Regulation of phosphorus uptake and utilization: transitioning from current knowledge to practical strategies

Phosphorus addition increases stability and complexity of co-occurrence network of soil microbes in an artificial Leymus chinensis grassland

Introduction

Understanding the response of cross-domain co-occurrence networks of soil microorganisms to phosphorus stability and the resulting impacts is critical in ecosystems, but the underlying mechanism is unclear in artificial grassland ecosystems.

Methods

In this study, the effects of four phosphorus concentrations, P0 (0 kg P ha-1), P1 (15.3 kg P ha-1), P2 (30.6 kg P ha-1), and P3 (45.9 kg P ha-1), on the cross-domain co-occurrence network of bacteria and fungi were investigated in an artificial Leymus chinensis grassland in an arid region.

Results and discussion

The results of the present study showed that phosphorus addition significantly altered the stem number, biomass and plant height of the Leymus chinensis but had no significant effect on the soil bacterial or fungal alpha (ACE) diversity or beta diversity. The phosphorus treatments all increased the cross-domain co-occurrence network edge, node, proportion of positively correlated edges, edge density, average degree, proximity to centrality, and robustness and increased the complexity and stability of the bacterial-fungal cross-domain co-occurrence network after 3 years of continuous phosphorus addition. Among them, fungi (Ascomycota, Basidiomycota, Mortierellomycota and Glomeromycota) play important roles as keystone species in the co-occurrence network, and they are significantly associated with soil AN, AK and EC. Finally, the growth of Leymus chinensis was mainly due to the influence of the soil phosphorus content and AN. This study revealed the factors affecting the growth of Leymus chinense in artificial grasslands in arid areas and provided a theoretical basis for the construction of artificial grasslands.

Nitrogen-fertilizer addition to an agricultural soil enhances biogenic non-extractable residue formation from 2-13C,15N-glyphosate

Glyphosate and nitrogen (N) or (P) phosphorus fertilizers are often applied in combination to agricultural fields. The additional P or N supply to microorganisms might drive glyphosate degradation towards sarcosine/glycine or aminomethylphosphonic acid (AMPA), and consequently determine the speciation of non-extractable residues (NERs): harmless biogenic NERs (bioNERs) or potentially hazardous xenobiotic NERs (xenoNERs). We therefore investigated the effect of P or N-fertilizers on microbial degradation of glyphosate and bioNER formation in an agricultural soil. Four different treatments were incubated at 20 °C for 75 days as follows; I: no fertilizer (2-13C,15N-glyphosate only, control), II: P-fertilizer (superphosphate + 2-13C,15N-glyphosate, effect of P-supply), III: N-fertilizer (ammonium nitrate + 2-13C,15N-glyphosate, effect of N-supply) and IV: 15N-fertilizer (15N-ammonium nitrate + 2-13C-glyphosate, differentiation between microbial assimilations of 15N: 15N-fertilizer versus 15N-glyphosate). We quantified 13C or 15N in mineralization, extractable residues, NERs and in amino acids (AAs). At the end, mineralization (36-41 % of the 13C), extractable 2-13C,15N-glyphosate/2-13C-glyphosate (0.42-0.49 %) & 15N-AMPA (1.2 %), and 13C/15N-NERs (40-43 % of the 13C, 40-50 % of the 15N) were comparable among treatments. Contrastingly, the 15N-NERs from 15N-fertlizer amounted to only 6.6 % of the 15N. Notably, N-fertilizer promoted an incorporation of 13C/15N from 2-13C,15N-glyphosate into AAs and thus the formation of 13C/15N-bioNERs. The 13C/15N-AAs were as follows: 16-21 % (N-fertilizer) > 11-13 % (control) > 7.2-7.3 % (P-fertilizer) of the initially added isotope. 2-13C,15N-glyphosate was degraded via the sarcosine/glycine and AMPA simultaneously in all treatments, regardless of the treatment type. The percentage share of bioNERs within the NERs in the N-fertilized soil was highest (13C: 80-82 %, 15N: 100 %) compared to 53 % (13C & 15N, control) and to only 30 % (13C & 15N, P-fertilizer). We thus concluded simultaneous N & glyphosate addition to soils could be beneficial for the environment due to the enhanced bioNER formation, while P & glyphosate application disadvantageous since it promoted xenoNER formation.

ZmARF1 positively regulates low phosphorus stress tolerance via modulating lateral root development in maize

Phosphorus (P) deficiency is one of the most critical factors for plant growth and productivity, including its inhibition of lateral root initiation. Auxin response factors (ARFs) play crucial roles in root development via auxin signaling mediated by genetic pathways. In this study, we found that the transcription factor ZmARF1 was associated with low inorganic phosphate (Pi) stress-related traits in maize. This superior root morphology and greater phosphate stress tolerance could be ascribed to the overexpression of ZmARF1. The knock out mutant zmarf1 had shorter primary roots, fewer root tip number, and lower root volume and surface area. Transcriptomic data indicate that ZmLBD1, a direct downstream target gene, is involved in lateral root development, which enhances phosphate starvation tolerance. A transcriptional activation assay revealed that ZmARF1 specifically binds to the GC-box motif in the promoter of ZmLBD1 and activates its expression. Moreover, ZmARF1 positively regulates the expression of ZmPHR1, ZmPHT1;2, and ZmPHO2, which are key transporters of Pi in maize. We propose that ZmARF1 promotes the transcription of ZmLBD1 to modulate lateral root development and Pi-starvation induced (PSI) genes to regulate phosphate mobilization and homeostasis under phosphorus starvation. In addition, ZmERF2 specifically binds to the ABRE motif of the promoter of ZmARF1 and represses its expression. Collectively, the findings of this study revealed that ZmARF1 is a pivotal factor that modulates root development and confers low-Pi stress tolerance through the transcriptional regulation of the biological function of ZmLBD1 and the expression of key Pi transport proteins.

Multi-omics strategies uncover the molecular mechanisms of nitrogen, phosphorus and potassium deficiency responses in Brassica napus

BACKGROUND

Nitrogen (N), phosphorus (P) and potassium (K) are critical macronutrients in crops, such that deficiency in any of N, P or K has substantial effects on crop growth. However, the specific commonalities of plant responses to different macronutrient deficiencies remain largely unknown.

METHODS

Here, we assessed the phenotypic and physiological performances along with whole transcriptome and metabolomic profiles of rapeseed seedlings exposed to N, P and K deficiency stresses.

RESULTS

Quantities of reactive oxygen species were significantly increased by all macronutrient deficiencies. N and K deficiencies resulted in more severe root development responses than P deficiency, as well as greater chlorophyll content reduction in leaves (associated with disrupted chloroplast structure). Transcriptome and metabolome analyses validated the macronutrient-specific responses, with more pronounced effects of N and P deficiencies on mRNAs, microRNAs (miRNAs), circular RNAs (circRNAs) and metabolites relative to K deficiency. Tissue-specific responses also occurred, with greater effects of macronutrient deficiencies on roots compared with shoots. We further uncovered a set of common responders with simultaneous roles in all three macronutrient deficiencies, including 112 mRNAs and 10 miRNAs involved in hormonal signaling, ion transport and oxidative stress in the root, and 33 mRNAs and 6 miRNAs with roles in abiotic stress response and photosynthesis in the shoot. 27 and seven common miRNA-mRNA pairs with role in miRNA-mediated regulation of oxidoreduction processes and ion transmembrane transport were identified in all three macronutrient deficiencies. No circRNA was responsive to three macronutrient deficiency stresses, but two common circRNAs were identified for two macronutrient deficiencies. Combined analysis of circRNAs, miRNAs and mRNAs suggested that two circRNAs act as decoys for miR156 and participate in oxidoreduction processes and transmembrane transport in both N- and P-deprived roots. Simultaneously, dramatic alterations of metabolites also occurred. Associations of RNAs with metabolites were observed, and suggested potential positive regulatory roles for tricarboxylic acids, azoles, carbohydrates, sterols and auxins, and negative regulatory roles for aromatic and aspartate amino acids, glucosamine-containing compounds, cinnamic acid, and nicotianamine in plant adaptation to macronutrient deficiency.

CONCLUSIONS

Our findings revealed strategies to rescue rapeseed from macronutrient deficiency stress, including reducing the expression of non-essential genes and activating or enhancing the expression of anti-stress genes, aided by plant hormones, ion transporters and stress responders. The common responders to different macronutrient deficiencies identified could be targeted to enhance nutrient use efficiency in rapeseed.

An insight into the role of the organic acids produced by Enterobacter sp. strain 15S in solubilizing tricalcium phosphate: in situ study on cucumber

BACKGROUND

The release of organic acids (OAs) is considered the main mechanism used by phosphate-solubilizing bacteria (PSB) to dissolve inorganic phosphate in soil. Nevertheless, little is known about the effect of individual OAs produced by a particular PSB in a soil-plant system. For these reasons, the present work aimed at investigating the effect of Enterobacter sp. strain 15S and the exogenous application of its OAs on (i) the solubilization of tricalcium phosphate (TCP), (ii) plant growth and (iii) P nutrition of cucumber. To this purpose two independent experiments have been performed.

RESULTS

In the first experiment, carried out in vitro, the phosphate solubilizing activity of Enterobacter 15S was associated with the release of citric, fumaric, ketoglutaric, malic, and oxalic acids. In the second experiment, cucumber plants were grown in a Leonard jar system consisting of a nutrient solution supplemented with the OAs previously identified in Enterobacter 15S (jar's base) and a substrate supplemented with the insoluble TCP where cucumber plants were grown (jar's top). The use of Enterobacter 15S and its secreted OAs proved to be efficient in the in situ TCP solubilization. In particular, the enhancement of the morpho-physiological traits of P-starved cucumber plants was evident when treated with Enterobacter 15S, oxalate, or citrate. The highest accumulation of P in roots and shoots induced by such treatments further corroborated this hypothesis.

CONCLUSION

In our study, the results presented suggest that organic acids released by Enterobacter 15S as well as the bacterium itself can enhance the P-acquisition by cucumber plants.

Responses of biomass accumulation and nutrient utilization along a phosphorus supply gradient in Leymus chinensis

Phosphorus (P) deficiencies are widespread in calcareous soils. The poor availability of nitrogen (N) and P in soils often restricts crop growth. However, the effects of P addition on plant growth and plant nutrient transport changes during the establishment of Leymus chinensis fields in Xinjiang are not clear. We investigated the responses of Leymus chinensis biomass and nutrient absorption and utilization to changes in soil N and P by adding P (0, 15.3, 30.6, and 45.9 kg P ha^-1 year^-1) with basally applied N fertilizer (150 kg N ha^-1 year^-1). The results showed that (a) Principal component analysis (PCA) of biomass, nutrient accumulation, soil available P, and soil available N during the different periods of Leymus chinensis growth showed that their cumulative contributions during the jointing and harvest periods reached 95.4% and 88%, respectively. (b) Phosphorus use efficiency (PUE) increased with the increase of P fertilizer gradient and then decreased and the maximum PUE was 13.14% under moderate P addition. The accumulation of biomass and nutrients in Leymus chinensis can be effectively improved by the addition of P fertilizer at 30.6 kg ha^-1. Different P additions either moderately promoted or excessively inhibited Leymus chinensis growth and nutrient utilization.

Prospects of genetics and breeding for low-phosphate tolerance: an integrated approach from soil to cell

Improving phosphorus (P) crop nutrition has emerged as a key factor toward achieving a more resilient and sustainable agriculture. P is an essential nutrient for plant development and reproduction, and phosphate (Pi)-based fertilizers represent one of the pillars that sustain food production systems. To meet the global food demand, the challenge for modern agriculture is to increase food production and improve food quality in a sustainable way by significantly optimizing Pi fertilizer use efficiency. The development of genetically improved crops with higher Pi uptake and Pi-use efficiency and higher adaptability to environments with low-Pi availability will play a crucial role toward this end. In this review, we summarize the current understanding of Pi nutrition and the regulation of Pi-starvation responses in plants, and provide new perspectives on how to harness the ample repertoire of genetic mechanisms behind these adaptive responses for crop improvement. We discuss on the potential of implementing more integrative, versatile, and effective strategies by incorporating systems biology approaches and tools such as genome editing and synthetic biology. These strategies will be invaluable for producing high-yielding crops that require reduced Pi fertilizer inputs and to develop a more sustainable global agriculture.

No-till improves selected soil properties, phosphorous availability and utilization efficiency, and soybean yield on some smallholder farms in South Africa

Some of the limiting factors for smallholder farmer soybean production in South Africa are low native soil phosphorus (P) availability and poor utilization efficiency of added P. Phosphorus fertilization, use of improved or high yield potential cultivars and appropriate cropping systems could increase soybean yields. The objective of this study was to determine the effects of tillage, cultivar and P fertilization levels on P uptake and P use efficiency, as well as plant growth, yield, grain protein and oil content, in a soybean based cropping system. The study was conducted under dryland conditions at Sheepmoor, Mpumalanga. A field experiment was established in a randomized complete block design. Treatments were arranged in a 2 × 3 × 3 strip-split-plot structure. There were two tillage systems [no-till (NT) and conventional tillage (CT)], three cultivars (PAN 1614R, PAN 1521R, and PAN 1532R), and three phosphorus rates (0, 30, and 60 kg/ha). All treatment combinations were replicated three times. P uptake improved with P application, although there were no differences between 30 and 60 kg/ha whilst PFP was significantly higher at 30 kg/ha P. Yield was significantly higher at 30 kg/ha P application under NT and varied with cultivars. P application at 30 and 60 kg/ha significantly reduced oil content by 11.3 and 7.16%, respectively, but had inverse effects on protein content. The activities of acid phosphatase (ACP) and alkaline phosphatase (ALP) also increased with P application. Improvement of soybean yield and its attributes, grain quality, P uptake, PFP, soil physicochemical and microbial properties emphasize the importance of fertilizer application, sustainable cropping systems coupled with careful cultivar selection. Therefore, in order to improve soil fertility and soybean yield under small farm conditions, the application of no-till and optimum application of fertilizers should be prioritized.

Role of WRKY Transcription Factors in Regulation of Abiotic Stress Responses in Cotton

Environmental factors are the major constraints in sustainable agriculture. WRKY proteins are a large family of transcription factors (TFs) that regulate various developmental processes and stress responses in plants, including cotton. On the basis of Gossypium raimondii genome sequencing, WRKY TFs have been identified in cotton and characterized for their functions in abiotic stress responses. WRKY members of cotton play a significant role in the regulation of abiotic stresses, i.e., drought, salt, and extreme temperatures. These TFs either activate or repress various signaling pathways such as abscisic acid, jasmonic acid, salicylic acid, mitogen-activated protein kinases (MAPK), and the scavenging of reactive oxygen species. WRKY-associated genes in cotton have been genetically engineered in Arabidopsis, Nicotiana, and Gossypium successfully, which subsequently enhanced tolerance in corresponding plants against abiotic stresses. Although a few review reports are available for WRKY TFs, there is no critical report available on the WRKY TFs of cotton. Hereby, the role of cotton WRKY TFs in environmental stress responses is studied to enhance the understanding of abiotic stress response and further improve in cotton plants.

Monogalactosyl diacylglycerol synthase 3 affects phosphate utilization and acquisition in rice

Galactolipids are essential to compensate for the loss of phospholipids by 'membrane lipid remodelling' in plants under phosphorus (P) deficiency conditions. Monogalactosyl diacylglycerol (MGDG) synthases catalyse the synthesis of MGDG which is further converted into digalactosyl diacylglycerol (DGDG), later replacing phospholipids in the extraplastidial membranes. However, the roles of these enzymes are not well explored in rice. In this study, the rice MGDG synthase 3 gene (OsMGD3) was identified and functionally characterized. We showed that the plant phosphate (Pi) status and the transcription factor PHOSPHATE STARVATION RESPONSE 2 (OsPHR2) are involved in the transcriptional regulation of OsMGD3. CRISPR/Cas9 knockout and overexpression lines of OsMGD3 were generated to explore its potential role in rice adaptation to Pi deficiency. Compared with the wild type, OsMGD3 knockout lines displayed a reduced Pi acquisition and utilization while overexpression lines showed an enhancement of the same. Further, OsMGD3 showed a predominant role in roots, altering lateral root growth. Our comprehensive lipidomic analysis revealed a role of OsMGD3 in membrane lipid remodelling, in addition to a role in regulating diacylglycerol and phosphatidic acid contents that affected the expression of Pi transporters. Our study highlights the role of OsMGD3 in affecting both internal P utilization and P acquisition in rice.

Genome Editing Targets for Improving Nutrient Use Efficiency and Nutrient Stress Adaptation

In recent years, the development of RNA-guided genome editing (CRISPR-Cas9 technology) has revolutionized plant genome editing. Under nutrient deficiency conditions, different transcription factors and regulatory gene networks work together to maintain nutrient homeostasis. Improvement in the use efficiency of nitrogen (N), phosphorus (P) and potassium (K) is essential to ensure sustainable yield with enhanced quality and tolerance to stresses. This review outlines potential targets suitable for genome editing for understanding and improving nutrient use (NtUE) efficiency and nutrient stress tolerance. The different genome editing strategies for employing crucial negative and positive regulators are also described. Negative regulators of nutrient signalling are the potential targets for genome editing, that may improve nutrient uptake and stress signalling under resource-poor conditions. The promoter engineering by CRISPR/dead (d) Cas9 (dCas9) cytosine and adenine base editing and prime editing is a successful strategy to generate precise changes. CRISPR/dCas9 system also offers the added advantage of exploiting transcriptional activators/repressors for overexpression of genes of interest in a targeted manner. CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) are variants of CRISPR in which a dCas9 dependent transcription activation or interference is achieved. dCas9-SunTag system can be employed to engineer targeted gene activation and DNA methylation in plants. The development of nutrient use efficient plants through CRISPR-Cas technology will enhance the pace of genetic improvement for nutrient stress tolerance of crops and improve the sustainability of agriculture.

Controlled release fertilizer: A review on developments, applications and potential in agriculture

Controlled release fertilizer (CRF) plays a crucial yet necessary part in the sustainable agriculture industry. An alarming rise in call for crop production directly influences the increasing need for synthetically derived fertilizers and pesticides production. The application of CRF has been a gamechanger as an environmentally sustainable pathway to increase crop yields by paving desired phase of plant growth via a direct or indirect mechanism. The mechanism of CRF does not only decreases nutrient dissipation due to volatilization and leaching, but also provides a precisely appropriate nutrient release design that is suitable in the physiological and biochemical aspect of the plant growth. However, CRF is not deployed on larger scale of commercial agriculture practices due to being expensive, has relatively low efficiency in releasing nutrients and its coatings are largely composed of petroleum-based synthetic polymers. Alternatively, there are many polymers derived from renewable and biodegradable sources that can be used as coating material for CRF in the form of bio-nanocomposites. Having said that, there is an apparent gap between the mechanism of the CRFs for promoting plant growth and the prominent role of the nanocomposites especially bio-nanocomposites as coating material for CRF synthesis, thus the importance of nanotechnology application in enhancing the effectiveness of CRF. Therefore, this review attempts to bridge the stated gap and summarizes the comprehensive developments, application mechanisms and future potential of CRF as a fertilizer for crop sustainability.

Soybean responds to phosphate starvation through reversible protein phosphorylation

Phosphorus (P) deficiency is considered as a major constraint on crop production. Although a set of adaptative strategies are extensively suggested in soybean (Glycine max) to phosphate (Pi) deprivation, molecular mechanisms underlying reversible protein phosphorylation in soybean responses to P deficiency remains largely unclear. In this study, isobaric tags for relative and absolute quantitation, combined with liquid chromatography and tandem mass spectrometry analysis was performed to identify differential phosphoproteins in soybean roots under Pi sufficient and deficient conditions. A total of 427 phosphoproteins were found to exhibit differential accumulations, with 213 up-regulated and 214 down-regulated. Among them, a nitrate reductase, GmNR4 exhibiting increased phosphorylation levels under low Pi conditions, was further selected to evaluate the effects of phosphorylation on its nitrate reductase activity and subcellular localization. Mutations of GmNR4 phosphorylation levels significantly influenced its activity in vitro, but not for its subcellular localization. Taken together, identification of differential phosphoproteins reveled the complex regulatory pathways for soybean adaptation to Pi starvation through reversible protein phosphorylation.

Genetic Dissection of Phosphorus Use Efficiency in a Maize Association Population under Two P Levels in the Field

Phosphorus (P) deficiency is an important challenge the world faces while having to increase crop yields. It is therefore necessary to select maize (Zea may L.) genotypes with high phosphorus use efficiency (PUE). Here, we extensively analyzed the biomass, grain yield, and PUE-related traits of 359 maize inbred lines grown under both low-P and normal-P conditions. A significant decrease in grain yield per plant and biomass, an increase in PUE under low-P condition, as well as significant correlations between the two treatments were observed. In a genome-wide association study, 49, 53, and 48 candidate genes were identified for eleven traits under low-P, normal-P conditions, and in low-P tolerance index (phenotype under low-P divided by phenotype under normal-P condition) datasets, respectively. Several gene ontology pathways were enriched for the genes identified under low-P condition. In addition, seven key genes related to phosphate transporter or stress response were molecularly characterized. Further analyses uncovered the favorable haplotype for several core genes, which is less prevalent in modern lines but often enriched in a specific subpopulation. Collectively, our research provides progress in the genetic dissection and molecular characterization of PUE in maize.

Accessing Legacy Phosphorus in Soils

Repeated applications of phosphorus (P) fertilizers result in the buildup of P in soil (commonly known as legacy P), a large fraction of which is not immediately available for plant use. Long-term applications and accumulations of soil P is an inefficient use of dwindling P supplies and can result in nutrient runoff, often leading to eutrophication of water bodies. Although soil legacy P is problematic in some regards, it conversely may serve as a source of P for crop use and could potentially decrease dependence on external P fertilizer inputs. This paper reviews the (1) current knowledge on the occurrence and bioaccessibility of different chemical forms of P in soil, (2) legacy P transformations with mineral and organic fertilizer applications in relation to their potential bioaccessibility, and (3) approaches and associated challenges for accessing native soil P that could be used to harness soil legacy P for crop production. We highlight how the occurrence and potential bioaccessibility of different forms of soil inorganic and organic P vary depending on soil properties, such as soil pH and organic matter content. We also found that accumulation of inorganic legacy P forms changes more than organic P species with fertilizer applications and cessations. We also discuss progress and challenges with current approaches for accessing native soil P that could be used for accessing legacy P, including natural and genetically modified plant-based strategies, the use of P-solubilizing microorganisms, and immobilized organic P-hydrolyzing enzymes. It is foreseeable that accessing legacy P will require multidisciplinary approaches to address these limitations.

Copper toxicity affects phosphorus uptake mechanisms at molecular and physiological levels in Cucumis sativus plants

Due to the deliberate use of cupric fungicides in the last century for crop-defence programs, copper (Cu) has considerably accumulated in the soil. The concentrations of Cu often exceed the safety limits of risk assessment for Cu in soil and this may cause toxicity in plants. Copper toxicity induces nutritional imbalances in plants and constraints to plants growth. These aspects might be of paramount importance in the case of phosphorus (P), which is an essential plant macronutrient. In this work, hydroponically grown cucumber plants were used to investigate the influence of the exposure to different Cu concentrations (0.2, 5, 25 and 50 μM) on i) the phenotypic traits of plants, particularly at root level, ii) the nutrient content in both roots and shoots, and iii) the P uptake mechanisms, considering both the biochemical and molecular aspects. At high Cu concentrations (i.e. above 25 μM), the shoot and root growth resulted stunted and the P influx rate diminished. Furthermore, two P transporter genes (i.e. CsPT1.4 and CsPT1.9) were upregulated at the highest Cu concentration, albeit with different induction kinetics. Overall, these results confirm that high Cu concentrations can limit the root acquisition of P, most likely via a direct action on the uptake mechanisms (e.g. transporters). However, the alteration of root plasma membrane permeability induced by Cu toxicity might also play a pivotal role in the observed phenomenon.

Role of root exudates on assimilation of phosphorus in young and old Arabidopsis thaliana plants

The role of root exudates has long been recognized for its potential to improve nutrient use efficiency in cropping systems. However, studies addressing the variability of root exudates involved in phosphorus solubilization across plant developmental stages remain scarce. Here, we grew Arabidopsis thaliana seedlings in sterile liquid culture with a low, medium, or high concentration of phosphate and measured the composition of the root exudate at seedling, vegetative, and bolting stages. The exudates changed in response to the incremental addition of phosphorus, starting from the vegetative stage. Specific metabolites decreased in relation to phosphate concentration supplementation at specific stages of development. Some of those metabolites were tested for their phosphate solubilizing activity, and 3-hydroxypropionic acid, malic acid, and nicotinic acid were able to solubilize calcium phosphate from both solid and liquid media. In summary, our data suggest that plants can release distinct compounds to deal with phosphorus deficiency needs influenced by the phosphorus nutritional status at varying developmental stages.

Physiological and biochemical response of wheat (Triticum aestivum) to TiO2 nanoparticles in phosphorous amended soil: A full life cycle study

Nanoparticles (NPs) application in soil as nano-fertilizers to increase crop yield is getting attention due to their higher efficiency and less environmental risks. This study investigated the interactive effects of variable titanium dioxide nanoparticles (TiO₂-NPs) levels (0, 30, 50 and 100 mg kg^-1) superimposed to phosphorus (P) fertilizer application in soil at the rates of 0, 25 and 50 mg kg^-1 on wheat crop. Physiological parameters of plants, their antioxidant enzymes activities (SOD, POD), and contents of crude protein, H₂O₂, MDA and metals/nutrients (Al, Ca, Mg, Fe, Zn and Cu) were measured. Data on physiological traits revealed that application of 50 mg kg^-1 of TiO₂-NPs without P fertilizer significantly enhanced the root and shoot length by 63 and 26%, respectively. Increased contents of nutrients in the shoots, viz., Ca (316%), Cu (296%), Al (171%) and Mg (187%) with 50 mg kg^-1 TiO₂-NPs treatment reflected improvement in crop growth and grain quality. Furthermore, P contents in plant tissues were raised up to 56% with 50 mg kg^-1 of TiO₂-NPs even in the absence of P fertilizer. In the soil, concentration of phytoavailable P was significantly increased up to 63.3% in the presence of 50 mg kg^-1 TiO₂-NPs as compared to control. Contents of crude protein in grain were also enhanced by 22.8% (at P₅₀) and 17.4% (at P₂₅) with 50 mg kg^-1 TiO₂-NPs application. Along with P application, TiO₂-NPs triggered the activities of SOD (2.06-33.97%) and POD (up to 13.19%), and H₂O₂ production (50.6-138.8%). However, MDA contents were not elevated significantly at any level of TiO₂-NPs, and remained at par with control. It was noteworthy that highest level of TiO₂-NPs, viz., 100 mg kg^-1 exhibited plant and nutrients response lower than that with 50 mg kg^-1. Further, TiO₂-NPs triggered the bioavailability of micronutrient heavy metals (Zn, Cu and Fe) and Al, which could have toxicity at higher concentrations. These results suggested that TiO₂-NPs might have some affinities with phosphate compounds and metal ions in the soil to bring them in soluble form, which enhanced their bioavailability. Although it improved the crop yield and quality, but toxic or negative impact of TiO₂-NPs was also apparent at higher dose. Therefore, investigations on the potential interactions of NPs with other nutrients and toxic metals are needed to enhance our understanding for the safer application of nano-fertilizer.