石羊河下游衰败人工固沙林中红砂定居过程及其驱动机理研究

The Dune-fixing plantation in the lower reaches of Shiyang River is an important ecological barrier for maintaining the survival and healthy development of Minqin oasis. It has been playing a vital role in ensuring industrial and agricultural production within the oasis. In recent years, however, large areas of the dune-fixing plantation seriously degraded or declined for some reasons. One of the most important reasons causing this situation is recruitment limitation. Reamuria songarica is the unique woody desert plant which can naturlly invade into the degraded dune-fixing plantation and can reproduce and regenerate successfully. But the recruitment and establishment in desert plant communities and its driving mechanism of this species remains unknown for us until today, especially in the degraded dune-fixing plantation in the lower reaches of Shiyang River. In this project, we will select successfully settled individuals and populations of Reamuria songarica in the degraded dune-fixing plantation of Minqin oasis as research objects to study its settlement habitat,seed dissemination， seed germination, seedling growth, plant flowering and fruiting, morphological characteristics, metabolites, photosynthetic activity, soil seed bank，population density, population age structure, population spatial distribution and so on, using combined methods of field observation and control experiments. Specifically, the aims of the project are to determine the establishing or recruitment process and its driving mechanism of Reamuria songarica in the degraded dune-fixing plantation. The results of this study will enrich the regeneration research of desert plants and provide the theory basis for restorating and reconstructing degraded dune-fixing plantation in the lower reaches of Shiyang River.

石羊河下游人工固沙林是维系民勤绿洲生存和发展的重要生态屏障，对保障绿洲内部正常工农业生产发挥着举足轻重的作用。近年来，由于多种因素，大面积的人工固沙林出现严重衰败的现象，其中一个重要原因就是群落更新限制。红砂是唯一一种可自然侵入该区域衰败人工固沙林，并能成功繁殖更新的木本荒漠植物。但目前对其迁移定居过程及其驱动机理缺乏深入研究。本项目以石羊河下游衰退人工固沙林地中定居的红砂个体和种群为研究对象，通过野外观测调查与控制实验相结合的方法，对红砂定居的生境条件、种子特性、种子传播、种子萌发、幼苗定居、植株生理生态、植株形态结构、土壤种子库、种群密度、种群年龄结构、种群空间格局分布等方面进行研究，揭示红砂在衰败人工固沙林中定居过程及其驱动机理，同时为石羊河下游衰败固沙林植被恢复与重建提供理论依据。

石羊河下游人工固沙林是维系民勤绿洲生存和发展的重要生态屏障，对保障绿洲内部正常工农业生产发挥着举足轻重的作用。近年来，大面积的人工固沙林出现严重衰败的现象，其中一个重要原因就是人工植被更新受限。然而，荒漠灌木红砂却能自然侵入衰败人工固沙林，并能实现繁殖更新及种群扩散。为此，本项目研究了人工固沙林衰败过程中林地地上植被组、土壤种子物种组成、优势种动态变化、地上植被与种子库关系、土壤理化性质、生物土壤结皮、土壤微生物数量以及红砂个体从种子——植株阶段的变化特征与生境、气象因子间的耦合关系。得出：在人工固沙林衰败过程中，林地植被、土壤种子库优势种均发生了从沙生植物向沙旱生植物演替，林地植被与土壤种子库之间具有很强的依赖性，种子库具有较强的植被恢复能力。人工固沙林从未衰败（ND）——中度衰败（MD）演替过程中，土壤质地被改善，土壤养分含量被提高，生物土壤结皮从低级向高级演替。红砂种群在人工固沙林轻度衰败期（SLD）已成功定居，其通过以下机制实现种群繁殖与扩散：种子通过风媒传播到固沙林中，林下生物结皮形成发育增大了林表的稳定性和粗糙度，从而提高了林地对红砂种子捕获能力；附着于林表的种子利用零星的降雨及沙尘使其种子表皮形成一层薄薄“种毛+土”“外衣”，在次年生长季第一场大型降雨之后种子周围形成一个短时间内湿润的微环境，促使其成功完成种子—幼苗过程；当单株根系逐渐发达，其逐渐从土壤中吸收少量的盐离子，通过木质层运输到叶片，增大叶片渗透势，提高其抗旱性；其次，红砂具极强物候自我调整能力，其通常在民勤沙区雨季7-10月份完成开花、结实，使其年年都具有大量的饱满种子。以上这些生理生态策略，保证了红砂在石羊河下游衰败人工固沙林中能够成功入侵——定居成功——种群长期处于增长型状态。