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| Titel |
Exploring the "overflow tap" theory: linking forest soil CO2 fluxes and individual mycorrhizosphere components to photosynthesis |
| VerfasserIn |
A. Heinemeyer, M. Wilkinson, R. Vargas, J.-A. Subke, E. Casella, J. I. L. Morison, P. Ineson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 1 ; Nr. 9, no. 1 (2012-01-06), S.79-95 |
| Datensatznummer |
250006653
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| Publikation (Nr.) |
 copernicus.org/bg-9-79-2012.pdf |
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| Zusammenfassung |
Quantifying soil organic carbon stocks (SOC) and their dynamics accurately is
crucial for better predictions of climate change feedbacks within the
atmosphere-vegetation-soil system. However, the components, environmental
responses and controls of the soil CO2 efflux (Rs) are still
unclear and limited by field data availability. The objectives of this study
were (1) to quantify the contribution of the various Rs components,
specifically its mycorrhizal component, (2) to determine their temporal
variability, and (3) to establish their environmental responses and
dependence on gross primary productivity (GPP). In a temperate deciduous oak
forest in south east England hourly soil and ecosystem CO2 fluxes over
four years were measured using automated soil chambers and eddy covariance
techniques. Mesh-bag and steel collar soil chamber treatments prevented root
or both root and mycorrhizal hyphal in-growth, respectively, to allow
separation of heterotrophic (Rh) and autotrophic (Ra) soil
CO2 fluxes and the Ra components, roots (Rr) and mycorrhizal
hyphae (Rm).
Annual cumulative Rs values were very similar between years
(740 ± 43 g C m−2 yr−1) with an average flux of 2.0 ± 0.3 μmol
CO2 m−2 s−1, but Rs components varied. On average,
annual Rr, Rm and Rh fluxes contributed 38, 18 and 44%,
respectively, showing a large Ra contribution (56%) with a
considerable Rm component varying seasonally. Soil temperature largely
explained the daily variation of Rs (R2 = 0.81), mostly because of
strong responses by Rh (R2 = 0.65) and less so for Rr
(R2 = 0.41) and Rm (R2 = 0.18). Time series analysis revealed
strong daily periodicities for Rs and Rr, whilst Rm was
dominated by seasonal (~150 days), and Rh by annual
periodicities. Wavelet coherence analysis revealed that Rr and Rm
were related to short-term (daily) GPP changes, but for Rm there was a
strong relationship with GPP over much longer (weekly to monthly) periods
and notably during periods of low Rr. The need to include individual
Rs components in C flux models is discussed, in particular, the need to
represent the linkage between GPP and Ra components, in addition to
temperature responses for each component. The potential consequences of
these findings for understanding the limitations for long-term forest C
sequestration are highlighted, as GPP via root-derived C including Rm
seems to function as a C "overflow tap", with implications on the turnover
of SOC. |
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