Separation of soil respiration: a site-specific comparison of partition methods

Without accurate data on soil heterotrophic respiration (R-h), assessments of soil carbon (C) sequestration rate and C balance are challenging to produce. Accordingly, it is essential to determine the contribution of the different sources of the total soil CO2 efflux (R-s) in different ecosystems, but to date, there are still many uncertainties and unknowns regarding the soil respiration partitioning procedures currently available. This study compared the suitability and relative accuracy of five different R s partitioning methods in a subtropical forest: (1) regression between root biomass and CO2 efflux, (2) lab incubations with minimally disturbed soil microcosm cores, (3) root exclusion bags with hand-sorted roots, (4) root exclusion bags with intact soil blocks and (5) soil delta C-13-CO(2 )natural abundance. The relationship between R-h and soil moisture and temperature was also investigated. A qualitative evaluation table of the partition methods with five performance parameters was produced. The R-s was measured weekly from 3 February to 19 April 2017 and found to average 6.1 +/- 0.3 Mg C ha(-1 )yr(-1 ). During this period, the Rh measured with the in situ mesh bags with intact soil blocks and hand-sorted roots was estimated to contribute 49 +/- 7 and 79 +/- 3 % of R-s, respectively. The Rh percentages estimated with the root biomass regression, microcosm incubation and delta C-13-CO2 natural abundance were 54 +/- 41, 8-17 and 61 +/- 39 %, respectively. Overall, no systematically superior or inferior R-s partition method was found. The paper discusses the strengths and weaknesses of each technique with the conclusion that combining two or more methods optimizes R-h assessment reliability.