『Abstract
　Green alder (Alnus viridis ssp. fruticosa) is a dominant understory shrub during secondary successional development of upland forests throughout interior Alaska, where it contributes substantially to the nitrogen (N) economy through atmospheric N2 fixation. Across a replicated 200+ year old vegetation chronosequence, we tested the hypothesis that green alder has strong effects on soil chemical properties, and that ecosystem-level N inputs via N2 fixation decrease with secondary successional stand development. Across early-, mid-, and late-successional stands, alder created islands of elevated soil N and carbon (C), depleted soil phosphorus (P), and more acidic soils. These effects translated to the stand-level in response to alder stem density. Although neither N2 fixation nor nodule biomass differed among stand types, increases in alder densities with successional time translated to increasing N inputs. Estimates of annual N inputs by A. viridis averaged across the upland chronosequence (6.6± 1.2 kg N ha^-1 year^-1) are substantially less than inputs during early succession by Alnus tenuifolia growing along Alaskan floodplains. However, late-succession upland forests, where densities of A. viridis are highest, many persist for centuries, depending on fire return interval. This pattern of prolonged N inputs to late successional forests contradicts established theory predicting declines in N2-fixation rates and N2-fixer abundance as stands age.

Keywords: Alder; Boreal; Nitrogen cycling; Nitrogen fixation; Secondary succession』

Introduction
Study area
Methods
　Experimental design
　Soil physical and chemical parameters
　Nodule biomass and N inputs
　Statistical analyses
Results
　Soil properties
　Alder stem density and canopy effects on soil properties
　Nodule biomass and N inputs
Discussion
　Alder interactions with soil parameters
　N inputs
Conclusions
Acknowledgments
References