Microorganisms

Dietary tryptophan may influence early host and microbial development, but responses to different supplementation levels in dairy calves remain unclear. This study examined the effects of tryptophan supplementation on organ development, hematological parameters, hepatic gene expression, and fecal microbial and tryptophan metabolic profiles. Thirty-six dairy calves were assigned to four treatments in a randomized complete block design, receiving 0, 0.25, 0.50, or 0.75 g tryptophan/calf/d, with nine calves per treatment. Fecal metagenomics and targeted tryptophan metabolite profiling were performed in all calves, and organ measurements and liver transcriptomics were conducted in six calves per treatment. No significant overall treatment effects were detected for organ weights, intestinal lengths, or hematological parameters. Fecal kynurenic acid showed an overall treatment effect (p = 0.026) and a negative linear contrast across supplementation levels (p = 0.005), with lower concentrations at 0.50 and 0.75 g/calf/d than in controls. Relative to controls, the 0.25, 0.50, and 0.75 g/calf/d groups had 197 upregulated and 170 downregulated, 447 upregulated and 315 downregulated, and 1691 upregulated and 267 downregulated hepatic genes, respectively. Upregulated genes were enriched in olfactory transduction, whereas downregulated genes were enriched in cytokine–cytokine receptor interaction at all supplementation levels and IL-17 signaling at the two higher levels. Fecal microbial alpha diversity did not differ among treatments, whereas community composition showed an overall treatment effect (p = 0.046). More differentially abundant microbial taxa and functional pathways were detected at the two lower supplementation levels than at the highest level. These findings describe distinct hepatic transcriptional and fecal microbial responses to tryptophan supplementation, but no causal link between these responses was established.

Microbial spatial distribution patterns represent a fundamental question in microbial biogeography. However, existing evidence primarily stems from regional and global scales. This study focused on Nematode-Trapping Fungi (NTF) within the Lasha Mountain small watershed (21.09 km²) in the Hengduan Mountains. A total of 119 soil sampling points were established across the watershed, adhering to a principle of spatial uniformity. Species identification was performed by integrating morphological characteristics with ITS molecular sequencing, thereby obtaining spatial distribution data for NTF species. By analyzing species occurrence frequency and the variance-to-mean ratio (VMR), and incorporating 12 environmental factors—encompassing topography, vegetation, and soil physicochemical properties—the spatial heterogeneity of NTF and its potential local environmental associations were examined. The results indicated that the species richness of all NTF exhibited a significant non-random distribution among the sampling points (VMR = 1.4816, p = 0.0003). Kernel density analysis indicated that high species richness was primarily concentrated in the middle-lower reaches of the watershed and the main channel confluence area. Clear geographic differentiation was observed at the genus level, with Dactylellina predominantly distributed in the northern part of the watershed, Arthrobotrys concentrated in the southern part and the main channel confluence area, and the few detections of Drechslerella were exclusively observed in the eastern part of the watershed. Low-occupancy restricted species were the main contributors to the non-random spatial heterogeneity of the community, whereas the distribution patterns of widespread species approached randomness. Marginal tests from permutational multivariate analysis of variance (PERMANOVA) demonstrated that soil moisture (p = 0.012), pH (p = 0.022), total phosphorus (p = 0.036), and gap size (p = 0.039) showed significant marginal associations with NTF community differentiation. Multivariate analyses incorporating both environmental and spatial variables explained only 38.19% of the community variation. This study demonstrates that detectable non-random variation in species richness persists at a small scale, providing an empirical case for microbial biogeography research in the small mountain watersheds of the Hengduan Mountains.

Plant species diversity can enhance soil organic carbon (SOC) storage, but the microbial processes associated with this relationship remain incompletely understood in subtropical forests. We surveyed 20 natural forest plots spanning a Shannon–Wiener diversity gradient and quantified SOC, soil nutrients, microbial biomass carbon, nitrogen, and phosphorus (MBC, MBN, and MBP), and extracellular enzyme activities. Based on linear regression predictions across the observed diversity gradient, SOC increased by 154.4%, total nitrogen by 67.0%, and dissolved organic carbon by 153.6%, whereas total phosphorus and available phosphorus decreased by 42.1% and 82.5%, respectively. SOC-normalized β-glucosidase (BG) activity decreased by 63.4%, while acid phosphatase (AP) activity increased by 359.2%, revealing contrasting patterns of extracellular enzyme activities associated with carbon and phosphorus acquisition. In contrast, leucine aminopeptidase (LAP) and β-N-acetylglucosaminidase (NAG) activities showed no significant relationships with plant diversity. The BG/AP ratio declined significantly along the diversity gradient (R² = 0.76, p < 0.001). SOC was positively associated with MBC (R² = 0.70), MBN (R² = 0.68), and MBP (R² = 0.47). These findings suggest that microbial biomass and extracellular enzyme patterns are closely associated with SOC variation along a natural plant diversity gradient, while declining phosphorus availability may influence belowground nutrient cycling. Further experimental studies are needed to clarify the microbial mechanisms underlying these associations.