Management practices regulate the response of Moso bamboo foliar stoichiometry to nitrogen deposition

Nitrogen fertilization practices alter microbial communities driven by clonal integration in Moso bamboo

Nitrogen (N) fertilization is crucial for maintaining plant productivity. Clonal plants can share resources between connected ramets through clonal integration influencing microbial communities and regulating soil biogeochemical cycling, especially in the rhizosphere. However, the effect of various N fertilization practices on microbial communities in the rhizosphere of clonal ramets remain unknown. In this study, clonal fragments of Moso bamboo (Phyllostachys edulis), consisting of a parent ramet, an offspring ramet, and an interconnecting rhizome, were established in the field. NH4NO3 solution was applied to the parent, offspring ramets or rhizomes to investigate the effect of fertilization practices on the structure and function of rhizosphere microbial communities. The differences in N availability, microbial biomass and community composition, and abundance of nitrifying genes among rhizosphere soils of ramets gradually decreased during the rapid growth of Moso bamboo, irrespective of fertilization practice. The soil N availability variation, particularly in NO3-, caused by fertilization practices altered the rhizosphere microbial community. Soil N availability and stable microbial biomass N in parent fertilization were the highest, being 9.0 % and 18.7 %, as well as 60.8 % and 90.4 % higher than rhizome and offspring fertilizations, respectively. The microbial network nodes and links in rhizome fertilization were 1.8 and 7.5 times higher than in parent and offspring fertilization, respectively. However, the diversity of bacterial community and abundance of nitrifying and denitrifying genes were the highest in offspring fertilization among three practices, which may be associated with increased N loss. Collectively, the rhizosphere microbial community characteristics depended on fertilization practices by altering the clonal integration of N in Moso bamboo. Parent and rhizome fertilization were favorable for N retention in plant-soil system and resulted in more stable microbial functions than offspring fertilization. Our findings provide new insights into precision fertilization for the sustainable Moso bamboo forest management.

Effects of on- and off-year management practices on the soil organic C fractions and microbial community in a Moso bamboo (Phyllostachys edulis) forest in subtropical China

On- and off-year management practices are usually adopted in Moso bamboo (Phyllostachys edulis) forests to achieve higher productivity. However, little is known about the effects of these management practices on soil C sequestration and microbial community structure. In the present study, soil nutrient content, organic C fractions, and bacterial and fungal communities were comparatively investigated in on- and off-year bamboo stands. The results showed that soil organic C (SOC), alkali-hydrolyzable N (AN), and available P (AP) in the on-year were significantly lower (p ≤ 0.05) than those in the off-year. Among the different soil organic C fractions, easily oxidizable organic C (EOC), microbial biomass C (MBC), Ca-bound SOC (Ca-SOC), and Fe/Al-bound SOC (Fe/Al-SOC) also had significantly higher contents in the off-year than in the on-year, with MBC and EOC decreasing by 56.3% and 24.5%, respectively, indicating that both active and passive soil organic C pools increased in the off-year. However, the alpha diversities of both soil bacteria and fungi were significantly lower in the off-year soils than in the on-year soils. The bacterial taxa Actinobacteria, Planctomycetes, WPS-2, Acidothermus, Candidatus_Solibacter, Burkholderia-Caballeronia-Paraburkholderia, and Candidatus_Xiphinematobacter were increased in off-year soils relative to on-year soils. Meanwhile, fungal taxa Ascomycota, Mortierella, Hypocrea, Cryptococcus, Clitopilus, and Ceratocystis were significantly increased in on-year soils. Soil pH, SOC, AP, MBC, EOC, and Ca-SOC were significantly correlated with bacterial and fungal communities, with soil pH being the most important driving factor for the shift in bacterial and fungal communities. Our findings showed that the studied bamboo forest possessed an inherent restorative ability in the off-year, which can reverse the soil nutrient and C depletion in the on-years and ensure soil fertility in the long term.

Nitrogen addition promotes early-stage and inhibits late-stage decomposition of fine roots in Pinus massoniana plantation

Increasing atmospheric nitrogen (N) deposition has a profound impact on the ecosystem functions and processes. Fine root decomposition is an important pathway for the reentry of nutrients into the soil. However, the effect of N addition on root decomposition and its potential mechanism is not well understood with respect to root branch orders. In this study, we conducted a 30-month decomposition experiment of fine roots under different concentrations of N addition treatments (0, 30, 60, and 90 kg N ha^-1 year^-1, respectively) in a typical Pinus massoniana plantation in the Three Gorges Reservoir Area of China. In the early stage of decomposition (0-18 months), N addition at all concentrations promoted the decomposition of fine roots, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were increased by 13.54%, 6.15% and 7.96% respectively. In the late stage of decomposition (18-30 months), high N addition inhibited the decomposition of fine root, and the average decomposition rates of order 1-2, order 3-4, order 5-6 fine roots were decreased by 58.35%, 35.43% and 47.56% respectively. At the same time, N addition promoted the release of lignin, carbon (C), N, and phosphorus (P) in the early-stage, whereas high N addition inhibited the release of lignin, C, N, and the activities of lignin-degrading enzyme (peroxidase and polyphenol oxidase) in the late-stage. The decomposition constant (k) was significantly correlated with the initial chemical quality of the fine roots and lignin-degrading enzyme activities. The higher-order (order 3-4 and order 5-6) fine roots decomposed faster than lower-order (order 1-2) fine roots due to higher initial cellulose, starch, sugar, C concentrations and higher C/N, C/P, lignin/N ratios and lower N, P concentrations. In addition, low N (30 kg N ha^-1 year^-1) treatments decreased soil organic matter content, whereas high N (90 kg N ha^-1 year^-1) treatment had the opposite effect. All the N treatments reduced soil pH and total P content, indicating that increased N deposition may led to soil acidification. Our findings indicated that the effect of N addition on decomposition varied with the decomposition stages. The decomposition difference between the lower-order and higher-order fine roots were controlled strongly by the initial chemical quality of the fine roots. This study provides new insights into understanding and predicting possible changes in plant root decomposition and soil properties in the future atmospheric N deposition increase scenarios.

Biochar Combined with Nitrogen Alters Rhizosphere Soil Nutrients and Microbial Communities, and Promotes Growth of Moso Bamboo Seedlings

Biochar, a soil conditioner, has the potential to improve soil properties and plant productivity. However, in forestry planting, especially in subtropical moso bamboo forests, the response of seedling growth to biochar addition is still not well known. We conducted a comprehensive factorial experiment with biochar and nitrogen (N) addition as factors (no biochar and no N addition; 0.64% biochar + 0% NH4NO3; 1.28% biochar + 0% NH4NO3; T3: 0% biochar + 1.28% NH4NO3; T4: 0.64% biochar + 1.28% NH4NO3; T5: 1.28% biochar + 1.28% NH4NO3) to study their effects on moso bamboo seedling growth, rhizosphere soil nutrient contents, and enzymatic activity. Our results indicate that applying biochar without N did not promote the growth of moso bamboo seedlings (biomass of leaves and branches) but increased soil nutrient content and affected soil-enzyme activity. The combined application of biochar and N significantly increased the leaf and branch biomass of moso bamboo seedlings and soil nutrient content and affected soil-enzyme activity. In conclusion, biochar should be mixed with an adequate amount of N for its application in subtropical moso bamboo forests to promote seedling growth and improve economic benefits.

Biochar Amendment Alters the Nutrient-Use Strategy of Moso Bamboo Under N Additions

Nutrient resorption can affect plant growth, litter decomposition, and nutrient cycling. Although the effects of nitrogen (N) and biochar fertilizers on soil nutrient concentrations and plant nutrient uptake have been studied, an understanding of how combined applications of N and biochar affect plant nutrient resorption in plantations is lacking. In this study, we applied N (0, 30, 60, and 90 kg N ha^-1 yr^-1 defined as N0, N30, N60, and N90, respectively) and biochar (0, 20, and 40 t biochar ha^-1 defined as BC0, BC20, and BC40, respectively) to the soil of a Moso bamboo plantation. We investigated the effects of these treatments on N and phosphorus (P) resorption by young and mature bamboo plants, as well as the relationships between nutrient resorption and leaf and soil nutrient concentrations. Young bamboo showed significantly greater foliar N resorption efficiency (NRE) and P resorption efficiency (PRE) than mature bamboo. N addition alone significantly increased the N resorption proficiency (NRP) and P resorption proficiency (PRP) but significantly decreased the NRE and PRE of both young and mature bamboo. In both the N-free and N-addition treatments, biochar amendments significantly reduced the foliar NRE and PRE of young bamboo but had the opposite effect on mature bamboo. Foliar NRE and PRE were significantly negatively correlated with fresh leaf N and P concentrations and soil total P concentration but significantly positively correlated with soil pH. Our findings suggest that N addition inhibits plant nutrient resorption and alters the nutrient-use strategy of young and mature bamboo from "conservative consumption" to "resource spending." Furthermore, biochar amendment enhanced the negative effect of N addition on nutrient resorption in young bamboo but reduced the negative effect on that of mature bamboo under N-addition treatments. This study provides new insights into the combined effects of N and biochar on the nutrient resorption of Moso bamboo and may assist in improving fertilization strategies in Moso bamboo plantations.

Effects of Different Management Practices on the Increase in Phytolith-Occluded Carbon in Moso Bamboo Forests

Phytolith-occluded carbon (PhytOC), a promising long-term biogeochemical carbon sequestration mode, plays a crucial role in the global carbon cycle and the regulation of atmospheric CO₂. Previous studies mostly focused on the estimation of the content and storage of PhytOC, while it remains unclear about how the management practices affect the PhytOC content and whether it varies with stand age. Moso bamboo (Phyllostachys heterocycla var. pubescens) has a great potential in carbon sequestration and is rich in PhytOC. Here, we selected four management treatments, including control (CK), compound fertilization (CF), silicon (Si) fertilization (SiF) (monosilicic acid can form phytoliths through silicification), and cut to investigate the variation of phytoliths and PhytOC contents in soil, leaves, and litters, and their storage in Moso bamboo forests. In soil, the SiF fertilizer treatment significantly (P < 0.05) increased phytolith content, PhytOC content, and storage compared to CK, while there were no significant differences between the treatments of CF and cut. In leaf, compared with CK, phytolith content of the second-degree leaves under SiF and the first-degree leaves under cut treatment significantly increased, and the three treatments significantly increased PhytOC storage for leaves with three age classes. In litter, the phytolith and PhytOC contents under the three treatments were not significantly different from that under the CK treatment. The PhytOC storage increased by 19.33% under SiF treatment, but significantly decreased by 40.63% under the CF treatment. For the entire Moso bamboo forest ecosystems, PhytOC storage of all the three management treatments increased compared with CK, with the largest increase by 102% under the SiF treatment. The effects of management practices on the accumulation of PhytOC varied with age. Our study implied that Si fertilization has a greater potential to significantly promote the capacity of sequestration of carbon in Moso bamboo forests.

Nitrogen form plays an important role in the growth of moso bamboo (Phyllostachys edulis) seedlings

Background

This study aimed to gain an understanding of the growth response of Phyllostachys edulis (moso bamboo) seedlings to nitrogen (N) and potassium (K) to benefit nutrient management practices and the design of proper fertilizer in nursery cultivation.

Methods

An orthogonal array L₈(4×2⁴) was used to study the effects of N forms (NH₄⁺, NO₃⁻), N concentrations (8, 32 mmol/L), and K⁺concentrations (0, 0.5, 1.5, 3 mmol/L) on seedling height, leaf number, chlorophyll content (SPAD value), biomass, root systems, and N content of P. edulis seedlings. Plants were grown in vermiculite under controlled greenhouse conditions.

Results

Our study showed that N form played a significant role in the overall performance of P. edulis seedlings, followed by the effect of N and K⁺ concentrations. Among the N forms, NH₄⁺ significantly improved the growth of P. edulis seedlings compared with NO₃⁻. Seedling height, leaf number, chlorophyll SPAD value, biomass, and root system architecture (root length, root surface area, root volume, and root tips) were greater with 8 mmol/L of NH₄⁺ treatments than with 32 mmol/L of NH₄⁺treatments, whereas root diameter and N content of P. edulis seedlings were higher with 32 mmol/L of NH₄⁺ than with 8 mmol/L of NH₄⁺. K displayed inconsistent effects on the growth of P. edulis seedlings. Specifically, seedling height, leaf number, biomass and root volume increased when the K⁺ concentration was increased from 0 to 0.5 mmol/L, followed by a decrease when the K⁺ concentration was further increased from 0.5 to 3 mmol/L. Root average diameter of the seedlings was the highest with a K⁺ concentration of 1.5 mmol/L, and K had some inhibitory effects on the chlorophyll SPAD value of the seedlings. P. edulis seedlings performed well with 8 mmol/L NH₄⁺and further tolerated a higher concentration of both NH₄⁺ and NO₃⁻, although excessive N could inhibit seedling growth. A lower concertation of K (≤ 0.5 mmol/L) promoted seedling growth and increasing K⁺ concentration in the nutrient solution did not alleviate the inhibitory effect of high N on the growth of P. edulis seedlings. Therefore, NH₄⁺nitrogen as the main form of N fertilizer, together with a low concertation of K⁺, should be supplied in the cultivation and nutrient management practices of moso bamboo.

Combined application of biochar and N increased temperature sensitivity of soil respiration but still decreased the soil CO2 emissions in moso bamboo plantations

Biochar addition to soil is increasing worldwide, the effect of combined application of biochar and nitrogen (N) fertilizer on soil respiration is still unknown. Understanding of the interactive effects of biochar and N fertilizer addition on temperature sensitivity of soil respiration and temporal dynamics of soil CO₂ emissions in forest ecosystems remains limited. We conducted a full factorial experiment with biochar (B₀, B₁ and B₂ with 0, 5 and 20 t·ha^-1, respectively) and N fertilizer addition (N₀ and N₁ with 0 and 50 kg·ha^-1 NH₄NO₃, respectively) as factors, to study their effects on soil respiration rate, temperature sensitivity (Q₁₀), soil available nutrients, and their relations in moso bamboo plantations in subtropical China from April 2014 to April 2016. We found that, irrespective of biochar addition rate, N fertilization increased Q₁₀ on the one hand, and irrespective of N fertilization rate, lower application rate of biochar resulted in a higher Q₁₀, on the other hand. In spite of increased Q₁₀, combined application of biochar and N decreased soil respiration rate in both growing season and non-growing season, as well as the annual cumulative soil CO₂ emissions. Annual cumulative soil CO₂ emissions were found to be significantly positively correlated with soil total nitrogen (STN) (p = 0.028) in 0-10 cm soil layer, and with soil ammonium (NH₄⁺) (p = 0.000) and soil microbial biomass carbon (MBC) (p = 0.000) in both 0-10 cm and 10-20 cm soil layer. The present study suggests that the combined application of biochar and N fertilizer can be widely used in subtropical forest ecosystems where soil N is limited, because it increases soil fertility and, at the same time, decreases soil CO₂ emissions.

Effects of nitrogen deposition and phosphorus addition on arbuscular mycorrhizal fungi of Chinese fir (Cunninghamia lanceolata)

Nitrogen (N) deposition is a key factor that affects terrestrial biogeochemical cycles with a growing trend, especially in the southeast region of China, where shortage of available phosphorus (P) is particularly acute and P has become a major factor limiting plant growth and productivity. Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with plants, and play an important role in enhancing plant stress resistance. However, the response of AMF to the combined effects of N deposition and P additions is poorly understood. Thus, in this study, a field experiment was conducted in 10-year Chinese fir forests to estimate the effects of simulated nitrogen (N) deposition (low-N, 30 kg ha-1 year-1 and high-N, 60 kg ha-1 year-1) and phosphorus (P) addition treatments (low-P, 20 mg kg-1 and high-P, 40 mg kg-1) on AMF since April 2017, which was reflected in AMF root colonization rates and spore density of rhizosphere soil. Our results showed that N deposition significantly decreased AMF root colonization rates and spore density. In N-free plots, P addition significantly decreased AMF root colonization rates, but did not significantly alter spore density. In low-N plots, colonization rates significantly decreased under low P addition, but significantly increased under high P addition, and spore density exhibited a significant decline under high P additions. In high-N plots, colonization rates and spore density significantly increased under P additions. Interactive effects of simulated N deposition and P addition on both colonization rates and spore density were significant. Moderate N deposition or P addition can weaken the symbiotic relationship between plants and AMF, significantly reducing AMF colonization rates and inhibiting spore production. However, a moderate addition of P greatly enhances spore yield. In the case of interactive effects, the AMF colonization rates and spore density are affected by the relative content of N and P in the soil.

Nitrogen addition increased CO2 uptake more than non-CO2 greenhouse gases emissions in a Moso bamboo forest

Atmospheric nitrogen (N) deposition affects the greenhouse gas (GHG) balance of ecosystems through the net atmospheric CO₂ exchange and the emission of non-CO₂ GHGs (CH₄ and N₂O). We quantified the effects of N deposition on biomass increment, soil organic carbon (SOC), and N₂O and CH₄ fluxes and, ultimately, the net GHG budget at ecosystem level of a Moso bamboo forest in China. Nitrogen addition significantly increased woody biomass increment and SOC decomposition, increased N₂O emission, and reduced soil CH₄ uptake. Despite higher N₂O and CH₄ fluxes, the ecosystem remained a net GHG sink of 26.8 to 29.4 megagrams of CO₂ equivalent hectare^-1 year^-1 after 4 years of N addition against 22.7 hectare^-1 year^-1 without N addition. The total net carbon benefits induced by atmospheric N deposition at current rates of 30 kilograms of N hectare^-1 year^-1 over Moso bamboo forests across China were estimated to be of 23.8 teragrams of CO₂ equivalent year^-1.

Photosynthesis, Ecological Stoichiometry, and Non-Structural Carbohydrate Response to Simulated Nitrogen Deposition and Phosphorus Addition in Chinese Fir Forests

Phosphorus (P) deficiency in soil affects plant growth and primary production. Accelerated nitrogen (N) deposition can cause ecological carbon:nitrogen:phosphorus (C:N:P) stoichiometry imbalance and increase the degree of relative P deficiency in the soil. However, it remains unclear how N deposition affects P uptake and C:N:P stoichiometry in coniferous timber forests, and whether P addition diminishes the effect of N-induced P limitation on plant growth. From January 2017 to April 2018, we investigated the effects of nine different N and P addition treatments on 10-year old trees of Chinese fir, Cunninghamia lanceolata (Lamb.) Hook. Our results demonstrated that N and P additions at a high concentration could improve the photosynthetic capacity in Chinese fir by increasing the chlorophyll content and stimulating the photosynthesis activity. The C:N:P stoichiometry varied with the season under different N and P addition treatments, indicating that N addition at a moderate concentration could diminish the effect of the P limitation on the growth of Chinese fir. The soluble sugar content in the leaves displayed more stable seasonal variations, compared with those of starch. However, the non-structural carbohydrate (NSC) content in the leaves did not vary with the season under both P and N addition treatment. The data suggested that N and P combination treatment at moderate concentrations promoted carbon assimilation by accelerating the photosynthetic rate. Thus, our results provide new insights into the adaptation mechanisms of coniferous timber forest ecosystems to the effects of N deposition under P deficiency and can help to estimate the ecological effects of environmental changes linked to human management practices.

Nitrogen Addition Affects Soil Respiration Primarily through Changes in Microbial Community Structure and Biomass in a Subtropical Natural Forest

Forest soil respiration plays an important role in global carbon (C) cycling. Owing to the high degree of C and nitrogen (N) cycle coupling, N deposition rates may greatly influence forest soil respiration, and possibly even global C cycling. Soil microbes play a crucial role in regulating the biosphere–atmosphere C exchange; however, how microbes respond to N addition remains uncertain. To better understand this process, the experiment was performed in the Castanopsis kawakamii Hayata Nature Reserve, in the subtropical zone of China. Treatments involved applying different levels of N (0, 40, and 80 kg ha−2 year−1) over a three-year period (January 2013–December 2015) to explore how soil physicochemical properties, respiration rate, phospholipid fatty acid (PLFA) concentration, and solid state 13C nuclear magnetic resonance responded to various N addition rate. Results showed that high levels of N addition significantly decreased soil respiration; however, low levels of N addition significantly increased soil respiration. High levels of N reduced soil pH and enhanced P and C co-limitation of microorganisms, leading to significant reductions in total PLFA and changes in the structure of microbial communities. Significant linear relationships were observed between annual cumulative respiration and the concentration of microbial biomass (total PLFA, gram-positive bacteria (G+), gram-negative bacteria (G−), total bacteria, and fungi) and the microbial community structure (G+: G− ratio). Taken together, increasing N deposition changed microbial community structure and suppressed microbial biomass, ultimately leading to recalcitrant C accumulation and soil C emissions decrease in subtropical forest.

Ecological stoichiometry of nitrogen and phosphorus in Moso bamboo (Phyllostachys edulis) during the explosive growth period of new emergent shoots

The ecological stoichiometry of Moso bamboo (Phyllostachys edulis) during the "explosive growth period" (EGP) remains unknown. In a previous study, we showed that the carbon (C) required by shoots during the EGP is derived from attached mature bamboos. In this study, we attempted to answer the following two questions: (1) Is the nitrogen (N) and phosphorus (P) required by shoots during the EGP also derived from attached mature bamboos? (2) Is the ecological stoichiometry of Moso bamboo during the EGP consistent with the growth rate hypothesis (GRH)? We simultaneously investigated changes in the N and P concentrations and N:P ratios of shoots (young bamboos) and attached mature bamboo over an 11-month period. During the EGP of Moso bamboo shoots (April 15-May 29), N and P concentrations in the shoots declined markedly because of the dilution of biomass and the transport to the germinated leaves and branches, and the N:P ratio remained at a low level. The significant correlations between relative height and biomass growth rates and the concentrations of N and P and N:P ratios during the EGP were consistent with the GRH. To meet the needs of "explosive growth," N was presumed to be transferred from the branches and rhizomes of attached mature bamboos to the shoots via underground rhizomes, while P likely came from mature bamboo leaves and branches. After the emergence of the branches and leaves of young bamboo: (1) the N concentration of the new leaves initially decreased and then increased, (2) P concentration exhibited a marked decrease, (3) and N:P ratio gradually increased. Our findings regarding the N:P ratio of shoots (young bamboos) during the EGP are consistent with the GRH, and we surmise that mature bamboo supplies N and P to attached young shoots via underground rhizomes.

Nitrogen Deposition Enhances Photosynthesis in Moso Bamboo but Increases Susceptibility to Other Stress Factors

Atmospheric nitrogen (N) deposition can increase the susceptibility of vascular plants to other stresses, but the physiological basis of such a response remains poorly understood. This study was designed to clarify the physiological mechanisms and to evaluate bioindicators of N deposition impact on vascular plants. We evaluate multiple physiological responses to ~4 years of simulated additional N deposition (30-90 kg N ha-1 year-1) on three age-classes (1a, 3a, and 5a) of Moso bamboo. A saturating response to the additional N deposition was found both in foliar N concentration and in Pn. However, 3- and 5-year-old bamboo seemed to be less tolerant to extremely high N deposition than 1-year-old bamboo since they were saturated at a lower N addition. Furthermore, C/N/P stoichiometric ratios were very sensitive to N deposition in all three-age classes of bamboo, but the responses to N deposition in the various age-classes were diverse. We also found that the highest additional N deposition suppressed stomatal conductance and transpiration rate, suggesting an induced water stress. The stress induced by the high N load was also seen in photochemistry, where it reduced potential and actual photosynthetic use of light energy, diminished photo-protection capacity, and increased risk of the photo-damage. High additional N deposition contributed to a decrease in the foliar soluble protein contents and to an increase in the peroxidase activity (POD). Our study suggested, for the first time, that although the photosynthetic rate was enhanced by the increased N deposition in Moso bamboo, long-term high N load causes negative effects, such as damage to photosystem II. In Moso bamboo photochemical parameters are more sensitive to N deposition than photosynthetic rate or foliar N concentration. Furthermore, plant age should be taken into account when assessing plants' susceptibility to changes in global change drivers, such as N deposition. These findings facilitate the revealing of the risks potentially caused to vascular plants by increased N deposition before any visible symptoms of injury are seen.

Nitrogen deposition and management practices increase soil microbial biomass carbon but decrease diversity in Moso bamboo plantations

Because microbial communities play a key role in carbon (C) and nitrogen (N) cycling, changes in the soil microbial community may directly affect ecosystem functioning. However, the effects of N deposition and management practices on soil microbes are still poorly understood. We studied the effects of these two factors on soil microbial biomass carbon (MBC) and community composition in Moso bamboo plantations using high-throughput sequencing of the 16S rRNA gene. Plantations under conventional (CM) or intensive management (IM) were subjected to one of four N treatments for 30 months. IM and N addition, both separately and in combination, significantly increased soil MBC while decreasing bacterial diversity. However, increases in soil MBC were inhibited when N addition exceeded 60 kg N∙ha⁻¹∙yr⁻¹. IM increased the relative abundances of Actinobacteria and Crenarchaeota but decreased that of Acidobacteria. N addition increased the relative abundances of Acidobacteria, Crenarchaeota, and Actinobacteria but decreased that of Proteobacteria. Soil bacterial diversity was significantly related to soil pH, C/N ratio, and nitrogen and available phosphorus content. Management practices exerted a greater influence over regulation of the soil MBC and microbial diversity compared to that of N deposition in Moso bamboo plantations.