Morphology‐Tailored Hydroxyapatite Nanocarrier for Rhizosphere‐Targeted Phosphorus Delivery

Abstract

High hydrophilicity and soil fixation collectively hamper the delivery of phosphorus (P) released from conventional chemical phosphorus fertilizers (CPFs) to plant rhizosphere for efficient uptake. Here, a phosphorus nutrient nanocarrier (PNC) based on morphology‐tailored nanohydroxyapatite (HAP) is constructed. By virtue of kinetic control of building blocks with designed calcium phosphate intermediates, rod‐like and hexagonal prism‐like PNCs are synthesized, both having satisfactory hydrophobicity (water contact angle of 105.4–132.9°) and zeta potential (−17.43 to −58.4 mV at pH range from 3 to 13). Greenhouse experiments demonstrate that the P contents increase by up to 183% in maize rhizosphere and up to 16% in maize biomass when compared to the CPF. Due to the water potential gradient driven by photosynthesis and transpiration, both PNCs are stably transported to maize rhizosphere, and they are capable to counteract soil fixation prior to uptake by plant roots. Within the synergies of the HAP morphological characteristics and triggered phosphate starvation response, root anatomy confirms that two pathways are elucidated to enhance plant P replenishment from the PNCs. Together with structure tunability and facile synthesis, our results offer a new nanodelivery prototype to accommodate plant physiological traits by tailoring the morphology of HAP.

Thermodynamics-Oriented Crystal Growth Enables Lignocellulose-Enticed Nanostructured Hydroxyapatite with Boosted Phosphorus Fertilizer Utility

“…These results demonstrate that these HAP-based NPFs derived from the three RCPs were configured with different configurations in HAP nanocrystals, thus leading to a difference in P supply when interacting with plant roots. As legacy P exists in the used soil referring to our previous work, 33 the negative controls (named NK and CK) had increased acid phosphatase activity when compared to CDP, again emphasizing the functions of PSR in dealing with P deficiency plants faced during growth. Further, the difference in the formulation of P supplier entailed the change of plant root cells, indicated by the TEM images of the sectioned primary root (Figure 4e).…”

“…Our previous work discovered that small organic acids secreted by plant roots due to the triggered phosphate starvation response (PSR) coordinated P uptake from nanostructured HAP . Citric acid (CA) and malic acid (MA) were reported as the two major organic acids when soybean initiated the PSR .…”

“…These slices were then stained with uranium acetate and osmium tetroxide to prepare specimens suitable for transmission electron microscopy (TEM) characterizations. Detailed descriptions of the staining procedure can be found in our previous work . The obtained specimens were characterized using a JEOL TEM (JEM-1400Flash, Japan) operating at a voltage of 80 kV.…”

“…Detailed descriptions of the staining procedure can be found in our previous work. 33 The obtained specimens were characterized using a JEOL TEM (JEM-1400Flash, Japan) operating at a voltage of 80 kV. 16S rRNA Sequencing of Rhizosphere Soil Samples.…”

“…The modified HAP nanoparticles had significantly decreased zeta potentials compared to the unmodified ones, and the zeta potential of mCHP-HAP was negatively higher between these modified HAP-based NPFs, which was probably attributed to the rod-like morphology where more negative-charged a-/b-planes were exposed. 33,51 Our previous work demonstrated that the negatively increased zeta potential benefited the transportation of HAP nanoparticles across bulky soils to reach plant rhizosphere for efficient P uptake, 33 also as proved by the significantly negative effect between the zeta potential of HAP-based NPFs and P content in rhizosphere soil (Figure 5e), and the morphology with more c-plane exposed indeed facilitated the release of bound P arising from the collapse of HAP nanocrystals induced by the reaction of vertically aligned OH groups with those organic acids. Therefore, it is inferred that the morphologies rendering on HAP nanoparticles derived from CPP and TCP were enabled to have more exposed c-planes compared to those in the case for CHP, which agreed with the P release profile in Figure 6a and the constructed atomic configurations of HAP in Figure S2.…”