Modeling Soil Temperature Effects on In Situ Decomposition Rates for Fine Roots of Loblolly Pine
A study was conducted to quantify the relationship between soil temperature and fine root decomposition. Undisturbed soil cores containing root systems of loblolly pine seedlings were incubated in the lab under field capacity moisture conditions at constant soil temperatures of 15° and 25°C. Some seedling root systems were allowed to decompose in situ outside, where soil moisture and temperature were recorded. Laboratory and outside in situ results were compared to decomposition rates for seedling roots that were washed, air-dried, and reburied outside in mesh bags. Laboratory decomposition rates of the seedling root system, which contained fine laterals and a small taproot, averaged 31% and 44% weight loss annually, while annual rates of only the fine lateral root component averaged 57% and 66% loss of total weight at 15° and 25°, respectively. Average annual Q-10s of 1.4 and 1.2 were calculated between 15° and 25° for whole root systems and lateral roots alone. Lab incubation results were used to construct a regression model for fine root decomposition as a function of cumulative average monthly temperature. The model was validated against data on the root systems that were allowed to decompose in situ outside. Decomposition of this material after 1 yr was 43% complete for the whole root system and 60% complete for laterals. The observed remaining weight at various time intervals was accurately predicted from the regression model. After 1 yr, roots in the buried bags displayed a weight loss similar to the outdoor in situ samples. However, their decomposition rate was linear, whereas both outdoor and incubator in situ samples followed a curvilinear decay path. FOR. SCI. 39(1):118-129.
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