Friendly neighbours: Hydraulic redistribution accounts for one quarter of water used by neighbouring drought stressed tree saplings

Hydraulic redistribution (HR) can buffer drought events of tree individuals, however, its relevance for neighbouring trees remains unclear. Here, we quantified HR to neighbouring trees in single- and mixed-species combinations. We hypothesized that uptake of HR water positively correlates with root length, number of root tips and root xylem hydraulic conductivity and that neighbours in single-species combinations receive more HR water than in phylogenetic distant mixed-species combinations. In a split-root experiment, a sapling with its roots split between two pots redistributed deuterium labelled water from a moist to a dry pot with an additional tree each. We quantified HR water received by the sapling in the dry pot for six temperate tree species. After 7 days, one quarter of the water in roots (2.1 +/- 0.4 ml), stems (0.8 +/- 0.2 ml) and transpiration (1.0 +/- 0.3 ml) of the drought stressed sapling originated from HR. The amount of HR water transpired by the receiving plant stayed constant throughout the experiment. While the uptake of HR water increased with root length, species identity did not affect HR as saplings ofPicea abies((L.) Karst) andFagus sylvatica(L.) in single- and mixed-species combinations received the same amount of HR water.

Automated summary

The study found that hydraulic redistribution can alleviate drought stress for individual trees, but its effects on neighboring trees are still unclear. Results showed that the uptake of HR water increases with root length, but the species identity does not significantly affect HR.