Differences in Soil and Leaf Litterfall Nitrogen Dynamics for Five Forest Plantations

Abstract Vegetation can influence N cycling in forest soils; however, it is difficult to isolate the positive feedback of vegetation on N cycling because other factors are often not held constant. The objective of this study was to measure and compare leaf litterfall N and in situ and laboratory N mineralization rates for 28‐yr‐old northern red oak ( Quercus rubra L.), European larch ( Larix decidua Miller), eastern white pine ( Pinus strobus L.), red pine ( P. resinosa Aiton), and Norway spruce [ Picea abies (L.) Karst.] plantations on a similar soil in southwestern Wisconsin. Average seasonal soil NO ‐ 3 and NH + 4 concentrations (mg kg −1 ) were 3.9 and 3.4 for red oak; 7.7 and 5.8 for European larch; 5.4 and 6.7 for white pine; 4.9 and 5.1 for red pine; and 5.2 and 6.2 for Norway spruce, respectively. Annual in situ net N mineralization in the top 20 cm of mineral soil differed significantly ( P < 0.01) among species and ranged from 46 kg ha −1 yr −1 for Norway spruce to 117 kg ha −1 yr −1 for European larch. Annual in situ nitrification differed significantly ( P < 0.001) among species and comprised from 42 (red oak) to 95% (European larch) of the total annual net N mineralized. Laboratory net N mineralization rates also differed significantly among the five species. Average annual leaf litterfall N content for a 2‐yr period ranged from 26 kg ha −1 yr −1 for white pine to 40 kg ha −1 yr −1 for Norway spruce but was not correlated to annual net N mineralization. We suggest that leaf litterfall lignin/N may be an important positive feedback mechanism that influences N mineralization.

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