The natures determine how a Pokemon grows, for more info go to: http://www.psypokes.com/lab/natures.php

There are 25 natures available, most raising one stat by 10% and decreasing another by 10%. However, there are five natures that are neutral, and don't improve or hinder any stats. Psypokes.com has a good table displaying all natures, their effects, and likes/dislikes. It can be found here: http://www.psypokes.com/lab/natures.php

For all thepokemon natures and what stat they help visit bulbapedia.bulbagarden.net and search for natures.

Light has two natures that can be thought of as both a wave and a particle.

decomposers