| Anthropogenic nitrogen deposition has the potential to alter forest soil carbon (C) and nitrogen (N) cycling, but to what extent different forest types are impacted is unclear. To address this, I studied the C and N cycling in forests of the Colorado Front Range, where ambient N deposition has been as high as 5-6 kg N ha-1 yr-1. Due to differences in the soil C:N ratio and anticipated differences in N cycling, I chose an aspen and a lodgepole pine forest and amended plots with 25 kg N ha -1 yr-1.; Following snowmelt, dissolved organic C (DOC) was greatest in the lodgepole pine soil, resulting in a DOC:DON ratio twice as great as the aspen. Nitrogen amendment decreased the DOC:DON ratio and increased the NO3 - concentration in the lodgepole pine soil from 26 mug NO3 -N L-1 to 346 mug NO3-N L-1. Nitrogen retention was high in both forests indicating a large capacity for retention of deposited N.; Surface soil incubations showed that the more lignin-rich, high C:N ratio lodgepole pine soil was more labile than the aspen soil. Apparently, the lower lignin content and lower C:N ratio soil in the aspen forest did not equate with a more labile soil organic matter (SOM). Nitrogen amendment did increase the CO2-C flux across both forests suggesting that decomposition was N limited in both forests, thus indicating a potential for increased CO 2-C flux from heterogeneous landscapes following N deposition.; Stabilization of mineral soil C and N was found to be much greater in the aspen soil due to higher Fe and Al hydroxide content, which in turn resulted in higher DOC sorption and explains the lower DOC during snowmelt. The sorption of humic and non-humic DOC was altered in the N amended soils indicating a potential for stabilization to disrupt the sorption mechanism and change the soil solution chemistry.; Results demonstrate that the inherent cycling of C and N differs substantially in these forests and yet a modest N amendment was capable of changing C and N cycling in both forests. However, the lodgepole pine soil appears more susceptible to change following N amendment. |
