岷江干旱河谷植物群落的复杂性

Plant community complexity in the arid valley of Minjiang River

通过对岷江干旱河谷植被及环境因子的系统取样调查,研究了该地区植物群落复杂性及其与环境因子的关系,探讨了群落复杂性与多样性、均匀度、物种丰富度之间的关系。随着海拔的增加,群落总复杂性和结构复杂性均表现为“高-低-高”的变化趋势,表明高海拔和低海拔段有较高的复杂性,中海拔段复杂性较低;位于干旱河谷核心区的样带3、4较北部过渡区样带1、2和南部过渡区样带5、6有着较低的群落总复杂性;不同坡位、坡形及坡向,群落总复杂性和结构复杂性,均表现为上坡位>下坡位>中坡位,凹坡>平破>凸坡,阴坡>半阴半阳坡>阳坡。华帚菊-小黄素馨灌丛的总复杂性最高,西南野丁香灌丛、驼绒藜灌丛的总复杂性最低,子栎灌丛和群小花滇紫草灌丛的结构复杂性较高;群落总复杂性与有机质、全N、土壤含水量、水解N、速效K呈现出显著的二次曲线关系,与全K、全P、速效P、pH值没有明显的相关关系。总复杂性与多样性、均匀度、物种丰富度的关系密切,均呈现显著的线性正相关关系。均匀度和结构复杂性呈现极显著的线性负相关,表明结构复杂性随均匀度的增加而减小。作为群落总复杂性与多样性的区分,结构复杂性对群落内物种数的变化较为敏感,不仅与均匀度有关,还与群落物种数量有关。结构复杂性和多样性作为群落总复杂性的两个组成部分,对总复杂性的影响随着研究区域和群落的不同而不同。

The upper reaches of the Minjiang fiver is the transition zone from the Qinghai-Tibet Plateau to the Sichuan basin. It has a typical arid valley climate with complex topography and variable water and heat conditions. A long history of anthropogenic impact in combination with a severe natural environment has resulted in degraded vegetation dominated by xeric shrubs. Therefore, it is important to understand the process of ecosystem dynamics. Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics. In this study, based on the field investigation of plant species and environmental factors （slope, elevation, aspect, soil water content and soil nutrients） in the arid valley of Minjiang River, we studied plant community complexity, and its relationship with environmental factors, community diversity, species evenness and richness. Six transects were set up along the arid valley of Minjiang River. Both total and structural complexity of communities showed a ＂high- low-high＂ tendency with the increase of elevation in the study area, which meant that the complexity of communities was highest at the sites of low and high elevation, while the lowest was at the sites of middle elevation. The transects at the center of the valley had lower total complexity than those at the north and south sides of the valley, which probably due to the differences of environmental conditions. We found that both total and structural community complexity varied with degree, shape and aspect of slope, with an order of upper slope 〉 middle slope 〉 lower slope, shaded slope 〉 half-shaded slope 〉 sunny slope, and concave slope 〉 straight slope 〉 convex slope. Our study indicated that Form. Pertyasinensis, Jasminumhumile had the highest total complexity, and Form Leptodermispurdomi and Form Ceratoidesarborescens communities had the lowest total complexity, while Form Quercuscocciferoides and Form Onosma farrerii communities had the highest structural complexity. We also found that total community complexity had significant quadratic correlations with soil organic matter （SOM） content, total nitrogen （N）,hydrolyzable N, soil water content, and available potassium （K）, respectively, while it had no significant correlations with soil total K, total phosphorus （P）, available P, and pH value. Total community complexity positively correlated with community diversity, evenness and species richness, while structural complexity negatively correlated with community evenness. As two components of total community complexity, structural complexity was more sensitive than diversity to the change of species in the community, which was not only related to community evenness, but also to community richness. The relative contribution of structural complexity and diversity to total complexity would be different for different study area or ecosystems.