Stress gradients and biodiversity: monoculture vulnerability drives stronger biodiversity effects during drought years

Wright, Alexandra J.; Mommer, Liesje; Barry, Kathryn E.; Ruijven, Jasper van

doi:10.1002/ecy.3193

Cited by 45 publications

(43 citation statements)

References 40 publications

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“…Tilman et al., 2001). However, for the first time, our work experimentally isolates a new mechanism underlying biodiversity‐stability trends during drought (Wright et al., 2021). Our focal species, P. secunda experienced apparent competition in higher diversity communities when relative humidity was high.…”

Section: Discussionmentioning

confidence: 95%

“…However, past studies rely solely on soil moisture manipulations and ignore the role of atmospheric drought and evaporative demand above‐ground. Evidence from the stress gradient hypothesis points us towards the importance of above‐ground facilitative interactions and an alternative mechanism for the biodiversity‐stability hypothesis during drought (Bertness & Callaway, 1994; Bruno et al., 2003; Wright et al., 2021). Higher diversity communities may also be ameliorating the microclimate (VPD, relative humidity and temperature) more comprehensively than lower diversity communities (Holmgren et al., 1997; Montgomery et al., 2010; Wright et al., 2014) and this might protect even sensitive species from the most negative effects of drought (Callaway et al., 2002; Tilman & Downing, 1994; Yang et al., 2012).…”

Section: Introductionmentioning

confidence: 99%

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The experimental manipulation of atmospheric drought: Teasing out the role of microclimate in biodiversity experiments

et al. 2021

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Drought occurrence is increasing due to anthropogenic climate change. Drought can negatively affect plants via reduced water below‐ground and increased evaporative demand or vapour pressure deficit (VPD) above‐ground. Past work has shown that plant diversity can ameliorate the negative effects of drought in plant communities, but these results are inconsistent between experimental and natural drought studies. Furthermore, while studies on the negative effects of reduced soil moisture on plant growth in drought experiments are abundant, the effects of predicted increases in atmospheric VPD have been neglected. We directly manipulated atmospheric relative humidity in a biodiversity and drought experiment at the California State University, Los Angeles (CA, USA) under three atmospheric conditions (ambient, dehumidified and humidified), two treatments of native perennial grass diversity (monoculture and eight species polyculture) and two soil drought treatments (control and drought). We assessed both polyculture plant community and individual species (Poa secunda) responses to atmospheric drought and soil drought. We found that soil drought only limits above‐ground biomass production when atmospheric conditions are also dry. We also found that P. secunda was limited by increased competition in polyculture when ambient atmospheric conditions were humid but was facilitated by diversity when atmospheric conditions were dry. Synthesis. Higher diversity ecosystems may be capable of protecting individual species from the negative effects of drought (facilitation). Without careful experimental manipulation of atmospheric drought, this important mechanism will be missed.

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Section: Discussionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

The experimental manipulation of atmospheric drought: Teasing out the role of microclimate in biodiversity experiments

et al. 2021

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“…One of the potential drivers of positive biodiversity–productivity relationships is interspecific facilitation (Barry et al., 2019; Wright et al., 2017). In biodiversity experiments, patterns of productivity within species or functional groups can sometimes serve as evidence for facilitation (Mulder et al., 2001; Fichtner et al., 2017; Wright et al., 2021), but they cannot tell us the physiological mechanisms that cause one species to facilitate another. Ecologists may need to understand these mechanisms to forecast species interactions and productivity under environmental change (Barry et al., 2019; Cabal et al., 2021; Wright et al., 2017).…”

Section: Introductionmentioning

confidence: 99%

Physiological responses to light explain competition and facilitation in a tree diversity experiment

2021

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Ecologists often invoke interspecific facilitation to help explain positive biodiversity–ecosystem function relationships in plant communities, but seldom test how it occurs. One mechanism through which one species may facilitate another is by ameliorating abiotic stress. Physiological experiments show that a chronic excess of light can cause stress that depresses carbon assimilation. If shading by a plant's neighbours reduces light stress enough, it may facilitate that plant's growth. If light is instead most often a limiting factor for photosynthesis, shading may have an adverse, competitive effect. In a temperate tree diversity experiment, we measured stem growth rates and photosynthetic physiology in broadleaf trees across a gradient of light availability imposed by their neighbours. At the extremes, trees experienced nearly full sun (monoculture), or were shaded by nearby fast‐growing conifers (shaded biculture). Most species had slower growth rates with larger neighbours, implying a net competitive effect. On the other hand, the two most shade‐tolerant species (Tilia americana and Acer negundo) and the most shade‐intolerant one (Betula papyrifera) had faster stem growth rates with larger neighbours. The two shade‐tolerant species had the greatest increases in photoinhibition (reduced dark‐acclimated Fv/Fm) across the gradient of increasing light availability, which suggests they are more vulnerable to chronic light stress. While most species had lower carbon assimilation rates in the shaded biculture treatment, T. americana had rates up to 25% higher. T. americana also dropped its leaves 3–4 weeks earlier in monocultures, curtailing its growing season. We conclude that although large neighbours can cause light limitation in shade‐intolerant species, they can also increase growth through abiotic stress amelioration in shade‐tolerant species. Finally, in shade‐intolerant B. papyrifera, we find a pattern of stem elongation in trees with larger neighbours, which suggests that a shade avoidance response may account for the apparent positive trend in stem volume. Synthesis. Both positive and negative species interactions in our experiment can be explained in large part by the photosynthetic responses of trees to the light environment created by their neighbours. We show that photosynthetic physiology can help explain the species interactions that underlie biodiversity–ecosystem function relationships. The insights that ecologists gain by searching for such physiological mechanisms may help us forecast species interactions under environmental change.

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“…Such microclimatic effects of plant diversity can even cascade down to influencing soil microbial processes (Eisenhauer et al., 2010; Lange et al., 2014). Despite the strong empirical evidence, the microclimate aspects of abiotic facilitation effects have thus far been underrepresented in the biodiversity–ecosystem functioning literature (Bachmann et al., 2018; Barry, Mommer, et al., 2019; but see Wright et al., 2021). We lack analyses focusing on factors affecting the surface temperature in upper canopy layers, which reflects microclimatic cooling and may be relevant for processes like canopy leaf physiology, herbivory or flower visitation (Herrera & Medrano, 2017; Whitney et al., 2008).…”

Section: Introductionmentioning

confidence: 99%

Biodiversity facets affect community surface temperature via 3D canopy structure in grassland communities

et al. 2021

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Canopy structure is an important driver of the energy budget of grassland ecosystem and is, at the same time, altered by plant diversity. Diverse plant communities typically have taller and more densely packed canopies than less diverse communities. With this, they absorb more radiation, have a higher transpiring leaf surface and are better coupled to the atmosphere which leads to cooler canopy surfaces. However, whether plant diversity generally translates into a cooling potential remains unclear and lacks empirical evidence. Here, we assessed how functional identity, functional diversity and species richness of grassland communities in the Jena Experiment predict the mean and variation of plant surface temperature mediated via effects of canopy structure. Using terrestrial laser scanning, we estimated canopy structure describing metrics of vertical structure (mean height, LAI), the distribution (evenness) and the highest allocation (centre of gravity) of biomass along height strata. As metrics of horizontal structure, we considered community stand gaps, canopy surface variation and emergent flowers. We measured surface temperature with a thermal camera. We used SEM models to predict biodiversity effects on the surface temperature during two seasonal peaks of biomass. Before the first cut in May, herb‐dominated communities directly promoted lower leaf surface temperatures. However, communities with lower centre of gravity (mostly herb dominated) also increased canopy surface temperatures compared with grass‐dominated communities with higher biomass stored in the top canopy. Grass‐dominated communities showed a smaller variation of surface temperatures, which was also positively affected by species richness via an increase in mean height. In August, mean surface temperature decreased with increasing community CC and LAI. The variation of surface temperature was greater in herb‐dominated than in grass‐dominated communities and increased with plant species richness (direct effects). Synthesis. The mean and variation of canopy surface temperature were driven by differences in functional group composition (herbs‐ vs. grass dominance) and to a lesser extent by plant diversity. These effects were partly mediated the metrics of canopy structure but also by direct effects unrelated to the structural metrics considered.

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Stress gradients and biodiversity: monoculture vulnerability drives stronger biodiversity effects during drought years

Cited by 45 publications

References 40 publications

The experimental manipulation of atmospheric drought: Teasing out the role of microclimate in biodiversity experiments

The experimental manipulation of atmospheric drought: Teasing out the role of microclimate in biodiversity experiments

Physiological responses to light explain competition and facilitation in a tree diversity experiment

Biodiversity facets affect community surface temperature via 3D canopy structure in grassland communities

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