If the complex structures on the curves in the sequence do not vary, only bubbles can occur; nodes can occur only if the complex structures on the domain are allowed to vary. Usually, the energy bound is achieved by considering a symplectic manifold with compatible almost-complex structure as the target, and assuming that curves to lie in a fixed homology class in the target.
If the intricate structures on the curves within the sequence remain constant, only bubbles can arise; nodes can emerge solely if the complex structures in the domain are permitted to vary. Typically, the energy barrier is attained by considering a symplectic manifold with a compatible almost-complex structure as the target and assuming that the curves lie in a fixed homology class within the target.