Opinion paperThe importance of water-soluble carbohydrates in the theoretical framework for nitrogen dilution in shoot biomass of wheat

Breeding for yield has increased the concentration of reserve water-soluble carbohydrates (WSC) in wheat from dry, low yielding environments of Australia to wet, high-yielding environments of the UK. This generalized increase in WSC can reduce the concentration of nitrogen (N) in shoots and consequently reduce the crop critical N concentration (%Nc: the minimum concentration of N to achieve maximum growth rates). This may cause errors when assessing a crop's N status using N dilution curves which relate critical N concentration (%Nc) and shoot biomass (W), i.e. %Nc = aW−b. Inaccurate diagnosis of a crops N status will have negative environmental and economic consequences such as N losses to the environment and yield gaps. Here, we (i) outline the drivers of variation in WSC, (ii) discuss the implications of WSC on wheat N status, (iii) propose an adjustment of the theoretical N dilution framework that makes explicit a WSC compartment, and (iv) provide estimates of the range of error derived from the current two-compartment model.