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

Abstract

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.

Terrestrial Laser Scanning Intensity Captures Diurnal Variation in Leaf Water Potential

“…Our results showed that a time-series of TLS intensity measurements can capture from 62 % to 78 % of the variation in ΨL. Our destructive ΨL measurements were complemented with estimated ΨL values that were based on stem diameter change measurements and existing knowledge on the time lag between the change in ΨL and stem diameter (Lintunen et al, 2020). The time lag of 90 minutes that we used is in line with earlier results (Sevanto et al, 2002).…”

Effects of Drought and Heat on Photosynthetic Performance, Water Use and Yield of Two Selected Fiber Hemp Cultivars at a Poor-Soil Site in Brandenburg (Germany)

“…Otherwise, stomatal inhibition of CO 2 gain seems to be the primary and initial control factor, as also may be reflected by the close relationship between both parameters observed for plants of both cultivars in the present study and reported by others (e.g., [21,50,64]. This, however, is quite obvious because of the direct control of stomatal conductance by soil water content, mediated by roots and the abscisic acid (ABA) concentration in the xylem as impressively shown by Bates and Hall [66] almost 40 years ago [67][68][69][70]. In this context, Gao et al [13] pointed out that ABA mediated stomatal but also plant developmental effects are important in the drought stress response of hemp.…”

Overview: Recent advances on the understanding of the Northern Eurasian environments and of the urban air quality in China - Pan Eurasian Experiment (PEEX) program perspective

“…A recent field and modelling study shows that cold soil decreases belowground hydraulic conductance (i.e. less root water uptake), and further canopy conductance in mature, boreal trees in spring (Lintunen et al 2020). Cold temperature also decreases sink strength (i.e.…”

“…Understanding stomatal regulation is fundamental in predicting the impact of changing environmental conditions on photosynthetic productivity. Lintunen et al (2020) showed that canopy conductance and soilto-leaf hydraulic conductance are strongly coupled, and that soil temperature and soil water content influences canopy conductance through changes in belowground hydraulic conductance. In particular, the finding that soil temperature strongly influenced belowground hydraulic conductance in mature, boreal trees may help to better understand tree behavior and photosynthetic productivity in cold environments.…”