FACE条件下小麦冠层能量平衡和水分利用率的变化

Energy balance and water use efficiency at wheat canopy under free-air CO_2 enrichment

本文利用中国开放式CO2浓度增高(Free-air CO2 Enrichment,简称FACE)系统平台,于2007年3月19日至5月24日小麦拔节至成熟期进行小麦冠层微气候及相关项目的连续观测,并结合能量平衡分析,研究中国FACE系统对小麦冠层能量平衡各分量的变化特征及水分利用率的影响。能量平衡分析结果表明,小麦冠层白天总显热通量FACE均高于对照,而总潜热通量FACE均低于对照,潜热通量FACE与对照的差异日最大值变化在-12～-63W·m-2之间,显热通量FACE与对照的差异最大值变化在12～78W·m-2之间。能量平衡是小气候变化的根本,利用P-M方程反演出的冠层群体气孔导度与实测的气孔导度相关关系较好,证明能量平衡的计算结果及小气候观测数据基本正确。观测期间内模拟计算结果表明,CO2浓度升高使小麦的水分利用减小约25.5mm,结合生物量的增加,FACE条件下小麦水分利用率增加约19%。

The effects of elevated atmospheric CO2 concentration on wheat canopy energy balance and water use efficiency were investigated with FACE （Free Air CO2 Enrichment approach）. Wheat canopy microclimate observations were conducted from March 19 to May 24, 2007 at elongation to maturity stage. The results show that daytime total canopy sensible heat flux of FACE is higher than the ambient sensible heat flux, while a lower latent heat flux of FACE is observed throughout the observation period. The maximum difference in wheat canopy sensible and latent heat flux between FACE and the ambient varies by 1278 W·m^-2and -12 -63 W·m^-2respectively. Canopy stomatal conductance from P-M calculation agrees well with measured leaf stomatal conductance of wheat, indicating that microclimate data, latent and sensible heat flux estimated from residual energy balance are accurate. Total water-use by wheat throughout the observation period is 25.5 mm less under FACE than that under control condition. Reduced tran- spiration combined with increased total biomass results in a 19% increase in water use efficiency of wheat in FACE.