A simple new method to determine leaf specific heat capacity

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_p). Existing literature offers only rough estimates of C_p and lacks simple and accurate methods to determine it.

We developed a non-invasive method to quantify k (the product of leaf thickness (lt), leaf density(ρ), and C_p), by fitting a leaf energy balance model to a leaf temperature (T_leaf) transient during and after a ~ 10 s light pulse. C_p was then estimated by dividing k by lt*ρ. Using this method, we quantified C_p for 13 horticultural and tropical plant species, and explored the relationship between C_p and leaf water content, specific leaf area and T_leaf response rate during the light pulse. Values of C_p ranged between 3200-4000 J kg^-1 K^-1, 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.

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