Variation in soil net mineralization rates with dissolved organic carbon additions

Northeastern forest are generally considered to be nitrogen limited, even t hough soil microbial populations may in fact be limited by the amount of ca rbon required as an energy source. Field studies have shown that with incre asing N availability, net mineralization rates increase initially but then decrease over time. One possible reason for a reduction in net mineralizati on rates is that labile soil carbon, such as dissolved organic carbon (DOC) , becomes depleted. Five-week laboratory incubations of organic and mineral soil samples with different carbon amendments were performed in order to d etermine the effect of carbon quality on potential net nitrification and ne t mineralization rates. Net nitrogen immobilization was greater in soils in cubated with glucose amendments than those incubated with more complex carb on compounds such as humic acid. Although this resulted in lower net minera lization rates overall, net immobilization is an indicator of immediate mic robial response to the carbon substrate. Net nitrification was not detected , likely due to the short duration of the incubations. Measurements of gros s mineralization rates may be necessary to see an overall effect of carbon substrate on N cycling in these soils. (C) 2000 Elsevier Science Ltd. All r ights reserved.