Comparing Two Field Methods to Measure Individual Shrubs’ Root Density Distribution and Establish Allometric Equations for Belowground Biomass

Purpose : A large fraction of a plant’s biomass is thought to be belowground, especially in shrublands that typically occur in episodically water-limited climates. Nonetheless, we have no standardized method to map individual plant’s root density distribution (IRDD) and lack of easily obtainable allometric predictors of shrubland belowground biomass. This type of information is difficult to collect, especially in woody plant communities in natural conditions where roots of different individuals can be highly intermingled. Methods : We assess three methods to map IRDD of field shrubs: soil drilling to extract roots, and plant injection with dyes and microsatellite analysis for individual-level root identification. Using the resulting data, we fitted IRDD models and integrated root density predictions from the models across three-dimensional space obtaining total root biomass of shrubs. We use the resulting individual-level data to establish allometric relations based on two easy-to-measure predictors: crown biovolume and stem diameter at the ground level. Results : We found plant injection to be a highly cost-effective technique to link root fragments from a soil sample to plant individuals. We fitted power law distributions predicting aboveground and belowground biomass. Conclusions : Core drilling machines and plant injection with dyes of different colors to link root fragments from the sample pool to plant individuals represent an affordable, reliable way to study the foraging behavior of woody plants which roots are highly intermingled. The resulting allometric relations allowed us to conclude that crown biovolume is the best proxy for shrub biomass, especially belowground.