ROOT REGENERATION AND PLANT WATER STATUS OF PINUS-RADIATA D DON SEEDLINGS TRANSPLANTED TO DIFFERENT SOIL TEMPERATURES

The regeneration and configuration of new roots on transplanted 8 month old Pinus radiata D. Don seedlings were measured in relation to soil temperature and time after transplanting. The effects of root wrenching and nutrition on root regeneration were compared. Low soil temperature adversely affected the initiation and elongation of new roots. The branching and morphology of the new roots were also influenced by soil temperature. The processes of initiation and elongation are greatly retarded below a critical root temperature between 11 and 14 °C. Wrenching and fertilization stimulated new root growth at low temperatures. There is a close interrelationship between the constituent parts of the network which forms the new root system. The first-order laterals on transplants are critical as a basic framework for extension and production of second-order laterals which form the major part of the regenerating root system.Needle water potential was closely related to the new root growth. The water stress experienced by the transplants for several weeks after planting was due primarily to the suppressive effect of low soil temperature on root regeneration. Wrenched plants were less water-stressed than unwrenched plants.Field measurements confirmed the finding from controlled experiments that, in southern Australia, the low soil temperature in the planting season imposes a major restriction on early root regeneration which in turn inflicts water stress in transplants. This needs to be considered during the planning of planting and fertilization. © 1979 Oxford University Press.