The ecology of Ramalina menziesii. IV. In situ photosynthetic patterns and water relations of reciprocal transplants between two sites on a coastal–inland gradient

The lichen Ramalina menziesii shows a clear coast–inland gradient in morphology. To investigate whether functional differences in the field were imposed by the environment or were relatively stable phenotypic characteristics, reciprocal transplants were made between coastal and inland habitats in central California. Patterns of gross photosynthesis and thallus water content, together with the driving environmental variables, were measured simultaneously on indigenous and transplanted samples. The comparison showed that thallus water content of the two morphological forms was not significantly different when atmospheric humidity was low. In a humid atmosphere, however, the coastal samples maintained a slightly higher hydration level than the inland samples. This resulted in slightly higher photosynthetic rates when water content was low. At higher hydration levels, the inland samples photosynthesized at a higher rate than the coastal samples. It is possible that these differences are an effect of increased salt load in coastal thalli.