Abstract
Quantifying links between pyOM dynamics, environmental factors and processes is central to predicting ecosystem function and response to future perturbations. In this study, changes in carbon (TC), nitrogen (TN) , pH and relative recalcitrance (R50) for pine- and cordgrass-derived pyOM were measured at 3-6 weeks intervals throughout the first year of burial in the soil. Objectives were to 1) identify key environmental factors and processes driving early-stage pyOM dynamics, and 2) develop quantitative relationships between environmental factors and changes in pyOM properties. The study was conducted in sandy soils of a forested ecosystem in the Longleaf pine range, US with a focus on links between changes in pyOM properties, fire history (FH), cumulative precipitation (Pcum), average temperature (Tavg) and soil residence time (SRT). Pcum, SRT and Tavg were the main factors controlling TC and TN accounting for 77-91% and 64-96% of their respective variability. Fire history, along with Pcum, SRT and Tavg, exhibited significant controlling effects on pyOM, pH and R50 - accounting for 48-91% and 88-93% of respective variability. Volatilization of volatiles and leaching of water-soluble components (in summer) and the sorption of exogenous organic matter (fall through spring) were most plausibly controlling pyOM dynamics in this study. Overall, our results point to climatic and land management factors and physicochemical process as the main drivers of pyOM dynamics in the pine ecosystems of the Southeastern US.
Highlights
Current evidence suggests that despite a relatively small annual global production rate (40–259 Gt/yr; Bird et al, 2015; Santin et al, 2015), carbon in the fire-derived/pyrogenic organic matter pool accounts for a significant quantity (2–45%) of the total organic carbon in terrestrial systems (Skjernstad et al, 1999; Skjemstad et al, 2002; Lehmann et al, 2008; Reisser et al, 2016)
Two-way analysis of variance examining the effect of time and sampling site on changes in pyrogenic organic matter (pyOM) properties indicated that time (SRT) accounted for 80–92% of total variability in pyOM-associated organic carbon, 38–79% in pyOM-associated nitrogen and 81–91% in pyOM pH over the course of the study
Properties associated with a given pyOM source and within a given fire zone could be considered as replicates and can be spatially-aggregated based on pyOM feedstock and fire history without any significant loss in the amount of variability captured in the study
Summary
Current evidence suggests that despite a relatively small annual global production rate (40–259 Gt/yr; Bird et al, 2015; Santin et al, 2015), carbon in the fire-derived/pyrogenic organic matter (pyOM) pool accounts for a significant quantity (2–45%) of the total organic carbon in terrestrial systems (Skjernstad et al, 1999; Skjemstad et al, 2002; Lehmann et al, 2008; Reisser et al, 2016). There is fairly widespread consensus that the significant quantity of terrestrial carbon held in the pyOM pool is largely attributable to a comparatively higher innate resistance/recalcitrance to abiotic/biotic degradation and, longer turnover times of pyrogenic carbon compared to its non-pyrogenic counterpart (Schmidt and Noack, 2000; Hammes et al, 2008). Current estimates for carbon sequestration potential in the pyOM pool are as high as 9.5 × 109 tons C/yr—comparable to estimated carbon emission from fossil fuel burning (9.1 × 109 tons C/yr; Lehmann et al, 2006). It is well-known that this sequestration potential will vary with pyOM composition/properties as well as field/environmental conditions. Increasing degrees of thermal alteration favor increasingly condensed carbonand/or nitrogen-rich structures of higher innate environmental recalcitrance/stability (Knicker et al, 2008; Knicker, 2010; Zimmerman, 2010; Harvey et al, 2012)
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