Answer:
In grassland ecosystem, grasses are producer because they produce food materials i. e. glucose which contains carbon by using sunlight in the process of photosynthesis. This food is eaten by rabbit and the carbon is transferred from grass into rabbit body. When this rabbit die, the microorganisms such as bacteria and fungi etc decompose its body and carbon which is present in rabbit body mixes to the soil and increases the fertility. These nutrients which contains carbon is used by the plants in the process of photosynthesis and make food materials and the carbon again transfer from rabbit to grass.