If I am not wrong, I believe the answer is Producers. The reason as to why I say that producers is the answer is because in every food chain, there needs to be a base. That base is what provides the starting energy that will later on move up in the food chain.
A buffer is a solution encompassing a weak acid and its conjugate base in alike amounts. This combination reduces the pH change upon addition of strong acid or base by converting H1+ (or OH1-) to weaker acids or bases. This primarily consist of compounds that stabilize the pH of a solution by removing or replacing hydrogen ions. Also, substances that resist change in pH.