青藏高原湖泊沉积物中有机碳组分构成及其对微生物群落结构的影响

Organic carbon composition in lake sediments on the Qinghai-Tibet Plateau and the influence on microbial community structure

摘要:

【目的】探究湖泊沉积物中有机碳组分构成及其对湖泊微生物群落结构的影响。【方法】本研究采集了青藏高原29个湖泊共81个沉积物样品，通过硫酸水解法分析样品中易降解和难降解有机碳含量及其与环境变量之间的相关性；同时使用高通量测序技术分析样品中原核微生物和真菌群落的多样性和组成及其与易降解和难降解有机碳含量的相关关系。【结果】本研究的青藏高原湖泊沉积物中易降解有机碳Ⅰ (labile organic carbon I, LOC Ⅰ)、易降解有机碳Ⅱ (labile organic carbon II, LOC Ⅱ)和难降解有机碳(recalcitrant organic carbon, ROC)的含量分别为0.03-29.62 mg/g、0.02-23.38 mg/g和0.64-75.72 mg/g，ROC是沉积物有机碳的主要组分(占比为54.97%±19.50%)。LOC Ⅰ含量与海拔、总氮、总磷、钙离子、活性钙和活性铁含量显著相关(P<0.05)；LOC Ⅱ含量与总氮、钙离子和活性钙含量显著相关；而ROC含量与海拔、总氮、总磷、钙离子和活性钙含量显著相关。其中，钙离子和活性钙的浓度与3种有机碳组分的含量均存在显著正相关，暗示有机质与钙结合的方式可能是青藏高原湖泊沉积物有机碳保存的重要机制。LOC Ⅰ、LOC Ⅱ和ROC含量与沉积物中原核微生物群落α多样性均呈显著正相关；ROC含量与真菌群落α多样性呈显著正相关。LOC Ⅰ含量与α变形杆菌(Alphaproteobacteria)、放线菌(Actinobacteria)、厌氧绳菌(Anaerolineae)、海藻球形菌(Phycisphaerae)和红嗜热菌(Rhodothermia)的相对丰度显著相关；LOC Ⅱ含量与Anaerolineae、γ变形菌(Gammaproteobacteria)和Phycisphaerae相对丰度显著相关；ROC含量与Actinobacteria和Anaerolineae的相对丰度显著相关。LOC Ⅰ含量是影响原核微生物和真菌群落组成的显著环境因子，其解释量分别为1.1%和0.3%。环境因素解释了样品间原核微生物群落7.2%和真菌群落3.9%的变化，而空间因子解释了原核微生物群落14.6%和真菌群落6.4%的变化。随机过程对原核微生物和真菌群落组成的贡献分别为50%和47%。【结论】本研究暗示湖泊沉积物有机碳的保存受到铁、钙元素化学保护机制的影响；有机碳组分含量显著影响原核微生物和真菌群落多样性和组成，但其贡献值较低；环境理化参数、空间因子和生态随机过程对湖泊沉积物原核微生物和真菌群落组成具有重要影响。本研究加深了我们对湖泊沉积物有机碳组分构成及其影响微生物群落组成的认识。

Abstract:

[Objective] To explore the organic carbon composition in lake sediments and the influence on the composition of lake microbial communities. [Methods] We collected 81 sediment samples from 29 lakes on the Qinghai-Tibet Plateau. The concentration of labile and recalcitrant organic carbon in the studied lake sediments was determined after sulfuric acid hydrolysis, and the correlation with environmental variables was analyzed. Meanwhile, the diversity and composition of prokaryotic and fungal communities in the sediments and their correlation with the concentration of labile and recalcitrant organic carbon were investigated by Illumina sequencing and ecological statistics. [Results] The concentration of labile organic carbon I (LOC Ⅰ), labile organic carbon Ⅱ (LOC Ⅱ), and recalcitrant organic carbon (ROC) in the studied lake sediments was 0.03-29.62 mg/g, 0.02-23.38 mg/g, and 0.64-75.72 mg/g, respectively. ROC was the major component of organic carbon in the studied lake sediments, accounting for 54.97%±19.50%. Concentration of LOC Ⅰ was significantly correlated with elevation, and concentration of total nitrogen, total phosphorus, calcium ion, active calcium, and iron (P<0.05). Concentration of LOC Ⅱ was significantly correlated with concentration of total nitrogen, calcium ion, and active calcium. ROC concentration was significantly correlated with elevation, concentration of total nitrogen, total phosphorus, calcium ion, and active calcium. Among them, the concentration of calcium ion and active calcium was positively correlated with the concentration of LOC Ⅰ, LOC Ⅱ, and ROC, suggesting that organic matter binding with calcium may be an important mechanism for the preservation of organic carbon in lake sediments on the Qinghai-Tibet Plateau. The alpha diversity of prokaryotic community was positively correlated with the concentration of LOC Ⅰ, LOC Ⅱ, and ROC, while the α diversity of fungal community was only positively correlated with ROC concentration. The relative abundance of Alphaproteobacteria, Actinobacteria, Anaerolineae, Phycisphaerae, and Rhodothermes was significantly correlated with LOC Ⅰ concentration. The relative abundance of Anaerolineae, Gammaproteobacteria, and Phycisphaerae was significantly correlated with the concentration of LOC Ⅱ. The relative abundance of Actinobacteria and Anaerolineae was significantly correlated with ROC concentration. The concentration of LOC Ⅰ significantly affected both prokaryotic and fungal community composition in the studied lake sediments with the variance explained of 1.1% and 0.3%, respectively. Environmental factors explained 7.2% and 3.9% of the variation in prokaryotic and fungal community composition among samples, respectively, while spatial factors explained 14.6% and 6.4%, separately. The contributions of stochastic process to prokaryotic and fungal community assembly were 50% and 47%, respectively. [Conclusion] Organic carbon preservation in the studied lake sediments was controlled by the chemical protection of iron and calcium. Organic carbon components significantly affected the diversity and composition of prokaryotic and fungal community, but the variance explained was low. Physicochemical variables, spatial factors, and stochastic processes exhibited important influence on prokaryotic and fungal community composition in the studied lake sediments. This study advances our understanding of organic carbon components in sediments and their impact on microbial community composition in lakes.