When Ti reaches high concentrations in the plant cell, it can compete with iron and other metals for binding sites, leading to disrupted photosynthesis and other processes. The authors of a review proposed that a soil concentration of up to 15 mg/kg be considered a beneficial level of Ti for plant growth. In contrast, concentrations above 50 mg/kg should be considered potentially toxic. In a greenhouse study of coriander, it was shown that Ti levels of 100-400 mg/L induced oxidative stress and inhibited growth.

The ability to take up Ti varies significantly between plant species. In a review of more than 40 different species, the author found that the Ti content of plants ranges from 1 to 578 mg/kg, with an average of 33 mg/kg. Some plants, such as horsetail, hyperaccumulating Ti in their tissues.

Titanium adsorbs to root surfaces and can be taken up by the plant, although little Ti is transported to above-ground growth. It is believed that titanium is transported through iron transporter proteins in the root and translocated through the plant by either forming chelates with citric acid or ascorbic acid or binding to transferrin-like proteins.

Ti is not considered a necessary nutrient but can be beneficial in low doses. The redox capabilities of Ti can enhance photosynthesis and other enzymatic reactions. Multiple studies report that Ti treatment improves nutrient uptake, biomass, photosynthesis, antioxidant activity, and protein synthesis. The mechanism by which Ti boosts plant growth is still unknown, but several hypotheses have been put forward. It has been proposed that the main benefit is due to titanium’s interactions with iron. When iron is deficient, Ti seems to promote the expression of genes related to the iron acquisition, improving plant growth. Foliar sprays of titanium have been shown to boost plant iron content by 30-100%. Foliar sprays are more practical for increasing leaf Ti content than a drench. Other studies have shown that Ti can compensate for a reduced dose of other nutrients, such as N and P.

TiO2 nanoparticles (TiO2NPs) are used to protect plants against specific abiotic stresses and boost plant growth. TiO2NPs have been demonstrated to increase plant tolerance to drought, cold stress, heat stress, and heavy metal toxicity. A soil amendment of 100 mg/kg TiO2NPs significantly reduced soil cadmium uptake by roots, resulting in lower bioaccumulation of cadmium. A greenhouse study investigated the effect of different concentrations of TiO2NPs on the growth traits of coriander. They found that at levels of 50 mg/L Ti, there was a slight but insignificant increase in biomass, but the uptake of K, Ca, Mg, Fe, Mn, Zn, and B was improved.