The soil bacterial communities show resilience in composition and function for 30 years of pine self-reforestation on agricultural lands in Western Russia

Abstract

The taxonomic and functional composition of the soil microbiome plays a crucial role in diverse ecosystem services including the carbon cycle and fertility, and is intricately linked to environmental conditions. Agricultural land abandonment followed by ecosystem changes and reforestation is widely spread in Eastern Europe and especially in Russia where up to 400,000 km² have been extracted from agricultural land-use and started to self-reforest. In boreal ecosystems, the reuse of abandoned lands for agriculture reduces the environmental risk connected with climate change. Therefore, there is a need to assess changes in soil parameters during long-term abandonment. This research aims to investigate the effect of natural pine reforestation on poor sandy ploughing lands on the taxonomic and functional composition of soil bacteria in Smolenskoe Poozerye National Park (western Russia). The soil microbial community of early stages (<30 years of pine reforestation) and older stages (>70 years of pine reforestation) differ significantly (p < 0.05): relative abundance of the dominant soil bacteria namely Acidobacteriota (13 % → 21 %), RCP2–54 (0.3 % → 6 %), Verrucomicrobiota (0.8 % → 0.9 %), Dependentiae (0.1 % → 0.7 %), WPS-2 (0.1 % → 1.2 %) increased, while the abundance of Actinobacteriota (24 % → 18 %), Chloroflexi (7 % → 0.7 %), Gemmatimonadota (2.8 % → 0.6 %), Myxococcota (3.2 % → 1.6 %), Bacteroidota (4.6 % → 1.5 %), Latescibacterota (0.1 % → 0 %), Nitrospirota (0.3 % → 0.01 %; p < 0.05) decreased. In the 0–30 cm topsoil humus horizon, the younger forest soil microbiome was more similar to soils of meadows and agrocoenoses than to the older forests due to previous plough. Differences between the upper and lower parts of the previously homogenized ploughed horizon become more evident during pine reforestation. In terms of predicted metabolic pathways, the younger soil microbiome produces siderophores and degrades organic substances more actively (p < 0.05). Older forest communities show higher activity of fermentation, photosynthesis, non-organic nutrient assimilation and respiration (p < 0.05). Our results also suggest that reforestation of poor sandy soils is not always beneficial for soil bacteria, since alpha-diversity decreases during succession and certain taxa are more abundant in soils of ploughing lands and native forests than at the transitional stages. The ploughing effect is preserved in soils studied for at least 30 years. The results obtained can be used in the environmental assessment to evaluate the degree and rate of restoration of soils in impacted areas.