金鱼藻茎叶腐烂分解对枯落物表面真菌的影响

Stem and Leaf of Ceratophyllum demersum Decomposition Alters Fungal Community Structure on Litter Surfaces

真菌是植物枯落物主要分解者之一,其在枯落物分解以及生物地球化学循环中发挥着重要作用。目前关于沉水植物枯落物分解对真菌群落结构等的影响研究较为匮乏。笔者以沉水植物金鱼藻(Ceratophyllum demersum)为研究对象,采用2种不同孔径分解袋构建枯落物腐烂分解野外实验系统,定期(6、28、145 d)采集枯落物样品,采用内部转录间隔区(ITS)高通量测序技术对枯落物表面真菌群落结构及多样性进行分析,并揭示枯落物理化参数及所在水域水质参数对真菌的影响。结果表明,18个金鱼藻枯落物样品共获得2786个可操纵分类单元(OTU),包含13门42纲110目262科542属,优势门为子囊菌门(Ascomycota),相对丰度为46.31%。3个分解时间内枯落物真菌α多样性指数无显著差异(P>0.05),而真菌群落结构则随着分解时间延长呈明显变化。基于韦恩图(Venn)、层级聚类以及主坐标分析(PCoA)结果证实,同一分解时间枯落物真菌群落组成较为相似,而不同分解时间枯落物真菌群落组成发生明显改变。相似性分析(ANOSIM)以及置换多元方差分析(PERMANOVA)表明,枯落物真菌群落结构的显著性差异受分解时间的影响(P<0.05),而不受枯落物分解袋孔径差异的影响(P>0.05)。典范对应分析(CCA)以及冗余分析(RDA)揭示了真菌群落结构变化与枯落物生物量、分解速率、全氮(TN)、全磷(TP)、全碳(TC)含量、碳氮比(C/N)以及氮磷比(N/P)等参数间存在显著相关性(P<0.05)。所在水域水体TN和TP浓度、COD、pH值、DO浓度以及温度因子亦对真菌群落结构的变化产生显著影响(P<0.05)。斯皮尔曼相关性热图以及曼特尔检验进一步验证了金鱼藻枯落物真菌物种及群落组成受枯落物理化特性及其所在水域水质参数的双重影响。

Fungi plays an important role in litter decomposition and the geochemical cycling of nutrient elements.However,limited information is currently available regarding the fungal communities during the litter decomposition,particularly for submerged plants.Thus,a 145-d field study was conducted to evaluate the extent and direction by which the litter decomposition of Ceratophyllum demersum in affecting fungi community and composition using litter bag incubation technique.Two kinds of decomposition bags with different pore sizes(0.15 vs.0.60 mm diameters)were used,and retrieved on the day 6,28,and 145 of the incubation to monitor the mass loss,nutrient release,and fungal community during the litter decomposition.Results show that totally 2786 operational taxonomic units(OTU)were obtained from 18 samples,including 13 phyla,42 classes,110 orders,262 families,and 542 genera.The dominant phylum was Ascomycota,with a relative abundance of 46.31%.There were no significant differences in alpha diversity indexes of fungi among the three decomposition times(P>0.05).However,fungal community composition was significantly different with the decomposition time.Analysis of similarity(ANOSIM)and permutation multivariate analysis of variance(PERMANOVA)show that the litter fungal community structure was affected by decomposition time(P<0.05),but not by the pore size of litter bag(P>0.05).Canonical correspondence analysis(CCA)and redundancy analysis(RDA)suggested that the fungal community structure was significantly correlated with litter biomass,decomposition rate,TN,TP,TC concentrations,C/N and C/P ratios(P<0.05).The concentration of TN,TP,COD,pH value,DO,and temperature also had a significant impact on the change of fungal community structure(P<0.05).Spearman correlation analysis and Mantel test further confirmed that the fungal species and community composition were co-affected by physio-chemical characteristics of the litter and water quality parameters.Overall,our results provide the essential data for evaluating the ecological functions of submerged plants during the litter decaying period.