Aboveground-canopy and belowground-root-trait correlations contribute to root system characteristics estimation: Insights from ground penetrating radar data

Understanding root system characteristics is crucial for predicting plant growth and ecological adaptability under varying environmental conditions. In this study, we investigated the shrub coarse roots to ask: whether the characteristics of the shrub root system (i.e., lateral root spread and its root biomass) can be estimated from the easily measurable canopy area of the shrubs. Firstly, we measured 62 individual full-root systems of Caragana microphylla Lam. (C. microphylla) by ground penetrating radar (GPR) and their aboveground canopy area. Secondly, the number of root points extracted from the radargrams was converted into root biomass, which was further used to calculate the cumulative root biomass. Thirdly, the logistic model was employed to characterize the coarse root horizontal spatial distribution pattern of cumulative biomass in the horizontal direction. The fitted function was then used to extract root parameters, including total root biomass, lateral root spread, intrinsic growth rate and root-shoot coverage ratio. Finally, the relationship between canopy area and extracted root parameters was investigated to determine the potential for rapid estimation of root parameters using shrub canopy area. The horizontal spatial distribution pattern of coarse roots in C. microphylla follows the logistic model. The logistic model exhibited the lowest R2 value (0.92) when fitted to the 62 shrub data. The mean values of root biomass, lateral root spread, intrinsic growth rate, and root-shoot coverage ratio extracted from the logistic model were 1.68 kg, 3.44 m, 3.64, and 14.59, respectively. The results indicated that the canopy area exhibited a positive correlation with total root biomass and lateral root spread, while it was negatively associated with intrinsic growth rate and root-shoot coverage ratio. The canopy area of a shrub is an effective parameter for estimating the characteristics of its root system.