Soil respiration is a major flux of carbon to the atmosphere in terrestrial ecosystems. If belowground carbon cycling processes are disrupted, as by N deposition in northern hardwood forests, there could be feedbacks to atmospheric CO2. Despite its importance in the global carbon budget, soil respiration is not widely studied across different levels of nutrient availability in soils. In this study, we measured soil respiration across northern hardwood forest sites of differing fertility and age in the White Mountains of New Hampshire.
Across the range of soil nutrient availability, soil respiration and belowground carbon allocation were lower in sites with relatively low nutrient availability compared with sites categorized as medium or high fertility. Soil respiration and belowground carbon allocation did not differ significantly with forest age.
Summer soil respiration rate was not correlated to soil P and Ca availability, but was low in soils with high N availability. This result suggests that greater N availability in soils may contribute to less belowground carbon allocation in northern hardwood forests.
To further study single and synergistic nutrient effects on soil or microbial respiration, nitrogen and phosphorus were applied in treatments of: N-only, P-only, N+P, and control. There were no significant N or P fertilization effects on soil or microbial respiration after two years of fertilization treatment.
To study microbial respiration alone, five stands (4 plots in each stand) were selected in which living roots were severed by digging trenches. Although total soil respiration did not change after fertilization, the contribution of microbial respiration to soil respiration increased significantly in N+P plots compared to N-only and control plots with trenches. Microbial respiration in laboratory incubations also suggested that there were no discernible changes in Oe and Oa horizons after fertilization.
Data from this study suggest that nutrient availability, particularly N, can affect soil respiration. The two-year study period was not long enough to detect fertilization effects on soil and microbial respiration, hence long-term tracking of the fertilization treatments in this study will be necessary to determine if belowground carbon flux changes in response to increased N and P availability in soils.
|Advisor:||Yanai, Ruth D.|
|Commitee:||Cleavitt, Natalie L., Fahey, Timothy J., Howard, Joel R., Volk, Timothy A.|
|School:||State University of New York College of Environmental Science and Forestry|
|Department:||Forest Resources Management|
|School Location:||United States -- New York|
|Source:||DAI-B 75/07(E), Dissertation Abstracts International|
|Keywords:||Bartlett experimental forest, Belowground carbon allocation, Fine root biomass, Hubbard brook experimental forest, Jeffers brook, New hampshire, Soil respiration, White mountains|
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