In the present study, we investigated whether Ca2+ application alleviates salinity-induced damage in foxtail millet (Setaria italica L.). We evaluated the stress-related ion balance, physiological activity and gene expression involved in plant defences against salinity exposure. Twenty-one-day-old foxtail millet was maintained in sand culture for 7 days and subjected to one of seven treatments: half-strength modified Hoagland solution (the control), 1.0% NaCl, 1.0% NaCl + 2.5 mM Ca2+, 1.0% NaCl + 5.0 mM Ca2+, 1.0% NaCl + 7.5 mM Ca2+, 1.0% NaCl + 10.0 mM Ca2+, 1.0% NaCl + 12.5 mM Ca2+. The addition of Ca2+ significantly increased shoot and root height and weight relative to calcium absent treatment and corrected the ion imbalance by increasing Ca2+, Mg2+ and K+, and decreasing Na+ in the leaves and roots. It increased chlorophyll content and root activity and decreased the relative electrolyte leakage in the roots and leaves. Calcium application significantly upregulated superoxide dismutase and catalase, increased total protein, and decreased malondialdehyde and H2O2. Finally, the addition of Ca2+ upregulated the expression of APX, SOD and CAT. It was found that 10.0 mM Ca2+ was the optimal concentration for alleviating salt stress injury in foxtail millet.

Foxtail millet (Setaria italica L.) is an important cereal for managing future water scarcity and ensuring food security, due to its strong drought and salt stress resistance owing to its developed root system. However, the molecular responses of foxtail millet leaves to salt stress are largely unknown. In this study, seeds of 104 foxtail millet accessions were subjected to 0.17 mol·L⁻¹ NaCl stress during germination, and various germination-related parameters were analyzed to derive 5 salt-sensitive accessions and 13 salt-tolerant accessions. Hong Gu 2000 and Pu Huang Yu were the most salt-tolerant and salt-sensitive accessions, respectively. To determine the mechanism of the salt stress response, transcriptomic differences between the control and salt-treated groups were investigated. We obtained 2019 and 736 differentially expressed genes under salt stress in the salt-sensitive and salt-tolerant accessions, respectively. The transcription factor families bHLH, WRKY, AP2/ERF, and MYB-MYC were found to play critical roles in foxtail millet’s response to salt stress. Additionally, the down-regulation of ribosomal protein-related genes causes stunted growth in the salt-sensitive accessions. The salt-tolerant accession alleviates salt stress by increasing energy production. Our findings provide novel insights into the molecular mechanism of foxtail millet’s response to salt stress.

Improving cropping systems together with suitable agronomic management practices can maintain dry farming productivity and reduce water competition with low N inputs. The objective of the study was to determine the photosynthetic and yield responses of maize and peanut under six treatments: sole maize, sole peanut, maize–peanut intercropping, maize–peanut rotation–intercropping, 20% and 40% N reductions for maize in the maize–peanut rotation–intercropping. Maize–peanut intercropping had no land-use advantage. Intercropped peanut is limited in carboxylation rates and electron transport rate (ETR), leading to a decrease in hundred-grain weight (HGW) and an increase in blighted pods number per plant (N_BP). Intercropped peanut adapts to light stress by decreasing light saturation point (I_sat) and light compensation point (I_comp) and increasing the electron transport efficiency. Intercropped maize showed an increase in maximum photosynthetic rate (Pn_max) and I_comp due to a combination of improved intercellular CO₂ concentration, carboxylation rates, PSII photochemical quantum efficiency, and ETR. Compare to maize–peanut intercropping, maize–peanut rotation–intercropping alleviated the continuous crop barriers of intercropped border row peanut by improving carboxylation rates, electron transport efficiency and decreasing I_sat, thereby increasing its HGW and N_BP. More importantly, the land equivalent ratio of maize–peanut rotation–intercropping in the second and third planting years were 1.05 and 1.07, respectively, showing obvious land use advantages. A 20% N reduction for maize in maize–peanut rotation–intercropping does not affect photosynthetic character and yield for intercropped crops. However, a 40% N reduction decreased significantly the carboxylation rates, ETR, I_comp and Pn_max of intercropped maize, thereby reducing in a 14.83% HGW and 5.75% lower grain number per spike, and making land-use efficiency negative.