Assessment of the phytotoxic potential of m-tyrosine in laboratory soil bioassays

The significance of soil-allelochemical interactions was addressed in this paper through studies conducted with m-tyrosine, an amino acid analogue and a potent plant growth inhibitor, in a series of laboratory assays performed in field soil or growth media. The studies were performed as a basis for further evaluation of m-tyrosine activity in field soils containing living plant roots. Here, we examined the role of common soil amendments, including ammonium nitrate fertilizer and activated carbon, in overcoming plant growth inhibition in soils in a laboratory setting by using lettuce as a sensitive indicator of plant toxicity. The phytotoxicity of m-tyrosine was not influenced significantly by soil N amendment; however, when significant amounts of activated carbon were added to the soil medium, growth inhibition in treated lettuce seedlings was strongly reduced. Soil texture did not influence the bioavailability or activity of m-tyrosine, as activity in high organic growth media was similar to that of sand and soil mixtures. Similar to other purported allelochemicals, soil persistence of m-tyrosine was limited, with a predicted half life of less than 1 day in soil in a controlled laboratory setting. Rapid degradation of this molecule likely was due to microbial activity but degradation did not appear to be influenced significantly by soil N amendment. Given the observed activity of m-tyrosine in soil and growth media on seedling growth, potential may exist for development of m-tyrosine as a soil applied herbicide if formulations can be stabilized under soil conditions.