岩溶石漠化区不同造林模式下土壤有机碳和微生物群落结构的变化特征OA

Afforestation is an important way for ecological restoration of karst rocky desertification area in southwest China.Studying the variation characteristics of soil organic carbon and microbial community structure under different afforestation modes can effectively indicate soil quality,which has great significance in guiding rocky desertification restoration.This study was conducted in Changchongli,Lingchuan county,Guilin City,Guangxi,a region characterized by typical karst peak-cluster depressions and valleys.The bedrock mainly consists of limestone and the soil layer is relatively shallow.Three representative afforestation modes,including Osmanthus fragrans Lour.,Pinus massoniana Lamb.,and Styphnolobium japonicum(L.)Schott,were selected as research subjects,with adjacent Citrus reticulata Blanco cv.'Shatangju'serving as the control.The four sites shared similar altitude,slope aspect,slope position,and slope gradient,and all soils were calcareous.In this study,Soil Organic Carbon(SOC)content and chemical composition,together with the abundance and community structure of soil microorganisms,were examined under different afforestation modes. The results showed that:compared to orchard soils,SOC and total nitrogen contents increased significantly under O.fragrans and S.japonicum plantations,with increases of 47.6％and 45.3％for O.fragrans and 126％and 121％for S.japonicum,respectively,whereas no significant variations occurred under P.massoniana.Water Holding Capacity(WHC)also increased significantly under O.fragrans and S.japonicum,while the C:N ratio showed no significant difference.In contrast,WHC showed no marked variation under P.massoniana but had a significantly elevated C:N ratio.The orchard soil was acidic(pH 4.34),whereas soils under the three afforestation modes were neutral(pH of 6.90 to 7.09).Total calcium was lowest in orchard soil(2.77 g·kg-1)but increased significantly in the afforested soils,reaching 11.8 g·kg-1under S.japonicum.In contrast,total phosphorus and potassium contents were significantly lower in afforested soils.Soil texture also changed following afforestation,with a reduction in clay content and increases in proportions of silt and sand.The chemical composition of SOC also differed among afforestation types.O-alkyl C dominated in soils under O.fragrans and S.japonicum,whereas aromatic C was the predominant component in P.massoniana soils.Compared to orchard soils,aromatic C in P.massoniana soils increased by 20.7％while O-alkyl C decreased by 16.4％,with no significant variations in alkyl C or carbonyl C.Conversely,O-alkyl C in soils under O.fragrans and SS.japonicum increased by 9.1％and 2.4％,respectively,while,aromatic C decreased by 21.1％and 11.8％.Compared to the orchard soil(0.65),the ratio of alkyl C to O-alkyl C rose significantly to 0.79 in P.massoniana soils,whereas no significant differences were observed under O.fragrans or S.japonicum.Afforestation significantly enhanced total soil microbial PLFA abundance under all three afforestation modes,reaching 14.4,9.00,and 16.3 nmol·g-1 under O.fragrans,P.massoniana,and S.japonicum,respectively.Except for fungi and Gram-positive bacteria in P.massoniana soils,the abundances of bacteria,Gram-negative bacteria,arbuscular mycorrhizal fungi,and actinomycetes were significantly higher than those in afforested soils,with the most pronounced increases observed under O.fragrans and S.japonicum.The relative abundance of microbial groups followed the order:bacteria＞Gram-positive bacteria＞Gram-negative bacteria＞actinomycetes＞fungi＞arbuscular mycorrhizal fungi across all soil types.Among all afforestation modes,the relative abundances of Gram-negative bacteria,arbuscular mycorrhizal fungi,and actinomycetes significantly increased,whereas Gram-positive bacteria declined non-significantly.Fungal abundance remained low across all plantations,with fungal/bacterial ratio(F:B)not exceeding 0.25.Compared to Shatangju orchard soil,the F:B ratio increased significantly under O.fragrans,slightly under S.japonicum,and showed a decling trend under P.massoniana.This findings indicate that O.fragrans and S.japonicum were more conducive to maintaining soil ecosystem stability in karst regions. In karst regions,soil under P.massoniana exhibited lower SOC content dominated by recalcitrant components,whereas O.fragrans and S.japonicum promoted SOC accumulation with a prevalence of labile fractions.Overall,these two species demonstrated significantly greater potential for improving soil quality,thereby fostering more effective soil ecosystem restoration.