Possible mechanisms underlying abundance and diversity responses of nematode communities to plant diversity

Abstract

Abstract. Plant diversity is known to influence the abundance and diversity of belowground biota; however, patterns are not well predictable and there is still much unknown about the driving mechanisms. We analyzed changes in soil nematode community composition as affected by long-term manipulations of plant species and functional group diversity in a field experiment with plant species diversity controlled by sowing a range of 1-60 species mixtures and controlling non-sown species by hand weeding. Nematode communities contain a variety of species feeding on bacteria, fungi, plants, invertebrates, while some are omnivorous. We analyzed responses of nematode abundance and diversity to plant species and functional diversity, and used structural equation modeling (SEM) to explore the possible mechanisms underlying the observed patterns. The abundance of individuals of all nematode feeding types, except for predatory nematodes, increased with both plant species and plant functional group diversity. The abundance of microbial-feeding nematodes was related positively to aboveground plant community biomass, whereas abundance of plant-feeding nematodes was related positively to shoot C:N ratio. The abundance of predatory nematodes, in turn, was positively related to numbers of plant-feeding nematodes, but not to the abundance of microbial feeders. Interestingly, the numbers of plant-feeding nematodes per unit root mass were lowest in the high-diversity plant communities, pointing at reduced exposure to belowground herbivores when plants grow in species-diverse communities. Taxon richness of plant-feeding and microbialfeeding nematodes increased with plant species and plant functional group diversity. Increasing plant functional group diversity also enhanced taxon richness of predatory nematodes. The SEM suggests that bottom-up control effects of plant species and plant functional group diversity on abundance of nematodes in the various feeding types predominantly involve mechanistic linkages related to plant quality instead of plant quantity; especially, C:N ratios of the shoot tissues, and/or effects of plants on the soil habitat, rather than shoot quantity explained nematode abundance. Although aboveground plant properties may only partly serve as a proxy for belowground resource quality and quantity, our results encourage further studies on nematode responses to variations in plant species and plant functional diversity in relation to both quantity and quality of the belowground resources.

Diversity‐dependent plant–soil feedbacks underlie long‐term plant diversity effects on primary productivity

“…, Cortois et al. ). Indeed, previous work in grassland plant diversity experiments has shown that the functional composition of soil nematode communities is significantly affected by plant diversity (De Deyn et al.…”

“…While the role of soil microorganisms in biodiversity-productivity relationships has been shown before (Maron et al 2011, Schnitzer et al 2011, Wagg et al 2011a, b, Latz et al 2012, we here focused on nematode communities. Nematodes represent the most abundant metazoans on Earth and are likely to exert various effects on plant growth, potentially providing a mechanistic explanation of PSFs (van der Putten et al 1993, Cortois et al 2017. Indeed, previous work in grassland plant diversity experiments has shown that the functional composition of soil nematode communities is significantly affected by plant diversity (De Deyn et al 2004, Viketoft et al 2009, Eisenhauer et al 2011, with likely feedback effects on plant growth and subsequently biodiversity-productivity relationships (Eisenhauer et al 2011).…”

A plant’s inheritance : Soil legacy effects of crops and wild relatives in relation to plant functional traits

“…Our increased root productivity of L+T mixtures had neutral effects on nematode abundances. These results are in line with Cortois et al (2017) who show a decrease of plant-feeding nematode density…”

“…Increased plant productivity could lead to increased feeding area for herbivorous nematodes (Thoden, Korthals & Termorshuizen 2011). Also, increase of bottom-up resource quantity (Chen et al 2016) or quality (Cortois et al 2017) can stimulate nematode herbivory. Additionally, mixtures were expected to dilute the abundance of nematode host plants, resulting in neutral to negative mixture effects.…”

“…Next-crop productivity is positively correlated with cover crop biomass and nitrogen concentration (Finney, White & Kaye 2016). Plant-feeding nematode densities decreased with increasing plant diversity in natural grasslands (Cortois et al 2017). Moreover, mixing cover crops could suppress nematode numbers as host plants are harder to find (Mitchell, Tilman & Groth 2002;Iverson et al 2014).…”