PS 24-47 - Exploring the role of plant detrital inputs in regulating soil temperature and moisture in a northern temperate forest

Background/Question/Methods

Plant detrital inputs influence soil organic matter (SOM) dynamics through complex biogeochemical processes that control rates of SOM accumulation and degradation, and in turn, regulate abiotic factors including soil temperature and moisture. Investigating how changes to detrital inputs impact these abiotic conditions is vital to our understanding of SOM decomposition and nutrient cycling on local and global scales, yet there are few studies that examine this interaction directly. By using a long-term litter manipulation experiment, the Detrital Input and Removal Treatments (DIRT) at the University of Michigan Biological Station, we monitored soil abiotic conditions in 8 different litter input/removal and chronic N addition treatments: control (C), N addition (F), doubled litter input (DL), doubled litter + N addition (DLF), wood addition (W), litter removal (NL), root exclusion (NR), and litter removal and root exclusion (NI). We collected bi-weekly soil temperature and moisture measurements over a 7 week period from Aug. through mid-Sep. 2019 and sampled soils for soil physical and chemical parameters including carbon and nitrogen content, and horizon depth.

Results/Conclusions

We predicted that treatments with increased litter/nutrient inputs (F, DL, DLF, W) would have less variable soil temperature and moisture than the control, and the treatments with decreased litter inputs (NL, NR, NI) would see more variable soil temperature and moisture. After 15 years of manipulations, the DIRT treatments had significant effects on organic (O) and topsoil (A) horizon depths and soil organic carbon (SOC) content. Mean soil moisture does not significantly vary for any of the treatments, but coefficients of variation are far lower than the control in all treatments except the wood addition (W) and litter removal (NL). This suggests that both increases and decreases in litter inputs from control inputs may mediate soil moisture better than the control depending on the organic matter source. Mean soil temperatures were significantly higher in the root exclusion treatments (NR, NI) while the N and wood addition treatments (F, W) had significantly lower mean temperatures. Soil temperature coefficients of variation were higher than the control in the litter removal treatments (NL, NI). Additionally, there was a strong negative relationship between O horizon mass and soil temperature variation (r2=0.699) suggesting surface plant litter buffers soil temperature even at 15cm depth.