Soil CO2 concentration does not affect growth or root respiration in bean or citrus

Contrasting effects of soil CO2 concentration on root respiration rates during short-term CO2 exposure, and on plant growth during long-term CO2 exposure, have been reported, Here we examine the effects of both short-and long-term exposure to soil CO2 on the root respiration of intact plants and on plant growth for bean (Phaseolus vulgaris L.) and citrus (Citrus volkameriana Tan. & Pasq.). For rapidly growing bean plants, the growth and maintenance components of root respiration were separated to determine whether they differ in sensitivity to soil CO2, Respiration rates of citrus roots were unaffected by the CO2 concentration used during the respiration measurements (200 and 2000 mu mol mol(-1)), regardless of the soil CO2 concentration during the previous month (600 and 20 000 mu mol mol(-1)). Bean plants were grown with their roots exposed to either a natural CO2 diffusion gradient, or to an artificially maintained CO2 concentration of 600 or 20 000 mu mol mol(-1), These treatments had no effect on shoot and root growth, Growth respiration and maintenance respiration of bean roots were also unaffected by CO2 pre-treatment and the CO2 concentration used during the respiration measurements (200-2000 mu mol mol(-1)). We conclude that soil CO2 concentrations in the range likely to be encountered in natural soils do not affect root respiration in citrus or bean.