氮添加土壤微生物群落结构影响微生物碳利用效率

The influence of soil microbial community structure on microbial carbon use efficiency under nitrogen addition

尽管近年来中国氮(N)沉降水平逐渐趋于稳定,但中国东南地区N沉降相比于其他地区仍处于较高水平。N沉降对陆地生态系统碳循环过程的影响不容忽视。微生物碳利用效率(CUE)是指微生物将吸收的碳转化为生物量碳的效率,高微生物CUE意味着高土壤有机碳存储潜力。因此,探究N沉降背景下微生物CUE的变化将有助于进一步认识陆地生态系统土壤碳存储的变化。然而,目前关于N沉降下微生物群落结构的变化如何影响微生物CUE鲜有报道。在福建省泉州市戴云山国家级自然保护区的罗浮栲林通过N添加模拟N沉降。实验共包括三个N添加处理:对照(CT,+0 kg hm^(-2)a^(-1))、低氮(LN,+40 kg hm^(-2)a^(-1))和高氮(HN,+80 kg hm^(-2)a^(-1))。测定不同处理土壤基本理化性质、微生物生物量、酶活性和CUE,并使用高通量测序对微生物群落结构和多样性进行测定。结果表明,N添加显著影响微生物CUE,随着N添加水平的增加,CUE逐渐增加;相反,土壤pH、可提取有机碳(EOC)和微生物生物量碳(MBC)均呈现下降趋势。N添加对土壤微生物群落α多样性总体上无显著影响。非度量多维度尺度(NMDS)分析表明,N添加显著改变了微生物的群落结构。尤其对于真菌而言,不同N添加处理的真菌群落明显分开为三簇。微生物CUE分别与土壤pH、EOC和真菌NMDS1呈显著的负相关关系,与矿质氮含量呈现显著正相关关系。随机森林分析表明,N添加下影响微生物CUE的类群主要是富营养菌(如变形菌门和子囊菌门)。研究表明N添加下,微生物CUE不仅受土壤养分有效性和pH的调控,同时还受土壤微生物群落结构的影响。未来进一步探究N添加下土壤微生物关键类群的变化可能有助于揭示森林生态系统碳存储过程。

Although the level of nitrogen(N)deposition in China has gradually stabilized in recent years,N deposition in Southeast China is still at a high level compared to other regions.The effect of N deposition on the carbon cycle of terrestrial ecosystems cannot be ignored.Microbial carbon utilization efficiency(CUE)refers to the efficiency of microorganisms in converting absorbed carbon into biomass carbon;high microbial CUE implies high soil organic carbon storage potential,while low microbial CUE implies high carbon loss from the soil.High microbial CUE means high soil organic carbon storage potential.Therefore,exploring the changes of microbial CUE under the N deposition will help to further understand the changes of soil carbon storage in terrestrial ecosystems.However,there are few reports about how the change of microbial community structure affects microbial CUE under N deposition.In this study,N deposition was simulated by N addition in Castanopsis fabri forest in Daiyunshan National Nature Reserve,Quanzhou City,Fujian Province.The experiment included three N addition treatments:control(CT,+0 kg hm^(-2)a^(-1)),low nitrogen(LN,+40 kg hm^(-2)a^(-1)),and high nitrogen(HN,+80 kg hm^(-2)a^(-1)).The soil physical and chemical properties,microbial biomass,enzyme activity,and CUE of different treatments were determined.The microbial community structure and diversity were determined using high⁃throughput sequencing.The results showed that the N addition significantly affected microbial CUE,which gradually increased with the increase of N addition.On the contrary,soil pH,extractable organic carbon(EOC),and microbial biomass carbon(MBC)showed a downward trend.There was no significant effect of N addition on soil microbial communityα⁃diversity.Non⁃metric multidimensional scale(NMDS)analysis showed that N addition significantly changed the microbial community structure.Especially for fungi,the fungal communities with different N addition treatments were obviously divided into three clusters.Microbial CUE was negatively correlated with soil pH,EOC,and fungal NMDS1,and positively correlated with mineral nitrogen.Random forest analyses showed that the taxa affecting microbial CUE under N addition were predominantly eutrophic(e.g.,Ascomycetes and Ascomycetes)and were able to devote more carbon to growth than respiration compared to nutrient⁃poor taxa.To sum up,this study shows that microbial CUE is not only regulated by soil nutrient availability and pH,but also affected by soil microbial community structure under N addition.Therefore,further exploration of changes in key soil microbial taxa under N addition in the future may help to reveal the carbon storage process in forest ecosystems.