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Water retained on tree leaves after rainfall, dew, or fog impacts transpiration. To determine the impact of leaf retained water (LRW) on the transpiration of trees, the difference between transpiration rates of different species with and without water sprayed on the leaves was measured. Results show that transpiration was inhibited by LRW. Both the inhibition extent and duration of LRW were higher on broadleaf species than on coniferous species. Under conditions of saturated LRW of the tree crown, mean transpiration inhibition rates of the test species were 0.32 (Quercus mongolica Fisch. ex Ledeb.), 0.25 (Acer mono), 0.37 (Tilia amurensis Rupr.), 0.31 (Fraxinus mandshurica Rupr.), 0.22 (Pinus koraiensis Siebold & Zucc.), 0.22 (Abies nephrolepis (Trautv. ex Maxim.) Maxim.), and 0.23 (Picea asperata Mast.). Mean inhibition rate and inhibition time for broadleaf species were 0.31 and 115 min, which were 40% higher and 27 min longer than those for coniferous species, respectively. The transpiration inhibition rate of LRW increased linearly with the LRW amount, and there was a higher transpiration inhibition rate in broadleaf species than in coniferous species for the same amount of LRW. Mean rising velocity of the inhibition with LRW amount for broadleaf species was 0.53%, whereas it was only 0.15% for the coniferous species. Key words: temperate tree species, leaf retained water, transpiration inhibition. L'eau retenue sur les feuilles des arbres apportee par la pluie, la rosee ou le brouillard a un impact sur la transpiration. Pour determiner l'impact sur la transpiration des arbres de l'eau retenue sur les feuilles (ERF), la difference entre le taux de transpiration apres avoir ou non pulverise de l'eau sur les feuilles de differentes especes a ete mesuree. Les resultats montrent que la transpiration est inhibee par l'ERF. Tant l'ampleur de l'inhibition que la persistance de l'ERF etaient plus elevees chez les feuillus que chez les coniferes. Lorsque que la cime des arbres etait saturee par l'ERF, le taux moyen d'inhibition de la transpiration des especes testees atteignait 0,32 (Quercus mongolica Fisch. ex Ledeb.), 0,25 (Acer mono), 0,37 (Tilia amurensis Rupr.), 0,31 (Fraxinus mandshurica Rupr.), 0,22 (Pinus koraiensis Siebold & Zucc.), 0,22 (Abies nephrolepis (Trautv. ex Maxim.) Maxim.) et 0,23 (Picea asperata Mast.). Chez les feuillus, le taux moyen et la duree moyenne de l'inhibition etaient de 0,31 et 115 min, soit respectivement 40 % plus eleve et 27 min plus longue que chez les coniferes. Le taux d'inhibition de la transpiration de l'ERF augmentait lineairement avec la quantite d'ERF et le taux d'inhibition de la transpiration etait plus eleve chez les feuillus que chez les coniferes pour la meme quantite d'ERF. L'augmentation moyenne de la vitesse d'inhibition en fonction de la quantite d'ERF atteignait 0,53 % chez les feuillus mais seulement 0,15 % chez les coniferes. [Traduit par la Redaction] Mots-cles: especes d'arbres des zones temperees, eau retenue sur les feuilles, inhibition de la transpiration., Introduction Tree transpiration is a critical component of land surface evapo-transpiration (Baldocchi et al. 1991; Yang et al. 1997; Amarakoon et al. 2000). To understand changes in forest water resources, [...]

Atmospheric nitrogen (N) deposition has been observed to impact plant structure and functional traits in terrestrial ecosystems. Although the effect of N deposition on plant water use has been well-evaluated in laboratories and in experimental forests, the linkages between water and carbon relations under N deposition are unclear. Here, we report on hydraulics, gas exchange and carbon reserves of two broad-leaved tree species (Quercus mongolica and Fraxinus mandshurica) in mature temperate forests after a seven-year experiment with different levels of N addition (control (CK), low (23 kg N ha−1 yr−1), medium (46 kg N ha−1 yr−1) and high (69 kg N ha−1 yr−1)). We investigated variation in hydraulic traits (xylem-specific hydraulic conductivity (K s), native percentage loss of conductivity (PLC) and leaf water potential), xylem anatomy (vessel diameter and density), gas exchange (maximum net photosynthesis rate and stomatal conductance) and carbon reserves (soluble sugars, starch and total nonstructural carbohydrates (NSC)) with different N addition levels. We found that medium N addition significantly increased K s and vessel diameter compared to control, but accompanied increasing PLC and decreasing leaf water potential, suggesting that N addition results in a greater hydraulic efficiency and higher risk of embolism. N addition promoted photosynthetic capacity via increasing foliar N concentration but did not change stomatal conductance. In addition, we found increase in foliar soluble sugar concentration and decrease in starch concentration with N addition, and positive correlations between hydraulic traits (vessel diameter and PLC) and soluble sugars. These coupled responses of tree hydraulics and carbon metabolism are consistent with a regulatory role of carbohydrates in maintaining hydraulic integrity. Our study provides an important insight into the relationship of plant water transport and carbon dynamics under increasing N deposition. [ABSTRACT FROM AUTHOR]

Drought and nitrogen (N) addition have been shown to affect tree hydraulic traits, but few studies have been made on their interactions across species with different wood types or leaf forms. We examined the responses of hydraulic conductance and xylem anatomical traits of Quercus mongolica (ring porous with simple leaves), Fraxinus mandshurica (ring porous with compound leaves) and Tilia amurensis (diffuse porous with simple leaves) to drought, N addition and their interactions. Drought stress decreased current-year xylem-specific conductivity in stems (K sx) and leaf hydraulic conductance (K leaf), but N addition affected K sx and K leaf differently among species and watering regimes. These divergent effects were associated with different responses of anatomical traits and leaf forms. Higher mean vessel diameter in stems and lower vessel density in leaves were observed with N addition. The three-way interactive effects of drought, N addition and tree species were significant for most values of anatomical traits. These results were also reflected in large differences in vessel diameter and density among species with different wood types or leaf forms. The two-way interactive effects of drought and N addition were significant on K leaf and predawn water potential, but not K sx, indicating that leaves were more sensitive than stems to a combination of drought stress and N addition. Our results provide mechanistic insight into the variable responses of xylem water transport to the interactions of drought and N availability. [ABSTRACT FROM AUTHOR]

To promote the awareness of Priestley–Taylor (PT) model and extend the knowledge of hydrological model under snow, performance of PT model was illustrated by comparing with eddy covariance (EC) measurements over a temperate meadow. The results showed that the mean half‐hourly averages and directly calculated daily value of PT parameter α is 0.47 ± 0.27 and 0.51 ± 0.32, respectively. Vapour pressure deficit VPD is the mainly factor influences α in the snow‐covered period, while soil moisture in the snow‐free period. PT method underestimated evaporation in the whole study period and showed remarkable difference in different phases. It performed best in the snow‐melting phase, better in the presnow phase, worse in the fresh snow phase and worst in the snow‐melted phase. These studies indicated that PT model could be used to estimate evaporation over temperate meadow in dormant season, but utility of a variable PT parameter α during different phases should be considered. [ABSTRACT FROM AUTHOR]