Monique Weemstra, Natasa Kiorapostolou, Jasper van Ruijven, Liesje Mommer, Jorad de Vries, Frank Sterck
A walk in a forest shows us that trees differ; they have different leaves, barks, flowers and fruits. Often invisible to us, tree roots differ too: in their thickness, amounts, color, smell, and branching. This variation in roots allows trees to take up water and nutrients in different environments that they need to grow. Studying the different shapes and sizes of roots may tell us why roots vary and how this influences how fast trees can grow.
In this study, we created digital model trees that we gave different roots: thick or thin, many or few roots. For each tree, we calculated how much resources it could acquire and how much it could grow based on its roots. These calculations were based on the costs and benefits of different root systems: making thin roots means that a tree has a large root surface area and can quickly acquire resources, but thin roots do not live very long and need to be replaced often; alternatively, having many roots means that a tree can take up many resources, but they are also costly to produce.
It is often expected that fast-growing trees adopt the latter strategy: producing thin but short-lived roots because these are assumed to be the most efficient for resource uptake. However, our study shows that the model trees with the fastest growth had thick, long-lived roots to reduce root turnover costs and produced more roots (i.e. more root biomass) to enlarge their root surface area. This work demonstrates 1) the importance of studying root biomass to understand and explain differences in tree growth, and 2) how building model trees can help us unravel the different root strategies that trees can adopt to improve their growth.