Root decomposition in three coniferous forests: effects of substrate quality, temperature, and moisture

Controls of substrate quality, temperature, and moisture on woody root decomposition in the Pacific Northwest were explored using chronosequences, time series, laboratory incubations, and simulation modeling approaches at three sites: Cascade Head(CAH), H. J. Andrews (I-IJA), and Pringle Falls Experimental Forests (PRF).

In the chronosequence study, a structural component-oriented approach provided a better estimation of long-term mass loss than initial substrate indices.Western hemlock and ponderosa pine had higher
decomposition rate-constants (k =0.033 to 0.077/year) than Sitka spruce, Douglas-fir, and lodgepole pine (k = 0.011 to 0.03/year). This was mainly due to the presence of root resin cores in the latterspecies. During the first 2-years of decomposition in a time series experiment, speciessignificantly affected mass loss in fine and small roots (

In laboratory incubations, dead root respiration was optimum at 30-40 °C. The Q10 of root decomposition was influenced significantly (P

A model, ROOTDK, captured the overall mass loss pattern of Sitka spruce, Douglas-fir, and western hemlock but not of lodgepole pine and ponderosa pine. Root decomposition at CAH and PRF is more sensitive to climatic changes than HJA.Thus, even within the Pacific Northwest region the response of root decomposition to an altered climate can be divergent.