Scaling Leaf Measurements to Estimate Whole Canopy Gas Exchanges of Cotton

Diurnal leaf and canopy gas exchanges ofwell-watered field grown cotton were measured. Our objective was to scaleleaf-level values of transpiration and net assimilation to the whole canopylevel using estimates of canopy leaf area. Single leaf gas exchangemeasurements were made with two portable photosynthesis systems and canopy measurementswith four open Canopy Evapo-Transpiration and Assimilation (CETA) chambersystems. Canopy leaf area was measured at the end of the experiment and estimatedduring gas exchange by fitting values to a growth curve. Leaf level measurementswere arithmetically scaled to estimate canopy level gas exchange based on canopyleaf area and then compared to the measured values. Scaled values of singleleaf transpiration were very similar to canopy transpiration measurements,although both whole canopy transpiration and assimilation were overestimatedaround mid-day. We conclude that canopy cotton transpiration of well-wateredfield grown plants could be estimated within 5% throughout the day by scalingleaf level measurements to the whole canopy using measured canopy leaf area.Estimating canopy assimilation from leaf level measurements remainsproblematic.