Grazing and resource availability control soil nematode body size and abundance–mass relationship in semi‐arid grassland

Abstract

Body size is a central functional trait in ecological communities. Despite recognition of the importance of above ground-below ground interactions, effects of above-ground herbivores on size and abundance-size relationships in soil fauna are almost uncharted. Depending on climate and soil properties, herbivores may increase basal resources of soil food webs, or reduce pore space, mechanisms expected to have contrasting effects on soil animal body size. We investigated how body size and shape of soil nematodes responded to mammalian grazers in three semi-arid grassland sites, along a gradient of soil texture and organic matter (OM) in a long-term herbivore removal study. We analysed nematode mass, length, diameter, body size distribution and biomass distribution. We formulated two mechanistic hypotheses to assess whether resource availability or pore space was the dominant abiotic control and modulated the effects of grazing. In ungrazed soils, average and maximum nematode size, as well as abundance and biomass of large nematodes, were greater in the high-OM than in the low-OM soil, and intermediate in the medium-OM soil. Grazing promoted larger sizes in the low-OM soil, where it had been shown to increase OM and microbial biomass, and led to more homogeneous average size and body size distribution across sites. The results support the hypothesis that nematode size was controlled by basal resource availability rather than by pore space. However, body shape might have been constrained by small pores in the fine-texture, high-OM soil, where nematodes were more elongated. Grazing may facilitate larger sizes in soil nematode communities by boosting basal resources where these are limiting, with important implications for estimations of nematode biomass and contribution to carbon and nutrient cycling. These findings contribute to the insofar-limited mechanistic understanding of how herbivores can shape functional traits of soil fauna and demonstrate that animals at one trophic level may control patterns in body size and abundance-size relationships in other trophic levels without a direct predator prey or competitive linkage between them.

Testate Amoeba Functional Traits and Their Use in Paleoecology

“…Functional traits have been well studied in various taxonomic groups such as plants (Weiher et al, 1999;Diaz et al, 2004;Wright et al, 2004;Cornwell et al, 2008;Kleyer et al, 2008;Kattge et al, 2020), invertebrates (Andriuzzi and Wall, 2018;Céréghino et al, 2018), birds (Bregman et al, 2014), and mammals (Porto et al, 2013). In the case of testate amoebae, some functional traits relevant to understanding the response of these organisms to environmental changes and their functional role in the soil ecosystem have also been identified (Fournier et al, 2012(Fournier et al, , 2015Jassey et al, 2013aJassey et al, , 2015Jassey et al, , 2016Lamentowicz et al, 2015;Marcisz et al, 2016;Koenig et al, 2017).…”

Bacterial (9A2H) enhancement alters the nematode community structure and decomposition pathway of amended nutrient-limited soil

“…It is not clear why the omnivores (Qudsianematidae, c-p: 4) dominated soil with no bacterial treatment. It was perhaps the length of time that allowed these large, long-lived nematodes (Ferris et al 2001;Andriuzzi and Wall 2018) to grow and reproduce. Such an opportunity is less available in bacterial enhancement treatments than in treatments without enhancement.…”

Decoupled recovery of ecological communities after reclamation

“…Although extraction using Baermann funnel has been shown to have certain drawbacks in the efficiency with which the method recovers certain nematode groups (generally being biased in favor of extracting greater numbers of smaller and more active individuals; Freckman, Mankau & Ferris, 1975), other methods also show biases in extraction efficiency (see McSorley & Frederick, 2004). For broad ecological studies such as ours where advantages of one method over another are unclear, Baermann funnel extraction is a commonly used approach (e.g., Garcia-Palacios et al, 2017; Sylvain & Mosseler, 2017; Andriuzzi & Wall, 2018).…”