A non-targeted metabolomics approach to quantifying differences in root storage between fast- and slow-growing plants

Life history theory posits that slower-growing species should invest proportionally more resources to storage, structural (e.g. stems) or defence traits than fast-growing species. Previously, we showed that the slower-growing monocarpic plants had lower mortality rates and higher bolting probabilities after two defoliation events. Here, we consider a mechanistic explanation, that the slower-growing species invested relatively more resources to storage. We compared the relative levels of root storage compounds between eight monocarpic species using metabolomic profiling, and characterized plant growth using a size-corrected estimate of relative growth rate (RGR). Growth rate was negatively correlated with the proportional allocation of root metabolites identified as sucrose, raffinose and stachyose and with amino acids known for their roles in nitrogen storage, particularly proline and arginine. The total amount and concentration of energy-corrected carbohydrates were also negatively correlated with RGR. Our results show for the first time that slower-growing species invest proportionally more of their total root metabolites in carbon- and nitrogen-storage compounds. We conclude that the increased investment in these reserves is an important resource allocation strategy underlying the growth-survival trade-off in plants.