ROOT BIOMASS FRACTION AS A FUNCTION OF GROWTH DEGREE DAYS IN WHEAT

Root, underground and above-ground biomass were measured on various wheat cultivars from 1986 to 1988 in the south-east of France. The results are expressed as root: total (f(r)) or underground: total (f(u)) biomass fractions. Observed f(r) and f(u) values are in good agreement with previous results. f(r) and f(u) decrease steadily from emergence to maturity, with an exponential tendency. When using cumulative growth degree days since emergence relative to cumulative growth degree days until ear emergence (theta*) as time scale, f(r) and f(u) can be expressed as simple functions of theta* f(r)(theta*) = 0.05 + 0.58e-1.48-theta* f(r)(theta*) = 0.12 + 0.88e-2.28-theta* The incremental root biomass partitioning coefficient, alpha(r) = (dW(r)/dt)/(dW(t)/dt), which describes the net increase in root biomass dW(r) over time dt relative to the increase in total biomass (dW(t)) over the same time period, has been derived from f(r) and the relative growth rate. Its time course is accurately represented by alpha(r)(theta*) = -0.15 + 0.63e-0.98-theta* Under our experimental conditions, with no severe water stresses or nutrient deficiencies, and for our sampling frequency, around 2 weeks, the development scale theta*, is the main factor governing the time courses of f(r), f(u) and alpha(r).