【作者】 何树斌；

【导师】 沈禹颖； 杨惠敏；

【作者基本信息】 兰州大学 ， 草业科学， 2012， 博士

【摘要】 紫花苜蓿(Medicago sativa)是当今世界分布最广的栽培牧草,在我国栽培面积达200万hm2,是保障饲草料安全供应,发展草畜产业的首选优良豆科牧草。紫花苜蓿能够通过生物固氮提供生长所需氮素,植物光合碳同化与氮素吸收利用存在着偶联效应,表现出一定的C/N计量关系,而干旱情况下氮素有效性将受影响,目前对此的研究尚不深入。本研究从植物光合生理生态的角度出发,采用大田试验和温室盆栽实验,研究了不同水分处理和氮素添加对陇东苜蓿生物量积累、光合碳同化和C/N计量比动态的影响,以探讨其生理机制。主要结果如下：1.大田条件下,相比于低氮(土壤基底氮素10kgN/hm2)环境,氮素添加显著提高了建植当年紫花苜蓿分枝期和初花期的生物量(P<0.01),其中高浓度氮素(100kgN/hm2)添加对紫花苜蓿生物量的提高效应大于中浓度氮素(50kgN/hm2)添加；在盛花期,中浓度氮素添加提高了生物量,而高浓度氮素添加没有明显提高效果。盆栽条件下,紫花苜蓿生物量积累表现出类似的规律。在大田建植第二年,中浓度氮素添加在分枝期和初花期显著提高了地上生物量(P<0.05),而在盛花期,中浓度和高浓度氮素添加均抑制了紫花苜蓿生物量的累积。2.大田条件下,中浓度氮素添加显著降低了建植当年紫花苜蓿分枝期叶片C/N(P<0.05),而初花期和盛花期,中浓度氮素添加提高了紫花苜蓿叶片C/N。在建植第二年,第一茬分枝期氮素添加降低了叶片C/N,而在第二茬分枝期,氮素添加提高了叶片C/N。盆栽条件下,在35%FWC水分胁迫下,中浓度氮素(5mmol/L)添加在处理前期均提高了紫花苜蓿的C/N,而且35%FWC下紫花苜蓿叶片C/N均低于70%FWC水分处理。3.大田条件下,氮素添加提高了建植当年紫花苜蓿分枝期和初花期紫花苜蓿叶片净光合速率(Pn),而抑制了盛花期叶片Pn。中浓度氮素添加显著提高了分枝期紫花苜蓿叶片水分利用效率(WUE),而在初花期和盛花期,均降低了叶片WUE。在建植第二年,氮素添加提高了第一茬分枝期和初花期紫花苜蓿叶片Pn,而在第二茬则相反。盆栽条件下,中浓度氮素添加没有显著提高紫花苜蓿叶片Pn,但提高了水分胁迫下午后紫花苜蓿叶片WUE。4.盆栽条件下,相比无氮素和高浓度氮素添加,中浓度氮素添加不但显著提高了紫花苜蓿叶片叶绿素a(Ca)含量,叶绿素b(Cb)、总叶绿素(Cab)和类胡萝卜素(Cx)含量也得到显著提高(P＜0.05),而且也提高了水分胁迫下叶绿素的各组分含量。5.盆栽条件下,高浓度氮素(10mmol/L)添加下,处理前期紫花苜蓿叶片在水分胁迫(35%FWC)下维持较高叶片相对含水量(RWC)(P<0.05);随着处理时间的延长,中浓度氮素添加显著提高了叶片RWC。但是,在水分充足(70%FWC)的条件下,氮素添加没有显著提高叶片RWC。此外,在35%FWC水分胁迫下,氮素添加提高了紫花苜蓿根系活力(RA)和叶片硝酸还原酶(NR)活性,尤其中浓度氮素添加显著提高了RA和叶片NR活性(P<0.05)。综合以上结果,得到以下结论：中浓度氮素添加能提高紫花苜蓿叶片叶绿素含量、叶片硝酸还原酶活性和根系活力,改善紫花苜蓿叶片光合碳同化和水分利用效率,提高叶片C/N、优化植株的碳同化和氮素利用的平衡关系,最终提高紫花苜蓿生物量。陇东(庆阳)黄土高原地区种植紫花苜蓿,可适时添加50kg N/hm2,能提高紫花苜蓿资源利用效率,获得较大生物量。更多还原

【Abstract】 Alfalfa (Medicago sativa) is the most widely distributed forage crop in China. It is cultivated on two million hectares nationally, making it the preferred legume to promote forage supply and the development of the livestock industry. As a legume, alfalfa can assimilate nitrogen through the process of biological nitrogen fixation, however this is often subject to soil nitrogen supply. Accordingly, the growth of alfalfa is regulated by soil nitrogen availability, particularly so in arid and semi-arid conditions. The process of biological nitrogen fixation is sensitive to drought stress and drought affects the soil nitrogen state of existence, influencing soil nitrogen availability. Photosynthetic carbon assimilation and nitrogen uptake in plants is coordinated and demonstrated in the C/N ratio. Therefore, in this study, field trials and greenhouse experiments were carried out to determine the physiological mechanisms of biomass accumulation, photosynthetic carbon assimilation and C/N ratio in the Longdong cultivar of alfalfa under different water and nitrogen treatments,The main results were as follows:(1) Under field conditions, the addition of nitrogen significantly improved the biomass of first year of alfalfa at the branching and early flowering stages (P<0.01) compared to the low nitrogen treatment (15kg N/ha). The stimulating effect of the high concentration of nitrogen treatment (100kg N/ha) on biomass was greater than the effect of moderate concentrations of nitrogen (50kg N/ha). Only the moderate concentration of nitrogen resulted in increased biomass at the flowering stage and high concentrations of nitrogen did not increase biomass. In the second year of the planting, the moderate concentration of nitrogen significantly improved aboveground biomass at the branching and early flowering stages (P<0.05), whereas moderate and high nitrogen treatments inhibited the accumulation of biomass at the stage of full bloom.(2) In the first year of the trial, adding a moderate concentration of nitrogen significantly reduced the C/N at the branching stage (P<0.05) whereas the opposite was true at the early flowering and full bloom stages. In the second year of planting, the addition of nitrogen promoted the accumulation of leaf N and reduced the C/N at the branching stage of the first crop. Conversely, nitrogen reduced the C/N at the branching stage in the second year. The greenhouse experiments showed that after nitrogen was added at5mmol/L concentration, the C/N ratio was increased during the early stage of exposure. The increase was greater under70%FWC treatment compared to35%FWC.(3) Under field conditions, nitrogen addition improved the net photosynthetic rate (Pn) at the branching and early flowering stages compared to low nitrogen growth conditions in the first year of planting, whilst it was inhibited at the stage of full bloom. The addition of a moderate concentration of nitrogen significantly improved water use efficiency (WUE) at the branching stage (P<0.05), however this was reversed at the early flowering and full bloom stages. In the second year of planting, the nitrogen addition improved WUE at the branching and early flowering stages of the first crop and the opposite was true in the second crop. Under greenhouse conditions, the addition of a moderate concentration of nitrogen did not increase Pn, however it did improve the WUE dynamic in the afternoon after water stress treatment (35%FWC).(4) In greenhouse experiments, the addition of the moderate concentration of nitrogen not only significantly improved alfalfa chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl (a+b) and carotenoids (Cx) content (P<0.05) compared to low nitrogen and high nitrogen treatments, it also increased the chlorophyll content of each component under water stress.(5) In greenhouse experiments under water stress, the addition of the high concentration of nitrogen (10mmol/L) and with the drought stress prolonged, the moderated concentration of nitrogen, significantly increased RWC in the leaves. Conversely, in conditions of adequate moisture (70%FWC), nitrogen addition did not significantly improve the RWC in leaves. Under water stress, nitrogen addition also resulted in improved alfalfa root activity (RA) and leaf nitrate reductase (NR) activity. Particularly, moderate concentration of nitrogen resulted in significantly increased RA and leaf NR activity (P <0.05).Based on the above results it was concluded that in alfalfa, moderate concentrations of nitrogen could improve leaf chlorophyll content, NR activity and root activity, leaf photosynthetic carbon assimilation, WUE C/N, and ultimately, improve biomass by optimizing the balance of carbon assimilation and nitrogen utilization. The addition of50kg N/ha can improve resource utilization efficiency by alfalfa and yield greater biomass in the Loess Plateau.更多还原