  In this study, we explore the information capacity of open quantum systems,
focusing on the effective channels formed by the subsystem of random quantum
circuits and quantum Hamiltonian evolution. By analyzing the subsystem
information capacity, which is closely linked to quantum coherent information
of these effective quantum channels, we uncover a diverse range of dynamical
and steady behaviors depending on the types of evolution. Therefore, the
subsystem information capacity serves as a valuable tool for studying the
intrinsic nature of various dynamical phases, such as integrable, localized,
thermalized, and topological systems. We also reveal the impact of different
initial information encoding schemes on information dynamics including
one-to-one, one-to-many, and many-to-many. To support our findings, we provide
representative examples for numerical simulations, including random quantum
circuits with or without mid-circuit measurements, random Clifford Floquet
circuits, free and interacting Aubry-Andr\'e models, and Su-Schrieffer-Heeger
models. Those numerical results are further quantitatively explained using the
effective statistical model mapping and the quasiparticle picture in the cases
of random circuits and non-interacting Hamiltonian dynamics, respectively.
