Potential of Intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for Phytoremediation of Heavy-metal Contaminated Soil around Mining Areas

Abstract

In order to study the potential of intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for phytoremediation of heavy-metal contaminated soil around mining areas, a pot experiment was conducted to investigate the effects of intercropping on plant biomass, heavy metal accumulation, dynamic changes in heavy metal content in soil solution, and response characteristics of the rhizosphere microbial community. The results indicated that the shoot biomass of P. purpureum and M. azedarach from their intercropping system (KX) was increased by 26.5% and 13.2%, respectively, and the shoot biomass of B. papyrifera from the intercropping system of P. purpureum and B. papyrifera (GX) was increased by 13.5% compared with their corresponding monoculture systems. The shoot Cd content of M. azedarach in the KX treatment was significantly increased by 24.9% (P<0.05), and their Cd and Pb accumulation in shoots were also significantly increased. The shoot contents and accumulations of Cd and Pb from P. purpureum in the GX treatment were significantly increased; however, those in B. papyrifera shoots were decreased. The total accumulations of Cd and Pb in each pot from intercropping systems were higher than that from the monoculture treatment, with that from the KX treatment being the highest at 1065 μg·pot-1. During the 150-day cultivation process, the pH value and dissolved organic carbon (DOC) content in the soil solution under the intercropping systems of KX and GX were higher than those of original soil (CK). After 150 d cultivation, the DOC contents of the soil solution under the KX and GX treatments were significantly increased by 40.5% and 33.1% in comparison with that under CK (P<0.05), respectively. Compared with those from CK and P. purpureum and B. papyrifera monoculture treatments, the Cd content in soil solution from the KX treatment was significantly decreased by 56.1%, 35.5%, and 46.5%, and that in the GX treatment was decreased by 54.5%, 33.2%, and 44.6% (P<0.05), respectively. The Shannon and Chao1 indices of rhizosphere microorganisms under the intercropping systems were significantly higher than those under CK. The number of unique OTUs in intercropping systems was significantly higher than that in CK and the M. azedarach and B. papyrifera monocultures. Intercropping improved the abundance of dominant bacteria such as Actinobacteriota and Acidobacteriota, and the abundance of Actinobacteriota increased by 31.6%, 20.9%, and 25.3% in the KX treatment and by 32.3%, 21.5%, and 25.9% in the GX treatment, respectively, in comparison with those in CK and the P. purpureum and M. azedarach monocultures. It was concluded that intercropping P. purpureum with wood plants could increase their shoot biomass and the accumulations of Cd and Pb, as well as soil environmental quality, whereas the availability and migration risk of heavy metals in soil were reduced. Moreover, the intercropping of P. purpureum and M. azedarach was more beneficial to the remediation of polymetallic-contaminated soil around mining areas.