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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]

In early spring, because the tree and shrub layers are still dormant, the absorption of nutrients by herbs is the key factor to maintain nutrients in temperate forest ecosystems, but it is not clear whether climate change will change the nutrient uptake strategy of herbs. Therefore, we measured the biomass, fine root morphology, and stoichiometry of five dominant herbs in response to environmental changes in early spring in a temperate forest in northeastern China. The results showed that (1) Fine root morphology had strong plasticity. Under nitrogen addition treatment, the herbs tended to change the fine root length to absorb soil nutrients and water. (2) Under drought treatment, the herbs distributed more biomass to the belowground. Maintaining a higher root-shoot ratio might increase the relative supply of water to the herbs. (3) Nitrogen addition significantly decreased the belowground biomass allocation, but increased the ratio of belowground nitrogen to phosphorus (N:P) and the root metabolic activity. (4) Ephemeral herbaceous fine root morphology was more sensitive to water and nitrogen than other herbaceous plants. Collectively, in the context of climate change, early spring herbs may respond to environmental pressure through self-regulation and change growth strategies in temperate forest ecosystems. [ABSTRACT FROM AUTHOR]

In order to study the response of fine root production (FRP), mortality (FRM) and turnover (FRT) to nitrogen (N) addition, we have conducted 12 years of continuous N addition experiments in the natural secondary forest in Northeast China. According to the local N deposition, three N treatments were set up. The response of FRP, FRM and FRT to N addition during the growing season was studied. The results showed that N addition would lead to phosphorus (P) limitation, and fine roots could increase the absorption of N and P by increasing their diameter. The increase in the diameter of fine roots led to a decrease in the FRT, and the soil layer also affected the FRT. Nitrogen addition increased the FRP and FRM in all soil layers. Nitrogen addition did not change the seasonal variation of FRP and FRM. The highest value of FRP occurred in May, and the lowest value of FRM occurred in August. Nitrogen addition increased the total number (TNLR) and surface area (TSALR) of live fine root in all soil layers. The TNLR and TSALR decreased with the deepening of soil layer. Collectively, fine roots may respond to environmental stress through self-regulation and changing growth strategies. [ABSTRACT FROM AUTHOR]

Fungi play an important role in mediating soil functioning and plant nutrients absorption. Although nitrogen (N) addition and reduced precipitation can affect fungal community composition, the response of fungal taxonomic and functional groups to changes in soil N and water availability is still unclear. Here, we established a long-term field manipulations experiment of N addition and throughfall exclusion to investigate fungal communities' response to N addition and reduced precipitation. Illumina Sequencing of ITS amplicons was used to examine soil fungal communities in winter and summer. Results showed that N addition, reduced precipitation and their combined effect significantly altered the soil fungal community composition. Basidiomycetes associated with humus decomposition dominated in ambient soil and Ascomycetes abundance dramatically increased and dominated in N addition in both winter and summer. Reduced precipitation and the combined effect significantly increased fungal richness and diversity. Moreover, the relative abundance of mycorrhizal and saprotroph fungal communities responded positively to reduced precipitation. Our results indicate reduced precipitation alleviated the competition between fungi, while N addition could reduce the rate decomposition of humus. [ABSTRACT FROM AUTHOR]