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Does clearcutting affect the quantity of soluble organic nitrogen in forest soil? Hannam, Kirsten Danielle


Soluble organic N (SON) is often more abundant than soluble inorganic N (SIN) in forest soils. The effects of forest management on the abundance of SON in forest soils are of interest because plants can take up some of this N. Studies investigating the impact of logging on SON concentrations have found inconsistent results. Concentrations of SON and SIN were measured in forests and clearcuts in coastal cedar-hemlock forests near Port McNeill, B.C. and in high-elevation spruce-fir forests near Sicamous, B.C. Soil samples were collected to a cumulative depth of 20 cm in order to characterize the forest soil environment exploited by young seedlings. At Port McNeill, samples from the forest consisted of F- and H-layer forest floor. In the clearcuts, samples consisted of H-layer forest floor only, because the F layer was absent. At Sicamous, samples of forest floor and mineral soil were collected from both the forest and clearcuts. SON was determined in 1 M KC1 extracts using persulphate oxidation. Amino acid-N and microbial N were determined on separate subsets of the samples. At both sites, forest soil SON content was significantly greater than SIN content. Free amino acid-N was estimated to comprise 1 to 1.5 % of the total SON content. SON content tended to be higher in the forests than in the clearcuts at both sites but differences were significant at Sicamous only. At Port McNeill, SON content tended to be higher in the forests than in the clearcuts because of the presence of a SON-rich F layer, which was absent in the clearcuts. At Sicamous, SON content tended to be higher in the forests than in the clearcuts because forest floor SON concentrations were significantly lower in the clearcuts. Correlation analysis indicated close relationships between moisture content, SIN, SON and microbial N. However, buried bag incubations suggested that changes in forest soil SON, SIN and microbial N concentrations cannot be explained simply by exchange among these three N pools.

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