Quantification of ozone exposure- and stomatal uptake-yield response relationships for soybean in Northeast China

Abstract

High ground-level O3 is a new threat to agricultural production in Northeast China with the increasing ambient O3 concentration. Little is known about its impacts on soybean production in this key agricultural region. Accumulated O3 exposure-response and stomatal O3 flux-response relationships were developed during two continuous growing seasons to evaluate O3-induced yield reduction of four typical soybean cultivars in Northeast China. Results showed that critical levels of AOT40 (accumulated hourly O3 concentrations over a threshold of 40nmol·mol−1), SUM06 (sum of all hourly average O3 concentrations over 0.06μmol·mol−1) and W126 (sum of O3 concentrations weighted by a sigmoidal function) in relation to 5% reduction in relative seed yield were 4.2, 7.6 and 6.8μmol·mol−1·h, respectively. The effect of O3 on plants was influenced by leaf position in canopy. An improved Jarvis stomatal conductance model including leaf (node) position fitted well with field measurements. The best linear relationship between stomatal O3 flux and relative soybean yield was obtained when phytotoxic ozone dose was integrated over a threshold of 9.6nmol·m−2·s−1 (POD9.6) to represent the detoxification capacity of soybean. POD9.6 and the commonly used POD6 in relation to 5% reduction in relative seed yield of soybean were 0.9mmol·m−2 and 1.8mmol·m−2, respectively. O3 concentrations above ~38nmol·mol−1 contributed to POD9.6 and caused seed yield loss in soybean. Current annual yield loss of soybean at ambient O3 was estimated to range between 23.4% and 30.2%. The O3 dose-response relationships and corresponding thresholds obtained here will benefit regional O3 risk assessment on soybean production in Northeast China.