Abstract
Diversity loss has been shown to change the soil community; however, little is known about long-term consequences and underlying mechanisms. Here, we investigated how nematode communities are affected by plant species richness and whether this is driven by resource quantity or quality in 15-year-old plant communities of a long-term grassland biodiversity experiment. We extracted nematodes from 93 experimental plots differing in plant species richness, and measured above- and belowground plant biomass production and soil organic carbon concentrations (Corg) as proxies for resource quantity, as well as C/Nleaf ratio and specific root length (SRL) as proxies for resource quality. We found that nematode community composition and diversity significantly differed among plant species richness levels. This was mostly due to positive plant diversity effects on the abundance and genus richness of bacterial-feeding, omnivorous, and predatory nematodes, which benefited from higher shoot mass and soil Corg in species-rich plant communities, suggesting control via resource quantity. In contrast, plant-feeding nematodes were negatively influenced by shoot mass, probably due to higher top–down control by predators, and were positively related to SRL and C/Nleaf, indicating control via resource quality. The decrease of the grazing pressure ratio (plant feeders per root mass) with plant species richness indicated a higher accumulation of plant-feeding nematodes in species-poor plant communities. Our results, therefore, support the hypothesis that soil-borne pathogens accumulate in low-diversity communities over time, while soil mutualists (bacterial-feeding, omnivorous, predatory nematodes) increase in abundance and richness in high-diversity plant communities, which may contribute to the widely-observed positive plant diversity–productivity relationship.
Highlights
The relationship between plants and soil biota is important for controlling plant productivity, decomposition, and nutrient cycling (Neher 2010; van der Heijden et al 2008)
We identified 51 different genera in total (Table S2), whereas most genera belonged to the plant feeder and bacterial feeder groups (18 genera, respectively)
Plant species richness effects on nematode community composition and diversity We generally found that nematode community composition (NMDS for abundance) and nematode diversity differed among the plant species richness levels, which is in line with recent studies (Cortois et al 2017; De Deyn et al 2004; Eisenhauer et al 2011; Guerrero‐Ramírez et al 2019)
Summary
The relationship between plants and soil biota is important for controlling plant productivity, decomposition, and nutrient cycling (Neher 2010; van der Heijden et al 2008). Increasing intensity of global change impacts and subsequent biodiversity loss might, disrupt this relationship (Classen et al 2015; Eisenhauer 2012), with unknown consequences for the ecosystems and the well-being of humans (FAO et al 2020; Wall et al 2015). It is essential to fully understand the underlying mechanisms of the complex relationships between plants and soil communities to better assess the future impact of global change. There is an overwhelming diversity of organisms living in the soil. One gram of soil can contain thousands of species of bacteria, fungi, protozoa, and nematodes (FAO et al 2020).
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