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Fig. 3. Average (with 95% confidence intervals) (a) 
13C values, (b) 15N values, and (c) C/N ratios from muffle furnace experiment for muffle burn duration using factorial data from all temperatures. The error term for the test of duration was the mean expected squared error from the factorial component of the ANOVA, which used sites and soil layers as replicates. Three preplanned contrasts were performed to compare means while respecting the overall experiment-wide alpha error rate of 0.05: 1 vs. 5 min, 5 vs. 15 min, and 15 vs. 60 min. Different letters under the lower confidence interval apply only to preplanned contrasts and indicate that means are significantly different at alpha = 0.05. Different letters were also assigned to the two most different means if the overall test was significant, but preplanned contrasts were all nonsignificant. Letters are not shown for 15N as the overall effects were not significant.
