Sarah and John have been working together at a marketing agency for over a year. Sarah recently received a promotion to a senior role, which includes supervising John's work. John, who has been with the company for three years, is upset that he was not considered for the promotion and feels that Sarah does not appreciate his contributions. As a result, John has become increasingly distant from Sarah, and their working relationship has become strained. Sarah has noticed the change in John's behaviour and wants to address the issue before it becomes a bigger problem.

Required:

How can negotiation techniques be employed by Sarah to address John's feelings of not being appreciated, and what conflict resolution strategies can be used to improve their working relationship? 

How can negotiation and conflict resolution skills be applied to mitigate the effects of cultural differences on communication within a team, and what strategies can be used to promote understanding and collaboration?