Root chemistry of Douglas-fir seedlings grown under different nitrogen andpotassium regimes

Root chemistry and biomass allocation of Douglas-fit (Pseudotsuga menziesii var, glauca (Bessn.) France) seedlings under optimal and deficient levels of nitrogen (N) and potassium (K) were studied. Seedlings receiving high-N treatments were significantly larger and allocated more dry matter to their stems and less to their roots than those receiving the low-N treatments. T he K treatments did not significantly affect total seedling biomass or root /shoot ratios. Root tip starch concentrations were significantly higher and root tip sugar concentrations were lower in plants receiving the low-N tre atments. Seedlings receiving the high-N, low-K treatment had significantly lower concentrations of phenolics and tannins and lower ratios of these com pounds to sugars in the root tips than seedlings receiving the high-g treat ments. Samples taken from two locations on the root system show that concen trations of phenolics, tannins, sugars, and starches were substantially hig her in the root collar than in the root tips. Because of lower within tissu e variation, we recommend sampling at root tips to better detect treatment differences. This study shows that N levels affect starch concentrations in the roots, while K levels affect root phenolic and tannin concentrations. Possible relationships between low root phenolic and tannin concentrations and lessened resistance of Douglas-fir to root disease are discussed.