A. Takiyama
R.L. Wershaw
R.G. Qualls
2003
<p><span>Since twice as much C is sequestered </span>in<span> soils as is contained </span>in<span> the atmosphere, the factors controlling the </span>decomposition<span> rate of soil C are important to the assessment of the effects of climatic change. The </span>formation<span> of chemically resistant </span>humic<span> </span>substances<span> might be an important process controlling recycling of CO</span><sub>2</sub><span> to the atmosphere. Our objectives were to measure the rate of </span>formation<span> and </span>loss<span> of </span>humic<span> </span>substances<span> during 13 yr of litter </span>decomposition<span>. We placed nets on the </span>floor<span> of </span>a<span> white </span>pine<span> (Pinus strobus) </span>forest<span> to separate each annual layer of litter for 13 yr and measured </span>humic<span> </span>substance<span> concentration using NaOH extraction followed by chromatographic fractionation. The </span>humic<span> acid fraction increased from 2.1% of the C </span>in<span> litterfall to 15.7% after 1 yr. On </span>a<span> grams per square meter (g m</span><sup>-2</sup><span>) basis the </span>humic<span> </span>substance<span> fraction increased during the first year and then declined, with </span>a<span> half decay time (t</span><sub>1/2</sub><span>) of 5.1 yr, which was significantly slower than the bulk litter (t</span><sub>1/2</sub><span> = 3.9 yr). The carboxylic C concentration estimated from </span><sup>13</sup><span>C nuclear magnetic resonance (NMR) increased </span>in<span> the litter over time, though total mass of carboxylic acid C </span>in<span> the </span>forest<span> </span>floor<span> also declined over the 13-yr period (t</span><sub>1/2</sub><span> = 4.6 yr). While </span>humic<span> </span>substances<span> </span>in<span> the </span>forest<span> </span>floor<span> decomposed at </span>a<span> somewhat slower rate than bulk litter during Years 1 to 13, they decomposed much faster than has been calculated from </span><sup>14</sup><span>C dating of the refractory fraction of organic matter </span>in<span> the mineral soil.</span></p>
application/pdf
10.2136/sssaj2003.0899
en
American Society of Agronomy
Formation and loss of humic substances during decomposition in a pine forest floor
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