基于探地雷达的灌丛群落根系分布特征及其在草原灌丛化过程中的作用机制研究

Shrub encroachment is the most important change ways of plant community composition in arid and semi-arid grasslands. With its serious implications on local husbandry economies, this phenomenon has become a significant ecological problem around the world. Investigation of the spatial distribution characteristics of shrub community root system at different stages of encroachment not only reveals the intrinsic driving or limiting mechanisms on shrub encroachment but also has a practical significance in the degenerated pasture restoration. However, limited by the traditional root investigation methods in field, quantitative studies in root spatial distribution characteristics of shrub community are so far seriously insufficient. In this project, a signal fusion method for multiple-frequency GPR data and an automatic recognition algorithm for GPR images of root detection will be developed. Ground-penetrating radar (GPR), with multiple-frequency antenna system, will be used to detect the root system of shrub community at different stages of encroachment. And then a noninvasive method for reconstruction root system architecture of shrub community will be established. Based on this, the spatial distribution characteristics of shrub community root system at different stages of encroachment will be acquired. Combining with Up-ground ecological parameters of shrub community measured, the interrelation of below- and up-ground of shrub community will be revealed. This project will enhance the noninvasive study of plant root in field. Findings in this project are of great scientific interest in understanding the intrinsic mechanisms of shrub encroachment and the protection of the grassland ecosystem in future.

草原灌丛化是干旱/半干旱区最重要的植被类型变化方式，严重影响草原及畜牧业生产的可持续发展，是全球干旱/半干旱区面临的重要生态问题。研究草原灌丛化发展过程中各阶段灌丛群落根系的分布特征，有助于揭示驱动或限制草原灌丛化过程的内在机制，对于草原退化治理和恢复具有实践意义。受传统根系调查方法的制约，群落尺度上的灌木根系空间分布特征的野外观测研究极为缺乏。本研究拟采用探地雷达技术，开发多频率探地雷达数据融合及根目标自动识别和提取的方法。在此基础上，应用探地雷达多个频率天线系统对内蒙古草原灌丛化过程中，不同发展阶段灌丛群落根系进行监测，恢复重建灌丛群落地下根系三维构型，进而获取灌丛斑块尺度上的根系空间分布特征。再结合地上部分生态参数的系统调查，揭示地下根系在灌丛化过程中的作用及其与地上部分的相互关系，为阐明干旱/半干旱区草原灌丛化过程的内在作用机制提供理论依据。

草原灌丛化是全球干旱/半干旱区面临的重要生态问题。灌丛群落中的土壤水分、灌木根系空间分布特征及其与地上部分的相互关系是理解草原灌丛化过程内在作用机制的关键。本项目从探地雷达的工作原理出发，结合野外控制实验，利用多频率的探地雷达系统对草原灌丛化的先锋物种，小叶锦鸡儿，在种群尺度上的地下根系进行了多季节、无损性探测。在此基础上，发展了基于随机霍夫变换的根目标自动识别和提取方法，实现了从雷达剖面图上自动定位和识别根目标；构建了根的走向估测算法，可通过雷达剖面图上的双曲线信号形状反演出根的伸展角度；提出了以灌木粗根为自然反射体的根区土壤水分无损性估测方法，可用于在识别根目标的同时估计根区土壤含水量。我们利用这些新方法对探地雷达测量得到根系数据进行了解译，分析了中尺度灌木根系空间分布模式以及根-根之间的相互关系；并结合灌木地上部分生态参数的系统调查，建立了小叶锦鸡儿的地上生物量、GPR估算出的地下生物量和种群密度之间的关系。结果表明，小叶锦鸡儿种群的植株密度是由地下根系的资源竞争机制来驱动的。本项目为阐明干旱/半干旱区草原灌丛化过程的内在机制提供了理论依据和技术手段。