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Soil ectomycorrhizal and saprotrophic fungi play pivotal roles in plant performance and ecosystem functioning. However, the effects of forest secondary succession on their abundance, diversity, and community structure remain unclear. We examined ectomycorrhizal and saprotrophic communities (Illumina Sequencing and FUNGuild database) in five forest secondary successional stages (20-, 32-, 47-, 61-, and > 200-year-old stands). Our results showed that ectomycorrhizal and saprotrophic communities varied with successional stages. The relative abundance of ectomycorrhizal fungi decreased from early to late stages but the relative abundance of saprotrophic fungi increased. In contrast to the abundance, diversity of ectomycorrhizal fungal communities increased with the succession, while saprotrophic fungal diversity dropped in the early successional stages and recovered later stages. Furthermore, there were significant differences in the community structure of ectomycorrhizal and saprotrophic fungi among different successional stages, and the main driving factor (tree productivity) of the shifts in two community structures was similar. Interestingly, there was a significant negative correlation between the variations in relative abundance and community structure of ectomycorrhizal and saprotrophic fungi along the secondary succession, which implied the interactions between ectomycorrhizal and saprotrophic fungi during the successional process. These results indicated that the secondary succession might not only increase decompositions of organic matter by increasing saprotrophic fungal abundance, but also stimulate the return of saprotrophic fungal diversity, which may be beneficial to plant function and ecosystem stability. [ABSTRACT FROM AUTHOR]

Soil extracellular enzymes play a key role in mediating the degradation of soil organic matter, but little is understood as to how the pattern of soil extracellular enzymes could be altered by nitrogen (N) addition. In this study, the effects of N addition (started from 2006, four treatments: control, 0 g N·m–2·yr–1; low N addition, 2.5 g N·m–2·yr–1; high N addition, 5.0 g N·m–2·yr–1) on soil extracellular enzymes and microbial biomass in a natural secondary forest of Northeastern China. The results showed that the activity of urease, sucrase, peroxidase and N-acetyl-β-D-glucosidase decreased with N addition, and the activity of acid phosphatase and leucine aminopeptidase increased significantly with N addition. Soil total N, temperature at 5 cm soil depth, pH value, microbial biomass carbon and microbial biomass N were the key factors affecting soil enzyme activity. In summary, the enzyme activity related to soil organic matter degradation shows a decreasing trend under N addition. The results suggest that the increase in N deposition will slow down the degradation of soil organic matter in natural secondary forest, which is more conducive to the accumulation of organic matter in the soil. [ABSTRACT FROM AUTHOR]

Secondary forest succession after clear‐cutting is one of the foremost ecosystem restoration strategies, while soil microbes play essential roles in the processes by modulating nutrient cycling. However, the assembly processes and driving factors of soil microbial communities across secondary forest succession remain unclear. Here, we studied the assembly processes of soil microbial communities and examined shifts in soil microbial community‐associated functional dynamics across secondary forest succession. Our results showed that the stochastic process was more important in shaping bacterial community assembly throughout the successional process [modified stochasticity ratio (MST) > 50%], while the fungal community assembly was initially governed by deterministic processes (MST < 50%), but there was a progressive increase in stochastic selection as succession proceeded. Soil organic carbon and pH were principal factors for the explanation of changes in the bacterial community structure (total explained 43% change), and tree richness and productivity were principal factors for the explanation of shifts in the fungal community structure (total explained 17% change). The relative abundance of nitrogen transformation and saprotroph functional groups increased gradually with succession, whereas ectomycorrhizal fungi significantly declined. The results suggested that microbial community succession might accelerate the soil carbon and nitrogen turnover rates. Used together, the mechanisms shaping fungal and bacterial community structure are different in secondary forest succession and highlight that those fungi and bacteria are primarily controlled by plant traits and soil properties, respectively. Variations in microbial functional groups provide new insight into the mechanisms underlying the soil microbe‐driven soil nutrient cycles during secondary forest succession. [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]

Elevated nitrogen (N) deposition is changing soil communities around the world and will have unknown consequences for terrestrial ecosystem functions. In this study, we investigated a field experiment that lasted for 13 years to explore the effect of simulated N deposition and seasonal variations on the soil faunal community structure in a temperate natural secondary forest. The experimental design included a control group (0 kg N ha−1 yr−1, CK), low N addition (25 kg N ha−1 yr−1, LN), and high N addition (50 kg N ha−1 yr−1, HN). The results showed that long-term high N addition reduced the soil pH, C/N ratio, and microbial biomass carbon (MBC) and increased the total phosphorus. The soil faunal community structure after high N addition was significantly different from those after the CK and low N addition treatments. The overall trend was that abundance and richness increased under low N addition and decreased under high N addition. Further analysis showed that the abundance of omnivores and detritivores was lowest after high N addition, significantly less than the CK and low N addition. The interaction of N addition and seasonal dynamics had a significant impact on herbivores. We found that these changes were driven by differences in ecological strategies such as food and environmental preferences. Furthermore, temperature, moisture, nutrients, and pH in the soil environment were the key factors driving ecological strategies and environmental factors. Seasonal variations significantly affected the soil faunal community structure, showing the highest abundance, richness, diversity, and functional group abundance and richness of the soil faunal community in September. Nitrogen addition and seasonal dynamics significantly affected the abundance and richness of soil fauna by changing soil nutrient concentrations, MBC, and plant diversity. Our study showed that long-term high N addition reduced the abundance and functional group abundance of the soil fauna in natural secondary forests, while low N addition had a positive effect on soil faunal community structure. Collectively, the results suggest that the seasonal balance of soil fauna is affected after long-term N addition, which increases the seasonal sensitivity of soil fauna. [ABSTRACT FROM AUTHOR]

The continuous increase in global atmospheric nitrogen deposition may change the stoichiometric balance of temperate forest plants and affect the nutrient absorption of plants and the carbon and nitrogen cycle of forests. Leaf, fine root and other ephemeral tissues are very sensitive to nutrient changes. However, it has been not clear whether nitrogen addition will affect the nutrient uptake strategies of plant leaves and fine roots. In order to explore the effects of long-term nitrogen addition on nutrient absorption and distribution of main dominant tree species in temperate secondary forests and to cope with the sustainable development of forests under the background of increasing atmospheric nitrogen deposition in the future, we conducted a 12-year continuous nitrogen addition experiment in the natural secondary forest in Changbai Mountains of Northeast China. Responses of fine root morphology, leaf nutrient resorption, fine root exudates and stoichiometry of Populus davidiana and Betula platyphylla to nitrogen addition were studied. Our study found that (1) nitrogen addition could lead to phosphorus limitation, and high nitrogen addition treatment significantly reduced the nitrogen resorption efficiency of B. platyphylla and P. davidiana and then increased the phosphorus resorption efficiency. (2) Nitrogen addition promoted the metabolism and activity of B. platyphylla fine root, which was more inclined to transport and store, while P. davidiana fine root was more inclined to capture and absorb nutrients. (3) Nitrogen addition increased the secretion rate of fine root exudates carbon and decreased that of fine root exudates nitrogen. The release of root exudates from roots to soil may stimulate soil microbial activity and nutrient availability. These different results indicate that both P. davidiana and B. platyphylla are attempting to improve resource acquisition under nitrogen deposition change, which will effectively change the soil carbon and nitrogen cycle of temperate forests. [ABSTRACT FROM AUTHOR]

• As secondary succession progresses, both GRSP and SOC content increase significantly. • Secondary succession promotes the formation of soil macroaggregates and increases soil stability. • The GRSP content of 61-year-old secondary forest reached the level of primary forest. • GRSP exhibited significant positive correlations with both SOC and MWD. • GRSP is a key indicator of soil restoration during the secondary succession. Despite the key role of glomalin-related soil protein (GRSP) in soil organic C (SOC) and soil aggregate stability, the influence of secondary successional processes on GRSP and the interrelationship of GRSP on SOC and its soil aggregate stability is unclear. Based on this, four stages of the secondary succession (including 20-, 32–, 47-, and 61-year-old stands) and the primary broad-leaved Korean pine (Pinus koraiensis) mixed forest were selected. The results showed that total GRSP (T-GRSP), easily extractable GRSP (EE-GRSP), SOC, mean weight diameter (MWD), and geometric mean diameter (GMD) all tended to increase with the secondary succession at 0–30 cm soil layer. The secondary succession contributed to the accumulation of GRSP content, so much so that after 61 years, both EE-GRSP and T-GRSP reached the level of the primary forest. EE-GRSP, T-GRSP, SOC, MWD, GMD, and GRSP/SOC significantly decreased with the deepening of soil depth in all successional stages. In addition, during the 20- and 32 year-old stands of secondary succession, the proportion of GRSP in the SOC was relatively high. With the progress of secondary succession, the content of macroaggregates (>0.25 mm) in the soil increased significantly and was not significantly different from the primary forest. The correlation analysis showed that T-GRSP was more correlated with SOC than EE-GRSP, while EE-GRSP was more correlated with MWD than T-GRSP. Additionally, there was also a significant positive correlation between MWD and SOC at 0–20 cm soil layer. Our results elucidate that GRSP may stabilize SOC pools by direct contribution to SOC in the early secondary succession, and the stabilizing effect on SOC is more pronounced in the later stages by forming macroaggregates. This enables us to understand the ecological functions played by GRSP in soil C sequestration and the enhancement of soil stability during the secondary succession. [ABSTRACT FROM AUTHOR]