Life forms, climate, soil. For each of these other answers are possible. Ability to withstand changing salinity. Ability to withstand changing water levels.
Vertical stratification defines layering of different plant species in the forest canopy.
This is related to available light. Answers will vary. Permanently frozen ground 7. Answers will vary. Specific answers will vary but all should include the idea that the available sunlight decreases with the depth of the lake.