ABSTRACT: The conversion of tropical forests into oil palm Elaeis guineensis (OP) monoculture alters stream physicochemical conditions, potentially threatening freshwater ecosystems. Understanding the responses of bacterial assemblages to environmental changes and riparian management efforts are vital for our understanding of stream ecosystem functioning. We used 16S rRNA gene sequencing techniques to investigate bacterial community dynamics on decomposing litter of 2 contrasting qualities, Macaranga tanarius and OP, in streams across a gradient of riparian disturbance in OP plantations. Bacterial community composition was more heavily influenced by litter quality, such as increased structural compounds (i.e. toughness, lignin, fibre) and nutrients in OP litter and increased secondary compounds in Macaranga litter, rather than changes in stream conditions due to different riparian buffer qualities. Bacterial colonization on Macaranga was susceptible to the increased stream temperatures and nutrients in OP streams, whereas significant alterations in bacterial community composition on OP litter were observed that were possibly due to long-term agricultural disturbances. Both litter species were dominated by Proteobacteria and Bacteroidetes with Chitinophaga and Caulobacteraceae contributing most to the differences observed. Compared to pristine streams, bacterial diversity and richness were significantly higher in OP streams with no buffer, whereas OP streams with forested riparian buffer and untreated buffer (i.e. no chemical inputs) had intermediate values. In conclusion, bacterial assemblages were regulated by the quality of litter. We therefore propose the retention of riparian vegetation with high tree diversity to mitigate impacts on the formation of litter bacterial assemblages and the ecosystem processes they mediate in oil palm plantation streams.

中文翻译：

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垃圾质量对油棕溪流中河岸缓冲液质量变化的影响比对细菌群落的影响更大

摘要：将热带森林转变为油棕油棕（OP）单一栽培会改变河流的理化条件，并可能威胁淡水生态系统。了解细菌群落对环境变化的响应和河岸管理工作对于我们了解河流生态系统功能至关重要。我们使用16S rRNA基因测序技术来研究细菌群落动力学，以分解2种不同品质的垃圾，即Macaranga tanarius和OP，穿过OP人工林中沿河岸扰动的梯度。细菌群落组成受垫料质量的影响更大，例如OP垫料中结构化合物（即韧性，木质素，纤维）和养分的增加以及Macaranga垫料中次生化合物的增加，而不是由于河岸缓冲液质量不同而导致的溪流条件变化。Macaranga上的细菌定植易受OP温度增加的溪流温度和养分的影响，而OP凋落物上细菌群落组成的显着变化可能是由于长期的农业干扰造成的。两种凋落物都以变形杆菌和拟杆菌为主导。与Chitinophaga和Caulobacteraceae贡献最大的差别观察到的。与原始流相比，没有缓冲液的OP流中细菌的多样性和丰富度显着更高，而具有森林河岸缓冲液和未经处理的缓冲液（即无化学输入）的OP流具有中间值。总之，细菌组合受垫料质量的调节。因此，我们建议保留具有高树多样性的河岸植被，以减轻对油棕人工林中凋落的细菌群落及其介导的生态系统过程的影响。