THE EFFECTS OF DOMESTICATION ON THE SCALING OF BELOW- VS. ABOVEGROUND BIOMASS IN FOUR SELECTED WHEAT (TRITICUM; POACEAE) GENOTYPES

Premise of the study: Theory and empirical studies have shown that, on average, belowground biomass (M-B) scales one-to-one (isometrically) with aboveground biomass (M-A) within and across plant species both at the individual and population level, i.e., M-B proportional to M-A(alpha=1), where alpha is the scaling exponent. However, little is known about how domestication affects this relationship. Methods: To examine the effects of domestication, we investigated the root vs. shoot biomass relationship during the first 30 d of growth of four wheat genotypes: two older genotypes, MO4 (T. monococcum, a diploid) and DM31 (T. dicoccum, a tetraploid) and two more recent genotypes, DX24 and L8275 (T. aestivum, both hexaploids). _ Results: Biomass allocation to roots scaled more or less isometrically with respect to shoot biomass allocation during the first 30 d of growth for both of the older genotypes, whereas shoot biomass allocation exceeded root allocation for the two more recent genotypes. This difference was attributable to the first 15 d of growth. Although root biomass allocation exceeded shoot biomass allocation during the first 15 d of growth for the two older genotypes, shoot biomass exceeded root biomass allocation during this critical phase of development for the two more recent genotypes. Conclusions: Based on a very limited sample of wheat genotypes, these results indicate that domestication has resulted in an increased biomass allocation to shoots compared to root biomass allocation. This shift possibly reflects artificial selection under agricultural conditions (for which water and nutrients are not limiting) favoring higher crop yields.