The influence of soil temperature and water content on belowground hydraulic conductance and leaf gas exchange in mature trees of three boreal species

• Published in: Plant, cell and environment Vol. 43; no. 3; pp. 532 - 547
• Main Authors: Lintunen, Anna, Paljakka, Teemu, Salmon, Yann, Dewar, Roderick, Riikonen, Anu, Hölttä, Teemu
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.03.2020; Wiley Subscription Services, Inc
• Subjects: Alnus - physiology; belowground hydraulic conductance; cold; Conductance; Correlation analysis; Dependence; Diameters; Environmental changes; Environmental conditions; Environmental impact; Gas exchange; Gases - metabolism; Hydraulics; Impact prediction; Leaves; Models, Biological; Moisture content; Optimization; Pine trees; Pinus - physiology; Plant Leaves - physiology; Plant Stems - physiology; point dendrometer; Resistance; sap flow; Soil; Soil environment; Soil temperature; Soil water; Soils; Species; Species Specificity; Stomata; stomatal control; Temperature; Tilia - physiology; Time Factors; Trees; Water - metabolism; Water content; water relations; Xylem; Xylem - physiology; sap flow; cold; water relations; stomatal control; belowground hydraulic conductance; point dendrometer
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1111/pce.13709

Understanding stomatal regulation is fundamental to predicting the impact of changing environmental conditions on vegetation. However, the influence of soil temperature (ST) and soil water content (SWC) on canopy conductance (gs) through changes in belowground hydraulic conductance (kbg) remains poorly understood, because kbg has seldom been measured in field conditions. Our aim was to (a) examine the dependence of kbg on ST and SWC, (b) examine the dependence of gs on kbg and (c) test a recent stomatal optimization model according to which gs and soil‐to‐leaf hydraulic conductance are strongly coupled. We estimated kbg from continuous sap flow and xylem diameter measurements in three boreal species. kbg increased strongly with increasing ST when ST was below +8°C, and typically increased with increasing SWC when ST was not limiting. gs was correlated with kbg in all three species, and modelled and measured gs were well correlated in Pinus sylvestris (a model comparison was only possible for this species). These results imply an important role for kbg in mediating linkages between the soil environment and leaf gas exchange. In particular, our finding that ST strongly influences kbg in mature trees may help us to better understand tree behaviour in cold environments. Soil temperature and water content are important factors influencing belowground hydraulic conductance and canopy conductance in mature boreal trees.