Wimmler Marie-Christin, Vovides Alejandra G, Peters Ronny, Walther Marc, Nadezhdina Nadezhda, Berger Uta
Faculty of Environmental Sciences, Department of Forest Sciences, Chair of Forest Biometrics and Systems Analysis, Technische Universität Dresden, 01062 Dresden, Germany.
School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK.
Ann Bot. 2022 Jun 10. doi: 10.1093/aob/mcac074.
Trees interconnected through functional root grafts can exchange resources, but the effect of exchange on trees remains under debate. A mechanistic understanding of resource exchange via functional root grafts will help understand their ecological implications for tree water exchange for individual trees, groups of trees and forest stands.
To identify the main patterns qualitatively describing the movement of sap between grafted trees, we reviewed the available literature on root grafting in woody plants that focus on tree allometry and resource translocation via root grafts. We then extended the BETTINA model, which simulates mangrove (Avicennia germinans) tree growth on the individual tree scale, to synthesize the available empirical information. Using allometric data from a field study in mangrove stands, we simulated potential water exchange and analysed movement patterns between grafted trees.
In the simulations, relative water exchange ranged between -9.17 and 20.3 %, and was driven by gradients of water potential, i.e. differences in tree size and water availability. Moreover, the exchange of water through root grafts alters the water balance of trees and their feedback with the soil: grafted trees that receive water from their neighbours reduce their water uptake.
Our individual-tree modelling study is a first theoretical attempt to quantify root graft-mediated water exchange between trees. Our findings indicate that functional root grafts represent a vector of hydraulic redistribution, helping to maintain the water balance of grafted trees. This non-invasive approach can serve as a basis for designing empirical studies to better understand the role of grafted root interaction networks on a broader scale.
通过功能性根嫁接相互连接的树木能够交换资源，但这种交换对树木的影响仍存在争议。从机制上理解通过功能性根嫁接进行的资源交换，将有助于理解其对单株树木、树木群体和林分的水分交换的生态意义。
为了定性识别描述嫁接树木之间树液流动的主要模式，我们回顾了有关木本植物根嫁接的现有文献，这些文献侧重于树木的异速生长和通过根嫁接的资源转运。然后，我们扩展了BETTINA模型，该模型在单株树木尺度上模拟红树林（白骨壤）的树木生长，以综合现有的实证信息。利用来自红树林实地研究的异速生长数据，我们模拟了潜在的水分交换，并分析了嫁接树木之间的流动模式。
在模拟中，相对水分交换率在-9.17%至20.3%之间，并且由水势梯度驱动，即树木大小和水分可利用性的差异。此外，通过根嫁接进行的水分交换改变了树木的水分平衡及其与土壤的反馈：从邻居那里获得水分的嫁接树木减少了它们的水分吸收。
我们的单株树木建模研究是首次从理论上尝试量化树木之间根嫁接介导的水分交换。我们的研究结果表明，功能性根嫁接代表了水力再分配的一个载体，有助于维持嫁接树木的水分平衡。这种非侵入性方法可以作为设计实证研究的基础，以便在更广泛的尺度上更好地理解嫁接根相互作用网络的作用。
