Nutrients from spawning salmon influence leaf area, tissue density, and nitrogen-15 in riparian plant leaves

Nutrient subsidies have significant impacts on ecosystems by connecting
disjunct habitats, often through long distance animal migrations. Salmon
migrations on the North Pacific coasts provide these kinds of nutrient
subsidies from senescent fish at the end of their life cycle, which can
have significant ecological effects on terrestrial species. This can
include impacts on individuals, populations, and communities, where shifts
in community composition towards nitrophilic plant species have been
documented. We investigated the effects of variation in salmon spawning
density on the leaf traits of four common riparian plant species on the
central coast of British Columbia, Canada. We found that all plant species
had higher foliar salmon-derived nitrogen on streams with a higher
spawning density. Three of the four species had larger leaves, and one
species also had higher leaf mass per area on streams with more salmon.
However, we found no differences in leaf greenness or foliar percent
nitrogen among our study streams. These results demonstrate that nutrient
subsidies from spawning salmon can have significant impacts on the
ecology, morphology, and physiology of riparian plants, which lends
support to a mechanism by which certain plants are more common on
productive salmon streams. Our findings therefore have broader
implications for salmon ecosystems.