Rapid evaluation of leaf photosynthesis using a closed-chamber system in a C4 plant, sugarcane

To accelerate research on improving sugarcane biomass production, a rapid phenotyping method for individual leaf photosynthetic rates is required. Recently, a closed-type measurement system, which is faster, lighter, and less expensive than conventional open-type systems, has been developed and utilized for C3 crops. For future utilization of the system in phenotyping photosynthetic rates in sugarcane, which exhibits higher photosynthetic rate than C3 crops, diurnal changes and genotypic differences were measured simultaneously using an open-type and a closed-type system to verify the accuracy of the measurements in assessing environmental responses and genetic variation. As the relative root-mean-square error, a regression accuracy between the measurements with two systems, was <20% when evaluating diurnal changes and genotypic differences, closed system accurately evaluated photosynthetic rates in multiple samples. Overall, the measured values with the closed system tended to be higher than those with the open system, especially in high values above 30 µmol m−2 s−1. The reason for this was presumably not leaf morphology, such as stomatal distribution, but a fundamental difference in the measurement systems (steady-state values for the open system and instantaneous values for the closed system). The open system required 5–7 min to measure a single record, whereas the closed system could measure at <40 s per record. Although it would be desirable to develop a regression equation using measurements involving the open system for each cultivar to examine physiological response in detail, we conclude that the closed system has greater potential for use in phenotyping sugarcane photosynthesis.