Contrasting thermal acclimation of leaf dark respiration and photosynthesis of Antarctic vascular plant species exposed to nocturnal warming.

Leaf respiration and photosynthesis will respond differently to an increase in temperature during night, which can be more relevant in sensitive ecosystems such as Antarctica. We postulate that the plant species able to colonize the Antarctic Peninsula - Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. - are able to acclimate their foliar respiration and to maintain photosynthesis under nocturnal warming to sustain a positive foliar carbon balance. We conducted a laboratory experiment to evaluate the effect of time of day (day and night) and nocturnal warming on dark respiration. Short (E0 and Q10 ) and long-term acclimation of respiration, leaf carbohydrates, photosynthesis (Asat ) and foliar carbon balance (R/A) were evaluated. The results suggest that the two species have differential thermal acclimation respiration, where D. antarctica showed more thermosensitivity to short-term changes in temperature than C. quitensis. Experimental nocturnal warming affected respiration at daytime differentially between the two species, with a significant increase of R10 and Asat in D. antarctica, while no changes on respiration were observed in C. quitensis. Long thermal treatments of the plants indicated that nocturnal but not diurnal respiration could acclimate in both species, and to a greater extent in C. quitensis. Non-structural carbohydrates were related with respiration in C. quitensis but not in D. antarctica, suggesting that respiration in the former species is likely controlled by total soluble sugars and starch during day and night, respectively. Finally, foliar carbon balance was differentially improved under warming conditions in Antarctic plants by different mechanisms, with C. quitensis deploying respiratory acclimation, while D. antarctica increased its Asat.