Di Feng

Abiotic stresses are various environmental factors that inhibit a normal plant growth and limit the crop productivity. Plant scientists have been attempting for a long time to understand how plants respond to these stresses and find an effective and feasible solution in mitigating their adverse impacts. Exogenous calcium ion as an essential element for the plant growth, development and reproduction has proven to be effective in alleviating plant stresses through enhancing its resistance or tolerance against them. With a comprehensive review of most recent advances and the analysis by VOSviewer in the researches on this focus of “exogenous calcium” and “stress” for last decade, this paper summarizes the mechanisms of exogenous calcium that are involved in plant defensive responses to abiotic stresses and classifies them accordingly into six categories: I) stabilization of cell walls and membranes; II) regulation of Na + and K + ratios; III) regulation of hormone levels in plants; IV) maintenance of photosynthesis; V) regulation of plant respiratory metabolism and improvement of root activities; and VI) induction of gene expressions and protein transcriptions for the stress resistance. Also, the progress and advances from the updated researches on exogenous calcium to alleviate seven abiotic stresses such as drought, flooding, salinity, high temperature, low temperature, heavy metals, and acid rain are outlined. Finally, the future research perspectives in agricultural production are discussed.

In the context of dwindling freshwater resources, it is imperative to comprehensively evaluate crop productivity and soil resource sustainability when considering the use of saline water for irrigation (SWI). This study aimed to investigate the effects of SWI on soil salinity variation and sustainability of flat sowing cotton (Gossypium hirsutum L.) through a comprehensive 15-year field experiment conducted in the North China Plain, encompassing six levels of irrigation water salinity (ECiw of 1.3, 3.4, 7.1, 10.6, 14.1, and 17.7 dS m−1, respectively). The results of the 15-year SWI revealed an increase in soil salinity within the cotton root zone, with increases of 5%, 20%, 39%, 67%, 116%, and 156%, respectively, observed across the six treatments. In treatments with higher ECiw values (14.1 and 17.7 dS m−1), salt accumulation extended to a depth of 3.0 m. Long-term SWI has a risk of causing soil sodicity and alkalinity. Sodium adsorption ratio (SAR) and pH in the treatments with ECiw ≥ 7.1 dS m−1 increased significantly (P < 0.05) after cotton harvest in the 15th year of continuous SWI. Cotton yield performance exhibited a distinct response to varying levels of ECiw. The treatment with an ECiw of 3.4 dS m−1 yielded the highest average cotton yield of 3419 kg ha−1, while cotton yields in treatments with an ECiw of 14.1 and 17.7 dS m−1 were more than 13% and 20%, respectively, lower than the maximum yield (P < 0.05). The sustainability index of cotton yield was at its lowest (0.68) in the treatments with an ECiw of 7.1 dS m−1, with values between 0.72 and 0.75 in the other treatments. Additionally, long-term SWI resulted in changes in cotton quality, including a decrease in micronaire value and an increase in elongation index. A quadratic correlation analysis identified a threshold ECiw of 6.8 dS m−1 for optimum cotton yield. In summary, it is recommended that the ECiw should not exceed 6.8 dS m−1 to ensure the sustainability and safety of long-term SWI for cotton production in this research region.