Byron. Does the crypt melt have any correlation to the wet/dry season change of their native habitats?
No. The "melt" is solely due to environmental changes such as light, water parameters, substrate. At least according to the botanists I have read. This is something that occurs in aquaria but seemingly not in nature. However, I will touch on this again in my response to the subsequent post.
I have experienced this as well with crypts, another plant apongetons also need a resting period. I believe it's a way that certain plant species need to reacclimate themselves to different water temperatures as well as lighting and PH will cause these plants to have a melting experience. I really am not sure why if you even replant certain echinodorous species they tend to not like to be rearranged in the tank as well as other plants that seem to take over there new arreas in the tank. I do know that they seem to respond a little better when you give them plant sticks or even plant tabs. Which I have tried both and seem to work very well on your root feeding plants.
Here we are getting into a couple of different things. The crypt melt is specific only to crypts and is a reaction to stress from environmental changes as I indicated previously.
Aponogeton species require a vegetative rest period when the plant leaves die and the plant remains alive by feeding off stored energy in the tuber or rhizome (sometimes called a bulb). [One species does not do this, I can't remember which now but I know it is one of those included in our plant profiles and I mention this there.] This natural cycle is related to the ecological conditions of the growing area for each species, and is sometimes but certainly not always connected to a drying out of the waters.
No aquatic plant, just as no terrestrial plant, really like to be moved, and some species moreso than others in both situations. However, sometimes moving can invigorate a plant; transplanting house plants for instance often does this. And Echinodorus in my experience do not seem much affected by being moved provided it does not involve significant water parameter or light differences. I have often moved swords around in the same aquarium with no reaction that I could notice, but moving them to another aquarium might.
All plants require a "rest" period between periods of more vigorous growth which may include flowering, and in species that are by nature bog or marsh plants--which includes the majority of our common aquarium plants--this rest period seems to coincide with the submersed period. In the tropics they do not generally die back as plants do in temperate regions, but they noticeably slow their growth. In some species different types of leaves will also appear, since the structure of leaves must change to accommodate emersed or submersed growth. We don't normally see this in the aquarium because the plants are permanently submersed, but the loss of existing leaves from swords when they are first placed in the aquarium relates to this. Most are cultivated emersed in nurseries because it is faster and thus less expensive, and those leaves die off when submersed and new growth will be the submersed leaf form.
Fertilizing the plant when it is moved is another trick of terrestrial garden plants, as this stimulates the plant to grow so it settles in to its new "home" more rapidly.