Vertical profiles of temperature, water vapor, carbon dioxide, and other scalars within plant canopies reflect a balance between turbulent transport and the distribution of scalar sources and sinks. Scalar sources and sinks depend on leaf biophysical and physiological processes, as well as at the soil surface. Vertical transport depends on turbulence within the canopy. This chapter develops the theory and mathematical equations to calculate scalar profiles in plant canopies. A common approach calculates scalar concentrations from one-dimensional conservation equations with a first-order turbulence closure in an Eulerian framework. Analytical solutions are possible with some assumptions. A more general numerical method requires an iterative solution because of the coupling between fluxes and concentrations. An implicit solution is possible for temperature and water vapor using the leaf energy budget as an additional constraint. An alternative approach represents fluid transport with a Lagrangian framework, either directly through use of a dispersion matrix to characterize turbulent motion or through use of localized near-field theory.