Pi Fertilizers Research Articles

Phosphite: a novel P fertilizer for weed management and pathogen control.

SummaryThe availability of orthophosphate (Pi) is a key determinant of crop productivity because its accessibility to plants is poor due to its conversion to unavailable forms. Weed's competition for this essential macronutrient further reduces its bio‐availability. To compensate for the low Pi use efficiency and address the weed hazard, excess Pi fertilizers and herbicides are routinely applied, resulting in increased production costs, soil degradation and eutrophication. These outcomes necessitate the identification of a suitable alternate technology that can address the problems associated with the overuse of Pi‐based fertilizers and herbicides in agriculture. The present review focuses on phosphite (Phi) as a novel molecule for its utility as a fertilizer, herbicide, biostimulant and biocide in modern agriculture. The use of Phi‐based fertilization will help to reduce the consumption of Pi fertilizers and facilitate weed and pathogen control using the same molecule, thereby providing significant advantages over current orthophosphate‐based fertilization.

Purification and Characterization of an Extracellular Phosphatase Enzyme From Bacillus spp.

Phosphorus is one of the most important nutrients for plant growth and development. Chemical Pi fertilizer is used to provide the phosphorus for the plants, but it is mostly fixed in the soil into insoluble form and become unavailable to the plants. Phosphate-solubilizing bacteria have lots of application in agriculture as biological fertilizer. Consumption of biofertilizers instead of chemical fertilizers can lead to environmental pollution reduction and crop production enhancement using sustainable farming. In this study, a phosphatase-producing bacterium was isolated from agricultural soil in Kerman. Screening of phosphate solubilizing bacteria was performed on the PVK medium, based on clear area diameter. The best bacterium (AG41) was identified based on 16s rDNA gene. The optimum condition for production of phosphatase was also determined and it was purified and characterized. Sequence alignment and phylogenetic tree results show that AG41 is closely related to Bacillus subtilis, with 98% homology. Phosphatase activity was determined by end point method. The best carbon, nitrogen and phosphate sources for enzyme production were 1.0% glucose, 0.5% ammonium sulfate and (0.25%) sodium phytate +(0.25%) tricalcium phosphate, respectively. Bacterial phosphatase was partially purified using ammonium sulfate fractionation followed by dialysis. Results showed that the optimum temperature for the purified enzyme activity was 40oC and it was stable at temperatures below 60°C. This enzyme was stable between pH 3.0-7.0, and the optimal pH activity was found to 5.0. These results indicated that this strain can be a notable candidate for using as biofertilizers.

Development of an In Planta system to monitor phosphorus status by agroinfiltration and agroinjection

An optimal supply of phosphate (Pi) fertilizer is important to ensure crop yield and quality and to maintain agricultural sustainability. In this study, an in planta monitoring system was developed to conveniently monitor the P status of crops. A phosphate starvation-induced gene (TPSI1) from tomato (Solanum lycopersicum L.) was used to reflect P status in plants. Using agroinfiltration and agroinjection techniques, the GUS reporter gene driven by the TPSI1 promoter was transiently expressed in tobacco (Nicotiana benthamiana) leaves and tomato fruits to reflect their P status. We showed that the vegetative growth of tobacco and the yield and quality of tomato were affected by the supply of Pi fertilizer. We further demonstrated that the expression of a GUS reporter gene driven by the TPSI1 promoter could accurately report on P status in tobacco leaves and tomato fruits in real time. Expression of the GUS reporter gene was independent of deficiencies in mineral nutrients other than P, demonstrating the specificity of this system. The above results indicate that the employed agroinfiltration/agroinjection-based diagnostic system is useful for monitoring P status in plants.

Phosphorus: The Underrated Element for Feeding the World.

Predictions on the lifetime of phosphate (Pi) reserves usually take into account only the need for crop production. A recent report predicts the global need of chemical Pi fertilizer for sustaining productivity in cropland and grassland. Here we discuss the implications of these predictions for the lifetime of Pi reserves.

Vascular-mediated signalling involved in early phosphate stress response in plants.

Depletion of finite global rock phosphate (Pi) reserves will impose major limitations on future agricultural productivity and food security. Hence, modern breeding programmes seek to develop Pi-efficient crops with sustainable yields under reduced Pi fertilizer inputs. In this regard, although the long-term responses of plants to Pi stress are well documented, the early signalling events have yet to be elucidated. Here, we show plant tissue-specific responses to early Pi stress at the transcription level and a predominant role of the plant vascular system in this process. Specifically, imposition of Pi stress induces rapid and major changes in the mRNA population in the phloem translocation stream, and grafting studies have revealed that many hundreds of phloem-mobile mRNAs are delivered to specific sink tissues. We propose that the shoot vascular system acts as the site of root-derived Pi stress perception, and the phloem serves to deliver a cascade of signals to various sinks, presumably to coordinate whole-plant Pi homeostasis.

Analysis of Phosphorus Use Efficiency Traits in Coffea Genotypes Reveals Coffea arabica and Coffea canephora Have Contrasting Phosphorus Uptake and Utilization Efficiencies.

Background and Aims: Phosphate (Pi) is one of the most limiting nutrients for agricultural production in Brazilian soils due to low soil Pi concentrations and rapid fixation of fertilizer Pi by adsorption to oxidic minerals and/or precipitation by iron and aluminum ions. The objectives of this study were to quantify phosphorus (P) uptake and use efficiency in cultivars of the species Coffea arabica L. and Coffea canephora L., and group them in terms of efficiency and response to Pi availability.Methods: Plants of 21 cultivars of C. arabica and four cultivars of C. canephora were grown under contrasting soil Pi availabilities. Biomass accumulation, tissue P concentration and accumulation and efficiency indices for P use were measured.Key Results: Coffee plant growth was significantly reduced under low Pi availability, and P concentration was higher in cultivars of C. canephora. The young leaves accumulated more P than any other tissue. The cultivars of C. canephora had a higher root/shoot ratio and were significantly more efficient in P uptake, while the cultivars of C. arabica were more efficient in P utilization. Agronomic P use efficiency varied among coffee cultivars and E16 Shoa, E22 Sidamo, Iêmen and Acaiá cultivars were classified as the most efficient and responsive to Pi supply. A positive correlation between P uptake efficiency and root to shoot ratio was observed across all cultivars at low Pi supply. These data identify Coffea genotypes better adapted to low soil Pi availabilities, and the traits that contribute to improved P uptake and use efficiency. These data could be used to select current genotypes with improved P uptake or utilization efficiencies for use on soils with low Pi availability and also provide potential breeding material and targets for breeding new cultivars better adapted to the low Pi status of Brazilian soils. This could ultimately reduce the use of Pi fertilizers in tropical soils, and contribute to more sustainable coffee production.

Fungal association and utilization of phosphate by plants: success, limitations, and future prospects.

Phosphorus (P) is a major macronutrient for plant health and development. The available form of P is generally low in the rhizosphere even in fertile soils. A major proportion of applied phosphate (Pi) fertilizers in the soil become fixed into insoluble, unavailable forms, which restricts crop production throughout the world. Roots possess two distinct modes of P uptake from the soil, direct and indirect uptake. The direct uptake of P is facilitated by the plant’s own Pi transporters while indirect uptake occurs via mycorrhizal symbiosis, where the host plant obtains P primarily from the fungal partner, while the fungus benefits from plant-derived reduced carbon. So far, only one Pi transporter has been characterized from the mycorrhizal fungus Glomus versiforme. As arbuscular mycorrhizal fungi cannot be cultured axenically, their Pi transporter network is difficult to exploite for large scale sustainable agriculture. Alternatively, the root-colonizing endophytic fungus Piriformospora indica can grow axenically and provides strong growth-promoting activity during its symbiosis with a broad spectrum of plants. P. indica contains a high affinity Pi transporter (PiPT) involved in improving Pi nutrition levels in the host plant under P limiting conditions. As P. indica can be manipulated genetically, it opens new vistas to be used in P deficient fields.

Phosphoproteome and proteome analyses reveal low-phosphate mediated plasticity of root developmental and metabolic regulation in maize (Zea mays L.)

Phosphate (Pi) deficiency has become a significant challenge to worldwide agriculture due to the depletion of accessible rock phosphate that is the major source of cheap Pi fertilizers. Previous research has identified a number of diverse adaptive responses to Pi starvation in the roots of higher plants. In this study, we found that accelerated axile root elongation of Pi-deprived maize plants resulted from enhanced cell proliferation. Comparative phosphoproteome and proteome profiles of maize axile roots were conducted in four stages in response to Pi deficiency by multiplex staining of high-resolution two dimensional gel separated proteins. Pro-Q DPS stained gels revealed that 6% of phosphoprotein spots displayed changes in phosphorylation state following low-Pi treatment. These proteins were involved in a large number of metabolic and cellular pathways including carbon metabolism and signal transduction. Changes in protein abundance of a number of enzymes indicated that low-Pi induced a number of carbon flux modifications in metabolic processes including sucrose breakdown and other downstream sugar metabolic pathways. A few key metabolic enzymes, including sucrose synthase (EC 2.4.1.13) and malate dehydrogenase (EC 1.1.1.37), and several signaling components involved in protein kinase or phosphatase cascades, auxin signaling and 14-3-3 proteins displayed low-Pi responsive changes in phosphorylation state or protein abundance. A variety of key enzymes and signaling components identified as potential targets for phosphorylation provide novel clues for comprehensive understanding of Pi regulation in plants. Protein phosphorylation, coordinating with changes in protein abundance, is required for maize root metabolic regulation and developmental acclimation to Pi starvation.

Phosphate depletion modulates auxin transport in Triticum aestivum leading to altered root branching.

Understanding the mechanisms by which nutritional signals impact upon root system architecture is a key facet in the drive for greater nutrient application efficiency in agricultural systems. Cereal plants reduce their rate of lateral root emergence under inorganic phosphate (Pi) shortage; this study uses molecular and pharmacological techniques to dissect this Pi response in Triticum aestivum. Plants were grown in coarse sand washed in high- or low-Pi nutrient solution before being assessed for their root branching density and expression of AUX/IAA and PIN genes. Seedlings were also grown on media containing [(14)C]indole acetic acid to measure basipetal auxin transport. Seedlings grown in low-Pi environments displayed less capacity to transport auxin basipetally from the seminal root apex, a reduction in root expression of PIN auxin transporter genes, and perturbed expression of a range of AUX/IAA auxin response genes. Given the known importance of basipetally transported auxin in stimulating lateral root initiation, it is proposed here that, in T. aestivum, Pi availability directly influences lateral root production through modulation of PIN expression. Understanding such processes is important in the drive for greater efficiency in crop use of Pi fertilizers in agricultural settings.

Phosphate and zinc transport and signalling in plants: toward a better understanding of their homeostasis interaction.

Inorganic phosphate (Pi) and zinc (Zn) are two essential nutrients for plant growth. In soils, these two minerals are either present in low amounts or are poorly available to plants. Consequently, worldwide agriculture has become dependent on external sources of Pi and Zn fertilizers to increase crop yields. However, this strategy is neither economically nor ecologically sustainable in the long term, particularly for Pi, which is a non-renewable resource. To date, research has emphasized the analysis of mineral nutrition considering each nutrient individually, and showed that Pi and Zn homeostasis is highly regulated in a complex process. Interestingly, numerous observations point to an unexpected interconnection between the homeostasis of the two nutrients. Nevertheless, despite their fundamental importance, the molecular bases and biological significance of these interactions remain largely unknown. Such interconnections can account for shortcomings of current agronomic models that typically focus on improving the assimilation of individual elements. Here, current knowledge on the regulation of the transport and signalling of Pi and Zn individually is reviewed, and then insights are provided on the recent progress made towards a better understanding of the Zn-Pi homeostasis interaction in plants.

Overexpression of rice phosphate transporter gene OsPT6 enhances phosphate uptake and accumulation in transgenic rice plants

Whereas the expression patterns and kinetic properties of the rice (Oryza sativa) phosphate transporter gene OsPht1; 6 (OsPT6) are well documented, little is known about the biological functions of this gene. The aim of this study was to investigate the roles of OsPT6 in inorganic phosphate (Pi) acquisition and mobilization, and examine its potential to enhance agricultural production. Here, we generated OsPT6 overexpression transgenic plants using Wuyujing 7, a widely cultivated variety of japonica rice, and then treated transgenic lines and wild type with different Pi supply in hydroponic and soil experiments to explore the functions of OsPT6 in rice. The OsPT6-overexpressing rice lines grew better and accumulated more biomass than wild-type plants, and exhibited significant increases in P accumulation in various tissues, including reproductive tissues under both hydroponic and soil culture conditions. Phosphate-uptake experiment using radiolabeled Pi (33P) showed that the rate of Pi uptake was 75 % and 73 % greater in transgenic plants grown under Pi-sufficient and -deficient conditions, respectively, than the wild-type controls, and that the shoot/root ratio of 33P was 104 % and 42 % greater, respectively. In addition, the grain yield per transgenic plant was much higher than that of the wild-type plants under field conditions. Taken together, our results demonstrate that OsPT6 plays a vital role in Pi acquisition and mobilization in rice and suggest that this gene may be used for genetic engineering rice plants that require less Pi fertilizer.

Effect of Carbon and Nitrogen Source and Concentration on Rock Phosphate Dissolution Induced by Fungi

Inorganic Phosphate (Pi) is an essential nutrient for plant growth and development, however that most soils have in low availability. To overcome this problem it is necessary to apply high amounts of Pi fertilizers, however this is inefficient and costly. Recently, there is increasing interest in the use of rock phosphate (RP) and microorganisms capable of increasing its agronomic effectiveness as crop fertilizer. However, it is unclear the impact that some critical nutrients such as carbon (C) and nitrogen (N) may have on the effectiveness of the microbial RP dissolution. The aim of this study was to evaluate the effect of C and N source and concentration on the RP dissolution by the fungus Mortierella sp. under in vitro conditions. The results indicate that the efficiency to dissolve RP was significantly higher with glucose, followed by arabinose; other sources were ineffective (fructose, sucrose, maltose, cellulose and molasses). On the other hand, NH4Cl was significantly the most effective N source, followed by NH 4 NO 3 . By contrast, KNO3 was ineffective to promote RP dissolution. The best concentration of glucose was 10 g L -1 , while for NH4Cl it was 1 g L -1 . These findings show that by varying nutrient supply, the RP dissolution reactions can be significantly enhanced.

Phosphate: the Silent Challenge

Phosphorus (P) is one of the most vital elements for all living organisms which acts as aconstituent of essential biomolecules such as nucleic acids, phospholipids, and phosphosugars,and as a major contributor to almost all metabolic reactions including photosynthesis,respiration, and energy delivery. It is one of the most needed nutrients for plant growth anddevelopment. Despite high levels of P in the soil, plants absorb it only in the soluble inorganicform of free phosphate ion (Pi) which is scarce in soil. Therefore, there has been a large demandfor Pi fertilizers to secure crop yields, yet its deposition in soil and gradual run-off into waterreservoirs lead to chains of events that cause irreversible damages to ecosystems. Researches,including genome-wide data analyses, have revealed interesting molecular aspects of plantadaptive strategies to deal with low Pi concentrations in soil. These include the higherexpression of acid phosphatases and Pi transporters as well as the secretion of organic acids inthe rhizosphere that maintain cellular Pi homeostasis in order to keep metabolic reactionsrunning. Describing the cycle of Pi exchange between physical and biological worlds, the extentto which current agricultural practices are disturbing the cycle, the necessity of introducing lessdestructivemethods of providing Pi, and alternative measures and solutions for sustainableagriculture will be discussed in this review.

Arbuscular mycorrhizal fungi differ in their ability to regulate the expression of phosphate transporters in maize (Zea mays L.)

Previous studies have found that some phosphate (Pi) starvation inducible transporter genes are downregulated and arbuscular mycorrhizal (AM) inducible Pi transporter genes are upregulated in maize roots associated with the fungus Glomus intraradices. However, little is known about the functional diversity of different AM fungal species in influencing the expression of Pi transporters in maize roots. Here, we studied the expression of two Pi transporter genes ZEAma:Pht1;3 (Pi starvation inducible) and ZEAma:Pht1;6 (AM inducible) in maize root colonized by different AM fungal inoculants. Non-mycorrhizal maize, maize colonized by Glomus deserticola (CA113), Glomus intraradices (IA506), Glomus mosseae (CA201), Gigaspora gigantea (MN922A) and the co-inoculation of all four species were established. The expression patterns of the two genes were quantified using real-time, reverse transcription polymerase chain reaction. The expression level of ZEAma:Pht1;6 was 26-135 times higher in AM plants than in non-mycorrhizal maize roots, whereas the expression level of ZEAma:Pht1;3 was five to 44 times lower in AM plants than in non-mycorrhizal plants. Expression of the two genes differed with inoculation treatment, and increasing the diversity of AM fungi in maize roots led to greater expression of ZEAma:Pht1;6 as well as Pi uptake in shoots. The expression of ZEAma:Pht1;6 was significantly positively correlated with AM colonization rate, concentration of AM biomarkers in maize roots, Pi uptake and dry weight of shoot, but negatively correlated with the expression of ZEAma:Pht1;3. Addition of Pi fertilizer at a low concentration significantly increased the expression of ZEAma:Pht1;6 but had no effect on the expression of ZEAma:Pht1;3.

Improved phosphate metabolism and biomass production by overexpression of AtPAP18 in tobacco

AbstractLimited availability of phosphate ion (Pi) reduces plant growth in natural ecosystems. Here, we report the functional effects of overexpressing an Arabidopsis thaliana purple acid phosphatase encoding gene, AtPAP18, in Nicotiana tabbacum as a crop model plant. Transgenic tobacco plants exhibited significant increases in acid phosphatase activity, total P and Pi contents leading to improved biomass production in both Pi-deficient and Pi-sufficient conditions. Transient expression of AtPAP18::green fluorescent fusion protein in onion epidermal cells indicated that AtPAP18 is a dual-targeted protein, which is detected mainly in the apoplast of the cells after 24 h and in the vacuole after 72 h. Possibly, AtPAP18 protein confers efficient retrieval of Pi from bonded extracellular compounds as well as expendable intracellular Pi-monoesters and anhydrides. These data clearly indicate that overexpression of AtPAP18 gene offers an effective approach for reducing the consumption of chemical Pi fertilizer through increased acquisition of soil Pi and mobilization of internal resources.

Impact of long-term fertilization on different forms of inorganic phosphorus in aquic brown-soil

为提高磷肥利用效率、维持并提高土壤供磷力,在潮棕壤上进行了15年的定位施肥试验，试验处理涵盖了中国典型的8种施肥模式：不施肥(CK)、施循环猪圈肥(M)、单施氮肥(N)、施氮肥+循环猪圈肥(N+M)、施氮磷肥(NP)、施氮磷肥+循环猪圈肥(NP+ M)、施氮磷钾肥(NPK）、施氮磷钾肥+循环猪圈肥(NPK+M)，对不同施肥模式下耕层(0～20 cm)土壤无机磷进行了分级测定。研究表明：有效或缓效态无机磷(Ca₂-P、Ca₈-P、Al-P、Fe-P)含量在无化学磷肥直接投入的情况下均有不同幅度的下降，导致土壤无机磷库亏损；在有化学磷肥直接投入的情况下这些形态的无机磷不但能满足当季作物需求还有盈余，且以NP+M处理盈余最多，丰富了土壤无机磷库。各处理O-P、Ca₁₀-P形态的无机磷均有所增加，且其中部分可由盈余的有效磷素缓慢转化而来。循环猪圈肥（M）的施用能减缓各形态无机磷含量的下降；氮肥和钾肥均能极大促进植物对磷素的吸收，加速土壤磷库亏损。NP+M施肥模式最有利于短期提高土壤供磷力，促进土壤供磷力发展。本研究还发现，有效或缓效态无机磷(Ca₂-P、Ca₈-P、Al-P、Fe-P)与有效磷相关性很好，这进一步完善了土壤供磷力的指标体系。

Phosphorus acquisition; PLANTS in the driver's seat!

Phosphorus is one of the important but least available plant nutrients in the natural ecosystem. Low availability stems mainly from two major soil-associated factors, inorganic interaction with cations and conversion into organic complexes by microbes. In acid soils, that represents nearly 40% of the world's arable land, P fixation and Al toxicity limit agricultural expansion, whereas, in alkaline calcareous soils, which represent more than 25% of the earth surface, P and Fe deficiency constrain crop production[1,2]. In addition, phosphate (Pi) fertilizers are produced using non-renewable resources and are unaffordable for most poor farmers of the tropics. These factors lie behind attempts to generate Pi acquisition-efficient plants. Some plants adapt to Pi-limiting conditions by secreting organic acids into the rhizosphere. Organic acids facilitate the release of Pi from inorganic ion complexes such as calcium phosphates. Luis Herrera-Estrella's research group[3] asked the logical question, what happens to the Pi nutrition of plants if the bacterial citrate synthase gene is over-expressed? As predicted, tobacco plants expressing the bacterial citrate synthase produced and secreted more citrate into the rhizosphere. This gave a distinct adaptive advantage to plants grown in soil containing calcium phosphate. It is interesting that over-expression of citrate synthase alone was able to enhance the Pi acquisition by transgenic plants. This suggests that both anion channels and Pi transporters are activated under Pi starvation, allowing rapid secretion of organic acids and uptake of Pi. This study provided the first molecular evidence to show that altering a major molecular determinant of Pi acquisition could lead to dramatic changes in P status and biomass production of transgenic plants. By over-expressing citrate synthase, plants have been transformed into a key determinant of Pi acquisition, defying the dogma that plants are always at the mercy of complex chemical and biological interactions that regulate available Pi in soil. This work is certain to have a profound impact on developing Pi-efficient plants for cultivation in marginal soils of the world.