Nighttime stomatal opening and consequent transpiration is typically considered rare because for most non-CAM plants stomatal closure at night limits water loss when there is no carbon to be gained from photosynthesis. Xylem parasites, however, also derive dilute carbon from their hosts’ xylem. Because this source is unaffected by darkness, xylem parasites are theoretically released from one of the major drivers of nighttime stomatal closure. I measured nighttime stomatal conductance in eight Castilleja species, a widespread genus of root hemiparasites, across eight sites in California. Each Castilleja measurement was paired with one made on a neighboring individual of a non-parasitic plant species common at that site.
Results/Conclusions
On average parasites’ nighttime stomatal conductance was 235% higher than the non-parasites, with values often in excess of 500 mmol H2O m-2 s-1, although all the plants displayed some nighttime stomatal conductance. Only one species of Castilleja had a lower average nighttime stomatal conductance than its non-parasitic neighbor. These data demonstrate that many Castilleja commonly transpire at night, adding them to the growing group of plants shown to open their stomata at night, and demonstrating a potential mechanism of benefit driving nighttime transpiration.