A Novel Approach for Determining Root Biomass in Plant-based Research

In plant-based research, root biomass is often recorded. To determine root dry weight, roots are traditionally separated from substrate. Methods include compressed air, pressurized water spray, and water baths. Despite use of screens, portions of roots are typically lost during separation processes. If root balls are dried and weighed at harvest and dry mass of substrate is known root dry weight could be extrapolated. On 5 October 2015, thirty-five 15-cm (1.6 L) containers were filled with 380 g substrate per container. Five containers were randomly selected and placed in a forced-air drying oven at 60˚C for one week to determine average dry mass of substrate per container. One Lantana camara ‘Chapel Hill Gold’ plug was transplanted from 60 count flats into each of 20 containers and topdressed with 6 g Osmocote Plus 15-9-12. The remaining ten filled containers were maintained with no plant to verify that no substrate was lost during the experiment due to hand watering which was applied as needed. On 1 December 2015, shoots were separated from root balls. Roots from ten randomly selected plants were separated from substrate by washing root balls in 5-gallon buckets filled with water until roots were relatively clean of substrate. Harvested shoots and roots were dried in a forced-air oven at 60 ^oC and weighed. The ten remaining root balls and ten filled containers with no plants were placed in a forced-air oven at 60 ^oC for five days and weighed. Shoot and root weights from both groups were analyzed using one-sample t-tests. Root dry weight harvested by washing averaged 4.29 g, while root dry weight calculated by drying root balls averaged 9.35 g (p<0.0001). Shoot dry weight was similar among both groups (p=0.8809). Although plants were similar in size, less root mass was measured by washing roots than by calculating root mass based on root ball dry weight. These data suggest significant root loss due to washing. Starting with a known mass of dry substrate and weighing root balls at experiment termination may improve accuracy when determining root biomass.