Effects of atmospheric acid deposition and single versus mixed leaf litters on foliar litter decomposition, carbon, nitrogen, phosphorus and calcium dynamics in a regenerating forest.

摘要

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. We conducted two litter decomposition studies at the Long-Term Soil Productivity (LTSP) study at the Fernow Experimental Forest (FEF) in West Virginia. In the LTSP study acid deposition is simulated by periodic ammonium sulfate additions (N+S). Other treatments include control (ref) (no additions or reference) and ammonium sulfate plus lime (lime). 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 snow melt. Mass loss, C, N, P and Ca dynamics were followed for 12 months.;Study 1: To understand how acid deposition interacts to affect ecosystem C, N, P, and Ca cycling and to assess the ability of lime to counteract that effect, we followed decomposition of a litter mix representative of the forest floor composition (oak 48%, yellow poplar 19%, maple 14%, magnolia 12%, cherry 4%, and birch 3%). At 6 and 7 months remaining N content in litter in N+S treatment was significantly lower than in reference and lime treatment (p 0.01) At 12 months, remaining mass was highest in lime treatment (43%) and it was significantly higher than the N+S (39%) and control (37%). Remaining C at 12 months was significantly higher in N+S (42%) treatment than in reference (36%) (p=0.0337). Remaining Ca was significantly higher in N+S treatment (42%) than in reference (36%) (p=0.0051). At 12 months, the remaining P in the N+S treatment (107%) was significantly higher than in the control (83%) and lime treatment (90%). Lower N immobilization and higher P immobilization during leaf litter decomposition in N deposition treatments indicate that high rates of atmospheric N deposition may affect nutrient dynamics during litter decomposition. 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 on counteracting the effects of acid deposition.;Study 2: To understand the effects of single versus mixed litters and their interaction with acid and lime treatments on the decomposition of Quercus rubra (oak) litter, we looked at oak in three different litter types. The three litter types: 1.ambient litter mix (48% oak, 19% poplar, 14% maple, 12% magnolia, 4% cherry, and 3% birch), 2. 50% oak and 50% maple leaves and 3. Pure oak. At each sampling oak leaves were sorted from other leaf litter species. Mass loss, C, N, P, and Ca dynamics were quantified in oak decomposing alone (Oak), oak decomposing with maple (Oak+), and oak decomposing with maple, yellow poplar, magnolia, cherry and birch (Oak++). The decay constant (k) was significantly higher in Oak++ (0.682) than in Oak+ (0.614) and in Oak (0.595) (p0.0030). Throughout the 12 months of decomposition, N and P were immobilized in Oak, Oak+, and Oak++ litters in all treatments. Mass loss of oak was significantly affected by litter type. At 12 months, remaining mass of oak was significantly lower in Oak++ (46 %) than in Oak (53 %) and Oak+ litter (51 %) (p0.0001). Presence of other species significantly influenced oak decomposition but had no significant effect on C, N, P or Ca dynamics.