A simple new method to determine leaf specific heat capacity.

Background: Quantifying plant transpiration via thermal imaging is desirable for applications in agriculture, plant breeding, and plant science. However, thermal imaging under natural non-steady state conditions is currently limited by the difficulty of quantifying thermal properties of leaves, especially specific heat capacity (C). Existing literature offers only rough estimates of C and lacks simple and accurate methods to determine it.

Results: We developed a non-invasive method to quantify k (the product of leaf thickness (lt), leaf density(ρ), and C), by fitting a leaf energy balance model to a leaf temperature (T) transient during and after a ~ 10 s light pulse. C was then estimated by dividing k by lt*ρ. Using this method, we quantified C for 13 horticultural and tropical plant species, and explored the relationship between C and leaf water content, specific leaf area and T response rate during the light pulse. Values of C ranged between 3200-4000 J kg K, and were positively correlated with leaf water content. In species with very thick leaves, such as Phalaenopsis amabilis, we found leaf thickness to be a major factor in the temperature response to a short light pulse.

Conclusions: Our method allows for easy determination of leaf C of different species, and may help pave the way to apply more accurate thermal imaging under natural non-steady state conditions.