Modelling the soil‐plant‐atmosphere continuum in a Quercus–Acer stand at Harvard Forest: the regulation of stomatal conductance by light, nitrogen and soil/plant hydraulic properties

Abstract

Quercus-Acer (oak-maple) st'.111d in c~ntral l\ l~1ssac~1u selts, US/\. The key hy pothesis J!OVe rnmg the b1oloA1cal component of the model is Urnt stomata! conductance (g,.) is var ied s o that d ail y carbon uptake per unit of foliar nit r oj:!en is maximized wit hin the limitations of ca1101>Y water avr1ilability. T he h ydraulic system is modelled as :m a nalo~ue to simple electr ical circuits in parallel. includinJ! a separate soil hydraulic resistance. plant resistance and plant capacitance for each c:m op y layer. Stomata! openin(! is initially controlled to conserve plant water stores and delay the o nset or water stress. Stomata! clos ure at :i threshold minimum l~1f water potential prevents xyle m cavitation and contr ols the maximum r:itc of wate r llux through the h ydraulic system. We show a strong correlat ion between predicted hourly C0 2 exchange rate (r2 = 0·86) and LE (r 2 = 0·87) with independent whole-forest measurements made by the eddy correlation method during the s ummer of 1992. Our theoretical derivation s hows that observed relationships between C0 2 assimilation a nd LE nux can he explained on the basis of s tomata! behaviour 01>timizing c:irhon gain, and provides mt exi>licit link hetwecn canopy structure, soil pro1>erties. atmos pheric conditions and stomatal conductance.Ke\'-111ords: Q11erc11s r11hm: l\cl'r rulnw11: soil-pla11t-a1r~10spherc coniinuum model: photosynlhcsis: plant hydr:1ulic conductance: s1o ma1al conduc tance.

Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought

“…It should also be cotnpared with calculations derived ft-otn a more rigorous modelling scheme. At present, theoretical methods exist that adjust g^ accot-ding to an optimal use of available soil water (Cowan 1982;Makela, Berninger & Had 1996) and hydraulic transport through boles (Williams et al 1996) atid as a function of leaf (Mott & Pat-khurst 1991) or canopy transpiration (Monteith 1995), Scaling stotnatal conductance according to changes in ABA (e,g. Tardieu & Davies 1992) has protnise for herbs, but there is no conclusive evidence showing that it may be valid for oak trees (Tt-iboulot (?r a/.…”

“…This test adds to the growing number of studies that demonstrate an ability to model foreststand fluxes of carbon and water under well-watered conditions (Amthor et al 1994;Baldocchi & Harley 1995;Aber. Reich & Gouiden 1996;Williams et al 1996). Only during the night do measurements and model calculations diverge appreciably.…”

Global evaluation of gross primary productivity in the JULES land surface model v3.4.1

“…In CARDAMOM, GPP is calculated as a function of LAI, air temperature and radiation using the aggregated-canopy model (ACM; Williams et al, 1997). ACM is an emulator of the soil plant atmosphere (SPA) model and uses a set of equations to simulate daily GPP estimates produced by SPA (Williams et al, 1996).…”

An analytical model of non‐photorespiratory CO2 release in the light and dark in leaves of C3 species based on stoichiometric flux balance

“…Photosynthesis is usually predicted in C3 plants by the model of Farquhar, von Caemmerer & Berry (1980) (FCB), whereas respiration is usually predicted empirically, for example, as a function of leaf nitrogen or ribulose 1·5-bisphosphate carboxylase/ oxygenase (Rubisco) content (Williams et al 1996;de Pury & Farquhar 1997), as a constant fraction of gross carbon gain (Waring, Landsberg & Williams 1998;DeLucia et al 2007), as a function of tissue pool size (Running & Coughlan 1988) or in relation to phenological state, based on empirical partitioning of respiration into growth and maintenance terms (Thornley 1970;Amthor et al 1994). …”