紫花针茅群落植物地下部竞争方式及其对氮沉降响应的研究

The below-ground competition of interspecies was an important factor to determine the structure of community and biodiversity, which competitive pattern was affected by the soil nutrient content and heterogeneity. Nitrogen disposition not only influenced on the soil available nitrogen content, but also affected the soil nutrient heterogeneous, which could enhance the complexity of root competition. The biomass of root was great proportion of total biomass in the alpine steppe at the north Tibet. The intensity of root competition was stronger than that of the shoot competition in the alpine steppe. It was unknown whether the competition pattern was asymmetric in the alpine steppe, or not. While the content of the nitrogen deposition increase, the content of soil nitrogen also increased. Whether the competitive pattern of below ground was affected by the nitrogen deposition, or not. What was the competitive pattern of below ground responded the nitrogen deposition. Those ecological effects need further study. Based on the results of our previous study，we want to study the pattern of below ground competition using 15N-labelled nitrate and controlling the root competition. We analysis the relationship between the root growth character and the different size of species (dominant species and accompany species) in the Stipa purpurea community at the alpine steppe. We also studied how the pattern of below ground competition respond to the nitrogen addition by simulating and control method. From these conclusions，we would reveal the pattern of below ground competition at the alpine grassland community，which would provide scientific information for forecasting the change of the community and biodiversity under the condition of global climatic changing.

植物地下部竞争对群落结构和生物多样性有着重要的作用，而植物地下部竞争方式受土壤养分含量和异质性分布影响较大。氮沉降在影响土壤活性氮含量同时，也会影响土壤资源异质性分布，增加植物地下部竞争的复杂性。在地下部竞争强度较高的高寒草原生态系统中，高寒草原植物地下部竞争方式是否会受到氮沉降的影响，以及对氮沉降如何响应都需要进行深入研究。本项研究拟在前期实验基础上，以高寒紫花针茅群落中个体体积不同的植物为研究对象，通过控制地下部竞争实验、同位素标记和模拟氮沉降实验，测量植物细根生物量、根表面积、细根氮元素含量等指标，分析其相对生长速率、相对竞争能力及其与个体体积的关系，初步揭示高寒草原植物地下部竞争方式及其对氮沉降的响应，为科学认知气候变化下高寒草原植物群落结构组成和生物多样性变化提供科学依据。

植物对资源的是影响群落稳定的主要因素之一。在高寒草原根系生物量占地上部的大部分。而根系竞争机制—对称与不对称竞争还不清楚。而且根系竞争对称性与不对称性争议的焦点在于土壤的均质性与营养元素利用效率改变。随着氮沉降的增加，高寒草原植物根系竞争是对称性还是不对称性，及其对群落稳定性的影响如何。本研究选择藏北地区半干旱紫花针茅高寒草原为研究对象，通过盆栽实验与野外控制实验在室内对根系扫描分析，探讨高寒草原植物根系竞争机制，分析了氮素添加对高寒草原植物根系竞争的影响以及对群落稳定性的影响。结果表明（1）通过分析竞争试验中不同功能型物种细根生物量、生长速率、形态性状、拓扑形态性状、功能性状，结果表明优势种紫花针茅对其他植物根系竞争表现出不对称性，而其他物种之间根系竞争表现为对称性竞争。（2）氮素添加增加了地上部生物量和地下部生物量，同时对植物群落组成产生影响，氮素添加后禾草类植物比例开始增加，杂类草比例开始降低，说明优势种根系不对称竞争会影响群落的结构，通过对植物生态化学计量学稳定性分析表明，植物在营养元素增加时倾向于快速生长，而且不同种植物对营养元素利用策略有趋同性。（3）通过对氮素添加后高寒草原稳定性分析，结果表明生物多样性与群落稳定性相关性较弱，而物种稳定性对群落稳定性影响较大，尤其是优势种对高寒植物群落的稳定性影响较大，这与优势种紫花针茅的根系不对称竞争对其稳定性具有较大的影响。