Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

B. Li,C. Liu,Y. Wang,H. Liu,X. Zheng,S. Haapanala,T. Vesala,G. Liu,F. Hu,K. Wang,M. Pihlatie

doi:10.5194/bg-10-6865-2013

Abstract

Abstract. Static and transparent automatic chamber (AC) technique is a necessary choice for measuring net ecosystem exchange (NEE) of carbon dioxide (CO2) in circumstances where eddy covariance (EC) technique is not applicable. However, a comparison of the two techniques for measurements on croplands has seldom been undertaken. We carried out NEE observations in a cotton field (for one year) and a winter wheat field (for one cropping season) using both AC and EC techniques, to (a) compare the NEE fluxes measured using each technique, and (b) test the NEE measurement performance of an automatic chamber system (AMEG), which was designed for simultaneous flux measurements of multiple gases. The half-hourly NEE fluxes measured with the two techniques were in approximate agreement, with the AC fluxes being 0.78 (cotton) and 1.06 (wheat) times the size of the EC fluxes. When integrated to daily timescale, the fluxes of the two techniques were in better agreement, showing an average ratio of 0.94 and 1.00 for the cotton and wheat, respectively. During the periods with comparable field conditions and normal performance of both instruments, the cumulative NEE fluxes revealed small differences between the two techniques (−9.0% ~ 7%, with a mean of 0.1%). The measurements resulted in an annual cumulative NEE of −40 g C m−2 yr−1 (EC) and −42 g C m−2 yr−1 (AC) in the cotton field, and a seasonal cumulative NEE of −251 g C m−2 (EC) and −205 g C m−2 (AC) in the wheat field. Our results indicate that, for cropland populated by short plants, the AMEG system and the data processing procedures applied in this study are able to provide NEE estimates comparable to those from EC measurements.

Highlights

The net ecosystem exchange (NEE) of carbon dioxide (CO2) is the difference between carbon assimilation by photosynthesis and (CO2) release via ecosystem respiration
There were six irrigation events, which supplied a total of 150.5 mm and 253.7 mm of water to the cotton and wheat fields, respectively (Fig. 3c)
The measurements were conducted in a cotton field for a year and in a winter wheat field for an entire cropping season

Summary

Introduction

The net ecosystem exchange (NEE) of carbon dioxide (CO2) is the difference between carbon assimilation by photosynthesis and (CO2) release via ecosystem respiration. The EC technique is based on micrometeorological theories It allows for continuous and non-disturbing measurements and provides spatially averaged fluxes on a scale of a few hectares to several square kilometers (Baldocchi, 2003). It has been widely used in different ecosystems (e.g., Goulden et al, 1996; Lafleur et al, 1997; Miyata et al, 2000). The technique of static chamber in combination with a close-path gas analyzer can be used for NEE measurement in ecosystems with low-stature canopies, such as grasslands and croplands (e.g., Maljanen et al, 2001; Steduto et al, 2002; Langensiepen et al, 2012). The chamber technique offers the advantages of being lower in cost

Methods

Results

Conclusion