How does salt and sugar affect plants growth?

How does salt and sugar affect plants growth?
What happens is that the higher concentration of salt in the soil outside of the plant cells causes water to move outside of the cells to try and equalize the concentration. Root cells die and, if bad enough, the plant will die. The damage gives the plant a burnt look- often on the leaf edges first.
The same thing happens with too much of any mineral.
Some types of plants can tolerate higher levels of salt and not be damaged. Their cells have a high concentration of salt already in them, so the water doesn't move out.
Sugar Water Effect Plants.
effect-of-sugared-water-on-plants.

How does sugar water affect bean plant growth?

"How does sugar water affect bean plant growth?"

Putting sugar in the water will possibly have several affects on plants. One effect you have already seen by noticing that the soil stays moister in the pots watered with sugar water.
Water moves across a membrane by a process called osmosis.
When you add sugar to your water you are changing the osmotic potential of the pure
water. Less water will move into the root because of this change in osmotic potential so the soil will be moister. I believe this was the main question you wanted answered. One way that the sugar water may affect plant growth is that it could influence microorganism growth in the area
surrounding the roots. This may be good for the plants or bad for the
plants. The sugar concentration may also have an effect.
Maybe a little is good or a lot is bad. Only your experiment can show you the effects.
Sugar Water Effect Plants.
how-does-salt-and-sugar-affect-plants.