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Aims: Nitrogen (N) fertilizer is applied to the soil to increase the nutrient level and plant productivity, but the effects of N addition on the soil microbial community diversity and functions are unclear. This study aimed to determine how changes in soil N influence soil microbial community diversity and potential functions. Methods: We evaluated plant characteristics, soil chemical properties, microbial composition, and potential functions (N-fixation and functional fungal guild) after 3 years of urea fertilization at four different levels (0, 25, 50, and 100 kg N ha−1 year−1) in a semiarid grassland in China. Compositions of bacterial and fungal communities were determined by high-throughput sequencing, and their potential functions were predicted by comparing their data with those in the Tax4Fun and FUNGuild databases, respectively. Results: Compared with the grassland without N input (N0), N fertilization significantly reduced soil bacterial diversity, possibly by reducing plant diversity. Fungal diversity increased with N fertilization and peaked in the N50 treatment, while the aboveground biomass showed a parallel increase and peak. A lower abundance of nif genes was found in the N100 than in the N0 treatment because the enhanced NO3− and NH4+ content alleviated the dependence of plants on biological N-fixation and reduced the N-fixation potential. N fertilization increased the relative abundance of saprotrophs (wood, plant, and dung saprotrophs) and pathogens (plant and animal pathogens). However, this promotion could be weakened when the excessive N fertilization was applied due to the lower abundance in the N100 than in the N50 treatment, and these changes could be attributed to the variation in aboveground biomass and soil organic C. Changes in the abundance of arbuscular mycorrhizal fungi were related to their host plants, exhibiting a transient increase in the N25 compared to the N0 treatment and then sharply decreasing. Conclusions: Our results show that N-induced environmental changes have considerable influence on the composition and potential functions of soil bacterial and fungal communities, which are likely to be dependent on interactions between plants and soil. [ABSTRACT FROM AUTHOR]

Aims: While the effects of destocking on soil nutrient and plant productivity are known, the effect on functional groups of fungi has received less attention. The objective of this study was to evaluate the effect of long-term destocking on fungal functional guilds and their association with plants and soil. Methods: We characterized the changes in five fungal functional guilds, including plant pathogens, animal pathogens, wood saprotrophs, dung saprotrophs, and arbuscular mycorrhizal fungi (AMF), along a 35-year chronosequence following destocking at 0–60 cm soil depths on the Chinese Loess Plateau. Fungal community composition was assigned by comparing with the FUNGuild database. Results: After 35 years of destocking, diversities of plant pathogens, wood saprotrophs, and AMF increased, while that of animal pathogens and dung saprotrophs decreased. Destocking had a greater effect in the near-surface layers (0–10 and 10–20 cm) owing to the greater influence of plant biomass and soil nutrients. Among the above- and belowground drivers, plant pathogen diversity was largely associated with plant diversity, while animal pathogens, dung saprotrophs, and wood saprotrophs were associated with aboveground biomass, AMF were responsive to soil conditions (e.g., organic C, NO3−-N, C:N ratio, and moisture). Conclusions: Long-term destocking can be considered to be an important predictor of fungal functional guilds, and changes in these microorganisms were associated with cessation-induced shifts in plants and soil by grazing. Our findings provide insights into the duration of destocking necessary to benefit fungal communities, and how this varies according to soil depth. [ABSTRACT FROM AUTHOR]