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Net ecosystem carbon dioxide exchange over grazed steppe in central Mongolia
Author(s) -
Li S.G.,
Asanuma J.,
Eugster W.,
Kotani A.,
Liu J.J.,
Urano T.,
Oikawa T.,
Davaa G.,
Oyunbaatar D.,
Sugita M.
Publication year - 2005
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2005.01047.x
Subject(s) - eddy covariance , steppe , ecosystem , ecosystem respiration , environmental science , abiotic component , primary production , atmospheric sciences , carbon cycle , carbon dioxide , canopy , productivity , ecology , hydrology (agriculture) , biology , geology , geotechnical engineering , macroeconomics , economics
This paper presents results of 1 year (from March 25, 2003 to March 24, 2004, 366 days) of continuous measurements of net ecosystem CO 2 exchange (NEE) above a steppe in Mongolia using the eddy covariance technique. The steppe, typical of central Mongolia, is dominated by C 3 plants adapted to the continental climate. The following two questions are addressed: (1) how do NEE and its components: gross ecosystem production (GEP) and total ecosystem respiration ( R eco ) vary seasonally? (2) how do NEE, GEP, and R eco respond to biotic and abiotic factors? The hourly minimal NEE and the hourly maximal R eco were −3.6 and 1.2 μmol m −2 s −1 , respectively (negative values denoting net carbon uptake by the canopy from the atmosphere). Peak daily sums of NEE, GEP, and R eco were −2.3, 3.5, and 1.5 g C m −2 day −1 , respectively. The annual sums of GEP, R eco , and NEE were 179, 138, and −41 g C m −2 , respectively. The carbon removal by sheep was estimated to range between 10 and 82 g C m −2 yr −1 using four different approaches. Including these estimates in the overall carbon budget yielded net ecosystem productivity of −23 to +20 g C m −2 yr −1 . Thus, within the remaining experimental uncertainty the carbon budget at this steppe site can be considered to be balanced. For the growing period (from April 23 to October 21, 2003), 26% and 53% of the variation in daily NEE and GEP, respectively, could be explained by the changes in leaf area index. Seasonality of GEP, R eco , and NEE was closely associated with precipitation, especially in the peak growing season when GEP and R eco were largest. Water stress was observed in late July to early August, which switched the steppe from a carbon sink to a carbon source. For the entire growing period, the light response curves of daytime NEE showed a rather low apparent quantum yield ( α =−0.0047 μmol CO 2 μmol −1 photons of photosynthetically active radiation). However, the α values varied with air temperature ( T a ), vapor pressure deficit, and soil water content.