Photosynthesis is limited by three main factors: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax). It is unclear how limiting factors vary under stress, particularly during long-term stress acclimation. In this work, we compared for the first time photosynthesis limitation resulting from long-term acclimation to three major abiotic stresses: drought, salinity and temperature. We used saplings of Ziziphus spina-christi, a thermophilic and drought-tolerant tree, which recently became more abundant in the Mediterranean, presumably due to increased winter temperatures. Stress acclimation was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. For each stress, photosynthesis-limiting factors were compared. We developed an integrative stress index that allowed us to precisely define stress level, enabling a comparison between stress types. Photosynthesis under all stresses was limited mostly by gs and gm (80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. In all the stresses, gm decreased only under progressive reduction in leaf physiological functionality and was associated with low turgor under drought, an increase in leaf Na+ under salinity and low leaf hydraulic conductance (Kleaf) at low temperatures. Mesophyll structure (mesophyll surface area exposed to the intercellular air spaces, leaf thickness, % intercellular air spaces) did not explain gm acclimation to stress. Current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change. The ability to minimize mesophyll-imposed limitations on photosynthesis was found as a strong indicator of progressive stress tolerance. Moreover, the results demonstrate how warming climate benefits the photosynthetic function in thermophilic species, such as Ziziphus spina-christi.

This study is aimed to explore the properties of cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) composite films with and without 1,2,3,4-butane tetracarboxylic acid (BTCA), a nontoxic crosslinker. CNC and CNC-PVA nanocomposite films are prepared using solution-casting technique. Differential scanning calorimetry (DSC) analyses show that crosslinking increased the glass transition temperature but reduced the melting temperature and crystallinity. Furthermore, high CNC concentrations in the PVA matrix interfere with PVA crystallinity, whereas in specific ratio between CNC and PVA, two different crystalline structures are observed within the PVA matrix. Film surfaces and fracture topographies characterized using scanning electron microscope indicate that at certain CNC-PVA ratios, micron-sized needle-like crystals have formed. These crystalline structures correlate with the remarkable improvement in mechanical properties of the CNC-PVA nanocomposite films, that is, enhanced tensile strain and toughness to 570% and 202 MJ m , respectively, as compared to pristine PVA. BTCA enhances the tensile strain, ultimate tensile stress, toughness, and modulus of CNC films compared to pristine CNC films. Water absorption of crosslinked CNC and CNC-PVA nanocomposite films is significantly reduced, while film transparency is significantly improved as a function of PVA and crosslinker content. The presented results indicate that CNC-PVA nanocomposite films may find applications in packaging, and though materials applications.