Dilemma of hydroxyapatite nanoparticles as phosphorus fertilizer: Potentials, challenges and effects on plants

Abstract Hydroxyapatite nanoparticles (nHAPs) are nanomaterials that have been evaluated to be appropriate for plants phosphorus nutrition. However, reports suggesting that these nanoparticles have negative effects on plants growth and development cannot be ignored either. These researches are in their infancy and there is still no proposal for their macroconsumption. Also, the cost-effectiveness of these nanofertilizers and their superiority over conventional fertilizers are questioned. Hence, the present study aims to investigate the effect of nHAPs on plants phosphorus nutrition. Positive effects of nHAPs on soybean, sorghum, pea and Pakchoi plants have been observed, which have been attributed to the longer permanence of these nanoparticles in the soil environment and thus to the longer phosphorus availability for plants. The next possible reasons can be calcium nutrition in addition to phosphorus nutrition and increased gibberellin hormone and heavy metal stress tolerance. Negative effects of nHAPs on mung bean sprouts, tomato and Pakchoi plants have been observed, which have been explained by the structure of nHAPs and the increase of Ca2＋ concentration in cells. In general, the effect of nHAPs on plants is affected by the plant type and concentration of nHAPs. Therefore, plants show different aptitudes to nHAPs application and probably the boundary of nHAPs toxicity varies among plants too. Therefore, further studies are needed to understand the mechanisms involved with the uptake of nHAPs into various plants and cells.