Photosynthetic Responses of "Specialty Greens" to Irradiance and Carbon Dioxide

Specialty greens crops are often high value crops in which there is a local demand that is not being filled.  We assessed the impact of temperature (10–28 °C), irradiance and carbon dioxide on photosynthesis of a variety of these crops to provide growers with information to maximize their yield.  Here, we summarize results of photosynthetic responses of a number of these specialty greens crops to irradiance and carbon dioxide.  Irradiance (0–1200 μmol·m^-2·s^-1; 200 μmol·m^-2·s^-1 increments), and carbon dioxide concentration (50–1200 ppm; 200 ppm increments) effects on photosynthesis of the uppermost fully expanded leaf of eleven specialty greens crops plus a number of cultivars/varieties of kale, chard, cress and spinach (3 kale cultivars, 4 chard cultivars, 2 cress cultivars, 3 spinach cultivars, collards, arugula, beet greens, sorrel, pea shoots, broccoli raab and nasturtium shoots) were determined.  Irradiance or carbon dioxide was varied while the other variable and temperature was held constant (irradiance was held at 300 μmol·m^-2·s^-1, carbon dioxide was held at 400 ppm; temperature held at 22 °C).  One leaf from each of five plants was measured for each cultivar/species.  At ambient carbon dioxide (400 ppm) and at 22C, maximum photosynthetic rate under high irradiance (1200 μmol·m^-2·s^-1) varied from 16.5  μmol·m^-2·s^-1 carbon dioxide fixed on crinkly cress, to 26.5 μmol·m^-2·s^-1 carbon dioxide fixed on Melody spinach.  In contrast, at ambient irradiance (300 μmol·m^-2·s^-1) and at 22 °C, maximum photosynthetic rate at a high carbon dioxide concentration (1200 ppm) varied from 13.2 μmol·m^-2·s^-1 carbon dioxide fixed on crinkly cress to 19.8 μmol·m^-2·s^-1 carbon dioxide fixed on Melody spinach.  As irradiance increased, Crinkly cress photosynthesis saturated at 600 μmol·m^-2·s^-1and Melody spinach photosynthesis saturated at 1000 μmol·m^-2·s^-1.  As carbon dioxide concentration increased, Crinkly cress photosynthesis saturated at 800 ppm and Melody spinach photosynthesis saturated at 1000 ppm.  Results here determined which crops benefit most, and to what extent, from altering irradiance or carbon dioxide with respect to impacting photosynthesis.