摘要
利用中国气象局固城农业气象生态试验站2004年玉米生育期通量观测资料,分析了CO2浓度和通量随玉米生长的变化,并估算了玉米生育期陆地与大气CO2净交换量。结果表明:CO2浓度变化对农户活动和作物生长极其敏感;浓度在整个生育期始终有明显的日变化规律,峰值(谷值)出现在日出(日落)前后,通量仅在7月中旬至10月上旬之间出现明显的日变化特点,且位相超前于浓度,开花期通量最大;玉米播种期、苗期和成熟后地面向大气净排放碳,拔节至成熟前地面从大气净吸收碳;开花期碳吸收最强,其后依次为吐丝-乳熟期和拔节期。比较分析了目前流行的通量计算方法对碳吸收估计的影响,结果显示不同计算方法能产生高达160%的碳吸收估计偏差,应当引起重视。生态系统碳平衡分析结果表明,玉米地在生长季表现为弱碳汇(大约660 kg/hm2),但这一结果可能低估了实际的碳汇强度,低估程度有待研究。
In order to better understand the global climate change, it is necessary to assess the budget of CO2 exchange as accurately as possible between the biosphere and atmosphere over representative ecosystems. Eddy covarianee technique, which has been adopted as a standard method in the global carbon flux observation network （FLUX- NET）, allows us to directly measure the exchange rate of CO2 across the interface between vegetation canopy and atmosphere. However, the results from different studies are not comparable because they use different interpreting and correcting methods to estimate CO2 flux. In this paper, the authors present the variation of CO2 concentration and flux measured at 16 m height by eddy covariance system over a typical corn canopy surface on the North China Plain. Three methods are used to calculate CO2 flux, which are direct fluctuation covariance, WPL method （Webb et al. , 1980）, and Liu method （Liu, 2005）. It is found that the direct estimation by fluctuation covariance contains errors and should be corrected. WPL method, which has been used to correct these errors in recent years, overcorrects the value of negative CO2 flux. Liu method compromises the results between direct estimation and WPL correction, and has the advantage of no any theoretical assumption as that of WPL correction. Therefore the authors consider that the CO2 flux from Liu method is reasonable. Based on Liu method, the authors then determine the net budget of CO2 at measurement height at the scales of day and the whole experiment period, respectively. The main results of this study show as follows. （1） The variation of CO2 concentration can reflect the influences of human＇s field activities （e. g. tillage and firing the residual） and corn plants growing. Tillage and firing the residual induce a sharp increase of CO2 concentration, while corn growth results in the vale value of CO2 concentration in U form. （2） CO2 concentration holds diurnal cycle during the whole period of measurement, but CO2 flux has not visible diurnal cycle until the corn canopy develops to some degree. The peak （vale） value of CO2 concentration usually appears at sunrise （sunset）, related to the altering direction of CO2 flux. The vale value of CO2 flux in the daytime is more distinct than the peak value in nighttime. （3） The maximum carbon taking by corn canopy occurs at the abloom stage, followed by spin-ripe stage and jointing stage. （4） Corn surface serves as carbon sink to atmosphere from young canopy stage to mature stage, but serves as a carbon source at other periods. The net exchange of CO2 flux at the measurement height over the whole period is -176 g/m^2 （C）. （5）The analysis of ecosystem carbon balance indicates a weak sink to the atmosphere （about 660 kg/hm^2 （C））. Because of omitting the carbon storage in the atmosphere under the measurement height, the true carbon sink may be stronger than this value. It is noted that the different methods mentioned above might bring as large as 160% bias to the net CO2 exchange estimations in this experiment. So, it is the most important thing to unify the formulation of estimating CO2 flux in the international comparison project and the state policy of limiting carbon emission.
出处
《大气科学》
CSCD
北大核心
2007年第4期695-707,共13页
Chinese Journal of Atmospheric Sciences
基金
长江学者和创新团队发展计划
科技部973预研项目200301500
中国气象局气候变化专项项目CCSF2005-3-DH12
关键词
华北平原
玉米
CO2
浓度
通量
净交换量
the North China Plain, corn canopy, CO2 concentration, flux, net ecosystem exchange of carbon
作者简介
郭建侠，女，1969年出生，博士，高级工程师，主要从事大气边界层、生态气候研究。E-mail：gjx01@sina．com
