华北平原典型农田水、热与CO2通量的测定

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（Fco2)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Fco2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1500μmolm^-2s^-1左右时，WUE却略有下降。

Measurement and Analysis of Water, Heat and CO2 Flux from a Farmland in the North China Plain

Surface energy fluxes including net radiation (R_n), latent heat flux (λE), sensible heat flux (H), soil heat flux (G) and carbon dioxide flux (F_CO2) were measured by Bowen-ratio energy balance technique and eddy correlation technique from a farmland at Luancheng Agro-ecosystem Station, Chinese Academy of Sciences in the North China Plain from 1999 to 2001. Seasonal variation of a ratio of latent heat flux (λE) divided by net radiation flux (R_n) showed that R_n is mainly used to evapotranspirate by crops. λE/R_n was all higher than 70% during the four observed seasons in the two years. λE/R_n above maize canopy is slightly higher than that above winter wheat canopy. Seasonal average ratio of sensible heat flux (H) divided by R_n keeps about 15% above the field surface; seasonal average ratio of conductive heat flux (G) divided by Rn varies between 5% and 13%, and the average G/R_n from wheat canopy is evidently higher than that from maize canopy. Under given environmental conditions, when the available energy (R_n-G) is less than 200 W/m², evaporative fraction (EF) decreases sharply; below R_n-G≈200 W/m², EF decreases gradually until stabilizing at some specific value less than 1.0. The response process of EF to Rn-G under winter wheat field conditions is similar to that under the given conditions. With the increase of photosynthesis photo flux density (PPFD), carbon dioxide flux (F_CO2) changes according to the curve of Michaelis-Mente. Water use efficiency (WUE) does not show the maximum when PPFD is the maximum at noon. On the contrary, WUE gradually decreased with PPFD equal to 1500 μmol m^-2 s^-1.