Dry matter accumulation by Piceasitchensis seedlings during winter

Abstract

Dry matter production by Sitka spruce seedlings (Piceasitchensis (Bong.) Carr) outside the period of shoot extension was determined in southern Scotland by harvesting plants from a nursery on 13 occasions between late September and mid-May. Air and soil temperature and incoming radiation were measured in an attempt to relate weight changes to climatic variables. Dry weight of the plants apparently doubled between late September and mid-April but subsequently changed little. Most dry weight increase occurred during October, late March, and April but there was also a slight increase in weight in midwinter. The relative increase in weight was similar in roots and shoots until mid-January but thereafter was proportionally much greater in shoots than in roots and was associated with a marked increase in needle weight. Lack of weight increase in late spring was attributed to the respiratory demands of bud expansion. Dry matter changes in the 12 harvest intervals was not related to mean daily temperature, incoming radiation, or photoperiod, but when averaged over periods of 1 month a much closer relationship was evident.