Abstract
Abstract. Without accurate data on soil heterotrophic respiration (Rh), 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 (Rs) 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 Rs 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 δ13C–CO2 natural abundance. The relationship between Rh and soil moisture and temperature was also investigated. A qualitative evaluation table of the partition methods with five performance parameters was produced. The Rs was measured weekly from 3 February to 19 April 2017 and found to average 6.1 ± 0.3 MgCha-1yr-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 Rs, respectively. The Rh percentages estimated with the root biomass regression, microcosm incubation and δ13C–CO2 natural abundance were 54 ± 41, 8–17 and 61 ± 39 %, respectively. Overall, no systematically superior or inferior Rs partition method was found. The paper discusses the strengths and weaknesses of each technique with the conclusion that combining two or more methods optimizes Rh assessment reliability.
Highlights
During the 2016 Convention of the Parties (COP21) of the United Nations Framework Convention on Climate Change (UNFCCC) in Paris, the goal of increasing global soil organic carbon (SOC) stocks by 0.4 % per year was set, with the aim of mitigating global anthropogenic greenhouse gas emissions (Minasny et al, 2017)
A portion of these fresh organic compounds is respired by organisms and the other portion is converted into SOC by the genesis of soil organic matter (SOM) (Janzen, 2006; Lal, 2005)
Values are means and standard error; n = 22 for the root biomass regression, n = 47 for soil incubation, n = 28 for both root exclusion bag techniques. a Rh: heterotrophic respiration. b root exclusion bags (Rs): total soil efflux taken alongside the Rh efflux. c Efflux range at temperature between 14 ◦C and 26 ◦C. d Calculated as Rh from incubation at 14 and 26 ◦C divided by average field Rs at 14 and 26 ◦C, respectively
Summary
During the 2016 Convention of the Parties (COP21) of the United Nations Framework Convention on Climate Change (UNFCCC) in Paris, the goal of increasing global soil organic carbon (SOC) stocks by 0.4 % per year was set, with the aim of mitigating global anthropogenic greenhouse gas emissions (Minasny et al, 2017). Of the carbon (C) that enters into ecosystems via photosynthesis, a fraction is directly respired by the roots and above-ground plant parts (autotrophic respiration) to produce energy (i.e., adenosine-5 -triphosphate), with the other fraction synthesized into organic molecules Some of these C-containing compounds are harvested or consumed by herbivores and the remainder is added to the soil as plant residues (Janzen et al, 1998).
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