Growers might be able to use CO2 more effectively if they had better information about the carbon status of their crops. In the experiments reported here, beefsteak tomato plants were grown with CO2 enrichment in commercial glasshouses in British Columbia.
Samples of leaves were taken monthly from every third leaf beginning with the leaf nearest to the youngest truss with open flowers (designated "leaf 1"). Fruit volumes were also measured monthly to enable fruit growth rates to be calculated.
Starch content was highest in leaf 1 and then declined sharply with each successively lower leaf down to leaf 9, after which it was stable and almost zero. Truss 5 had the highest growth rate and was near leaves that had little starch. This led the authors to suggest that the upper leaves had high starch contents because they did not have to supply nearby developing fruits.
Researchers also suggested that leaf mass per unit leaf area would probably be easier to measure on a nursery than starch content and so may be a better marker of carbohydrate status. If so, leaves 7 to 9 would probably be the best "marker" leaves of tomato because they are fully expanded and near to developing fruits.
Canopy Profiles of Starch and Leaf Mass Per Area in Greenhouse Tomato and the Relationship with Leaf Area and Fruit Growth by Edwards, Jolliffe and Ehret (2010). Scientia Horticulturae 125 (4): 637-647. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti
Dr Ken Cockshull is an associate fellow, Warwick Crop Centre, University of Warwick.