Responses Of Soil Carbon-fixing Bacteria To Forest Types And Soil Physical And Chemical Properties In Zhejiang Province

Forest ecosystem is one of the most important organic carbon pools on the earth.China has abundant subtropical forest resources,and soil carbon-fixing microorganisms have an important carbon sink function.Forest stand and soil texture have important effects on the conversion and accumulation of plant-derived organic carbon,as well as soil carbon-fixing microorganisms.It can not only help us enhance the understanding of the carbon sink function of subtropical forest ecosystems,but also provide technical guidance for the reasonable and effective forest carbon storage management by exploring the differences in the impact of the forest stand and soil texture on soil carbon-fixing microorganisms in forest ecosystems.In this study,soil from four planting quilts(Moso banboo,Broad-leaved forest,Chinese fir and Masson pine)and three types of soil-forming parent soils(Siltstone and Shale in Anji,Tuff in Lin'an and Granite in Longquan)were examined;We would also collect two soils layers including surface layer(0?20 cm)and subsurface layer(20?40 cm)soil and regard cbb L as an indicator gene for carbon-fixing bacteria and to further compare the abundance and community composition of carbon-fixing bacteria from four forest stands of the same parent soil in Lin'an and different parent soils in broad-leaved forest by using real-time quantitative PCR and Mi Seq high-throughput sequencing;meanwhile,We would analyze the relationship between carbon components and the abundance of soil carbon-fixing bacteria in four forest stands and three parent rocks and reveal the response of carbon-fixing bacteria to forest stand and soil physical and chemical properties.The main results are as follows:The effects of four planting types on soil carbon-fixing bacteria in Linglong Mountain showed that the abundance of bacterial 16S r RNA gene and carbon-fixing bacteria cbb L gene in four forest stands were 5.40×10¹⁰?2.81×10¹¹ copies g^-1 dry soil and 4.55×10⁸?3.53×10⁹ copies g^-1dry soil,respectively.i Phyllostachys pubescens forest is significantly higher than the other three forests(P<0.05);the physical and chemical properties of the cbb L gene abundance are significantly related to the Available Phosphorus(AP)in the broad-leaved forest,p H in Masson pine forest and the p H in top-soil(P<0.05).The diversity of carbon-fixing bacteria in topsoil of Chinese fir was significantly lower than the other three forest stands(P<0.05)and there was no difference between different forest stands in subsoil;The diversity of carbon-fixing bacteria in subsoil of four forest stands was higher than that in topsoil;Two-factor analysis showed that both forest types and soil layers had significant or extremely significant impact on soil carbon-fixing bacterial diversity.Shannon and Simpson index showed that the influence of forest types was larger than that of soil layers,and the Chao1 and ACE index showed the reverse trends.The dominant phylums of soil carbon-fixing bacteria in four forests were Proteobacteria,Actinobacteria,Cyanobacteria and Verrucomicrobia;The proportions of Methylibium and Nocardia in Phyllostachys pubescens and Chinese fir soil were significantly higher than those in broad-leaved forest and masson pine forest.The heat map results showed that the similarity of soil carbon-fixing bacterial community composition in the Phyllostachys pubescens and Chinese fir soil was high,while that in the broad-leaved forest and the masson pine forest was high in the topsoil.RDA results show that the differences of soil p H,soil organic carbon(SOC),AP,and total nitrogen(TN)in different forest stands are the main factors affecting soil carbon-fixing bacterial community composition.Preliminary conclusions:Four forest types had significant effects on the abundance and community structure of soil carbon-fixing microorganisms.,The results showed that the bamboo forest had the best effects on soil fertility and carbon fixing bacteria from the aspects of soil physical and chemical properties,gene abundance,diversity,and community composition of carbon-fixing bacterial.Carbon-fixing microorganisms contribute more to the accumulation of soil organic matter in Phyllostachys pubescens forest than broad-leaved forest.The exact conclusion needs to be further explored.Comparing the soil particle composition in different parent soils of broad-leaved forests,it was found that the composition and texture of soil particles in different parent rocks were significantly different.The particle composition of silt and tuff soil was similar,and the sandy clay loam developed by granite had a higher content Coarse sand and lower silt;soil nutrient is the silt soil were significantly different with the other two types of soil,showing higher available nitrogen,phosphorus,potassium and lower organic carbon and total nitrogen;parent rock(Except SOC)and soil layer(except p H)have significant effects on soil physical and chemical properties(P<0.05).The effects of the parent rock on soil bacteria were greater than that of soil carbon-fixing bacteria.The gene abundance of granite soil is significantly different from that of the other two types of soil,showing the lowest soil bacterial abundance and the highest carbon-fixing bacteria ratio(cbb L:16S r RNA,granite15%VS silty shale,tuff about 1%).The diversity of carbon-fixing bacteria in granite soils were significantly different from those of powder shale and tuff,with low diversity(Simpson and Shannon)and high abundance(Chao1 and ACE index).The most three dominant phylums(Nocardia,Methylobacterium,and Red Longevity)in granite soil had low percentage,especially the Red Longevity.The factors driving the changes of cbb L abundance were complex,and only the effective P in granite soil had a significant correlation;carbon-fixing bacterial community structure is mainly driven by soil AK,SOC and AN in topsoil(P<0.05),and subsoil Driven by AP(P<0.05).The effects of soil organic carbon components on the abundance of carbon-fixing bacteria showed that the effects of different forest types on soil organic carbon components vary form different parent rocks,and there is no consistent order between four forest types.The effects of parent rocks on soil organic carbon are greater than forest types.The carbon-fixing bacteria in Anji and Lin'an showed that the Phyllostachys pubescens forest and Pinus massoniana forest were significantly higher(P<0.05)than the broad-leaved forest and Chinese fir forest,and the overall level was significantly higher than that of Longquan;cbb L gene abundance was positively correlated with EOC,but negatively correlated with WSOC and BR.Soil ECO content is the main factor controlling variation of soil cbb L gene abundance.Conclusion:The parent rock and forest types had significant effects on soil organic carbon composition and cbb L gene abundance,but the former is greater than the latter.Conclusion:The study showed that the parent rocks had greater impact on soil physical and chemical properties,organic carbon components,and abundance and community composition of carbon-fixing bacteria than forest types.Among them,granite develops soil had significant differences with powde,shale and tuff,showing the highest SOC and lowest EOC,cbb L occupied15%of 16S r RNA and it was speculated to have a large carbon function in granite develops soil.