The Climate in Growth Chamber (1)

Abstract

In recent years, the chamber method in determining photosynthesis and transpiration of crops has become in common use among the crop scientist, and a number of studies have been published of the amount of transpiration and photosynthesis of crops. But little attention has been paid into the control of microclimatic environments in a chamber. In this paper, the relationship between microclimatic conditions and the ventilation rate was numerically studied on the basis of heat balance, water vapor and carbon dioxide balance techniques. Vertical profiles of several microclimatic elements within a plant canopy in the chamber were also studied by the micrometeorological method.As can be seen in Eq. (5), the difference in temperature between in and out the chamber is determined in terms of total heat transfer coefficient ht, advectional heat transfer coefficient had, net radiant energy iS0, apparent vapor deficit {r·e(Ta)-0ea}, coefficient of keeping warm R=Af/Aw and relative humidity r in the chamber. The results obtained from Eq. (5) is presented in Fig. 1. It was found that the value of water vapor pressure in the chamber is closely related to net radiant energy, Bowen ratio and ventilating rate per unit area of the chamber floor. The relationship between ventilating rate and water vapor pressure in the chamber is shown in Fig. 1.Carbon dioxide concentration in the chamber was found to be determined in terms of total gas exchange coefficient Dt and ventilating rate per unit leaf surface. The result obtained from Eq. (13) is presented in Fig. 1. The value of total gas exchange coefficient for several crops is summarized in. Table 1. The efficiency of photosynthesis of crops in the chamber was evaluated from Eq. (14) and compared with experimental results obtained by MURATA (1961) in Fig. 2. In the range lower than ventila. ting the rate of about 1000cc/leaf cm2hr, the photosynthetic efficiency of crops in the chamber decreased drastically with the decrease of ventilating rate. Fig. 4 illustrates the vertical profiles of relevant quantities within a canopy of crops in the chamber obtained by micrometeorological techniques. A notable result shown in this figure is that the remarkable discrepancy in amount is between foliage Bowen. ratio and ordinary Bowen ratio. This result agreed with that obtained within a corn plant canopy under field conditions.