Growth and marketable-yield responses of potato to increased CO2 and ozone

Central to the CHanging climate and potential Impacts on Potato yield and quality project (CHIP) was the consideration of the potential impacts of ozone and CO2 on growth and yield of future European Potato crops. Potato crops, cv. Bintje, were exposed to ambient or elevated ozone; targeted daily average, 60 nl 1(-1) for 8 h, and ambient or elevated CO2; targeted 680 mul 1(-1) averaged over the full growing season, in open top chambers (OTCs) at six European sites in 1998 and 1999, or to elevated CO2 (550 mul 1(-1)) in Free Air Carbon dioxide Enrichment facilities (FACE) at two sites in both years. Some OTC experiments included 550 mul 1(-1). Above and below ground biomass were measured at two destructive harvests; at maximum leaf area (MLA) and at final-harvest. Final-harvest fresh weight yields of marketable-size tubers, >35 turn diameter, from ambient conditions ranged from 1 to 12 kg m(-2). There was no consistent (P > 0.1) CO2 x 03 interaction for growth or yield variables at either harvest. No consistent effects of ozone were detected at the maximum-leaf-area harvest. However, at final harvest, ozone had reduced both above-ground biomass and tuber dry weight (P < 0.05), particularly of the largest ( > 50 mm) size class. These yield losses showed linear relationships both with accumulated ozone exposure; AOT40 expressed as nl 1(-1) h over 40 nl 1(-1), and with yields from chambered ambient-ozone treatments (P < 0.05) but, because of partial confounding between the treatment AOT40s and the ambient-ozone yields in the data, the two relationships were not completely independent. Yields from ambient-ozone treatments, however, explained a significant (P < 0.01) amount of the residual variation in ozone effects unexplained by AOT40. When averaged over all experiments, mean dry weights and tuber numbers from both harvests were increased by elevated CO2. Only green leaf number at the MLA harvest was reduced. The CO2 responses varied between sites and years. For marketable-size tubers, this variation was unrelated to variation in ambient-CO2 treatment yields. Yield increases resulting from the 680 mul 1(-1) and 550 mul 1(-1) treatments were similar. Thus elevating [CO2] from 550 to 680 mul 1(-1) was less effective than elevating [CO2] from ambient to 550 mul 1(-1). On average, CO2 elevation to 680 mul 1(-1) increased the dry weight of marketable-size tubers by about 17%, which far exceeded the average ozone-induced yield loss of about 5%. The net effect of raising CO2 and O-3 concentrations on the European potato crop would be an increase marketable yield.