Deciduous forest litter decomposition at two sulfur input rates

Author

Robert Philip Larkin

Date of Award

12-1981

Degree Type

Thesis

Degree Name

Master of Science

Major Professor

Frank W. Woods

Committee Members

J. M. Kelly, Jeffrey Wolt

Abstract

Two similar forested watersheds in East Tennessee were studied to determine the effects of atmospheric sulfur inputs on litter decomposition. Cross Creek watershed, located near a large coal-fired power plant, has received greater sulfur inputs than the more remote Camp Branch watershed. Decomposition was estimated through the measurement of forest floor respiration, litter microflora populations, litter and soil microarthropod populations, and litter nutrient status. A laboratory study was also conducted in which microcosms taken from the forest floor were exposed to different levels of sulfur inputs and their respiration rate measured over time.

Average forest floor respiration rates were very similar, 4.84 g CO₂•m^-2•day^-1 or 1766 g•m^-2•yr^-1 at Camp Branch and 4.90 g CO₂•m^-2•day^-1 or 1789 g•m^-2•yr^-1 at Cross Creek. Fractional loss rates provided estimates of annual decay rates(k) of .35 and .39 for Camp Branch and Cross Creek, respectively. Litter decomposition was estimated to contribute 31.5% of the total CO₂ output at Camp Branch and 35% at Cross Creek, while root respiration accounts for about 60-65%.

High sulfur inputs were found to reduce respiration rates in soil and litter microcosms over a period of time. Initial sulfur additions at all levels produced a slight stimulation of respiration, but low to moderate inputs produced no lasting effects. There was no difference between microcosms taken from the two watersheds regarding physical characteristics, respiration rates, or response to sulfur treatments.

Bacterial and fungal populations were about equal in size at both watersheds, with bacteria averaging 100 x 10⁶ per gram litter and fungi 23 x 10⁶ per gram litter. Total numbers of arthropods were consistently greater (averaging 34% greater) at Camp Branch. Acarina populations averaged 59% higher at Camp Branch, but Collembola populations were about equal at the two watersheds.

Nutrient element mobility in the litter and soil was similar at both watersheds and followed the order K>Mg>Ca>S>N≥P. Litterfall nutrient concentrations were slightly higher for all elements at Cross Creek, resulting in greater litter concentrations of calcium and magnesium. Litter concentrations of sulfur and nitrogen, however, were significantly greater at Camp Branch, indicating differences in the loss rates and cycling processes of these elements between the watersheds. There was no difference between the loss rates or litter concentrations of phosphorus, potassium, and sodium at the two watersheds.

Overall, decomposition was similar at the two watersheds. Present levels of sulfur inputs did not appear to have a major effect on decomposition rate, although sulfur inputs did appear to influence some mineralization and cycling processes and possibly lowered arthropod populations. Sulfur inputs when at high enough levels over a sufficient period of time can have an inhibitory effect on decomposition, but at lower levels, the influence of sulfur inputs on decomposition appear to be minimal.

Recommended Citation

Larkin, Robert Philip, "Deciduous forest litter decomposition at two sulfur input rates. " Master's Thesis, University of Tennessee, 1981.
https://trace.tennessee.edu/utk_gradthes/15221