An automated chamber system for measurements of whole-vine gas exchange

The reported system interfaces a commercially available portable infrared gas analyzer with a measurement and control module for continuous and automated measurements of whole-canopy gas exchange. Readings were taken for several days, under mostly sunny or partly cloudy conditions, on two potted vines (total leaf area per vine of ≃1.3 m2) enclosed in inflated polyethylene chambers. The air flow rate through the chambers was provided by a centrifugal blower and set at 5 L·s-1 by a butterfly valve. It prevented ΔCO2 from dropping below -40 mL·L-1. Switching of the two CO2 analysis channels to the infrared gas analyzer (operated in a differential mode) was achieved by solenoid valves, whereas wet and dry-bulb temperatures at chambers' inlet and outlet were measured by low-cost, custom -made thermocouple psychrometers. Whole-vine assimilation rate (WVA) and whole-vine transpiration rate were calculated from the inlet-outlet differences in CO2 and absolute humidity. When compared to assimilation measured on single leaves (SLA) under saturating light at equivalent times, the WVA reduction (area basis) was ≃50%, suggesting that whole-canopy photosynthetic efficiency based on SLA readings can be greatly overestimated.