增密节氮栽培对双季稻根系特征和氮素吸收的调控效应及其机制

It is an important development direction of rice cultivation to reduce the amount of nitrogen (N) fertilizer while ensuring the high and stable yield. The N uptake of rice mainly happens between the transplanting stage and the jointing stage. However, in this period, the high N application and the underdeveloped root system result in the low N uptake. Our preliminary study showed that the increment of planting density and the decrement of basic tiller fertilizer could both improve both the nitrogen use efficiency (NUE) and achieve high yield of double cropping rice. So we put forward the hypothesis that the planting of increased density and reduced N fertilizer could construct the strong root system in rice early stage and improve the NUE. To verify this hypothesis and discuss the effects and relative mechanisms of increased density and reduced N fertilizer on the root characteristics and N uptake of double rice, this project, by using field experiment and 15N tracer micro-plot experiment, will study the N uptake differences of individual and population among different growing stages of early and late rice, the source and efficiency of plant N uptake. Meanwhile, the characteristics of root distribution, morphology and activities in the whole growth period of early and late rice, which will be carried on the regression analysis with NUE to identify the root characteristics impacting the NUE of early and late rice. Our results will reveal the mechanisms of increased density and reduced N fertilizer on the root characteristics and NUE of double rice, and provide theoretical basis and technical reference for low N application and high yield technology of double rice cultivation.

在高产稳产的前提下减少氮肥用量，是水稻栽培的一个重要发展方向。水稻氮素吸收主要集中在移栽至拔节阶段，但此阶段施氮量大、根系不发达导致了氮素利用率低。本课题前期研究发现，增加移栽密度和减少基蘖肥氮肥用量可提高双季稻氮素利用效率，并实现丰产，故本项目提出增密节氮栽培可为水稻构建前期发达的根系群体、提高水稻氮素利用效率的假说。为了验证这一假说并探讨增密节氮栽培对双季稻根系特征和氮素吸收的调控效应及其机制，本项目利用田间试验，运用15N示踪微区研究增密节氮栽培下早、晚稻不同生育阶段个体和群体氮素吸收、植株氮素吸收来源以及利用效率差异；研究增密节氮栽培下早、晚稻全生育期根系分布、形态和活性的变化特征，并与氮素利用率进行回归分析，以明确影响双季稻氮素吸收利用的关键根系特征。本研究可揭示增密节氮栽培对双季稻根系特征和氮素吸收利用的影响机制，为双季稻节氮高产栽培技术提供理论依据和技术参考。

密植与降低施氮量是保持水稻产量和提高氮素利用效率的有效措施。本项目研究了增密节氮栽培下双季稻不同生育阶段个体和群体生长发育、氮素吸收、植株氮素吸、根系分布、形态和酶活性的变化特征，并通过相关性明确了影响双季稻氮素吸收利用的关键根系特征。15N示踪结果表明，减少基蘖肥氮素投入和密植均提高了肥料氮素吸收效率，N1处理植株15N-尿素吸收率较N2处理提高了10.6%，D3和D2处理的15N-尿素吸收率平均比D1处理高13.5%和6.6%（P<0.05），且与N2D1处理相比，N1D2和N1D3处理植株15N-尿素吸收量虽然降低，但植株15N-尿素吸收效率分别显著提高了16.4%和25.6%。氮肥减施下密植降低了个体根系生物量、根系长度、根系表面积和根系体积，但群体根系生物量、根系长度、根系表面积和根系体积显著增加。相关性分析显示，根长、根表面积、根表面积、根体积、根干重与氮素吸收量在分蘖期、齐穗期和成熟期显著相关，相关系数为0.477 *~0.765 * *。此外，节氮后增加密度对双季稻产量无显著影响。因此，密度增加20%、基蘖肥减少总施氮量的20%条件下，双季水稻可以通过改善群体根系形态来维持水稻产量，提高氮肥利用率。