Nitrogen Fixation and the Nitrogen Balance in Peatland Ecosystems

Abstract

A survey of heterotrophic nitrogen fixation was carried out using the acetylene reduction assay on peat from mires in Canada, England, Scotland, Ireland, Norway, Germany, Italy, and Malaysia. A detailed study of the relationship between nitrogen fixation and peatland ecology was carried out on the German sites. Nitrogenase activity was detected in all 16 fen sites examined, with the highest rates of activity being >100 nmol C2H4°mL peat—1°d—1 . Lower rates were found in both extreme rich fen and poor fen sites, with the lower rates found in bogs. A multiple regression analysis indicated pH and K to be positively correlated with nitrogenase activity whilst the correlation with Ca was negative. These results suggest that the systems as a whole may be in balance with regard to nitrogen. The rate of nitrogenase in peat from lower latitudes is greater than in peat from higher latitudes when temperatures are allowed for. The concentration of soluble nitrogen was higher, and the rate of nitrogenase activity lower in peat from beneath fen woodland than in peat from the early unwooded phase of succession. The estimated amount of nitrogen fixed annually by heterotrophic bacteria in peat from the south German mires is as follows (mg N/m2): fen, 2100; poor fen, 530; and bog, 70.

Methanotrophy induces nitrogen fixation during peatland development

“…Our areal estimations for fen stages and fen-bog transition are within the wide range of the admittedly few estimates available for Sphagnum-associated N 2 fixation in temperate, boreal, and subarctic ecosystems. These range from 0.1-6.4 g of N·m −2 ·y −1 for fens (11,16,24) and 0.1-1 g·m −2 ·y −1 for bogs (9,25). Nevertheless, our estimates may be rough because of the large SEs and the extrapolation over time:…”

Adaptive significance of evergreen vs. deciduous leaves: solving the triple paradox

“…Cations help buffer the acidifi cation of peatland soils and groundwater by humic acids and cation exchange by Sphagnum (Clymo 1963, Gorham et al 1984. Nitrogenase activity and N 2 -fi xation by soil microbes peaks between pH 5.4 and 6.5, falling toward lower and higher pH in bogs and rich fens, respectively (Waughman andBellamy 1980, Malmer 1986). Intermediate pH is also associated with Alnus and Myrica (Tilton 1978, Waughman and Bellamy 1980, Kenkel 1987, which harbor the N 2 -fi xing actinomycete Frankia and cast N-rich foliage.…”

“…Nitrogenase activity and N 2 -fi xation by soil microbes peaks between pH 5.4 and 6.5, falling toward lower and higher pH in bogs and rich fens, respectively (Waughman andBellamy 1980, Malmer 1986). Intermediate pH is also associated with Alnus and Myrica (Tilton 1978, Waughman and Bellamy 1980, Kenkel 1987, which harbor the N 2 -fi xing actinomycete Frankia and cast N-rich foliage. High soil N content should accelerate nitrate and/or ammonium production, by lowering peat C: N ratio and stimulating peat decomposition (Malmer 1986).…”

Denitrification and dinitrogen fixation in two quaking fens in the Vechtplassen area, The Netherlands

“…Dinitrogen fixation has been found to occur in every mire complex studied in Europe, North America and Asia (Moore & Bellamy 1974;Waughman & Bellamy 1980;Dickinson 1983). Intrasite comparisons show that the activity is higher in minerotrophic than in ombrotrophic mires (Moore & Bellamy 1974;Waughman & Bellamy 1980).…”

“…Dinitrogen fixation has been found to occur in every mire complex studied in Europe, North America and Asia (Moore & Bellamy 1974;Waughman & Bellamy 1980;Dickinson 1983). Intrasite comparisons show that the activity is higher in minerotrophic than in ombrotrophic mires (Moore & Bellamy 1974;Waughman & Bellamy 1980). The ability to incorporate atmospheric molecular dinitrogen into organic compounds in peatlands has been demonstrated in free-living bacteria, cyanobacteria (free-living as well as associated with Sphagnum species), and symbiotic Actinomycetes associated with Alnus spp.…”