Differential tolerance of coniferous species to the microbially produced herbicide bialaphos. II. Metabolic effects

The effect of the microbially produced herbicide bialaphos on ammonium accumulation and photosynthesis of white spruce (Piceaglauca (Moench) Voss) and red pine (Pinusresinosa Ait.) seedlings was studied under controlled environmental conditions. Ammonium accumulation increased markedly during the first 48 h for seedlings treated in June and was greater in red pine than in white spruce. Ammonium accumulation also increased with higher doses of bialaphos. In contrast, the accumulation of ammonium following bialaphos application in August was minimal for both species and for doses up to an equivalent of 3.0 kg active ingredient (bialaphos) per hectare. Continuous measurements of photosynthesis for the first 12 h following bialaphos application showed a slight negative effect of the herbicide on photosynthetic activity within 2 h of treatment. The decrease was greater for red pine than for white spruce. Photosynthesis measurements taken under three different levels of photosynthetic photon flux density 24 h a...