Stomatal Behaviour of Two Heliophile Understorey Species of a Tropical Deciduous Forest in Mexico

SUMMARY (1) Stomatal conductance (g) was measured on leaves of Jacquinia pungens A. Gray and Coccoloba liebmannii Lindau during the dry season in a tropical deciduous forest of western Mexico. (2) The daily courses of g observed in January and April indicate that stomatal behaviour of both species was very similar. On days in January stomata showed an opening and closing cycle but in April a pronounced midday closure was observed. (3) For C. liebmannii and J. pungens, leaf water potential (v) fell from -1 2 and -2.8 MPa in January to -3-5 to -4.0 MPa in April, respectively. (4) In January g was dominantly controlled by irradiance (Q) and temperature and there was no evidence that stomata were sensitive to leaf-air vapour pressure difference (vpd). In April the sensitivity of g to Q decreased and stomata closed mainly in response to by and leaf-air vpd in a manner consistent with the classical feedback control. (5) A model relating g to environmental variables and v accounted for 81% of the