
TY  - JOUR
A1  - Lloyd, J 
T1  - Modelling Stomatal Responses to Environment in <I>Macadamia integrifolia</I>
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1991
VL  - 18
IS  - 6
SP  - 649
EP  - 660
KW  - 
UR  - https://doi.org/10.1071/PP9910649 
N2  - Gas exchange measurements were made of photosynthetic and stomatal responses of Macadamia integrifolia under controlled conditions. Test leaves were subjected to a range of temperatures, humidities and photon irradiances. When stomatal responses to humidity were plotted as a function of vapour mol fraction difference (D) a similar curvilinear response was observed at all temperatures and at photon irradiances of 200 and 1500 &#956;mol quanta m-2 s-1. By contrast, when expressed as a function of relative humidity, different slopes in the humidity response were observed, and at high photon irradiances, stomatal conductances (gs) appeared to have an optimum temperature below 15ºC. Simple equations to quantify responses to leaf temperature (TI) and D were developed, the best of which was                             gs = [1-k1(1-[Tl/Topt)]/k2&#8730;D,  where Topt is the leaf temperature at which maximal stomatal opening is observed and k1 and k2 are constants fitted by non-linear least squares regression analysis.      Calculation of the gain ratio of CO2 assimilation (A) to transpiration (E) (&#948;A/&#948;E) was complicated by effects of D on the relationship between A and leaf intercellular mol fraction of CO2 (CI). Calculation of &#948;A/&#948;E using A/CI relationships derived by varying external CO2 mol fraction at constant D showed the gain ratio to be virtually constant (1.5 mmol mol-1) across a range of leaf temperatures and vapour mol fraction differences but, when calculated directly from the relationship between A and gs, a decrease in &#948;A/&#948;E with D was observed. Macadamia leaves have heavily sclerified bundle sheath extensions and it is considered that this dependence was an artefact due to non-uniform stomatal closure in response to increasing D. It is shown that, at any given temperature, a stomatal response of the form gsD-1/2 gives rise to an approximately constant &#948;A/&#948;E. 
ER  -

