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

Abstract

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.

Extreme droughts in oligotrophic mountain grasslands cause substantial species abundance changes and amplify community filtering

“…Limitations in our experiment arise from strong year effects (Werner et al, 2020). Under the exceptionally dry ambient conditions during most of the annual experimental period in 2018 and 2019, the additional rainfall exclusion did not develop its full treatment effect (Aguirre et al, 2021). However, by considering year effects together with the treatment effects in our analyses, we were able to separate the relative importance of these natural and artificial factors for the observed community changes.…”

Rapid transgenerational adaptation in response to intercropping reduces competition

“…The mechanisms of selection for plant facilitation remain very poorly understood ( Bronstein, 2009 ; Brooker, 2008 ). Whereas some facilitative traits characterizing facilitator species are well known in some systems — for example legume species fostering soil nitrogen enrichment ( Wright et al, 2017 ), microclimate amelioration through shading by large canopy ( Aguirre et al, 2021 ), nectar reward to attract pollinators ( Losapio et al, 2021 ) — traits of facilitated species remain much more obscure ( Bronstein, 2009 ). These ‘facilitated’ traits, which allow organisms to benefit from their neighbours, may be a target of evolutionary selection in natural systems ( Bronstein, 2009 ), and it is therefore reasonable to think that they might depend on neighbour identity ( Schöb et al, 2018 ).…”

Condiciones climáticas y microclimáticas en sistemas de producción de vainilla (Vanilla planifolia Jacks. ex Andrews) en México

“…vanillae (Solano et al, 2021). El DPV es un indicador importante de la respuesta de la planta al ambiente que representa la demanda evaporativa de la atmósfera (Aguirre et al, 2021), que de acuerdo con Grossiord et al (2020), podría volverse una variable prioritaria para estudiar la dinámica de las plantas, debido a su incremento a escala global como consecuencia del cambio climático.…”