沙地草地牧鸡的养分添加效应及对植物群落的影响

The sandy grassland in northern China, covers an area of 15,000,000 ha, has degraded seriously by long-term irrational use which has resulted in infertile soil and imbalance between water and nutrient, making it more difficult to restore the vegetation. It is of important ecological significance of nutrient especially nitrogen addition to help recover vegetation and maintain the balance between water and nitrogen, which has aroused worldwide attentions. However, the sandy soil is characterized of a low additional nutrient holding capacity, leading to low utilization rates of nutrients. There is lack of empirical evaluation of how to supply nutrient to the sandy grassland and of the ecological effects of nutrient addition. This project is planned to add nutrient to the sandy grassland during growing seasons respectively by regularly scattering chicken litter and by the way of chicken farming in the field. We plan to focus on the following ecological issues by means of experimental ecology and measurements: 1) changes of soil physical characteristics and soil nutrients content after adding chicken manure, 2) growth responses of different functional plant groups and changes of plant community diversity, 3) ecophysiological responses in terms of assimilation capacity,carbon allocation and nutrinet/water use efficiency of different functional plant groups to nutrient addition of chicken litter. By carrying out the above researches, we can explain the impacts of nutrient addition by chicken farming on the content of soil nutrient and its impact on plant community structure and function. This project can provide some scientific guidance for the restoration of degraded sandy grassland and its rational use.

我国北方沙地草地面积达15万平方公里，连续多年的不合理利用，造成草地生态系统的肥力下降、水肥平衡严重失调，进而导致植被退化严重、恢复难度加大。以氮素为主的养分添加措施对植被的恢复和水氮平衡的维持具有重要生态学意义，已有较多的研究。然而，沙地草地的生境特点决定了添加养分的易流失性，养分直接利用率低，养分补给的方式及其生态学效应值得深入研究。本项目拟通过定期撒施鸡粪和草原牧鸡添加鸡粪的方式在生长季节对沙地草地进行养分添加，通过实验生态学的手段和测定技术，研究：1）鸡粪添加对沙地土壤物理性状和土壤养分含量的影响；2）鸡粪添加对不同功能型植物物种生长发育及植物群落特性的影响；3）鸡粪添加对不同功能型植物物种光合物质生产能力、同化物分配和养分/水分利用效率的影响。探明草原牧鸡对沙地的养分添加效应及其对植物群落结构与功能的影响，为沙地退化生态系统植被恢复和合理利用提供科学依据。

土壤养分亏缺是草地退化的一个重要因素，严重制约着草地生态系统功能的发挥。有机肥添加不仅能够增加土壤肥力，还可以改善土壤的理化性状，有利于提高养分和水分利用效率，促进草地生态系统的可持续性利用。实践表明，在我国北方草地开发的草原牧鸡生态经济技术已经开始推广，其养分添加效应也受到了关注。在本项目的资助下，课题组成员研究了牧鸡和人工撒施鸡粪处理对退化草地土壤理化性状和植被群落特征的影响，结果表明：①牧鸡（250-500只/公顷）显著增加草地土壤养分，其中，土壤有机质含量增加12%-19%，有效氮、有效磷和速效钾的增加幅度分别为23%-34%, 42%-121%, 22%-39%；土壤含水量可增加10%-21%，而土壤容重降低6%-10%；土壤pH值没有发生显著变化；②牧鸡草场的植被盖度、高度、初级生产力均显著提高，可达到对照区的2-3倍，而且这些指标的变化与土壤养分含量呈显著正相关；③与传统草地利用方式（围封禁牧、牧羊）相比，牧鸡对植物群落的物种多样性和丰富度没有产生显著影响；④无论以牧鸡的方式还是人工撒施的方式进行鸡粪添加，均显著增加牧草的叶面积和植株氮素含量，降低叶片C/N比值；植株单位面积的日间最大净光合速率在低鸡粪添加水平下显著高于对照，在高添加水平下却与对照无显著差异，而午间净光合速率却在高添加水平显著高于对照，表明养分添加提高了牧草的抗逆性；⑤δ13C稳定同位素比率的结果显示，养分添加显著提高牧草的水分利用效率，并随着添加水平的提高而提高。该项目研究结果有力地说明了养分亏缺显著限制了我国北方半干旱草地的生产力；通过牧鸡的方式向草地生态系统输入养分，能够提高降水利用效率，提高初级生产力，同时保护物种多样性，有利于天然草场的功能发挥。研究结论可为干旱半干旱草地的合理利用提供理论依据。在本项目的资助下，培养硕士研究生1名；发表学术论文1篇(Agriculture, Ecosystems and Environment. DOI: 10.1016/j.agee.2014.02.001)。