ORCID Profile
0000-0002-3841-8942
Current Organisations
Swedish University of Agricultural Sciences
,
Czech Academy of Sciences, Global Change Research Institute
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Publisher: Wiley
Date: 18-08-2022
DOI: 10.1111/PCE.14415
Abstract: Alternative water uptake pathways through leaves and bark complement water supply with interception, fog or dew. Bark water‐uptake contributes to embolism‐repair, as demonstrated in cut branches. We tested whether bark water‐uptake could also contribute to supplement xylem‐water for transpiration. We applied bandages injected with 2 H‐enriched water on intact upper‐canopy branches of Pinus sylvestris and Fagus sylvatica in a boreal and in a temperate forest, in summer and winter, and monitored transpiration and online isotopic composition (δ 2 H and δ 18 O) of water vapour, before s ling for analyses of δ 2 H and δ 18 O in tissue waters. Xylem, bark and leaf waters from segments downstream from the bandages were 2 H‐enriched whereas δ 18 O was similar to controls. Transpiration was positively correlated with 2 H‐enrichment. Isotopic compositions of transpiration and xylem water allowed us to calculate isotopic exchange through the bark via vapour exchange, which was negligible in comparison to estimated bark water‐uptake, suggesting that water‐uptake occurred via liquid phase. Results were consistent across species, forests and seasons, indicating that bark water‐uptake may be more ubiquitous than previously considered. We suggest that water taken up through the bark could be incorporated into the transpiration stream, which could imply that sap‐flow measurements underestimate transpiration when bark is wet.
Publisher: Wiley
Date: 13-12-2020
DOI: 10.1111/NPH.17088
Abstract: Photosynthetic water‐use efficiency (WUE) describes the link between terrestrial carbon (C) and water cycles. Estimates of intrinsic WUE (iWUE) from gas exchange and C isotopic composition (δ 13 C) differ due to an internal conductance in the leaf mesophyll ( g m ) that is variable and seldom computed. We present the first direct estimates of whole‐tree g m , together with iWUE from whole‐tree gas exchange and δ 13 C of the phloem (δ 13 C ph ). We measured gas exchange, online 13 C‐discrimination, and δ 13 C ph monthly throughout spring, summer, and autumn in Eucalyptus tereticornis grown in large whole‐tree chambers. Six trees were grown at ambient temperatures and six at a 3°C warmer air temperature a late‐summer drought was also imposed. Drought reduced whole‐tree g m . Warming had few direct effects, but lified drought‐induced reductions in whole‐tree g m . Whole‐tree g m was similar to leaf g m for these same trees. iWUE estimates from δ 13 C ph agreed with iWUE from gas exchange, but only after incorporating g m . δ 13 C ph was also correlated with whole‐tree 13 C‐discrimination, but offset by −2.5 ± 0.7‰, presumably due to post‐photosynthetic fractionations. We conclude that δ 13 C ph is a good proxy for whole‐tree iWUE, with the caveats that post‐photosynthetic fractionations and intrinsic variability of g m should be incorporated to provide reliable estimates of this trait in response to abiotic stress.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-16180
Abstract: & & In plants, the constant demand for water driven by transpiration is supplied by uptake from the soil through the roots. Alternative water-uptake pathways through the leaves and the bark have been demonstrated for some species, mainly conifers. Alternative water-uptake pathways could allow plants to complement their water supply with canopy interception, fog or dew, sources often assumed unavailable as they are lost via evaporation before they can contribute to soil water recharge. Bark water-uptake has been putatively linked to repair of xylem embolism, although this has only been demonstrated in cut branches and/or under artificial conditions. We hypothesized that besides embolism repair, bark water uptake might also contribute to maintaining the transpiration stream in upper canopy branches when the xylem water column is subject to excess negative pressure, either because temperature drops, and water viscosity increases, or under high vapour pressure deficit and low soil water availability. We used a novel labelling methodology combining online measurements of the isotope composition (& #948 & sup& & /sup& H and & #948 & sup& & /sup& O) of the transpiration stream with analyses of & #948 & sup& & /sup& H and & #948 & sup& & /sup& O from leaf, bark and xylem water in & em& Pinus sylvestris& /em& and & em& Fagus sylvatica& /em& . We conducted s ling c aigns in two study sites: a boreal (northern Sweden) and a temperate (northern Spain) forest. We applied semi-permeable bandages injected with & sup& & /sup& H-enriched water (0.8% & sup& & /sup& H& sub& & /sub& O), on intact upper canopy branches (7-13& m), and monitored & #948 & sup& & /sup& H and & #948 & sup& & /sup& O of the transpiration stream with a Cavity Ring-Down Spectrometer (CRDS) in three branches (only & em& P. sylvestris& /em& in Sweden) for 24 h and then s led branch segments 2& cm upstream and downstream of the bandage. We determined & #948 & sup& & /sup& H and & #948 & sup& & /sup& O of leaf, bark and xylem water from s led segments with a CRDS after cryogenic extraction. Xylem, bark and leaf water from segments downstream of the bandage were enriched in & #948 & sup& & /sup& H with respect to their corresponding upstream segments. The & #948 & sup& & /sup& H and & #948 & sup& & /sup& O from leaf, bark and xylem water from upstream segments were similar to those of control branches (no bandages). Results were similar for both study species, sites and c aigns, indicating that bark water uptake is not restricted to gymnosperms and may be more ubiquitous than previously considered. Enrichment in & #948 & sup& & /sup& H in the transpiration stream was also detected in one out of the three continuously monitored pine branches within the 12& h following the bandage application. Our results demonstrate that water taken up through the bark may be incorporated into the transpiration stream and that transpiration might not solely rely on water absorbed through the roots and transported through the main stem. This could imply, for ex le, that sapflux measurements would underestimate canopy transpiration. Combining empirical flux measurements with stable isotopes and/or other atmospheric tracers could render more realistic estimates of transpiration and help constrain partitioning of evaporation and transpiration and its coupling to gross primary productivity.& &
Location: Czechia
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