Document: CHR-3-30-43

Plant gas exchange in urban and suburban landscapes.

MARTIN, C.A.* and L.STABLER

Arizona State University, Tempe, AZ USA 85287-1601 ¹

Abstract:
Effects of current and former land use on plant gas exchange in urban residential landscapes were evaluated in Phoenix, Arizona, USA. Monthly gas exchange measurements were made during July 1998 to June 1999 on plants at three site replicates of a factorial matrix of former desert or agricultural land use and xeric or mesic landscape design. Measurements at three sites each in nearby remnant Sonoran Desert and an agricultural alfalfa field were used as controls. Rainfall for the year was 207 mm. Residential sites and the alfalfa field received regular supplemental water. Contrary to our initial hypothesis, homeowners did not apply less supplemental water to residential landscapes with xeric planting designs than mesic designs. Maximum leaf and stem carbon assimilation (A), conductance (gs), and transpiration (E) were measured with a portable infrared gas analyzer on recently physiologically mature tissues of three woody plant life forms; trees, shrubs, and ground covers. Measurements were made at the time of day for maximum photosynthetic fluxes based on preliminary seasonal diel measurements of gas exchange patterns in irrigated and non-irrigated landscapes. In general, A, E, and gs were lower for plants in remnant desert sites and higher for alfalfa plants than for residential plants. Within the residential site matrix, land use history and design interacted to affect A, E and gs. Fluxes of A, E, and gs were highest for plants in formerly agricultural/xeric residential sites and lowest for plants in formerly desert/xeric residential sites. Former land use and landscape design type had no effect on ITE. Overall, ITE varied seasonally in all land uses and was negatively correlated with shoot temperature (r = -0.67). Based on these data, irrigation most affected plant gas exchange. Under well-watered conditions, concomitant diel and seasonal changes in A, gs, shoot temperature and ITE suggest that maximum landscape carbon assimilation was limited by shoot conductance during cooler seasons, but might have been limited by high temperature extremes during the hottest time of year.

Keywords: gasexchange

This abstract is being presented at: 10:30 AM in session:
GAS EXCHANGE