Effects of neighbour location and nutrient distributions on root foraging behaviour of the common sunflower

Abstract

Plants regularly encounter patchily distributed soil nutrients. A common foraging response is to proliferate roots within high-quality patches. The influence of the social environment on this behaviour has been given limited attention, despite important fitness consequences of competition for soil resources among plants. Using the common sunflower ( Helianthus annuus L.), we compared localized root proliferation in a high-quality patch by plants grown alone to that of plants in two different social environments: with a neighbouring plant sharing equal access to the high-quality patch, and with a neighbouring plant present but farther from the high-quality patch such that the focal individual was in closer proximity to the high-quality patch. Sunflowers grown alone proliferated more roots within high-nutrient patches than lower-nutrient soil. Plants decreased root proliferation within a high-nutrient patch when it was equidistant to a neighbour. Conversely, plants increased root proliferation when they were in closer proximity to the patch relative to a nearby neighbour. Such contingent responses may allow sunflowers to avoid competition in highly contested patches, but to also pre-empt soil resources from neighbours when they have better access to a high-quality patch. We also compared patch occupancy by sunflowers grown alone with two equidistant high-quality patches to occupancy by sunflowers grown with two high-quality patches and a neighbour. Plants grown with a neighbour decreased root length within shared patches but did not increase root length within high-quality patches they were in closer proximity to, perhaps because resource pre-emption may be less important for individuals when resources are more abundant. These results show that nutrient foraging responses in plants can be socially contingent, and that plants may account for the possibility of pre-empting limited resources in their foraging decisions.

Root exudate signals in plant–plant interactions

“…Chemical cues from neighbouring roots also modify sunflower nitrogen foraging and maize phosphorus foraging (Ljubotina & Cahill, 2019; Zhang et al, 2020). In calcareous soil, intercropping with graminaceous plants improves Fe nutrition of legume crops such as peanut and soybean or fruits such as citrus, grape and pear (Dai et al, 2019).…”

Spatial mapping of root systems reveals diverse strategies of soil exploration and resource contest in grassland plants

“…Due to a lack of easy tools to quantify and characterise root spatial distributions, our knowledge of how roots are distributed in soil at different spatial scales and how spatial patterns change in response to competitive interactions is limited (Cahill et al., 2010; Semchenko et al., 2007; Yang et al., 2018). On the other hand, root systems share qualities with certain animals whose foraging and territorial behaviour has been extensively studied, offering new ways of exploring and quantifying plant root behaviour (Ljubotina & Cahill, 2019; McNickle & Brown, 2012; Novoplansky, 2009).…”

The exploitative segregation of plant roots

“…The former considers only the foraging range but neglects the distribution of root density within that range, and the latter ignores the spatial distribution of roots. Few have considered both features of root systems together [but see (20)].…”