Empirical Relationships Between Light Intensity and Crop Net Carbon Exchange Rate at the Leaf and Full Canopy Scale: Towards Integration of a Higher Plant Chamber in MELiSSA 2005-01-3071

The process of integrating a Higher Plant Chamber (HPC) in the MELiSSA Pilot Plant demands reliable data on crop photosynthetic responses to varying light intensity. Such data allow for the development of dynamic photosynthetic models which, in turn, are used in the control of the HPC. A number of full canopy research trials have been conducted using sealed environment chambers with beet (Beta vulgaris cv. Detroit Medium Red) and lettuce (Lactuca sativa L. cv. Grand Rapids) as candidate crops. In this study, data were collected at the full canopy scale using a differential-compensating CO₂ analysis system and at the leaf scale using a LI-6400 leaf gas exchange system in an attempt to derive parameter estimates for a leaf and canopy photosynthesis model. Results indicate that a rectangular hyperbola model was suitable in defining the leaf and the linear phase of full canopy Net Carbon Exchange Rate (NCER) response to light. No significant differences in the estimates of quantum yield and dark respiration were observed among atmospheric CO₂ concentration treatments imposed during the leaf response studies. There was, however, significant variation in the maximum gross photosynthesis estimates for both crops. Results of full canopy light response studies indicated an upward trend in the apparent quantum yield of the stand owing to increased leaf area index throughout canopy maturation which makes the canopy more difficult to light saturate (i.e. light is limiting). The data have application to the further development of models of canopy photosynthesis within the MELiSSA framework.