Increase in rainfall intensity promotes soil nematode diversity but offset by nitrogen addition in a temperate grassland

Seasonal dynamics and functional diversity of soil nematode communities under treated wastewater irrigation in abandoned agricultural soils

The use of treated wastewater (TWW) for agricultural irrigation is becoming more popular as a sustainable alternative to freshwater due to increasing water scarcity. While considerable research exists on the effects of TWW on soil microorganisms, its impact on soil nematodes, key indicators of soil health remains unexplored. This study assessed the effects of two years of TWW irrigation on soil nematode communities in abandoned fields cultivated with Lavender, Anise, Olive and Pomegranate trees. Seasonal soil samples were analyzed for nematode abundance, community composition and ecological indices. TWW irrigation modified soil nematode community structure, favoring the dominance of bacterivores (Acrobeloides) while suppressing plant-parasitic nematodes (Pratylenchus, Bitylenchus). Nematode-based indices showed no significant differences between TWW- and freshwater-irrigated soils, indicating stable and resilient communities. Seasonal precipitation levels strongly influenced nematode abundances, highlighting environmental resilience. Plant species did not create ecological niches, probably due to the strong influence of precipitation and soil properties; nevertheless, plant establishment increased nematode diversity over time, with omnivores and predators emerging alongside bacterivores and fungivores, reflecting recovery dynamics. Even though TWW irrigation is considered a type of disturbance, it facilitated soil nematode diversity and maintained ecological stability. Properly treated wastewater serves as a sustainable irrigation method that enhances soil health and biodiversity, rendering it a viable alternative for agricultural systems in degraded and water-scarce areas under changing climatic conditions.

Context-dependent responses of terrestrial invertebrates to anthropogenic nitrogen enrichment: A meta-analysis

Anthropogenic increases in nitrogen (N) concentrations in the environment are affecting plant diversity and ecosystems worldwide, but relatively little is known about N impacts on terrestrial invertebrate communities. Here, we performed an exploratory meta-analysis of 4365 observations from 126 publications reporting on the richness (number of taxa) or abundance (number of individuals per taxon) of terrestrial arthropods or nematodes in relation to N addition. We found that the response of invertebrates to N enrichment is highly dependent on both species' traits and local climate. The abundance of arthropods with incomplete metamorphosis, including agricultural pest species, increased in response to N enrichment. In contrast, arthropods exhibiting complete or no metamorphosis, including pollinators and detritivores, showed a declining abundance trend with increasing N enrichment, particularly in warmer climates. These contrasting and context-dependent responses may explain why we detected no overall response of arthropod richness. For nematodes, the abundance response to N enrichment was dependent on mean annual precipitation and varied between feeding guilds. We found a declining trend in abundance with N enrichment in dry areas and an increasing trend in wet areas, with slopes differing between feeding guilds. For example, at mean levels of precipitation, bacterivore abundance showed a positive trend in response to N addition while fungivore abundance declined. We further observed an overall decline in nematode richness with N addition. These N-induced changes in invertebrate communities could have negative consequences for various ecosystem functions and services, including those contributing to human food production.