Biogeochemical cycles of key elements in the paddy-rice rhizosphere: Microbial mechanisms and coupling processes

Abstract

Rice feeds more than 50% of the world’s population, 88% of which is planted in paddy fields. Paddy-rice rhizosphere is a unique habitat characterized by redox heterogeneity that is generated from radial O 2 loss from roots and intensive water management, which allows the differentiation of microbial niches in the narrow rhizosphere and leads to strong couplings of functional processes. This review summarizes the biogeochemical processes of key elements (C, N, P, and Fe) in the rice rhizosphere and their coupling mechanisms. We emphasize the redox gradient in rice rhizosphere and the role of microorganisms in element cycling under altering redox conditions. We argue that C turnover and nutrient (N and P) availability are closely linked to each other, during which Fe reduction and oxidation play important roles. For further development in this field, we suggest further effort to reveal several key processes, including, the high resolution in situ distribution of biotic and abiotic factors, stoichiometric regulations on microbial processes, and the functions of key microbial guilds or species in element cycles.