Let Σ be an orientbale closed surface and let Σ' be a nonorientable closed surface. In the paper, we show that for any nontrivial orientable S² fiber bundles X= Σ S² and X' = Σ' S², there are surjective homomorphisms from both MCG₀ (X) and MCG₀ (X') to Z^. The proof is an application of generalization of Dax invariants for embedded surfaces in 4-manifolds. The property of MCG₀ (X) and MCG₀ (X') inherits from trivial fiber bundle Σ S².
Huizheng Guo (Sat,) studied this question.