Effects of a decade of litter manipulation on soil carbon-dioxide effluxes from a temperate mixed-deciduous forest

Project Overview
Project Abstract: 
Soils store more than 3 times the carbon in the atmosphere and all terrestrial vegetation. As a result, they are critical global carbon stores, the management of which will affect the long-term manifestations of global climate change impacts. Soil organic matter (SOM) correlates very strongly with model-predicted changes to future global carbon stores (Carvalhais et al 2014), and thus SOM dynamics have been well-studied and -understood at short time scales (Schmidt et al 2011); however, the factors and mechanisms affecting long-term SOM dynamics are not well understood. This study used the DIRT litter manipulation plots at UMBS to answer questions about how litter inputs and removals affect CO2 efflux at decadal scales. This study also analyzed the isotopic signature of treatment-specific CO2 effluxes to test for SOM priming—the accelerated decrease in old SOM caused by the addition of fresh SOM—, a process that has recently been hypothesized based on observed SOM dynamics at other DIRT sites. Soil respiration rates were measured with a LI-COR 6400 attached to an infrared gas analyzer across 3 replicates of litter manipulations including control, double litter, wood, no litter, no roots, no inputs, and fertilizer. These measurements were taken throughout the growing season and compared between 2014 and 2005. We also measured the δ13C of the CO2 respired. No differences in mean seasonal CO2 effluxes were found except in the No Litter treatment. Furthermore, seasonal differences in CO2 efflux within-year effects of litter additions and removals were present in both 2005 and 2014. Specifically, there was less seasonality in 2014 than in 2005 for all treatments except in the wood and fertilizer, which was not explained by soil temperature differences at 5 cm depth. Finally, the double litter and wood treatments were significantly depleted of δ13CO2 compared to control, and 13CO2 efflux rates were observed to be primarily a function of treatment-controlled total CO2 efflux rates. The results from the litter-removal treatments supported the priming hypothesis, but those from the litter-addition treatments did not. We conclude at minimum that long-term litter additions cause significant relative depletions in seasonal δ13CO2 effluxes in sandy temperate forest soils. Future studies include more isotopic analyses of effluxes and physical soil samples to compare SOM pools across treatments.
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Investigator Info
Years research project active: 
2013 to 2014