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| Titel |
Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China |
| VerfasserIn |
X. Jia, T. S. Zha, B. Wu, Y. Q. Zhang, J. N. Gong, S. G. Qin, G. P. Chen, D. Qian, S. Kellomäki, H. Peltola |
| 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 ; 11, no. 17 ; Nr. 11, no. 17 (2014-09-08), S.4679-4693 |
| Datensatznummer |
250117577
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| Publikation (Nr.) |
 copernicus.org/bg-11-4679-2014.pdf |
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| Zusammenfassung |
| The carbon (C) cycling in semiarid and arid areas remains largely
unexplored, despite the wide distribution of drylands globally.
Rehabilitation practices have been carried out in many desertified areas,
but information on the C sequestration capacity of recovering vegetation is
still largely lacking. Using the eddy-covariance technique, we measured the
net ecosystem CO2 exchange (NEE) over a recovering shrub ecosystem in
northwest China throughout 2012 in order to (1) quantify NEE and its
components and to (2) examine the dependence of C fluxes on biophysical factors at
multiple timescales. The annual budget showed a gross ecosystem productivity
(GEP) of 456 g C m−2 yr−1 (with a 90% prediction interval of
449–463 g C m−2 yr−1) and an ecosystem respiration (Re) of 379 g C m−2 yr−1
(with a 90% prediction interval of 370–389 g C m−2 yr−1), resulting in a net C sink of 77 g C m−2 yr−1
(with a 90% prediction interval of 68–87 g C m−2 yr−1). The
maximum daily NEE, GEP and Re were −4.7, 6.8 and 3.3 g C m−2 day−1,
respectively. Both the maximum C assimilation rate (i.e., at the
optimum light intensity) and the quantum yield varied over the growing
season, being higher in summer and lower in spring and autumn. At the
half-hourly scale, water deficit exerted a major control over daytime NEE,
and interacted with other stresses (e.g., heat and photoinhibition) in
constraining C fixation by the vegetation. Low soil moisture also reduced
the temperature sensitivity of Re (Q10). At the synoptic scale, rain
events triggered immediate pulses of C release from the ecosystem, followed
by peaks of CO2 uptake 1–2 days later. Over the entire growing season,
leaf area index accounted for 45 and 65% of the seasonal variation in NEE
and GEP, respectively. There was a linear dependence of daily Re on GEP,
with a slope of 0.34. These results highlight the role of abiotic stresses
and their alleviation in regulating C cycling in the face of an increasing
frequency and intensity of extreme climatic events. |
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