Effects of lime application and test branch position on 14C-photosynthate partitioning in 3-year-old Sitka spruce (Picea sitchensis plants growing in pots containing peat soils

Experiments were carried out to determine the effects of lime and test branch position on percentage 14C-distribution within the plant, sink activities of plant fractions and total 14Crecovered in plants. The investigation was conducted with 3-year-old Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings planted in pots containing either limed or unlimed peat soils. To determine effects of test branch position on the above processes, upper test branches (UTB) and lower test branches (LTB) of plants were exposed to CO2 in October 1993, April 1994 and July 1994. These dates represented 100, 160 and 263 days after plants had been established under limed and unlimed conditions. Percentage 14C-distribution to the leader fraction decreased in October and increased in both April and July as a result of liming. In October, percentage 14C-distribution to the coarse-root fraction and sink activity of this fraction were increased by lime application. In July, the LTB and UTB of the limed plants retained 49 per cent and 51 per cent respectively higher concentrations of 14C as disintegrations per minute per gram dry weight compared with those of the unlimed plants. On all sampling occasions, sink activities of below-ground parts of the plant receiving 14C from the LTB were higher than when 14C was received from the UTB; such increases ranged from 55 per cent to over 300 per cent and were seemingly unrelated to liming treatment. In July, sink activity of above-ground parts of the limed plants importing 14C from the UTB was 100 per cent higher than when 14C was imported from the LTB. During the period of shoot elongation in April, both the UTB and LTB exported high percentages of their current photosynthate to the above-ground parts of the plant. When shoot elongation slowed down in July, the UTB and LTB exported high current photosynthate more equally to the above and below-ground parts of the plants. Concentrations of