Nitrogen sources in Adirondack wetlands dominated by nitrogen-fixing shrubs

Hurd, Todd M.; Gökkaya, Kemal; Kiernan, Brian D.; Raynal, Dudley J.

doi:10.1672/0277-5212(2005)025[0192:nsiawd]2.0.co;2

Cited by 6 publications

(5 citation statements)

References 41 publications

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“…Fraction of biologically fixed N was estimated using the natural abundance of 15 Significant differences among thickets are noted by different letters thickets (F = 1.178, P = 0.362) so data were pooled across all sites before further analysis. Isotopic composition of the N-limited fixers was -1.2 ± 0.1 d 15 N which compares very well to values observed in other studies for seedlings grown in an N-free medium (Hurd et al 2005). The difference in d 15 N between non-fixers and fixers was only 0.8.…”

Section: Resultssupporting

confidence: 87%

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Brantley

Young

2007

Oecologia

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Woody encroachment into herbaceous ecosystems is emerging as an important ecological response to global change. A primary concern is alterations in C and N cycling and associated variations across a variety of ecosystems. We quantified seasonal variation in litterfall and litter N concentration in Morella cerifera shrub thickets to assess changes in litterfall and associated N input after shrub expansion on an Atlantic coast barrier island. We also used the natural abundance of (15)N to estimate the proportion of litterfall N originating from symbiotic N fixation. Litterfall for shrub thickets ranged from 8,991 +/- 247 to 3,810 +/- 399 kg ha(-1) year(-1) and generally declined with increasing thicket age. Litterfall in three of the four thickets exceeded previous estimates of aboveground annual net primary production in adjacent grasslands by 300-400%. Leaf N concentration was also higher after shrub expansion and, coupled with low N resorption efficiency and high litterfall, resulted in a return of as much as 169 kg N ha(-1) year(-1) to the soil. We estimated that approximately 70% of N returned to the soil was from symbiotic N fixation resulting in an ecosystem input of between 37 and 118 kg ha(-1) year(-1) of atmospheric N depending on site. Considering the extensive cover of shrub thickets on Virginia barrier islands, N fixation by shrubs is likely the largest single source of N to the system. The shift from grassland to shrub thicket on barrier islands results in a substantial increase in litterfall and foliar N concentration that will likely have a major impact on the size and cycling of ecosystem C and N pools. Increasing C and N availability in these nutrient-poor soils is likely to permanently reduce cover of native grasses and alter community structure by favoring species with greater N requirements.

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Section: Resultssupporting

confidence: 87%

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Brantley

Young

2007

Oecologia

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“…We did not explicitly consider inputs to watersheds via nitrogen fixation or losses from watersheds via denitrification. Nitrogen fixation rates are roughly similar to Ndeposition (Cleveland et al 1999, Hurd et al 2005. Denitrification losses are also about equal to N-fixation based on studies of forests in the region (e.g., Groffman et al 2001).…”

Section: Discussionmentioning

confidence: 60%

Nitrogen deposition and lake nitrogen concentrations: a regional analysis of terrestrial controls and aquatic linkages

et al. 2012

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Abstract. Loading of nutrients from terrestrial ecosystems strongly influences the productivity and biogeochemistry of aquatic ecosystems. Human activities can supplement and even dominate nutrient loading to many lakes, particularly in agricultural and urbanized settings. For lakes in more remote regions such as the Adirondack Mountains of New York, N deposition represents the primary potential anthropogenic nutrient source. We combined a spatial model of N deposition with data on lake-N concentrations and spatial data on watershed configuration to identify the sources of watershed N loading for over 250 lakes in the Adirondacks. The analysis indicates that while wetlands are stronger sources of N loading per unit area than forests in the absence of inorganic N deposition, wetlands retain essentially all N deposition, while forests retained ;87% of N deposition. Since forests cover close to 90% of the watersheds, upland forests are, on average, the single largest source of N loading to Adirondack lakes. Direct deposition of N to the lake surface accounted for as large a fraction of loading as that from wetlands in the watersheds. We found no evidence that presence of wetlands along flowpaths to lakes reduced loading from upland forests. Moreover, there was no evidence that net loading to lakes declined with increasing distance of a source area to the lake. Lake N-concentrations thus primarily reflect N-loading from forests in concert with loss rates determined by water residence time and within-lake processes.

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“…Nevertheless, the 15 N natural abundance and acetylene reduction methods gave similar mean (+/− SE) values, 43 ± 20 and 37 ± 10 kg ha −1 , respectively, for the foliar N derived from N 2 fixation in a stand of Alnus incana over a year. In a study subsequent to that of Hurd et al (2001) in the Adirondack wetlands, 15 N natural abundance gave a value of 85 %Ndfa for A. incana but only 40-45 %Ndfa for Myrica gale which occurred sympatrically with A. incana (Hurd et al 2005). These results indicate that under similar conditions actinorhizal species can differ substantially in the proportion of N they obtain from N 2 fixation.…”

Section: N 2 Fixation In Actinorhizal Plantsmentioning

confidence: 92%

“…These results indicate that under similar conditions actinorhizal species can differ substantially in the proportion of N they obtain from N 2 fixation. However, Hurd et al (2005) highlighted that M. gale tends to occur in lake outlet systems rather than the lake inlet systems dominated by A. incana. It was estimated that N 2 fixation of A. incana added 7-18 kg N ha −1 year −1 to the lake inlet systems, but that N 2 fixation of M. gale added at most only 3 kg N ha −1 year −1 to the lake outlet systems.…”

Section: N 2 Fixation In Actinorhizal Plantsmentioning

confidence: 99%

Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using¹⁵N natural abundance

Andrews

James

Sprent

et al. 2011

Plant Ecology & Diversity

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Nitrogen sources in Adirondack wetlands dominated by nitrogen-fixing shrubs

Cited by 6 publications

References 41 publications

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Nitrogen deposition and lake nitrogen concentrations: a regional analysis of terrestrial controls and aquatic linkages

Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using¹⁵N natural abundance

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Nitrogen sources in Adirondack wetlands dominated by nitrogen-fixing shrubs

Cited by 6 publications

References 41 publications

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Shifts in litterfall and dominant nitrogen sources after expansion of shrub thickets

Nitrogen deposition and lake nitrogen concentrations: a regional analysis of terrestrial controls and aquatic linkages

Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using15N natural abundance

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Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using¹⁵N natural abundance