Uptake of water and solutes through twigs of Picea abies (L.) Karst

Katz, C.; Oren, Ram; Schulze, Ernst Detlef; Milburn, John A.

doi:10.1007/bf00202398

Cited by 96 publications

(78 citation statements)

References 19 publications

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“…At the alpine timberline, even more than one-half was taken up via the branch surface. Katz et al (1989) previously reported water uptake via the surface of P. abies twigs. Their experiments with fluorescent dyes revealed pathways for the absorption of water and solutes through the twig bark and ray tissue.…”

Section: Discussionmentioning

confidence: 97%

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

et al. 2014

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Xylem embolism is a limiting factor for woody species worldwide. Conifers at the alpine timberline are exposed to drought and freeze-thaw stress during winter, which induce potentially lethal embolism. Previous studies indicated that timberline trees survive by xylem refilling. In this study on Picea abies, refilling was monitored during winter and spring seasons and analyzed in the laboratory and in situ experiments, based on hydraulic, anatomical, and histochemical methods. Refilling started in late winter, when the soil was frozen and soil water not available for the trees. Xylem embolism caused up to 86.2% ± 3.1% loss of conductivity and was correlated with the ratio of closed pits. Refilling of xylem as well as recovery in shoot conductance started in February and corresponded with starch accumulation in secondary phloem and in the mesophyll of needles, where we also observed increasing aquaporin densities in the phloem and endodermis. This indicates that active, cellular processes play a role for refilling even under winter conditions. As demonstrated by our experiments, water for refilling was thereby taken up via the branches, likely by foliar water uptake. Our results suggest that refilling is based on water shifts to embolized tracheids via intact xylem, phloem, and parenchyma, whereby aquaporins reduce resistances along the symplastic pathway and aspirated pits facilitate isolation of refilling tracheids. Refilling must be taken into account as a key process in plant hydraulics and in estimating future effects of climate change on forests and alpine tree ecosystems.

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Section: Discussionmentioning

confidence: 97%

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

et al. 2014

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“…Seasonal courses reported by Sperry et al (1994) and Sperry and Sullivan (1992) also indicated refilling in L. laricina and P. glauca during spring and in A. lasiocarpa during winter. Katz et al (1989) and Sparks et al (2001) suggested water uptake by branches or leaves during warm (when snow melts on twigs) or rainy periods. Nevertheless, due to the low temperatures during winter, sufficient metabolic activity of living tissues (ray parenchyma) is hardly probable.…”

Section: Discussionmentioning

confidence: 99%

Winter at the Alpine Timberline. Why Does Embolism Occur in Norway Spruce But Not in Stone Pine?

2003

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Conifers growing at the alpine timberline are exposed to frost drought and freeze-thaw cycles during winter-stress factors known to induce embolism in tree xylem. The two dominant species of the European Central Alps timberline were studied: Norway spruce (Picea abies [L.] Karst) and stone pine (Pinus cembra), which usually reaches higher altitudes. We hypothesized to find embolism only at the timberline and to observe less embolism in stone pine than in Norway spruce due to avoidance mechanisms. Seasonal courses of embolism and water potential were studied at 1,700 and 2,100 m during two winter seasons and correlated to vulnerability (to drought-induced embolism), leaf conductance, and micrometeorological data. Embolism was observed only at the timberline and only in Norway spruce (up to 49.2% loss of conductivity). Conductivity losses corresponded to low water potentials (down to Ϫ3.5 MPa) but also to the number of freeze-thaw events indicating both stress factors to contribute to embolism induction. Decreasing embolism rates-probably due to refillingwere observed already in winter. Stone pine did not exhibit an adapted vulnerability (50% loss of conductivity at Ϫ3.5 MPa) but avoided critical potentials (minimum Ϫ2.3 MPa): Cuticulare conductance was 3.5-fold lower than in Norway spruce, and angles between needles and axes were found to decrease in dehydrating branches. The extent of conductivity losses in Norway spruce and the spectrum of avoidance and recovery mechanisms in both species indicates winter embolism to be relevant for tree line formation.During the winter season, trees growing at the alpine timberline have to withstand conditions extremely unfavorable for plant water status. Water supply is permanently blocked because soil and stem are frozen, on the other hand, the shoot is exposed to water losses ("Frosttrocknis"; e.g. Michaelis, 1934;Pisek and Larcher, 1954;Larcher, 1972;Tranquillini, 1980) and to frequent freeze-thaw events (Gross et al., 1991).Drought and freeze-thaw cycles are known to induce the formation of gas bubbles in the water transport system of trees. This "embolism" interrupts the transmission of negative pressure to the soil and subsequently the flow of water through xylem conduits ("cohesion theory"; e.g. Boehm, 1893;Dixon and Joly, 1894;Richter, 1972;Jackson and Grace, 1994). Drought stress leads to high tensions in the water columns causing entry of air bubbles (air seeding) from adjacent air-filled conduits through the pits (e.g. Zimmermann, 1983;Tyree et al., 1994). Vulnerability analysis revealed species-specific water potential () thresholds for the onset of cavitation, whereby conifers were found to be very resistant due to their special pit anatomy (see e.g. Sperry and Tyree, 1990;Cochard, 1992;Jackson et al., 1995;Brodribb and Hill, 1999). Freeze-thaw events induce embolism because air is not soluble in ice-remaining gas bubbles can expand during thawing and lead to cavitation. However, this effect was reported to be of minor importance in conifers (e.g. Sucoff, 1969;Ro...

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“…Recently, several papers have shown that water uptake across the cuticle (i.e. aerial absorption) can be sufficient for a major increase of leaf and/or plant water potential (Ψ L ) [3,19,29]. In Pinus sylvestris the likely route for absorption is through the non-cuticularised surface below the needle sheath [22].…”

Section: Discussionmentioning

confidence: 99%

Xylem acoustic signals from mature Pinus sylvestris during an extended drought

2004

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-Mature Scots pine (Pinus sylvestris L.) were subjected to an 11 month imposed soil drought, from November 1994. Control plots received rainfall plus irrigation. The extent of cavitation in the xylem of branches and boles was compared using ultrasonic acoustic emission (UAE) measurements. Supporting measurements of the relative water content (R w ) of the bole and shoot were recorded. Acoustic emissions were detected in both treatments. An effect of water-stress, in both boles and branches, at the height of the drought, was noted. Differences in vulnerability were found and suggest a reduced vulnerability to cavitation of remaining functional conduits, after loss of the most vulnerable conduits, in the water-stressed trees. Bole R w was lower than branch R w . In 1-year-old shoots of droughted trees a significant increase in xylem embolism was found. Seasonal changes in shoot R w were interpreted as the occurrence and recovery (refilling) of emboli in xylem tissues: an active role of precipitation is hypothesised. It was estimated that 15% of tracheids were cavitated without affecting above-ground hydraulic resistances. It is suggested that runaway cavitation was avoided through stomatal closure maintaining leaf water potential (indicative of xylem tension) below the cavitation threshold, and thereby little effect of drought was evident in above ground tissues. Les émissions acoustiques ont été détectées dans les deux traitements. L'effet du stress hydrique a été noté sur branches et fûts au stade du pic de sécheresse. Sur les arbres soumis à stress hydrique, on a mis en évidence des différences de vulnérabilité à la cavitation ; les vaisseaux encore fonctionnels apparaissent moins vulnérables après la perte des plus vulnérables. Le Rw des troncs était inférieur à celui des branches. On a constaté une augmentation du phénomène d'embolie dans les pousses de 1 an des arbres soumis à la sécheresse. Les changements saisonniers de Rw des pousses ont été interprétés comme étant une conséquence du bon rétablissement du remplissage des vaisseaux des tissus du xylème frappé d'embolie. L'hypothèse d'un rôle actif des précipitations a été avancée. On a estimé que le phénomène de cavitation a affecté 15 % des trachéides sans que les résistances hydrauliques dans les parties aériennes soient affectées. Il est suggéré que la cavitation généralisée était évitée grâce à la fermeture des stomates permettant de maintenir le potentiel hydrique des feuilles (indicateur de la tension du xylème) au dessous du seuil de cavitation, avec comme conséquence un faible effet de la sécheresse sur les tissus situés au dessous du sol. Pinus sylvestris (pin sylvestre) / émissions acoustiques ultrasoniques / cavitation du xylem / TDR

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Uptake of water and solutes through twigs of Picea abies (L.) Karst

Cited by 96 publications

References 19 publications

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

Winter at the Alpine Timberline. Why Does Embolism Occur in Norway Spruce But Not in Stone Pine?

Xylem acoustic signals from mature Pinus sylvestris during an extended drought

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