饲料桑-苜蓿间作对土壤异质氮素利用的种间互作关系解析

The mulberry (Morus alba) is perennial tree, which has highly adaptable, well nutritious and high yield in foliage. It is well recognized that mulberry could be exploited a new-style feed source for livestock and poultry. At present, the physiological mechanism of nitrogen fertilizer application and its effect on mulberry is still in the exploratory stage. Our previous studies showed that mulberry intercropped alfalfa has obviously advantages, compared with monoculture, intercropping could increase biomass and forage quality. The measures of regular nitrogen applying often supply equal quantity to soil, while the plants need soil nitrogen were difference. According to the characters of plants on soil nitrogen requirement, the reserach of nitrogen management regulation in intercropping system is becoming more and more attention. However, research of nitrogen regulation on “mulberry/alfalfa" intercropping system is less. Therefore, in this project, we will take the effective using of heterogeneous soil nitrogen as the breakthrough point, using the method of field experiment combined with potted plants, in which the soil environment of the heterogeneous nitrogen was created by reducted and the local supplying nitrogen. The target is to explore the response characteristics of nitrogen fixation and nitrogen uptake and utilization in the intercropping system, and to compare the annual biomass forage quality, carbon and nitrogen metabolism, root growth and rhizosphere microenvironment in different intercropping patterns. Andthen, to explored the interspecific interaction in the optimal intercropping pattern and the mechanism of efficient utilization soil nitrogen, the results will provide basic data and technical reference for scientifical nitrogen supplying in mulberry/alfalfa intercropping system.

饲料桑适应性强、产量高、营养丰富，是畜牧业新型高蛋白饲料源。目前，有关饲料桑栽培，尤其是氮肥高效利用的研究较少。前期研究发现，饲料桑/苜蓿间作优势明显，促进饲料桑枝叶生长。常规施氮措施常采用人为均等供给土壤，而不同植物对土壤氮素的需求存在差异。根据植物对土壤氮素需求特征，调控间作体系氮素运筹的研究日益受到重视。而有关“饲料桑/苜蓿间作”体系中的氮肥调控的研究较少。为此，本项目拟以“饲料桑/苜蓿间作”对不均等供氮的有效利用为切入点，采用大田试验结合盆栽的方法，通过减量和局部供氮营造土壤异质氮素的环境，研究“饲料桑/苜蓿间作”利用土壤氮素的种间互作关系、饲料桑对苜蓿固氮的影响，比较间作体系的生物量、饲草品质、蛋白质组、叶片碳氮代谢、根系生长和根际微环境等对土壤异质氮素的响应特征，探索“饲料桑/苜蓿间作”种间互作高效利用氮素的实质，揭示“饲料桑/苜蓿间作”利用土壤异质氮素的种间互作及其适应机制。

饲料桑适应性强、枝叶产量高、营养丰富，是畜牧业的新型高蛋白饲料源，豆科植物本身具有生物固氮的特性。针对目前农业生产中氮素投入量过高，利用效率低的问题，提出在桑树苜蓿间作系统试行减量和局部施氮策略，探索其内在的生理机制给予科学的解析，结果发现，饲料桑和苜蓿间作优势的生理机质，在于间作饲料桑可促进苜蓿生物固氮的能力，同时两者根际微生物群体、种类和数量上存在明显的差异，说明其在土壤养分利用上存在着策略性的互补。也表征间作系统中的饲料桑和苜蓿在利用根际土营养方面具有显著的互补性，进而提高其利用土壤养分的能力。同时，对间作系统地上部净光合速率的监测分析，我们发现间作可促进饲料桑和苜蓿的净光合速率和光合日同化量，进而提高间作系统的生物量。此外，品质分析发现，施氮和间作可显著提高饲料桑粗纤维、中性洗涤纤维、酸性洗涤纤维、木质素和半纤维素的含量，而间作却降低饲料桑粗蛋白。种间和种内施氮营造的氮素异质性可提高饲料粗蛋白含量。其研究结果可为桑树/苜蓿间作模式在苜蓿种植区域大面积推广提供理论基础和技术支持。本项目的科学意义：饲料桑/苜蓿间作可提高土地利用效率，增加单位面积的产量，施行减量局部施肥，省工省肥，提高当地农民的收入的同时减少氮素污染；桑树和苜蓿具有广泛的适应性，可在贫瘠的土地及荒山坡地上耕种，可充分利用困难立地，保持水土流失，具有一定的生态价值。