What is the primary form of iron that plants take up from the soil?

Plants primarily take up iron from the soil in its ferrous ion form (Fe²⁺). This is due to several factors related to iron solubility and availability in different pH environments.

In the soil, iron typically exists in two forms: ferric (Fe³⁺) and ferrous (Fe²⁺) ions. The ferric ion can become less available for plant uptake, especially in alkaline soils, where it tends to form insoluble compounds. Conversely, the ferrous ion remains soluble in lower pH environments, making it more readily absorbable by plant roots.

Additionally, many plants have adapted mechanisms to enhance the uptake of ferrous ions, such as root exudates that acidify the rhizosphere, increasing solubility. The ability to use Fe²⁺ efficiently allows the plants to maintain essential processes such as photosynthesis and respiration, where iron serves as a crucial cofactor in various enzymes and proteins.

In contrast, the cupric ion (Cu²⁺) and nitrate ion (NO₃⁻) are not forms of iron, and therefore are not relevant to the question regarding iron uptake.