Soil Microbial Community Properties Across A Chinese Cedar (Cryptomeria Japonica Var.sinensis) Chronosequence

Chinese cedar(Cryptomeria japonica var.sinensis)is one of the important afforestation tree species in China,widely planted in the Sichuan Basin.Soil microorganisms are an important component of ecosystems and important indicators that characterize soil quality and productivity.Soil microbial communities are regulated by multiple factors such as climate,soil nutrients,and vegetation types.Forest stand age is an important factor affecting plant-soil-microbial feedback.Currently,there is still a knowledge gap on how stand age would affect soil microbial communities in Chinese cedar plantations.In view of this,this study took Chinese cedar plantations of different stand ages(7-year young forest,13-year middle-aged forest,24-year near-mature forest,33-year mature forest,and 53-year overmature forest)in the state-owned forest farm of Hongya County,Sichuan Province as the research object.Studied characteristics of soil bacterial and fungal microbial communities in two soil layers(0～15cm and 15～30 cm)through high-throughput sequencing,combined with soil physicochemical properties,analyzed the changes and driving factors of soil microbial community with stand age.The main results are as follows:1.Stand age and soil layer significantly affected soil physicochemical properties.Statistics show that the physicochemical of the two depths of soil have similar trends with stand age,namely,soil water content,organic carbon(OC),total nitrogen(TN),total phosphorus(TP),and ammonium N content show a trend of first increased and then decreased with stand age.The maximum values appear in the near mature or mature forest stands.The soil bulk density and p H value showed opposite trends,with the lowest value being observed in the near mature or mature stands.The soil nitrate N content increased with the increase of stand age,showing the lowest performance in the young stand.Except for the total phosphorus(TP)content,there are significant differences in soil physicochemical properties between soil depths.The soil bulk density and p H of the15～30 cm soil are significantly higher than those of the 0～15 cm soil,while the water content,OC,TN,ammonium N,and nitrate N content are opposite.2.Stand age significantly affected the soil fungal richness index(Chao1)and diversity index(Shannon),both of which were higher in near mature and mature forests than in other forest age groups.However,stand age significantly affected the richness index of soil bacteria,with the highest performance in middle-aged forests.The soil depth significantly affected the richness index of the fungal community and the diversity index of the bacterial community,which were greater in the 0～15 cm than in the 15～30 cm layer.PCo A analysis showed that the first two axes explained 50.43% and 39.92%,respectively,of variation in bacterial and fungal communities.Permutational multivariate analysis of variance showed that there were significant differences in the composition of soil bacterial and fungal communities among forest age and between soil depths.3.The dominant bacterial phyla were Proteobacteria,Acidobacteriota,Chloroflexi,and Actinobacteria,accounting for 28.2%,26.5%,16.1%,and 14.5% in relative abundance,respectively.Bacterial community composition was significantly affected by stand ages rather than by soil depths.Relative abundance of Proteobacteria varied,following the orders of 33 a > 24 a > 7 a > 13 a > 53 a in the 0～15 cm soil,and 24 a > 33 a > 7 a > 53 a > 13 a in the 15～30 cm layer.The relative abundance of Acidobacteriota in both soil layers followed the order of 13 a > 33 a > 53 a > 24 a > 7a.The dominant bacterial genera were Acidobacteriota subgroup-2,Acidothermus,Xanthobacteriaceae,and Elstralasse,accounting for 13.2%,6.1%,5.9%,and 5.7%,respectively,in relative abundance.Bacterial genera composition was significantly affected by different stand ages,as well.Among them,the relative abundance of Acidobacterium subgroup-2 in the 0～15 cm soil showed the highest relative abundance in the 13 a and 33 a stands,while the relative abundance of Acidobacterium subgroup-2 in the 15～30 cm soil was the highest in the33-and 53-year-old stands.4.The dominant fungal phyla were Ascomycota,Basidiomycota,Rozellomycota,and Mortierellomycota,accounting for 42.1%,18.9%,17.6%,and 8.9%,respectively,in relative abundance.The relative abundance of Ascomycetes and Basidiomycetes was significantly affected by stand age.In the 0～15 cm soil,abundances of Ascomycetes and Basidiomycetes were the highest in the 33 a,while in the 15～30 cm soil,both were the most abundant in the 13 a.Mortierella and Saitozyma were the dominant fungal genera accounting for 8.9%,and 8.2%,respectively,of relative abundance.Stand age significantly affected the relative abundance of Mortierella and Saitozyma.The relative abundance of Mortierella in the two soil depths was the highest in the 24 a and 13 a,respectively,while the relative abundance of Saitozyma in the two soil depths was the highest in the 24 a.5.The redundancy analysis(RDA)and Monte Carlo test showed soil p H and nitrate concentration had statistically significant correlations with the relative abundance of soil bacteria,while soil OC concentration was significantly correlated with the relative abundance of soil fungi.Soil p H,nitrate concentration,and SOC concentration were important factors affecting the soil bacterial and fungal communities.In summary,stand age and soil depth have a significant impact on the composition,diversity,and structure of soil microbial communities in the Chinese cedar plantation in Yuping District,West China.The influence of stand age on soil fungal communities is stronger than that of bacterial communities.Soil p H and N availability are the main factors affecting soil bacterial communities,while soil OC is the main factor affecting soil fungal communities.The research results can provide scientific basis for the ecosystem management of Chinese cedar plantation.