【摘要】 在中国科学院栾城农业生态试验站用波文比－能量平衡法与涡度相关技术对净辐射通量(Rn)、潜热通量(λE)、感热通量(H)、土壤热通量(G)与冠层CO2通量(F∞2)进行了长期定位研究。结果显示Rn大部分用于作物潜热的消耗,连续 2年 4个生长季λE/Rn都在 70%以上,在作物生育盛期,夏玉米λE/Rn略高于冬小麦,H/Rn都在15%左右,G/Rn在 5%－13%之间,且冬小麦G/Rn明显高于夏玉米。蒸发比值(EF)在不同的理想环境条件下,随着可供能量(Rn－G)的增加表现出先迅速下降,后缓慢下降,最后趋于稳定的趋势,并在冬小麦环境条件下得到了验证。直角双曲线模型可以模拟 F∞2随光通量密度(PPFD)的响应过程。晴天冠层水分利用效率(WUE)不是在正午出现最高值,当PPFD达到1500μmol m-2 s-1左右时,WUE却略有下降。更多还原

【Abstract】 surface energy fluxes including net radiation (Rn), latent heat flux (λE ), sensible heat flux (H),soil heat flux (G ) and carbon dioxide flux (F∞2 ) were measured by Bowen-ratio energy balance techniqueand eddy corre1ation technique from a farmland at Luancheng Agro-ecosystem Station, Chinese Academy ofSciences in the North China Plain from 1999 to 200l. Seasonal variation of a ratio of latent heat flux (λE)divided by net radiation flux (Rn ) showed tha R. is mainly used to evapotranspirate by crops. λE/Rn wasall higher than 70% during the four observed seasons in the two years. λE/Rn above maize canopy is slightlyhigher than that above winter wheat canopy. seasonal average ratio of sensible heat flux (H ) divided by Rnkeeps about l5% above the field surface; seasonal average ratio of conductive heat flux (G) divided by Rnvaries between 5% and l3%, and the average G/Rn from wheat canopy is evidently higher than that frommaze canopy. Undr given environmental conditions, when the available energy (Rn-G ) is less than 200W/m2, evaporative fraction (EF ) decreases sharply; below Rn-G≈200 W/m2, EF decreases gradually untilstabilizing at some specific value less than l.0. The response process of EF to Rn-G under winter wheatfield conditions is similar to that under the given conditions. With the increase of photosynthesis photo fluxdensity (PPFD), carbon dioxide flux (F∞2 ) changes according to the curve of Michaelis-Mente. Water useefficiency (WUE ) does not show the maximum when PPFD is the maximum at noon. On the contrary,WUE gradually decreased with PPFD equal to l500 μmol m-2 s-l.更多还原