Transpiration of detached mycorrhizal and nonmycorrhizal leaves fed varying abscisic acid, pH, calcium and phosphorus

Mycorrhizal colonization can alter stomatal behavior of host leaves during drought without obvious changes in plant size or nutrition. This may be related to an altered production or reception of a chemical signal of soil drying. I tested whether intact root systems were required to observe a mycorrhizal effect on leaf transpiration (E), or whether some residual mycorrhizal influence on leaves could affect E of foliage detached from root systems. Transpiration assays were performed in the presence of several possible candidates for a chemical signal of soil drying. Although colonization alone did not alter E of detached leaves of Vigna unguiculata (cowpea), colonization interacted significantly with ABA and pH in regulating transpiration. Colonization affected E of detached Rosa hybrida (rose) leaves but had no effect on E of detached leaves of Pelargonium hortorum (geranium). In each species tested, increasing the ABA concentration decreased E. In cowpea, calcium appeared to alter stomatal sensitivity to ABA, as well as regulate stomatal activity directly. The pH of the feeding solution affected E in rose, but did not change E independently in cowpea or geranium. Adding phosphorus to the feeding solution did not alter E, but did change the apparent sensitivity of cowpea stomata to ABA. Colonization of roots by mycorrhizal fungi can result in residual effects in detached leaves, that can alter the stomatal reception of chemical signals in both rose and cowpea.