CaFe-layered double hydroxide corn straw biochar reduced heavy metal uptake by Brassica campestris L. and Ipomoea aquatic F.: Rhizosphere effects and oxidative stress alleviation.

In the present study, CaFe-layered double hydroxide corn straw biochar (CaFe-LDH@CSB) was applied to the rhizosphere soil of both pakchoi (Brassica campestris L. ssp. Chinensis Makino, B. campestris L.) and water spinach (Ipomoea aquatic F., I. aquatic F.) to explore and clarify the potential mechanism by which CaFe-LDH@CSB helps vegetables reduce heavy metal (HM) uptake and alleviate oxidative stress. Pot experiments were conducted with CaFe-LDH@CSB applied at four levels: control (CK), T1 (5 g kg-1), T2 (10 g kg-1) and T3 (20 g kg-1). The results indicated that the application of CaFe-LDH@CSB significantly increased pH and decreased the acid-soluble forms of Cd, Pb, Zn and Cu in the rhizosphere soil of both B. campestris L. and I. aquatic F.; decreases of 39.4%, 18.0%, 10.0% and 33.3% in B. campestris L. and of 26.6%, 49.1%, 13.2% and 36.8% in I. aquatic F., respectively, were observed at the T3 level. Moreover, CaFe-LDH@CSB application reduced HM uptake by B. campestris L. and decreased HM-induced oxidative stress through the regulation of soil physicochemical properties and microbial abundance. For B. campestris L., variations in Sordariomycetes helped alleviate the accumulation of HMs in the aerial part, while GSH and -SH from the nonenzymatic system played an important role in scavenging H2O2 in leaves, thus helping B. campestris L. alleviate HM-induced oxidative stress. For I. aquatica F., variations in Vicinamibacteria and Mortierellomycetes helped alleviate the accumulation of HMs in plants, while GSH and PCs from nonenzymatic systems played an important role in removing ·O2- in leaves, thereby helping I. aquatica F. alleviate HM-induced oxidation stress. Our study indicated that the application of CaFe-LDH@CSB improved the rhizosphere soil environment and rebuilt the soil microbial community, helping B. campestris L. and I. aquatica F. alleviate HM-induced oxidative stress and promoting the growth of both vegetables.