封育对半干旱区沙化草地群落特征的影响

选取宁夏盐池封育5、10、20年及未封育(对照)的沙化草地,采用样线和样方结合法进行野外植被调查,运用重要值、Levins生态位宽度指数和Pianka生态位重叠指数进行分析,以揭示不同封育年限沙化草地群落中种群生态位格局。结果表明,不同围封年限研究区群落组成均以多年生草本或半灌木为主,而未封育区以1年生草本植物为主。生态位宽度较大的物种之间具有较高的生态位重叠,而生态位重叠最大值却均出现在低生态位宽度物种之间,说明研究区植物的生态位宽度和重叠并不存在直接的线性相关关系。封育5、10 年区通过围栏封育促进植被恢复效果明显,而封育20 年区群落数量特征值出现下降趋势,这与土壤结皮的影响密切相关。结皮试验表明,结皮盖度分别与植被盖度、土壤入渗深度呈显著负相关性,封育20 年区结皮盖度、厚度远高于其他封育年限区,生物结皮的存在不仅阻碍外部有效降水入渗,也阻碍内部土壤水分向深层渗透,这使得适应干旱环境的深根系半灌木植物生长稀疏,而促进浅根系沙生植物占据较大的生存空间;生物结皮与其周边植物争水争肥,相互争夺生存空间,同时致密的生物结皮不利于出苗,从而抑制植物生长。长期的竞争排除等生态过程作用使得种群之间演替产生了某种程度的生态位分离,群落结构特征出现波动,建议适当人为干扰以促进植物生长。 

How enclosure affects community characteristics of the sandy grassland in semi-arid areas of northwestern China

Using line transect and quadrat sampling methods, vegetation was investigated in the semi-arid areas with different enclosure periods ( 5 , 10 and 20 years ) and one non-enclosed area ( contrast area ) in Yanchi County of Ningxia Province, northwestern China in 2013. The patterns of population niche on the community of sandy grasslands with different enclosure periods were revealed after analyzing the importance value, Levins index of niche breadth and Pianka index of niche overlap. The results showed that perennial herbs or subshrubs were dominant in the enclosed areas and annual herbs were dominant in non-enclosed area. There was a high niche overlap among the species with high niche breadth;however, the maximum niche overlap emerged among species with low niche breadth, which implied that there was no direct linear correlation between the niche breadth and niche overlap. The research showed that there was a significant vegetation recovery in the areas with 5 and 10 years of enclosure, but value of quantitative characteristics, i. e. , the number of population in the area with longer enclosure time of 20 years decreased, which might closely relate to the soil crust. Crust test showed that its coverage was negatively correlated with vegetation coverage and soil infiltration depth. In the area enclosed for 20 years, the coverage and thickness of crust were much higher than those in other enclosed areas. The biological crust prevented water to penetrate deeper, and hindered the effective precipitation infiltration, which led to the recession of deep-rooted shrubs and the spread of shallow-rooted subshrubs and annual herbs. Biological crust competed for water, fertilizer and living space with surrounding plants, and dense biological crust was not conducive to the emergence of seedling and thus inhibited plant growth. Long-term succession and ecological process of competitive exclusion among population resulted in a certain degree of niche differentiation and fluctuation of inter-specific relationships and community structure. It is suggested that appropriate human disturbance should be used in this region to promote plant growth.