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

Consequences of warming and postwarming events on photosynthetic thermotolerance (P ) and photoprotective responses in tropical evergreen species remain elusive. We chose Citrus to answer some of the emerging questions related to tropical evergreen species' P behaviour including (i) how wide is the genotypic variation in P ? (ii) how does P respond to short-term warming and (iii) how do photosynthesis and photoprotective functions respond over short-term warming and postwarming events? A study on 21 genotypes revealed significant genotypic differences in P , though these were not large. We selected five genotypes with divergent P and simulated warming events: T 26/20°C (day-time highest maximum/night-time lowest maximum) (Week 1) < T 33/30°C (Week 2) < T 36/32°C (Week 3) followed by T 26/16°C (Week 4, recovery). The P of all genotypes remained unaltered despite strong leaf megathermy (leaf temperature > air temperature) during warming events. Though moderate warming showed genotype-specific stimulation in photosynthesis, higher warming unequivocally led to severe loss in net photosynthesis and induced higher nonphotochemical quenching. Even after a week of postwarming, photoprotective mechanisms strongly persisted. Our study points towards a conservative P in evergreen citrus genotypes and their need for sustaining higher photoprotection during warming as well as postwarming recovery conditions.