Effects of Nitrogen Deposition on Foliar Litter Decomposition and C, N, Ca, and P Dynamics in a Regenerating Forest

Increases in atmospheric N deposition over the past decades have raised concerns over nitrogen (N) retention and carbon (C) and nutrient cycling in forest ecosystems. Implications for C and nutrient cycling are particularly acute in forests with periodic biomass harvesting. To understand how acid deposition interacts with harvesting removals to affect ecosystem C, N, calcium (Ca) and phosphorus (P) cycling and to assess the ability of dolomitic lime to counteract that effect, we followed decomposition and element dynamics in foliar litter at the Long-Term Soil Productivity (LTSP) study at the Fernow Experimental Forest (FEF) in West Virginia. N deposition in the regenerating hardwood forest LTSP site is enhanced by periodic ammonium sulfate additions (N+S). Other treatments include reference (ref) plot (no additions) and ammonium sulfate plus lime (lime). Fresh litter collected from the forest floor at the LTSP study had oak (48%), yellow poplar (19%), maple (14%), magnolia (12%), cherry (4%), and birch (3%). Fresh litter was collected from treatment plots in November. Air-dried litter was weighed, and placed in nylon litter bags. Litter bags were placed in treatment plots in March after the snow melt. Mass loss, C, N, Ca and P dynamics were followed for 12 months. During the first 7 months of decomposition, N and P were immobilized in litter in all treatments. At 6 months, N immobilization was significantly lower (p=0.006) in the ammonium sulfate treatment (117%) than in the reference (128%) and lime (125%) treatments. At 7 months, N immobilization was significantly lower (p=0.009) in the N+S treatment (104%) than in the reference (113%) and in lime (115%) treatment. After twelve months, there were significant differences among treatments for mass loss, C, Ca, and P dynamics. Remaining mass was highest in lime treatment (43%) and it was significantly higher than the N+S (39%) and reference (37%) treatments. Remaining C was higher in both lime (41%) and N+S (42%) treatments than in reference (36%), and it was significantly different in ammonium sulfate treatment than in reference (p=0.0337). Remaining Ca was significantly higher in ammonium sulfate treatment (42%) than in reference (36%) (p=0.0051). Nitrogen mineralized at 12 months in all treatments, and the remaining P in the N+S treatment (107%) was significantly higher than in the reference (83%) and lime treatment (90%). Increase in N and P contents during decomposition suggest that both N and P are limiting to microbial growth and forests. Decreasing N immobilization and increasing P immobilization during leaf litter decomposition in N addition treatments indicate that atmospheric N deposition may affect nutrient dynamics during litter decomposition and may have an impact on ecosystem scale C cycling and forest productivity. Our results also showed that lime plays a significant role in decreasing litter decay, increasing N immobilization and decreasing P immobilization, which shows the potential of lime to counteract the effects of N deposition.

DOI: http://dx.doi.org/10.4038/jepsl.v3i1.7312