Chapter 1: Microbiome ecosystem ecology: unseen majority in an anthropogenic ecosystem -- Chapter 2: Theories, mechanisms and patterns of microbiome species coexistence in an era of climate change -- Chapter 3: Eco-evolutionary processes regulating microbiome community assembly in a changing global ecosystem -- Chapter 4: Loss of microbiome ecological niches and diversity by global change and trophic downgrading -- Chapter 5: Microbiome mediated multitrophic interactions in an age of microbial extinction -- Chapter 6: Global microbiome for agroecology, industry and human well-being: opportunities and challenges in climate change.