制种苜蓿根瘤菌固氮效能对氮素输入的响应

A great gap exists between alfalfa seed industry in China and that in the developed countries, which mainly due to the low yield per hectare in China. Research on factors influencing the alfalfa seed yield therefore becomes the focus of this industry, and the impact of fertilization is one of the large concerns. However, differences still exists as to whether nitrogen could improve alfalfa seed yield, partly due to alfalfa’s nitrogen uptake sources and the nutrient needing law were seldom studied, and partly due to the effect of nitrogen fertilization on the performance of alfalfa’s nitrogen-fixing rhizobia was unclear. To solve this problem, we studied the impacts of nitrogen application rate and fertilization time on the performance of alfalfa’s rhizobia by using the 15N natural abundance approach and the 15N isotope tracer technique in both a pot experiment and a field experiment. Ryegrass, a non-nitrogen-fixing plant, was selected as the reference plant. The purposes of this study were to understand the alfalfa’s nitrogen uptake sources, the nitrogen uptake amount from different sources, and the nutrient needing law, to reveal the physiological mechanism of alfalfa’s nitrogen-fixing rhizobia under the influence of nitrogen fertilization, and to determine the best nitrogen application amount and time for the highest alfalfa yield. This study aims at providing a theoretical basis for the high-yield and high-efficiency alfalfa seed industry of Xinjiang by reasonable management and regulation nitrogen fertilization.

我国苜蓿种子产业和发达国家相比存在较大差距，主要表现为单产产量低，因此围绕苜蓿种子产量影响因素方面的研究成为该产业的焦点，其中对施肥这一增产措施最为关注，尤其是关于氮肥对制种苜蓿种子产量的作用存在很大分歧，主要是对制种苜蓿氮素吸收来源和营养规律缺乏深入研究、氮素对制种苜蓿根瘤菌固氮效能的影响机制不清造成的。针对这一问题本研究综合利用15Ｎ自然丰度法和15N同位素示踪技术，以氮素作为调控因素，以制种苜蓿为研究对象，同时选择非固氮植物黑麦草为参比植物，采用盆栽试验和田间微区试验，深入研究不同氮素施用量和施用时期对制种苜蓿根瘤菌固氮效能的影响，掌握制种苜蓿的氮素吸收来源、不同来源氮素吸收量和营养规律，揭示氮素对制种苜蓿根瘤菌固氮效能和种子产量影响的生理机制，确定高产制种苜蓿的最佳氮肥施用量和施用期，从而对制种苜蓿的氮肥管理进行合理调控，以期为新疆优质高产高效的苜蓿种子产业提供一定的理论依据。

为明确氮肥施用对制种苜蓿根系生长、根瘤菌特性和种子产量的影响，本研究以“新牧4号”紫花苜蓿为研究对象，采用盆栽试验和田间小区试验相结合的方式，研究了不同氮肥施用量对制种苜蓿生长发育、根系特征、根瘤菌数量和活性以及种子产量的影响，掌握了氮肥运筹对制种苜蓿生长的动态调控过程和制种苜蓿的氮素营养规律，揭示了氮素对制种苜蓿根瘤菌固氮效能、种子产量和质量影响的机制，确定高产制种苜蓿的最佳氮肥施用量，从而对制种苜蓿的氮肥管理进行合理运筹调控，为新疆优质高产高效的苜蓿种子产业提供了一定的理论依据。主要结论如下：. 1、盆栽试验：.（1）5种不同施氮处理下，紫花苜蓿的根系总长度，表面积，体积，平均直径及根尖数均表现为：在施氮量为100 kg/hm2时最好，在150 kg/hm2时次之，在不施氮肥（即对照）时最低。.（2）各施氮处理下，紫花苜蓿根系含量均高不施氮肥（即对照），其中在100 kg/hm2时，紫花苜蓿地下生物量的全氮含量最高。.（3）施氮处理的种子产量均大于无氮处理，且种子产量在100 kg/hm2时最大，制种苜蓿的最佳施氮量为102.74 kg/hm2，最高产量为189.18 kg/hm2。.2、田间小区试验：.（1）紫花苜蓿的根瘤菌重量、数量和活性均是在施氮量为100 kg/hm2时表现最好；根瘤菌的重量和活性均是在施氮量为200 kg/hm2时表现最差；因此适量的施入氮肥有利于根瘤菌的固氮，过量的氮肥会抑制根瘤菌的生长。整个生育期中花期的根瘤菌数量、重量和活性最好。.（2）紫花苜蓿的地上、地下生物量在100 kg/hm2时表现最好。由根冠比可知，整个生育期中，地上部分的物质积累量比地下部分的物质积累量高。.（3）施氮处理的种子产量均大于无氮处理，且种子产量在施氮量100 kg/hm2时最大，得出制种苜蓿的最佳施氮量为105.89 kg/hm2，最高产量为350.54 kg/hm2。