Effects of management intensity, soil properties and region on the nematode communities in temperate forests in Germany

A key to forest productivity is structure and function of the biotic microbiome in the soil, which determines nutrient mineralisation and consequently tree growth and fitness. Soil nematodes are a dominant part of these assemblages, with an important role in the associated micro-food web. However, nothing is known about how forest management and soil properties affect soil nematodes. This study investigated the nematode communities in the organic layer and mineral soil of 150 forests located in three different German regions. Fifty forest stands each were studied in Schwabische Alb (ALB), Hainch-Diin (HAI) and Schorfheide-Chorin (SCH). The effect of forest management (forest management index - ForMI, silvicultural management intensity indicator - SMI), soil properties (total C, N, S, P, organic C, inorganic C, pH, water content) and microbial food source (phospholipid fatty acids - PLFA) on nematode density, community and ecological indices were assessed. The nematode density in the organic layer of the forests was with a mean of 290 individuals g(-1)DW comparable across all three regions, while in the mineral soil nematode density was significant lower in SCH. Here, dry sandy soils are frequently stocked with intensively managed pine forests, and the associated fungal-based decomposition is reflected in a greater proportion of fungal-feeding nematodes and a higher Channel Index. Effects of region and soil layer were mirrored by the structure of the nematode community. Organic layer and mineral soil differed distinctly, while in the latter SCH separated from ALB and HAI. The nematode community was predominantly affected by region, soil properties and resources, with microbial diet as driving factor in the organic layer, whereas soil parameters were more important in mineral soil. In comparison, the influence of forest management was low, with ForMI and SIM together explaining 8% (organic layer) and 4% (mineral soil) of the overall variation. Most remarkable, the nematode community in HAI, a region dominated by broad-leaf forests, was resilient to management intensity in the organic layer. On the other hand, management practice had family-specific impact: In the organic layer of ALB, the density of the bacterial-feeding Teratocephalidae and the fungal-feeding Aphelenchoididae increased with higher Inonat (indicates non-natural tree species) and higher SMIr (addresses stand age and species selection related to the risk of stand loss). In sum, the structure and function of nematode communities were driven by both, biotic factors such food source (i.e. the soil layer inhabited) and abiotic factors such as soil type and climate (i.e. region). Furthermore, forest management can affect nematode communities, mainly by the selected tree species, but also by stand age and density.

Automated summary

The structure and function of the biotic microbiome in the soil, especially the soil nematodes, play a crucial role in forest productivity. This study investigated the nematode communities in 150 forests in Germany to analyze the effects of forest management, soil properties, and microbial food source on nematode density and community. The results showed that region and soil layer had significant influences on the nematode community, while forest management had a low impact.