Crushed maize seeds enhance soil biological activity and salt tolerance in caper (Capparis spinosa L.)

[Display omitted] •Applying biostimulant increased plant biomass and proline.•Applying biostimulant significantly enhanced soil enzymes activity.•Using biostimulant significantly increased the rutin bioflavonoid of caper.•Applying biostimulant increased the phenol content of caper. Caper (Capparis spinosa L.) is an ancient plant with ecological, industrial, medicinal and economical benefits which at its primary growth phase is sensitive to salt stress. This study was conducted to investigate the biostimulant effect of supplementing crushed maize (Zea mays L.) seeds (CMS) (0, 10 and 20 %) into growing media on caper salt tolerance and soil biological activity under different salinity level (0, 5, 10 and 15 dS/m). Applying 20 % biostimulant increased the number of leaves and roots by 200.0 and 56.0 %, respectively, compared with untreated seedlings at the same salinity level. The application of 20 % biostimulant also enhanced the proline content (by 40.5 %), total phenolic contents (34.0 %), rutin (356.4 %) and leaf K content (29.8 %) of treated capers compared with untreated seedlings. Applying 20 % biostimulant also significantly increased the soil enzymes activity including urease, dehydrogenase, and phosphatase as well as soil bacteria population. Whereas, using biostimulant significantly decreased the content of Na in different caper’s organs. However, the total flavonoid content, soil fungi population and most of the morphological parameters of caper were not significantly affected by the application of CMS. In total, the soil application of CMS had a substantial effect on physiological and biochemical parameters of salinized capers and soil biological activity based on principal component analysis (PCA). In conclusion, using CMS as a soil supplement can be recommended as a safe and natural biostimulant to alleviate the negative impacts of salt stress in caper seedlings.