多枝柽柳幼苗发生及其根系生长对输水漫溢的响应研究

Tamarix ramosissima is the dominant plant species of shrub layer in the lower reaches of Tarim River, which is important to restore and preserve the degraded desert riparian forest. It is necessary for keeping its ecosystem stability to implement ecological water dilivery. However, more than ten years of the water dilivery have made the adaption to floods of Tamarix ramosissima's reproduction broken. And the seedling emergence of the plant had depended on the water dilivery, the survival of the seedlings had mainly depended on the root growth under the effect of soil water as well. Based on existed research results, we will try to study responses of the seedling emergence and the root growth of Tamarix ramosissima to overflowing in water delivery in this region by genecology, autecology, root-system-ecology and some monitoring equipments and analysis software. The aim of the study is to examine the seedling emergence and root growth under riverway overflowing and plant community rehabilitation in the lower reaches of Tarim River.It will illustrate the temporal and spatial patterns of the seedling emergence and adaptation of root to soil water variations under the condition of ecological water dilivery, which will be helpful to reveal the ecological functions of Tamarix ramasissima in restoring and preserving the degraded desert riparian forest, meanwhile, propose more practical suggestion to ecological water dilivery patterns.

多枝柽柳（Tamarix ramosissima）是塔里木河下游荒漠河岸林灌木层的建群种，对下游退化荒漠生态系统的恢复和维系极其重要。生态输水已成为下游河岸林群落稳定性维持不可或缺的环节，但十余年的输水过程打破了已往多枝柽柳种群生繁对自然洪水的适应，其生活史中幼苗发生已与输水时间和强度紧密关联，幼苗的生存也和输水过程中根系的"逐水"生长密不可分。本项目基于已有研究工作和成果，以多枝柽柳实生幼苗为研究对象，运用种群生态学、个体生态学、根系生态学等学科的理论，采用样方调查、定位监测、根系分析等方法，解析输水漫溢和生态恢复中多枝柽柳幼苗发生及其根系生长对幼苗种群发育的驱动过程，揭示幼苗发生的时空格局和根系形态的调整对输水中地表水过程和土壤水分变化的响应规律与生态适应性，从而为进一步解读多枝柽柳的更新繁育在维系荒漠河岸生态系统中的功能机制，以及生态输水模式的实践过程提供理论基础。

本项目针对多枝柽柳实生幼苗，解析塔里木河下游生态输水漫溢条件下，荒漠河岸林优势种多枝柽柳，其幼苗发生及其根系生长对幼苗种群的驱动过程，揭示幼苗发生的时空格局和根系生长对输水中地表水过程和土壤水分变化的响应规律与生态适应性。研究表明：.（1）塔里木河下游年初和年末连续较强的生态输水，虽能够使漫溢区多枝柽柳幼苗的种群在年初大量更新，但年末大量幼苗又受淹死亡，从而使漫溢区的多枝柽柳幼苗种群不能形成一定的规模。因此，建议采取强弱交替的方式进行生态输水，即在一次强输水漫溢促进种群更新的基础上，随后减少输水量，在补充幼苗生长所需的水分基础上使其稳定生长和存活，从而使幼苗种群持续扩大，形成规模。多枝柽柳幼苗生长最适土壤含水量为12.1%-16.9%，当土壤含水量过高或过低时，其通过增加根冠比和比根长，产生发达的根系来获得更多的水资源，以适应胁迫环境。.（2）水分、盐分和氮素是多枝柽柳幼苗的生长和存活三个限制因子，幼苗根系对限制因子最为敏感。水分渗透的深度对诱导多枝柽柳幼苗根系更积极地向土壤深层生长作用显著；水盐胁迫对多枝柽柳幼苗的生长产生交互影响，而且与水分胁迫相比，盐胁迫是决定多枝柽柳幼苗分布更为重要的生态因子；幼苗通过调整生长、生物量投入、形态解剖结构的变化来适应水盐胁迫，并对水分胁迫有较高的耐受性，可通过不断调节根系表皮、皮层厚度以及导管孔径、密度等来适应土壤水分和盐分的变化；水分和氮素是影响多枝柽柳幼苗早期生长不可分割的两个重要因子，氮素在不同的水分胁迫下对幼苗地上地下部分生长产生显著影响，氮素和水分在多枝柽柳幼苗生长的关键期具有互补效应，水和氮素二者的耦合作用可以有效的帮助幼苗渡过不良时期。.通过项目研究，建立了一个较为成熟的研究团队；在塔里木河下游确立两个长期的野外监测区和实验区；培养了3名硕士研究生，吸引了25名本科生加入课题组；撰写8篇期刊文章，完成2篇硕士论文。