No neighbour-induced increase in root growth of soybean and sunflower in mesh-divider experiments after controlling for nutrient concentration and soil volume.

Bin J W Chen,Heinjo J During,Niels P R Anten,Jiahe Wei,Li Huang,Xinyu Wang

doi:10.1093/aobpla/plab020

Bin J W Chen, Heinjo J During + Show 4 more

Open Access

https://doi.org/10.1093/aobpla/plab020

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Abstract

Root competition is a key factor determining plant performance, community structure and ecosystem productivity. To adequately estimate the extent of root proliferation of plants in response to neighbours independently of nutrient availability, one should use a set-up that can simultaneously control for both nutrient concentration and soil volume at plant individual level. With a mesh-divider design, which was suggested as a promising solution for this problem, we conducted two intraspecific root competition experiments: one with soybean (Glycine max) and the other with sunflower (Helianthus annuus). We found no response of root growth or biomass allocation to intraspecific neighbours, i.e. an ‘ideal free distribution’ (IFD) norm, in soybean; and even a reduced growth as a negative response in sunflower. These responses are all inconsistent with the hypothesis that plants should produce more roots even at the expense of reduced fitness in response to neighbours, i.e. root over-proliferation. Our results suggest that neighbour-induced root over-proliferation is not a ubiquitous feature in plants. By integrating the findings with results from other soybean studies, we conclude that for some species this response could be a genotype-dependent response as a result of natural or artificial selection, or a context-dependent response so that plants can switch from root over-proliferation to IFD depending on the environment of competition. We also critically discuss whether the mesh-divider design is an ideal solution for root competition experiments.

Highlights

Root competition for soil resources is a ubiquitous feature in terrestrial plant communities
We found no response of root growth or biomass allocation to intraspecific neighbours, i.e. an ‘ideal free distribution’ (IFD) norm, in soybean; and even a reduced growth as a negative response in sunflower
Gametheoretical models predict that when resource investment in root production of a plant is based on an assessment of cost and benefit balance in response to the decline of nutrient availability caused by the consumption from both the plant and its neighbours, the plant should over-proliferate roots to an extent that exceeds the optimal level for maximized performance in below-ground competition with neighbours (Gersani et al 2001)

Summary

Introduction

Root competition for soil resources is a ubiquitous feature in terrestrial plant communities (de Kroon et al 2003). Some of them were confirmatory finding a TOC root response to neighbours (Maina et al 2002; O’Brien et al 2005; Zhu et al 2019); while others, for instance, found their results to better fit an ‘ideal free distribution’ (IFD) response, i.e. a norm describing that root growth is based on nutrient availability regardless of neighbours (Semchenko et al 2007; Markham and Halwas 2011; McNickle and Brown 2014a) As this deals with a fundamental aspect of our understanding of diversity and coexistence in natural communities (Vincent and Brown 2005) with potentially farreaching consequences for agriculture (Anten and Vermeulen 2016; Weiner et al 2017), further experiments trying to elucidate the processes underlying these differences are urgently needed

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