Importance of current photosynthate to new root growth in planted conifer seedlings

Abstract

A series of experiments were conducted to examine the importance of current photosynthate for development of new roots in planted conifer seedlings and to assess the possible importance of carbohydrate reserves. Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and Sitka spruce (Piceasitchensis (Bong.) Carr.) seedlings, labelled with 14 CO 2 in October, contained 14 C in old roots but little in new roots when placed into growing conditions in January. New roots of seedlings labelled after 12 days growth in January were highly radioactive, indicating that current photosynthate was the primary carbon source for new roots. These results agreed with an experiment in which the amount of new root growth of 1 + 1 Douglas-fir transplants was proportional to light intensity. Net photosynthesis (P n ) of similar Douglas-fir nursery stock was inadequate to supply carbon for respiration and new root growth at 200 μE•m −2 •s −1 , although new root growth occurred. The ability to achieve gas exchange from the moment of planting in moist soil was evident from photosynthesis measurements and transpiration weighings, but although preconditioning affected new root growth in lodgepole pine (Pinuscontorta Loud.), no relationship between new root growth and P n was observed.