Abstract: Seed germination and seedling settlement are the most fragile two stages in life history of plants. To clarify habitat selection of Stellera chamaejasme in seedling settlement, both the effect of litter covering on micro-environment factors and the seedling settlement performance (i.e. emergence and survival) under different microhabitat conditions were investigated through artificial control experiments in the original habitat in alpine grassland. The results showed that litter mulching, on the whole, could decrease soil temperature, increase soil moisture, and significantly reduce the daily amplitudes of both factors especially in surface soil of grassland. Compared with the control (without litter), the treatment of litter covering significantly reduced the rate of emergence and seedlings settlement, but had little effect on overwintering survival rate of the seedings. The soil burial depth had significant effects on the emergence and overwintering survival of seeds, and both the indicators for the seeds in surface soil (< 0.5 cm) were significantly higher than those in deeper soil (2 cm and 4 cm). In conclusion, litter mulching and burying seeds in deep layer was not conducive to and the settlement of S. chamaejasme seedings in alpine grassland. Therefore, both soil bareness and seed superficialization may contribute to the establishment of S.chamaejasme population, which should be the main ecological factors leading to the spread of S.chamaejasme population in degraded grassland.

Key words: Litter, Burial depth, Stellera chamaejasme, Seeding settlement, Micro-environment

摘要： 种子萌发和幼苗定居是植物生活史中最为脆弱的两个阶段。为了探明高寒草地狼毒（Stellera chamaejasme）种苗定居的生境选择，本研究在其原生境下通过人工控制试验，研究凋落物覆盖对土壤微环境（温、湿度）的影响以及狼毒种子在不同生境条件下的出苗和定居表现。结果表明：凋落物覆盖总体上能够降低土壤温度，提高土壤含水量，且能显著降低表层土壤温度和含水量的日振幅；与对照（土壤裸露）相比，凋落物覆盖显著降低狼毒种子的出苗率和成苗率，但对其越冬存活率的影响并不显著；土壤埋深对狼毒种子的出苗产生显著影响，埋植于表层土壤（< 0.5 cm）的狼毒种子其出苗率和越冬成活率均显著高于深层土壤（2 cm和4 cm）的种子。分析表明，高寒草地凋落物的存在或种子埋植太深均不利于狼毒种苗的定居；因此，草地裸露或促使土壤浅表化的扰动均可促进狼毒种群建立，是导致退化草地狼毒种群扩散的主要生态因素。

关键词: 凋落物, 埋深, 狼毒, 种苗定居, 微环境