Abstract
Increasing frequency and magnitude of climatic extremes, such as heat waves are expected to enhance abiotic stresses on ecological communities. It has been proposed that ecological communities in disturbed habitats may be most sensitive to climatic extremes, as disturbance may reduce density and diversity of higher trophic level organisms like predators. However, there is little experimental evidence that climatic extremes indeed have stronger impact on functioning of such trophically downgraded ecosystems. Here, we experimentally examine how removal of predators from soil communities affects plant performance under periodic heat waves. We used a native plant species, and a congeneric native that is currently expanding its range because of climate change. We used soil nematode communities as the model system, as these are most abundant soil animals and their communities are trophically diverse. Predatory nematodes were manually removed from intact soil nematode communities (mainly the adults as some juveniles are impossible to manually remove) to create a trophically downgraded soil. Intact nematode communities and communities with reduced predatory nematodes were added separately to soils that were planted with either the native Centaurea jacea or the range-expanding congener Centaurea stoebe. Half the experimental units were exposed periodically to experimental heat waves of 10 °C above the control temperature. Our results show that the C: N and C: N: P ratio of plant shoots in predator-reduced soils became lower when exposed to periodic heat waves, however, only in the native plant C. jacea. The decrease in C: N ratio corresponded with increase of an herbivorous nematode in trophically intact soils of C. jacea independent of warming, whereas this relationships disappeared in warmed and predator-reduced soils. Our results accordingly highlight that periodic heat waves may affect stoichiometry of certain plant species by altering trophic interactions in predator-reduced soils.
Highlights
Anthropogenic climate warming continues to alter biodiversity and ecosystem functioning in many ecosystems (Pecl et al, 2017; Thakur et al, 2017; Yvon-Durocher et al, 2015)
Total bacterial DNA and fungal DNA were quantified by quantitative PCR (qPCR) and Ct values were converted to biomass as described by (Harkes et al, 2017)
We show that pe riodic heat waves alter plant performance by changing their shoot stoichiometry in soils with reduced predatory nematodes
Summary
Anthropogenic climate warming continues to alter biodiversity and ecosystem functioning in many ecosystems (Pecl et al, 2017; Thakur et al, 2017; Yvon-Durocher et al, 2015). A common biotic response in such landscapes is lower density and/or diversity of predators given their higher sensitivity to distur bances (Estes et al, 2011; Odum, 1985; Voigt et al, 2003). Such reduced density and/or diversity of predatory species in ecosystems is commonly referred to as trophic downgrading (Estes et al, 2011). The cur rent understanding of the effects of trophic downgrading on ecosystems in a warmer world is mainly limited to studies of large predators living aboveground and in aquatic ecosystems (Estes et al, 2011; McCauley et al, 2015; Ripple et al, 2014)
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