This balance has been suggested to be a ‘functional equilibrium’, with plants that experience low water or nutrient supply investing more in roots, and plants growing under low light or CO2 conditions investing more in leaves or stems.
Conceptually this is simple to envisage, but to quantify the flow of sugars is challenging and requires sophisticated machinery.
[8] For plants growing under steady state conditions, it is feasible to determine sugar-allocation by constructing a C-budget.
This requires determination of the C-uptake by the whole plant during photosynthesis, and the C-losses of shoots and roots during respiration.
Further C-losses may occur when sugars and other C-based compounds are exuded by the roots, or disappear as volatiles in the leaves.
The fractions of biomass present in leaves and roots are also relevant variables in Plant growth analysis.
A common way to characterize the biomass allocation of a vegetative plant is to separate the plant in the organs of interest (e.g. leaves, stems, roots) and determine the biomass of these organs – generally on a dry mass basis - independently.
However, changes are often smaller at different water supply, and effects of CO2 concentration, UV-B radiation, ozone and salinity on allocation are generally negligible.
Plants growing at higher temperature mostly decrease RMF and increase LMF.
Grasses generally have lower LMF values that herbaceous dicots, with a much higher proportion of their biomass present in roots.