Calculation method of carbon transportation and storage

A method to estimate carbon export for certain maize leaves has been proposed by Kalt-Torres et al. [28], who calculated the transport rate by carbon assimilation and the variation in leaf disk dry weight during a certain interval. However, they did not assess the total fixed C and the allocation between starch and soluble sugar. It has been considered difficult to measure accurately dry weight in field conditions with small leaf disks. Based on a C-balance model, which was established by Pilkington et al. [25] and Sulpice et al. [27] and was used to estimate the rate of growth during the day and night for Arabidopsis, we proposed a method to calculate carbon turnover for maize leaves.

The total amount of C assimilation (A_D) during the day can be estimated as the sum area of net photosynthesis [A_D = ∑ (A × Hours)]. The assimilation export rate (C_E) can be estimated as A_D minus the C accumulated in leaves (C_E = A_D-C_A). C_A represents the sum of daily variation of C accumulated in starch, soluble sugar, amino acids, organic acids. We did not consider amino acids and organic acids [27]. Hence, C_A is the sum of starch and total soluble sugars [27].

One of the critical feasibility factors in this method was the unit conversion from μmol CO₂ m^− 2 s^− 1 into μmol CO₂ g^− 1 s^− 1 of net photosynthesis by the ratio of specific leaf area (SLA), which may be more accurate and representative than small sample disks. Hence, area and relevant dry weight of the leaf measured for photosynthesis were determined for each hybrid. The other essential factor was the constant content of molecular C from CO₂ to (CH₂O) irrespective of the existence of different forms of sugars.