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Formation and Loss of Humic Substances During Decomposition in a Pine Forest Floor

^a Dep. of Environmental and Resource Sciences, Univ. of Nevada, Reno, NV 89557
^b U.S. Geological Survey, Box 25046, MS 408, Denver, CO 80225

View larger version (42K): [in a new window]   Fig. 1. Extraction and fractionation procedure.

View larger version (19K): [in a new window]   Fig. 2. Loss of C and humic substances from the forest floor as a function of time. Each point represents one of five replicate plots. Data for the first year is connected by a dashed line. Data for Years 1 to 13 are represented by a solid exponential regression line and the regression statistics refer to data from 1 to 13 yr. As a statistical rationale for excluding the first year decomposition from the regression, we found that neither the 95% nor the 99% confidence intervals for the data at x = 0 yr included the intercept predicted from the regressions in Fig. 2.

View larger version (12K): [in a new window]   Fig. 3. Loss of carboxylic C functional groups from the forest floor. Each data point represents one of five replicate plots.

View larger version (33K): [in a new window]   Fig. 4. (A) Carbon-13 direct polarization magic angle spinning (13C DP/MAS) and (B) 13C cross polarization magic angle spinning (CP/MAS) and spectra for litter samples. Spectra for the humic acid and humin fractions are not shown.