such as "Introduction", "Conclusion"..etc
Nitrogen deficiencies are known to limit plant growth [13-15]
while additions of nitrogen, such as that from salmon carcasses, could
potentially increase primary and secondary productivity. For example,
Sitka spruce (Picea sitchensis) has higher growth rate adjacent to salmon streams relative to sites without salmon . Increased nitrogen can also lead to changes in plant species composition, diversity and dominance [16-20], in part by shifting biomass allocation from roots to shoots and leaves [14,21].
Additionally, recent evidence suggests that these shifts in
salmon-nutrient levels may have cascading effects in higher trophic
levels and ecosystem structure .
Multiple parameters remain poorly characterized in these expanding
studies linking the role of salmon to productivity and diversity in
terrestrial ecosystems. Interpretations of the nitrogen and carbon
isotope ratios, which provide the major proxy for quantifying
contribution of salmon-derived nutrients to other taxa, are based on
the assumption that the amount of isotopic enrichment is directly
proportional to the relative contribution of salmon [8,22]. However, isotopic enrichment in vegetation can also be influenced by slope, precipitation, substrate and other factors [23-26],
which confound estimates of the direct contribution of salmon.
Recently, we examined isotopic signatures in riparian vegetation from
salmon watersheds of Vancouver Island, British Columbia, and observed
substantial site variability in 15N signatures in watersheds without salmon .
In order to reduce confounding effects on isotopic signature, we
investigate in this paper the contribution of salmon-derived nitrogen
to multiple plant species collected immediately above and below
waterfalls that are barriers to salmon migration in two geographically
separated watersheds on the central coast of British Columbia, Canada.
We use foliar δ15N values to
determine the extent of N cycling from salmon into terrestrial
vegetation. We determine %N values in foliar tissue. This may be a
proxy for primary productivity given that total nitrogen in plant
tissue is often a direct measure of metabolic activity and
photosynthetic rate [27,28].
We also assess plant community structure by examining relative
abundance of taxa previously identified as indicators of soil nitrogen
status . This project is part of an ongoing assessment of salmon-bear interactions and nutrient cycling in riparian taxa [6,11,30].
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