多年冻土区高寒草甸根系分布与活动层温度变化特征的关系

Relationship between alpine meadow root distribution and active layer temperature variation in permafrost areas

多年冻土区植物根系的地下分布格局是其适应高寒、反复冻融作用等特殊环境条件的重要体现.针对目前青藏高原高寒植物根系研究不足的现状,对青藏铁路沿线高寒草甸植物群落根系的分布特征及多年冻土活动层地温变化等进行调查观测.研究高寒植物群落根系在活动层土壤中的垂直分布特征,重点探讨多年冻土活动层温度变化对于高寒植物根系分布和格局的影响,揭示植物根系对冻土环境变化的响应特征及其对逆境条件的适应策略.研究结果表明：活动层季节性冻融对于高寒植物和地下根系分布格局具有深刻的影响,多年冻土表层最先具备适宜根系生长的温度和水分条件,导致高寒草甸根系分布浅层化,生物量大量累积在土壤表层,并随深度增加而减少.高寒草甸地下平均总根量为3.38 kg·m-2,0～10 cm土层根量密度平均为21.41 kg·m-3,约占地下根系总量的63.4%.高寒草甸植物群落具极高的根茎比,活动层长期的低温环境增加了根系的干物质总量和高寒植物总的生物产量.活动层0℃以上积温是根系分布的主要影响因子.

The belowground root system can be a good indicator of adapting special permafrost environments,such as high-cold climate,repeatedly freezing and thawing process. In viewof the lack of alpine root research on the Tibetan Plateau,different alpine meadowcommunities were selected to observe roots distribution and active layer temperature variations in permafrost areas along Qinghai-Tibetan Railway. The effects of active layer temperature variation on root spatial distributions and patterns were studied to reveal the adaptive mechanism of roots system in the changing permafrost environment. The results showthat root growth and distribution are significantly impacted by change in soil temperature during the seasonally freezing and thawing process. In general,the upper soil layers are the most optimal location for roots in permafrost areas,roots have no enough living time to reach deep soil layers without impediments of frozen soil. So vast biomass is accumulated within the top soil and decreases sharply with depth. The overall mean root biomass of alpine grasslands was 3. 38 kg m- 2,with the density of 21. 41 kg m- 3in 0 ～ 10 depth range,accounting for 63. 4% of the total root biomass.Long-term cold environmental condition around root zone tends to increase root dry mass as well as overall productivity of alpine meadowcommunities. There is a tight relationship between alpine meadowroot density and cumulative temperature of 0 ℃. Further research will help to have better knowledge and understanding of root growth and root function as related to permafrost heat and water status.