Physiology and Microclimate in a Hemiparasite Castilleja Chromosa (Scrophulariaceae)

The hypothesis, that through use of a host, a hemiparasitic angiosperm will be able to “uncouple” physiological functions from microenvironmental variations, was tested by field measurements of water and carbohydrate balance between Castilleja chromosa and host Artemisia tridentata in three different microhabitats in the White Mountains of California. Movement of reducing sugars from host to parasite correlated with the water potential gradient from host to parasite, and the gradient occurred when water potentials of the host‐parasite system exceeded 15 bars. Changes in carbohydrate and water balance in Castilleja were unaffected by microclimatic differences, whereas these same functions in the host were tightly coupled with differences in microhabitat.