Aboveground Production and N and P Cycling Along a Nitrogen Mineralization Gradient on Blackhawk Island, Wisconsin

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Abstract
Net aboveground production (4.1—9.5 Mg°ha—1) across a series of edaphic climax forests was highly correlated with field measurements of soil N mineralization (26—84 kg°ha—1°yr—1; r2 = 0.902, P < .001) and with soil silt + clay content (5—74%; r2 = 0.883, P < .001). Soil N mineralization was positively correlated with litter production and N and P return in litter. Soil N mineralization was negatively correlated with litter C:N and C:P ratios and with efficiency of P use in litter production. Efficiency of N use in litter production declined with increasing N mineralization except for inefficient use of N in a hemlock stand at low N mineralization. Changes of litter quality across the mineralization—soil texture gradient were due to species replacement rather than changes in litter quality within each species. Nitrification was not correlated with aboveground production. Both mineralization and nitrification were highly correlated with humus P content. Differences in nitrification among the soils appeared to be related to PO4—P supply in the spring and early summer and to NH4—N supply in mid— to late summer.