马尾松根际碳氮利用效率对土壤微生物群落结构的影响

Effect of carbon and nitrogen utilization efficiencies in rhizosphere on soil microbial community on Pinus massoniana

微生物元素利用效率在调节土壤碳(C)和氮(N)矿化过程中有重要作用,然而土壤微生物转化的有机碳(SOC)、N比例研究尚不充分。以千岛湖5年生、9年生、19年生、29年生、35年生马尾松林为研究对象,测定根际SOC、土壤总氮(TN)、土壤微生物量碳氮(MBC、MBN)、土壤C、N获得酶活性和土壤微生物群落结构,阐明土壤微生物C、N利用效率(CUE、NUE)和元素阈值比(TER)与微生物群落结构关系。结果表明:5年生马尾松根际SOC、TN均明显高于其它林分(P<0.05),其土壤微生物量C/N比则显著(除9年生)低于其它林分(P<0.05),证实了微生物CUE对底物养分状态敏感性较低。35年生马尾松根际微生物NUE均显著高于其它林龄(除19年生),说明土壤中大部分N转化为MBN,与35年生马尾松土壤微生物生物量显著高于其它林分一致。马尾松根际NUE和TER与土壤微生物总生物量及其组分生物量均呈显著正相关关系(P<0.05),说明土壤微生物生长繁殖受NUE影响。所有林龄马尾松TER均大于土壤C/N比,表示研究区域生态系统处于C或者能源限制,而非N限制;证实了土壤C/N比减少到TER以下时,土壤有机物获得C的成本高于获得N的成本。5年生马尾松微生物CUE和TER均最低,二者没有明显的相关关系,可能低龄马尾松林CUE和NUE有补偿性关系。研究强调了土壤根际微生物元素利用效率和微生物群落对土壤C和N循环过程的重要性,为亚热带森林生态系统土壤经营管理提供了依据。

The use efficiencies of microbial elements play an important role in regulating mineralization processes of soil carbon(C)and nitrogen(N),however,the transformation proportion of soil microbial to soil organic C(SOC)and N has not been adequately studied.In this study,we measured SOC,soil total nitrogen(TN),soil microbial biomass carbon and nitrogen(MBC,MBN),soil C and N acquisition enzyme activity and soil microbial community structure in rhizosphere soil in 5-year-old,9-year-old,19-year-old,29-year-old,and 35-year-old Pinus massoniana Lamb.stands in Thousand-island Lake forest farm.,and elucidated the relationships between the microbial community structure and the soil microbial carbon utilization efficiency(CUE)and nitrogen utilization efficiency(NUE),as well as the threshold elemental ratio(TER).The results showed that SOC and TN in rhizosphere soil of 5-year-old P.massoniana stands were significantly higher than other stands(P<0.05),and its soil microbial C/N ratio was significantly lower than that of other stands(except for 9-year-old)(P<0.05),confirming that the microbial CUE was less sensitive to the substrate nutrient status.Microbial NUE in rhizosphere soil of 35-year-old P.massoniana stands was significantly higher than that of other stands(except for 19-year-old),indicating that most of the TN was transferred to MBN.This was consistent with the result that there was a significantly higher soil microbial biomass in 35-year-old P.massoniana than in other stands.The microbial NUE and TER in soil rhizosphere were significantly positively correlated with total soil microbial biomass and its component biomass(P<0.05),indicating that soil microbial reproduction is influenced by microbial NUE.In this study,the TER were greater than the soil C/N ratio in all P.massoniana stands,indicating that the ecosystem in the study area was C or energy-limited instead of N-limited.This result confirmed the fact that if the soil C/N ratio is lower TER,the cost of C acquisition in soil organic matter would be higher than that for N acquisition.The microbial CUE and TER in 5-year-old P.massoniana stand soils in this study were the lowest,and there was no relation with each other;implying that a compensatory relationship probably exists between CUE and NUE in young P.massoniana stands.This study highlights the importance of microbial element use efficiency and microbial communities in soil C and N cycling processes in rhizosphere,which provides reference for soil management in subtropical forest ecosystems.