Macronutrient - Carbon plays a pivotal role in the development of sugars during the process of photosynthesis. The element is part of the carbohydrate molecule - CHO.

Sources - The most  common source of carbon is through the carbon dioxide molecule that is broken down during photosynthesis.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.