Response of Net Carbon Exchange Rate of Soybean to Ozone at Different Stages of Growth and its Relation to Yield

Abstract

AbstractHigh concentrations of ozone (O3) occur episodically during the growing season, but the impacts of O3 stress on photosynthesis and crop yield when O3 episodes occur at various stages of growth are not known. Also, quantitative relationships between reduction of photosynthesis and yield suppresion by O3 have not been established for most species. Field experiments with soybean [Glycine max (Merr.) cv. Davis] were performed to determine the impact of O3 exposure at different stages of plant development on net carbon exchange rate (NCER) and to establish the relationship between NCER and yield for different O3 exposure periods. The growing season was divided into four quarters (Q1–Q4) of 31 d each for O3 treatment. In each quarter, O3 treatments in open‐top chambers were either charcoal‐filtered air (C) or nonfiltered air (N) to which O3 was added to achieve approximately 100 nL L−1 O3 (mean 7 h d−1 average for the quarter). The NCER was measured in eight O3 treatments (CCCC, NNCC, CNCN, NCCN, CNNC, NCNC, CCNN, and NNNN) where each letter indicates the O3 treatment for successive quarters. The NCER measurements during Q4 (R6–R7) provided the best relationship to yield in a linear regression model (R2 = 0.919). A significant relationship with yield was obtained also with NCER measurements from Q3 (R2–R5) (R2 = 0.626), whereas measurments during Q2 (V10‐R1) were poorly related to yield (R2 = 0.072). Good linear relationships of yield and NCER were found also when Q3 and Q4 or Q2, Q3, and Q4 data were combined. In all cases, however, Q4 data were essential to a good correlation between NCER and yield. It is likely that NCER measurements taken during Q4 correlated well with yield, because that was the period when the requirement for energy from photosynthesis is most critical for yield.