Disentangling the contributions of osmotic and ionic effects of salinity on stomatal, mesophyll, biochemical and light limitations to photosynthesis

Abstract

There are conflicting opinions on the relative importance of photosynthetic limitations under salinity. Quantitative limitation analysis of photosynthesis provides insight into the contributions of different photosynthetic limitations, but it has only been applied under saturating light conditions. Using experimental data and modelling approaches, we examined the influence of light intensity on photosynthetic limitations and quantified the osmotic and ionic effects of salinity on stomatal (LS ), mesophyll (LM ), biochemical (LB ) and light (LL ) limitations in cucumber (Cucumis sativus L.) under different light intensities. Non-linear dependencies of LS , LM and LL to light intensity were found. Osmotic effects on LS and LM increased with the salt concentration in the nutrient solution (Ss ) and the magnitude of LM depended on light intensity. LS increased with the Na(+) concentration in the leaf water (Sl ) and its magnitude depended on Ss . Biochemical capacity declined linearly with Sl but, surprisingly, the relationship between LB and Sl was influenced by Ss . Our results suggest that (1) improvement of stomatal regulation under ionic stress would be the most effective way to alleviate salinity stress in cucumber and (2) osmotic stress may alleviate the ionic effects on LB but aggravate the ionic effects on LS .

Diffusional conductance to CO2 is the key limitation to photosynthesis in salt‐stressed leaves of rice (Oryza sativa)

“…The contributions of LB to reducing A in salt‐stressed rice leaves were relatively small (Fig. ), in disagreement with two studies on H. vulgare (Perez‐Lopez et al ) and C. sativus (Chen et al ) under salt stress. This might be explained by a lower C c in the current study than in the other studies.…”

“…After 7 days of NaCl treatment, A decreased significantly in LYP9, SY63 and TXZ25 but not in N22. Generally, it is assumed that stomatal closure is the first response to salinity due to osmotic stress (Delfine et al , Delfine et al , Centritto et al , Moradi and Ismail , Chaves et al , Chen et al ). However, we observed that g s , g m and ETR decreased dramatically in some of the genotypes one day after NaCl treatment, and multiple leaf parameters involving biochemical and physiological traits were affected in almost all of the genotypes after 7 days of treatment (Fig.…”

“…Limitation analysis is a helpful tool to quantify the stress effects of changes in various factors on A (Grassi and Magnani , Buckley and Diaz‐Espejo ), and it has been widely used in recent years (Flexas et al , Galle et al , Galle et al , Chen et al , Tosens et al ). Relative photosynthetic limitations including stomatal ( l s ), mesophyll ( l s ) and biochemical ( l b ) relative limitations were calculated according to Grassi and Magnani ().…”

Anatomical variation of mesophyll conductance under potassium deficiency has a vital role in determining leaf photosynthesis

“…Then, the relative change of A , g sc , g m and J in Eqn can be approximated by the following (Chen et al . ): where , , and are the reference values. The reference maximum values of net CO 2 assimilation rate, stomatal and mesophyll conductance and the rate of electron transport were obtained in +K treatments; therefore, its parameters were defined as standard.…”

Salinity and crop yield

“…It is also very likely that salt ions accumulate in mitochondria and chloroplasts disturbing electron flow and causing electrons to leak to molecular oxygen, thereby triggering O 2 À production. Apart from loss of ionic homeostasis, the rise in osmotic potential and salts interferes with specific processes like cell expansion, stomata development and stomatal movement (Kumari et al 2014;Chen et al 2015;Z€ orb et al 2015;Geilfus et al 2017) (Fig. 1).…”