Soil moisture and nitrogen content influence wheat yield through their effects on the root system and soil bacterial diversity under drip irrigation

Soil properties and plants influence soil microbial community diversity, and their role in nutrient cycling could influence plant productivity; however, it is not clear the relationships between soil bacterial communities, soil moisture, and nitrogen (N) content, and whether these associations influence plant productivity. In this study, we investigated how the soil microbial community affects root zone productivity in winter wheat. We also verified whether productivity can be improved by water adjustment and N management in drip irrigation field experiments (I0, natural condition; I1, jointing to heading stage S1 55%-80%theta(f), field capacity, anthesis to mature stage S2 70%-80%theta(f); I2, S1 55%-90%theta(f), S2 70%-90%theta(f); and I3, S1 55%-100%theta(f), S2 70%-100%theta(f)) and under different N application rates (N0, N1, N2, and N3 represent 0, 150, 200, and 250 kg N ha(-1)). Soil moisture and N application rate significantly influenced water use efficiency (WUE), N use efficiency (NUE), yield, and soil bacterial abundance and diversity in the wheat root zone. N application decreased the richness indices in un-irrigated soils (I0), whereas it initially increased, and then decreased the indices in irrigated soils (I1, I2, and I3). The primary factor influencing the dominant bacterial taxa was soil moisture content (SMC), followed by root length density (RLD). The root system and soil bacterial diversity strong influenced wheat yield. The I1N1 treatment resulted in the highest root weight density (RWD), WUE, and NUE, and thus increased wheat yield; furthermore, it had the least influence on the diversity of soil bacteria. Our work suggests that the response of bacterial communities to soil moisture and nitrogen content largely regulates crop production in agro-ecosystems, and that regulating soil moisture and nitrogen fertilizer use may provide a sustainable solution for maintaining farmland productivity.