The Scaling Relationship of Below and Above-ground Biomass of Different Grain Crops during the Seedling Stage

Allometric partitioning theory showed that root biomass (MB) scales in a nearly isometric manner with respect to shoot biomass (MA) for natural plants. Artificial selection has fundamentally transformed plants; for example, the biomass allocation pattern has changed in grain crops. This study investigated 32 genotypes from 20 grain crop species to test the effects of domestication and seed size on the scaling relationship of MB vs. MA for grain crops. The scaling exponent of MB vs. MA during 30 days of growth was 0.937 across the 32 grain crop genotypes, 0.999 for the dicotyledons and 1.034 for the monocotyledons. Based on the 95% CIs of the MB vs. MA scaling exponent (RMA) of the data sets for the 32 genotypes, eight values exceeded 1.0, nine values were less than 1.0 and the remaining 15 values were statistically indistinguishable from 1.0. Seed size was positively correlated with the scaling exponents of MB vs. MA for the 32 genotypes (P<0.05), which means large-seeded species generally had more potential for allocating biomass to roots during the seedling stage. These findings suggest that a uniform isometric relationship exists in grain crop species and that artificial selection in crop species has not changed this relationship. In addition, larger seeds are an evolutionarily-stable strategy based on high grain yield per area.