Nitrogen acquisition and competitive ability of Kalmia angustifolia L., paper birch (Betula papyrifera Marsh.) and black spruce (Picea mariana (Mill.) B.S.P.) seedlings grown on different humus forms.

摘要

Seedlings of paper birch (B. papyrifera), black spruce (P. mariana) and K. angustifolia were grown in pots with humus from a birch-dominated site and two spruce-Kalmia sites. Root systems interacted with humus form in controlling soil N cycling as well as energy and nutritional deficiencies of soil microorganisms. In general, Kalmia seedlings affected microbial dynamics and N cycling differently than birch and spruce seedlings. Birch and spruce seedlings reduced gross N mineralization and immobilization rates, soil mineral-N pools and the amounts of NH4+-N accreted on buried cation exchange resins in all three soils. Compared with birch and spruce seedlings, the growth of Kalmia resulted in significantly higher gross N mineralization rates, soil mineral-N pools and resin-NH4+ accretion in soil from the fertile birch site. Gross N immobilization rates in all soils were generally higher with Kalmia than with spruce or birch seedlings. All three species acquired N from the birch soil, whereas only Kalmia seedlings acquired N from the two spruce-Kalmia soils. Relative to control treatments with no seedlings, the amount of N mineralized anaerobically increased in the birch soil and decreased in the poor spruce-Kalmia soil with all three species. Allseedlings increased the microbial biomass in the birch soil. Kalmia humus and Kalmia root systems increased microbial energy deficiency and decreased microbial nutritional deficiency compared with the other humus types and seedlings used. Results are discussed in terms of each species' nutrient acquisition mechanism and its competitive ability during secondary succession.