Variation in hydraulic architecture of Picea abies (L.) Karst. trees grown under different environmental conditions

http://www.ester.ee/record=b1065879~S1*es

Within-crown variation in leaf conductance of Norway spruce: effects of irradiance, vapour pressure deficit, leaf water status and plant hydraulic constraints

Responses of leaf conductance (gL) to variation in photosynthetic photon flux density, leaf-to-air vapour pressure difference, shoot water potential and soil-to-leaf hydraulic conductance (GT) were studied in Picea abies (L.) Karst. foliage with respect to shoot age and position within the canopy. The upper canopy shoots demonstrated on average 1.6 times higher daily maximum gL as compared to the lower canopy shoots growing in the shadow of upper branches. Functional acclimation of the shade foliage occurred in the form of both a steeper initial slope of the light-response curve and a lower light-saturation point of gL. The mean GT was 1.6–1.8 times bigger for the upper canopy compared to the lower canopy. We set up an hypothesis that stomatal conductance at the base of the live crown is constrained not only by low light availability but also by plant’s inner hydraulic limitations.Variation de la conductance foliaire dans les couronnes de l’Epicea : effets de l’éclairement, du déficit de vapeur d’eau dans l’air, de l’état hydrique des feuilles et des contraintes hydrauliques des arbres. Les réponses de la conductance foliaire (gL) aux variations de la densité de flux photosynthétique de photons, du déficit de saturation de l’air, du potentiel hydrique des rameaux et de la conductance hydraulique (GT) dans le transfert Sol-feuille ont été étudiées chez Picea abies (L) Karst. En relation avec l’âge des rameaux et leur position dans la canopée. Les rameaux de la partie supérieure de la canopée présentent des valeurs journalières maximum moyennes de gL1,6 fois plus élevées que les valeurs correspondantes de gL des rameaux des parties basses de la canopée se développant à l’ombre des branches les plus hautes. Une acclimatation fonctionnelle du feuillage à l’ombre se manifeste par une pente initiale plus élevée de la courbe de réponse à la lumière et un point de saturation de gL plus bas. La moyenne de GT était de 1,6 à 1,8 fois plus grande pour la partie basse de la canopée. Nous avançons l’hypothèse que la conductance stomatique à la base de la couronne vivante est conditionnée par les bas niveaux de lumière disponible mais aussi par les limitations hydrauliques internes de l’arbre

Does elevated air humidity modify hydraulically relevant anatomical traits of wood in Betula pendula?

We studied responses of wood anatomical traits in silver birch (Betula pendula) to artificially elevated air humidity to simulate a climate trend predicted for northern latitudes. The study was performed on saplings growing at Free Air Humidity Manipulation (FAHM) site, eastern Estonia, with the long-term mean relative air humidity (RH) increased by 7% over the ambient level. The humidification treatment did not significantly affect xylem traits or specific hydraulic conductivity, confirming a conservative nature of the wood anatomical structure with respect to air humidity. Only wood density decreased in response to elevated RH. The reduced atmospheric evaporative demand had a weak effect on the development of the plant water-conducting system in moderately humid climates in the northern temperate zone under conditions of ample soil water availability. The wood anatomical traits of both branches and main stems varied substantially with canopy position, with larger height effects in main stems. In main stems, vessel hydraulic diameter and theoretical (kt) and specific conductivities (ks) of the xylem decreased in the apical direction. In contrast, upper-crown branches had wider vessels and a bigger vessel relative area that resulted in kt and ks both increasing from the crown base upward. Vessel size and xylem hydraulic efficiency were positively associated with radial growth rate of stems

Coppicing improves the growth response of short-rotation hybrid aspen to elevated atmospheric humidity

Aspens are fast-growing clonal trees with a wide circumboreal distribution range, suitable for the production of pulp and bioenergy. The adaptability of aspen short-rotation coppice systems to climate change has rarely been investigated. For a large part of aspens' northern range, climate models predict an increase in precipitation and, consequently, in atmospheric humidity. Our aim was to clarify the long-term effect of elevated air humidity on vegetative reproduction capacity and dynamics of above-ground growth and size structure in aspen stands. We analysed tree growth data from two consecutive 6-year rotations (a planted and a coppice generation) in experimental short-rotation hybrid aspen (Populus tremula L. x P. tremuloides Michx.) stands in the Free Air Humidity Manipulation (FAHM) experiment in Estonia. In three plots, mean relative air humidity was elevated by 7% and three plots were controls. Across two rotation periods, the humidification effect on tree height and/or stem basal area increment was year-dependent (p < 0.001): negative in 4 years, positive also in 4 years and non-significant in 3 years. Mean basal area of humidified (11.6 +/- 0.8 cm(2)) and control trees (15.0 +/- 1.0 cm(2)) differed significantly (p = 0.035) at the end of the first but not the second rotation period (9.3 +/- 0.9 cm(2) and 9.3 +/- 1.2 cm(2), respectively). Average growth differences levelled out already in the beginning of the second rotation, suggesting that some root-level acclimation must have taken place. The annual size-growth relationships (SGR) indicated a more size-symmetric growth in humidified (SGR = 1.00 +/- 0.05) and a size-asymmetric growth (SGR = 1.12 +/- 0.04) in control stands, implying a greater role of root-competition in humidified stands. In humidified stands, the growth of re-sprouting trees was more strongly determined by parent tree size, indicating a stronger carry-over of size hierarchy. The tree height diversity fluctuated more in control stands, where mortality was higher, especially after dry years. To summarise, short- and long-term responses of hybrid aspen to elevated air humidity varied, emphasizing the importance of long-term climate manipulations with trees. Generally, hybrid aspen short-rotation coppice forests showed promising acclimation capacity with future more humid climate predicted for northern latitudes

Leaf and Branch Hydraulic Plasticity of Two Light-Demanding Broadleaved Tree Species Differing in Water-Use Strategy

International audienceGlobal climate change creates new environmental scenarios and selective pressures; thus, a better understanding of the plasticity of plant functional traits is needed to predict how plant species will respond to shifts in climate. Among the important functional traits for plants are their hydraulic properties which ultimately determine their photosynthetic capacity, growth rate, and survival in a changing environment. In this study, the light sensitivity of leaf (KL) and branch hydraulic conductance (KB) to fast changes in irradiance, and hydraulic plasticity (PIh) was studied in two broadleaved tree species differing in water-use strategy-silver birch (Betula pendula) and hybrid aspen (Populus × wettsteinii). The KL increased by a factor of 3.5 and 1.5 from minimal values recorded in darkness to maximal values in high light conditions for birch and aspen, respectively, indicating a significantly higher PIh for birch (0.72) than for aspen leaves (0.35). KB increased 1.5fold from dark to light conditions for both species. The high light sensitivity of KL and KB provides a regulatory mechanism to maintain a balance between transpirational demand and hydraulic supply. The plasticity of these traits increases the ability of plants to cope with a rapidly changing environment and to adapt to global climate change

Variation in nocturnal stomatal conductance and development of predawn disequilibrium between soil and leaf water potentials in nine temperate deciduous tree species

It is widely acknowledged that many plant species can keep stomata open during night. We examined how nocturnal stomatal conductance differs among potted saplings of nine temperate tree species from diverse native habitats in wet and dry soil conditions, and how it affects plant predawn water status. Nocturnal stomatal conductance in dry soil conditions was low in all the species (with a maximum value of 14.6 mmol m(-2) s(-1)); in wet conditions, it was the highest in Populus tremula L., a fast-growing and anisohydric pioneer species, and the lowest in Quercus robur L., a late-successional and isohydric species. Relatively high nocturnal stomatal conductance in wet conditions in P. tremula compared with the other species resulted in the highest difference in water potential values between the leaves and soil at predawn. As drought progressed, different species tended to keep stomata almost closed at night, and the observed differences between anisohydric and isohydric species disappeared. At an ample soil water supply, nocturnal stomatal behaviour was species dependent and varied according to both the water-use and the life strategies of the species. Keeping that in mind, one should therefore be careful when using predawn leaf water potential as a proxy for soil water potential, sampling different species

Long-term effect of elevated air humidity on seasonal variability in diurnal leaf conductance and gas exchange in silver birch

Environmental conditions and photoperiod length drive the seasonal variability of gas exchange in plants. Still, little is known about trees’ adaptation to climate change, expressed as a delay in decreasing photosynthetic capacity at the end of the growing season. We investigated the effect of elevated air humidity (RH) and sampling period (from July to September) on the variability of net photosynthesis (An), dark respiration (R), daytime (gl_day) and night-time (gl_night) leaf conductance, an index of leaf chlorophyll content (SPAD) and An:SPAD ratio in cut shoots of silver birch. Measurements of cut shoots were conducted in a climate chamber to eliminate the direct effect of field conditions. The An, An:SPAD ratio and gl_day were higher in the humidification (H) than in the control (C) treatment (PThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

“Diminishing returns” in the scaling of functional leaf traits across and within species groups

More than 5,000 measurements from 1,943 plant species were used to explore the scaling relationships among the foliar surface area and the dry, water, and nitrogen/phosphorus mass of mature individual leaves. Although they differed statistically, the exponents for the relationships among these variables were numerically similar among six species groups (ferns, graminoids, forbs, shrubs, trees, and vines) and within 19 individual species. In general, at least one among the many scaling exponents was <1.0, such that increases in one or more features influencing foliar function (e.g., surface area or living leaf mass) failed to keep pace with increases in mature leaf size. Thus, a general set of scaling relationships exists that negatively affects increases in leaf size. We argue that this set reflects a fundamental property of all plants and helps to explain why annual growth fails to keep pace with increases in total body mass across species