Ecohydrological Behaviour of Mountain Beech Forest: Quantification of Stomatal Conductance Using Sap Flow Measurements

Abstract

In forested regions, transpiration as a main component of evaporation fluxes is important for evaporation partitioning. Physiological behaviours among various vegetation species are quite different. Thus, an accurate estimation of the transpiration rate from a certain tree species needs specific parameterization of stomatal response to multiple environmental conditions. In this study, we chose a 300-m2 beech forest plot located in Vydra basin, the Czech Republic, to investigate the transpiration of beech (Fagus sylvatica) from the middle of the vegetative period to the beginning of the deciduous period, covering 100 days. The sap flow equipment was installed in six trees with varying ages among 32 trees in the plot, and the measurements were used to infer the stomatal conductance. The diurnal pattern of stomatal conductance and the response of stomatal conductance under the multiple environmental conditions were analysed. The results show that the stomatal conductance inferred from sap flow reached the highest at midday but, on some days, there was a significant drop at midday, which might be attributed to the limits of the hydraulic potential of leaves (trees). The response of stomatal conductance showed no pattern with solar radiation and soil moisture, but it did show a clear correlation with the vapour deficit, in particular when explaining the midday drop. The relation to temperature was rather scattered as the measured period was in the moderate climate. The findings highlighted that the parametrization of stress functions based on the typical deciduous forest does not perfectly represent the measured stomatal response of beech. Therefore, measurements of sap flow can assist in better understanding transpiration in newly formed beech stands after bark beetle outbreaks in Central Europe.

Leveraging sap flow data in a catchment-scale hybrid model to improve soil moisture and transpiration estimates

“…Regardless, the spearman rank correlation between gcJarvis and gcsap is 0.85 and the rmse is 0.01 m s -1 . The gcsap estimates are within a reasonable range for a beech-dominated temperate forests and comparable to literature values using a similar approach (inverse Penman-Monteith equation) based on six beech trees in the Czech Republic (Su et al 2019). Differences between gcJarvis and gcsap are also reflected, although weaker, in the monthly transpiration estimates (Fig.…”

“…gcsap is about twice as high in June compared to August and shows a stronger decline in conductance during midday in July and August. While such patterns are typical for humid forests under dry conditions(Su et al, 2019), they are not or only weakly captured by the Jarvis-Stewart model (gcJarvis), which suggests a relatively constant conductance during day time. As already indicated by the high correlation between gcDL and gcsap, the former also captures the dynamics of the diurnal cycles well.…”

A modified Jarvis model to improve the expressing of stomatal response in a beech forest

“…and Woodrush ( Luzula ). In 2013, the bark beetle outbreak caused the extinction of large fractions of spruce (Su et al, 2019). The sap flow experiment was conducted after the infestation when the land cover of the experimental site transited to a nearly homogeneous single‐species beech forest, allowing to investigate the transpiration mechanism of the beech forest.…”

“…The sap flow experiment, following the study bySu et al (2019), was conducted for a square area (30 Â 30 m) containing 32 beechF I G U R E 1 (a)Sketch of the study site with a mild slope angle of 3.5 ; (b) soil condition at different depths; (c) Soil texture based on the WRB classification: <0.002 mm clay particles, 0.002-0.05 mm slit particles, and 0.05-2 mm sand particles and water retention curves measured at depth 20 cm (Bvs) and 60 cm (B/C) below the soil surface.…”

TRANSPIRATION OF OIL PALM (Elaeis guineensis Jacq.) BASED ON SAP FLOW MEASUREMENT: THE RELATION TO SOIL AND CLIMATE VARIABLES

“…These findings were similar to the previous studies that described a decrease in transpiration of oil palm when VPD was 1.7-2.0 kPa (Carr, 2011;Meijide et al, 2017;Waite et al, 2019). A decrease in transpiration rate is closely associated with stomatal conductance (g s ), where the high value of VPD (Hernandez et al, 2016;Ocheltree et al, 2014;Su et al, 2019) or Qs (Francesconi et al, 1997;Massonnet et al, 2007) cause a depression in the stomatal conductance. Li et al (2019a) added that the concentration of phytohormones, i.e., abscisic acid (ABA), in leaf was correlated positively with the sensitivity of stomata conductances to VPD.…”