期刊
BIOGEOCHEMISTRY
卷 95, 期 2-3, 页码 215-229出版社
SPRINGER
DOI: 10.1007/s10533-009-9332-x
关键词
Alder; Boreal; Nitrogen cycling; Nitrogen fixation; Secondary succession
资金
- NSF [DEB-0423442]
- USDA Forest Service, Pacific Northwest Research Station [PNW01-JV11261952-231]
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 N-2 fixation. Across a replicated 200+ year old vegetation chronosequence, we tested the hypotheses that green alder has strong effects on soil chemical properties, and that ecosystem-level N inputs via N-2 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 N-2 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 +/- A 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, may persist for centuries, depending on fire return interval. This pattern of prolonged N inputs to late successional forests contradicts established theory predicting declines in N-2-fixation rates and N-2-fixer abundance as stands age.
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