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The Soil-Plant-Atmosphere (SPA) Model. Multilayer canopy and soils, 30 minute time-step Standard components Radiative transfer scheme (sun/shade) Soil water and heat transfer Surface energy balance and evaporation (soil/leaf) Farquhar model of photosynthesis Novel components
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The Soil-Plant-Atmosphere (SPA) Model • Multilayer canopy and soils, 30 minute time-step • Standard components • Radiative transfer scheme (sun/shade) • Soil water and heat transfer • Surface energy balance and evaporation (soil/leaf) • Farquhar model of photosynthesis • Novel components • Fully coupled liquid and vapour phase water fluxes • Dynamic modelling of soil and leaf water potential (LWP)_ • Plant capacitance • Stomatal conductance operates to regulate LWP.
Input/output • Key parameters: LAI, photosynthetic parameters (Farquhar), soil and plant hydraulic conductance, soil water release curves • Key drivers: air temperature, precip, VPD, irradiance, atmos. CO2 • Key outputs: GPP, LE (soils, water surfaces and plant transpiration), gs, LWP, soil moisture and temperature
CO2 Atmosphere gs E Leaf Yl Rp Stem C Rs1 Rr1 Roots Ys1 Rs2 Rr2 Ys2 Rsn Rrn Ysn Soil Plant Root resistance (Rr) Plant resistance (Rp) Soil resistance (Rs) Soil water potential (Yl)
SPA Applications • Existing studies • Temperate deciduous forest (Williams et al 1996, Engel et al 2002) • Pine forest, Oregon (Law et al 2000, Williams et al 2001 a, b, Schwarz et al 2004) • Amazonia (Williams et al 1998, Fisher et al 2006, 2007) • Arctic tundra, Alaska (Williams et al 2000, Van Wijk et al 2003) • Current studies • Boreal forests, Canada – T Hill et al (submitted) • Australia, Eucalyptus – D Eamus et al (submitted) • Spain, Oak – J Martinez (in prep) • Crops, temperate zones (Oli Sus, PhD student)