入侵植物紫茎泽兰根围土壤化学及微生物属性海拔变化格局

Shifts in chemical and microbiological properties belowground of invader Ageratina adenophora along an altitudinal gradient

热带地区山地生态系统是外来植物入侵的重要区域,是研究外来植物扩散机制的“天然实验室”。本研究试图探明入侵植物紫茎泽兰(Ageratina adenophora)根围土壤化学(pH及土壤养分)和微生物(酶活性和细菌群落)特性沿海拔梯度的变化规律。本研究以哀牢山(1400–2400 m)不同海拔梯度分布的紫茎泽兰为研究对象,采集根围土,测定土壤有机碳及养分含量,以及植物根系碳和氮含量。分析与土壤有机碳、氮及磷循环的酶活性,通过计算土壤酶化学计量参数,探究微生物生长代谢利用碳、氮及磷的规律。借助高通量测序技术对16S rDNA的V4区测序,分析细菌群落结构。研究结果显示,海拔显著影响紫茎泽兰根系氮及及其根围土壤有机碳含量,且这些测量指标在海拔2000 m出现拐点。处在低海拔,入侵植物快速生长耗竭土壤中相对缺乏的磷,磷素是限制微生物生长的重要养分元素;而在高海拔,微生物需要投入更多的能量降解有机质获取碳,导致微生物生长的碳限制。细菌群落β多样性及pH是决定不同海拔酶化学计量参数差异的重要因子;变形菌门和酸杆菌门是决定微生物养分利用状况的主要细菌门类。这些结果阐明了不同海拔梯度上紫茎泽兰根围土壤微生物的养分利用规律,有助于认识入侵植物沿海拔扩散机制。

Tropical mountain ecosystems are usually colonized by numerous invasive plant species and represent an ideal‘natural laboratory’to study the effects of altitude on plant invasion.The aim of this study was to investigate the soil chemical and microbiological properties along an altitudinal gradient on a mountain colonized by the invader Ageratina adenophora.Rhizosphere soil of A.adenophora was collected over an altitudinal gradient(1400–2400 m)in Ailao Shan,China.We determined soil organic carbon(C),nutrient contents,enzyme activities,bacterial community composition as well as C and nitrogen(N)contents of the plant roots.Ecoenzymatic stoichiometric indices were calculated to estimate the relative C,N or P limitations of the microbial community.There was a significant effect of altitude on soil organic C in the rhizosphere,and a turning point in these measured variables was detected at an altitude of 2000 m.At low elevations,the rapid growth of invasive plants depleted the deficient phosphorus(P)in tropical soils,leading to microbial P limitation;at high elevations,microbes invested more energy to obtain C from resistant litter,leading to microbial C limitation.Bacterial beta diversity and soil pH contributed most to the altitudinal differences in ecoenzymatic stoichiometry,and Proteobacteria and Acidobacteria were the dominant bacterial phyla that determined the nutrient uptake status of microorganisms.These results demonstrate how microbial nutrient acquisition belowground of A.adenophora along an altitudinal gradient,which could contribute to further knowledge about the effects of altitude on biological invasion.