Different sets of belowground traits predict the ability of plant species to suppress and tolerate their competitors

Plant and Soil, Jun 2017

Background and aims Functional traits may underlie differences in niches, which promote plant species co-existence, but also differences in competitive ability, which drive competitive exclusion. Empirical evidence concerning the contribution of different traits to niche differentiation and the ability to supress and tolerate competitors is very limited, particularly when considering belowground interactions. Methods We grew 26 temperate grassland species along a density gradient of interspecific competitors to determine which belowground traits a) explain species’ ability to suppress and tolerate neighbours and b) contribute to niche differentiation, such that species with dissimilar trait values experience reduced competition. Results We found that having larger root systems with extensive horizontal spread and lower root tissue density enabled efficient suppression of neighbours but did not significantly contribute to the ability to tolerate competition. Species with deeper root systems, lower specific root length and less branched roots were better at tolerating competition, but these traits did not significantly affect the ability to suppress neighbours. None of the measured traits contributed significantly to niche differentiation, either individually or in combination. Conclusions This study provides little support for belowground traits contributing to species co-existence through niche differentiation. Instead, different sets of weakly correlated traits enable plants to either suppress or tolerate their competitors.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs11104-017-3282-1.pdf

Different sets of belowground traits predict the ability of plant species to suppress and tolerate their competitors

Different sets of belowground traits predict the ability of plant species to suppress and tolerate their competitors Marina Semchenko Anu Lepik Maria Abakumova Kristjan Zobel Responsible Editor: Amandine Erktan. 0 ) School of Earth and Environmental Sciences, University of Manchester , M13 9PT, Manchester , UK Background and aims Functional traits may underlie differences in niches, which promote plant species coexistence, but also differences in competitive ability, which drive competitive exclusion. Empirical evidence concerning the contribution of different traits to niche differentiation and the ability to supress and tolerate competitors is very limited, particularly when considering belowground interactions. Methods We grew 26 temperate grassland species along a density gradient of interspecific competitors to determine which belowground traits a) explain species' ability to suppress and tolerate neighbours and b) contribute to niche differentiation, such that species with dissimilar trait values experience reduced competition. Results We found that having larger root systems with extensive horizontal spread and lower root tissue density enabled efficient suppression of neighbours but did not significantly contribute to the ability to tolerate competition. Species with deeper root systems, lower specific root length and less branched roots were better at tolerating competition, but these traits did not significantly affect the ability to suppress neighbours. None of the measured traits contributed significantly to niche differentiation, either individually or in combination. Conclusions This study provides little support for belowground traits contributing to species co-existence through niche differentiation. Instead, different sets of weakly correlated traits enable plants to either suppress or tolerate their competitors. Belowground interactions; Species coexistence; Competitive ability; Functional traits; Niche differentiation; Phenotypic plasticity; Rooting depth; Stress tolerance - Plant functional traits have been extensively used as a means to understand plant community assembly (Lavorel and Garnier 2002; de Bello et al. 2010; Gotzenberger et al. 2012). Differences in functional traits have been used as a proxy for stabilising niche differences, based on the principle of limiting similarity, which predicts stronger competition between species with similar trait values (MacArthur and Levins 1967; Chesson 2000). However, plant traits may also influence competitive ability and contribute to competitive exclusion of species with inferior trait values (Chesson 2000; Grime 2006; Mayfield and Levine 2010). Indeed, an increasing number of studies have found that commonly used functional traits are more strongly related to competitive hierarchies than to niches (Kunstler et al. 2012; Herben and Goldberg 2014; Kraft et al. 2015). This apparent contradiction highlights the current lack of a mechanistic understanding of the way in which easily measured traits relate to plant function and the way in which different traits contribute to competitive hierarchies versus niche differentiation between species (Kraft et al. 2015; Shipley et al. 2016). The existence of competitive hierarchies among plant species is well documented. Plant size has been repeatedly identified as a trait that is central to competitive success (Goldberg 1996; Keddy et al. 2002). Several aboveground traits such as greater maximum height, larger leaf area, higher leaf nitrogen content and lower leaf dry matter content have also been shown to provide an advantage in interspecific competition (Goldberg and Landa 1991; Herben and Goldberg 2014; Bennett et al. 2016). Competitively superior species are also frequently characterised by high specific leaf area (Kunstler et al. 2012; Fort et al. 2014; Kraft et al. 2015). These traits are often used to describe the leaf economics spectrum and suggest that species with strongly acquisitive traits are good competitors, whereas species with more conservative traits are less competitive (Wright et al. 2004; Reich 2014). Despite the importance of roots for plant functioning and ecosystem processes (Bardgett et al. 2014) and competition for soil-based resources being equally or even more important than competition for light (Kiaer et al. 2013), most trait-based studies of plant community assembly have concentrated on aboveground traits. Current knowledge of belowground traits and their contribution to species co-existence still consists of too few traits and species to draw robust generalisations. It has been shown that higher competitive ability is associated with greater root system size, either achieved through greater allocation of biomass to roots or through higher specific root length (Wang et al. 2010; Ravenek et al. 2016). Specific root length and a combination of specific root length and aboveground traits have also been shown to contribute to niche differentiation (Kraft et al. 2015; (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs11104-017-3282-1.pdf

Marina Semchenko, Anu Lepik, Maria Abakumova, Kristjan Zobel. Different sets of belowground traits predict the ability of plant species to suppress and tolerate their competitors, Plant and Soil, 2017, pp. 1-13, DOI: 10.1007/s11104-017-3282-1