A Canopy Transpiration Model Based on Scaling Up Stomatal Conductance and Radiation Interception as Affected by Leaf Area Index

Abstract

Estimating transpiration as an individual component of canopy evapotranspiration using a theoretical approach is extremely useful as it eliminates the complexity involved in partitioning evapotranspiration. A model to predict transpiration based on radiation intercepted at various levels of canopy leaf area index (LAI) was developed in a controlled environment using a pasture species, tall fescue (Festuca arundinacea var. Demeter). The canopy was assumed to be a composite of two indistinct layers defined as sunlit and shaded; the proportion of which was calculated by utilizing a weighted model (W model). The radiation energy utilized by each layer was calculated from the PAR at the top of the canopy and the fraction of absorbed photosynthetically active radiation (fAPAR) corresponding to the LAI of the sunlit and shaded layers. A relationship between LAI and fAPAR was also established for this specific canopy to aid the calculation of energy interception. Canopy conductance was estimated from scaling up of stomatal conductance measured at the individual leaf level. Other environmental factors that drive transpiration were monitored accordingly for each individual layer. The Penman–Monteith and Jarvis evapotranspiration models were used as the basis to construct a modified transpiration model suitable for controlled environment conditions. Specially, constructed self-watering tubs were used to measure actual transpiration to validate the model output. The model provided good agreement of measured transpiration (actual transpiration = 0.96 × calculated transpiration, R2 = 0.98; p < 0.001) with the predicted values. This was particularly so at lower LAIs. Probable reasons for the discrepancy at higher LAI are explained. Both the predicted and experimental transpiration varied from 0.21 to 0.56 mm h−1 for the range of available LAIs. The physical proportion of the shaded layer exceeded that of the sunlit layer near LAI of 3.0, however, the contribution of the sunlit layer to the total transpiration remains higher throughout the entire growing season.

From Selfies to Science – Precise 3D Leaf Measurement with iPhone 13 and Its Implications for Plant Development and Transpiration

“…12). This finding aligns with existing knowledge, as transpiration is a fundamental process in plants, regulating water uptake and nutrient transport and is directly affected by canopy area [14].…”

Canopy Height and Climate Dryness Parsimoniously Explain Spatial Variation of Unstressed Stomatal Conductance

“…The cut‐off point of LAI = 6 was used to account for the nonlinear scaling between stomata and canopy conductances due to shading in dense canopy (Alam et al., 2021; Granier et al., 2000; Novick et al., 2009). Lastly, the unstressed stomatal conductance ( g s , u ) was quantified as the 90th percentile of the g s time series satisfying all the filters described above at each site.…”

Mixed nitrate and ammonium supply improves maize growth and leaf water status by regulating concentration ratios of phytohormones in the xylem sap

“…Stomatal conductance was measured using an AP4 Porometer (AP4-UM-3, Delta -T Devices Ltd, Cambridge, UK) according to Alam (2021). The measurements were performed between 12:00 and 15:00 on the day before the harvest.…”