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Glomalin-related soil protein (GRSP) is a widely distributed glycoprotein produced by arbuscular mycorrhizal fungi (AMF), plays a crucial role in soil structure, aggregate stability, and ecological restoration. However, few studies have explored soil nutrient and GRSP changes, as well as aggregate stability mechanisms during vegetation restoration in boreal forests. We used a “space-for-time substitution” approach and selected four habitats (grassland, Betula platyphyllaforest, Larix gmeliniiand Betula platyphyllamixed forest, and Larix gmeliniiforest) in Greater Khingan Mountains of northeastern China to study the changes in AMF abundance, soil aggregate stability, EE-GRSP, and T-GRSP with succession. (1) The abundance of AMF, soil organic carbon (SOC), GRSP were increased with the successional process, and the stability of aggregates and soil structure (mean weight diameter, MWD, and geometric mean diameter, GMD) were also significantly enhanced. (2) During the successional process, there was an increase in the percentage of large aggregates (>0.25 mm) and a decrease in the percentage of microaggregates (<0.25 mm). Soil macroaggregates (>2 mm) were the primary contributors to SOC. (3) Compared with the stage of Betula platyphyllaforest, SOC in the stage of Larix gmeliniiforest was more protected by soil aggregates; the increase of GRSP caused by the water stress may be the main reason for the increase of soil aggregate stability. The successional process of boreal forests contributes to the stability of aggregates and the accumulation of carbon storage. We emphasize the importance of GRSP in the stability of soil structure and aggregates. Our research is significant for understanding the stability of aggregates and the ecological restoration mechanisms in boreal forests.

Soil extracellular enzymes can regulate the decomposition processes of soil organic carbon (SOC). Thus, understanding how extracellular enzyme activity (EEA) and ecoenzymatic stoichiometry respond to altered nitrogen (N) deposition and precipitation patterns may establish a link between changes in soil organic matter and microbial responses in the context of climate change. The long-term field simulation experiments including the control, N deposition (N50, 50 kg·ha−1·yr−1), throughfall reduction (TR, − 30%), and their interactions (TR + N50) were built in a temperate forest in 2009. N50 significantly increased all EEAs except leucine aminopeptidase (LAP) and acid phosphatase (ACP). In addition, TR significantly reduced other EEAs except for ACP and polyphenol oxidase (PPO). N50 mainly promotes EEAs by influenced pH, increased SOC, and microbial biomass carbon (MBC). TR inhibited EEAs mainly by reducing soil moisture content (SMC), SOC, and MBC. Furthermore, the positive effects of N50 on EEAs were offset by the negative effects of TR under the interactive of N deposition and penetration reduction. In the control, C acquisition enzyme (C-acq):N acquisition enzyme (N-acq):P acquisition enzyme (P-acq) ≈ 1:1:1, N50, and TR resulted in alterations in the ecoenzymatic stoichiometric equilibrium. Wherein, N50 reduced BG: NAG + LAP but increased BG:ACP and NAG + LAP:ACP. The effect of TR on the ecoenzymatic stoichiometric ratio showed completely opposite to N50. TR + N50 reduced all ecoenzymatic stoichiometric ratios. Our study suggests that pH, SMC, substrate quality, and microbial biomass may be the main drivers for changes in EEAs. Our results elucidate the response mechanism of extracellular enzyme activity to N deposition and precipitation reduction, providing insights into the dynamics of SOC pools in the context of global change. In addition, this study proves that N limitation rather than phosphorus limitation exists in northeast temperate forests, providing a theoretical basis for future forest management.

Long term atmospheric nitrogen (N) deposition affects carbon (C) and N cycling in forest ecosystems, thus changing the stable C isotope abundance of plants and soils. It is still unclear whether the input of extra nitrogen will affect the response of the δ13C and δ15N of dominant tree species and soil to long-term N addition in forest ecosystems, especially in a temperate secondary forest. We conducted a 14-year experiment of N addition to study the effects of long-term N addition on the δ13C and δ15N of Populus davidiana (PD)and Betula platyphylla (BP). The results showed that after 14 years of continuous N addition, the sample plot was still in the N limited state. Nitrogen addition significantly increased the 15N in PDand BPleaves, but high N addition did not enrich the 15N by increasing N loss in N rich sites. With the increase of soil depth, soil organic carbon (SOC) decreased significantly, and the soil 13C and 15N were enriched. PDand BP13C and C had high stability, and were not affected by N addition. PDwas more “N deficient” than BP, while BPwas more 15N rich than PD. Under the condition of N limitation, the addition of low and high N inhibited the turnover of organic C in PDwhich was beneficial to its C sequestration. However, high N treatment promoted the turnover of SOC. These results further deepen our understanding of the C and N cycle mechanism in temperate forests under the background of N deposition.

The exogenous fresh carbon (C) inputs affect soil organic C (SOC) decomposition, resulting in priming effect (PE). However, under different long-term nitrogen (N) addition levels, it is still unclear whether the input of extra organic C will affect the SOC decomposition and the magnitude of PE in the boreal zone. We conducted a long-term N addition field experiment in a boreal forest, by collecting the soil after N addition, and we conducted a 40-day culture experiment with 13C-glucose labeling. The results showed that the addition of glucose significantly promoted the mineralization of SOC and the magnitude of PE, while the addition of N inhibited both of them. However, regardless of the level of N addition, the addition of 13C-glucose would accelerate the mineralization of SOC, resulting in a positive PE. Microbial biomass C was the main regulating factor of PE. After N addition, the residual C in soil was significantly higher than the decomposition amount of SOC, resulting in the increase of net C content. Collectively, N additions inhibit the soil PE, but the inhibition weakens with the increase of C input, which is conducive to the SOC sequestration of boreal forests.

The effects of precipitation reduction and nitrogen deposition increase on soil bacterial communities and functions impact soil nitrogen cycling. Seasonal changes could modify the effects of precipitation reduction and nitrogen deposition increase on bacterial communities and functions by changing soil environments and properties. Understanding soil microbial communities and the seasonal response of functions to precipitation reduction and nitrogen deposition increase may be important for the accurate prediction of changes in the soil nitrogen dynamics. Thus, a long-term field simulation experiment of nitrogen deposition increase and throughfall exclusion was established to investigate soil bacterial communities' response to nitrogen deposition increase and/or precipitation reduction, with no nitrogen deposition increase and no precipation reduction as a control, in a temperate forest. We examined soil bacterial communities (Illumina sequencing) under different treatments during the winter, freezing-thawing cycle periods (FTCs), and growing season. The bacterial functional groups were predicted by the FAPROTAX database. The results showed that nitrogen deposition increase, precipitation reduction, the combined effect of nitrogen deposition increase and precipitation reduction, and seasonal changes significantly altered the soil bacterial community composition. Interestingly, by combining the result of a previous study in which nitrogen deposition increase increased the nitrous oxide flux in the same experimental system, the loss of soil nitrogen was increased by the decrease in denitrification and increase of nitrification bacteria under nitrogen deposition increase, while ammonification bacteria significantly increased and N-fixing bacteria significantly decreased with precipitation reduction compared to the control. In relation to seasonal changes, the aromatic-degrading, cellulolytic, and ureolytic bacteria were lowest during FTCs, which indicated that FTCs might inhibit biodegradation. Nitrification and nitrite-oxidizing bacteria increased with nitrogen deposition increase or precipitation reduction and in FTCs compared to the control or other seasons. The interaction between treatment and season significantly changed the soil bacterial communities and functions. These results highlight that nitrogen deposition increase, precipitation reduction, seasonal changes, and their interactions might directly alter bacterial communities and indirectly alter the dynamics of soil N.

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.

The shear resistance at cement-formation interface (CFI) in coalbed methane (CBM) well has a great influence on the success rate of hydraulic fracturing for CBM reservoir. In this paper, the mud cake to agglomerated cake (MTA) method was used to improve the shear resistance at CFI and to reduce the risk of fluid channeling after hydraulic fracturing. The experimental results showed that the mud cake modifier (MCM) had slight effect on the drilling fluid rheological properties while the MCM addition. When the curing time was 2, 3, 15 and 90 days, the shear resistance at CFI increased by 5.30, 4.32, 3.63 and 3.15 times, respectively. The analysis showed that the mud cake solidification and interface crosslinking were main reasons. The fluid channeling coefficient at CFI was smaller than 1 after 5 days, which indicated that the risk of fluid channeling in CBM well after hydraulic fracturing was greatly reduced. [Received: September 30, 2015; Accepted: November 2, 2015]

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 gmeliniiforest in Greater Khingan Mountains, Northeast China. Four N treatments (0, 25, 50, 75 kg N ha−1year−1) were built. The effects of N addition on the δ13C and δ15N of needle, branch, bark, and fine root of Larix gmeliniiand 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 gmeliniicould 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.