*3.6. Conclusions*

The Asian leafy green mizuna (*Brassica rapa* var. *japonica*) grows faster than oakleaf lettuce (*Lactuca sativa* 'Green Salad Bowl') when PPFD <sup>≥</sup> <sup>125</sup> <sup>µ</sup>mol m−<sup>2</sup> s −1 . This faster growth of mizuna is the result of a higher CCI and larger PCS (at PPFDs <sup>≥</sup> <sup>125</sup> <sup>µ</sup>mol m−<sup>2</sup> s −1 ), allowing mizuna to capture more light, a higher ΦPSII and net CO<sup>2</sup> assimilation, and a higher LUE than lettuce. This study provides a framework for determining underlying morphological and physiological reasons for growth differences among crops. Understanding the basic determinants of crop growth is important to increase crop productivity and energy efficiency in vertical farms. Canopy imaging can be used to select crops that will grow well in vertical farms. Although we looked at a multitude of morphological and physiological factors, quantifying PCS and LUE would be adequate for the selection of crops with fast growth. Perhaps most intriguingly, our results confirm that early differences in PCS (8–10 days after seeding) are a good predictor of final biomass. Therefore, it may be possible to simply use early PCS to screen crops for rapid growth in controlled environment agriculture. This would allow for rapid throughput phenotyping and greatly accelerate the selection of promising genotypes.
