古尔班通古特沙漠梭梭根系吸收功能的垂直分异研究

Haloxylon ammodendron is a xeric plant widely distributed in arid regions. Its deep and well developed root system plays an important role in its drought-resistant ability. Based on previous research, we proposed a scientific hypothesis: root system of H. ammodendron has vertical differentiation in water and nutrients absorption. Because treatments are limited only on upper layer roots, it is necessary to know firstly the differences between fine roots in upper and deep layer. Then we can explore how upper and deep roots respond to different treatments. Finally, we can analyze the correlation and causality between variations in root traits and changes in physiological and morphological traits of the aboveground part. Based on the compensation effect, linear mixing model will be used to study "difference" among differences, namely to make sure whether the "difference" is resulted from the treatments or variation of the root function. The scientific hypothesis is then verified: upper roots focuses on absorption of nutrient, and deep roots focuses on absorption of water. By comparing growth rate of H. ammodendron, which with or without stem flow, another scientific hypothesis is verified: the taproot H. ammodendron seedlings are induced to go through the dry sand layer and reach groundwater table. The implementation of this project can give us a novel vision on previous data and research results, and expand our understanding on how desert plants utilize water and nutrient in this harsh environment.

梭梭是广泛分布于干旱地区的典型旱生植物，深而发达的根系是其抗旱能力的重要构件。基于已有的研究，我们提出一个科学假设：梭梭根系存在对水分和养分吸收的的垂直功能分异。由于只能处理表层根系，需要在了解自然条件下表层与底层根系差异的基础上，研究表层与底层根系对处理的响应差异，进而建立根系性状及功能变化与地上部生理及形态变化之间的联系，探讨它们的对应与因果关系。基于补偿效应，利用线性混合模型研究差异之间的“差异”，即明确“差异”是来自于处理差异还是来自于根系的功能分异，验证前述科学假设：表层根系侧重于养分吸收，底层根系侧重于水分吸收。最后我们拟通过去除梭梭幼苗树干茎流（壤中优先流）的方式，验证梭梭双层细根形成的科学假设：树干茎流（优先流）导致的主根尖下局部湿润，诱导根系穿越了干沙层。该项研究从新的角度看待已有的数据和研究结果，从而可以深化和拓展我们对荒漠植物水分与养分利用策略的认识与理解。

本项目在中国科学院阜康荒漠生态研究站的野外实验场进行，结合野外与室内实验，以白梭梭为对照，探讨了梭梭的根系垂直分布特征，树干茎流养分的组成及来源，叶圈微生物的组成及固氮功能，初步确定了梭梭根系垂直分异的生态学意义：高频次的凝结水激活了梭梭冠层表面微生物的固氮作用，较大的降水则以树干茎流的形式，将固定的氮素，汇集、传输到梭梭的根系，通过水力提升，梭梭在干燥土壤中保持了表层吸收根系的活性，从而最大限度地利用树干茎流携带的养分。主要内容包括： 1、不同基径梭梭根系特征及其对水分胁迫的生理响应；2、梭梭和白梭梭树干茎流养分特征及其叶圈微生物的固氮作用。通过对梭梭和白梭梭根系、树干茎流和叶圈微生物的研究，初步确定了梭梭确实存在根系功能的垂直分异，并结合养分（氮素）吸收的研究，明确了其根系垂直分异的生态学意义：深层根系侧重于吸收养分，通过水力提升，维持了干沙层中表层吸收根的活性，进而可以最大限度地吸收养分，基本完成了预定目标。目前发表SCI 论文1篇，CSCD论文4篇，培养硕士研究生3名。