RESPONSE OF GROWTH AND CARBON ALLOCATION TO ELEVATED CO2 IN YOUNG CHERRY (PRUNUS-AVIUM L) SAPLINGS IN RELATION TO ROOT ENVIRONMENT

The hypothesis that inadequate rooting volume may reduce the growth stimulation by elevated CO2 in potted tree seedlings and saplings was tested experimentally and by surveying the literature. One-year-old cherry saplings were grown for one season in naturally lit growth chambers in eight combinations of CO2 concentration (ambient; ambient + 250 ppm) and root environment (four types). The latter included (1) moderately restrictive pot volume (4 l) in combination with two levels of fertilizer addition (1a, 1b); (2) 10 l pots with total fertilizer content per pot as in treatment 1a, and (3) 20 l pots with five plants sharing five times the space and nutrient resources of treatment 1a. Plants were harvested in April, May, June, August and September. The overall mean effect of high CO2 plant dry mass by the end of the season was +24%. Interactive effects of root environments and CO2 concentrations on dry mass were not significant at the 5% level, but repeated measurements of basal stem diameter of individual plants indicated a significant impact of root environment on the response to CO2. Overall growth enhancement by elevated CO2 did not differ significantly between harvests, but it tended to increase during the season in those root environments which restricted growth in ambient CO2 most strongly (1a and 3). The hypothesis was rejected for this experiment. Leaf area and stem height were not affected by any treatment. The variation of carbon allocation to roots and shoots with plant size was very similar in all treatments. Plants grew faster in elevated CO2 very early in the season, and this resulted in small but significant differences between seasonal patterns of biomass partitioning in ambient and elevated CO2. A survey of 33 studies on growth responses of 47 tree species to elevated CO2 (600-800 ppm) showed that the relative change in biomass was not related to the ratio of plant biomass and pot volume found in either ambient or elevated CO2. We conclude that there is no evidence that inadequate pot volume had a negative impact on the stimulation of growth of tree species in elevated CO2