Progress 10/01/03 to 09/30/06
Outputs
The effects of organic matter and nutrient supply on the solution chemistry of forest soils were determined by sampling soil solution from lysimeters at three long-term experimental manipulations. At the Harvard Forest (HF), soil solution was sampled at the DIRT plots and the chronic N plots; in the Luquillo Experimental Forest (LEF), soil solution was sampled at the chronic N plots. The DIRT plots at HF involve manipulations of soil organic matter inputs, including 2 times litter input, no litter input, no OA horizon, trenched (no root input), trenched/no litter, and control. The chronic N plots at HF have additions of 50 and 150 kg N per ha per year; at the LEF, two different forest sites are fertilized with 50 kg N per ha per year. Results pooled across all the sites and experiments show that production of dissolved organic carbon (DOC) is remarkably insensitive to N additions and the changes in ecosystem structure (primary productivity, soil microflora) that
accompany N fertilization. Nor is DOC production strongly related to organic matter supply; only litter doubling significantly affects DOC concentrations. Dissolved organic nitrogen (DON), in contrast, is very sensitive to inorganic N application, with concentrations doubling or tripling with fertilization. This suggests a fundamental decoupling of the C and N cycles with changes in N inputs, as production of DOC and DON appear to be regulated by different mechanisms.
Impacts
Dissolved organic carbon (DOC), an important contaminant in water supplies, changes its character but not its overall concentration when forests are amended with nitrogen. In contrast, concentrations of DOC increase when organic matter is added to forest soils, such as with increased leaf litter inputs. Better understanding of how forest nutrient cycles affect the DOC in groundwater will improve forest management, and result in better predictions of the impacts that changing forest conditions will have on water quality.
Publications
- McDowell, W.H., A. Zsolnay, J. A. Aitkenhead-Peterson, E.G. Gregorich, D. L. Jones, D. Jodemann, K. Kalbitz, B. Marschner, and D. Schwesig. 2006. A comparison of methods to determine the biodegradable dissolved organic carbon from different terrestrial sources. Soil Biology and Biochemistry 38:1933-1942.
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Progress 10/01/04 to 09/30/05
Outputs
The effects of organic matter and nutrient supply on the solution chemistry of forest soils were determined by sampling soil solution from lysimeters at three long-term experimental manipulations. At the Harvard Forest (HF), soil solution was sampled at the DIRT plots and the chronic N plots; in the Luquillo Experimental Forest (LEF), soil solution was sampled at the chronic N plots. The DIRT plots at HF involve manipulations of soil organic matter inputs, including 2 times litter input, no litter input, no OA horizon, trenched (no root input), trenched/no litter, and control. The chronic N plots at HF have additions of 50 and 150 kg N per ha per year; at the LEF, two different forest sites are fertilized with 50 kg N per ha per year. Results pooled across all the sites and experiments show that production of dissolved organic carbon (DOC) is remarkably insensitive to N additions and the changes in ecosystem structure (primary productivity, soil microflora) that
accompany N fertilization. Nor is DOC production strongly related to organic matter supply; only litter doubling significantly affects DOC concentrations. Dissolved organic nitrogen (DON), in contrast, is very sensitive to inorganic N application, with concentrations doubling or tripling with fertilization. This suggests a fundamental decoupling of the C and N cycles with changes in N inputs, as production of DOC and DON appear to be regulated by different mechanisms.
Impacts
This project provides fundamental information about controls on soil solution chemistry in forest ecosystems, with an emphasis on factors controlling the production and delivery of dissolved organic carbon and nitrogen (DOC and DON) to surface waters. DOC and DON are important in aquatic nutrient cycles and as contaminants in drinking water supplies. Better understanding of forest nutrient cycles will improve forest management and facilitate predictions of changes in forests with changing climate.
Publications
- Macy, Jordan. 2005. Initial effects of N additions in two rain forest ecosystems of Puerto Rico. M.S. thesis, University of New Hampshire, Durham, 66 pps.
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Progress 10/01/03 to 09/30/04
Outputs
The effects of organic matter and nutrient supply on the solution chemistry of forest soils were determined by sampling soil solution from lysimeters at three long-term experimental manipulations. At the Harvard Forest (HF), soil solution was sampled at the DIRT plots and the chronic N plots; in the Luquillo Experimental Forest (LEF), soil solution was sampled at the chronic N plots. The DIRT plots at HF involve manipulations of soil organic matter inputs, including 2 times litter input, no litter input, no OA horizon, trenched (no root input), trenched/no litter, and control. The chronic N plots at HF have additions of 50 and 150 kg N per ha per year; at the LEF, two different forest sites are fertilized with 50 kg N per ha per year. Results pooled across all the sites and experiments show that production of dissolved organic carbon (DOC) is remarkably insensitive to N additions and the changes in ecosystem structure (primary productivity, soil microflora) that
accompany N fertilization. Nor is DOC production strongly related to organic matter supply; only litter doubling significantly affects DOC concentrations. Dissolved organic nitrogen (DON), in contrast, is very sensitive to inorganic N application, with concentrations doubling or tripling with fertilization. This suggests a fundamental decoupling of the C and N cycles with changes in N inputs, as production of DOC and DON appear to be regulated by different mechanisms.
Impacts
This project provides fundamental information about controls on soil solution chemistry in forest ecosystems, with an emphasis on factors controlling the production and delivery of dissolved organic carbon and nitrogen (DOC and DON) to surface waters. DOC and DON are important in aquatic nutrient cycles and as contaminants in drinking water supplies. Better understanding of forest nutrient cycles will improve forest management and facilitate predictions of changes in forests with changing climate.
Publications
- Aitkenhead-Peterson J.A., W.H. McDowell and J.C. Neff. 2003. Sources, production and regulation of allochthonous dissolved organic matter In S.E.G. Findlay and R.L. Sinsabaugh (Eds). Aquatic Ecosystems: Interactivity of Dissolved Organic matter. Academic Press, San Diego.
- McDowell, W.H. 2003. Dissolved organic matter in soils-future directions and unanswered questions. Geoderma 113:179-186.
- Nadelhoffer, K., R. Boone, R. Bowden, J. Canary, J. Kaye, P. Micks, A. Ricca, W. McDowell, and J. Aitkenhead. 2004. The DIRT experiment: litter and root influences on forest soil organic matter stocks and function. pp. 300-315 In: D. Foster and J. Aber (eds.), Forests in Time: The environmental consequences of 1,000 years of change in New England. Yale University Press.
- Aber, J., A. Magill, K. Nadelhoffer, J. Melillo, P. Steudler, P. Micks, J. Hendricks, R. Bowden, W. Currie, W. McDowell, and G. Berntson. 2004. Exploring the process of nitrogen saturation. pp. 259-279 In: D. Foster and J. Aber (eds.), Forests in Time: The environmental consequences of 1,000 years of change in New England. Yale University Press.
- McDowell, W.H., A.H. Magill, J. A. Aitkenhead-Peterson, J.D. Aber, J.L. Merriam, S.S. Kaushal. 2004. Effects of chronic nitrogen amendment on dissolved organic matter and inorganic nitrogen in soil solution. Forest Ecology and Management 196:29-41.
- Magill, A.H., J.D. Aber, W.S. Currie, K.J. Nadelhoffer, M.E. Martin, W.H. McDowell, J.M. Mellillo, and P. Steudler. 2004. Ecosystem response to 15 years of chronic nitrogen additions at the Harvard Forest LTER, Massachusetts, USA. Forest Ecology and Management 196:7-28.
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