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Agricultural soils with (M+) or without (M−) organic amendment were collected from four long-term field experiments to investigate soil fungal community composition and its relationship to the soil ionome by employing both the sequencing of fungal internal transcription spacer (ITS) fragments and inductively coupled plasma mass spectrometry (ICP-MS). Fungal community composition was primarily impacted by physical location while organic amendment triggered community shifts in the same direction in all four sites. Overall, the fungal community was strongly correlated to soil pH that, conversely, impacted soil ion availability. Fungal community dissimilarity was strongly correlated to soil ionome (ionic profile) variability. Network analysis has been conducted to explore the biotic interactions in soil ecosystem, in which species (nodes) are connected by pairwise interactions (links). The results revealed that organic amendment led to a higher number of correlated nodes to soil ions, links, modules (a group of nodes more densely connected to each other than to nodes outside the group), and positive links within and between modules. Moreover, specific fungal modules were independently correlated with soil ions, suggesting that each module represents a functional guild or collection of similar fungal ecotypes. Module size (number of nodes in a module) exhibited no apparent influence on the scale of these correlations. The increase in cooperative/synergistic interactions with organic amendment suggests that application results in a better-organized and more efficient community with enhanced potential soil fungal interactions mediated by alterations in the soil ionome. Overall, this study indicates that these less commonly measured soil ions play an important role and may be used to reveal previously undetermined drivers of the soil microbial community. [ABSTRACT FROM AUTHOR]

Particle-size soils were fractionated for evaluating changes in the composition of bacterial community and enzyme activity in response to 13 years of fertilization. This study focused on Mollisol and its particle-size fractions of 200-2,000 μm (coarse sand sized), 63 to 200 μm (fine sand sized), 2 to 63 μm (silt sized), and 0.1 to 2 to μm (clay-sized). Long-term chemical fertilization lowered the pH of all particle fractions, whereas organic fertilizer application mitigated soil acidification. Nutrient concentrations depended on both fertilizer treatment and particle fractions and enzymes were unevenly active throughout the soil. Generally, the highest enzyme activities were observed in the silt and clay fractions of control soil and the soil treated with chemical fertilizer (N, P, and K (NPK)) and in the sand-sized fraction of soil treated with manure and chemical fertilizer (MNPK). Except for acid phosphomonoesterase, the other tested enzyme activities in coarse-sized fractions of MNPK soil were significantly higher than those of the control and NPK soils. Fertilization and soil fraction interactively ( p < 0.05) affected the enzyme activity. Denaturing gradient gel electrophoresis analysis showed that the bacterial community structure significantly differed in different particle sizes with a higher bacterial diversity in small-sized than in coarse-sized fractions. Dominant bands were excised and sequenced. We have found the following bacterial groups: Actinobacteria, γ-proteobacteria, and Acidobacteria. In addition, enrichment of organic matter in coarser fractions was related to greater bacterial diversity than any other treatment. Principal component analysis showed a smaller variability among fractions of the organic amended treatment. Redundancy analysis showed that the tested properties significantly affected the composition of bacterial community with the exception of C/N and available P. No significant correlation between enzyme activity and bacterial community composition was detected, whereas positive correlations between other soil properties and enzyme activities were observed to various extents. Probably, enzyme activities might be affected by specific functional bacterial communities rather than by the overall bacterial community. We concluded that the long-term application of organic manures contributed to the increase of soil organic matter content of particles higher than 200 mm, with higher bacterial diversity and increases in most of the enzyme activities. [ABSTRACT FROM AUTHOR]