The amount of carbon per kilogram of spinach is determined by its content of water. This is unlikely to change much. More CO2 that is captured is likely to st

The amount of carbon per kilogram of spinach is determined by its content of water. This is unlikely to change much. More CO2 that is captured is likely to stimulate the synthesis of more cellulose, i.e. of more cell walls, so the plants should grow faster, possibly also bigger. Even when grown in soil with the same amount of minerals, the plants that grow faster and/or bigger may be more depleted in anything else besides carbohydrates.