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. CO 2 Key outputs: GPP, LE (soils, water surfaces and plant transpiration), g s, LWP, soil moisture and temperature

Rs2Rs2 RpRp R sn R s1 C s1s1 snsn s2s2 E R r1 R r2 R rn Plant Soil Atmosphere CO 2 gsgs Leaf Stem Roots ll Root resistance (R r ) Plant resistance (R p ) Soil resistance (R s ) Soil water potential (  l )

Predicting seasonal behaviour in a deciduous forest

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)