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

USDA-ARS, Air Quality Program and Dep. of Crop Science, North Carolina State Univ., 1509 Varsity Dr., Raleigh, NC 27606;

Walter A. Pursley

Dep. of Crop Science, North Carolina State Univ., Raleigh, NC 27695;

Steven F. Vozzo

Dep. of Plant Pathology, North Carolina State Univ., Raleigh, NC 27695;

Allen S. Heagle

USDA-ARS, Air Quality Program and Dep. of Plant Pathology, North Carolina State Univ., Raleigh, NC 27695.

^* Corresponding author.

ABSTRACT

High 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.

Cooperative investigations of the USDA-ARS and the North Carolina State Univ. The research reported in this publication was funded in part by the North Carolina Agric. Res. Service. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Service or the USDA of the products named, nor criticism of similar ones not mentioned.

Received for publication August 20, 1990.

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