Carbon dioxide exchange and the mechanism of environmental control in a farmland ecosystem in North China Plain

Abstract

CO 2 flux was measured continuously in a wheat and maize rotation system of North China Plain using the eddy covariance technique to study the characteristic of CO 2 exchange and its response to key environmental factors. The results show that nighttime net ecosystem exchange (NEE) varied exponentially with soil temperature. The temperature sensitivities of the ecosystem (Q 10 ) were 2. 94 and 2.49 in years 2002-2003 and 2003-2004, respectively. The response of gross primary productivity (GPP) to photosynthetically active radiation (PAR) in the crop field can be expressed by a rectangular hyperbolic function. Average A max and α for maize were more than those for wheat. The values of α increased positively with leaf area index (LAI) of wheat. Diurnal variations of NEE were significant from March to May and from July to September, but not remarkable in other months. NEE, GPP and ecosystem respiration (R ec ) showed significantly seasonal variations in the crop field. The highest mean daily CO 2 uptake rate was −10.20 and −12.50 gC·m −2 ·d −1 in 2003 and 2004, for the maize field, respectively, and −8.19 and −9.50 gC·m −2 ·d −1 in 2003 and 2004 for the wheat field, respectively. The maximal CO 2 uptake appeared in April or May for wheat and mid-August for maize. During the main growing seasons of winter wheat and summer maize, NEE was controlled by GPP which was chiefly influenced by PAR and LAI. R ec reached its annual maximum in July when R ec and GPP contributed to NEE equally. NEE was dominated by R ec in other months and temperature became a key factor controlling NEE. Total NEE for the wheat field was −77.6 and −152.2 gC·m −2 ·a

Spatial-Temporal Dynamics of China’s Terrestrial Biodiversity: A Dynamic Habitat Index Diagnostic

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Improving the light use efficiency model for simulating terrestrial vegetation gross primary production by the inclusion of diffuse radiation across ecosystems in China

“…That was partly because the penetration of solar radiation through the canopy of the semiarid steppe at NMG could be greater than those at other two grassland sites (HB and DX), and the leaf area index (LAI) of those two grassland sites was higher than what at NMG site (Zhang et al, 2011). At the cropland site (YC), the correlation relationship between CI and LUE of growing season was less significant than those in forest sites and grassland sites, which was partly due to the field managements (Li et al, 2006).…”

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“…Crops were harvested at maturity. More detailed descriptions of the experimental results are given in Li et al (2006).…”

“…These data enable a coupled analysis of CO 2 and water fluxes and quantification of crop radiation and water use efficiency. Li et al (2006) studied the annual variation and control mechanism of carbon fluxes in farmland using data collected over two years. Zhao et al (2007) studied seasonal variations in the WUE of wheat and analysed the effects of weather variables on WUE.…”