Surface Energy Balance Affects Gas Exchange of Three Containerized Shrub Speicesby Thayne Montague , Roger Kjelgren , Larry Rupp |
| We investigated energy balance of vegetated and non-vegetated surfaces for a one week period during the month of July, 1995. We then studied how surface energy balance influenced gas ex-change of three shrub species growing over each surface. Insolation, surface temperature, soil-surface interface temperature, and soil heat flux below turf and pine bark mulch were measured. Air temperature and relative humidity at two heights, 2.0 and 0.3 m (6.5 and 1.0 feet), were also measured. Although insolation was equal for each surface, on average, mulch surface tempera-ture was 5 to 35 C (9.7 to 64.8) warmer and the soil-surface interface was 2 to 6 C (4.1 to 12.4 F) cooler than turf throughout each day. For the majority of each day, average soil heat flux below turf was greater than mulch. Mean air temperature over mulch at 2.0 and 0.3 meters, was up to 3 and 6 C (5.9 and 12.56 F) warmer than mean air temperature over turf, respectively. Average relative humidity was greatest at 0.3 m (1.0 feet) over turf than for any other height or surface. During a dawn-to-dusk study, we measured stomatal conductance, leaf temperature, and total water loss for three containerized shrub species (Rhus trilobata, Euonymus kiatschovicus, and Cornus sericea) growing over each surface. Leaf temperature and leaf to air vapor pressure dif-ference were greatest for each species over pine bark mulch. Rhus trilobata had greater stomatal conductance and water loss over turf than over mulch. However, for E. kiatschovicus, and C. sericea there was no difference in stomatal conductance and water loss between turf and mulch treatments.
Isolated woody plants placed in non-vegetated urban surfaces intercept increased convected and long-wave energy, resulting in higher leaf temperatures (Tl) (Heilman and Brittin, 1989; Za-jicek and Heilman, 1991), greater leaf-air vapor pressure gradients (Zajicek and Heilman, 1991), and more water loss (Halvorson and Potts, 1981; Miller, 1980; Zajicek and Heilman, 1991) com-pared to plants growing over vegetative surfaces. How much Tl or transpiration will increase depends on the extent to which a tree regulates stomatal opening (Jarvis and McNaughton, 1985). Plants able to maintain open stomata dissipate the energy by evaporative cooling but transpire more (Whitlow and Bassuk, 1988). Those closing stomata reduce transpiration, but may limit photosynthesis and increase respiration due to higher Tl (Kjelgren and Clark, 1992). This study investigated how energy balance varies among three surfaces, mulch, asphalt, and turf, and the stomatal response and water use of two ornamental tree species isolated over these surfaces. Supporting pdf: Surface Energy Balance Affects Gas Exchange of Three Containerized Shrub Speices |
