Soil application of effective microorganisms and nitrogen alleviates salt stress in hot pepper ( Capsicum annum L.) plants

The application of effective microorganisms (EMs) and/or nitrogen (N) have a stimulating effect on plants against abiotic stress conditions. The aim of the present study was to determine the impact of the co-application of EMs and N on growth, physio-biochemical attributes, anatomical structures, nutrients acquisition, capsaicin, protein, and osmoprotectant contents, as well as the antioxidative defense system of hot pepper ( Capsicum annum L.) plants. In the field trials, EMs were not applied (EMs ^-) or applied (EMs ⁺) along with three N rates of 120, 150, and 180 kg unit N ha ^-1 (designated as N ₁₂₀, N ₁₅₀, and N ₁₈₀, respectively) to hot pepper plants grown in saline soils (9.6 dS m ^-1). The application of EMs and/or high N levels attenuated the salt-induced damages to hot pepper growth and yield. The application of EMs ⁺ with either N ₁₅₀ or N ₁₈₀ increased the number, average weight and yield of fruits by 14.4 or 17.0%, 20.8 or 20.8% and 28.4 or 27.5%, respectively, compared to hot pepper plants treated with the recommended dose (EMs ^- × N ₁₅₀). When EMs ⁺ was individually applied or combined with either N ₁₅₀ or N ₁₈₀, increased accumulation of capsaicin were observed by 16.7 or 20.8%, protein by 12.5 or 16.7%, proline by 19.0 or 14.3%, and total soluble sugars by 3.7 or 7.4%, respectively, in comparison with those treated with the integrative EMs ^- × N ₁₅₀. In addition, the non-enzymatic contents (ascorbate, and glutathione) and enzymatic activities (catalase, superoxide dismutase, and glutathione reductase) of the antioxidant defense systems significantly increased in hot pepper plants treated with EMs ⁺ alone or combined with N ₁₅₀ or N ₁₈₀ under salt stress conditions. Higher accumulation of nutrients (N, P, K ⁺, and Ca ²⁺) along with reduced Na ⁺ acquisition was also evidenced in response to EMs ⁺ or/and high N levels. Most anatomical features of stems and leaves recovered in hot pepper plants grown in saline soils and supplied with EMs ⁺ and N. The application of EMs and N is undoubtedly opening new sustainable approaches toward enhancing abiotic stress tolerance in crops (e.g. hot pepper).