Entropy budgets of deciduous plant leaves and a theorem of oscillating entropy production

Abstract

From an energy budget of a deciduous plant leaf in moderate conditions, entropy fluxes into or out of the leaf due to solar radiation, infrared radiation, evaporation of water and heat conduction are calculated. Net entropy flow into the leaf is negative. On the assumption that the entropy in the leaf is in a steady state, the entropy production in the typical deciduous leaf in moderate conditions [the solar energy absorbed by both sides of the leaf isE _solar=0.0602 (J cm⁻² s⁻¹)] becomesS _prod=1.8×10⁻⁴ (J cm⁻² s⁻¹ K⁻¹). The positiveness of the entropy production shows that the Second Law of Thermodynamics certainly holds in the plant leaf. Entropy productions in other conditions are also calculated. The entropy production in the leafS _prod becomes a linear function of the solar energy absorbed by the leafE _solar:S _prod≈-(29.5E _solar)×10⁻⁴. A theorem is presented: the entropy production in plant leaves oscillates during the period of one day, paralleling the daily solar energy absorbed by leaves.