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The life strategies of bacterial communities determine their structure and function and are an important driver of biogeochemical cycling. However, the variations in these strategies under different soil resource conditions remain largely unknown. We explored the bacterial life strategies and changes in structure and functions between Antarctic soils and forest (temperate, subtropical, and tropical) soils. The results showed that the weighted mean rRNA operon copy number in temperate soils was 19.5% lower than that in Antarctic soils, whereas no significant differences were observed among Antarctic, subtropical, and tropical soils. An unexpected result was that bacterial communities in Antarctic soils tended to be copiotrophs, such as Actinobacteriota and Bacteroidota, whereas those in temperate soils tended to be oligotrophs, such as Acidobacteriota and Chloroflexi. Functional predictions showed that in comparison to copiotrophs in Antarctic soils, temperate-inhabiting oligotrophic bacteria exhibited an 84.2–91.1% lower abundance of labile C decomposition genes (hemicellulose, cellulose, monosaccharides, and disaccharides), whereas a 74.4% higher abundance of stable C decomposition (lignin). Genes involved in N cycling (nitrogen fixation, assimilatory nitrate reduction, and denitrification) were 24.3–64.4% lower in temperate soils than in Antarctic soils. Collectively, our study provides a framework for describing the life strategies of soil bacteria, which are crucial to global biogeochemical cycles. [ABSTRACT FROM AUTHOR]

Purpose: Carbohydrate-active enzymes (CAZymes) mediate carbohydrate turnover and play vital roles in plant- and microbial-derived carbon decomposition. However, the changes of genes that encoding enzymes for plant- and microbial-derived carbon decomposition along environmental gradients remains unclear. Methods: We used metagenomic sequencing to explore changes in genes encoding enzymes for carbon decomposition in five forest sites along an elevational gradient (1503–3182 m) on Qinling Mountain, China. Results: The genes encoding CAZymes showed various patterns along the elevational gradient. In particular, the abundance of genes encoding auxiliary enzymes and glycoside hydrolases decreased with increasing elevation. The abundance of genes encoding enzymes for plant- and fungi-derived carbon decomposition was higher at low elevations than at high elevations, whereas the abundance of genes encoding enzymes for bacteria-derived carbon decomposition was higher at high elevations than at low elevations. The results indicate contrasting patterns of fungal- and bacterial-derived carbon decomposition with elevation. Proteobacteria and Acidobacteria were the dominant species that decomposed dead plant and microbial biomass. Moreover, our results reveal that soil properties (i.e., ammonium nitrogen and bulk density) and vegetation properties dominated the CAZymes gene distribution along the elevational gradient. Conclusion: Bacteria- and fungi-derived carbon decomposition potentials show contrasting elevational patterns in forest soils; soil and vegetation properties are common controls for the elevational patterns. [ABSTRACT FROM AUTHOR]

Soil net nitrogen (N) mineralisation, the difference between organic nitrogen mineralisation and mineral nitrogen immobilisation, changes with elevation, thereby determining plant productivity and soil N cycling along elevation gradients. However, it has yet to be established how different microbial functional genes influence the rate of soil net N mineralisation along such gradients. To address this deficiency in our current knowledge, we performed metagenomic sequencing to identify soil microbial functional genes encoding enzymes involved in N cycling at five forest sites along an elevational gradient spanning a range from 1503 to 3182 m above sea level. Our results indicate that the rate of net N mineralisation follows a unimodal pattern with increasing elevation, with a peak (0.18 mg kg−1 d−1) being detected at the mid‐high elevation site. Further, we detected a significant correlation between the abundance of genes encoding enzymes involved in denitrification and ammonia assimilation pathways and net N mineralisation rate (p < 0.05). Moreover, we established that microbial species in the phyla Cyanobacteria, Acidobacteria and Planctomycetes, harbouring keystone functional genes, play a predominant role in determining the rate of net N mineralisation. Our findings also revealed soil substrate content (ammonium nitrogen and nitrite nitrogen, soil organic carbon, and C:N ratio) and soil environment (soil temperature and soil moisture) to be the major drivers of net N mineralisation in soil via their regulatory effects on the composition of microbial communities and functional genes. Our characterisation of the microbial metagenomic basis of net N mineralisation in forest soils accordingly highlights the importance of the combined contributions of soil microbial functional genes, soil substrate, and environmental factors in determining the cycling of N in forest soils at different elevations. Highlights: Net N mineralisation rate followed a unimodal pattern along an elevational gradient.Denitrification and ammonia assimilation genes were correlated with net N mineralisation rate.Cyanobacteria play a dominant role in determining net N mineralisation rate.Soil substrate and environment determine microbial functional gene distribution. [ABSTRACT FROM AUTHOR]

Soil priming is a microbial‐driven process, which determines key soil–climate feedbacks in response to fresh carbon inputs. Despite its importance, the microbial traits behind this process are largely undetermined. Knowledge of the role of these traits is integral to advance our understanding of how soil microbes regulate carbon (C) emissions in forests, which support the largest soil carbon stocks globally. Using metagenomic sequencing and 13C‐glucose, we provide unprecedented evidence that microbial traits explain a unique portion of the variation in soil priming across forest biomes from tropical to cold temperature regions. We show that microbial functional profiles associated with the degradation of labile C, especially rapid simple sugar metabolism, drive soil priming in different forests. Genes involved in the degradation of lignin and aromatic compounds were negatively associated with priming effects in temperate forests, whereas the highest level of soil priming was associated with β‐glucosidase genes in tropical/subtropical forests. Moreover, we reconstructed, for the first time, 42 whole bacterial genomes associated with the soil priming effect and found that these organisms support important gene machinery involved in priming effect. Collectively, our work demonstrates the importance of microbial traits to explain soil priming across forest biomes and suggests that rapid carbon metabolism is responsible for priming effects in forests. This knowledge is important because it advances our understanding on the microbial mechanisms mediating soil–climate feedbacks at a continental scale. [ABSTRACT FROM AUTHOR]

Forest development gradually changes the above-ground plant community, but the potential effects on the below-ground microbial community remain unclear, particularly at the various succession stages. Here, we investigated six vegetation types that covered two succession stages (early and late stages) during forest development. The early stage showed changes from two pioneer communities (Betula platyphylla and Populus davidiana) to two mixed communities (Populus davidiana with Pinus tabuliformis), while the late stage showed changes from the two mixed communities to two climax communities (Quercus wutaishanica and Pinus tabuliformis). Illumina sequencing of the 16S rRNA gene and ITS gene were carried out to analyze soil microbial (bacterial and fungal) diversity and composition. Soil properties (i.e., moisture, bulk density, texture, ammonium nitrogen, nitrate nitrogen, organic carbon, total nitrogen, and total phosphorus) were also determined. The results showed that forest development had positive effects on microbial diversity. Particularly, bacterial diversity successions proceed faster than that of fungi at the early stage. Proteobacteria and Bacteroidetes significantly increased, but Actinobacteria and Acidobacteria significantly decreased during forest development. In contrast, the effect sizes of Proteobacteria , Actinobacteria , and Acidobacteria at the early stage were larger than those at the late stage. The dominant fungi phyla (i.e., Ascomycota , Basidiomycota , and Zygomycota) across all soil samples responded insignificantly to forest development. Such differential responses of the microbial diversity and dominant phyla were significantly correlated with soil texture, soil organic carbon, and total nitrogen. In contrast, the effect size of soil properties on bacterial phyla was larger than that on fungal phyla. Collectively, these results emphasize that the responses of the microbial community to forest development depend on the succession stage, and also suggest that bacteria and fungi may not follow the same successional trajectories due to the differed responses of bacteria and fungi to changing soil texture and carbon/nitrogen contents during forest development. • Forest development has positive and significant effects on microbial diversity. • Bacterial diversity successions proceed faster than that of fungi at early stage. • Forest development largely affected bacterial composition but not fungal composition. • Microbial community differed with ST and SOC at early stage rather than at late stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thinning promoted the increase of soil recalcitrant C and stability of SOC pool. • Increase of ligninase activity was associated with soil moisture and temperature. • Thinning induced SOC pool stability was mainly related to soil C-degrading enzyme. Forest thinning greatly affects the soil organic carbon (SOC) pool by changing the soil microenvironment, organic matter input, and microbial metabolism. However, the heterogeneity of thinning intensity, recovery stage, and microclimatic conditions increases uncertainty about the effect of thinning on SOC. The activities of C-degrading enzymes (ligninases and cellulases) secreted by soil microorganisms can be used to explore the effects of thinning on soil C storage. Our meta-analysis showed that forest thinning significantly increased soil temperature (ST), soil moisture (SM), and pH, but significantly decreased litter and fine root biomass. Moderate thinning and recovery time extension increased soil C storage, SOC, and recalcitrant organic C (ROC). An increase in the thinning intensity significantly improved ligninase activity, while decreasing cellulase activity and extending recovery time after thinning. Increased SOC, soil labile organic C (LOC), and ROC with thinning were associated with increased ligninase activity that was significantly positively correlated with soil pH, SM, and ST after thinning. The variation in soil ligninase: cellulase ratio induced by thinning was significantly positively correlated with the increases of soil ROC: LOC ratio and SOC after thinning. Therefore, forest thinning enhanced SOC pool stability through the effect of ligninases and cellulases on SOC sequestration. The global pattern of soil C-degrading enzymes in response to thinning has deepened our understanding of the mechanism by which thinning affects the SOC cycle. [ABSTRACT FROM AUTHOR]

Changes in the composition of organic carbon lead to shifts in the selective environment, which in turn contribute to changes in the composition and assembly process of soil bacterial communities at different successional stages. Deterministic and stochastic processes are expected to clarify bacterial community assembly process during long-term ecosystem recovery. Therefore, by studying the bacterial community of the organic horizon and mineral horizon during forest succession, the main role of organic carbon composition in determining soil bacterial community structure and assembly process during forest succession in the arid regions of Loess Plateau, China was revealed. Stochastic assembly was predominant in the organic horizon (75.0%) and mineral horizon (71.6%), and its relative contribution of stochastic assembly was similar in two horizons. In addition, network analyses demonstrated that bacterial nodes (as individual taxa) and connectivity between them was higher in the organic horizon (nodes: 297 and edges: 5242) than mineral horizon (nodes: 251 and edges: 1694). During forest succession, the bacterial community gradually changed to a K-strategy, and the degree of bacterial network connection cross the organic horizon and mineral horizon gradually decreased. The taxon- organic carbon composition cooccurrence network aided in identifying the relationship between the composition of organic carbon and the bacterial community, and ploysaccharide, methyl and aliphatic carbon were the main reason for the differences in the bacterial community. Meanwhile, the relationship between the composition of organic carbon in bacterial assembly was different in the organic horizon and mineral horizon: ploysaccharide, methyl, aliphatic, aromatics and carboxylic carbon were the main factors driving bacterial assembly in the organic horizon, whereas the interaction of them with bacterial traits jointly participated the assembly process in the mineral horizon. Our results highlight the importance of resource availability, particularly the composition of organic carbon, in determining how the microbial community composition assembles during forest succession. • Bacterial network connectivity decreased with forest succession. • Stochastic processes dominated microbial community assembly in the organic horizon. • The relative influence of deterministic processes increased in the mineral soil layer. • Organic carbon structures were essential drivers of organic versus mineral soil layer bacterial communities. [ABSTRACT FROM AUTHOR]

The priming effect is a pivotal mechanism for microbial regulation of soil C cycling; however, the microbial mechanisms underlying priming effects remain elusive. Here, we combined an isotopic approach with metagenomic sequencing to investigate priming effects at five forest sites along an elevational gradient. Positive priming effects were found across the Quercus aliena var. acutiserrata (low elevation), Q. wutaishanica (low-mid elevation), Betula albosinensis (mid elevation), Abies fargesii Franch (mid-high elevation), and Larix chinensis Beissn (high elevation) forest sites. A significant positive correlation was found between the abundance of microbial C decomposition genes and priming effects (p < 0.05). Further analysis revealed that the microbial functional genes for breaking down stable C (lignin, lipids, and chitin) predominately drove the positive priming effects. Moreover, we found strong correlations between the relative abundance of eight near-complete bacterial genome bins and the priming effect. Five out of the eight genomes were associated with the Proteobacteria , indicating their predominant role in priming effects. Our results revealed that SOM quality (soil organic C, total nitrogen, and ratio of alkyl-C to O-alkyl-C), and soil environment (pH and bulk density) were the major drivers of the priming effect in forest soils as they regulated the abundance of microbial decomposition genes. In conclusion, the present study investigated the metagenomic basis of the priming effect, highlighting the importance of bacteria in association with substrate and environmental factors for C decomposition in forest soils. • Positive priming effects were found in forest sites, the magnitude declined with elevation. • Microbial functional genes for breaking down the stable C drive the positive priming effects. • Soil substrates and soil environment drive of priming effect by regulating microbial genes. [ABSTRACT FROM AUTHOR]