Which form of phosphorus is primarily taken up by plants?

Plants primarily take up phosphorus in the form of phosphate ions. Phosphorus is an essential macronutrient required for various vital functions within the plant, including energy transfer (through ATP), photosynthesis, and the synthesis of nucleic acids (DNA and RNA).

In the soil, phosphorus often exists as inorganic phosphate ions, typically in the forms of H2PO4^- and HPO4^2-. These ions are soluble and available for plant absorption. The ability of plants to absorb them is crucial for their growth and development.

While ammonium, sulfate, and chloride ions are important for the nutrition of plants, they represent different nutrient categories: ammonium is a nitrogen source, sulfate is a source of sulfur, and chloride is involved in osmoregulation and photosynthesis. However, none of these forms provide the phosphorus that is so critical for plant life. Therefore, the phosphate ion is the correct answer for the form of phosphorus that plants primarily take up.