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

Abstract

Root systems are highly plastic as they express a range of responses to acquire patchily distributed nutrients. However, the ecological significance of placing roots selectively in nutrient hotspots is still unclear. Here, we investigate under what conditions selective root placement may be a significant functional trait that determines belowground competitive ability. We studied two grasses differing in root foraging behaviour, Festuca rubra and Anthoxanthum odoratum. The plants were grown in stable and more dynamic heterogeneous environments, by switching nutrient patches halfway through the experiment. A. odoratum was a factor of two less selective in placing its roots into nutrient-rich patches than F. rubra. A. odoratum produced overall higher root length densities with higher specific root length than F. rubra and acquired more nutrients. A. odoratum appeared to be the superior competitor, irrespective of the nutrient dynamics. Our results suggest that root behaviour consisting of producing high root length densities at relatively low biomass investments can be a more effective foraging strategy than placing roots selectively in nutrient hotspots. When understanding the functionality of root traits among different species, specific root length may play a key role.

Root architecture might account for contrasting establishment success of Pseudotsuga menziesii var. menziesii and Pinus sylvestris in Central Europe under dry conditions

“…The wide field of uncertainties that lies between the propagation of Pseudotsuga menziesii for wood production and the risks of its natural spread might be reduced by assessing the species' potential to naturally regenerate under current and future climatic conditions. The successful establishment of any (tree) species is primarily driven by its ability to efficiently capture resources such as light, water and nutrients (Rewald and Leuschner 2009;Schulte et al 2013) and is consequently related to its ability to quickly extend roots and occupy a large soil volume (Mommer et al 2011;Rajaniemi 2007;Zhang et al 2012). Root architecture and soil exploitation strategy are thus important components of a species' competitive ability (Messier et al 2009).…”

“…Seedling establishment and successful regeneration are thus to a large extent driven by the soil exploitation strategy of a species and its belowground interaction with neighbouring species (Messier et al 2009). High rates of root extension (Zhang et al 2012) and the ability to quickly occupy a large soil volume seem to be major attributes of competitive species (Mommer et al 2011;Rajaniemi 2007). The competitive hierarchy of coexisting species may change with resource availability, depending on the plasticity of a species' root system in response to stress (Fort et al 2014;Zhang et al 2012).…”

Warming alters competition for organic and inorganic nitrogen between co-existing grassland plant species

“…In a study conducted by Schippers and Olff (2000), A. odoratum was still more vigorous than F. ovina at 15°C, indicating that the optimum temperature of F. ovina is rather closer to 12°C than to 22°C. The lower root:shoot ratio and plant N concentrations of F. ovina compared to A. odoratum indicate that the differences in competiveness between our test species can be related to a more effective nutrient uptake by A. odoratum compared to F. ovina in the warmed treatment (Mommer et al 2011). Otherwise, the low root biomass of F. ovina under warming might have been a consequence of the high soil water availability in the F. ovina monoculture relative to A. odoratum and mixtures.…”

“…When grown in mixture, however, A. odoratum, but not F. ovina, switched from taking up more N from ammonium than alanine, to greater uptake of N supplied as tri-alanine than as alanine or ammonium. The difference in N uptake between these species in mixture is reflected in their functional root traits: Festuca is known to place roots selectively in nutrient-rich hotspots, whereas Anthoxanthum spreads its roots more evenly in soil, allowing uptake of a greater variety of N forms (Mommer et al 2011). This suggests that when grown in mixture, F. ovina was more competitive than A. odoratum in taking up the same N form as in monoculture, thereby reducing A. odoratum's ammonium uptake.…”

“…These species have previously been shown to differ in their acquisition of organic and inorganic N forms in monoculture. Festuca rubra L., as a close relative to F. ovina, displays a selective placement in nutrient-rich patches with shorter roots and has been reported to take up relatively more inorganic than organic N, whereas A. odoratum, with its longer roots spread more evenly in the soil, relies equally on both forms (Elberse and Berendse 1993;Harrison et al 2007;Harrison et al 2008;Mommer et al 2011;Schippers and Olff 2000;Weigelt et al 2005).…”