Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and bi...Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China.We hypothesized that(1)topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2)different understory strata respond differently to environmental factors;shrubs may be significantly affected by the overstory stratum,and herbs may be more affected by surface soil conditions.To test these hypotheses,we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity,using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity,and individual tree size inequality(DBH variation)was the dominant biotic driver of understory species diversity;soil water content was the main edaphic factors affecting herb layers.Elevation,slope aspect,and DBH variation accounted for 36.4,14.5,and 12.1%,respectively,of shrub stratum diversity.Shrub diversity decreased with elevation within the range of altitude of this study,but increased with DBH variation;shrub diversity was highest on north-oriented slopes.The strongest factor affecting herb stratum species diversity was slope aspect,accounting for 25.9%of the diversity,followed by elevation(15.7%),slope(12.2%),and soil water content(10.3%).The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes;herb diversity decreased with elevation and soil water content,but increased with slope.The results of the study provide a reference for scientific management and biodiversity protection in cold temperate coniferous forests of North China.展开更多
Fe-based catalysts have been discovered as the best elementary metal-based heterogeneous catalysts for the ammonia synthesis in industrial application during the last century.Herein,a novel and scalable strategy is de...Fe-based catalysts have been discovered as the best elementary metal-based heterogeneous catalysts for the ammonia synthesis in industrial application during the last century.Herein,a novel and scalable strategy is developed to prepare the K-promoted Fe/C catalyst with extremely high Fe loading (> 50 wt.%) through pyrolysis of the Fe-based metal-organic framework (MOF) xerogel.The obtained K-Fe/C catalysts exhibited superior activity and stability towards ammonia synthesis.The weight-specific reaction rate of Fe/C with K2O as promoter can achieve 12.4 mmol·g-1·h-1 at 350 ℃ and 30.4 mmol·g-1·h-1 at 400 ℃,approximately four and two times higher than that of the commercial fused-iron catalyst (3.4 mmol·g-1·h-1 at 350 ℃ and 16.7 mmol·g-1·h-1 at 400 ℃) under the same condition,respectively.The excellent performance of K-Fe/C can be ascribed to the inherited structure derived from the metal-organic frame precursors and the promotion of potassium,which can modify the binding energy of reactant molecules on the Fe surface,transfer electrons to iron for effective activation of nitrogen,prevent agglomeration of Fe nanoparticle (NPs) and restrain side reaction of carbon matrix to methane.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.31470630)Shanxi Forestry Science and Technology Innovation Project
文摘Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures,function realization,and community succession.However,little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China.We hypothesized that(1)topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2)different understory strata respond differently to environmental factors;shrubs may be significantly affected by the overstory stratum,and herbs may be more affected by surface soil conditions.To test these hypotheses,we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity,using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity,and individual tree size inequality(DBH variation)was the dominant biotic driver of understory species diversity;soil water content was the main edaphic factors affecting herb layers.Elevation,slope aspect,and DBH variation accounted for 36.4,14.5,and 12.1%,respectively,of shrub stratum diversity.Shrub diversity decreased with elevation within the range of altitude of this study,but increased with DBH variation;shrub diversity was highest on north-oriented slopes.The strongest factor affecting herb stratum species diversity was slope aspect,accounting for 25.9%of the diversity,followed by elevation(15.7%),slope(12.2%),and soil water content(10.3%).The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes;herb diversity decreased with elevation and soil water content,but increased with slope.The results of the study provide a reference for scientific management and biodiversity protection in cold temperate coniferous forests of North China.
基金This work was financially supported by the National Key Research and Development Program of China(Nos.2017YFB0602200 and 2017YFA0206701)National Program for Support of Top-notch Young Professionals,Changjiang Scholar Program and the National Natural Science Foundation of China(Nos.21725301,91645115,21673273,21473003,21872104,and 21821004)The XPS experiments were conducted at Lab of Multitechniques Electron&Ion Spectrometer for Surface Analysis of Peking University.We thank Jinglin Xie for XPS data discussion.
文摘Fe-based catalysts have been discovered as the best elementary metal-based heterogeneous catalysts for the ammonia synthesis in industrial application during the last century.Herein,a novel and scalable strategy is developed to prepare the K-promoted Fe/C catalyst with extremely high Fe loading (> 50 wt.%) through pyrolysis of the Fe-based metal-organic framework (MOF) xerogel.The obtained K-Fe/C catalysts exhibited superior activity and stability towards ammonia synthesis.The weight-specific reaction rate of Fe/C with K2O as promoter can achieve 12.4 mmol·g-1·h-1 at 350 ℃ and 30.4 mmol·g-1·h-1 at 400 ℃,approximately four and two times higher than that of the commercial fused-iron catalyst (3.4 mmol·g-1·h-1 at 350 ℃ and 16.7 mmol·g-1·h-1 at 400 ℃) under the same condition,respectively.The excellent performance of K-Fe/C can be ascribed to the inherited structure derived from the metal-organic frame precursors and the promotion of potassium,which can modify the binding energy of reactant molecules on the Fe surface,transfer electrons to iron for effective activation of nitrogen,prevent agglomeration of Fe nanoparticle (NPs) and restrain side reaction of carbon matrix to methane.
