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As the interface between plants and soil, the response of the rhizosphere to nitrogen deposition is particularly important. The rhizosphere responses to nitrogen deposition are not consistent. Here, four levels of nitrogen addition treatments were applied in boreal forests of China for 8 years: control, low nitrogen, medium nitrogen, and high nitrogen. We analyzed the soil properties and microbial communities of rhizosphere and bulk soils under different nitrogen application levels and assessed the relationship between the main species and environmental factors. The results showed that long-term nitrogen addition significantly reduced the content of total carbon in the soil and increased the soil microbial biomass nitrogen in the rhizosphere. The total carbon content in the rhizosphere under high nitrogen was 40.79 g * [kg.sup.-1], which was significantly lower than that in the control (51.82 g * [kg.sup.-1]). The diversity of the rhizosphere and bulk soil fungal communities had different significant responses to nitrogen addition. Some specific microbial taxa could be used as rhizosphere bacterial biomarkers under different nitrogen treatments. The soil microbial biomass nitrogen was the significant environmental variable affecting bacterial species variation in the rhizosphere. Nitrogen addition will change the diversity of the rhizosphere microbial community by changing soil microenvironmental factors. Key words: rhizosphere, soil microbiome, rhizosphere effects, nitrogen deposition, boreal forest En tant qu'interface entre les plantes et le sol, la reponse de la rhizosphere au depot d'azote est particulierement importante. Les reponses de la rhizosphere au depot d'azote ne sont pas coherentes. Ici, quatre niveaux de traitements d'ajout d'azote ont ete appliques dans des forets boreales de Chine pendant 8 ans : controle, faible azote, azote moyen et fort azote. Nous avons analyse les proprietes du sol et les communautes microbiennes de la rhizosphere et des sols en vrac sous differents niveaux d'application d'azote et evalue la relation entre les principales especes et les facteurs environnementaux. Les resultats ont montre que l'ajout d'azote a long terme a reduit de maniere significative la teneur en carbone total dans le sol et a augmente l'azote de la biomasse microbienne du sol dans la rhizosphere. Le contenu en carbone total dans la rhizosphere sous une forte dose d'azote etait de 40,79 g * [kg.sup.-1], ce qui etait significativement inferieur a celui du controle (51,82 g * [kg.sup.-1]). La diversite des communautes fongiques de la rhizosphere et du sol en general a eu des reponses differentes et significatives a l'ajout d'azote. Certains taxons microbiens specifiques pourraient etre utilises comme biomarqueurs bacteriens de la rhizosphere sous differents traitements azotes. L'azote de la biomasse microbienne du sol etait la variable environnementale significative affectant la variation des especes bacteriennes dans la rhizosphere. L'ajout d'azote modifiera la diversite de la communaute microbienne de la rhizosphere en changeant les facteurs micro-environnementaux du sol. [Traduit par la Redaction] Mots-cles: rhizosphere, microbiome du sol, effets de la rhizosphere, depot d'azote, foret boreale, 1. Introduction Since the Industrial Revolution, the emission of reactive nitrogen in the atmosphere has increased sharply (Vitousek et al. 1997; Galloway et al. 2008). The increase in atmospheric nitrogen [...]

We conducted a short-term field hydroponic 15N labeling experiment to study the effects of different nitrogen (N) addition treatment on the N uptake preference and rate of plant fine roots in a temperate old growth forest in 2018. The results indicated that the N preference of dominant tree species for different N chemical forms was not influenced by the N addition, with the N acquisition pattern being ammonium > nitrate > glycine. However, N addition altered the plant's N uptake rates. Under low N treatment, the uptake rates of glycine for three target tree species significantly increased. Both low and medium N additions significantly enhanced the NH4–N uptake rate, but had little impact on the NO3–N uptake rate. Conversely, high N addition exerted negative effects on NO3–N and NH4–N uptake rate. Different tree species may flexibly adapt to new environmental conditions by adapting to their root morphology and the relationship between plant growth and N uptake. N addition has pronounced effects on N uptake rate and root morphology traits of dominant tree species. Overall, this study contributes to a deeper understanding of the response of N uptake patterns in temperate forests to long-term N addition. [ABSTRACT FROM AUTHOR]

Background: Given the ubiquitous nature of mycorrhizal symbioses, different symbiotic fungi have obvious differences in structure and function, which may affect associated tree aboveground and belowground C allocation dynamics. However, the mechanisms underlying tree aboveground and belowground C allocation and its response to symbiotic mycorrhizal types and other factors (e.g., resource availability) remain poorly understood. Results: We used forest inventory data to explore the potential mechanism of tree aboveground and belowground C allocation patterns in Northeast China. Our results showed that tree-fungal symbioses were related to the patterns of tree C allocation. The ratio of aboveground to belowground C pool was significantly higher in ectomycorrhizal (EM)-associated trees than that in arbuscular mycorrhizal (AM)-associated trees. Symbiotic mycorrhizal types were associated with the responses of tree aboveground and belowground C allocation to different factors, such as mean annual precipitation (MAP) and mean annual temperature (MAT). Almost all factors significantly increased aboveground C allocation in AM-associated trees but significantly decreased it in EM-associated trees. Moreover, after controlling the other factors, the effects of climate factors (MAT and MAP) on the C allocation of AM- and EM-associated trees were similar. Increases in MAT and MAP significantly increased belowground and aboveground C allocation, respectively. Conclusions: Our results demonstrate symbiotic mycorrhizal types play an important role in controlling tree aboveground and belowground C allocation and dynamics. [ABSTRACT FROM AUTHOR]

Background: Natural abundance of carbon (C) and nitrogen (N) stable isotope ratios (δ13C and δ15N) has been used to indicate the state and cycle of ecosystem C and N. However, it is still unclear how C and N cycle of boreal forests respond to the N deposition. Results: We conducted an 8-year continuous N addition field experiment in a Larix gmelinii forest in Greater Khingan Mountains, Northeast China. Four N treatments (0, 25, 50, 75 kg N ha−1 year−1) were built. The effects of N addition on the δ13C and δ15N of needle, branch, bark, and fine root of Larix gmelinii and soil were studied. The result of the balance between the N input and output flux showed that N addition significantly increased the δ15N in each organ of Larix gmelinii, but did not change the δ15N of soil. We also found that the N absorption by needles of Larix gmelinii could increase the needle photosynthesis rate and δ13C by increasing carboxylation, but N addition had no significant effect on the δ13C of soil and other organs. In addition, both the soil δ15N and δ13C increased with the soil depth. Conclusions: Long-term N addition may lead to more open C and N cycles and further affect plant nutrient acquisition strategies in boreal forest ecosystems. [ABSTRACT FROM AUTHOR]