No abstract

Ecosystem nitrogen (N), phosphorus (P), and calcium (Ca) fluxes are affected by inputs of atmospheric N. Oak litter may additionally affect these fluxes because of its high-lignin content. We analyzed nutrient dynamics in ambient mixed-species litter in an aggrading hardwood stand at the Fernow Experimental Forest in West Virginia. We separated oak from the mix for analysis (oak) and compared it with total litter (all species) to understand how oak affects nutrient fluxes in the litter layer. The study was conducted under ambient atmospheric deposition, under elevated atmospheric deposition, and under elevated deposition plus mitigation with dolomite. N flux between litterfall and 12 months later indicated a net loss in all-species litter of up to 7.3 kg N·ha–1 and a retention of up to 0.6 kg N·ha–1 in oak. P flux included losses in all species in ambient and in dolomite treatments of up to 0.19 kg P·ha–1 and gains of up to 0.12 kg P·ha–1 in oak in all treatments. Oak mineralized Ca at an average across treatments of 4.6 kg Ca·ha–1 compared with 16 kg Ca·ha–1 in all species, with half of that when trees were dormant. Percent immobilization and release over initial litter were greater in oak than in all species, but nutrient fluxes were lower in oak than in all species because of low oak litter mass. Elevated deposition lowered N and increased P immobilization. Dolomite appeared to affect early N dynamics only. With an increase in litterfall mass when forests mature, these effects are also likely to increase.

The abundance of oak is declining in the central hardwood forest, resulting in structural and functional changes in the litter layer. We hypothesized that a decline in oak litter mass associated with a lower oak component will result in an increase in nutrient cycling rates in the litterlayer. To test this hypothesis, we compared mass loss and C, N, P, and Ca dynamics in pure oak litter and in litter made of 48% oak plus 52% five other deciduous species in a central hardwood forest in West Virginia. In 12 months of litter decomposition, pure oak litter decomposed more slowly,retained more C and N, immobilized more and subsequently did not release P, and released less Ca than litter consisting of 48% oak plus five other species. Annual stand-level nutrient fluxes in pure oak and in 48% oak plus five other species litter were correspondingly +4.1 and −4.4kg ha−1 N, +0.22 and −0.17 kg ha−1 P, and −9.3 and −16.7 kg ha−1 Ca. These results indicate that a decline in oak will cause more rapid nutrient cycling in the litter layer of affected central hardwood stands.