Responses of bacterial and fungal communities to short-term nitrogen and phosphorus additions in temperate forest soil aggregates in northeastern China

With the widespread use of nitrogen (N) and phosphorus (P) fertilizers, increased N and P deposition also regulate microbial growth by altering the effectiveness of forest soil nutrients. Soil microbes residing within or among soil aggregates serve as functional components of soil ecosystems and serve as sources and reservoirs of soil nutrients capable of reflecting minor alterations in soil ecosystems. Understanding the impact of N and P additions on soil microbial community structure is vital for predicting the consequences of N and P additions on ecosystems. Therefore, soils from short-term NP (nitrogen plus phosphorus) addition experiments were utilized, and high-throughput sequencing analysis was performed to ascertain how bacterial and fungal alpha - diversity and community composition across different aggregate-size fractions (macroaggregates: 2000-250 mu m; and microaggregates: < 250 mu m) were altered in response to short-term NP addition in a broad-leaved Korean pine forest. There were four treatments: CK (no addition), N1P1 (50 kg N ha(-1) a(-1) + 50 kg P ha(-1) a(-1)), N2P2 (150 kg N ha(-1) a(-1) + 100 kg P ha(-1) a(-1)), and N3P3 (300 kg N ha(-1) a(-1) + 200 kg P ha(-1) a(-1)). In this study, all the NP-treated soil samples had lower fungal diversity than bacterial diversity and demonstrated a tendency toward a negative response to NP addition. NMDS and RDA analyses revealed that the bacterial communities in macroaggregates and microaggregates differed in composition, while the fungal composition was similar. In addition, the bacterial and fungal communities in the CK, medium-concentration NP addition treatment, and low-concentration NP addition groups were closely related and were distinct from those in the high-concentration NP addition treatment group. PERMANOVA further revealed that the community composition and structure of bacteria and fungi were significantly affected by NP addition, with a greater responsiveness observed in fungal communities. Bacterial and fungal functional groups were predicted using the PICRUSt2 and FUNGuild databases. It was observed that high-NP addition led to a significant reduction in the number of bacterial metabolism-related pathways and an increase in the relative abundance of fungal saprotrophs within the soil aggregates. Overall, our findings suggest that short-term NP addition results in a reduction in fungal alpha -diversity and alters the community composition of soil aggregates, with a comparatively lesser impact on bacteria. Higher NP concentrations exerted a more pronounced influence on both bacterial and fungal communities compared to lower concentrations. These results contribute valuable insights into the influence of NP addition on diverse microbial communities within aggregates and their associated functions. This approach enhances our comprehensive understanding of the impact of environmental changes on microbial communities within soil aggregates in temperate forest ecosystems, facilitating predictions related to microbial-mediated soil carbon, nitrogen, and phosphorus cycles.