北京东灵山白桦和蒙古栎的根际效应及其季节动态

Rhizosphere effects of Betula platyphylla and Quercus mongolica and their seasonal dynamics in Dongling Mountain,Beijing

为了探究木本植物根际效应的季节动态及其驱动因素,以北京市东灵山地区两种主要植被类型——白桦(Betula platyphylla)林和蒙古栎(Quercus mongolica)林中的优势树种为研究对象,于2017年的春(5月)、夏(7月)、秋(9月)、冬(12月)4个季节分别测定根际土壤与非根际土壤的理化性质、微生物生物量、碳矿化速率及净氮矿化速率、胞外酶活性和矢量特征以及植物的根系、叶片功能性状,分析根际效应的季节变化动态。结果发现:(1)土壤pH及铵态氮含量、微生物生物量、碳氮矿化速率、胞外酶活性和矢量特征指标在根际土壤与非根际土壤之间存在显著差异,根际效应主要呈现为正效应,即根际土壤高于非根际土壤。(2)根际效应存在显著的季节动态,表现为秋季的根际效应最强。(3)根际效应与植物根系和叶片功能性状之间存在显著相关关系。细根生物量与可提取有机碳、土壤总碳、总氮含量的根际效应显著正相关;叶干物质含量、叶碳氮比与微生物生物量碳含量、微生物生物量氮含量、碳矿化速率、酸性磷酸酶活性的根际效应显著正相关。研究结果表明,植物功能性状对于植物的根际效应具有重要作用;在东灵山的温带落叶阔叶林,可能由于秋季植物地下碳输入量最高,导致根际微生物数量和活性增加,从而出现秋季微生物生物量及活性的根际效应高于其他季节的现象。

Aims The objective of this study was to explore the seasonal variations of the rhizosphere effects of woody plants and their driving factors,and to assess the importance of plant functional traits in the control of rhizosphere processes.Methods We collected paired rhizosphere and bulk soils of the dominant tree species of two main types of vegetation in Dongling Mountain,Beijing,Betula platyphylla forest and Quercus mongolica forest.Soil physiochemical properties,microbial biomass,carbon and net nitrogen mineralization rates,extracellular enzyme activities and vector characteristics of rhizosphere and bulk soils,as well as plant root and leaf functional traits,in spring(May),summer(July),autumn(September),and winter(December)of 2017 were measured to analyze the seasonal dynamics of rhizosphere effects and their driving factors.Important findings(1)There were significant differences in soil pH,NH4+-N,microbial biomass,carbon and net nitrogen mineralization rates,extracellular enzyme activities and vector characteristics between rhizosphere soil and bulk soil,and these rhizosphere effects were mainly positive.(2)The rhizosphere effects had significant seasonal dynamics,usually being strongest in autumn.(3)There were often significant correlations between rhizosphere effects and plant root and leaf functional traits.Among them,fine root biomass was significantly and positively correlated with the rhizosphere effect on contents of extractable organic carbon,soil total carbon and total nitrogen.Leaf dry matter content and leaf carbon and nitrogen ratio were significantly and positively correlated with the rhizosphere effect on microbial biomass carbon content,microbial biomass nitrogen content,carbon mineralization rate,and acid phosphatase activity.These results showed that the functional traits of plants were of great significance in rhizosphere processes.In the temperate deciduous broadleaf forest in Dongling Mountain,the highest belowground carbon allocation of plants leads to an increase in the biomass and activity of rhizosphere microorganisms in autumn,which makes the rhizosphere effect of microbial biomass and activity in autumn higher than that in other seasons.