Long-term acclimation to drought, salinity and temperature in the thermophilic tree Ziziphus spina-christi: revealing different tradeoffs between mesophyll and stomatal conductance. (31st December 2018)

• Record Type: Journal Article
• Authors: Zait, Yotam; Shtein, Ilana; Schwartz, Amnon
• Editors: Ball, Marilyn
• Is Part Of: Tree physiology. Volume 39:Number 5(2019)
• Page Start: 701
• Page End: 716
• Publication Date: 2018-12-31
• Subjects: limitations -- mesophyll conductance -- photosynthesis -- stomatal conductance -- stress -- Ziziphus; Trees -- Physiology -- Periodicals; 582.16
• DOI: 10.1093/treephys/tpy133
• Languages: English
• ISSNs: 0829-318X

Abstract

Abstract: Photosynthesis is limited by three main factors: stomatal conductance ( g s ), mesophyll conductance ( g m ) and maximum capacity for Rubisco carboxylation ( V cmax ). 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 g s and g m (80–90%); whereas biochemistry ( V cmax ) made a minor contribution (10–20%). The relative contribution of g s and g m on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in g s, while intolerance to low temperatures was driven by decline in g m . In all the stresses, g m 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 ( K leaf ) at low temperatures. Mesophyll structure (mesophyll surface area exposed to the intercellular air spaces, leaf thickness, % intercellular air spaces) did not explain g m 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 .