Stomatal and non-stomatal regulations of photosynthesis in response to salinity, and K and Ca fertigation in cotton (Gossypium hirsutum L cv.)
Yingying Ma, Zuoqiang Yuan, Zhenhua Wei, Fei Yan, Xuezhi Liu, Xiangnan Li, Jingxiang Hou, Zhanqing Hao, Fulai Liu
Abstract
To study the response of photosynthesis of cotton plants to salinity, and K and Ca fertigation, leaf gas exchange, light and CO 2 response curves, chlorophyll fluorescence parameters, leaf N, P, Mg, K, Na and Ca concentrations, and antioxidant enzyme activities were measured. Cotton plants were grown at either 0 or 150 mM NaCl salinity (C and S treatment, respectively), and fertigated with or without K and Ca addition (O and K+Ca treatment, respectively). The results showed that 150 mM NaCl salinity decreased stomatal conductance (g s ), transpiration rate (T r ) and chloroplast CO 2 concentration (C c ). Yet it increased light saturated photosynthetic rate (A L ), CO 2 saturated photosynthetic rate (A C ), mesophyll conductance (g m ), maximum electron transport rate (J max ), maximum Rubisco carboxylation rate (V cmax ) and triose phosphates use rate (TPU), resulting in a similar net photosynthesis rate (A n ) to that of C plants. K+Ca treatment enhanced A n , g s , T r and C c , particular under S condition, while it had no significant effects on g m , J max , V cmax and TPU. Salt-induced increases in J max , V cmax and TPU were associated with higher [N] leaf and [P] leaf , whereas the J max /V cmax ratio decreased with increasing [N] leaf and [P] leaf , and C c decreased with increasing [N] leaf . Salt-induced improvement in A C was linked to lower J max/ V cmax ratio and C c , while the increase in A L could be ascribed to the lower non-photochemical quenching and higher photosystem II efficiency, which could be partially attributed to the salt-caused improvement in leaf superoxide dismutase, peroxidase and catalase activies. In conclusion, 150 mM NaCl salinity increased stomatal limitation but decreased non-stomatal limitation on A n , resulting in sustained A n and significantly lowered g s and T r , and hence an improved water use efficiency. K and Ca addition could alleviate the salinity-induced decrease in g s and increase in stomatal limitation. • 150 mM NaCl salinity increased stomatal limitation but decreased non-stomatal limitation on A n . • Increased g m , V cmax , J max and TPU associated with decreased non-stomatal limitation on A n under salinity stress. • K + and Ca 2+ fertigation alleviated salinity-induced decrease in g s and increase in stomatal limitation.