Elevated CO2 concentration in the air (e[CO2]) decreases stomatal density (SD) and stomatal conductance (gs) where abscisic acid (ABA) may play a role, yet the underlying mechanism remains largely elusive. We investigated the effects of e[CO2] (800 ppm) on leaf gas exchange and water relations of two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (WT) and its ABA-deficient mutant (flacca). Compared to plants grown at ambient CO2 (400 ppm), e[CO2] stimulated photosynthetic rate in both genotypes, while depressed the gs only in WT. SD showed a similar response to e[CO2] as gs, although the change was not significant. e[CO2] increased leaf and xylem ABA concentrations and xylem sap pH, where the increases were larger in WT than in flacca. Although leaf water potential was unaffected by CO2 growth environment, e[CO2] lowered osmotic potential, hence tended to increase turgor pressure particularly for WT. e[CO2] reduced hydraulic conductance of leaf and root in WT but not in flacca, which was associated with downregulation of gene expression of aquaporins. It is concluded that ABA-mediated regulation of gs, SD, and gene expression of aquaporins coordinates the whole-plant hydraulics of tomato grown at different CO2 environments.

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As drought and heat stress are major challenges for crop productivity under future climate changes, tolerant cultivars are highly in demand. This study investigated the potential of existing Nordic wheat genotypes to resist unfavorable conditions. Four genotypes were selected based on their heat sensitivity (heat-sensitive: LM19, SF1; heat-tolerant: LM62, NS3). At the tillering stage, the plants were subjected to four treatments under controlled conditions: control, drought, heat and combined drought and heat stress. The morpho-physiological performance was quantified during the early and late phase of stress, as well as the recovery phase. We applied an integrative image-based phenotyping approach monitoring plant growth dynamics by structural Red Green Blue (RGB) imaging, photosynthetic performance by chlorophyll fluorescence imaging and transpiration efficiency by thermal infrared imaging. The results demonstrated that the selected genotypes were moderately affected in their photosynthetic efficiency and growth under drought stress, whereas heat and combined stress caused rapid reductions in photosynthesis and growth. Furthermore, drought stress had a major impact on canopy temperature. The NS3 genotype was the most robust genotype, as indicated by its improved response under all stress treatments due to its relatively small biomass. However, the genotypes showed different tolerance to individual and combined stress.

Due to climate change, multiple heat events are expected to be an additional limiting factor that will adversely affect wheat production. The study aimed to analyze the physiological response to heat stress in four winter wheat cultivars at different physiological stages under greenhouse conditions during 2019. The net photosynthetic rate, stomatal conductance, chlorophyll index, maximum quantum efficiency of photosystem II, fructose, glucose and sucrose content, grain yield per plant, grain weight and number of grains per plant were analyzed in wheat cultivars under short periods of heat stress at anthesis and mid‐grain filling, and combined stress at anthesis and mid‐grain filling. The results of the study indicated that heat stress modified the photosynthesis‐related and grain yield–related traits. Moreover, heat stress caused a decrease of sucrose content, while fructose and glucose content increased. Heat stress had more pronounced effects on the photosynthetic parameters and grain yield during grain filling than during anthesis. A significant variation observed among cultivar responses to the negative impact of heat stress highlighted the fact that cultivars Pobeda and Gladius were more tolerant than Renesansa and Simonida. Different cultivar reactions to heat stress during anthesis and grain filling indicated the need to conduct further studies with wheat cultivars of different origin in order to identify additional sources of tolerance.