Abstract Detail


Guha, Anirban [1], Vharachumu, Talent [2], Khalid, Muhammad Fasih [3], Keeley, Mark [4], Avenson, Thomas [5], Vincent, Christopher [6].

Citrus reveals novel insights into genotypic variation, acclimation, and plasticity in photosynthetic thermotolerance of tropical evergreens.

Tropical tees manifest high levels of genetic variation which could be critical in enhancing species adaptability in a warming world, reshaping tropical forest ecosystems, and sustaining forestry and agroforestry needs. Studies appeared in last two decades, indicate that many tropical forest species are functioning close to their thermal thresholds. Thus, deeper insights are warranted to understand responses of tropical trees to global warming, and species genetic variation in heat tolerance and acclimation capacity. Among different plant functional types in tropics, the need for photoprotection may be quintessential for evergreen trees due to their longer leaf lifespan, but very limited information is available on intraspecific variation in heat tolerance capacity and photoprotective physiology of evergreens. Therefore, it is likely that predictions of tropical species' thermal vulnerability or tolerance miss a comprehensive view. We chose Citrus, an evergreen tropical tree species to address some of the uncertainties related to photosynthetic thermotolerance (PT) behavior including (i) the magnitude of intraspecies genotypic variation in PT, (ii) response of PT to varying degrees of warming exposure (iii), response of key photoprotective functions over short‐term warming events, and (iv) whether there are postwarming legacy effects. To understand genotypic variation in PT, we assessed 21 citrus genotypes, commercially used in United States either as rootstock or scion cultivars. The genotypes exhibited moderate but significant variation in PT. Later, we selected five genotypes with divergent PT to understand their acclimation and plasticity in PT and postwarming recovery responses. Inside a greenhouse mesocosm, we exposed the genotypes to simulated warming events: Tmax 26/20°C (day‐time highest maximum/night‐time lowest maximum) (Week 1) < Tmax 33/30°C (Week 2) < Tmax 36/32°C (Week 3) followed by Tmax 26/16°C (Week 4, recovery). The genotypes showed no modulations in PT, despite an increase of about 10°C in ambient air temperature and leaf megathermy behavior (midday leaf temperatures>air temperature). We found significant genotypic variations in intrinsic photoprotection capacity, measured weekly as the quantum yield of nonphotochemical quenching (ΦNPQ). Higher warming events dramatically enhanced the rates of ΦNPQ rise with a concurrent loss in net photosynthetic rates though genotypic variation in these responses was evident. The ΦNPQ stayed high along with declined photosynthetic rates even after a week of postwarming recovery. Our study points towards a conservative and non-plastic PT in tropical evergreen species and their need for sustaining higher photoprotection during warming as well as postwarming recovery days. Our results depict that even the current summer temperature of tropics and subtropics could cause intermittent extended loss in CO2 fixation capacity and push these evergreens species to favor photoprotective rather than photosynthetic processes. High intrinsic PT (which translates to high photosystem membrane stability) might support the need and mechanisms for high and long lasting photoprotective heat dissipation activities in evergreen trees. Although we did not find any evidence of acquired enhancement in PT, the response needs to be further assessed under more pressing situations, including compounded heat and drought stress, acute heatwave events and under biotic stress conditions including pathogen infection and pest infestation.

1 - Citrus Research And Education Center, 700 Experiment Station Rd, Lake Alfred, FL, 33850 , United States
2 - Earth University, Earth University, San José, Mercedes, San Jose, Costa Rica
3 - Bahauddin Zakariya University, Multan, Punjab, Pakistan
4 - Florida Ag Research, Thonotosassa, Florida, 33592, United States
5 - Vindara Inc., 7455 Emerald Dunes Drive, #2100, Orlando, FL, 32822, United States
6 - University Of Florida, Citrus Research And Education Center, 700 Experiment Station Rd, Lake Alfred, FL, 33850, United States

Short-term warming
Non-photochemical quenching.

Presentation Type: Oral Paper
Number: EPH3004
Abstract ID:287
Candidate for Awards:None

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