Etiolated Growth as Measure of Non-structural Biomass in Lucerne Taproots

Abstract

Enzymatic hydrolysis of starch in lucerne (Medicago sativa L.) taproots is the conventional method used to determine the quantity of carbohydrates allocated to regrowth. Etiolated growth from a taproot could be used to quantify total root biomass allocated to regrowth. This study compared concentrations of non-structural carbohydrates, as measured by α-amylase hydrolysis of starch to glucose, to concentrations of non-structural biomass, as measured by etiolated growth from lucerne taproots placed in an incubator and plants in situ. The concentration of starch from enzymatically assayed taproots was 325 g kg-1 expressed as glucose equivalents. Etiolated growth and weight loss by respiration from plants grown in the incubator accounted for 524 g of actual biomass per kg of root. There was 46·2 g kg-1 of N, 3·1 of P, and 33·1 of K in the etiolated growth. An 88% increase in etiolated growth dry weight was observed from plants in situ compared to taproots placed in the incubator. Accurate quantification on non-structural biomass should not be limited to sampling just the taproot, but must included the entire root system. Compared to determining non-structural carbohydrates by enzymatic hydrolysis of starch, the procedure used in determining non-structural biomass by etiolate growth gave results in units relative to the plant. The use of etiolate growth also provided information on mineral nutrient partitioning from root to shoots, was less technically demanding, and could be applied to the entire root system.