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N2 fixing alder (Alnus viridis spp. fruticosa) effects on soil properties across a secondary successional chronosequence in interior Alaska

TitleN2 fixing alder (Alnus viridis spp. fruticosa) effects on soil properties across a secondary successional chronosequence in interior Alaska
Publication TypeJournal Article
Year of Publication2009
AuthorsMitchell, JS, Ruess, RW
JournalBiogeochemistry
Volume95
Pagination215–229
Abstract

Green alder (Alnus viridis ssp. fruticosa)is a dominant understory shrub during secondarysuccessional development of upland forests throughoutinterior Alaska, where it contributes substantiallyto the nitrogen (N) economy through atmospheric N2fixation. Across a replicated 200? year old vegetationchronosequence, we tested the hypotheses thatgreen alder has strong effects on soil chemicalproperties, and that ecosystem-level N inputs via N2fixation decrease with secondary successional standdevelopment. Across early-, mid-, and late-successionalstands, alder created islands of elevated soil Nand carbon (C), depleted soil phosphorus (P), andmore acidic soils. These effects translated to thestand-level in response to alder stem density.Although neither N2 fixation nor nodule biomassdiffered among stand types, increases in alder densitieswith successional time translated to increasingN inputs. Estimates of annual N inputs by A. viridisaveraged across the upland chronosequence (6.6 ±1.2 kg N ha-1 year-1) are substantially less thaninputs during early succession by Alnus tenuifoliagrowing along Alaskan floodplains. However, latesuccessionupland forests, where densities of A. viridisare highest, may persist for centuries, depending onfire return interval. This pattern of prolonged N inputsto late successional forests contradicts establishedtheory predicting declines in N2-fixation rates andN2-fixer abundance as stands age.

DOI10.1007/s10533-009-9332-x
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