Root system size and precision in nutrient foraging: responses to spatial pattern of nutrient supply in six herbaceous species

1 An experiment was carried out to test the hypotheses that in heterogeneous environments: (i) the size of species’ root systems will be negatively correlated with their ability to place roots precisely in nutrient-rich patches; (ii) precision of root placement will be less affected by distance to nutrient patches in species with large root systems; (iii) species with greater precision in root placement will show greater variation in biomass (sensitivity) in response to heterogeneity in nutrient supply; and (iv) plants will be less precise in root placement, and will invest more biomass in above-ground structures or in fitness-related attributes, when in association with mycorrhizas. 2 Single plants of six herbaceous species ( Arrhenatherum elatius , Festuca ovina , Plantago lanceolata , Campanula rotundifolia , Papaver rhoeas and Sonchus oleraceus ) were grown in pots with mycorrhizas either present or absent. The same amount of nutrients was supplied either homogeneously or heterogeneously at different distances from the plants. Pots received the same quantity of nutrients in all treatments. 3 There was a significant negative correlation between species’ root system biomass and precision. Several species, including some with large root systems, showed small but highly significant differences in precision between the various treatments. Only the highprecision species Papaver and the low-precision species Campanula exhibited sensitivity in biomass produced in response to different patterns of heterogeneity. 4 The precision with which roots were placed in nutrient-rich patches was affected by distance from patches in Papaver , the smallest-rooted species used in the experiment, and in Plantago , one of the larger-rooted species. There was no evidence to support the hypothesis that precision would be affected more by distance from nutrient patches in small-rooted species than in large-rooted species. 5 The presence of mycorrhizas did not affect precision of root placement in any species. However, allocation of biomass to roots was significantly lower in Arrhenatherum , and allocation to reproductive structures was significantly higher in Campanula , when mycorrhizas were present. 6 This study confirms that there are differences between species in precision of nutrient foraging that are related to root system size. It also shows that there is variation in precision within species in response to the location of nutrient-rich patches, and that the ability of a species to display precision in nutrient foraging is dependent on its environmental setting.