Green plants are autotrophs are that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates). The carbohydrates which are not immediately consumed by plants are stored as starch.Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupies first trophic level in food chain and serve as source of food and energy for all other organisms of higher trophic levels (heterotrophs/ consumers).
Hence, in absence of these plants, whole functioning of whole ecosystem will come to hault due to lack of food and energy source for consumers (herbivores, carnivores and omnivores)