A Method to Measure the Dynamic Response of Net Photosynthetic Rate in the Controlled-Environment Chamber

Abstract

A method to measure the net photosynthetic rate under varing CO2 concentration in an assimiration chamber was presented. The method was based on the nonstationary CO2 budget equation (see Fig. 1):P=v(C1-C2)-VΔC/Δt-B, where P is the net photosynthetic rate, v is the air flow rate, V is the volume of the chamber, C1 and C2 are CO2 concentrations at inlet and outlet, (C1-C2) is the mean difference of CO2 concentrations over a period of Δt(=t2-t1), C is the CO2 concentration in the chamber, and B is CO2 influx to the chamber. We can determine P from the above equation, by measuring (C1-C2) and ΔC/Δt for a given assimilation chamber system with known v, V, and B. Such a system to measure P based on the above equation was constructed (Fig. 2) and used to test the validity of the method.The overall error in the measurement of P is the sum of the errors of V(ΔC/Δt) and v(C1-C2), provided the value of B is known. Generally, the error of V(ΔC/Δt) seems to be larger than that of v(C1-C2). The error in V(ΔC/Δt) decreases linerly with increasing Δt.The time lag (R) of P as measured by the proposed method may be expressed as follows:R=Δt/2+R1where R1 is the time lag required for detecting CO2 concentration.The ratio (A/A0) of the amplitude of output (A) to that of a sinusoidal input (A0) decreased almost linerly with the increase in Δt/α, where α is the period of the sinusoidal input (Fig. 5 and Fig. 6). The time lag (φ) relative to the sinusoidal input phase is expressed as follows:φ=Δt/2+φ1, where φ1 is the time lag of the output required for detecting CO2 concentration (Fig. 5 and Fig. 6).In the above two equations, Δt/2 is artificially introduced from the fact that the outputs were calculated at the time of t2. When the output is calculated at the time of (t1-t2)/2 and used as the mean net photosynthetic rate at the time over a period of Δt, the response time (R) and the time lag (φ) are respectively equal to the response time (R1) and time lag (φ1) required for detecting CO2 concentration. In this case the value for R and φ was only 1.5 minutes for the system used in the tests.Thus, the proposed method enables us to measure continuously the dynamic and quick response of net photosynthetic rate to the change in CO2 concentration (see Fig. 7) and to the change in other environmental factors.