不同施氮量下缺钾对水稻叶片营养及生理性状的影响

【目的】氮和钾是作物生长所必需的大量元素，在水稻生长发育、产量形成等过程中发挥着至关重要的作用。南方稻田缺钾以及氮钾肥不合理施用已成为限制水稻高产的重要影响因子。本研究在田间条件下，探讨了不同施氮量下缺钾对水稻生长发育与叶片生理特性的影响，进而阐明缺钾导致营养生长期水稻叶色暗绿的营养及生理机制。【方法】采用两因素完全随机设计田间试验，因素A为不同施氮水平，包括不施氮、低氮（N 90 kg/hm2）和正常施氮（N 180 kg/hm2）；因素B为不同施钾水平，包括不施钾和正常施钾（K₂O 120 kg/hm2）。测定水稻分蘖期和幼穗分化期地上部干物质，叶面积指数，叶片氮、钾、镁和叶绿素含量（叶色值），叶片含水率、叶片可溶性糖含量、比叶重以及叶片SPAD值。【结果】1）在不施氮条件下缺钾对水稻分蘖期和幼穗分化期干物质、叶面积指数均无显著影响，而在施氮条件下显著降低水稻分蘖期和幼穗分化期干物质、叶面积指数；随施氮量的增加，缺钾对干物质及叶面积指数的影响加剧，其中N₁₈₀K₀处理的降幅最为明显；氮钾交互作用对水稻各生育期的干物质和叶面积指数均有显著或极显著影响。2）在不施氮条件下缺钾对分蘖期和幼穗分化期叶片氮含量和叶绿素含量、叶片可溶性糖含量、比叶重以及叶片SPAD值均无显著影响，而在施氮条件下以上各指标显著增加，其中N₉₀K₀处理的叶片氮含量和叶绿素含量均可以达到N₁₈₀K₁₂₀处理水平；无论施氮与否，缺钾均显著降低分蘖期和幼穗分化期叶片钾含量，而显著增加叶片镁含量。3）回归分析结果表明，比叶重与叶片可溶性糖含量呈极显著正相关关系（P < 0.01）。【结论】水稻干物质、叶面积指数、叶片营养及生理状况、叶色表现等对缺钾的响应明显受到施氮量的影响。在施氮条件下缺钾造成叶片中可溶性糖大量积累，进而导致比叶重增加；结合田间试验观察及叶片营养及生理性状可知，水稻叶色（叶绿素含量）在不施氮条件下不受缺钾的影响；而在施氮条件下，缺钾造成水稻叶片单位质量及单位叶面积氮含量和叶绿素含量显著增加，这是田间条件下水稻叶色呈现暗绿的主要原因，从而也影响生育期植株氮素营养诊断。

Nutritional and physiological characters of rice leaves exposure to potassium deficiency under different nitrogen rates

Objectives]Nitrogen (N) and potassium (K) play important roles in rice growth, development and yield formation. K deficiency stress and unbalanced fertilization of N and K in paddy fields have been the most important factors restricting rice grain yields. A field trial was carried out to explore the effects of K deficiency stress on rice growth, leaf nutrients and physiological status under different N rates, and further to clarify the physiological mechanism of leaf color dark green due to potassium deficiency.Methods]A completely random two-factor field trial was conducted. The first factor was N application rates: 0, 90 kg/hm2 (low N) and 180 kg/hm2 (normal N); the second factor was K2O application rates of 0 and 120 kg/hm2 (normal K). The dry matter, leaf area index, contents of N, K and Mg of leaves, and chlorophyll (leaf color value) of leaves, leaf water content, leaf soluble sugar content, specific leaf weight, and leaf SPAD value at the tillering and panicle initiation stages were measured.Results]1) Without N application, the rice dry matter and leaf area index were not significantly affected by K deficiency at tillering and initial panicle stages, but with N application, the effect became significant, and the decrease became larger with the higher N application, . The interaction of N and K fertilization was significant on the dry matter and leaf area index in all the growth stages. 2) Without N application, neither the contents of N, chlorophyll and soluble sugar in leaves, nor leaf weight and leaf SPAD values were significantly affected by K deficiency at the tillering and panicle initiation stages, on the contrary, these index values were increased significantly under the N application condition, and the leaf N and chlorophyll contents in treatment of N 90 kg/hm2 plus zero K were similar to those under the combination of N 180 kg/hm2 plus K2O 120 kg/hm2. No matter with or without N application, K deficiency significantly reduced the leaf K content while increased leaf Mg content at the tillering and panicle initiation stages. 3) There was a significant (P < 0.01) and positive relationship between the specific leaf weight and the leaf soluble sugar content.Conclusions]The responses of leaf nutritional and physiological status to K deficiency are affected significantly by N application rates. The K deficiency stress results in high soluble sugar content and leads to the increased unit leaf weight in case of N application. However, K deficiency stress significantly increases leaf N contents and leaf chlorophyll contents and weight of unit leaf area under the condition of N application, which is the most important cause of the dark green leaf and this phenomenon might be detrimental to plant nitrogen nutrition diagnosis at the early growth stage of rice.