Title

Canopy tree-soil-microbial interactions in a northern hardwood ecosystem: Effects of soil freezing disturbance on soil solution chemistry and nutrient loss

Date of Award

8-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Charles Driscoll

Keywords

Canopy tree-soil-microbial, Northern hardwood ecosystem, Soil freezing, Nutrient loss, Phosphorus, Nitrogen

Subject Categories

Biogeochemistry | Environmental Engineering | Terrestrial and Aquatic Ecology

Abstract

As the result of reductions in snow cover, soil freezing events may become more common under a warmer climate in northern temperate ecosystems. This thesis utilized a field manipulation of snow cover to examine the effects of soil freezing on soil solution chemistry at four experimental plots (two sugar maple and two yellow birch) at the Hubbard Brook Experimental Forest (HBEF). Soil freezing resulted in enhanced leaching of nitrogen, calcium, and magnesium from the forest floor at all four experimental plots. Subsequent to soil freezing, nitrate was the dominant nitrogen species mobilized in the forest floor of sugar maple plots while ammonium and dissolved organic nitrogen were the dominant forms leaching from the forest floor of yellow birch plots. The majority of nitrogen, calcium, and magnesium mobilized in the forest floor was removed from solution before leaching from the Bs soil horizon. The accelerated leaching of total nitrogen from the soil profile suggested that soil freezing events in the future may increase rates of nitrogen loss. Accelerated leaching of inorganic phosphorus from the forest floor, coupled with enhanced retention in the mineral soil, coincided with heightened nitrate leaching at sugar maple plots. The enhanced removal of soil solution phosphorus into unavailable forms in the mineral soil could affect the relative roles of nitrogen and phosphorus as limiting nutrients for forest growth. Fine root mortality was an important mechanism mobilizing nitrogen, phosphorus, and magnesium from the forest floor. Soil freezing resulted in pronounced acidification of soil solutions, driven by nitric acid and dissociation of organic acids, in the forest floor of sugar maple plots. From 1970 through 1989, the annual variability of soil freezing severity was significantly correlated with the variability of deviations of annual stream concentrations of calcium, magnesium, potassium and, nitrate from running averages at the HBEF. Soil freezing disturbance of the belowground environment may significantly disrupt the cycling, retention, and loss of nitrogen, phosphorus, magnesium, and calcium by resulting in the enhanced supply and or the decreased biotic demand for these nutrients.

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