Growth and Photosynthetic Responses of Cuttings of a Hybrid Larch (Larix gmelinii var. japonica x L. kaempferi) to Elevated Ozone and/or Carbon Dioxide

ABSTRACT:We studied the effects of elevated ozone ([O3]) and CO2 concentrations ([CO2]) on the growth and photosynthesis of the hybrid larch F1 (F1) and on its parents (the Dahurian larch and Japanese larch). F1 is a promising species for timber production in northeast Asia. Seedlings of the three species were grown in 16 open top chambers and were exposed to two levels of O3 (⁄10 ppb and 60 ppb for 7 h per day) in combination with two levels of CO2 (ambient and 600 ppm for daytime) over an entire growing season. Ozone reduced the growth as measured by height and diameter, and reduced the needle dry mass and net photosynthetic rate of F1, but had almost no effect on the Dahurian larch or Japanese larch. There was a significant increase in whole-plant dry mass induced by elevated [CO2] in F1 but not in the other two species. Photosynthetic acclimation to elevated [CO2] was observed in all species. The net photosynthetic rate measured at the growing [CO2] (i.e. 380 ppm for ambient treatment and 600 ppm for elevated CO2 treatment) was nevertheless greater in the seedlings of all species grown at elevated [CO2]. The high [CO2] partly compensated for the reduction of stem diameter growth of F1 at high [O3]; no similar trend was found in the other growth and photosynthetic parameters, or in the other species