A FIELD FUMIGATION SYSTEM FOR ELEVATED CARBON-DIOXIDE EXPOSURE IN CHAPARRAL SHRUBS

1. Modifications and improvements in the hardware and software of a fr ee-air CO2 enrichment (FACE) system are described. The modifications w ere undertaken to minimize the amount of structure required and to imp rove software control of CO2 set points. 2. A new low-cost CO2 flow co ntroller which provides increased reliability is described. 3, Analysi s of system performance during a 79-day evaluation period of operation (13 h day(-1)) showed that for 1 min averages, the system is capable of maintaining a 550 p.p.m. +/- 10% CO2 set point during 78% of the op erating time and a 550 p.p.m. +/- 20% set point during 95% of the oper ating time. Ten-minute averages were within +/- 10% and 20% during 87% and 96% of the operating time, respectively. 4, Continuous measuremen ts of the spatial variation in CO2 concentration inside the FACE ring over an 18-day period showed that of the total 16-m diameter treatment area, the central 11-m diameter portion remains within the 550 p.p.m. +/- 10% set point. 5, Daily course gas-exchange measurements in match ed individuals of the chaparral shrub Adenostoma fasciculatum just pri or to and following a 6-week fumigation period at 550 p.p.m. CO2 in th e FACE treatment ring showed the FACE plants with reduced photosynthet ic rates and higher (less stressful) water potentials compared with co ntrol A. fasciculatum plants measured at the same times and conditions , indicating the responsiveness of this species to elevated CO2 condit ions.