Temperature‐dependent shift from labile to recalcitrant carbon sources of arctic heterotrophs

Abstract

Soils of high latitudes store approximately one-third of the global soil carbon pool. Decomposition of soil organic matter (SOM) is expected to increase in response to global warming, which is most pronounced in northern latitudes. It is, however, unclear if microorganisms are able to utilize more stable, recalcitrant C pools, when labile soil carbon pools will be depleted due to increasing temperatures. Here we report on an incubation experiment with intact soil cores of a frost-boil tundra ecosystem at three different temperatures (2 degrees C, 12 degrees C and 24 degrees C). In order to assess which fractions of the SOM are available for decomposition at various temperatures, we analyzed the isotopic signature of respired CO2 and of different SOM fractions. The delta13C values of CO2 respired were negatively correlated with temperature, indicating the utilization of SOM fractions that were depleted in 13C at higher temperatures. Chemical fractionation of SOM showed that the water-soluble fraction (presumably the most easily available substrates for microbial respiration) was most enriched in 13C, while the acid-insoluble pool (recalcitrant substrates) was most depleted in 13C. Our results therefore suggest that, at higher temperatures, recalcitrant compounds are preferentially respired by arctic microbes. When the isotopic signatures of respired CO2 of soils which had been incubated at 24 degrees C were measured at 12 degrees C, the delta13C values shifted to values found in soils incubated at 12 degrees C, indicating the reversible use of more easily available substrates. Analysis of phospholipid fatty acid profiles showed significant differences in microbial community structure at various incubation temperatures indicating that microorganisms with preference for more recalcitrant compounds establish as temperatures increase. In summary our results demonstrate that a large portion of tundra SOM is potentially mineralizable.

Peat decomposability in managed organic soils in relation to land use, organic matter composition and temperature

“…The temperature sensitivity of peat mineralization, as expressed by its Q 10 value, is a useful parameter for characterizing the intrinsic decomposability of SOM (Hogg et al, 1992;Biasi et al, 2005;Davidson and Janssens, 2006;Conant et al, 2008;Boddy et al, 2008;Karhu et al, 2010;Hilasvuori et al, 2013). In line with the biochemical and elemental evidence reviewed above, it was reported to increase with increasing resistance of peat soils against OM decomposition (Scanlon and Moore, 2000), soil depth and peat age (Hardie et al, 2011;Hilasvuori et al, 2013).…”

“…In contrast to other studies on unmanaged organic soils reporting no trend or increasing Q 10 values with depth (Scanlon and Moore, 2000; Wang et al, 2010;Hardie et al, 2011;Hilasvuori et al, 2013), the cropland and grassland profiles in our study had a lower Q 10 below the 60 cm depth. Various studies on SOM decomposition used Q 10 values as an indicator of SOM recalcitrance (Hogg et al, 1992;Biasi et al, 2005;Davidson and Janssens, 2006;Conant et al, 2008Conant et al, , 2011Hartley and Ineson, 2008;Hilasvuori et al, 2013). Considering that the presence of labile crop residues would decrease Q 10 in the topsoil rather than in the subsoil, the higher topsoil Q 10 may be explained by an extended accumulation of recalcitrant moieties.…”

Responses of peat carbon at different depths to simulated warming and oxidizing

“…The effect of temperature on Rs has been illustrated in a wide range of studies (Eliasson et al, 2005;Fierer et al, 2005;Lloyd and Taylor, 1994;Tucker et al, 2013). Biasi et al (2005) reported that temperature could influence the utilization of carbon source by microbes or microbial metabolism leading to Rs rate changes. Treat et al (2014) found that warmer and drier climate could result in substantial increase in carbon loss (Biasi et al, 2005;Dutta et al, 2006;Treat et al, 2014).…”

“…Biasi et al (2005) reported that temperature could influence the utilization of carbon source by microbes or microbial metabolism leading to Rs rate changes. Treat et al (2014) found that warmer and drier climate could result in substantial increase in carbon loss (Biasi et al, 2005;Dutta et al, 2006;Treat et al, 2014). DOC also was driven by temperature rising (Freeman et al, 2001b).…”

“…The deposited carbon was stored away from atmosphere and was sensitive to warming and oxidizing (Bosatta and Agren, 1999;Dorrepaal et al, 2009;Knorr et al, 2005). It would be decomposed when enough energy was supplied (Biasi et al, 2005). CO 2 emission from deeper depths (21-100 cm) kept stable under 8°C-AN condition but had unequal increases under warming and oxidizing conditions.…”