© 1991 Heron Publishing—Victoria, Canada
Loblolly pine photosynthesis is enhanced by sublethal hexazinone concentrations
Jon D. Johnson (1) and Henry E. Stelzer (1, 2)
1. Department of Forestry, University of Florida, Gainesville, FL 32605, USA / 2. Proctor and Gamble-Cellulose, Perry, FL, USA / Received September 26, 1990
Summary
The effects of hexazinone on gas exchange and chlorophyll a fluorescence kinetics were investigated in container-grown loblolly
pine (Pinus taeda L.) seedlings. Hexazinone at concentrations from 10–4 to 10–8 M was applied as a soil drench. Photosynthesis in seedlings treated with hexazinone concentrations greater than 10–6 M was partially or completely inhibited throughout the 14-day study. Chlorophyll a fluorescence kinetics indicated that
the inhibition was due to disruption of PSII electron transport. At hexazinone concentrations below 10–5 M, quantum yield and rates of photosynthesis and transpiration were increased on Day 1 and remained elevated through Day
7, whereas chlorophyll a fluorescence was unaffected. The results suggest that, in loblolly pine, hexazinone at sublethal
concentrations may function in a manner similar to cytokinins.
