Abstract
Purpose It is unknown how the Cd-mediated changes in the rhizospheric nitrifier community affect plant growth under different water management practices. This study examined the effect of Cd on microbial N transformation and its association with rice growth in two water regimes, continuous flooding (CF) and alternate wetting and drying (AWD), in a paddy soil.
Methods The 16S rRNA, amoA genes in the rhizosphere and endosphere, and OsNTRs were determined using qPCR. Nitrifier community analysis was performed by sequencing the amoA genes. Concentrations of N and Cd in shoots and roots, and IAA in the roots were determined by flow injection analyzer, ICP-MS and enzyme-linked immunosorbent (ELISA), respectively.
Results The direct and indirect negative effects of Cd bioavailability in the rhizosphere on plant growth and ultra-structure of roots and leaves were greater under AWD than CF after 56-day growth. Nitrifier community was changed by water and Cd treatments. Crenarchaeota, Nitrosopumilus, Nitrosopira, and Nitrosovibrio tenuis related species were the dominant nitrifier players. Increasing Cd level decreased plant N uptake, root-IAA concentration, and the abundance of 16S rRNA gene in the rhizosphere and endosphere to a greater extent under AWD than under CF. This in turn decreased the colonization of endophytes and the surface area of the roots, leading to decreased N uptake from the soil.
Conclusion The results imply that appropriate water management and rhizospheric engineering in Cd-contaminated paddy fields may be important approaches to decreasing plant Cd uptake and rhizospheric nitrification.