Temperature response of litter and soil organic matter decomposition is determined by chemical composition of organic material

Abstract

The global soil carbon pool is approximately three times larger than the contemporary atmospheric pool, therefore even minor changes to its integrity may have major implications for atmospheric CO2 concentrations. While theory predicts that the chemical composition of organic matter should constitute a master control on the temperature response of its decomposition, this relationship has not yet been fully demonstrated. We used laboratory incubations of forest soil organic matter (SOM) and fresh litter material together with NMR spectroscopy to make this connection between organic chemical composition and temperature sensitivity of decomposition. Temperature response of decomposition in both fresh litter and SOM was directly related to the chemical composition of the constituent organic matter, explaining 90% and 70% of the variance in Q10 in litter and SOM, respectively. The Q10 of litter decreased with increasing proportions of aromatic and O-aromatic compounds, and increased with increased contents of alkyl- and O-alkyl carbons. In contrast, in SOM, decomposition was affected only by carbonyl compounds. To reveal why a certain group of organic chemical compounds affected the temperature sensitivity of organic matter decomposition in litter and SOM, a more detailed characterization of the (13) C aromatic region using Heteronuclear Single Quantum Coherence (HSQC) was conducted. The results revealed considerable differences in the aromatic region between litter and SOM. This suggests that the correlation between chemical composition of organic matter and the temperature response of decomposition differed between litter and SOM. The temperature response of soil decomposition processes can thus be described by the chemical composition of its constituent organic matter, this paves the way for improved ecosystem modeling of biosphere feedbacks under a changing climate.

Environmental correlates of peatland carbon fluxes in a thawing landscape: do transitional thaw stages matter?

“…Lower temperature sensitivity in the intact permafrost could also be related to DOC quality. Olefeldt et al (2012) report higher aromaticity in DOC exported from palsa and bog catchments at Stordalen compared to fen catchments and a high proportion of aromatic compounds in litter is generally associated with decreased temperature sensitivity (e.g., Erhagen et al, 2013). High temperature sensitivity in wetter sites has also been reported by Olefeldt et al (2013) in a meta-analysis of CH 4 emissions from terrestrial ecosystems worldwide.…”

Biochemical proxies indicate differences in soil C cycling induced by long-term tillage and residue management in a tropical agroecosystem

“…Changes in relative absorbance of organic functional groups were statistically significant, but minor (<7%). However, even small changes in SOM composition can reflect alteration of soil C cycling (e.g., Erhagen et al 2013;Haberhauer et al 2000;Shi et al 2006). Despite the semi-quantitative nature of DRIFT spectroscopy, the changes in relative absorbance of selected organic functional groups identify relative differences in SOM composition that are consistent with soil enzyme activities.…”

The effect of temperature and substrate quality on the carbon use efficiency of saprotrophic decomposition

“…The OM content was 0.93 ± 0.004(SD)kg kg −1 with a C content of 0.53 kg kg −1 and N content of 0.014 kg kg −1 , the C:N ration being 38. The composition of the OM (derived from CP-MAS 13 C NMR spectra) were as follow: alkyl C, 26%; methoxy−/N-alkyl, 6.5%; O-alkyl, 37%; di-Oalkyl, 11%; aromatic C, 9%; O-aromatic C, 6.6% and Carbonyl C, 4% (Erhagen et al 2013). …”

“…The version of the Respicond used had four different insulated water baths set to 4, 9, 14, or 19°C. The temperature in the baths is highly controlled and target temperature is maintained at ±0.02°C (Erhagen et al 2013). 48 subsamples of soil (1 g OM dry weight (dw; corresponding to 1.06 g soil dw) were placed in 250 ml incubation vessels and incubated at one of four temperatures (4, 9, 14, or 19°C).…”

“…Glucose is the single most common C-monomer derived from biopolymers. Carbohydrate polymers, including cellulose, normally constitute 40-45% of the O-horizon in boreal forests (Drotz et al 2010b;Erhagen et al 2013), and glucose is the dominant monomer following cellulose hydrolysis. The 13 C-labelled substrates were added together with nutrients to allow unlimited growth (Nordgren 1992).…”