Nutrients such as nitrogen, phosphorus, and iron are essential resources for primary producers (plants and phytoplankton) and microbial decomposers (bacteria and fungi) in ecosystems. The theories of resource competition and ecological stoichiometry address that the availability of these resources affects the population dynamics and interspecific competition, structuring the community of plants and microbes. These theories predict how ecosystem properties such as productivity and nutrient cycling determine the community properties such as species richness and species abundance distribution. At the same time, these theories also provide mechanistic insights into how community properties can regulate ecosystem properties (i.e., biodiversity-ecosystem function relationship). One of the emerging directions in community ecology is to provide a practical solution to other fields of ecosystem sciences (e.g. macroecology and global ecosystem modeling) for more quantitative description of the roles of (1) resource competition and other-interspecific interactions, (2) biodiversity, and (3) feedback between community dynamics and nutrient cycling, in structuring ecosystem. This will help to better project the dynamics of populations, communities, and ecosystems in a directionally changing world.