Energy and CO2 exchanges and influencing factors in spring wheat ecosystem along the Heihe River, northwestern China

Abstract

Spring wheat (Triticum aestivum Linn.) is an important crop for food security in the desert-oasis farmland in the middle reaches of the Heihe River in northwestern China. We measured fluxes using eddy covariance and meteorological parameters to explore the energy fluxes and the relationship between CO 2 flux and climate change in this region during the wheat growing seasons in 2013 and 2014. The energy balance closures were 70.5% and 72.7% in the 2013 and 2014 growing season, respectively. The wheat ecosystem had distinct seasonal and diurnal dynamics of CO 2 fluxes with U-shaped curves. The accumulated net ecosystemic CO 2 exchanges (NEE) were −111.6 and −142.2 g C/m 2 in 2013 and 2014 growing season, respectively. The ecosystem generally acted as a CO 2 sink during the growing season but became a CO 2 source after the wheat harvest. A correlation analysis indicated that night-time CO 2 fluxes were exponentially dependent on air temperature and soil temperature at a depth of 5 cm but were not correlated with soil-water content, water-vapour pressure, or vapour-pressure deficit. CO 2 flux was not correlated with the meteorological parameters during daytime. However, irrigation and precipitation, may complicate the response of CO 2 fluxes to other meteorological parameters. Keywords. Eddy covariance; energy and CO 2 fluxes; desert-oasis ecotone; spring wheat.

CO2 flux in a wheat‐soybean succession in subtropical Brazil: A carbon sink

“…The climatic conditions of this subtropical Brazilian region allow the soil to be cultivated throughout the year, thereby increasing its CO 2 sink potential. Although wheat grown in subtropical Brazilian regions is of the spring type, the sink value (NEE = −347 ± 4 g C m −2 ) is almost two times higher than other studies in the literature for other types of spring wheat (values ranging from −142.2 to −107 g C m −2 ; Sun et al [2016] and Vick et al [2016], respectively). Thus, the accumulated NEE values described herein are similar to those found in the literature for winter wheat, in which most studies reported values between −250 and −600 g C m −2 (Aubinet et al, 2009;Bajgain et al, 2018;Schmidt et al, 2012;Senapati et al, 2018;Shen et al, 2013;Wagle et al, 2019;Waldo et al, 2016;Yesilkoy et al, 2017).…”

“…Thus, the accumulated NEE values described herein are similar to those found in the literature for winter wheat, in which most studies reported values between −250 and −600 g C m −2 (Aubinet et al., 2009; Bajgain et al., 2018; Schmidt et al., 2012; Senapati et al., 2018; Shen et al., 2013; Wagle et al., 2019; Waldo et al., 2016; Wang, Liao, et al., 2013; Yesilkoy et al., 2017). The total R eco and GPP values were also almost twice the values found in the literature for spring wheat and winter wheat in other parts of the world (Bajgain et al., 2018; Raz‐Yaseef et al., 2015; Sun et al., 2016; Wagle et al., 2019; Wang, Liao, et al., 2013). This may be a consequence of the milder climatic conditions in which wheat is grown in southern Brazil.…”

“…Although wheat grown in subtropical Brazilian regions is of the spring type, the sink value (NEE = −347 ± 4 g C m −2 ) is almost two times higher than other studies in the literature for other types of spring wheat (values ranging from −142.2 to −107 g C m −2 ; Sun et al. [2016] and Vick et al. [2016], respectively).…”

“…In addition, fluxes in the fallow periods between crops were evaluated. The evaluations were carried out with spring wheat because the climatic conditions in this region allow the use of wheat with cycles of just over 4 mo, which are sown in the winter and harvested in the spring (Sun et al., 2016; Vick et al., 2016). Most research on CO 2 fluxes in wheat are performed in the northern hemisphere using winter wheat with cycles of around 8 mo and sown early in autumn before the accumulation of snow on the surface, with germination occurring after melting and harvesting occurring in the summer (Vick et al., 2016; Wang, Cheng Liao, et al., 2013; Wang et al., 2015).…”