Effects of Air Current Speed on Net Photosynthetic and Evapotranspiration Rates of a Tomato Plug Sheet under Artificial Light

Abstract

In the production of plug seedlings, the air current speed around the seedlings is an important environmental factor affecting the rates of net photosynthesis (P) and evapotranspiration (E) . In the present experiment, a plug sheet consisting of tomato plug seedlings and soil mix was placed in a wind tunnel with artificial lights, and the P and E rates of the plug sheet were examined under different air current speeds, at an air temperature of 29-30°C, relative humidity of 60-70%, CO₂ concentration of 340-360 μmol mol^-1 and photosynthetic photon flux density of 270 μmol m^-2s^-1 At the inlet and outlet of the wind tunnel, absolute humidities (y_in and y_out, respectively) and CO₂ concentrations (C_in and C_out, respectively) were determined with a dew point analyzer and an infrared CO₂ analyzer, respectively. The weight of the plug sheet was measured with an electronic balance. The E was estimated based on the change with time in the weight of plug sheet. The air flow rate in the wind tunnel, F, was determined using an equation : E = F (y_out-y_in) /A, where A is the area of plug sheet. The P was determined using the equation : P=F (C_in - C_out) /A. The P and E increased as the air current speed and LA! (leaf area index of the seedlings) increased. However, the increase in P with the increase in LAI was less than the increase in E with the increase in LAI. Eleven days after seeding, when LAI=0.43, the P and E at an air current speed of 0.6 m s^-1 were 1.4 and 1.9 times those at an air current of 0.1 m s^-1, respectively.