Differences in biochemical, gas exchange and hydraulic response to water stress in desiccation tolerant and sensitive fronds of the fern Anemia caffrorum

Desiccation tolerant plants can survive extreme water loss in their vegetative tissues. The fern Anemia caffrorum produces desiccation tolerant (DT) fronds in the dry season and desiccation sensitive (DS) fronds in the wet season, providing a unique opportunity to explore the physiological mechanisms associated with desiccation tolerance. Anemia caffrorum plants with either DT or DS fronds were acclimated in growth chambers. Photosynthesis, frond structure and anatomy, water relations and minimum conductance to water vapour were measured under well-watered conditions. Photosynthesis, hydraulics, frond pigments, antioxidants and abscisic acid contents were monitored under water deficit. A comparison between DT and DS fronds under well-watered conditions showed that the former presented higher leaf mass per area, minimum conductance, tissue elasticity and lower CO2 assimilation. Water deficit resulted in a similar induction of abscisic acid in both frond types, but DT fronds maintained higher stomatal conductance and upregulated more prominently lipophilic antioxidants. The seasonal alternation in production of DT and DS fronds in A. caffrorum represents a mechanism by which carbon gain can be maximized during the rainy season, and a greater investment in protective mechanisms occurs during the hot dry season, enabling the exploitation of episodic water availability.This work was supported by the projects CTM2014-53902-C2-1-P from the Ministerio de Economia y Competitividad (MINECO, Spain) and the European Regional Development Fund (ERDF) and PGC2018-093824-B-C41/PGC2018-093824-B-C44 from the Ministerio de Ciencia, Innovacion y Universidades (MCIU, Spain) and the ERDF; and the Basque Government (grant UPV/EHU IT-1018-16, Spain). MN was supported by the MINECO and the European Social Fund (predoctoral fellowship BES-2015-072578). AVP-C was supported by the Ministerio de Educacion, Cultura y Deporte (MECD; pre-doctoral fellowship FPU-02054). MIA was supported by a pre-doctoral grant from the Basque Government. We thank the technical support for microscopy preparation provided by the Universitat de Valencia (Seccio de Microscopia Electrnica, SCSIE), Dr. Ferran Hierro (UIB, Serveis Cientificotecnics) and Margalida Roig Oliver (UIB). JMF provided funding for work conducted in South Africa from her South African Department of Science and Innovation, National Research Foundation Research Chair, grant no. 9840