Tree growth is better explained by absorptive fine roots than transport fine roots

Quantifying plant trait variation yields insights into trade-offs inherent in the ecological strategies of plants and is the basis for a trait-based prediction of plant performance and ecosystem functioning. Although the interest in root traits has increased in recent years, we still have limited knowledge of i) whether functionally discrete fine roots—absorptive versus transport roots—have similar trait coordination and ii) how they help to explain plant performance, such as growth.

We measured traits of 28 European broadleaved tree species growing in a research arboretum to study i) the coordination within absorptive and transport fine root traits and ii) the degree of trait-tree growth relationships. To do so, we combined a suite of morphological (root diameter, specific root length and root tissue density) and anatomical (cortex to stele ratio and mycorrhizal colonization rate) traits for each of the absorptive and transport roots.

Despite remarkable differences in average trait values between absorptive and transport roots, our study shows that trait coordination within absorptive and transport roots is comparable. Our results also show that tree growth is better explained by absorptive root traits than by transport roots and is higher in species with a thinner root diameter.

Synthesis. The significant relationship between absorptive roots and tree growth and the lack of such a relationship for transport highlight that roots mostly involved with resource absorption are more important in explaining tree growth than roots involved in transport.