Forests provide important products and services to our planet and people: they offer wood and other products, regulate our climate and are an important source of entertainment. To maintain our forests, it is important to understand the growth of trees. Leaves play an important role in tree growth: by means of photosynthesis, biomass is being produced which we .. as e.g. wood production. Equally important processes occur however belowground: well hidden from our sight, tree roots acquire water and nutrients essential to growth. As these processes are still largely unknown, this thesis studies the role of roots in tree growth.
My thesis shows the complexity of the role of roots in tree growth; it is not easily or straightforwardly summarized. While carrying out an important task – water and nutrient uptake – roots have to survive and function in a challenging environment. In the soil, roots have to deal with chemical, potentially harmful, substance and with dense soils that can exert pressure on the roots. Also, the resources they acquire, vary in their availability and mobility. This implies that trees have to adjust their roots to the resources most needed. Thin, fast-growing roots are for example better suited at capturing immobile resources than thick, slow-growing roots. Yet thicker roots may be more resistant to droughts or can grow better in dense soils. Besides these size differences, roots can form symbiotic relationships with mycorrhizal fungi. These fungi efficiently acquire nutrients and supply these to the tree in exchange for sugars. This symbiosis can be very important for trees that form less efficient roots.
This thesis demonstrates that trees can adopt a variety of root strategies in different environments. It implies that fast tree growth is not achieved by one specific type of root (e.g. thick or thin). Understanding the growth of trees therefore requires appropriately studying this diversity of belowground uptake strategies.