Solution Additions to Seedling Systems

Complete solution changes for multiple phenolic acid treatments were used because phenolic acids supplied to seedlings in the nutrient culture system disappeared from the nutrient solution within 24-48 h (Blum and Dalton 1985 Blum and Gerig 2005). This was due to microbial metabolism, physical breakdown, and/or root uptake. Since we did not want to confound nutrient and phenolic acid effects, complete solution changes were made. An additional benefit of this approach was to reset phenolic acid concentrations to the initial treatment levels for each solution change. This was important since recovery of seedling processes occurred rapidly after phenolic acid depletion (Blum and Dalton 1985 Blum and Rebbeck 1989 Blum and Gerig 2005). 

2 Plant-Plant AUelopathic Interactions. Phase I The Laboratory 

Multiple additions of phenolic acids were used because phenolic acid concentrations in soil decline rapidly after each addition of phenolic acids (Blum et al. 1987 Blum and Gerig 2006). This was due to microbial metabolism, physical breakdown, root uptake, and/or soil particle sorption. Recovery of seedling processes, although considerably slower than in nutrient culture, also occurred in seedling-soil systems (Blum et al. 1987 Blum and Gerig 2006). To maintain inhibition for extended time periods multiple additions of phenolic acids were required. 

For the soil columns (Fig. 2.2), water, nutrient solution, or various concentrations of phenolic acid in water or nutrient solution was supplied to the top of each column at 2-3.5 ml/h with a cassette pump (Blum et al. 1999a). Solutions were collected from the bottom of the column for 30 min at 12-h intervals during phenolic acid treatment to estimate the amount of phenolic acid lost (leached) from the systems. 

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