Hohenheim University Nutrient uptake by forest trees Forest trees often grow on nutrient-poor soils, but environmental pollution or fertilisation schemes may cause higher soil nutrient supply. Roots of most tree species are usually colonised by mycorrhizal fungi. We investigate the uptake of nitrogen, phosphorus, magnesium, and other elements by tree roots, and also study the effect of varied nutrient supply in forest soil on tree root growth and function. Although per growing season nutrient uptake of adequately growing forest trees is less than the nutrient uptake of annual crop species, nutrient uptake per unit root length in trees is considerable. Because of high heterogeneity of soil conditions and root growth in forest soils, modelling of uptake processes is even more difficult for forest than for crop stands.
Detailed studies show that white tips of growing tree roots have a high nutrient uptake capacity.
However, most root tips are usually colonised by mycorrhizal fungi. These fungi can participate substantially in tree nutrient uptake, in particular in the utilisation of organically-bound phosphorus and nitrogen in soils. Mycorrhizal hyphae, root tips, and older root zones can all absorb water, but their actual contribution is difficult to assess. Experimental results from our laboratory and literature data describe the potential activity of tree roots and mycorrhizas in nutrient and water uptake. Methodology for in situ measurements must be developed to quantify at different forest sites the actual contribution of mycorrhizas and different root parts.