The role of root grafting in competitive/cooperative relationships between trees

***自然嫁接（吻合）挑战了植物个体性的概念，也挑战了森林是个体树木相互竞争资源的概念。树木之间共享物质（如水、糖），使合作关系得以发生。本研究计划的长期目标是证明嫁接的生态意义。在短期内，我想回答以下问题：嫁接的树木是更好的竞争对手吗？首先，对杂交杨树、白杨和挪威云杉单株人工林嫁接的发生、时机和间距效应进行了评价。移植物将被收集并带到实验室进行树突年代学分析。嫁接时根系的大小和年龄以及嫁接树之间的距离将决定并与嫁接频率和时间联系起来。然后，使用密集种植的地块，将评估混合物种地块中与根嫁接相关的种间与种内竞争/促进关系。树木之间的关系将使用距离依赖和独立的竞争指数来表征。利用树木年代学技术，将确定嫁接的时间，并将其与整个林分生命周期的时间竞争指数值联系起来。这将使我们能够确定林分发育是否表现出可预测的时间序列空间模式，这是由于资源竞争造成的，还是由于树根嫁接允许树木作为一个群体而不是单个茎来响应（和竞争）而阻碍了林分发育。不同的间距和混合树种人工林也将使我们能够检查林分发育序列，看看竞争力量是否作为相邻树木之间形成根嫁接的触发因素。***嫁接的生态意义迫使我们重新思考竞争、优势和演替等传统林分动态概念，这些概念是现代林业的基础。本研究将通过观察人工林和香脂冷杉天然林的林分水平嫁接，揭示根系嫁接在林分进化过程中树与树相互作用中的作用。到目前为止，我的研究表明，根嫁接对连体树木的生长有普遍的积极影响，并表明嫁接的树木群体在面对压力时相互受益。从应用的角度来看，很少有从业者将成功或不成功的造林作业与根系联系联系起来。例如，人们常说，一些受抑制的树木无法对间伐（竞争减少）做出反应，而答案是由于共用根系的林分的叶面积减少而造成的根冠比倾斜。因此，我们在种植园中的工作有可能影响如何建立集约化管理的种植园。＊＊＊＊＊

***Natural root grafting (anastomosis) challenges the notion of plant individuality and the consideration of forests as groups of individual trees competing with each other for resources. The sharing of substances (e.g. water, sugars) between trees, allows for cooperative relationships to occur. The long term objective of this research program is to demonstrate the ecological significance of root grafting. In the short term, I want to answer the following question: are root-grafted trees better competitors? First, occurrence, timing and effect of spacing on root grafting will be assessed in monospecific plantations of hybrid poplar, white and Norway spruce. Root grafts will be collected and brought to the lab for dendrochronological analysis. Size and age of roots at grafting, and distance between grafted trees will be determined and linked to root grafting frequency and timing. Then, using densely planted plots, inter- vs intraspecific competition/facilitation relationships will be evaluated in mixed-species plots in relation to root grafting. Relationships between trees will be characterized using distance-dependent and independent competition indices. Using dendrochronology techniques, timing of root grafting will be determined and linked with chronological competition index values throughout the lifespan of the stands. This will enable us to determine if stand development exhibited a predictable time-sequence spatial pattern resulting from competition for resources or if root grafting stalled stand development by allowing trees to respond (and compete) as a group rather than as individual stems. The different spacings and mixed species plantations will also allow us to examine stand development sequence to see if competition forces act as a trigger for root grafts to form between neighboring trees.***Ecological significance of root grafting forces us to reconsider traditional forest stand dynamics concepts such as competition, dominance and succession, concepts on which modern forestry is based on. The proposed research will throw light on the role that root grafting plays in tree-to-tree interactions during stand evolution by looking at stand-level grafting in plantations and in balsam fir natural forests. So far, my research has shown a general positive impact of root grafting on growth of connected trees, and suggests that grafted groups of trees benefit from each other to confront stress. From an applied perspective, few practitioners have associated successful or unsuccessful silvicultural operations to root connections. For example, it is often said that some suppressed trees are unable to respond to thinning (reduced competition), while the answer lies in skewed root-shoot ratios created by reducing leaf area of stands sharing communal root systems. Our work in plantations thus has the potential to impact how intensively managed plantations are established. *****