Tesi etd-03102025-184333
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Tipo di tesi
Dottorato
Autore
QUATTROCELLI, PIERA
Indirizzo email
pieraquattrocelli@gmail.com
URN
etd-03102025-184333
Titolo
Hydroxyapatite nanoparticles as phosphorus fertilizer combined with microbial biostimulants for a sustainable agroecological transition
Settore scientifico disciplinare
AGR/02
Corso di studi
Istituto di Scienze della Vita - PHD IN AGROBIOSCIENZE
Commissione
relatore Prof. FERRANTE, ANTONIO
Parole chiave
- environmental effects
- maize RNAseq
- microbial consortia
- phosphate-solubilizing bacteria
- phosphorus nanofertilizers
- tillage
Data inizio appello
09/06/2025;
Disponibilità
parziale
Riassunto analitico
Phosphorus (P) is crucial for plant metabolism, but its low soil availability limits crop productivity. Traditional P fertilization depletes finite rock P reserves and causes eutrophication. Sustainable recycling strategies are needed, with one promising approach being the recovery of hydroxyapatite (HA) from fish scales. As a key soil component, HA is biocompatible and suitable as a fertilizer, while its nanoform (nHA) offers advantages like smaller particle size and better root access. However, the low solubility of nHA can reduce the effectiveness. Combining nHA with phosphate-solubilizing bacteria (PSB) can improve P availability, but selecting efficient PSB strains and optimizing their application remains challenging. Soil inoculation effective but costly due to high inoculum volumes, while seed coating (SC) is more practical but limited by low bacterial attachment. Selecting the PSB strains is also crucial: lab-trained strains may be highly efficient but struggle to compete with native microbes, while native strains are better adapted but may have lower solubilization efficiency due to agricultural history.
This project aimed to optimize the combined application of nHAs and PSB strains and to unravel the mechanisms of phosphate solubilization and uptake in maize through an integrated, multidisciplinary approach. It also assessed the long-term impacts of tillage practices on crop performance, soil characteristics, and microbial communities across different climatic zones to guide the selection of native, site-adapted PSB strains with high efficiency and environmental compatibility.
The first study (Chapter 2) examined P solubilization from salmon and tuna bone-derived hydroxyapatite (SnHAs and TnHAs) using fifteen PSB strains in vitro. The most effective strains were combined into a consortium for maize SC and tested in vivo on maize. We hypothesized that applying nHAs with PSB via SC would enhance plant growth and P-cycling more than individual treatments while ensuring bacterial establishment without additional inoculation (BR). The synergistic effect of nHAs and SC increased maize root (+22%) and total biomass (+29%), as well as P (+32%) and K (+66%) uptake. P-use efficiency and recovery improved by 25% and three-time, respectively, with nHAs and SC compared to nHAs alone or with BR Additionally, SC with SnHAs strongly promoted maize growth and P uptake while downregulating P-related genes compared to SnHAs alone. Linking in vitro and in vivo results, propionic acid production and PSB-mediated P solubilization were identified as key drivers of maize growth and P uptake.
The second experiment (Chapter 3) investigated the long-term effects of conventional tillage (CT) and no-tillage (NT) on crop yield, soil properties, and microbial diversity across Arid, Mediterranean, and Continental climates. Results showed NT increased soil organic carbon (SOC) and microbial biomass by 30% in the Continental region but had no significant impact in Arid and Mediterranean soils. Crop productivity responses were site-dependent, with NT improving harvest index in Arid soil but reducing barley yield in Continental soil. Bacterial diversity was more influenced by site than tillage, while arbuscular mycorrhizal fungal (AMF) diversity showed site-specific responses. NT promoted a more specialized microbial community, enhancing nutrient cycling and organic matter decomposition. Overall, NT improves microbial diversity and carbon sequestration in temperate regions but its effect on crop productivity varies across environments.
The third study (Chapter 4) addressed the environmental implications of using native and exotic PSB, alone or in combination with nHAs across native soils (Arid, Continental, Mediterranean). A total of 59 native PSB strains were isolated, identified and characterized for P solubilization from the Arid, Continental, and Mediterranean sites. Based on the efficiency of SnHAs solubilization and phylogenetic diversity, three site-specific native consortia were established, along with exotic PSB, and applied alone and with nHAs. Their effects were evaluated on soil bacterial communities, diversity, and functionality. The co-application of PSB and SnHAs changed the community structure, with notable differences in the diversity across treatments, particularly given by the application of PSB rather than SnHAs. These effects were driven by the site, with relevant impacts in the Arid and Mediterranean sites. Moreover, in the Arid site, native PSB increased methane-related processes, while exotic PSB enhanced nitrification and ammonia oxidation. In the Cont site, PSB primarily influenced N cycling, with no significant changes in methane cycle. In the Med site, native PSB enhanced nitrification and ammonia oxidation, while SnHAs reduced methylotrophy and methanotrophy. Our findings empathize the benefits of combining PSB and SnHAs, and highlight that the choice of consortium—native or exotic—should be tailored to specific sites for maintaining and optimizing soil microbial functionality and taking into account the environmental risks.
The Chapter 5 addressed the effects of nHAs, native and exotic PSB consortia, as single treatments or as co-application, on maize productivity, while also dissecting the transcriptomic changes in maize in response to these inputs. The main results underscored the synergistic effects of PSB and nHAs on plant growth and P cycling, especially in the Arid (sandy) soil. RNA sequencing (RNAseq) was used to analyze gene expression in maize roots under PSB and nHAs treatments, to assess the full extent of maize responses. Maize roots showed greater transcriptional shifts when treated with exotic PSB and nHAs than with native PSB and nHAs. Moreover, maize exhibited the most substantial transcriptomic changes, with the highest DEG count and pathway enrichment, in the Arid soil, suggesting that treatment effects are more pronounced under nutrient-limited conditions than in nutrient-rich Continental and Mediterranean soils. Most of the enriched pathways across sites and treatments were linked to plant–microbe interactions and nutrient cycling, including the biosynthesis of primary and secondary metabolites such as amino acids and cytokinins. Results indicated also that co-application of microbial inoculants and nHAs likely induced a priming response in maize, functioning as nutrient enhancers and stress mitigators under challenging or resource-limited environments.
In this thesis, a multidisciplinary approach was employed to investigate microbial consortia design and the use of P-nanoparticles, considering their environmental safety and plant transcriptomic responses across different soils. The study highlighted the positive impact and underlying mechanisms of PSB–nHAs co-application on maize growth and P-cycling, especially relevant for low-input agriculture.
These findings emphasize that PSB-nHA interactions must be tailored to specific environmental conditions to optimize plant growth and soil microbial health, supporting a more efficient and sustainable use of P fertilizers.
This project aimed to optimize the combined application of nHAs and PSB strains and to unravel the mechanisms of phosphate solubilization and uptake in maize through an integrated, multidisciplinary approach. It also assessed the long-term impacts of tillage practices on crop performance, soil characteristics, and microbial communities across different climatic zones to guide the selection of native, site-adapted PSB strains with high efficiency and environmental compatibility.
The first study (Chapter 2) examined P solubilization from salmon and tuna bone-derived hydroxyapatite (SnHAs and TnHAs) using fifteen PSB strains in vitro. The most effective strains were combined into a consortium for maize SC and tested in vivo on maize. We hypothesized that applying nHAs with PSB via SC would enhance plant growth and P-cycling more than individual treatments while ensuring bacterial establishment without additional inoculation (BR). The synergistic effect of nHAs and SC increased maize root (+22%) and total biomass (+29%), as well as P (+32%) and K (+66%) uptake. P-use efficiency and recovery improved by 25% and three-time, respectively, with nHAs and SC compared to nHAs alone or with BR Additionally, SC with SnHAs strongly promoted maize growth and P uptake while downregulating P-related genes compared to SnHAs alone. Linking in vitro and in vivo results, propionic acid production and PSB-mediated P solubilization were identified as key drivers of maize growth and P uptake.
The second experiment (Chapter 3) investigated the long-term effects of conventional tillage (CT) and no-tillage (NT) on crop yield, soil properties, and microbial diversity across Arid, Mediterranean, and Continental climates. Results showed NT increased soil organic carbon (SOC) and microbial biomass by 30% in the Continental region but had no significant impact in Arid and Mediterranean soils. Crop productivity responses were site-dependent, with NT improving harvest index in Arid soil but reducing barley yield in Continental soil. Bacterial diversity was more influenced by site than tillage, while arbuscular mycorrhizal fungal (AMF) diversity showed site-specific responses. NT promoted a more specialized microbial community, enhancing nutrient cycling and organic matter decomposition. Overall, NT improves microbial diversity and carbon sequestration in temperate regions but its effect on crop productivity varies across environments.
The third study (Chapter 4) addressed the environmental implications of using native and exotic PSB, alone or in combination with nHAs across native soils (Arid, Continental, Mediterranean). A total of 59 native PSB strains were isolated, identified and characterized for P solubilization from the Arid, Continental, and Mediterranean sites. Based on the efficiency of SnHAs solubilization and phylogenetic diversity, three site-specific native consortia were established, along with exotic PSB, and applied alone and with nHAs. Their effects were evaluated on soil bacterial communities, diversity, and functionality. The co-application of PSB and SnHAs changed the community structure, with notable differences in the diversity across treatments, particularly given by the application of PSB rather than SnHAs. These effects were driven by the site, with relevant impacts in the Arid and Mediterranean sites. Moreover, in the Arid site, native PSB increased methane-related processes, while exotic PSB enhanced nitrification and ammonia oxidation. In the Cont site, PSB primarily influenced N cycling, with no significant changes in methane cycle. In the Med site, native PSB enhanced nitrification and ammonia oxidation, while SnHAs reduced methylotrophy and methanotrophy. Our findings empathize the benefits of combining PSB and SnHAs, and highlight that the choice of consortium—native or exotic—should be tailored to specific sites for maintaining and optimizing soil microbial functionality and taking into account the environmental risks.
The Chapter 5 addressed the effects of nHAs, native and exotic PSB consortia, as single treatments or as co-application, on maize productivity, while also dissecting the transcriptomic changes in maize in response to these inputs. The main results underscored the synergistic effects of PSB and nHAs on plant growth and P cycling, especially in the Arid (sandy) soil. RNA sequencing (RNAseq) was used to analyze gene expression in maize roots under PSB and nHAs treatments, to assess the full extent of maize responses. Maize roots showed greater transcriptional shifts when treated with exotic PSB and nHAs than with native PSB and nHAs. Moreover, maize exhibited the most substantial transcriptomic changes, with the highest DEG count and pathway enrichment, in the Arid soil, suggesting that treatment effects are more pronounced under nutrient-limited conditions than in nutrient-rich Continental and Mediterranean soils. Most of the enriched pathways across sites and treatments were linked to plant–microbe interactions and nutrient cycling, including the biosynthesis of primary and secondary metabolites such as amino acids and cytokinins. Results indicated also that co-application of microbial inoculants and nHAs likely induced a priming response in maize, functioning as nutrient enhancers and stress mitigators under challenging or resource-limited environments.
In this thesis, a multidisciplinary approach was employed to investigate microbial consortia design and the use of P-nanoparticles, considering their environmental safety and plant transcriptomic responses across different soils. The study highlighted the positive impact and underlying mechanisms of PSB–nHAs co-application on maize growth and P-cycling, especially relevant for low-input agriculture.
These findings emphasize that PSB-nHA interactions must be tailored to specific environmental conditions to optimize plant growth and soil microbial health, supporting a more efficient and sustainable use of P fertilizers.
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