林木幼苗对切根的生理生态响应及根-冠互作机制

Rapid establishment after transplanting is important for seedlings to compete efficiently for site resources both below and above ground. Ecology and vegetation restoration are concerned with the relationship between structure and function, but the excellent tree individiul and the perfect performance of seedling to the tasks would be the core of the restoration study of nature. Tree seedlings are normally root pruned in the nursery to facilitate transplanting and to induce branching of the root system and hence more growth apices. However, in many woody species the ideal root system size and architecture for transplanting are not known. Root prunning must be consided as a stress or damage to the seedling inherent characters, though the mechanisms of morphological, physiological and biochemical responses and the control to root –shoot interaction remain unclear. Understanding the morphological, physiological responses to root prunning stress is essential for a holistic opinion of vegetation restoration strategy. In this study, we use two species, a conifer Platy cladusorientalis and a deciduous species Quercus variabilis, and focus on the response of seedling morphological, physiological and biochemical characters and the interaction of root-shoot to different root-prunning ratio. We try to understand the process of signal transport and the mechnism of root-shoot signaling by exploring the concentrations of root secretion and xylem sap inclusions including hormone and protein. The seedling mortality and growth potential can be significantly affected by abiotic stresses such as drought or root damage. To address the tolerance to drought of seedlings with different root-prunning ratio, we study the response of two species potted seedlings subjected to different drought stress. Based on these results, we can achieve a comprehensive index to indicate the optimum root architecture for transplanting probably consists of some balanced combination of fine and coarse roots. The purpose of this study is to give a theoretical support to success vegetation restoration strategies of higher ecological benefits.

研究森林群落或生态系统的结构与功能，一直是生态学家和植被恢复领域研究的热点。但优良林木个体质量和造林后的表现，是影响植被恢复能否成功的最根本因素。切根是发生在植被恢复过程中的常见现象，但其作为伤害胁迫因子，是如何影响苗木生理生化过程及调节形态-生理和根-冠相互关系，仍是一个没有解决的科学问题。本研究以侧柏和栓皮栎为研究对象，探明不同切根比例对幼苗形态结构和生理特征的影响及形态-生理互作机理，探索不同树种苗木根系分泌物和木质部汁液内含物对不同切根伤害的应激反应特征，揭示切根伤害信号的传导及根-冠互作机制，判明不同比例切根苗木对环境胁迫的反应，把握根构型影响造林后苗木成活和生长的生理机制，建立客观全面科学描述侧柏和栓皮栎根系理想构型的综合指标体系以及根构型的生态评价体系。为今后建立科学有效的植被恢复技术措施打下良好的理论基础。

植被恢复过程中，营造具有与天然林功能和形态相近的植物群落十分重要。苗木个体是植被恢复的基础。根系作为苗木最重要的功能器官，其生长发育程度对苗木质量及其移栽或造林效果起决定性作用。人工林(植苗更新)和天然林(种子更新)相比，根本差异就是移栽过程中根系受到损伤，这严重影响了苗木根系的生长发育，进而直接影响了苗木的成活率和生长。因此，本研究把切根作为一种对植物根系伤害的胁迫因子，选取我国北方最常用植被恢复树种侧柏(Platycladus orientalis L.)和栓皮栎(Quercus variabilis Bl.)为主要研究对象，比较分析不同比例切根下林木幼苗根系的形态和生长状况差异。研究发现侧柏和栓皮栎幼苗的存活率和生长状况对切根的响应策略不同，相对于侧柏，栓皮栎幼苗的反应随切根比例增加更敏感。从时间序列上研究空气切根对幼苗根系形态、生理和解剖特征的动态变化规律，发现与对照相比，空气切根10 d、30 d和50 d与120 d、150 d和190 d侧柏根系形态特征参数值均明显上升，且120−190 d上升趋势更明显，尤其是细根。同时，发现空气切根使侧柏细根的皮层细胞层数的变化可能直接改变了皮层厚度，是导致细根形态发生变化的主要原因。进一步从蛋白组水平出发，利用iTRAQ技术，结合LC-MS/MS，鉴定到5942个蛋白，结果分析表明678个蛋白发生显著差异表达，其中6 h、72 h和504 h分别有271、360和106个蛋白差异表达，这些蛋白包括过氧化物酶、钙网蛋白3、几丁质酶、热激蛋白和脂氧合酶等参与侧柏根系对切根的响应。GO功能分析结果表明切根后这些上调或下调蛋白参与了胁迫/防御、激素调节和信号传导等多个功能。KEGG通路分析表明，这些蛋白参与了植物激素信号转导、苯丙烷生物合成和α-亚麻酸等途径，这些研究结果揭示了切根调控林木根系发育的生物学机制，为丰富林木育苗和植被恢复技术体系提供理论支持。