Estimating the air exchange rate using water vapour as a tracer gas in a semi-closed growth chamber.

摘要

Net photosynthetic rate of whole-plant (P_n) can be used to estimate plant growth and CO₂ use efficiency (CUE) in a 'closed system with artificial lighting' (CSAL). CUE is defined as the ratio of the canopy net photosynthetic rate in a CSAL to the CO₂ supply rate. P_n can be estimated based on the CO₂ balance in the CSAL if the air exchange rate is known. The air exchange rate is usually estimated using CO₂ as a tracer gas, but this method cannot be applied in the presence of plants. We propose a method for estimating P_n in a CSAL based on the air exchange rate estimated using water vapour instead of CO₂ as a tracer gas. In this study, a growth chamber was used as an experimental CSAL. The air exchange rate was defined as the number of air exchanges per hour (N), which is the ratio of the hourly exchanged air volume to the air volume of the CSAL. Firstly, N was estimated using water vapour (N_W) and CO₂ (N_C) as tracer gases in the absence of plants. Then, P_n and CUE of the tomato plants were estimated using the proposed method. The results showed that N_W agreed well with N_C, and P_n was accurately estimated by the proposed method. The estimated CUE decreased with increases in N and CO₂ concentration inside the growth chamber. It was concluded that the method can be used to estimate P_n and CUE in a CSAL.