Effects of root or shoot exposure before planting on the water relations, growth, and survival of Sitka spruce

Abstract

Sitka spruce (Piceasitchensis (Bong.) Carr.) seedlings were exposed either by the root or the shoot to drying conditions in a growthroom. Changes in leaf water potential (ψ1) and rate of water loss were determined and measurements were made on the moisture content (MC) of the shoot, woody root, and fine roots.Exposure of the root or shoot reduced the MC of all tissues measured and reduced ψ1. When the root was exposed, water moved from the shoot into the root system, but this water movement did not prevent a substantial reduction in the MC of the root system. The greatest reduction occurred in the fine roots. Exposure of the root caused a faster decrease in fine root MC than exposure of the shoot.Treated seedlings were planted in root observation boxes, and those which had been exposed by the roots to give ψ1 of −20 × 105 Pa were found to be under increased water stress when measured 12 days after planting indicating that water uptake had been impaired. Root exposure also reduced plant survival and the growth of roots and shoots of plants which survived. Although exposure of the shoot to give ψ1 of −20 × 105 Pa resulted in a similar reduction in total plant MC as exposure of the root, the treatment was not damaging in terms of growth or survival after planting. It is concluded that measurement of neither whole plant MC nor ψ1 prior to planting can show whether a plant has been subjected to damaging conditions. Root exposure of plants in different stages of growth indicated increased sensitivity to exposure the farther the plants were removed from dormancy.