Responses of wheat nitrogen uptake and utilization, rhizosphere bacterial composition and nitrogen-cycling functional genes to nitrogen application rate, planting density and their interactions

Abstract

The nitrogen application rate and planting density affect soil physiochemical properties, plant physiological characteristics, and soil bacterial community composition. In this study, a two-factor randomized block design was adopted with two planting density levels (high density, HD and low density, LD), and three nitrogen application rate levels (no nitrogen application, N0, low nitrogen application, LN and high nitrogen application, HN). The results showed that the highest yield was produced by LDHN and HDLN, while HDLN had the highest nitrogen use efficiency. Root dry weight was highest in HDHN, followed by HDLN, LDHN and LDLN, while the root nitrogen content was highest in LDHN and HDLN. In the 0–20 cm soil, LDLN had the highest pH and lowest nitrate nitrogen content, HDHN had the lowest pH, and HDLN had the highest content of soluble organic nitrogen and free amino acids. In addition, compared to LDHN, the bacterial community in HDLN and LDLN had higher α diversity and a higher relative abundance of functional genes involved in nitrate reduction. However, HDHN was the opposite. Additionally, correlation analysis also found that the abundance of some bacterial modules was significantly correlated with wheat nitrogen partial factor productivity. Overall, nitrogen application rates and planting density, through changing the physicochemical properties of rhizosphere soil, bacterial composition and function, and wheat root physiological properties, changed the nitrogen utilization and yield of wheat.