Direct Penman–Monteith parameterization for estimating stomatal conductance and modeling sap flow

Abstract

The Penman-Monteith equation of evaporation is often combined with sap flow measurements to describe canopy transpiration and stomatal conductance. The traditional approach involves a two-step calculation. In the first step, stomatal conductance is computed using an inverted form of Penman-Monteith equation. The second step correlates these values with environmental factors. In this work, we present an improved approach for direct parameterization of the Penman-Monteith equation developed to compute diurnal courses of stand canopy conductance (gc) from sap flow. The main advantages of this proposed approach versus using the classical approach are: (1) the calculation process is faster and involves fewer steps, (2) parameterization provides realistic values of canopy conductance, including conditions of low atmospheric vapor pressure deficit (D) whereas the traditional approach tends to yield unrealistic values for low D and (3) the new calculation method does not require enveloping curves to describe dependence of gc on D and thus avoids subjective data selection but it still allows to visualize separable responses of gc to environmental drivers (i.e. global radiation and vapor pressure deficit). The proposed approach was tested to calculate gc and to model the sap flow of a high mountain Pinus canariensis forest. The new calculation method permitted us to describe the stand canopy conductance and stand sap flow in sub-hour resolution for both day and night conditions. Direct parameterization of the Penman-Monteith approach as implemented in this study proved sufficiently sensitive for detecting diurnal variation in gc and for predicting sap flow from environmental variables Manuscript Click here to download Manuscript JU_stomata_161005.doc Click here to view linked References 2 under various atmospheric evapotranspirative demands and differing levels of soil water availability.

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

“…The stomatal conductance is controlled by stomatal aperture in response to the availability of energy, carbon, and water in soil [14,17]. Considering the impact of multiple environmental factors on stomatal conductance, this study adopted the Jarvis-Stewart model [43,44], which consists of multiplicative nonlinear functions of environmental variables [19,20,43,45]:…”

“…The measured sap flow rate of individual trees can upscale to an experimental area to provide species-specific transpiration rates, which can be used to inversely estimate the response of g c to multiple environmental stresses during a continuous time span. Kucera et al [17] used a novel approach where a direct parameterization of the Penman-Monteith equation was developed to compute the diurnal courses of stand canopy conductance from sap flow. Previous studies also showed that the inversely estimated g c commonly shows complex patterns that are intimately related to meteorological variables (i.e., solar radiation, wind speed, the concentration of carbon dioxide in air, air humidity, and temperature), and soil moisture stress [12,[18][19][20].…”

Input-Output Budgets of Nutrients in Adjacent Norway Spruce and European Beech Monocultures Recovering from Acidification

“…Tree sap flow was measured by the tissue heat balance method with constant heating power (EMS; Brno, Czech Republic). The scaling up of sap flow from sample trees to the stand level was based on the DBH distribution of the trees in each forest stand [33].…”

Drought and irrigation affect transpiration rate and morning tree water status of a mature European beech (Fagus sylvatica L.) forest in Central Europe

“…On average, transpiration accounts for 39% of terrestrial precipitation and for 61% of evapotranspiration (Schlesinger & Jasechko, ). This means that most water evaporation from ecosystems passes through the plant, with its precise amount being regulated by vegetation (Kučera, Brito, Jiménez, & Urban, ). Transpiration is an important loss term of the water balance (Jasechko et al, ), and in forest ecosystems, it plays a significant role in the production of biomass (Kool et al, ).…”

“…On average, transpiration accounts for 39% of terrestrial precipitation and for 61% of evapotranspiration (Schlesinger & Jasechko, 2014). This means that most water evaporation from ecosystems passes through the plant, with its precise amount being regulated by vegetation (Kučera, Brito, Jiménez, & Urban, 2016).…”