Ozone exposure- and flux-based response relationships with photosynthesis, leaf morphology and biomass in two poplar clones

摘要

Poplar clones 546 (P. de/toides cv. '55/56' x P. deltoides cv. 'Imperial') and 107 (P. euramericana cv. 74/76') were exposed to five ozone concentrations in 15 open-top chambers (OTCs). Both ozone exposure (AOT40, Accumulation Over a Threshold hourly ozone concentration of 40 ppb) and flux-based (POD_7, Phytotoxic Ozone Dose above an hourly flux threshold of 7 nmol O_3 m~2 PLA (projected leaf area) s~(-1)) response relationships were established with photosynthesis, leaf morphology and biomass variables. Increases in both metrics showed significant negative relationships with light-saturated photosynthesis rate, chlorophyll content, leaf mass per area, actual photochemical efficiency of PSII in the light and root biomass but not with stomatal conductance (g_s), leaf and stem biomass. Ozone had a greater impact on belowground than on aboveground biomass. The ranking of these indicators from higher to lower sensitivity to ozone was: photosynthetic parameters, morphological index, and biomass. Clone 546 had a higher sensitivity to ozone than clone 107. The coefficients of determination (R~2) were similar between exposure- and flux-based dose-response relationships for each variable. The critical levels (CLs) for a 5% reduction in total biomass for the two poplar clones were 14.8 ppm h for AOT40 and 9.8 mmol O_3 m~(-2) PLA for POD_7. In comparison, equivalent reduction occurred at much lower values in photosynthetic parameters (4 ppm h for AOT40 and 3 mmol O3 m~(-2_ PLA for POD_7) and LMA (5.8 ppm h for AOT40 and 4 mmol O_3 m~(-2) PLA for POD_7). While in recent decades different CLs have been proposed for several plant receptors especially in Europe, studies focusing on both flux-based dose-response relationships and CLs are still scarce in Asia. This study is therefore valuable for regional O_3 risk assessment in Asia.