Living in extreme environments: a photosynthetic and desiccation stress tolerance trade-off story, but not for everyone.

Abstract

A trade-off between allocated resources for photosynthesis and stress tolerance is generally observed in nature. Thus, the search for outlier species breaking this trend is an interesting approach to identity new mechanisms for plant breeding purposes. Hypothetically, outlier extremophyte species present a distinctive arrangement of physiological functions that favor stress tolerance mechanisms without jeopardizing investment allocation into photosynthesis. We explored this trade-off, analyzing twenty-one plant species for desiccation tolerance, and photosynthetic capacity, under the extreme arid environments of the Atacama Desert and the Surire Salar in the Chilean Altiplano. Most of the studied species followed the trade-off tendency, however, we did find one outlier species, Prosopis tamarugo. To study the mechanisms involved in this atypical response, the Prosopis genus was analyzed more deeply. Our results suggest that the outlier response of P. tamarugo is multifactorial. This species presented a high photochemistry activity, associated with a higher synthesis of chlorophylls, photoprotective pigments, and complex antioxidant molecules. Moreover, the synthesis of no-nitrogen osmoprotectant molecules, such as ciceritol and mannitol in P. tamarugo, would allow the allocation of nitrogen to support its high photosynthetic capacity, without compromising its leaf desiccation stress tolerance.