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Carbon and nitrogen transformations in some forest floors Lacelle, Larry E. H.


An incubation technique was used to examine carbon mineralization and inorganic nitrogen accumulation in samples of Douglas-fir and alder forest floors developed over soils derived from granitic, ultrabasic and limestone parent materials in western British Columbia and Washington. Samples included L, F, and H or Hi horizons of Douglas-fir mor, raw moder, mull-like moder and mull forest floors and alder typical moder forest floors. Carbon dioxide production by the forest floor materials provided an estimate of gross carbon mineralization and an approximate indication of gross nitrogen mineralization. Comparison of inorganic nitrogen accumulated and gross carbon mineralized indicated that a large fraction of the mineralized inorganic nitrogen is immobilized by the microbial population and (or) lost to denitrification. The Hi horizons (organic horizons containing considerable incorporated mineral matter) accumulated more inorganic nitrogen than did the L and F horizons. Alder forest floors accumulated more inorganic nitrogen than did Douglas-fir forest floor materials. Alder L horizons tended to accumulate ammonium nitrogen while the F and Hi horizons accumulated nitrate nitrogen. Douglas-fir mor forest floors were distinguished from their mull and moder counterparts by slower decomposition and less inorganic nitrogen accumulation, and by largely accumulating ammonium nitrogen in all horizons. Irregular nitrogen accumulation curves, for some samples of Douglas-fir L and F horizons were probably due to denitrification losses. Incubation conditions favoring nitrification, with no plant sinks to remove accumulated inorganic nitrogen, may have favored denitrification losses.

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