The Effect of Light and Moisture on Columbia Milkvetch Toxicity in Lodgepole Pine Forests

Abstract

Variations in miserotoxin concentration of Columbia milkvetch located in pure lodgepole pine forests were compared to changes in rainfall patterns during the period 1973 to 1976. The substantial increase in precipitation for 1976 was reflected in soil and plant moisture changes and these conditions appeared to induce the formation of higher miserotoxin levels. In addition, a number of secondary miserotoxin peaks were generated during pod development in 1976. Understory light regimes at 12 lodgepole pine sites were determined by chemical actinometry, which expressed duration in direct sun at each plot as a percentage of "full sun" (FS) control. Sites with <15% FS exhibited lower miserotoxin levels than either the 15-35% or >35% FS groups. Miserotoxin levels above 6% predominated in the latter two categories. A positive relationship between light and toxicity was not apparent in the Douglasfir stands where miserotoxin levels remained low. A gas chromatography method was developed to speed up miserotoxin determinations and to screen Columbia milkvetch samples for the presence of free 3-nitropropanol.