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Soil greenhouse gas (GHG) fluxes relate to soil carbon and nitrogen budgets and have a significant impact on climate change. Nevertheless, the temporal variation and magnitude of the fluxes of all three major GHGs (CO2, CH4 and N2O) and their influencing factors have not been elucidated clearly in primary forests on the eastern Qinghai-Tibetan Plateau. Herein, field chamber GHG fluxes from May to November, soil microbial community and enzyme activity were analyzed in a fir-dominated (Abies fargesii var. faxoniana) primary forest. The emission rates of CO2 and N2O ranged between 64.69–243.22 mg CO2 m−2 h−1 and 1.69–5.46 ug N2O m−2 h−1, exhibiting a temporally unimodal pattern with a peak in July. The soil acted as a CH4 sink, and the uptake rate varied between 52.96 and 84.67 μg CH4 m−2 h−1 with the higher uptake rates in June and November. The temporal variation in the CO2 flux was significantly correlated with the geometric mean of enzyme activities, suggesting that the soil CO2 flux was determined by microbial activity rather than soil microbial biomass. The soil N2O flux was positively related to nitrate concentration with marginal significance, probably because N2O was a byproduct of nitrification and denitrification processes. The soil CH4 uptake was closely associated with methanotrophic biomass (18:1ω7c). The results highlight divergent temporal dynamics of GHG fluxes owing to different driving mechanisms and an important CH4 sink in the primary forest soil, helping to evaluate the carbon and nitrogen budgets of primary forests on the eastern Qinghai-Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• The forest productivity of mixed plantations was 18–39.5% greater than that of pure plantations. • Understory vegetation diversity in MCC was significantly higher than in PCL and PCF, by 15.8–20% and 13.2–35.7%, respectively. • The water conservation capacity of MCC is significantly higher (by 19.4–42.9%) than that of PCL and PCF. • Performance against the soil fauna diversity index was similar in all three stands. Many studies of biodiversity-ecosystem functioning (BEF) relationships indicate that mixed plantations can enhance ecological benefits by enabling ecological niche differentiation between species. However, few studies explore multi-dimensional evidence to fully evaluate the integrated ecological benefits of mixed plantations. This paper aims to assess the stand characteristics and ecological benefits of different forest types, drawing on multiple lines of evidence (trees, shrubs, herbs, soil fauna, and soils) to understand the effects of mixed plantations on integrated ecological benefits. Our study focused on pure Cunninghamia lanceolata (Chinese Fir) plantations (PCL), pure Cryptomeria fortunei (Chinese Cedar) plantations (PCF), and mixed C. lanceolata - C. fortunei plantations (MCC), which are common in the mountainous areas of the Sichuan Basin in southwestern China. We analysed the growth status, spatial structure, understory vegetation diversity, soil fauna characteristics, and physical and chemical soil properties found in plots representing these three forest types. The results showed that productivity was significantly higher in the MCC than in PCL or PCF, by 39.5% and 18%, respectively. Mixed plantations showed higher stand growth rates, but this effect was limited by interspecific competition. The results further showed that mixed plantations promote forest growth by allocating spatial locations between different tree species. In addition, the spatial stand structure in the mixed plantations was more stable than that in the two pure plantations, and the management potential of the mixed plantations was greater. Understory vegetation in MCC was significantly more diverse than in PCL and PCF, by 15.8–20% and 13.2–35.7%, respectively. Moreover, mixed plantations performed better in terms of soil water and soil fertility. Interestingly, we found no difference in soil fauna diversity between mixed and pure plantations. We conclude that, overall, planting mixed plantations can enhance the integrated ecological benefits of afforestation and may be an essential strategy for ensuring that plantations can cope with climate extremes. [ABSTRACT FROM AUTHOR]

Root activity creates a unique microbial hotspot in the rhizosphere, profoundly regulating free-living nitrogen fixation (FLNF). However, empirical assessments of rhizosphere FLNF and its ecological consequences for nitrogen (N) budgets remain lacking, particularly for different root functional modules. Here, we separately collected rhizosphere soils attached to two root functional modules, absorptive roots and transport roots, and investigated the rates (15N 2 incorporation) and regulators of rhizosphere FLNF in a N-limited subalpine coniferous forest. The measured rates were further extrapolated to annual fluxes based on the volume of the rhizosphere and the relationship between FLNF rate and temperature. We found that absorptive roots drove significantly higher rhizosphere FLNF rates than did transport roots (12.2 vs. 7.5 ng N g−1 d−1), with both rhizosphere compartments exhibiting rates well exceeding those in the bulk soil (0.9 ng N g−1 d−1). The FLNF rates were positively correlated with soil organic carbon content but showed no significant relationship with the abundance or composition of the diazotrophic community. Moreover, when extrapolated to the ecosystem level the FLNF fluxes were 2-fold greater in the rhizosphere of absorptive roots than in that of transport roots (0.13 vs. 0.04 kg N ha−1 yr−1). Taken together, despite representing only 6.0% of the soil volume, the two rhizosphere compartments contributed as much as 47.2% to the total soil FLNF fluxes. Overall, we provide empirical evidence that despite its limited volume, the rhizosphere contributes disproportionately to the FLNF in subalpine forest soils. Our findings also underscore the critical role of root functional differentiation in regulating rhizosphere FLNF, which is essential for integrating this process into the ecosystem-level N cycle. • Rhizosphere free-living nitrogen fixation (FLNF) was assessed in a coniferous forest. • Absorptive roots drove significantly higher rhizosphere FLNF rates than did transport roots. • The rhizosphere soil presented FLNF rates one order of magnitude greater than those of the bulk soil. • Despite representing 6% of soil volume, the rhizosphere contributed 47% of soil FLNF flux. [ABSTRACT FROM AUTHOR]

The triangular arrow from thin to thick indicates that the value of a variable gradually increases, the shape from thin to thick to thin indicates that the value of the variable increases and then decreases. [Display omitted] • Soil micro-food web attributes and soil multifunctionality (SMF) exhibited a similar single hump-shaped pattern with increasing elevation. • Multitrophic composition and multitrophic diversity indirectly driven SMF through soil micro-food web complexity. • The soil micro-food web complexity was of greater importance in regulating SMF. Variations in soil micro-food web characteristics under changing environments can exert profound consequences on soil multifunctionality. However, the intrinsic relationship between these changes and their dependence on long-term environmental factors remains largely unquantified. Here, we investigated the soil micro-food web attributes (i.e., multitrophic diversity, multitrophic composition and network complexity) and multiple types of soil functions (soil multifunctionality) along an elevation gradient on the Eastern Tibetan Plateau. The results showed that elevation significantly affected the multitrophic composition, and multitrophic diversity, soil micro-food web complexity and soil multifunctionality exhibited a similar single hump-shaped pattern with increasing elevation. Compared to multitrophic composition and multitrophic diversity, the soil micro-food web complexity was significantly and positively correlated with soil multifunctionality and was of greater importance in regulating soil multifunctionality. However, multitrophic composition and multitrophic diversity indirectly driven soil multifunctionality through soil micro-food web complexity. This empirical evidence demonstrates that soil micro-food web complexity is a better predictor of soil functions than the multitrophic composition and diversity metrics that have been commonly used in previous studies. In conclusion, our findings highlighted the perceived importance of soil micro-food web complexity in regulating soil multifunctionality in forests under changing environments. [ABSTRACT FROM AUTHOR]