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Disease-mediated declines in N-fixation inputs by Alder tenuifolia to early-successional floodplains in Interior and south-central Alaska

TitleDisease-mediated declines in N-fixation inputs by Alder tenuifolia to early-successional floodplains in Interior and south-central Alaska
Publication TypeJournal Article
Year of Publication2009
AuthorsRuess, RW, McFarland, JM, Trummer, LM, Rohrs-Richey, JK
JournalEcosystems
Volume12
Pagination489–502
Abstract

Atmospheric nitrogen (N) fixation by Alnus tenuifoliacan account for up to 70% of the N accumulatedduring vegetation development along river floodplainsin interior Alaska. We assessed disease incidenceand related mortality of a recent outbreakof fungal stem cankers on A. tenuifolia across threeregions inAlaska during the 2005 growing season, anddetermined the impacts on N-fixation rates, nodulebiomass, and stand-level N-fixation inputs. Thehighest percentage of ramets colonized or dead withcanker was found on Tanana River plots, suggestingthe epidemic ismost severe in the Fairbanks region. Apositive relationship between % basal area loss tocanker and%canopy loss provides a simplemeans forassessing stand-level mortality associated with diseasein the field. Although specific N-fixation (SNF) rateswere not influenced by canker disease incidenceof individual genets, live nodule biomass beneathalder canopies was inversely correlated with the percentageof ramets dead or with main ramet canker.Variations in SNF and live nodule biomass translatedto differences in N-fixation inputs, which ranged from22 to 107 kg N ha-1 y-1 across study regions. Nodulebiomass was reduced by incidence of canker diseaseand related mortality an average of 24% across allsites, which translates to N input reductions of 8, 16,and 33 kg N ha-1 y-1 for the three regions, respectively.During the 2008 growing season, we resurveyedthe Tanana River plots and found that of theramets larger than 4-cm diameter having main rametcanker in 2005, 74% are now dead; and for thosewithout main ramet canker in 2005, 25% havedevelopedmain ramet canker, and8%are dead. Thus,it is likely that N-fixation inputs have declined furtherbelow what we estimated for 2005.

DOI10.1007/s10021-009-9237-5
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