Zions Bancorporation is down 3% in trading today as WTI crude falls to just $48 per barrel (Brent crude is at $51), and there are serious concerns that it will have to stop releasing loan loss reserves, if not build them back up a bit, cutting off a major driver of recent growth. “We recognize that there are many factors in the loan loss reserve calculation but question if ZION can continue to release reserves in light of the potential risk within its energy portfolio,” write Sterne Agee analysts Terry McEvoy and Austin Nicholas, who rate Zions as Neutral. Zions…