Surface Energy Balance Affects Gas Exchange of Three Shrub Species

We investigated the energy balance of vegetative and nonvegetative surfaces and gas exchange for 3 shrub species growing over each surface. During a 1 -week period, incoming short-wave radiation, surface and soil temperature, and soil heat flux for turf and pine-bark mulch surfaces were gathered. Air temperature and relative humidity at 2 heights over each surface were also measured. Mulch surface and air temperatures were warmer and soil temperature below mulch was cooler than turf throughout each day. Relative humidity varied with height above turf, but each height was comparable over mulch. For the majority of each day, soil heat flux below turf was greater than mulch. Dawn-to-dusk measurements of stomatal conductance, leaf temperature, and water loss for containerized skunkbush sumac {Rhus trilobata), spreading euonymus (Euonymus kiautschovicus 'Manhattan'), and redosier dogwood {Cornus sericea) were measured. Shrubs in mulch had higher leaf temperatures and greater leaf-to-air vapor pressure differences than shrubs in turf. Rhus trilobata had greater stomatal conductance and water loss in turf than mulch. However, for E. kiautschovicus and C. sericea, there were no differences in stomatal conductance or water loss between surface treatments. Midday photosynthetic rate was generally greatest for shrubs over turf. Shrub gas exchange differed according to how stomata responded to the leaf-toair vapor pressure difference over each surface.