Evaluation and Screening of Nitrogen Efficiency at Seedling Stage of Rice Germplasm Resources
: Excessive nitrogen fertilizer application increases production costs and environmental burdens in rice cultivation, highlighting the need to identify low-nitrogen-tolerant germplasm. In this study, 266 rice accessions were evaluated in hydroponic culture for 35 d under normal-nitrogen conditions (NN: 1.6 mM NO 3 − and 1.6 mM NH 4+ ) and low-nitrogen conditions (LN: 0.4 mM NO 3 − and 0.4 mM NH 4+ ). Fifteen seedling traits related to growth, chlorophyll status, nitrogen accumulation, and nitrogen utilization were measured, and the corresponding low-nitrogen tolerance indices were evaluated using correlation analysis, principal component analysis (PCA), membership-function analysis, and cluster analysis. All measured traits had coefficients of variation greater than 10%, indicating substantial variation among accessions. PCA extracted six principal components that explained 82.533% of the total variation. Relative shoot dry weight, relative total dry weight, and relative aboveground nitrogen accumulation were major indicators of seedling performance under LN. The LNTI-based D-values classified the 266 accessions into four tolerance groups. Comparison of this classification with the treatment-specific comprehensive evaluation identified six overlapping accessions—Q3-2, Q3-3, Q5-1, TD201, Jijing 88, and Jiadao 37—with both high relative low-nitrogen tolerance and high nitrogen-efficiency-related performance under NN and LN. These accessions represent preliminary candidates for further evaluation across nitrogen gradients, reproductive stages, field environments, and years before their breeding value and underlying physiological and molecular mechanisms can be confirmed.