Short‐term warming does not affect intrinsic thermotolerance but induces strong sustaining photoprotection in tropical evergreen citrus genotypes
Anirban Guha, Talent Vharachumu, Muhammad Fasih Khalid, Mark Keeley, Thomas J. Avenson, Christopher Vincent
Abstract
Abstract Consequences of warming and postwarming events on photosynthetic thermotolerance (P T ) 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 T behaviour including (i) how wide is the genotypic variation in P T ? (ii) how does P T 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 T , though these were not large. We selected five genotypes with divergent P T and simulated warming events: T max 26/20°C (day‐time highest maximum/night‐time lowest maximum) (Week 1) < T max 33/30°C (Week 2) < T max 36/32°C (Week 3) followed by T max 26/16°C (Week 4, recovery). The P T 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 T in evergreen citrus genotypes and their need for sustaining higher photoprotection during warming as well as postwarming recovery conditions.