Leaf structural and hydraulic adjustment with respect to air humidity and canopy position in silver birch (Betula pendula)

• Published in: Journal of plant research Vol. 132; no. 3; pp. 369 - 381
• Main Authors: Sellin, Arne, Taneda, Haruhiko, Alber, Meeli
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 01-05-2019; Springer Nature B.V
• Subjects: Air temperature; Betula - anatomy & histology; Betula - physiology; Betula pendula; Biomedical and Life Sciences; Canopies; Climate change; Conductance; Digital imaging; Environmental conditions; Foliage; Forests; Global climate; Humidity; Hydraulic properties; Hydraulics; Image processing; Laminates; Leaves; Life Sciences; Light microscopy; Plant Biochemistry; Plant Ecology; Plant Leaves - anatomy & histology; Plant Leaves - physiology; Plant Physiology; Plant Sciences; Plant Stomata - anatomy & histology; Plant Stomata - physiology; Plant Transpiration - physiology; Plants (botany); Precipitation; Rainfall; Regular Paper; Relative humidity; Resistance; Stomata; Transpiration; Trees - anatomy & histology; Trees - physiology; Trends; Water - metabolism; Vessel diameter; Stomatal density; Vascular bundle; Air humidity; Vein density; Leaf hydraulic conductance
• ISSN: 0918-9440; 1618-0860
• DOI: 10.1007/s10265-019-01106-w

Climate change scenarios predict an increase in air temperature and precipitation in northern temperate regions of Europe by the end of the century. Increasing atmospheric humidity inevitably resulting from more frequent rainfall events reduces water flux through vegetation, influencing plants’ structure and functioning. We investigated the extent to which artificially elevated air humidity affects the anatomical structure of the vascular system and hydraulic conductance of leaves in
Betula pendula
. A field experiment was carried out at the Free Air Humidity Manipulation (FAHM) site with a mean increase in relative air humidity (RH) by 7% over the ambient level across the growing period. Leaf hydraulic properties were determined with a high-pressure flow meter; changes in leaf anatomical structure were studied by means of conventional light microscopy and digital image processing techniques. Leaf development under elevated RH reduced leaf-blade hydraulic conductance and petiole conductivity and had a weak effect on leaf vascular traits (vessel diameters decreased), but had no significant influence on stomatal traits or tissue proportions in laminae. Both hydraulic traits and relevant anatomical characteristics demonstrated pronounced trends with respect to leaf location in the canopy—they increased from crown base to top. Stomatal traits were positively correlated with several petiole and leaf midrib vascular traits. The reduction in leaf hydraulic conductance in response to increasing air humidity is primarily attributable to reduced vessel size, while higher hydraulic efficiency of upper-crown foliage is associated with vertical trends in the size of vascular bundles, vessel number and vein density. Although we observed co-ordinated adjustment of vascular and hydraulic traits, the reduced leaf hydraulic efficiency could lead to an imbalance between hydraulic supply and transpiration demand under the extreme environmental conditions likely to become more frequent in light of global climate change.