Symbiotic N2 fixation of Alnus incana ssp. rugosa in shrub wetlands of the Adirondack Mountains, New York, USA

Abstract

Surface waters in forested watersheds in the Adirondack Mountains and northern New York State are susceptible to nitrogen (N) saturation. Atmospheric deposition of N to watersheds in this region has been measured but the extent of internal N inputs from symbiotic N fixation in alder-dominated wetlands is not known. We estimated N fixation by speckled alder in these wetlands by the N natural abundance method and by acetylene reduction using a flow-through system. Foliar N derived from fixation (%N) was estimated for five wetlands. The δN of speckled alder foliage from four of the five sites did not differ significantly (P≤0.05) from that of nodulated speckled alders grown in N-free water culture (-1.2±0.1‰). Estimates from the N natural abundance method indicated that alders at these sites derive 85-100% of their foliar N from N fixation. At one of the sites, we also measured biomass and N content and estimated that the alder foliage contained 43 kg N ha of fixed N in 1997. This estimate was based on a foliar N content of 55.4±7 kg N ha (mean±SE), 86±4%N, and an assumption that 10% of foliar N was derived from reserves in woody tissues. At this site, we further estimated via acetylene reduction that 37±10 kg N ha was fixed by speckled alders in 1998. This estimate used the theoretical 4:1 CH reduction to N fixation ratio and assumed no night-time fixation late in the season. Nitrogen inputs in wet and dry deposition at this site are approximately 8 kg N ha year. We conclude that speckled alder in wetlands of northern New York State relies heavily on N fixation to meet N demands, and symbiotic N fixation in speckled alders adds substantial amounts of N to alder-dominated wetlands in the Adirondack Mountains. These additions may be important for watershed N budgets, where alder-dominated wetlands occupy a large proportion of watershed area.

Influence of pulverized limestone and amphibolite mixture on the growth performance of Alnus incana (L.) Moench plantation on an acidified mountain site

“…In more concrete terms, according to Myrold and HussDanell (2003) the percentage of N derived from the atmosphere ranges between 70% and almost 100%. Similarly Hurd et al (2001) reported that speckled alder (Alnus incana ssp. rugosa) was able to derive 85-100% of its foliar N from N 2 fixation.…”

Wetland nutrient removal: a review of the evidence

“…Vegetation may also influence nitrification and denitrification by influencing the oxygen concentration of the wetland substrate within the rhizosphere (Armstrong, 1964) or by providing bacteria which can fix N in root nodules, such as in the wetland tree Alnus spp. (Hurd et al, 2001). There is evidence that N removal efficiency is not affected by the length of time the wetland has received N pollution while, in contrast, the ability of a wetland to remove P is known to decline with time (Nichols, 1983;Richardson, 1985).…”

The importance of catchment slope to soil water N and C concentrations in riparian zones: implications for riparian buffer width

“…Due to the importance of various Alnus species with respect to forest ecosystem N cycling, the abundance of speckled alder within each plot was assessed by assigning a value representing no alder present (0), some alder present (1), or abundant alder present (2). Alder species support symbiotic Nfixing bacteria in root nodules and can provide a significant internal source of N to alder-dominated terrestrial ecosys-tems (Wurtz 1995;Hurd et al 2001). Depths of forest floor horizons were determined at seven locations within each plot and moss plus L, F, and H layers were sampled separately from 0.1 m 2 quadrats.…”