Introduction Understanding how human activities affect biodiversity is needed to inform systemic policies and targets for achieving sustainable development goals. Shallow tillage to remove Artemisia ...ordosica is commonly conducted in the Mu Us Desert. However, the impacts of shallow tillage on plant community species diversity, phylogenetic structure, and community assembly processes remain poorly understood. Methods This study explores the effects of shallow tillage on species diversity including three a-diversity and two b-diversity indicators, as well as phylogenetic structure phylogenetic diversity (PD), net relatedness index (NRI), and nearest taxon index (NTI). Additionally, this research analyzes the effects of shallow tillage on the community assembly process. Results and discussion The results showed that the a-diversity index, b-diversity index, and PD of the shallow tillage (ST) communities were significantly higher than those of the non-shallow tillage (NT) communities, and the phylogenetic structures of both the ST and NT communities tended to be differentiated, with competitive exclusion being the main mechanism of plant assembly. However, shallow tillage increased the relative importance of the stochastic processes dominated by dispersal limitation, mitigating plant competition in the communities. This conclusion was supported by the Raup–Crick difference index-based analysis. Conclusion Therefore, for the ecological restoration of the Mu Us Desert, species with adaptability and low niche overlap should be selected to increase the utilization efficiency of the environmental resources. The results of this study provide a foundation for policy development for ecosystem management and restoration in the Mu Us Desert.
Background and Aims
Soil bacteria are essential in maintaining multiple grassland ecosystem functions that are significantly altered by mowing. Assembly processes govern bacterial community ...composition and in turn determine their functions. However, the ecological processes governing bacterial community assembly response to mowing remain largely unexplored.
Methods
In the present study, we characterized soil bacterial community assembly processes under different mowing intensities, including no mowing (CK), light mowing (LM, mowing annually with 8 cm stubble), moderate mowing (MM, mowing annually with 5 cm stubble), and heavy mowing (HM, mowing annually with 2 cm stubble) in typical grassland of Inner Mongolia. We further analyzed multiple environmental factors to explore the drivers of bacterial community assembly under different mowing intensities.
Results
Our results showed that stochastic processes primarily governed the bacterial community assembly in CK, LM, and HM; however, MM was governed by deterministic processes. Our research found that different mowing intensities did not visibly affect the bacterial α-diversity. However, MM and HM significantly altered the bacterial community's overall structure compared to the control. MM possessed the most complex and connective bacterial communities. Soil organic carbon (SOC) was the most critical environmental factor mediating the changes in bacterial community assembly processes induced by mowing. Increased SOC in MM worked as an ecological filter to deterministically select bacterial taxa (
Streptomyces
and
RB41
) with carbon metabolism-related function assembly.
Conclusions
Our findings showed that when the grass was mowed annually to a height of 5 cm, it increased the concentration of SOC and governed the deterministic assembly of bacterial communities in the semiarid grassland ecosystem. By studying these findings, we can better understand how bacterial communities support the long-term health of grassland ecosystems.
Mowing removes plant photosynthetic organs, thus decreasing plant biomass and nutrients in the community. Responses of community functional diversity, biomass, and nutrient status to mowing play a ...crucial role in the restoration and sustainable use of degraded grasslands, but have not been well studied. Our study linked functional diversity with forage biomass and nutrition in a semiarid grassland. We found that annual mowing reduced community biomass, in particular significantly reduced the dominant plants biomass, which was maintained with biennial mowing. In addition, this study showed that functional diversity could be maintained at a high level under biennial mowing compared to unmowed, but significantly decreased under annual mowing. Structural equation modeling indicated that annual mowing reduced dominant plants biomass by reducing community functional diversity. Mowing decreased dominant plants nutrients by decreasing community functional diversity and soil nutrients, but had no significant effect on nutrients of community and nondominant plants. Furthermore, there was a strong positive correlation between community functional diversity with forage production and nutrition. In conclusion, our study demonstrated that biennial mowing increases community biomass, litter mass, and dominant plant nutrition by regulating functional diversity. Therefore, biennial mowing can provide better conservation of grassland ecosystems and is a suitable grassland management practice in semiarid grasslands.
The influence of hierarchical structure and SiO2 modification of ZSM-5 on the mechanism of methanol to aromatics was studied. The formation of benzene and toluene through reaction pathways of ...carbenium ions with high carbon number was discussed over ZSM-5 and modified ZSM-5, respectively. The results demonstrated that the energy barriers for the formation of aromatics over hierarchical ZSM-5 were higher than that over ZSM-5, indicating that aromatics were easier to form in micropores thermodynamically. Moreover, higher activation energy was observed over mesoporous ZSM-5 with SiO2 modification indicating greater difficulty in the reaction. A decrease in the acid strength by desilication then SiO2 modification was benefit to suppressing the production of aromatics. In addition, the reactions related to hydride transfer needed overcome higher barriers and thus were the rate-determining steps for aromatization compared with those in deprotonation and cyclization steps. Meanwhile, the length of C–O bond for alkoxy groups increased obviously from ZSM-5 to modified ZSM-5 zeolite in such step, which was ascribed to the reduction of acidic site strength of modified ZSM-5.
The influence of hierarchical structure and SiO2 modification of ZSM-5 on the mechanism of methanol to aromatics was studied using DFT calculations. Aromatics were easier to form over ZSM-5 thermodynamically than that over mesoporous ZSM-5 due to the decrease of reaction barriers. It was considered that acid strength effectively enhanced the selectivity of aromatics by decreasing the reaction barriers. In addition, the reactions related to hydride transfer needed overcome higher barriers and were the rate-determining steps for aromatization of higher carbocations. Display omitted
•Aromatics were easier to form over ZSM-5 thermodynamically compared to mesoporous ZSM-5.•The reactions related to hydride transfer needed overcome higher barriers and were the rate-determining steps for aromatization of C6+ and C7+.•Acid strength effectively enhanced the selectivity of aromatics by decreasing the reaction barriers.
Soil enzyme activities can be used to characterize microbial metabolism given their importance as catalysts in various biochemical processes. However, how soil microbial metabolism in the desert ...steppe responds to long-term grazing remains poorly understood. Here, utilized data from a 19-year grazing experiment with four grazing intensities (no grazing CK, light grazing LG, moderate grazing MG, and heavy grazing HG) in Inner Mongolia, we evaluated microbial metabolic limitations using soil enzymatic stoichiometry, and assessed the effects of these limitations on microbial carbon use efficiency (CUE) using a biogeochemical equilibrium model. Activity of C-, N-, and P-acquiring enzymes as well as soil hydrology, nutrient content, and microbial biomass were quantified to determine the drivers of microbial metabolic limitations. Long-term grazing reduced soil carbon (C), nitrogen, and phosphorus (P) acquisition enzyme activity. Microbial metabolism was restricted by C and P in the absence of grazing, and these nutrient limitations became more severe with increasing grazing intensity. Furthermore, structural equation modeling revealed that the microbial biomass, available nutrients, and total nutrient ratios affected the extent to which C was limiting, while only available nutrients affected the severity of P limitation. Meanwhile, microbial CUE decreased with grazing intensity and was regulated by microbial relative C limitation. Our findings emphasize that long term light grazing did not change microbial carbon use efficiency. Thus, it may be a proper utilization way for regulating soil nutrient cycles and facilitating the sustainable management of regional grassland.
•Microbial communities were co-limited by C and P under long-term grazing.•C- and P- limitation increased with the increase of grazing intensity.•Moderate and heavy grazing weakened microbial carbon use efficiency.•Carbon use efficiency is regulated by C limitation rather than P limitation.
Livestock grazing strongly influences the accumulation of soil organic carbon (SOC) in grasslands. However, whether the changes occurring in SOC content under different intensities of continuous ...summer long grazing are associated with the changes in microbially-derived necromass C remains unclear. Here, we established a sheep grazing experiment in northern China in 2004 with four different stocking rates. Soil samples were collected after 17 years of grazing and analyzed for physical, chemical, and microbial characteristics. Grazing decreased SOC and microbial necromass carbon (MNC). Notably, grazing also diminished contributions of MNC to SOC. MNC declined with decreasing plant carbon inputs with degradation of the soil environment. Direct reductions in microbial necromass C, which indirectly reduced SOC, resulted from reduced in plant C inputs and microbial abundance and diversity. Our study highlights the key role of stocking rate in governing microbial necromass C and SOC and the complex relationships these variables.
•Grazing-induced organic carbon decline is related to decreased microbial necromass.•High stocking rates led to lower contributions of necromass carbon to organic carbon.•Lower stocking rates maintained higher microbial necromass and organic carbon.•Microbial necromass declined with decreasing plant carbon inputs and soil environment.
Mesoporous ZSM-5 with various morphologies loading cobalt were prepared and applied in Fischer-Tropsch synthesis. Smaller ZSM-5 particles showed higher intensity of strong acid sites resulting in ...higher cobalt-support interaction. The activity and CH4 selectivity were remarkably related with cobalt-support interaction over such acidic supports. Cobalt loaded on spindle mesoporous ZSM-5 exhibited the lowest activity and the highest CH4 selectivity due to the strongest cobalt-support interaction, but the highest activity was obtained over cubic mesoporous ZSM-5 with the lowest cobalt-support interaction originating from weaker acid sites. In addition, adjusting acid intensity and mesopore volumes could successfully tuned hydrocarbon distribution. Spherical ZSM-5 with hierarchical structure containing larger mesopore volumes and moderate acid intensity effectively promoted the production of C12-18 hydrocarbons. The highest C5-11 selectivity was observed over cobalt supported on hexagonal meso-ZSM-5 due to the enhancement in diffusion limitation over lower mesopore volumes and hydrocracking of primary hydrocarbons over higher Brønsted acid sites.
•Smaller ZSM-5 particles showed higher intensity of strong acid sites resulting in higher cobalt-support interaction, which affected on the activity and CH4 selectivity.•The highest C5-11 selectivity was observed over cobalt supported on hexagonal meso-ZSM-5 with lower mesopore volumes and higher Brønsted acid sites.•Spherical ZSM-5 with hierarchical structure containing larger mesopore volumes and moderate acid intensity promoted the production of C12-18 hydrocarbons.
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