Response strategies of slash pine (Pinus elliottii) to cadmium stress and the gain effects of inoculation with Herbaspirillum sp. YTG72 in alleviating phytotoxicity and enhancing accumulation of cadmium.

ABSTRACT

Phytoremediation using fast-growing woody plants assisted by plant growth-promoting bacteria (PGPB) on cadmium (Cd)-contaminated sites is considered a promising technique; however, its remediation efficiency is still affected by multiple factors. In this study, the mining areas' soil conditions were simulated with different Cd addition levels (0, 3, 6, 9 mg kg-1) in order to investigate the response strategy to Cd stress of fast-growing economic tree species, slash pine (Pinus elliottii), and the effects of inoculation with the PGPB strain Herbaspirillum sp. YTG72 on the physiological activity and Cd accumulation of plants. The main results showed that there were significant (p < 0.05) increases in contents of chlorophyll and nutrient elements (P, K, Ca, and Mg) at low Cd addition level (3 mg kg-1) compared to non-Cd addition treatment. When the additive amount of Cd increased, the growth of plants was severely inhibited and the content of proline was increased, as well as Cd in plants. Besides, the ratios of KP, CaP, and MgP in plants were negatively correlated with the contents of Cd in plants and soils. Inoculation of P. elliottii with the PGPB strain Herbaspirillum sp. YTG72 improved the physiological functions of the plants under Cd stress and activated the antioxidant system, reduced the accumulation of proline, and decreased the ratios of KP, CaP, and MgP in plant. More importantly, planting P. elliottii in Cd-contaminated soil could significantly (p < 0.05) reduce the Cd content in the rhizosphere soil, and furthermore, inoculation treatment could promote the reduction of soil Cd content and increased the accumulation of Cd by root. The results of the present study emphasized the Cd response mechanism of P. elliottii based on multifaceted regulation, as well as the feasibility of strain Herbaspirillum sp. YTG72 assisted P. elliottii for the remediation on Cd-contaminated sites.