土壤细菌呼吸对西双版纳热带森林恢复的响应

Response of soil bacterial respiration to tropical forest restoration in Xishuangbanna,China

揭示不同恢复阶段热带森林土壤细菌呼吸季节变化及其主控因素,对于探明土壤细菌呼吸对热带森林恢复的响应机制具有重要的科学意义。以西双版纳不同恢复阶段热带森林(白背桐群落、崖豆藤群落和高檐蒲桃群落)为研究对象,运用真菌呼吸抑制法及高通量宏基因组测序技术分别测定土壤细菌呼吸速率和细菌多样性,并采用回归分析及结构方程模型揭示热带森林恢复过程中土壤细菌多样性、pH、土壤碳氮组分变化对土壤细菌呼吸速率的影响特征。结果表明:1)不同恢复阶段热带森林土壤细菌呼吸速率表现为:高檐蒲桃群落((1.51±0.62)CO_(2)mg g^(-1)h^(-1))显著高于崖豆藤群落((1.16±0.56)CO_(2)mg g^(-1)h^(-1))和白背桐群落((0.82±0.60)CO_(2)mg g^(-1)h^(-1))(P<0.05)。2)不同恢复阶段土壤细菌呼吸速率呈显著的单峰型季节变化(P<0.05),最大值均出现在9月:高檐蒲桃群落((2.41±0.29)CO_(2)mg g^(-1)h^(-1))>崖豆藤群落((1.75±0.33)CO_(2)mg g^(-1)h^(-1))>白背桐群落((1.60±0.66)CO_(2)mg g^(-1)h^(-1))。3)土壤微生物量碳含量随热带森林恢复亦呈增加的变化趋势,即高檐蒲桃群落((3.06±1.45)g/kg)>崖豆藤群落((2.22±1.40)g/kg)>白背桐群落((1.75±1.14)g/kg);微生物量碳的季节变化可解释21%—35%的土壤细菌呼吸变化。4)不同恢复阶段土壤细菌多样性随热带森林恢复呈显著的增加趋势,其对土壤细菌呼吸的解释量大小顺序为:高檐蒲桃群落(72.60%)>崖豆藤群落(67.90%)>白背桐群落(64.80%)。5)相较于恢复初期,恢复后期碳库(总有机碳、微生物量碳、易氧化有机碳)和氮库(全氮、水解氮、铵氮、硝氮)提升了4.27%—58.77%;土壤细菌呼吸与总有机碳、铵态氮达到极显著正相关(P<0.01),与土壤全氮和pH显著正相关(P<0.05)。6)结构方程表明,细菌香侬指数、微生物量碳、全氮、铵态氮及pH能直接调控细菌呼吸,其中香侬指数及微生物量碳是细菌呼吸的主要贡献者;土壤有机碳、全氮及铵态氮会通过升高香侬指数及微生物量碳含量间接促进细菌呼吸。因此,西双版纳热带森林恢复显著促进了土壤细菌呼吸,土壤细菌呼吸变化主要由土壤细菌香侬多样性和微生物量碳直接调控,而土壤总有机碳、全氮和铵氮对细菌呼吸具有间接影响。

This study aimed to explore the seasonal variations and their main controlling factors for soil bacterial respiration rates along secondary tropical forest succession,thus identifying the response mechanism of soil bacterial respiration to tropical forest restoration.In this study,the substrate-induced respiration technique and high-throughput sequencing technology were utilized to determine the soil bacterial respiration rate and bacterial diversity,respectively,at three secondary restoration stages(i.e.,Mallotus paniculatus,Mellettia leptobotrya,and Syzygium oblatum communities)of Xishuangbanna.We also analyzed the effects of the shifts in soil bacterial diversity,pH,carbon pool and nitrogen pool on soil bacterial respiration rate,using regression and structural equation model analyses.The results showed that:1)the soil bacterial respiration rates were significantly higher in S.oblatum((1.51±0.62)CO_(2)mg g^(-1)h^(-1))than in those in M.leptobotrya((1.16±0.56)CO_(2)mg g^(-1)h^(-1))and M.paniculatus((0.82±0.60)CO_(2)mg g^(-1)h^(-1)).2)Soil bacterial respiration rates showed an obvious single-peak seasonal trend with the maximum value occurred in September.In September,soil bacterial respiration rates were ranked as S.oblatum community((2.41±0.29)CO_(2)mg g^(-1)h^(-1))>M.leptobotrya community((1.75±0.33)CO_(2)mg g^(-1)h^(-1))>M.paniculatus community((1.60±0.66)CO_(2)mg g^(-1)h^(-1)).3)Soil microbial carbon also showed an increasing trend along the tropical forest restoration;the order of soil microbial carbon was S.oblatum community((3.06±1.45)g/kg)>M.leptobotrya community((2.22±1.40)g/kg)>M.paniculatus community((1.75±1.14)g/kg).Microbial carbon showed a significantly seasonal variation,which could explain 21%to 35%of the variations in soil bacterial respiration rates.4)Soil bacterial diversity increased along the tropical forest restoration;the contribution of bacterial diversity to soil bacterial respiration dynamics was ranked as S.oblatum(72.60%)>M.leptobotrya(67.90%)>M.paniculatus(64.80%).5)The concentrations of carbon and nitrogen pools in later restoration stage increased by 4.27%—58.77%,compared with the early restoration stage.Soil bacterial respiration rates were significantly positively correlated with soil organic carbon and ammonium nitrogen(P<0.01),as well as total nitrogen and soil pH(P<0.05).6)The structural equation modeling showed that bacterial Shannon index,microbial biomass carbon,total nitrogen,ammonium nitrogen,and soil pH could directly regulate bacterial respiration;bacterial Shannon index and microbial biomass carbon primarily contributed to soil bacterial respiration dynamics.In contrast,soil organic carbon,total nitrogen,and ammonium nitrogen indirectly promoted bacterial respiration by increasing Shannon index and microbial biomass carbon.Therefore,the secondary tropical forest succession in Xishuangbanna significantly promoted the soil bacterial respiration.The temporal variations in soil bacterial respiration rates were primarily directly determined by microbial carbon and bacterial Shannon diversity,while they were indirectly regulated by total organic carbon,ammonium nitrogen,and total nitrogen.