Chen Yinglong, Liu Yang, Ge Jianfei, Li Rongkai, Zhang Rui, Zhang Yang, Huo Zhongyang, Xu Ke, Wei Huanhe, Dai Qigen
Key Laboratory of Saline-Alkali Soil Improvement and Utilization (Coastal Saline-Alkali Lands), Jiangsu Key Laboratory of Crop Genetics and Physiology, Jiangsu Key Laboratory of Crop Cultivation and Physiology, Ministry of Agriculture and Rural Affairs, Jiangsu Co-innovation Center for Modern Production Technology of Grain Crops, Research Institute of Rice Industrial Engineering Technology, Yangzhou University, Yangzhou, China.
College of Environmental Science and Engineering, Yangzhou University, Yangzhou, China.
Front Plant Sci. 2022 Jul 29;13:982637. doi: 10.3389/fpls.2022.982637. eCollection 2022.
Numerous papers studied the relations between nitrogen rate and rice yield in saline soils, whereas the rice root morphological and physiological characteristics mediating nitrogen rates in yield formation under varied salinity levels remain less concerns. Through a field experiment applied with five nitrogen rates (0, 210, 255, 300, 345, and 390 kg ha) in saline land, we found that rice yield peaked at 7.7 t ha under 300 kg ha nitrogen, and excessive N was not conductive for increasing yield. To further elucidate its internal physiological mechanism, a pot experiment was designed with three N rates (210 [N1], 300 [N2], 390 [N3] kg ha) and three salt concentrations (0 [S0], 1.5 [S1], 3.0 [S2] g kg NaCl). Results showed that the average grain yield was decreased by 19.1 and 51.1% under S1 and S2, respectively, while notably increased by 18.5 and 14.5% under N2 and N3, respectively. Salinity stress significantly inhibited root biomass, root length and surface area, root oxidation capacity (ROC), K and K/Na ratio, and nitrogen metabolism-related enzyme activities, whereas root Na and antioxidant enzyme activities were notably increased. The mechanism of how insufficient N supply (N1) affected rice yield formation was consistent at different salinity levels, which displayed adverse impacts on root morphological and physiological traits, thereby significantly inhibiting leaf photosynthesis and grain yield of rice. However, the mechanism thorough which excessive N (N3) affected yield formation was quite different under varied salinity levels. Under lower salinity (S0 and S1), no significant differences on root morphological traits and grain yield were observed except the significantly decline in activities of NR and GS between N3 and N2 treatments. Under higher salinity level (S2), the decreased ROC, K/Na ratio due to increased Na, antioxidant enzyme activities, and NR and GS activities were the main reason leading to undesirable root morphological traits and leaf photosynthesis, which further triggered decreased grain yield under N3 treatment, compared to that under N2 treatment. Overall, our results suggest that improved physiological and morphological traits of root synergistically enhanced salinity tolerance in rice under appropriate nitrogen application rate.
众多论文研究了盐渍土中施氮量与水稻产量之间的关系，然而，在不同盐度水平下，介导产量形成中施氮量的水稻根系形态和生理特征仍较少受到关注。通过在盐碱地进行的一项田间试验，设置了5个施氮量水平（0、210、255、300、345和390千克/公顷），我们发现，施氮量为300千克/公顷时，水稻产量最高，达7.7吨/公顷，过量施氮不利于增产。为进一步阐明其内在生理机制，设计了一项盆栽试验，设置3个施氮量水平（210 [N1]、300 [N2]、390 [N3]千克/公顷）和3个盐浓度水平（0 [S0]、1.5 [S1]、3.0 [S2]克/千克氯化钠）。结果表明，在S1和S2条件下，平均籽粒产量分别降低了19.1%和51.1%，而在N2和N3条件下，分别显著提高了18.5%和14.5%。盐胁迫显著抑制了根生物量、根长和表面积、根系氧化能力（ROC）、钾离子和钾/钠离子比以及氮代谢相关酶活性，而根中钠离子含量和抗氧化酶活性显著增加。在不同盐度水平下，氮素供应不足（N1）影响水稻产量形成的机制是一致的，即对根系形态和生理性状产生不利影响，从而显著抑制水稻叶片光合作用和籽粒产量。然而，过量施氮（N3）在不同盐度水平下影响产量形成的机制却大不相同。在低盐度（S0和S1）条件下，除了N3和N2处理之间硝酸还原酶（NR）和谷氨酰胺合成酶（GS）活性显著下降外，根系形态性状和籽粒产量没有显著差异。在高盐度水平（S2）下，由于钠离子增加导致的ROC、钾/钠离子比下降、抗氧化酶活性以及NR和GS活性下降，是导致根系形态性状不良和叶片光合作用下降的主要原因，与N2处理相比，这进一步导致了N3处理下籽粒产量下降。总体而言，我们的结果表明，在适宜的施氮量下，改善根系的生理和形态性状可协同增强水稻的耐盐性。
