Canadian Forest Service Publications

Asymbiotic nitrogen fixation and soil metabolism in three Ontario forests. 1990. Hendrickson, O.Q. Soil Biology and Biochemistry 22(7): 967-971.

Year: 1990

Issued by: Pacific Forestry Centre

Catalog ID: 4464

Language: English

CFS Availability: Order paper copy (free)

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Abstract

Field and laboratory incubations were used to assess nitrogenase (acetylene reduction) activity, nitrogen mineralisation and respiration in three mature forests in the northen hardwoods-boreal transition zone of eastern North America. A 66-yr-old jack pine (Pinus banksiana Lamb.) forest had 45.4 t ha-1 of forest floor, ca 33% more than older mixedwood and hardwood forets in the same vicinity. Jack pine forest floor was more acid, mineralized only one-third as much N and half as much C during laboratory incubations, had little or no nitrogenase activity on eight sampling dates during the growing season, and contained 40- to 70-fold lower nmbers of N2-fixing bacteria. Low nutrient turnover in older jack pine stands may result in buildup of surface organic horizons and declining tree growth. At the moister hardwood site, temperature variations largely accounted for seasonal trends in C2H2 reduction; activity at the drier mixedwood site increased following rainfall events. Although asymbiotic N2 fixation in surface soils is a small N input (< 1 kg ha-1 yr-1) compared to precipitation in these more productive northern forests, it may stimulate litter decay and N dynamics.