Manipulating forests to increase soil carbon storage: Calcium and nitrogen fertilization of red spruce stands (Picea rubens)

Sequestering atmospheric carbon (C) in forests is a commonly suggested approach to mitigating global climate change. Most analyses have considered vegetation as the primary forest C sink, It has been assumed that soil C pools can be changed only over long time periods. In the research presented here, it was hypothesized that experimental manipulation of calcium (Ca) and nitrogen (N) could increase soil C storage over a short (5-year) period, through effects on the quantity and chemical quality of decomposing litter.; This study examined the effects of Ca and N fertilization on tree productivity, litterfall, and soil C storage in three red spruce (Picea rubens) stands in northeastern U.S. (Big Moose NY (BM), Groton VT (GR), and Hubbard Brook NH (HB)). Thirty-m square plots were fertilized with calcium (160 kg ha--1 yr--1), nitrogen (100 kg ha --1 yr--1), or calcium+nitrogen each year from 1992--1999 (in addition to unfertilized controls). Tree species and diameter at breast height (DBH) were recorded. Litterfall was collected annually and analyzed for C and N. Soil cores were taken in November 1996.; Soil inputs of C and N from litterfall increased in all treatments. There was a significant increase in soil C and N at HB in the calcium+nitrogen treatment after 5 years of fertilization. At BM, soil C and N were lower in fertilized plots than in controls, suggesting a different pattern of forest floor decomposition due to treatment. However, soil C content in unfertilized plots was significantly greater at BM than at HB or GR.; The observed increase in litterfall C was insufficient to account for the increased soil C at HB. It is suggested that, in some stands, nitrogen forms complexes with organic matter that make it more resistant to decomposition, increasing soil C storage over a short time. However, individual site characteristics strongly affected sequestration capacity. Furthermore, it appears that more soil C can be stored in a system changing to a different forest type, as at BM (a spruce stand converting to mixed hardwood-spruce).