东祁连山杜鹃灌丛生态系统特征及干扰的影响

The Characteristics of Rhododendron Shrubs Ecosystem in Eastern Qilian Mountains and Its Response to Disturbing

分布于东祁连山高山带的杜鹃灌丛优势种为头花杜鹃和百里香杜鹃，分盖度２０％～４０％。群落中绝大多数植物为地面芽（３３.３％）、矮高位芽（３０.１％）和地下芽（２６．１％），一年生植物和地上芽植物仅占少数（１０.５％）。常绿植物杜鹃的物候期早于其它植物，其中以青海杜鹃（Ｒ. Ｐｒｅｚｗａｌｓｋｉｉ）最早。地上植物量呈单峰变化趋势， ８月干物质量达最高值 ９５０．２ ｇ／ｍ２。灌木地上地下植物量的主体以杜鹃为主，分别占 ７２．５％和 ６２．６％，且地上植物量大于地下。全群落地下植物量以草本为主。百里香杜鹃和头花杜鹃的热值含量分别为 ２１．９４ ｋＪ／ｇ和 ２１．６８ ｋＪ／ｇ，高于其它灌木，也明显高于世界陆生植被的平均热值。两种杜鹃不同部位热值含量的顺序为叶＞茎＞根。群落地上净第一性生产力为３０１.７ｇ／ｍ２干物质，光能转化率为０.１０２１％。群落在生长季保持低增长状态，具有顶级群落的特征。砍伐后第１年内群落的植被成分无明显变化，但自然滑坡地段的植被成分变化明显，植物种类由１８种变为１０种，优势种变为鬼箭锦鸡儿，对杜鹃和苔藓影响较大。

The dominants of the Rhododendron community that distributed in the alpine area are Rhododendron capitatum and Rhododendron thymifolium with 20%--40% of subcoverage. Most of the species in the community are hemicryptophytes, phanerophytes and geophytes, meanwhile, the therophytes and chamaephytes account for only 10.5 %. The phenophase of evergreen Rhododendron is earlier than other plants, and in which the R. prezwalskii is the earliest, followed by R. thymifolium and R. capitatum. The aboveground phytomass of the community shows a single peak curve, and it reaches the peak value (950.2 g/m2.DM) within August. The phytomass variation of leaf is remarkably higher than that of stem. The community phytomass is comprised mainly by Rhododendron, it accounts for 72.5 % of aboveground phytomass and 62.8 % of underground phytomass. The aboveground phytomass of shrubs is more than underground phytomass due to the limiting of frozen soil to root growth. The total underground phytomass is comprised mainly by grasses. The caloric values of R. capitatum and R. thymifolium (21 .94 kJ/g and 21.68 kJ/g) are higher than other shrubs, and considerably higher than mean value of the vegetation on earth. The caloric value order of R. capitatum and R. thymifolium for different part is leaf > stem > root. The aboveground net primary productivity of Rhododendron is 301.7g/m2.DM, and its total solar conversion efficiency is 0. 102 1%. The community keeps a low increasing pattern during growth period, this is one of features of climax. The components of Rhododendron community changed significantly and it changed severely in the landslip area and the dominant is replaced by Calagana. jubata Rhododendron and moss were influenced intensely by disturbing.