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

Abstract

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.

Soil nutrient heterogeneity and competitive ability of three grass species (Festuca ovina, Arrhenatherum elatius and Calamagrostis epigejos) in experimental conditions

“…Our results are mostly in agreement with data obtained by Wijesinghe et al (2001) that indicated that species with large root systems are less selective in placing their roots in nutrient rich patches than species with smaller root systems. They found a significant negative correlation between the mean root biomass of each species and its precision of root placement in nutrient-rich patches.…”

Contrasting root behaviour in two grass species: a test of functionality in dynamic heterogeneous conditions

“…Differences in root foraging behaviour have long been interpreted as a trade-off between precision and scale (Campbell et al 1991;Farley and Fitter 1999;Wijesinghe et al 2001;Rajaniemi and Reynolds 2004), with dominant species employing low-precision foraging at high scale and subordinate species vice versa. It has been argued (Kembel and Cahill 2005;Kembel et al 2008;de Kroon and Mommer 2006) that the concept of 'scale' as the spatial extent or size of the root system was imprecisely defined, but 'scale' may also be interpreted as root densities per unit soil volume.…”

Selection for protection in an ant–plant mutualism: host sanctions, host modularity, and the principal–agent game

“…Many genera in the Agavaceae, of which Yucca is a member, abscise flowers after damage by insect feeding or oviposition (Sutherland 1987;Becerra & Lloyd 1992;Pellmyr 1997), despite not being associated with pollinating seed predators (see also Marr & Pellmyr 2003). Similarly, non-leguminous plants, which do not associate with rhizobia, respond to nitrogen soil availability via differential root investment, which would be a preadaptation for legume host sanctions if the trait occurs in the non-rhizobia-associated ancestors of legumes (Hodge et al 1998(Hodge et al , 1999Farley & Fitter 1999;Wijesinghe et al 2001). Thus, it is modularity that provides stronger evidence of adaptation.…”