Effects of soil decomposer invertebrates (protozoa and earthworms) on an above‐ground phytophagous insect (cereal aphid) mediated through changes in the host plant

Abstract

2001. Effects of soil decomposer invertebrates (protozoa and earthworms) on an above-ground phytophagous insect (cereal aphid) mediated through changes in the host plant. -Oikos 95: 441-450.We investigated if the activity of soil invertebrates (protozoa and earthworms) affected the performance of barley and if effects propagated higher up the aboveground food chain into herbivores (cereal aphid, Sitobion a6enae). Barley plants were grown individually in microcosms containing defaunated soil and grass residues. Plants were grown in soil containing: a) no added fauna, b) protozoa, c) earthworms, or d) protozoa and earthworms. After 7 weeks growth at 20°C three adult cereal aphids were added to each plant on separate leaves. The aphids were allowed to grow and reproduce for another 2 weeks before the experiment was destructively sampled. Amounts of mineral N in the soil and leached from the microcosms were significantly reduced by the presence of soil animals. Correspondingly plant biomass and total plant N content were increased significantly by soil animals, protozoa in particular. The different mechanisms responsible for changes in nutrient turnover in presence of protozoa and earthworms are discussed. Aphid performance was strongly influenced by the presence of protozoa, but not by earthworms. In the presence of protozoa the numbers and biomass of adult and juvenile aphids were significantly increased. These effects are likely due to an increased N content in barley plants and consequently increased nitrogen availability to aphids. The results underline that the detritivore and herbivore systems are intimately linked. M. Bonkowski, Technische Uni6ersität Darmstadt, Fachbereich

Long term changes in abundance of Coccinella septempunctata (Coleoptera: Coccinellidae) in the Czech Republic

“…This was probably because (i) growing cereals continued only in favourable areas and (ii) the use of efficient cultivars compensated for decreased fertilization and (iii) residual N that persisted in the soil from years of over-fertilization. Effect of fertilizers also might be compensated by increased activity of soil decomposers that favour cereal plant vigour and aphid performance (Bonkowski et al, 2001). Even so, we suppose that low fertilizer doses were an important factor influencing cereal aphid abundance, although other factors may have contributed.…”

Ecological importance of soil bacterivores for ecosystem functions

“…For instance, the presence of protozoa increased the number of ears (+ 60 %), seeds (24 %) and the individual seed weight (+32 %) of barley plants, and the crop was even more tolerant to aphid herbivores (Bonkowski et al 2001a). More recently, Krome et al (2009a) showed that A. castellanii enhanced the seed production of Arabidopsis thaliana (Brassicaceae) more than 3-and 7-fold compared to treatments with bacteria and sterile grown plants, respectively.…”

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.…”