Redistribution of water via layering branches between connected parent and daughter trees in Norway spruce clonal groups

Abstract

Key message We measured sap flow and shoot water potentials in clonally connected parent and daughter trees. We found bidirectional flow patterns in branches mediating the connection between parent and daughter trees. Abstract Layering is an important mode of vegetative reproduction at treeline, in which clonal daughter trees are formed by the rooting of lower (''layering'') branches of the parent tree. These branches mediate the connection between parent (PT) and daughter tree (DT). Here, we measured quantity and direction of sap flow in layering branches as well as PT and DT, and measured shoot water potentials in the crowns of a connected PT and DT. We found bidirectional sap flow pattern in layering branches, with the bidirectionality of the flow resulting from water potential dynamics of the parent and daughter trees varying diurnally. We found that 4.3 % of the total water transpired by the DT was supplied by the PT root system, with up to 25 % of the instantaneous daughter tree sap flow coming from the parent tree. In contrast, water provided by the daughter's root system to the parent tree comprised only a negligible amount, less than 1 % of the parent's entire sap flow. Additionally, after experimental excavation of part of the DT roots, layering branch flow towards the DT in- creased, while flows in the opposite direction almost van- ished. This study showed that aboveground clonal connections can facilitate a new type of hydraulic redis- tribution where water is transported bidirectionally through branches. This transfer of water and nutrients is vital especially in the first years of the daughter tree but supplies considerable amounts of water even several years after the establishment of a new clonal tree.