What's the effect of temperature on buffering capacity?
You question is too broad to answer since there is no "universal answer." In chemistry there is a "tends too" answer and then a list of exceptions.

By and large the root of the question centers around the change in the equilibrium constant as a function of temperature. The equilibrium constants do depend on temperature, but how much "tends" to depend on the particular equilibrium under consideration. However the Arrhenius equation can offer some insight.