Agronomy, Vol. 14, Pages 2321: Exogenous N Supply on N Transportation and Reuse during the Rice Grain-Filling Stage and Its Relationship with Leaf Color-Changing Parameters

Agronomy, Vol. 14, Pages 2321: Exogenous N Supply on N Transportation and Reuse during the Rice Grain-Filling Stage and Its Relationship with Leaf Color-Changing Parameters

Agronomy doi: 10.3390/agronomy14102321

Authors: Yi Tao Yanan Xu Chang Ye Junlin Zhu Deshun Xiao Wenli Liao Yijun Zhu Guang Chu Chunmei Xu Danying Wang

During the later reproductive period of rice growth, the chlorophyll in the leaves degraded, accompanied by the nitrogen (N) transportation from leaves to panicle, resulting in a change in leaf color from green to yellow. This study aimed to investigate the effects of exogenous N supply on leaf color-changing, N accumulation, N transportation, and N loss of indica-japonica hybrid rice during the grain-filling stage. Two indica-japonica hybrid rice cultivars, Chunyou 167 (CY167) and Chunyou 927 (CY927), which exhibited significant differences in leaf color-changing during the grain-filling stage, were selected as materials for field experiment and hydroponic experiment with low, medium, and high N treatments (LN, MN, and HN). The dynamic changes in SPAD value from heading to maturity were measured and fitted with quadratic function to extract leaf color-changing parameters; labeled 15N was used as N source after heading to trace the source of N in the panicle and the remobilization of vegetative organ N. The results showed that 67.37–72.38% of the panicle N was transported from vegetative organs, the N transport efficiency was the upper three leaves > lower leaves > stem, and about 3.1–35.0% of the transported N was lost via volatilization. The effects of exogenous N concentration on N harvest index, N dry matter/grain production efficiency, N reuse efficiency, and N loss were closely related to leaf color-changing parameters. In MN and HN treatment, the N loss was negatively correlated with the onset time of leaf color-changing (T0) and the final leaf color index (CIf), but positively correlated with the leaf color-changing rate (Rmean). Increasing the supply of exogenous N increased T0 and CIf, but decreased Rmean, N transport/reuse efficiency, N harvest index, and N dry matter/grain production efficiency. Compared to the cultivar CY167 with normal leaf color-changing, the “stay-green” cultivar CY927 had higher T0, CIf, and lower Rmean, resulting in less N volatilization loss, lower N harvest index and N transport efficiency, while higher N reuse efficiency. In conclusion, the exogenous N supply affects leaf color by influencing the transportation and reuse of leaf N during the grain-filling stage.