Abstract
As changes in air temperature, precipitation, and air humidity are expected in the coming decades, studies on the impact of these environmental shifts on plant growth and functioning are of major importance. Greatly understudied aspects of climate change include consequences of increasing air humidity on forest ecosystems, predicted for high latitudes. The main objective of this study was to find a link between hydraulic acclimation and shifts in trees’ resource allocation in silver birch (Betula pendula Roth) in response to elevated air relative humidity (RH). A second question was whether the changes in hydraulic architecture depend on tree size. Two years of application of increased RH decreased the biomass accumulation in birch saplings, but the biomass partitioning among aboveground parts (leaves, branches, and stems) remained unaffected. Increased stem Huber values (xylem cross-sectional area to leaf area ratio) observed in trees under elevated RH did not entail changes in the ratio of non-photosynthetic to photosynthetic tissues. The reduction of stem–wood density is attributable to diminished mechanical load imposed on the stem, since humidified trees had relatively shorter crowns. Growing under higher RH caused hydraulic conductance of the root system (KR) to increase, while KR (expressed per unit leaf area) decreased and leaf hydraulic conductance increased with tree size. Saplings of silver birch acclimate to increasing air humidity by adjusting plant morphology (live crown length, slenderness, specific leaf area, and fine-root traits) and wood density rather than biomass distribution among aboveground organs. The treatment had a significant effect on several hydraulic properties of the trees, while the shifts were largely associated with changes in tree size but not in biomass allocation.
Highlights
For Europe, climate change is predicted to bring about both a decrease as well as increase in precipitation and environmental humidity (IPCC, 2013)
Since stem–wood density did not depend on aboveground biomass distribution, the second hypothesis − the reduction of wood density of trees grown under high relative humidity (RH) is associated with biomass distribution − remained unproven
The variation in mean branch-wood density (Sellin et al, 2013) is attributable to the mechanical load subjected to the branch axis and is related to branch-level resource allocation
Summary
For Europe, climate change is predicted to bring about both a decrease (southern and central Europe) as well as increase (northern Europe) in precipitation and environmental humidity (IPCC, 2013). Many studies have proven that drought significantly reduces tree diameter increment across mid- and southern-Europe (Pasho et al, 2012; Weemstra et al, 2013; Lévesque et al, 2014), and even low air relative humidity (RH) alone results in declined productivity and biomass of European beech (Lendzion and Leuschner, 2008). The knowledge of the influence of increased precipitation or air humidity on tree growth allocation and the concurrent hydraulic acclimation is much more limited. More experimental research in tree carbon allocation and storage under environmental stress in relation to global change is needed (Niinemets, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
