Yup. Peat moss is the cheapest. You can use something like laterite, but peat moss will do about the same, if not more.
As far as nutrient absorption, Ryan is partly correct. Plants will normally absorb nutrients via the root system, however, aquatics are different. Very few are root feeders, a majority absorb nutrients via the leaf structure. This one though, is a heavy root feeder, so some nutrients under your substrate will be appreciated by it. It does appear to be a lotus of some sort. I assume the plant shop you bought it from sells pond plants as well?
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