Peanut photosynthesis response to drought can include diffusive and biochemical limitations depending on cultivar

Photosynthesis, understood as the photosynthetic carbon assimilation rate, is one of the key processes affected by drought stress. The effects can be via decreased CO₂ diffusion and biochemical constraints. However, there is still no unified consensus about the contribution of each mechanism to the drought response. This research assessed the underlying limitations to photosynthesis in nine peanut genotypes (Arachis hypogaea L.) with different water strategies (water savers vs water spenders) under progressive drought. Water saver cultivars close the stomata earlier during drought, resulting in decreased transpiration and photosynthesis, which results in less water depletion in the soil, while water spenders maintain the stomata open during drought. In order to test the performance of these genotypes, growth, transpiration per plant, gas exchange measurements, chlorophyll fluorescence and A/C_i response curves were analyzed under drought and well-watered conditions. In general, drought first affected photosynthesis (at the leaf and canopy level) via stomatal closure and then by impacts on chlorophyll fluorescence in all genotypes, but at different intensity levels. The maximum rate of carboxylation and the maximum rate of electron transport, physiological characteristics related to biochemical constraints, were not affected during the onset of drought, but they were decreased at the end of the drought period, with the exception of the PI 493329 genotype that showed higher stomatal conductance due to a bigger root system. The findings presented here highlight the importance of genetic variation in the photosynthetic response of peanut to drought, which should be considered when breeding for future climates.