Wednesday, June 6, 2007 - 5:15 PM
326

Spawning Salmon Alleviate Nitrogen Limitation in a 100-Year Riparian Succession Chronosequence of a Kamchatka (Russian Federation) River

Michael R. Morris and Jack A. Stanford. Flathead Lake Biological Station and Division of Biological Sciences, The University of Montana, 32125 Bio Station Lane, Polson, MT 59860-9659

Some five million salmon return annually to the Kol River, contributing 270,000 kg N yr-1.  We quantified N dynamics in soils and vegetation across a 100-year riparian chronosequence.  Soil of early succession alluvial bars (0-5 yrs) contained 200 kg total N ha-1 (to 10 cm depth) and net mineralization was 0.05 kg N ha-1 day-1 before the salmon migration.  In 100 year-old stands, total N and mineralization were an order of magnitude higher.  Thus, as is in most terrestrial ecosystems, early succession should have been N-limited.  However, flood-deposited carcasses contributed up to 150 kg N ha-1 yr-1 to these otherwise N-poor alluvial bars.  Early successional willows actively assimilated N and doubled in mass during the decomposition of salmon carcasses, even though this N-pulse was late in the growing season.  Early succession foliage was highly enriched with the 15N isotope (δ15N: 2 to 6, depending on species) relative to terrestrially fixed N (δ15N: -1), confirming salmon were a major N-source in early succession.  Unlike other Pacific-rim succession studies, vegetation across this chronosequence was composed of fast growing, N-rich (foliar C:N = 8 to 14 versus avg. for temperate forests: 35) species and, thus, we concluded vegetation growth was not N-limited.