Carbon Economy of Carrots During Initiation of the Storage Root in Cultivars Contrasting in Shoot: Root Ratio at Maturity

Abstract

Photosynthesis, respiration and growth of two cultivars of carrot with contrasting ratios of shoot: storage root weight at maturity, were compared during initiation of the storage root at 20 °C. Partition of assimilate between shoot, roots and respiration showed no varietal differences but distribution between storage and fibrous roots was different from the time that the storage root could be morphologically identified. For both cultivars over the period investigated, approximately 64% of net photosynthesis was partitioned to the shoot with 5% lost as respiration during the dark and 59% used in growth. Of that exported to the root system (36%), 19% (of net photosynthesis) was used in growth and 17% was lost in respiration. In the cultivar with greater shoot: storage root ratio at maturity, 4.6% was allocated to the storage root in contrast to 7.5% in the cultivar with a lesser shoot: storage ratio at maturity. It is concluded that greater dry matter accumulation in the storage root of the latter cultivar does not result from transient differences in respiratory loss and is not evident in shoot to total root dry matter distribution over this period.