Applicability of a Closed and Rapid Gas-exchange System to Leaf Photosynthetic Measurements in Tropical Fruit Trees

Abstract

Leaf photosynthesis is a powerful indicator for evaluating growth and tolerance to environmental stresses in tropical fruit trees; however, its measurement requires an expensive system. To examine the applicability of a new, low-cost, closed system for leaf photosynthetic measurement in tropical fruit trees, the photosynthetic rates of each two genotypes of 16 species were measured simultaneously using closed and open systems following accuracy evaluation by regression analysis with values from a standard open system as an explanatory variable. For all measurement combinations, significant and strong positive correlations were obtained with "Fair" accuracy. Photosynthetic rates tended to be overestimated in the closed system. Significant and strong positive correlations were observed for each species. Accuracy differed among species and measurement periods, with a tendency toward inferior accuracy at lower rates. The accuracy was sometimes inferior ("Poor" or "Fair") for seven species, whereas the remaining species showed generally higher accuracy ("Good" or "Excellent"). Although the accuracy was "Good" for three species, the relationship between the two measurements varied between genotypes and periods. For seven species, the universal regression line was adopted for the relationship between two measurements, consequently demonstrating that the closed rapid gas-exchange system facilitated accurate ("Good") and rapid (Ϸ40 s/record) measurements.