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Document Type:Latin Dissertation
Language of Document:English
Record Number:53768
Doc. No:TL23722
Call number:‭3171900‬
Main Entry:Jorge Francisco Perez Quezada
Title & Author:Carbon flux patterns in agroecosystems of northern KazakhstanJorge Francisco Perez Quezada
College:University of California, Davis
Date:2005
Degree:Ph.D.
student score:2005
Page No:132
Abstract:Carbon dioxide flux (FCO2) patterns were assessed on four agroecosystems of the semiarid steppe in northern Kazakhstan (51°37' N, 71°05' E). Fields representing virgin land (VL), crested wheatgrass (CW), wheat (W) and abandoned land (AL) were sampled in four blocks, separated about 20 km from each other. Measurements were done during the growing season of 2002, using two mobile eddy covariance (EC) towers, one Bowen ratio (BR) station and one closed chamber (CC) system. The large amount of flux data collected required a quality control protocol before being used. A sequential fitting of a time series model (second-order autoregressive) to variables involved in the calculation of FCO2 performed well in all conditions. An automated version of this protocol could be used as a standard, which would eliminate the “observer” error when comparing FCO2 estimations from different research groups and make the process considerably faster. The main environmental drivers of net ecosystem exchange (NEE) and ecosystem respiration (Re) were photosynthetically active radiation (PAR) and soil temperature (Tsoil) respectively. Gross photosynthesis reached a maximum around 0.95 mg m−2 s−1 for W-AL and 0.5 mg m−2 s−1 for CW-VL; the latter had lower NEE_season but higher levels at the beginning and end of the season. The parameter extraction from nonlinear light-response models allowed obtaining the daily FCO2 patterns for agroecosystems sampled only intermittently by using continuous measurements of the driving variables. Seasonal gross primary productivity and Re were correctly predicted by NDVI_days (R 2 = 0.82) and Tsoil (R2 = 0.83) respectively. Fluxes on W and AL were compared in more detail. No difference in fluxes was found when considering the effect of blocks and rotations. When the effect of PAR was added to the model, AL had a significantly higher (P = 0.024) daytime NEE than W. This relation was consistent only in two blocks, which demonstrated the importance of sampling more than one location. The NEE_season for AL and W was 853 and 574 g m−2. Based on land use statistics from the 1992–2004 period, the NEE_season was estimated to fluctuate between 0.1047 and 0.1099 Petagram (1015 g) for the 15 M ha of W-AL area.
Subject:Health and environmental sciences; Earth sciences; Biological sciences; Agroecosystems; Carbon flux; Kazakhstan; Primary production; Ecology; Environmental science; Agriculture; Biogeochemistry; 0768:Environmental science; 0473:Agriculture; 0329:Ecology; 0425:Biogeochemistry
Added Entry:E. Laca
Added Entry:University of California, Davis