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Soil nitrogen (N) availability plays an important role in regulating priming effects (PE). In this study, we aimed to investigate the effects of long-term N fertilization on PE under single and more frequent additions of labile carbon (C) inputs (13C-labeled glucose). The soils collected from a 6-year-long inorganic N fertilization experiment in a subtropical Phyllostachys edulis forest in China were incubated at a constant temperature of 25 °C for 90 days. Regardless of the mode of glucose addition, the cumulative primed C was lower in the previously fertilized soil and showed a positive relationship with soil pH and peroxidase activity. When comparing the amount of cumulative primed C and the remaining added glucose-C after 90 days of incubation, the fertilized soil had a higher net C increase than the control. These results indicate that atmospheric N deposition and N fertilization might reduce the PE caused by labile organic matter inputs, thereby increasing soil organic C sequestration. The effect of N fertilization on PE under a single glucose addition (reduced by 11%) was smaller than that of repeated additions (reduced by 24%). Previously fertilized soil with a single glucose addition exhibited higher microbial P deficiency, which had a negative impact on PE; in contrast, in soil with repeated glucose additions, higher abundance of Gram-positive bacteria contributed to the negative PE. As such, the frequency of glucose addition affects the intensity and regulation of soil PE. Regardless of the N fertilization treatment, soil with a single glucose addition exhibited stronger PE but lower soil net C increases than those with repeated additions, which might be related to higher microbial activities. Collectively, our findings provide insights regarding soil PE in subtropical forests under the combined effects of increasing N deposition and glucose addition. [ABSTRACT FROM AUTHOR]

Single and mixed vegetation types have significant effects on soil parameters and the composition and diversity of soil bacterial community. To understand the influence of different vegetation types on the structure of soil bacterial community across soil depth in a subtropical forest, we assessed the relative abundance of edaphic bacterial community and soil parameters, including pH, cation exchange capacity (CEC), and dissolved organic C in Daiyun Mountain Nature Reserve in Fujian Province, southeastern China. The study area constitutes pine coniferous forest (CF) of Pinus taiwanensis Hayata, broad‐leaved forest (BF) of Castanopsis fabri Hance, and a mixed forest comprising CF and BF (MF). Quantitative polymerase chain reaction (PCR) and Illumina sequencing of 16S ribosomal DNA were used to analyze the abundance, diversity, and composition of soil bacteria. The results showed that the pH, CEC, and diversity of tree species are all associated with the composition of bacterial community in the soil. It was found that CEC, soluble organic N, and pH largely affected the structure of soil bacterial community in A horizon, whereas CEC, moisture content, and organic P affected the structure of soil bacterial community in B horizon. We found that the dominant taxa in the CF and BF were Proteobacteria and Acidobacteria, respectively. The results of both mental and random forest analyses displayed groups according to vegetation types, indicating that the bacterial communities in the research site were significantly influenced by vegetation types in subtropical forests. The study highlights the ecological effects of forest management and elucidates the differences in the functional structure of soil bacterial communities under different vegetation types and soil depths. Core Ideas: Broad‐leaved forests have the highest soil nutrient content in subtropical forests.Acidobacteria and Proteobacteria are biomarker phyla in subtropical forests.Vegetation type affects soil bacterial community structure in subtropical forests.Soil moisture content and organic P affect bacterial community composition in the A horizon.Cation exchange capacity and pH affect bacterial community composition in the B horizon. [ABSTRACT FROM AUTHOR]

Purpose: Dissolved organic matter (DOM) plays an important role in soil C and N cycling. However, the driving mechanisms of DOM concentration and composition under the background of N deposition remains ill-defined. Through experimental N addition, we explored the influence and contribution of microbial community characteristics on DOM concentration and composition. Materials and methods: Field experiments with different N-addition levels were set up in the Daiyunshan Nature Reserve, Fujian, China. Using water extraction and DAX-8 resin separation and phospholipid fatty acids as well as 96-well microplate methods, we mainly probed into the response of DOM concentration and composition, microbial community structure, and extracellular enzyme activity at two soil depths (0–10 and 10–20 cm) to N addition, separately. Furthermore, structural equation models (SEMs) were constructed to explore the effects of microbial community characteristics on the DOM concentration and composition. Results and discussion: The dissolved organic carbon and hydrophilic matter (HIM) decreased significantly with N addition. Moreover, low N addition significantly increased the abundance of gram-negative bacteria and microbial biomass nitrogen, and the activities of urease and cellobiohydrolase in soil. SEMs revealed that the contribution rates of microbial community characteristics to dissolved organic matter (DOM) concentration and HIM were 65% and 60%, respectively. This study focused on the microbial regulation paths for the DOM concentration and composition, including mechanical decomposition, extracellular enzyme secretion, and absorption assimilation. Conclusion: Short-term N addition stimulated microbial communities to regulate soil DOM concentration and composition via three pathways in the subtropical Pinus taiwanensis forest. Under short-term N addition, the absorption and utilization of unstable hydrophilic DOM by microbial communities is the main regulation process, which eventually leads to soil C loss in the form of water-soluble organic C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low N addition is beneficial to copiotrophs and reduces bacterial Shannon diversity. • N addition strengthens the association between BCC-DOM. • The key role of rare bacterial taxa on DOM components was emphasized. • Total nitrogen directly affects key bacterial taxa and association between BCC-DOM. • The importance of rare bacterial taxa to forest ecosystem is highlighted. The interaction between soil bacterial communities and dissolved organic matter (DOM) is the central link of soil carbon and other nutrient cycle. However, how nitrogen (N) addition changes the relationship between forest soil bacterial community composition and DOM components (BCC-DOM) and which key bacterial taxa affect DOM components is not clear. After two years of N addition, we used parallel factor analysis and high-throughput sequencing to explore the changes of DOM fluorescent components, microbial community composition, and diversity at three N addition levels in a subtropical Pinus taiwanensis forest and presented the relationship between BCC-DOM through co-occurrence networks. The results show that low N addition, but not high N addition, transitions the surface bacterial community into a eutrophic state and reduces the Shannon index in the subsoil. Short-term N addition decreases the dissolved organic carbon (DOC) content but increases DOM humification degree and humus-like components (C1 and C2) in the topsoil. Network analysis revealed that the relationships between BCC-DOM are more complex after N addition and the negative associations were dominant. Random forest analysis showed that Chloroflexi (TK10, Ktedonobacteria, and JG37.AG.4) and Nitrospirae (Nitrospira) are key factors for predicting humus-like DOM. Protein-like DOM was mainly related to Firmicutes (Clostridia). Furthermore, structural equation models revealed that soil pH and DOC content do not determine the key bacterial taxa and DOM components, but total N content significantly affects these parameters. Short-term N addition reduces soluble substances in forest soil but improves the obstinacy of carbon substrates. Further, N addition helps to regulate forest soil bacterial communities and strengthen the interactions with DOM. [ABSTRACT FROM AUTHOR]

• Effects of warming and N addition on microbial functional genes were studied. • There was no interaction between warming and N addition on functional genes. • Warming had minimal effect on functional genes associated with soil C and N cycling. • The increase in gene abundance due to N addition was related to pH and available N. Climate warming and nitrogen (N) deposition are expected to increase in the coming decades. The consequences of the interaction between warming and N deposition on forest ecosystems and their functions (i.e., carbon sequestration) remain uncertain. In this study, we examined the composition, diversities, and abundances of soil microbial functional genes in a subtropical forest after four years of exposure to warming and N addition. We found that warming alone did not have a significant effect on the composition, diversities, and abundances of functional genes, suggesting that four years were not long enough to reach the critical threshold that would activate a response to warming from soil functional genes in the subtropical forest. Conversely, warming significantly decreased soil labile carbon (C) content. The application of N in combination with warming significantly enhanced the diversities and abundances of functional genes associated with C and N cycling, leading to an accelerated loss of soil N. Interestingly, the interaction between warming and N addition did not have a significant effect on the diversities and abundances of functional genes associated with C and N cycling. Redundancy analysis indicated that a decrease in pH caused by N addition significantly affected the abundances of those functional genes. Overall, our study fills a research gap by examining the effect of simultaneous warming and N deposition on soil microbial functional genes in subtropical forests. Additionally, the study indicates that microbial functional genes are more sensitive to a combination of warming and N addition than to warming alone. Therefore, the effects of multi-factor global change on soil microbial functional genes cannot be underestimated. [ABSTRACT FROM AUTHOR]

The priming effect (PE) induced by fresh carbon inputs generally stimulates soil organic matter (SOM) mineralization. However, the magnitude of the PE will vary according to the chemical composition of plant litter and nitrogen (N) deposition, due to the effect of these factors on soil microbial community composition and activity. This needs to be considered explicitly in ecosystem models, for more accurate prediction of soil carbon dynamics and stocks. Thus, we conducted a 100-day incubation experiment with additions of three 13C-labeled litters and inorganic N to evaluate the effects of plant litter in combination with N additions on SOM mineralization, PE, microbial community composition and activity in a subtropical Cunninghamia lanceolata forest soil. We found no difference in SOM mineralization and PE among three litter types, but the addition of litter together with N increased the PE by approximately 11–42%, apparently through a microbial stoichiometry decomposition process. When N was added, the PE response, biomass of microbial groups and enzyme activities were related to the litter chemical composition. The direction of PE varied with time, and different microbial mechanisms operated at different decomposition stages. Moreover, microbial activity seemed to be energy-limited by the late decomposition stage, based on the incorporation of litter-derived carbon into soil microbial phospholipid fatty acids with high-lignin litter than other litter types. In conclusion, our findings emphasize that different chemical composition litters in combination with N inputs into soil can have a strong effect on soil carbon stocks by stimulating the priming of native SOM mineralization in subtropical forests. Our results also highlight that changes in litter chemical composition, nutrient availability and microbial processes need to be considered from short to long term, which is of great importance to accurately evaluate the variability of the PE under future climate change scenarios. • We studied the effects of litter and inorganic N addition on SOC mineralization. • We included three litters with different chemical composition and a subtropical forest soil. • N addition stimulated the magnitude of litter-induced PE across all litter types. • Only under N addition, the litter-induced PE was related to litter chemical composition. • The direction of PE varied over time, associated with different mechanisms. [ABSTRACT FROM AUTHOR]

Key message: The nitrogen (N) cycle is likely to accelerate under future climate change. Leaf δ15N enrichment factor is an indicator of N status in young Cunninghamia lanceolata (Lamb.) plantation ecosystems. Given that N dynamics across the plant-soil continuum respond more strongly to N addition during the dry season when N leaching is minimal, fertilization during this period represents an optimal strategy for improving soil fertility. Context: The effects of N deposition on N dynamics across the plant–soil continuum in subtropical regions are poorly understood. Aims: We investigated the effects of N addition on the N dynamics across the plant–soil continuum in young C. lanceolata plantations in different seasons as well as the effects of N addition on the soil microbial community. Methods: During the dry and wet seasons, we measured the concentrations of soil inorganic N, dissolved organic N in soil solution, leaf and root N concentrations, and stable isotope abundances, and soil microbial community characteristics. Results: Short-term N addition decreased the levels of inorganic N, dissolved organic N, and leaf N concentration in the dry season; root N concentration was significantly higher in the high N and low N addition plots. Irrespective of treatment, the NH4+/NO3− ratio was higher in the wet season than in the dry season. The δ15N enrichment factors of the leaf and root in our experiments were closer to zero for all N addition treatments. Redundancy analysis revealed that the variation in the soil microbial community had low correlation with pH. Conclusion: Nitrogen dynamics across the plant–soil continuum respond more strongly to N addition in the dry season. High N deposition in N-saturated subtropical forest soil may rapidly increase leaching, particularly during the wet season. Nutrients in roots are more sensitive to changes in soil nutrient availability than those in leaves. The microbial community is primarily regulated by nutrient availability in the soil rather than by pH. [ABSTRACT FROM AUTHOR]

Microorganisms play an integral role in driving phosphorus (P) transformation in forest soils; however, studies on soil P cycling and the molecular mechanisms of microbes activated in response to elevated nitrogen (N) deposition are limited. In this study, we conducted a multilevel field N enrichment experiment in a subtropical P-deficient Moso bamboo (Phyllostachys heterocycla) system to evaluate the microbial ecological traits of P transformation (e.g., organic P mineralization and inorganic P solubilization) over three consecutive years. N addition significantly decreased available and organic P levels in the soil and increased the microbial biomass C:P and N:P ratios, indicative of severe microbial P limitation. Consequently, N addition increased the absolute abundance of P starvation response regulation genes (phoU and phoR), which further induced an increase in organic P mineralization (phoN , phoD, appA), but not that of inorganic P solubilization genes (ppx and gcd). This suggests that microbes enhance P availability by organic P mineralization rather than inorganic P solubilization to ameliorate reduced P availability. Furthermore, a bacterial functional module (B_Mod#0) consisting of Proteobacteria, Actinobacteria , and Firmicutes accounted for more than 60% of the changes in the abundance of genes responsible for organic P-mineralization in the soil, suggesting that B_Mod#0 acts as a keystone phylotype in enhancing functional P-cycling potential. This study provides novel insights into microorganism-driven P cycling in P-deficient forest soils with N addition. • N addition reduced soil P availability and intensified microbial P limitation. • N addition activated microbial P starvation response and enhanced expression of P mineralization genes. • B_Mod#0 acts as a keystone phylotype in enhancing functional potential for organic P mineralization. • Organic P mineralization is more important than inorganic P desorption for microbial amelioration of P limitation. [ABSTRACT FROM AUTHOR]

• Prokaryotic communities were more intensely affected by soil heterogeneity than eukaryotes. • The complexity and stability of microbial networks are regulated by heterogeneous soils. • Soil heterogeneity had the same effect on the symbiosis pattern of microbial functions and taxa. • There are obvious differences in multiple prokaryotic functions but not eukaryotes. Although microbes are crucial in ecological cycling in forest soil, the response of the network structure and ecological functions of these microorganisms to soil heterogeneity remains elusive. Here, we analyzed the composition and co-occurrence network patterns of microorganisms in heterogeneous soil areas and evaluated their potential ecological functions, taking the scenic area (SA) and nature reserve (NR) of Wuyishan National Park as examples. Our results showed that the soil properties of SA and NR could almost be clustered separately, and soil heterogeneity between them has been found. Prokaryotic communities in both areas were also divided and showed higher similarities individually than those of eukaryotes. The prokaryotic community composition in both areas was mainly affected by pH and ammonia, while the eukaryotic community composition was mainly affected by total carbon and the carbon to nitrogen ratio. Both the microbial network and ecological function network in SA were more complex than those of NR, while those of NR were more stable than those of SA. The keystone taxa of pro- and eukaryotes with important ecological functions were enriched in SA and NR, respectively. Moreover, significant discrepancies between SA and NR were found in the prokaryotic functions related to nitrogen cycling, sulfur cycling, and compound degradation. Our study illuminated that the soil heterogeneity in subtropical areas changed microbial community diversity, interaction patterns, and keystone taxa composition, and might further affect their ecological functions. [ABSTRACT FROM AUTHOR]