| Given the exacerbated background of global climate change,appropriate vegetation restoration patterns are regarded as key measures to improve soil quality,regulate microbial community characteristics,and enhance soil carbon(C)sequestration potential.In the ecologically fragile Loess Plateau region,restoring cropland to forest and grass has been proven to contribute effectively to soil C stocks.Yet,soil C fixing effect not only hinges on the C pool size,but also governed by persistence impacted by organic C chemistry,which is still underexplored fully.Meanwhile,microbial ecological adaptation strategies emphasize the differences in C source preferences and metabolic intensities among different taxa.However,present studies have mainly focused on exploring the ecological links between microbial and environmental physicochemical variables,ignoring the effects of C substrate chemistry on microbial community construction,which may blur our understanding of microbial environmental adaptation patterns.In this paper,by combining physicochemical analysis,FTIR(Fourier Transform infrared)spectroscopy,and biosequencing techniques,we determined the basic chemical characteristics and organic carbon chemical structure of soils and plant leaf of three plant community types,as well as the composition and metabolic characteristics of soil microbial communities,aiming to reveal the deep connection between nutrient structure,soil carbon chemical stability and microbial characteristics,and to provide research references for selecting a reasonable vegetation restoration model in the Loess Plateau.The major findings are as follows.(1)There were significant differences in leaf and soil properties among three community types.Compared to A(Abandoned grassland),RF(Robinia pseudoacacia L.)and S(Caragana korshinskii.)exhibited higher LTN contents and STN: STP ratios and lower LTC: LTN ratios(p < 0.05).Similarly,soil organic C(SOC)and total nitrogen(STN)were richer in RF and S than in A soil(p < 0.05).However,there were no significant differences in total phosphorus(STP)among the three restoration community,which may contribute to higher SOC: STP and STN: STP ratios in RF and S soil.(2)FTIR analysis showed that the relative content of organic carbon groups of plant leaf and soil exhibited aliphatic groups > hydrophilic groups > aromatic groups.Compared with A community,leaf and soil carbon fractions of RF and S showed higher proportions of hydrophilic and aromatic groups and higher aromaticity.The hydrophobicity of SOC was highest in the A soil,followed by RF and S soil,indicating that agricultural abandonment is more helpful in improving soil C stability in the current restoration stage.(3)Soil microbial community characteristics differed significantly between community types.The lowest bacterial: fungal ratio(B: F = 19.90)was recorded in A,showing that that the microbial community was dominated by fungi.The diversity indices of alpha(Shannon and Simpson),Chao 1 and ACE of bacterial and fungal communities in RF soil were higher than those of S and A.The dominant Proteobacteria and Bacteroidetes,which were classified as r-strategists in the bacterial community,had higher relative abundance in both RF and S soil than A,while Acidobacteria and Chloroflexi,which were K-strategists,exhibited the highest relative abundance in A soil.Ascomycota was the dominant fungal phylum in the three soil environments,with the highest percentage on A soil.(4)Microbial co-occurrence network analysis showed that the number of strongly correlated nodes of bacterial and fungal communities in the three soils ranged from 204 to213 and 83 to 99,respectively.Despite the similar numbers of strongly correlated nodes,the number of bacterial and fungal network edges was much higher in RF and A than in S.The bacterial network exhibited the most complex and highest network connectivity in RF soil,while the dominance of fungal co-occurrence network was mainly present in A soil.In S soil,bacterial and fungal networks tended to increasing evenness and homogenization,with poorer network connectivity.(5)The analysis of microbial carbon metabolism function on the seventh day showed that the overall microbial carbon metabolism capacity(AWCD)and metabolic uniformity(Mclntosh index)of RF soil were 0.123 and 1.332,respectively,which were significantly higher than those of S and A soils.The abundance(Shannon index)and dominance(Simpson index)of microbial metabolism in S soil were 2.062 and 0.749,respectively,which were lower than those of RF and A soils.The absolute and relative utilization analysis of the six major carbon sources showed that RF soil microorganisms preferred to utilize polysaccharides and amino acids as easily available hydrophilic compounds,and A soil microorganisms were the most capable of metabolizing polymeric recalcitrant carbon compounds.Principal component analysis showed that microbial carbon metabolism functions of RF,and S,A soils were separated along the PC 1 axis,with polysaccharide and amino acid compounds being the main carbon sources that played a divergent role.In summary,choosing different vegetation restoration patterns will significantly affect soil nutrient and carbon chemical stability characteristics,which are primarily related to plant leaf chemistry,and the carbon stability of RF and A soil are superior than that of S,according to present study.The microbial community in the A soil was dominated by Kstrategists and had the strongest metabolism targeted to recalcitrant carbon compounds,which predicted that the A soil might face more loss of stable carbon in the future.Meanwhile,the RF soil represented the largest diversity of bacterial and fungal communities,dominated by r-strategists and had the strongest metabolism of hydrophilic compounds,which predicted that the RF soil might accumulate a larger proportion of stable carbon.From the holistic perspective of soil nutrient structure,carbon chemical composition and microbiological characteristics,RF may be a more suitable tree species choice for future afforestation in this region for serving more advantageous eco-function. |
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