Size-asymmetric root competition in deep, nutrient-poor soil

Rasmussen, Camilla Ruø; Weisbach, Anne Nygaard; Thorup‐Kristensen, Kristian; Weiner, Jacob

doi:10.1093/jpe/rtx064

Cited by 17 publications

(11 citation statements)

References 30 publications

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“…The theory of how larger individuals gain benefits from nutrient patches is that large individuals can pre‐empt high‐nutrient patches (Schwinning & Weiner, ), usually through root foraging (Craine & Dybzinski, ). However, we found that the presence of a high‐nutrient patch either had no effect or decreased the degree of size‐asymmetric competition (Figure b), which has also been seen in plant populations (Rasmussen et al, ). Although our experiment did not look at root placement of individuals, a potential mechanism for the presence of high‐quality patches reducing size‐asymmetric competition could be that smaller individuals are more precise foragers than larger individuals (Campbell, Grime, & Mackey, ; Wijesinghe, John, Beurskens, & Hutchings, , but see Kembel & Cahill, ), where the higher proportion of their root systems they are able to place in nutrient patches would reduce their competitive response, which is consistent with the scale‐precision hypothesis (Campbell et al, ).…”

Section: Discussionsupporting

confidence: 64%

“…Soil fertility and distribution could promote size‐asymmetric competition directly, by switching root competition from size symmetric to size asymmetric (Schwinning & Weiner, ), or indirectly, by enhancing the size asymmetry of shoot competition (Cahill, ). A switch in the size dependence of competition could occur when resources are heterogeneously distributed (Fransen, de Kroon, & Berendse, ; Rajaniemi & Reynolds, ; Rasmussen, Weisbach, Thorup‐Kristensen, & Weiner, ; Schwinning & Weiner, ), if larger individuals are better able to reach and uptake a nutrient patch before their smaller neighbours (Craine & Dybzinski, ; Schwinning & Weiner, ). Additionally, the presence of microbial communities (Merrild, Ambus, Rosendahl, & Jakobsen, ; Schwinning & Weiner, ) could switch the size dependence of competition if larger individuals have more microbial associations that increase their nutrient uptake (Schwinning & Weiner, ) or if the presence of microbes leads to resource sharing within the community (Beiler, Durall, Simard, Maxwell, & Kretzer, ; Simard et al, ), where larger individuals give resources to smaller individuals (Beiler et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Species‐specific size vulnerabilities in a competitive arena: Nutrient heterogeneity and soil fertility alter plant competitive size asymmetries

2019

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The size dependence of competitive interactions is starting to be highlighted as an important driver of species diversity within communities; however, it is still unknown whether all species are equally impacted by size‐asymmetric competition and what resources drive it. Here, we test species‐specific responses to size‐asymmetric competition under various soil environments by manipulating plant size as well as soil fertility, nutrient heterogeneity and the initial suppression of microbial communities within a three‐species community. Competition was primarily size‐asymmetric; however, the degree to which competition was size‐asymmetric was species‐specific, where three out of five soil treatments resulted in size‐asymmetric competition in some species but size‐symmetric competition in others. Overall, soil fertility and nutrient heterogeneity altered the degree of size‐asymmetric competition, while the initial suppression of microbial communities had no effect. Contrary to past predictions, when they had an effect, increased soil fertility and the presence of a high‐quality patch reduced the degree of size‐asymmetric competition, while the presence of a low‐quality patch increased it. This suggests that the role nutrient heterogeneity plays on the degree of size‐asymmetric competition is dependent on the quality and location of the patch relative to an individual's neighbours. These findings challenge the current understanding that competition for soil resources is always size‐symmetric and demonstrate that species within the same community may not experience the same degree of size‐dependent competition. These differential responses suggest we must consider variations in tolerance and suppression between species during size‐dependent plant–plant interactions, which may promote species coexistence as all small individuals may not be negatively impacted during size‐dependent competition. A plain language summary is available for this article.

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Section: Discussionsupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Species‐specific size vulnerabilities in a competitive arena: Nutrient heterogeneity and soil fertility alter plant competitive size asymmetries

2019

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“…We focussed on a single form of competition, for light, while plants compete for a plethora of other critical resources such as water, nitrogen and phosphorous. Knowledge on the physiology and ecology of competition for light is well established (Ballaré & Pierik, ), and great progress is being made on the physiology of root architectural responses to nutrient availability (Bisseling & Scheres, ) and their effects on nutrient competition (Rasmussen, Weisbach, Thorup‐Kristensen, & Weiner, ). This study focusses on a generic plant–herbivore interaction while we know from studies on plant–herbivore communities (Poelman & Kessler, ) and the rhizosphere microbiome (Berendsen, Pieterse, & Bakker, ; Mommer, Kirkegaard, & van Ruijven, ; Philippot, Raaijmakers, Lemanceau, & Putten, ) that the individual interactions in these complex communities can be highly species specific yet play a major role in plant performance (Berendsen et al, ).…”

Section: Discussionmentioning

confidence: 99%

Ecological interactions shape the adaptive value of plant defence: Herbivore attack versus competition for light

et al. 2018

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Plants defend themselves against diverse communities of herbivorous insects. This requires an investment of limited resources, for which plants also compete with neighbours. The consequences of an investment in defence are determined by the metabolic costs of defence as well as indirect or ecological costs through interactions with other organisms. These ecological costs have a potentially strong impact on the evolution of defensive traits, but have proven to be difficult to quantify. We aimed to quantify the relative impact of the direct and indirect or ecological costs and benefits of an investment in plant defence in relation to herbivory and intergenotypic competition for light. Additionally, we evaluated how the benefits of plant defence balance its costs in the context of herbivory and intergenotypic competition. To this end, we utilised a functional‐structural plant (FSP) model of Brassica nigra that simulates plant growth and development, morphogenesis, herbivory and plant defence. In the model, a simulated investment in defences affected plant growth by competing with other plant organs for resources and affected the level and distribution of herbivore damage. Our results show that the ecological costs of intergenotypic competition for light are highly detrimental to the fitness of defended plants, as it amplifies the size difference between defended and undefended plants. This leads to herbivore damage counteracting the effects of intergenotypic competition under the assumption that herbivore damage scales with plant size. Additionally, we show that plant defence relies on reducing herbivore damage rather than the dispersion of herbivore damage, which is only beneficial under high levels of herbivore damage. We conclude that the adaptive value of plant defence is highly dependent on ecological interactions and is predominantly determined by the outcome of competition for light. plain language summary is available for this article.

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“…However, it is unclear whether light availability is the mechanism driving height inequalities in this system. Another potential mechanism could be a decrease in soil nutrient heterogeneity with increasing productivity, which would also result in a decrease in height inequality with increased productivity either directly by altering individual plant access to nutrients (Casper & Cahill, 1998) or indirectly by altering the degree of size-asymmetric competition (Brown et al, 2019;Rasmussen, Weisbach, Thorup-Kristensen, & Weiner, 2019).…”

Section: Journal Of Vegetation Sciencementioning

confidence: 99%

Vertical size structure is associated with productivity and species diversity in a short‐stature grassland: Evidence for the importance of height variability within herbaceous communities

Brown

Cahill

2019

J Vegetation Science

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Questions Local size structure is frequently measured in plant populations and forested systems due to its association with population‐ and community‐level processes. In contrast, size structure is rarely examined within herbaceous communities despite evidence for size‐dependent processes in these systems, suggesting an important functional vegetation property may be widely overlooked. Here, we test whether vertical size structure (a) varies within a short‐stature grassland, (b) varies along a productivity gradient, and (c) enhances the understanding of a foundational ecological pattern: the diversity–productivity relationship. Location Rough fescue grassland in Alberta, Canada. Methods We measured the heights of individuals within 32 plots and used average height, the Gini coefficient, and a two‐parameter Weibull distribution to estimate community‐level vertical size structure. Linear mixed models were used to test whether size structure parameters were significantly associated with productivity, species richness, and species evenness. Results Vertical size structure varied significantly among local communities, such that some were dominated by short individuals while others were comprised of a more equal number of taller individuals. With increasing productivity, there was an increase in average plant height and a decrease in height inequality. Decreased height inequality was associated with reduced species richness with evidence that loss was not size‐dependent. The inclusion of vertical size structure parameters increased the explained variance of the diversity–productivity relationship by ~35% while also increasing its parsimony. Conclusions Even within a short‐stature grassland, there is substantial functional variation in vertical size structure. Productivity is strongly associated with size structure patterns, and the inclusion of height inequalities greatly enhances productivity–diversity relationships, likely because they are the product of assembly mechanisms such as size‐asymmetric competition, assemblage‐level thinning, and niche complementarity. Overall, this demonstrates that vertical size structure has been a missing mechanism in most community assembly theories and models and should be included in the future.

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Size-asymmetric root competition in deep, nutrient-poor soil

Cited by 17 publications

References 30 publications

Species‐specific size vulnerabilities in a competitive arena: Nutrient heterogeneity and soil fertility alter plant competitive size asymmetries

Species‐specific size vulnerabilities in a competitive arena: Nutrient heterogeneity and soil fertility alter plant competitive size asymmetries

Ecological interactions shape the adaptive value of plant defence: Herbivore attack versus competition for light

Vertical size structure is associated with productivity and species diversity in a short‐stature grassland: Evidence for the importance of height variability within herbaceous communities

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