(Sorry for the delay in postings -- the holidays are over and we'll do some catching up this week!)
At the heart of this word is one of the most common words in Hebrew: kol. (By the way, here is the hazard of transliteration; this "kol" is spelled with a kaf, not a kuf, and is not connected to the word meaning "voice.") Kol means "all," and while you will find the root of "m'khalkeil" in the dictionary implying sustenance and economic matters, the key to understanding it is in the little word that is doubled in its root.
The Hebrew verb form implies causitive action, so if I broke down the word into its component parts, I could legitimately interpret m'khalkeil as "makes all for all." It's easy to see how that meaning becomes "sustains." When we pray for "kalkalah," we indeed are hoping that our material needs will be comprehesively met.
However, this word in this context -- one recited so often -- carries with it the richest connotations, no pun intended. It is God who sustains life, that is, who provides all for all, everything for everyone. The Source of all has caused a world, a genuine comprehensive ecosystem, in which the needsof each life are met by God's actions.
And perhaps most important, God sustains life "b'chessed," in love;.