Exploring the overflow tap theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis

A study of a temperate deciduous oak forest in south east England analyzed the components of soil CO2 efflux (Rs), finding that autotrophic respiration (Ra)—comprising root (Rr) and mycorrhizal hyphae (Rm) respiration—contributes 56% of the total flux, with Rm acting as a carbon "overflow tap" linked to gross primary productivity (GPP).

• In a temperate deciduous oak forest in south east England, annual cumulative soil CO2 efflux (Rs) values averaged 740 ± 43 g C m−2 yr−1. The total flux is composed of heterotrophic (Rh) and autotrophic (Ra) components, with Rh contributing 44% and Ra contributing 56%. Within the Ra component, root respiration (Rr) accounts for 38% and mycorrhizal hyphae respiration (Rm) accounts for 18% of the total Rs.
• Soil temperature is the primary driver of daily Rs variation (R2 = 0.81), with the strongest response seen in Rh (R2 = 0.65), followed by Rr (R2 = 0.41) and Rm (R2 = 0.18). Temporal analysis shows that Rs and Rr exhibit strong daily periodicities, Rh exhibits annual periodicities, and Rm is dominated by seasonal periodicities of approximately 150 days.
• Wavelet coherence analysis indicates that both Rr and Rm relate to short-term daily changes in gross primary productivity (GPP). However, Rm shows a strong relationship with GPP over longer weekly to monthly periods, particularly when Rr is low. This suggests that GPP, via root-derived carbon including Rm, functions as a carbon "overflow tap," which has implications for the turnover of soil organic carbon (SOC).

APA

Stockholm Environment Institute (2012). Exploring the overflow tap theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis. https://www.sei.org/publications/exploring-the-overflow-tap-theory-linking-forest-soil-co2-fluxes-and-individual-mycorrhizosphere-components-to-photosynthesis/

Chicago

Stockholm Environment Institute. Exploring the overflow tap theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis. 2012. https://www.sei.org/publications/exploring-the-overflow-tap-theory-linking-forest-soil-co2-fluxes-and-individual-mycorrhizosphere-components-to-photosynthesis/.

Wikipedia

{{cite report |author=Stockholm Environment Institute |title=Exploring the overflow tap theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis |date=9 January 2012 |url=https://www.sei.org/publications/exploring-the-overflow-tap-theory-linking-forest-soil-co2-fluxes-and-individual-mycorrhizosphere-components-to-photosynthesis/ |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{stockholmenvironmentinstitute2012exploring, author = {{Stockholm Environment Institute}}, title = {{Exploring the overflow tap theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis}}, institution = {Stockholm Environment Institute}, year = {2012}, month = jan, url = {https://www.sei.org/publications/exploring-the-overflow-tap-theory-linking-forest-soil-co2-fluxes-and-individual-mycorrhizosphere-components-to-photosynthesis/}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }