Embedded Files
Mechanistic drivers and the evolution of PSII heat tolerance
Mechanistic drivers and the evolution of PSII heat tolerance
The kinetic basis of PSII heat tolerance
Current approaches to quantifying photosynthetic heat tolerance often focus solely on temperature, overlooking exposure time, or rely on temperature-time correlations that do not identify causal mechanisms, limiting inference and prediction. Here we develop a mechanistic theory for heat inactivation of photosynthesis based on principles of chemical kinetics and test it using data for photosystem II (PSII), allowing us to 1) link the effects of both temperature and exposure time and 2) directly test competing hypotheses for how heat impairs photosynthesis. Data from diverse plant species suggest that protein (not lipid membrane) denaturation is the primary mechanism of heat-induced inactivation of PSII. The theory also predicts a general upper temperature limit of 55-60 °C for acclimation of photosynthetic heat tolerance, a prediction supported by global PSII data.
Citation:
Bison NN, Michaletz S. The kinetics basis of photosynthetic heat tolerance. in review.
Variation in leaf carbon economics, energy balance, and heat tolerance traits highlights differing time scales of adaptation and acclimation
Multivariate leaf trait correlations are hypothesized to originate from natural selection on carbon economics traits that control lifetime leaf carbon gain, and energy balance traits governing leaf temperatures, physiological rates, and heat injury. However, it is unclear whether macroevolution of leaf traits primarily reflects selection for lifetime carbon gain or energy balance, and whether photosynthetic heat tolerance is coordinated along these axes. To evaluate these hypotheses, we measured carbon economics, energy balance, and photosynthetic heat tolerance traits for 177 species (157 families) in a common garden that minimizes co-variation of taxa and climate. We observed wide variation in carbon economics, energy balance, and heat tolerance traits. Carbon economics and energy balance (but not heat tolerance) traits were phylogenetically structured, suggesting macroevolution of leaf mass per area and leaf dry matter content reflects selection on carbon gain rather than energy balance. Carbon economics and energy balance traits varied along a common axis orthogonal to heat tolerance traits. Our results highlight a fundamental mismatch in the timescales over which morphological and heat tolerance traits respond to environmental variation. Whereas carbon economics and energy balance traits are constrained by species' evolutionary histories, photosynthetic heat tolerance traits are not and can acclimate readily to leaf microclimates.
Citation:
Bison, NN and Michaletz ST. 2024. Variation in leaf carbon economics, energy balance, and heat tolerance traits highlights differing timescales of adaptation and acclimation. New Phytologist 242: 1919-1931. https://doi.org/10.1111/nph.19702
Predicting vulnerability to wildfire
Predicting vulnerability to wildfire
Trait phenology and fire seasonality co-drive seasonal variation in fire effects on tree crowns
The plume of hot gases rising above a wildfire can heat and kill the buds in tree crowns. This can reduce leaf area and rates of photosynthesis, growth, and reproduction, and may ultimately lead to mortality. These effects vary seasonally, but the mechanisms governing this seasonality are not well understood. A trait-based physical model combining buoyant plume and energy budget theories shows the seasonality of bud necrosis height may originate from temporal variation in climate, fire behaviour, and/or bud functional traits. To assess the relative importance of these drivers, we parameterized the model with time-series data for air temperature, fireline intensity, and bud traits from Pinus contorta, Picea glauca, and Populus tremuloides. Air temperature, fireline intensity, and bud traits all varied significantly through time, causing significant seasonal variation in predicted necrosis height. Bud traits and fireline intensity explained almost all the variation in necrosis height, with air temperature explaining relatively minor amounts of variation. The seasonality of fire effects on tree crowns appears to originate from seasonal variation in functional traits and fire behaviour. Our approach and results provide needed insight into the physical mechanisms linking environmental variation to plant performance via functional traits.
Citation:
Bison, NN and Michaletz ST. 2022. Trait phenology and fire intensity co-drive seasonal variation in fire effects on tree crowns. New Phytologist 234(5): 1654-1663. http://doi.org/10.1111/nph.18047
Page updated
Google Sites
Report abuse