Root foraging : the consequences for nutrient acquisition and competition in heterogeneous environments

In natural habitats, the availability of essential mineral nutrients may vary widely from place to place and from time to time, at scales relevant to individual plants. Plants have developed root foraging mechanisms that enable them to acquire adequate amounts of nutrients in these heterogeneous environments. The ability of plants to proliferate roots in nutrient-rich patches has been shown frequently, but both the timing and the degree of root proliferation varied widely. Species from inherently nutrient-rich habitats in general display a higher relative increase in root density in nutrient-rich patches than species from inherently nutrient-poor habitats. This observation prompted the hypothesis that root foraging mechanisms differ between species from habitats of different nutrient availability.Overall, the results described in this thesis contradict this hypothesis. The higher degree of selective root placement displayed by species from more nutrient-rich habitats compared to species from more nutrient-poor habitats may result from differences in growth rate rather than from differences in root morphological plasticity. The results further indicate that selective root placement may confer an advantage in terms of nutrient acquisition in heterogeneous environments in the short-term, but in the long-term the increased root density may result in a lower rather than a higher biomass production in heterogeneous environments. However, root foraging abilities by which local nutrient patches are exploited may still be profitable when plants are grown in competition. The ability to rapidly exploit nutrient-rich patches due to root foraging characteristics seems to confer a competitive advantage in heterogeneous environments, even in the long-term.