A review of nematodes as biological indicators of sustainable functioning for northern soils undergoing land-use conversion

Food webs and the functional status of soils are governed primarily by microbial carbon and nitrogen fluxes as determined by ecosystem type and management. In boreal regions, expanding and intensifying agriculture affects the functional status of soils due to biodiversity, carbon, and nitrogen losses. The status of northern soils must be monitored using informative, standardised methods that are comparable across land uses, managements, and scales. Food web nodes sensitive to complex changes in the soil environment, such as free-living nematodes, can be utilised to monitor alterations in the functional state of natural systems and inform management decisions to ensure that new and established agriculture is environmentally sustainable. The objectives of this a-priori review were to 1) describe the likely impacts of land use and land use change on nematode communities and indices in boreal regions, 2) determine if nematodes respond differently to land use and land use change in the global biomes, and 3) identify literature gaps related to nematodes in the boreal biome to draw attention to future research needs. Soil quality bioindicators were compared and 31 published, peer-reviewed, in-situ studies found in Web of Science and Scopus databases in March 2020 that assessed the impacts of land use and land use change on free-living nematode parameters across global biomes were systematically summarised. While the northern biomes have greater abundances of nematodes than other biomes, the literature search found zero articles pertaining to nematodes in boreal or Arctic agricultural systems highlighting the need for future work. Given the key roles that free-living nematodes have in the food web, their longer and more stable generation times than microbes, and relatively well-known taxonomy, life history traits, and feeding habits, the authors propose that nematodes could and ought to be employed as indicators of functional changes in boreal agricultural soils.