Fertilizer nitrogen as a significant driver of rhizosphere microbiome in rice paddies

Abstract

Rice, a globally important cereal crop, is chiefly cultivated under irrigated conditions. It is a key contributor to the food, nutritional, and economic security, especially in the Asian countries. To meet the growing demand of human population, innovative or improved, but above all, sustainable production strategies are required for important reasons such as (i) most farmers are poor and many external inputs are expensive, (ii) the water use and chemical fertilizer use efficiencies in farmers’ fields are often low, and (iii) potential risks to the ecological health because of chemical fertilizers and pesticides are high. In the strategies for sustainable agriculture, the important challenge is to stimulate the appropriate microbial activities at the optimal rates for plant health and productivities. Microbial activities in the rhizosphere are of great importance to rice plants. Nutrient cycling, especially carbon and nitrogen, stimulation or inhibition of rice plant growth, and the onset of diseases are largely due to the functioning of microbial communities; no single organism alone can be considered decisive to their functions. Interestingly, the rhizosphere of rice supports simultaneously both oxic (aerobic) processes, such as oxidation of ammonia, iron, sulfur, and methane, and anoxic (anaerobic) processes, such as reduction of nitrate, ferric iron, and sulfate and methanogenesis in different niches. To successfully manage the rhizosphere with desired microbial activities, with or without fertilizer application, it is necessary to identify all the microbial and plant factors that determine root colonization, to understand the structure and functions of microbial communities in greater detail, and to develop rapid and reliable methods to measure and monitor the dynamics of microbial communities.