Partitioning sources of soil‐respired CO₂ and their seasonal variation using a unique radiocarbon tracer

Abstract

Soil respiration is derived from heterotrophic (decomposition of soil organic matter) and autotrophic (root/rhizosphere respiration) sources, but there is considerable uncertainty about what factors control variations in their relative contributions in space and time. We took advantage of a unique whole-ecosystem radiocarbon label in a temperate forest to partition soil respiration into three sources: (1) recently photosynthesized carbon (C), which dominates root and rhizosphere respiration; (2) leaf litter decomposition and (3) decomposition of root litter and soil organic matter 41-2 years old.Heterotrophic sources and specifically leaf litter decomposition were large contributors to total soil respiration during the growing season. Relative contributions from leaf litter decomposition ranged from a low of $ 1 AE 3% of total soil respiration (6 AE 3 mg C m À2 h À1 ) when leaf litter was extremely dry, to a high of 42 AE 16% (96 AE 38 mg C m À2 h À1 ). Total soil respiration fluxes varied with the strength of the leaf litter decomposition source, indicating that moisture-dependent changes in litter decomposition drive variability in total soil respiration fluxes. In the surface mineral soil layer, decomposition of C fixed in the original labeling event (3-5 years earlier) dominated the isotopic signature of heterotrophic respiration.Root/rhizosphere respiration accounted for 16 AE 10% to 64 AE 22% of total soil respiration, with highest relative contributions coinciding with low overall soil respiration fluxes. In contrast to leaf litter decomposition, root respiration fluxes did not exhibit marked temporal variation ranging from 34 AE 14 to 40 AE 16 mg C m À2 h À1 at different times in the growing season with a single exception (88 AE 35 mg C m À2 h À1 ). Radiocarbon signatures of root respired CO 2 changed markedly between early and late spring (March vs. May), suggesting a switch from stored nonstructural carbohydrate sources to more recent photosynthetic products.

Soil Respiration in Different Ages of Teak Plantations in Thailand

“…As Hashimoto 8 suggested that forest soils in Thailand responded to soil temperature by soil incubation experiments, a temperature parameter 4 also may improve the estimation of annual CO 2 efflux to some extent. Moreover, seasonal variation in CO 2 sources should be studied in future because respiration of soil microbes and that of plant roots respond differently to seasonal environment 2,18 . In conclusion, carbon dynamics in the soil under teak plantations in western Thailand were determined by the soil moisture regime, which is controlled by seasonal rainfall pattern and annual rainfall.…”

Temperature response functions introduce high uncertainty in modelled carbon stocks in cold temperature regimes

“…We have to bear in mind, however, that measured data at each individual site may be influenced by additional factors apart from the temperature response function, such as soil moisture conditions (Rodrigo et al, 1997;Cisneros-Dozal et al, 2006), litter chemistry (Berg and Laskowski, 2005b) and soil quality (Conant et al, 2008). Still, the regression analysis based on the compound data set shows that the default response equation of Lloyd-Taylor in LPJ-GUESS can still be used for further work.…”

“…It is often conceptualised as several distinct pools with increasing residence times (Knorr et al, 2005;Kirschbaum, 2004;Eliasson et al, 2005) or as a continuous entity with gradually changing decay rates (Ågren and Bosatta, 1987;Bosatta andÅgren, 1999). Decomposition of SOM is highly complex, as it is driven by a combination of factors such as temperature (Berg and Laskowski, 2005a), moisture conditions (Cisneros-Dozal et al, 2006) and its chemical quality (Berg and Laskowski, 2005b;Weedon et al, 2009;Cornwell et al, 2008). Many biogeochemical models have been developed and applied to study the response of the carbon cycle to past, current and future changes in climate.…”

Frontiers and challenges in soil respiration research: from measurements to model-data integration

“…To date, this approach has been used to look at autotrophic and heterotrophic contributions over seasonal to interannual timescales in temperate (Cisneros-Dozal et al 2006;Gaudinski et al 2000), boreal (Czimczik et al 2006;Hahn et al 2006;Schuur and Trumbore 2006), and semi-arid ecosystems; and with manipulations of rain (Borken et al 2006) and snow ). In addition, 14 C partitioning may also be an effective approach to test more specific process-level hypotheses on shorter timescales, particularly when combined with automated soil respiration measurements .…”