Gain of the feedback loop involving carbon dioxide and stomata: theory and measurement

The physiological and physical components of the feedback loop involving intercellular CO₂ concentration (c_i) and stomata are identified. The loop gain (G) is a measure of the degree of homeostasis in a negative feedback loop the expression 1/(1-G) represents the fraction to which feedback reduces a perturbance]. Estimates are given for the effects of G on responses of stomata and c_i to changes in ambient CO₂ concentration, light intensity, and perturbations in the water relations of a leaf. At normal ambient CO₂ concentration, the gain of the loop involving stomatal conductance and c_i was found to be −2.2 in field-grown Zea mays, −3.6 if plants of this species were grown in a growth chamber, and zero in well watered Xanthium strumarium in the vegetative state.