  Quantum key distribution (QKD) protocols are essential to guarantee
information-theoretic security in quantum communication. Although there was
some previous work on quantum group key distribution, they still face many
challenges under a ``\textit{dynamic}'' group communication scenario. In
particular, when the group keys need to be updated in real-time for each user
joining or leaving to ensure secure communication properties, i.e., forward
confidentiality and backward confidentiality. However, current protocols
require a large amount of quantum resources to update the group keys, and this
makes them impractical for handling large and dynamic communication groups. In
this paper, we apply the notion of ``{\em tree key graph}'' to the quantum key
agreement and propose two dynamic Quantum Group Key Agreement (QGKA) protocols
for a join or leave request in group communications. In addition, we analyze
the quantum resource consumption of our proposed protocols. The number of
qubits required per join or leave only increases logarithmically with the group
size. As a result, our proposed protocols are more practical and scalable for
large and dynamic quantum group communications.
