南亚热带常绿阔叶林土壤微生物生物量碳氮年际动态特征及其影响因子

Inter⁃annual dynamics of soil microbial biomass carbon and nitrogen in subtropical evergreen broad⁃leaved forest and its environmental impact factors

土壤微生物是土壤有机质和养分循环的主要驱动者,研究土壤微生物生物量碳氮变化、稳态特征及其对环境因子内在的长期响应机理具有重要意义。以南亚热带常绿阔叶林土壤为对象,对土壤微生物生物量碳和氮(MBC和MBN)、土壤有机碳(SOC)、总氮(TN)、总磷(TP)、可溶性碳(ROC)、速效氮(AN)、pH、土壤温度(ST)和土壤含水量(SWC)进行连续10年监测;应用方差分析、相关性和回归分析及稳态分析等探究MBC和MBN的年际变化和稳态特征及主要影响因素。研究结果表明:(1)旱季MBC和MBN含量分别在171.32—358.45和25.90—54.08 mg/kg区间波动,雨季分别在394.01—507.97和68.40—88.05 mg/kg区间波动;旱、雨季的MBC含量年际间变化显著(P<0.05),但MBN含量仅在旱季变化显著(P<0.05)。雨季MBC和MBN含量均显著高于旱季(P<0.01),且雨季的MBC和MBN含量是旱季的2倍以上。(2)旱、雨季的MBC与MBN之间均呈显著正相关(P<0.05)。在旱季,MBC和MBN均与ROC和AN含量显著正相关(P<0.05),此外,MBN含量也与TP(P<0.05)和SOC(P<0.01)显著正相关。在雨季,仅SOC与MBN呈显著正相关(P<0.05)。(3)在旱季,MBC含量变化主要受ROC(P<0.05)和AN(P<0.001)影响,MBN则受AN控制(P<0.05)。在雨季,AN(P<0.05)主导了MBC的变化,TP(P<0.05)和SOC(P<0.05)是MBN变异的主导因子。AN(P<0.001)和SOC(P<0.001)是旱、雨季土壤MBC和MBN变化的主导因子。(4)土壤MBC和MBC/MBN稳态指数在年际间均为绝对稳态型(P>0.05);雨季的MBN(P=0.685)为绝对稳态型,但旱季为非稳态(P<0.01,H>1)。雨季微生物熵显著高于旱季(P<0.01),表明土壤有机质质量及养分利用效率更高。综上,MBC和MBN含量受季节更替显著影响,且主要受土壤SOC和AN的影响;受旱季水分限制,MBN的稳态更差。

Soil microbes are the primary drivers of soil organic matter and nutrient cycling.It is critical to study carbon and nitrogen variations in soil microbial biomass,as well as their steady-state properties and inherent long-term response mechanisms to environmental variables.Soil microbial biomass carbon and nitrogen(MBC and MBN),organic carbon,total nitrogen,total phosphorus,readily oxidizable carbon(ROC),available nitrogen,pH,temperature,and water content have been continuously monitored in a subtropical evergreen broad-leaved forest soil for 10 years in this study.The ANOVA,correlation and regression analysis,and steady-state analysis were employed to investigate the interannual variations and steady-state characteristics of MBC and MBN and the main factors influencing them.The results demonstrated that(1)the MBC and MBN contents varied between 171.32 to 358.45 mg/kg and 25.90 to 54.08 mg/kg in the dry season and from 394.01 to 507.97 mg/kg and 68.40 to 88.05 mg/kg in the rainy season,respectively.Significant inter-annual variation of MBC content in both dry and rainy seasons was detected(P<0.05).Whereas,the content of MBN only changed significantly between years in the dry season(P<0.05).The MBC and MBN contents in the rainy season were significantly higher than those in the dry season(P<0.01)and it′s twice as high in the dry season than in the rainy season.(2)There was a significantly positive correlation between MBC and MBN in both dry and rainy seasons(P<0.05).Both MBC and MBN were positively correlated with ROC and AN in the dry season.Meanwhile,MBN was significantly positively correlated with TP(P<0.05)and SOC(P<0.01).In the rainy season,only MBN was significantly positively correlated with SOC(P<0.05).(3)In the dry season,the variety of the MBC content was mainly influenced by ROC(P<0.05)and AN(P<0.001),whereas MBN variation was primarily influenced by AN(P<0.05).AN(P<0.05)dominated the variation of MBC in the rainy season,while TP(P<0.05)and SOC(P<0.05)were the dominant factors of MBN variation.Taken together,these results suggested that AN(P<0.001)and SOC(P<0.001)were the soil factors with the highest contribution to the variation of MBC and MBN contents.(4)The homeostasis index of MBC and MBC/MBN were absolutely steady-state on an annual scale(P>0.05),and MBN(P=0.685)was an absolutely steady-state in the rainy season.In contrast,the MBN homeostasis index of soil was found to be in an unstable state(P<0.01,H>1)in the dry season.Soil microbial quotient was significantly higher in the rainy season than that in the dry season(P<0.01),implying the quality of soil organic matter and efficiency of nutrient utilization were higher in the rainy season.In summary,the MBC and MBN were significantly influenced by seasonal turnover,and the dominant soil factors on MBC and MBN variation were SOC and AN.Soil MBN was in an unstable state due to water limitations in the dry season.