Plants bridge the soil environment with the above-ground ecosystem. Almost all plants perform photosynthesis, using energy from sunlight to fix CO2 from the atmosphere into carbohydrates. They are a conduit of energy (carbon in the form of carbohydrates) from the atmosphere to the belowground community. In turn, plants rely on soil for water and nutrients like nitrogen and phosphorous. Plants are often the foundation of terrestrial biological communities, and soil organisms are the foundation of nutrient cycling on which plants rely.