Abstract:
Transplant shock was induced by applying a range of soil water contents to unstored and cold-stored two-yearold (2+0) bareroot Douglas-fir seedlings graded by root volume. Moisture stress had the greatest influence on
morphological characteristics commonly associated with transplant shock. Terminal growth, lateral growth, stem diameter growth, and needle length increased dramatically in seedlings from 6% to 24% soil water content. In addition, number of needles per centimeter on the terminal
greatly decreased with increasing soil water content. Higher root volume seedlings tended to have slow initial growth under high moisture stress but later showed a
significant positive impact on overall growth regardless of soil water content. In every case, seedlings grown in the driest soil had the lowest dry weights and those grown in the most moist soil had the highest weights for all seedling components. Likewise, seedlings with the smallest initial root volumes had the lowest dry weights and the largest root volume seedlings had the highest weights. In addition, macronutrient concentrations and contents of the older foliar tissue was determined. Decreasing soil water content resulted in higher nutrient concentrations of
nitrogen, phosphorous and potassium, particularly of nitrogen, in the old foliar tissue. This is primarily due to reduced growth and hence reduced translocation,
metabolic activity, and nutrient requirement caused by moisture stress. Seedlings with higher root volumes had higher nutrient concentrations and contents and increased
growth. This may be due to increased total root biomass per unit of soil area with increasing seedling root volume resulting in greater nutrient use, supply, uptake, and
storage. The results indicate that moisture stress is a primary cause of transplant shock and that seedlings with increasing root volume may be better able to avoid shock
following outplanting to a specific site.
