Handling the heat – photosynthetic thermal stress in tropical trees

Abstract

Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate.Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient.Heat tolerance acclimated to maximum leaf temperature (T leaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest T leaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest T leaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling.More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.

Pre-Acclimation to Elevated Temperature Stabilizes the Activity of Photosystem I in Wheat Plants Exposed to an Episode of Severe Heat Stress

“…Heat stress is one of the main abiotic stresses that negatively affects agricultural areas around the world due to the induction of a wide range of adverse physiological, biochemical, morphological anatomical, and genetic reactions of plants [ 1 ]. The global increase in average temperature is expected to occur in line with more intense and frequent heat waves [ 2 ]. The effect of high temperatures on photosynthesis significantly determines the effects of global warming on crop yields [ 3 , 4 ].…”

Warming Scenarios and Phytophthora cinnamomi Infection in Chestnut (Castanea sativa Mill.)

“…The causes of this decrease may have differed depending on the scenario. At high ambient temperature, plants may have undergone heat acclimation [ 55 ] by altering the optimum temperature at which P n was maximum. Conversely, seedlings subjected to the two heat waves could have had their PSII damaged and/or stress memory induced [ 56 ].…”

Contrasting growth and mortality responses of different species lead to shifts in tropical montane tree community composition in a warmer climate

“…Bennett et al, 2021;Clark et al, 2003Clark et al, & 2010Damptey et al, 2021;Herrera-Ramírez et al, 2021;Hubau et al, 2020;McDowell et al, 2018;Slot et al, 2021;Sullivan et al, 2020) or controlled warming experiments on small plants grown in chambers (e.g. Cheesman & Winter, 2013a, Cheesman & Winter, 2013bSlot & Winter, 2018;Wittemann et al 2022). The semi-controlled experimental approach of Rwanda TREE bridges the gap between these two types of studies by using large plantations with the same species and genotypes grown at three sites spanning 5.4 °C in MAT, with irrigation to compensate 470 for site differences in precipitation.…”

“…Large variability across studies and species has been observed from positive to negative effects (e.g. Slot & Winter, 2018;Dusenge et al, 2021;Wittemann et al, 2022), possibly due to which 60 tropical temperature zone, e.g. lowland vs highland, the species originate from.…”