Gauthey, AliceBachofen, ChristophDeluigi, JanisseDidion-Gency, MargauxD'Odorico, PetraGisler, JonasMas, EugenieSchaub, MarcusSchuler, PhilippStill, Christopher J.Tunas, AlexGrossiord, Charlotte2023-08-282023-08-282023-08-282023-07-2210.1111/nph.19136https://infoscience.epfl.ch/handle/20.500.14299/200166WOS:001034629300001center dot Global warming and droughts push forests closer to their thermal limits, altering tree carbon uptake and growth. To prevent critical overheating, trees can adjust their thermotolerance (T-crit), temperature and photosynthetic optima (T-opt and A(opt)), and canopy temperature (T-can) to stay below damaging thresholds. However, we lack an understanding of how soil droughts affect photosynthetic thermal plasticity and T-can regulation.center dot In this study, we measured the effect of soil moisture on the seasonal and diurnal dynamics of net photosynthesis (A), stomatal conductance (g(s)), and T-can, as well as the thermal plasticity of photosynthesis (T-crit, T-opt, and A(opt)), over the course of 1 yr using a long-term irrigation experiment in a drought-prone Pinus sylvestris forest in Switzerland.center dot Irrigation resulted in higher needle-level A, g(s), T-opt, and A(opt) compared with naturally drought-exposed trees. No daily or seasonal differences in T-can were observed between treatments. Trees operated below their thermal thresholds (T-crit), independently of soil moisture content.center dot Despite strong T-can and T-air coupling, we provide evidence that drought reduces trees' temperature optimum due to a substantial reduction of g(s) during warm and dry periods of the year. These findings provide important insights regarding the effects of soil drought on the thermal tolerance of P. sylvestris.Plant SciencesPlant Sciencesdroughtirrigationphotosynthesispinus sylvestris lplasticitytemperature responsethermoregulationheat toleranceleaf sizeacclimationphotosynthesisdroughttreeplasticityseedlingsgrowthplantstext::journal::journal article::research article