不同分解程度木麻黄凋落物的养分特征及微生物功能多样性分析

【目的】通过了解木麻黄凋落物分解过程中的养分变化以及微生物碳源的利用特征,明确凋落物微生物多样性与养分之间的关系。【方法】在海南省海口市桂林洋海滨选取10~15年生木麻黄林,按照“S”形五点取样法,分别采集0~5 cm、≥5~10 cm、≥10~15 cm 等3种不同分解程度的凋落物样品,测定其理化性质,并利用Biolog微孔板法测定凋落物外生菌和内生菌的群落功能多样性,对其进行主成分PCA分析和冗余RDA分析。【结果】①凋落物的分解程度越高,其有机碳、全氮、全磷含量越低。②不同分解程度木麻黄凋落物中外生菌和内生菌功能多样性差异显著,外生菌平均颜色变化率(AWCD)随分解程度增加而增大,而内生菌AWCD则降低。③凋落物分解程度越高,外生菌的Shannon、Simpson指数明显升高,McIntosh指数无显著差异;内生菌的Shannon、Simpson指数也随之增加,而McIntosh指数则明显降低。④外生菌和内生菌对6大类碳源利用强度存在差异,优势碳源分别为糖类和多聚物,分解后期胺类和酚类的利用率均有提高。⑤主成分PCA分析表明,不同分解程度的凋落物外生菌和内生菌对31种碳源的利用均有显著差异;RDA分析表明,碳、氮含量与凋落物外生菌微生物功能多样性指数呈最大相关。【结论】木麻黄凋落物分解程度越大,外生菌碳代谢强度和多样性越高,而内生菌碳代谢强度越低,其多样性越高;凋落物的氮、碳含量是影响凋落物微生物功能多样性的主要因素。因此,外生菌和内生菌在木麻黄凋落物的分解中发挥着不同的作用。

Nutrient composition of litters and functional diversity of different microorganisms in various decomposition stages of Casuarina equisetifolia plantations

【Objective】We focused on the relationship between the microbial diversity and nutrient composition of Casuarina equisetifolia litter by determining changes in the pattern of litter nutrient decomposition and the characteristics of microbial carbon source utilization.【Method】As a study site,we selected a C.equisetifolia plantation along the coast of the Guilinyang area of Haikou City in Hainan Province,China,which comprises trees of between 10 and 15 years of age.Using the S-type five-point sampling method,we obtained samples representative of three stages of litter decomposition from soil depths of 0-5 cm,≥5-10 cm and≥10-15 cm,respectively.The Biolog microporosity plate method was used to determine the functional variation in the diversity of the surface microbes and endophytes of litters at the different stages of decomposition.Principal component analysis(PCA)and redundancy analysis(RDA)analyses were used to determine differences in the utilization of different carbon sources.【Result】①With an increase in the degree of litter decomposition,we observed decreases in the contents of organic carbon,total nitrogen and total phosphorus.②We also detected significant differences in the functional diversities of exogenous and endophytic bacterial communities at the different stages of decomposition.The average well color development(AWCD)of exogenous microbes increased with an increase in the degree of decomposition,whereas that of endophytes decreased.③The Shannon and Simpson diversity index of surface microbes were obviously increased with the increasing decomposition degree of litters.However,there were no significant differences in McIntosh indexes.The Shannon and Simpson diversity index of endophytes of litters showed a similar trend with surface microbes,but the McIntosh index significantly decreased.④Exogenous and endophytic bacteria showed different efficiencies in the utilization of six major categories of carbon sources.For both surface microbes and endophytes,the primary carbon sources utilized during the early stages of decomposition were carbohydrates,followed by amides and phenolic acids in the latter stages.⑤The PCA results revealed significant differences in litter microbial function among the different degrees of decomposition,and RDA indicated that organic matter and total nitrogen can significantly affect the diversity of surface microbes.【Conclusion】Our results revealed that carbon metabolic activity and surface microbe diversity increased with an increase in the degree of litter decomposition,whereas endophyte metabolic activity decreased in response to an increase in microbial diversity.Moreover,we found that pH and total nitrogen content were the two critical factors determining microbial diversity,and that the surface microbes and endophytes associated with litter play different roles during the different stages of decomposition.