Branch water uptake and redistribution in two conifers at the alpine treeline

Adriano Losso,Stefan Mayr,Andreas Bär,Lucrezia Unterholzner,Michael Bahn

doi:10.1038/s41598-021-00436-x

Adriano Losso, Stefan Mayr + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-00436-x

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Abstract

During winter, conifers at the alpine treeline suffer dramatic losses of hydraulic conductivity, which are successfully recovered during late winter. Previous studies indicated branch water uptake to support hydraulic recovery. We analyzed water absorption and redistribution in Picea abies and Larix decidua growing at the treeline by in situ exposure of branches to δ2H-labelled water. Both species suffered high winter embolism rates (> 40–60% loss of conductivity) and recovered in late winter (< 20%). Isotopic analysis showed water to be absorbed over branches and redistributed within the crown during late winter. Labelled water was redistributed over 425 ± 5 cm within the axes system and shifted to the trunk, lower and higher branches (tree height 330 ± 40 cm). This demonstrated relevant branch water uptake and re-distribution in treeline conifers. The extent of water absorption and re-distribution was species-specific, with L. decidua showing higher rates. In natura, melting snow might be the prime source for absorbed and redistributed water, enabling embolism repair and restoration of water reservoirs prior to the vegetation period. Pronounced water uptake in the deciduous L. decidua indicated bark to participate in the process of water absorption.

Highlights

Treeline conifers would benefit from long-distance water transport, as it may enable embolism repair in tree parts which do not have access to external water and/or exhibit low water potential and embolism[4]
We mimicked snow melting on the crown of specimens of the evergreen species Picea abies and the deciduous species Larix decidua growing at the alpine treeline by in situ exposure of branches to δ2H-labelled water
The course in Ψ did not correspond to seasonal changes in δ18O and δ2H measured on P. abies trunk microcores. Both conifer species under study were demonstrated to take up water over the branch surface and to redistribute absorbed water over significant distances within the crown. This confirms previous studies suggesting branch/ foliar water uptake in conifers[3,23,26,27,28] and proves for the first time that water can be redistributed over large distances from branches towards the trunk and side branches under winter conditions

Summary

Introduction

Treeline conifers would benefit from long-distance water transport, as it may enable embolism repair in tree parts which do not have access to external water (e.g., the main stem is hardly covered by snow) and/or exhibit low water potential and embolism[4]. We mimicked snow melting on the crown of specimens of the evergreen species Picea abies and the deciduous species Larix decidua growing at the alpine treeline by in situ exposure of branches to δ2H-labelled water. The resulting water isotopic composition of samples collected at different positions within the crown was monitored over the end of winter until beginning of summer 2017. Analyses were complemented by meteorological data and hydraulics measurements (i.e., Ψ and percent loss of conductivity), which enabled to monitor plant water status

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Conclusion