Using an IR camera to improve leaf area and temperature measurements: A new method for increasing the accuracy of photosynthesis-related parameters

Abstract

Accurate measurements of leaf temperature and area are crucial to calculate leaf gas exchange parameters when using portable gas analysers such as the LI-6400 XT portable photosynthesis system (LI‐COR Inc., Lincoln, USA). The importance of leaf temperature data is well known for robust measurements, but there are still technical limitations in measuring it with full accuracy. Here we present a tentative solution by incorporating leaf temperature measurements with thermal imaging. An infrared (IR) camera (IRay T3 Pro, Shandong, China) was combined with a LI-6400XT to measure mean leaf temperatures while avoiding leaf thermal heterogeneity and to accurately calculate leaf area while avoiding destructive sampling. The thermal heterogeneity of Helianthus annuus and Zea mays leaves were studied. We then evaluated the accuracies of leaf area and temperature measurements obtained for 9 species and discussed the influences of these measurements on the resulting photosynthesis-related parameters. Our results provide direct visual evidence of the thermal heterogeneity of leaves in an infrared gas analyzer (IRGA) chamber. The temperature differences across the leaf surface were as high as 0.28°C∼1.38°C, causing large errors in stomatal conductance (gs, -5.07%∼-55.02%) and intercellular CO2 concentrations (Ci, -0.41%∼-6.72%). The IR camera reduced the area measurement error (-0.71∼0.29 cm2) and greatly increased the accuracy by -11.12%∼17.60% for the net photosynthesis (Pn) and transpiration rate (E) and by -11.24%∼17.69% for gs calculations. Our results showed that combining an IR camera with LI-6400XT can improve leaf area measurements, avoid thermal heterogeneity in leaves and thus dramatically improve the accuracy of photosynthesis-related parameter calculations under semi controlled and moderate climate conditions.