Estimating NEE in a wheat-planted plot with an automatically controlled chamber

Abstract: We observed carbon dioxide (CO₂) flux at two experimental plots (wheat (Triticum aestivum L.) -planted and bare) for a year using an automatically controlled chamber. At each plot, two chambers were installed at six observation points by rotation. Consequently, the total installment duration at each point was one-third of the entire experimental period. Although we manually moved the chambers periodically, they hampered wheat growth and reduced the dried weight of harvested wheat by 65%. However, they did not influence the carbon (C) content ratio of harvested wheat. The rate of decrease of soil water contents after rainfall in the wheat plot was higher than that in the bare plot, especially after the canopy height reached around 30 cm. The maximum gap of soil water content at 5 cm depth between the two plots was about 5%. Wheat mitigated the increase of soil temperature in the daytime. The gap of soil temperature at 2 cm depth between the two plots sometimes exceeded 10°C. Considering the difference between dried weights of harvested wheat per unit ground area inside and outside the chamber collar, the annual net ecosystem exchange (NEE), whole ecosystem respiration and gross primary production were estimated respectively as –103 g C m⁻² y⁻¹, 831 g C m⁻² y⁻¹ and–934 g C m⁻² y⁻¹. The absolute values of each were smaller than those reported from past studies. Adding the exported carbon of harvested wheat (364 g C m⁻²) and subtracting the imported carbon of the seeds (3.1 g C m⁻²) to the NEE, net biome production across the ground surface was 259 g C m⁻². It was greater than that in the bare plot (187 g C m⁻²). Although further improvements of measurements and more accurate estimated equations are necessary to evaluate the carbon budget correctly with chamber measurements, our chamber measurement captured the NEE variation, responding to seasonal, meteorological and biological changes.