The effects of various host plants on growth, water relations, and carbon balance of the hemiparasite Castilleja indivisa (Indian paintbrush)

Castilleja indivisa grows hemiparasitically, attached to the roots of nearby host plants. Many Castilleja species may be capable of autotrophic growth. Studies examined the effects of parasitism on growth of C. indivisa and host plants. The feasibility of commercial production of C. indivisa, grown parasitically and autotrophically was considered. Transpiration rates, stomatal conductances, and leafwater potentials of C. indivisa and hosts were measured over varied soil moisture levels. The movement of carbon between host plants and C. indivisa was examined using a ;Hosts enhanced the growth of C. indivisa by 100-774% compared to nonparasitic C. indivisa, and growth of host plants was reduced by 30-400%. This study indicates that commercial production of C. indivisa using parasitic and autotrophic methodology is feasible. Transpiration rates of C. indivisa generally exceed those of the host at low to medium soil moisture levels, but not at high soil moisture levels. Maximum transpiration rates of C. indivisa were dependent on maximum transpiration rates of each host. Transpiration rates of nonparasitic C. indivisa controls remained low regardless of soil moisture level. Stomatal conductances reflect similar trends to transpiration. Leaf water potentials indicated few differences between host and hemiparasite at any soil moisture level, except LWPs of C. indivisa controls were lower than other treatments. This research indicates that the acquisition of water by the hemiparasite from the host is important for hemiparasitic growth. Carbon transfer from the various host plants to C. indivisa was insignificant except when L. texana was used as a host, and this transfer of carbon was relatively small. Carbon transfer in the C. indivisa host system may not be an important aspect of this relationship, and should be examined further.