Except by procedures provided in this charter, the terms of office of the elective officers and of members of boards and commissions appointed for definite terms shall not be shortened. The terms of elective officers of the city shall not extend beyond the period for which any such officer was elected, except that an elective officer shall, after his term has expired, continue to hold office until his successor is elected and has qualified. The council shall not grant or authorize extra compensation to any officer or employee after the service has been rendered. The salary of any elective officer shall not be increased or decreased from the time of his election or appointment until the end of his term of office for which he was elected or appointed.