Reduced 15N Losses by Winter and Spring Night-Warming Are Related to Root Distribution of Winter Wheat

To develop efficient N management strategies for high wheat NUE and minimizing the environmental impact of N losses under asymmetric warming, ¹⁵N micro-plot experiments were conducted to investigate the effects of night-warming during winter (warming by 1.47-1.56°C from tillering to jointing), spring (warming by 1.68-1.82°C from jointing to booting), and winter + spring (warming by 1.53-1.64°C from tillering to booting) on root growth and distribution of winter wheat, the fates of ¹⁵N-labeled fertilizer, and their relationships in 2015-2017. The results showed that night-warming increased the recovery of basal ¹⁵N and top-dressed ¹⁵N, while reduced the residual and loss of basal ¹⁵N and top-dressed ¹⁵N. The losses decreases of top-dressed ¹⁵N were higher than those of basal ¹⁵N, indicating that night-warming reduced losses of fertilizer ¹⁵N mainly by reducing losses of top-dressed ¹⁵N. Moreover, pre-anthesis root dry matter accumulation rate in 0-60 cm soil layer were promoted, resulted in improved root biomass and root/shoot ratio, which favored increasing recovery of fertilizer ¹⁵N and reducing losses of fertilizer ¹⁵N. Furthermore, residual fertilizer ¹⁵N content in 0-100 cm soil layer was reduced, which was associated with improved root weight density in 0-60 cm soil layer, resulted in reduced leaching losses of fertilizer ¹⁵N. The path analysis showed that root dry matter distribution in 0-20 cm soil layer was the most important in contributing to reducing losses of total fertilizer ¹⁵N compared with other soil layers. Two years data showed that winter and spring night-warming gave better root growth and distribution in 0-20 cm soil layer, resulted in reduced the losses of fertilizer ¹⁵N and improved the recovery of fertilizer ¹⁵N, while maximizing grain yield of winter wheat, and winter + spring night-warming resulted in higher advantages than winter night-warming and spring night-warming.