Inhibition of Crustose Lichen Spore Germination by Lichen Acids

Ascospore germination of the crustose lichens Graphis scripta and Caloplaca citrina was observed in the presence ofatranorin (A TR), vulpinic acid (VUL), evernic acid (E VE) and stictic acid (STC) on buffered media ranging in pH from 4 to 7. Caloplaca citrina spore germination was much reduced in the presence of VUL, EVE and A TR. Spores of G. scripta were also severely inhibited by VUL and EVE, but were not affected by ATR. Neither species showed significant germination reductions in the presence of STC. These results, and those of previous studies, dem- onstrate the allelopathic potential of lichen compounds in biochemically diverse lichen communities. We previously reported (Whiton & Lawrey 1982) results of laboratory studies designed to test the hy- pothesis that lichen secondary compounds are ca- pable of inhibiting lichen ascospore germination. We found that spore germination of the lichen Cla- donia cristatella was slightly but significantly re- duced by vulpinic acid (VUL), but not by evernic (EVE) or stictic (STC) acids. Spore germination of a nonlichenized ascomycete, Sordariafimicola, was reduced by VUL and EVE; furthermore, the inhib- itory effect was much more pronounced than in C. cristatella. These results led us to infer that: (1) li- chen compounds can function as allelopathic agents in lichen communities; and (2) lichenized fungi have a greater physiological tolerance of these com- pounds than nonlichenized fungi. We tested these inferences further by subjecting spores of the crustose lichens Graphis scripta (L.) Ach. and Caloplaca citrina (Hoffm.) Th. Fr. to the same treatments as in our previous study; we also added a fourth lichen compound, the cortical sub- stance atranorin. We reasoned that crustose lichens rely more heavily on spores for dispersal than fo- liose and fruticose lichens that frequently have veg- etative dispersal structures. For this reason, chem- ical inhibition of ascospore germination is likely to influence dispersal and establishment success more directly in crustose lichens than in others.