperature treatments (i.e.…”

Short‐term warming does not affect intrinsic thermotolerance but induces strong sustaining photoprotection in tropical evergreen citrus genotypes

“…There are growing interests to understand the underlying causes behind the variation in intrinsic and/or acquired P T . Different leaf structural and biochemical factors were attributed to the variation in P T including the leaf mass per unit area (Sastry & Barua, 2017; Slot et al, 2021), leaf thermoregulatory traits (Perez & Feeley, 2020), abundance of cellular heat‐shock proteins (Barua et al, 2008) and saturated fatty acids (Zhu et al, 2018), foliar Ca concentration (Zhang et al, 2012) and epicuticular wax load (Tischler & Burson, 1995). Studies that investigated intraspecific or genotypic variation in P T predominantly come from model crop systems (Cottee et al, 2010; Hall et al, 2014), some herbaceous crop species (Barua et al, 2008), and few agroforestry tree species (Gomes‐Laranjo et al, 2006; Gomes‐Laranjo et al, 2012).…”

“…There are growing interests to understand the underlying causes behind the variation in intrinsic and/or acquired P T . Different leaf structural and biochemical factors were attributed to the variation in P T including the leaf mass per unit area (Sastry & Barua, 2017;Slot et al, 2021), leaf thermoregulatory traits , abundance of cellular heat-shock proteins (Barua et al, 2008) and saturated fatty acids (Zhu et al, 2018), foliar…”

Scaling plant responses to high temperature from cell to ecosystem

“…Carbon balance can be viewed as a push-pull dynamic that is driven by mitochondrial respiration and pho- considered a limiting factor in the ability to maintain photosynthesis under high temperatures, an idea that is explored by Perez, Socha, Tserej, and Feeley (2021) and . Perez et al (2021) found that high heat tolerance of PSII was associated with species that were thermal generalists, thus providing a proxy for evaluating the thermal niche of plants, while Slot, Cala, et al (2021) showed that PSII heat tolerance varies in a predictable way with site temperature and elevation. The ability to acclimate CO 2 uptake rates to higher temperatures is often related to shifts in the thermal sensitivity and capacity of photosynthetic processes, and can occur quite quickly (Slot, Rifai, & Winter, 2021).…”