南方现代化温室黄瓜冬季蒸腾测量与模拟研究

MEASUREMENT AND SIMULATION OF CUCUMBER CANOPY TRANSPIRATION IN A SUBTROPICAL MODERN GREENHOUSE UNDER WINTER CLIMATE CONDITIONS

温室作物蒸腾直接影响到温室内空气温湿度 ,是进行温室温度和湿度优化调控所必需的信息。通过冬季温室小气候和蒸腾速率与气孔阻力的实验观测 ,分析了冬季南方温室黄瓜 (Cucumissativus)蒸腾速率的变化特征及其与温室小气候要素之间的定量关系 ,确定了南方现代温室冬季黄瓜冠层阻力rc 和边界层动力学阻力ra 的特征值和作物蒸腾消耗的潜热占到达冠层上方的净辐射的比例 ,并采用Penman_Monteith方法模拟计算了冬季温室内黄瓜作物蒸腾速率。结果表明 ,冬季温室内作物蒸腾速率的日变化趋势与净辐射的日变化基本一致 ,在正午达一天中的最大值。而空气饱和水汽压差 (VPD)的日最大值则基本出现在午后 1～ 2h。在我国南方温室冬季高湿的环境下 (VPD <2kPa) ,作物蒸腾速率日变化主要取决于太阳辐射日变化。冠层上方的净辐射和VPD及作物冠层蒸腾速率日最大值分别在 35 0W·m-2 、2 .0kPa和 2 0 0W·m-2 以下。冬季温室作物蒸腾消耗的潜热占到达冠层上方的净辐射的比例为 4 6 %。冬季黄瓜作物的rc 和ra 特征值分别为 10 0s·m-1和 6 0 0s·m-1。采用实际变化的rc 与ra 值和rc与ra 的特征值计算的作物蒸腾速率和累积蒸腾量均与实测值基本一致。作物蒸腾消耗的潜热占到达冠层上方的净辐射的比例及rc 和ra 特征值的确?

Canopy transpiration of crops grown in greenhouses affects greenhouse air temperature and humidity and is therefore important for the optimization of greenhouse climate control. In this study, cucumbers (Cucumis sativus) were grown in a subtropical modern greenhouse under winter climate conditions, canopy transpiration was measured every 30 minutes and greenhouse microclimatic factors were sampled with 1 second interval and 30 minutes average values were saved in a datalogger and mean values of canopy resistance r c and boundary layer resistance r a were estimated based on experimental measurements made in the greenhouse. The Penman-Monteith equation was used to estimate canopy transpiration rates. The results showed that the diurnal time course of canopy transpiration rates followed that of the net radiation above the canopy with the daily maximum value occurring at 12∶00. In contrast, maximum water vapor pressure deficit (VPD) occurred between 13∶00 and 14∶00. These results indicate that under winter climate conditions of China, subtropical greenhouse microclimate conditions are characterized by low VPD level and that daytime variations of crop canopy transpiration rates depend primarily on net radiation above the canopy. The daily maximum values of net radiation and VPD above the canopy and crop canopy transpiration rates were below 350 W·m -2, 2.0 kPa and 200 W·m -2, respectively; the ratio of latent heat caused by crop transpiration to the net radiation above the canopy in winter averaged 46%; and r c and r a were 100 s·m -1 and 600 s·m -1, respectively. The crop canopy transpiration rate and total cumulative crop transpiration calculated by Penman-Monteith equations using both the actual r c and r a values and the mean values of r c and r a agreed well with the measured results. The determination of the ratio of latent heat to the net radiation above the canopy (46%) and the characteristic values of r c (=100 s·m -1) and r a (600 s·m -1) facilitates the development of a crop transpiration model to optimize greenhouse climate and irrigation control systems. More experiments are needed to determine if these values are valid for other sites and types of greenhouses.