Above‐ and Belowground Interactions Are Mediated by Nutrient Availability

Abstract

By influencing nutrient mineralization in the soil, decomposers may affect the performance of plants and their associated herbivores. The strength of above-belowground linkages may therefore depend on the availability of nutrients in ecosystems. We investigated the dependency of decomposer-and leaf-herbivore-mediated changes in plant performance on soil nutrient availability in microcosm systems. In separate treatments, Poa annua was used as host plant for the herbivore and was grown in combination with different herb species: Plantago lanceolata, Trifolium repens, and Sanguisorba minor. At three different levels of nutrient availability, the impact of Collembola (Folsomia candida) and aphids (Rhopalosiphum padi), as well as their interacting effects on plant performance, were investigated. We further assessed the effects of Collembola on the performance of aphids and vice versa, as well as the effects on element contents in P. annua and soil nutrients.Collembola increased total aboveground biomass and biomass of single plant species (except T. repens) only at low and moderate nutrient availability, whereas the negative effects of aphids on P. annua and total aboveground biomass were highest at high nutrient availability. Collembola decreased relative root allocation. The negative effect of aphids on plant biomass was more pronounced in the presence of Collembola. Nitrogen concentration in shoots of P. annua was increased by Collembola. Aphids decreased the nitrogen concentration in grass shoots only when Collembola were present. These interacting effects can be related to indirect effects of decomposers on herbivore performance. At low and moderate nutrient availability, aphid numbers strongly increased due to decomposers, whereas at high nutrient availability this effect was much weaker. In turn, aphid herbivory increased the number of Collembola only at high nutrient availability.We conclude that the role of both below-and aboveground food webs for the dynamics of vegetation depend on each other and the availability of nutrients in ecosystems. This suggests that nutrient enrichment of ecosystems may have important consequences for abovebelowground linkages and their effects on natural communities.

Plant-mediated links between detritivores and aboveground herbivores

“…Earthworms had a strong positive, but also transient effect on aphid reproduction on both plant species. Subsequent studies investigated the impacts of earthworms (Bonkowski et al, 2001; Wurst and Jones, 2003; Wurst et al, 2003, 2004a, b; Newington et al, 2004; Poveda et al, 2005; Eisenhauer et al, 2010; Wurst and Forstreuter, 2010; Johnson et al, 2011) and Collembola (Haase et al, 2008; Ke and Scheu, 2008; Schütz et al, 2008) on aboveground herbivores. In the majority of studies, the impact of earthworms and Collembola was investigated on aboveground phloem-feeding aphids.…”

Earthworms, Collembola and residue management change wheat (Triticum aestivum) and herbivore pest performance (Aphidina: Rhophalosiphum padi)

“…Soil decomposer animals such as Protozoa, earthworms and Collembola, and litter distribution in soil, have been shown to increase (Scheu et al 1999a;Bonkowski et al 2001;Wurst et al 2004;Haase et al 2008) but also decrease Schütz et al 2008) aphid reproduction. However, in contrast to the general view that herbivore performance correlates with N concentration in the diet, the eVects of soil animals and litter distribution on aphid reproduction and biomass were not correlated with plant tissue N concentration.…”

“…Aphids are known to respond to changes in host plant quality (Srivastava 1987;Tjallingii and Esch 1993;Dixon 1998); in particular the availability of N limits the development of aphids and also that of other herbivores (Mattson 1980;Hartley and Jones 1997;Schütz et al 2008;Haase et al 2008). The strongest evidence for limitation of herbivores by plant N comes from experiments where plants had been fertilized with mineral N (Hartley and Jones 1997).…”

“…In previous studies aphid reproduction was correlated with host plant N concentration (Mattson 1980;Hartley and Jones 1997;Schütz et al 2008;Haase et al 2008). However, for evaluating the limitation of aphids by N the N concentration in aphid tissue needs to be investigated.…”

Aboveground dominant functional group predicts belowground properties in an alpine grassland community of western China

“…Soil nutrient availability is crucial for understanding the consequences of above-and belowground trophic interactions for ecosystem functioning (Ettema and Wardle 2002). The strength of above-belowground linkages may therefore depend on the availability of nutrients in ecosystems (Haase et al 2008).…”