鼠丘土壤与植被退化演替机制研究

Owing to the burrowing and excavating activity of plateau pikas (Ochotona curzoniae) and plateau zokors (Eospalaxbaileyi), high density of rodent-making mounds covered a large proportion of the alpine grassland and leading to a landscape fragmentation or even naked ground (heitutan). The fates of the rodent-making mounds are two exactly different patterns, one is gradually restored by plant and the other is eroded by water and wind and finally changed into naked ground. The mechanisms of progressive succession of rodent-making mounds have been researched by many programs, but the mechanisms of retrogressive succession were largely neglected. To explore the mechanisms of retrogressive succession, the following questions must be answered: (1) What is the driving force of retrogressive succession? (2) How do wind and water take part in forging the retrogressive succession of rodent-making mounds? (3) How long does it take from the establishment of rodent-making mounds to the formulation of naked ground? (4) How does the survival condition of mounds-covered plant related to the building time, size and height of mounds, and to the functional type of plant itself? (5) What are the relationship between the decease of covered plant and the formulation of naked ground? (6) What are the conditions of soil seed bank and how does it play role in the retrogressive succession of rodent-making mounds? To find answers to the above questions, we designed a serial of experiments to investigate them. Through this program, we will finally get knowledge to the retrogressive succession of rodent-making mounds and provide scientific theory base for the ecology management and restoration of the alpine grassland.

在高寒草地，随处可见鼠类挖掘行为造成的土丘堆积现象，即草地破碎化景观，并最终形成黑土滩。鼠类挖掘活动产生的土丘，有的向有植被定居的恢复演替方向发展，而有的向无植被定居、土壤逐渐流失的退化演替方向发展。对鼠丘恢复演替的研究较多，但要探明鼠丘退化演替的机制，尚需回答以下科学问题：①鼠丘退化演替的驱动力是什么？②气候和地形条件在鼠丘土壤剥蚀扮演了何种角色？③从鼠丘形成到最终形成砂石裸地的退化演替需多长时间？④鼠丘覆盖下的植被的生存状态与鼠丘的形成时间、大小以及植被类型是否有关？⑤被鼠丘覆压的植被死亡与黑土滩的形成是否有关系？⑥鼠丘退化演替的存在说明土壤种子库没有发挥相应的作用，这是否与鼠类挖掘堆土活动导致的土壤种子库的垂直分布可能发生逆转有关？是否与鼠丘土壤水分不足和质量恶化等因素有关？本课题设计了一系列实验，试图回答以上科学问题，以初步了解鼠丘退化演替的机制，为高寒草地的生态恢复提供依据。

高原鼠兔和高原鼢鼠的掘洞行为造成高寒草地破碎的景观，挖掘活动产生的土丘明显地向两个截然相反的方向演替，即挖掘活动形成的新土丘向有植被定居的恢复演替方向发展和土壤逐渐流失最后向只保留较大石砾的退化演替方向发展。新土丘向哪个方向演替？鼠丘退化演替过程中土壤与植被发生哪些变化？是本项目需要解决的问题。为此开展了以下研究：鼠丘覆盖下的植被生长发育，鼠丘土壤种子库动态及种子命运，高寒草甸种子雨特征，气候、地形条件、植被类型及鼠种对鼠丘土壤剥蚀影响，鼠丘退化演替过程中的形态及土壤质量变化，以及鼠丘植被的演替。研究结果表明：植物种子（果实）形态、表皮特征研究，可作为土壤种子库种子鉴定的重要资料。随着鼠丘形成时间的延长，鼠丘向有植被定居的恢复演替方向发展，植被覆盖度逐渐增加。天然草地土壤种子库中的种子数量和种子质量均高于鼠丘土壤种子库，发芽率表现为天然草地土壤种子库>新鼠丘>旧鼠丘，原生植被的土壤种子库呈明显的上层多下层少的垂直分布格局，新、旧鼠丘上下层间无明显的垂直分布规律；鼠丘土壤种子库与天然草地土壤种子库的相似性越高，鼠丘植被向原生植被恢复演替的几率越大。具有层次分化的草地，上层种子雨散布具有显著优势；种子雨受植被类型与地域的影响，种子雨中出现了地上植被中不存在的种子可能是长距离扩散而来的。不同地域平滩和坡地鼠丘土壤的剥蚀速率和剥蚀量均表现为新鼠丘最高。土壤大团聚体含量表现为随鼠丘土壤的剥蚀逐年增大。鼠丘土壤的剥蚀量与鼠丘大小呈正相关，风蚀量和水蚀量均随形成时间逐渐减小。随演替的进行鼠丘植被总盖度呈递增趋势。.通过研究为揭示鼠丘土壤与植被演替提供了理论依据，为退化草地的恢复奠定理论基础。