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Response of White Clover to Ozone in Different Environments

USDA-ARS, Air Quality Res. Unit, 1509 Varsity Drive, Raleigh, NC 27606 and Dep. of Plant Pathology, North Carolina State Univ.;

Joseph E. Miller

USDA-ARS, Air Quality Res. Unit, 1509 Varsity Drive, Raleigh, NC 27606 and Dep. of Crop Science, North Carolina State Univ.

^* Corresponding author (asheagle{at}unity.ncsu.edu).

ABSTRACT

The value of research on effects of O₃ done in greenhouse or field exposure systems is often questioned because chamber environments may affect plant response. Foliar injury, chlorophyll, and forage weight responses of two clones of white clover (Trifolium repens L.) to ambient O₃ were compared for plants grown in charcoal-filtered (CF) and nonfiltered air (NF) in greenhouse and open-top field chambers and in ambient air (AA) plots at Raleigh, NC. One clone is sensitive to O₃ (NC-S), whereas the other is resistant (NC-R). Comparisons of individual clone responses in CF vs. NF treatments in the greenhouse and in the field and the proportional response of the clones (defined as the NC-S/NC-R response ratio) were used to indicate the relative response to O₃ in the different environments. Foliar injury and chlorophyll responses of NC-S to O₃ were similar in the NF greenhouse, NF open-top chambers, and in AA. However, for individual harvests, the percentage decrease in NC-S forage weight in NF compared with CF was 7 to 23% greater in the greenhouse than in open-top chambers. The NC-S/NC-R forage ratios indicated that clover response to O₃ in NF open-top field chambers was the same as in AA. Large environmental differences between greenhouse and open-top chambers apparently caused differences in plant responses to O₃, whereas relatively small environmental differences between open-top chambers and ambient air did not.

Cooperative investigations of the USDA-ARS and the North Carolina State Univ. Funded in part by the North Carolina Agric. Res. Service and the USEPA through an Interagency Agreement (no. DW123934170-6) in support of the Agricultural Lands Resource Group of the Environmental Monitoring and Assessment program. 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. This paper has not been subject to USEPA peer review and should not be construed to represent the policy of the agency.

Received for publication June 1, 1995.