Abstract
Quantifying the impact of natural and anthropogenic disturbances such as deforestation, forest fires and vegetation thinning among others on net ecosystem—atmosphere exchanges of carbon dioxide, water vapor and heat—is an important aspect in the context of modeling global carbon, water and energy cycles. The absence of canopy architectural variation in horizontal and vertical directions is a major source of uncertainty in current climate models attempting to address these issues. This manuscript demonstrates the importance of considering the vertical distribution of foliage density by coupling a leaf level plant biophysics model with analytical solutions of wind flow and light attenuation in a horizontally homogeneous canopy. It is demonstrated that plant physiological response in terms of carbon assimilation, transpiration and canopy surface temperature can be widely different for two canopies with the same leaf area index (LAI) but different leaf area density distributions, under several conditions of wind speed, light availability, soil moisture availability and atmospheric evaporative demand.
Highlights
Carbon, water and biogeochemical cycles of forest ecosystems are critically important in determining Earth’s energy balance
The first one is top heavy—meaning most of the foliage are concentrated at the top and the other one is bottom heavy—meaning most of the foliage are concentrated at the bottom, representing two end cases of foliage distribution
We investigated the effect of vertical canopy architecture variation on plant physiological response. large scale climate models often use a big-leaf approximation, ignoring the three dimensional structural variation of the canopy
Summary
Water and biogeochemical cycles of forest ecosystems are critically important in determining Earth’s energy balance. During drought-like conditions, the marginal water use efficiency will increase and the combination of low soil moisture availability and higher vapor pressure deficit (VPD) reduces stomatal conductance further (on top of reduced stomatal conductance from elevated CO2 ) This could lead to negative carbon balances for individual leaves causing the plant to shed leaves (called ‘leaf-out’) and reduce LAI [13]. The current work uses such a model which can solve plant atmosphere exchange processes at the leaf level and systematically explores the effect of vertical canopy architectural variation on canopy transpiration, carbon uptake and thermoregulation. The variations of plant physiological response for the same canopy LAI but with different LAD distributions across a multitude of water supply and demand conditions will highlight the importance of capturing canopy architecture in models aimed at quantifying ecosystem-atmosphere interaction
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