8.1. Carbon dioxide (CO2) level
CO2 enrichment has been used for many years in greenhouses to increase crop growth and yield. Since nectar production may be related to photosynthesis level, we might expect an increase in floral rewards in greenhouses with enriched CO2 (Dag and Eisikowitch, 2000). On the other hand, if the greenhouse is completely closed and contains high biomass, intensive photosynthesis may lead to a reduction in CO2 to lower than ambient (350 ppm) levels. There are different sensors available on the market to assess CO2 level. Sensors that use non-dispersive infrared (NDIR) technology to measure CO2 concentration in the greenhouse air are common and generally reliable. The sensor is placed near the leaf, i.e. the organ most affected by CO2 levels.