P-deficient Conditions Research Articles

Choice of activated sludge microorganisms under phosphate deficiency: Competition for inorganic phosphate or change to organophosphorus metabolism

Phosphorus (P) plays a crucial role in the microbial processes of wastewater treatment. However, the current understanding of P metabolic pathways in wastewater is incomplete, and the mechanisms of microbial P metabolism under P deficient conditions remain unclear. This study explores the succession patterns of activated sludge bacterial communities and their potential P utilization strategies under P-deficient conditions. The results indicate that changes in phosphorus concentration and composition drive microbial community succession. Under P deficiency, microorganisms initially focus on inorganic phosphorus (IP) metabolism, prioritizing competition for IP. Subsequently, the bacterial community shifts to predominantly utilizing organic phosphorus (OP), with over 94% of genomes carrying OP metabolism genes. The OP in the system primarily consists of phosphonates and phosphoester. Consequently, distinct bacterial responses to phosphoester and phosphonates were observed, with the bacterial community transitioning from low modular to highly modular communities with differentiated niches. Phosphoester and phosphonate metabolism emerged as the two main OP metabolic pathways within the community. By reconstructing the P metabolic pathways of dominant genera, including Pannonibacter (Proteobacteria) and f_Saprospiraceae (Bacteroidota), metabolic models of phosphonate and phosphoester were developed in a wastewater treatment system for the first time. This study provides new insights into biological P metabolism in wastewater treatment, expanding our understanding of P metabolic pathways in wastewater.

Down-regulation of the rice HRS1 HOMOLOG3 transcriptional repressor gene due to N deficiency directly co-activates ammonium and phosphate transporter genes.

Rice HRS1 HOMOLOG3 (OsHHO3) acts as a transcriptional repressor of AMMONIUM TRANSPORTER1 (OsAMT1) genes in rice; thus, reduced OsHHO3 expression in nitrogen (N)-deficient environments promotes ammonium uptake. In this study, we show that OsHHO3 also functions as a repressor of a specific subset of phosphate (Pi) transporter (PT) genes involved in the uptake and root-to-shoot translocation of Pi, including OsPT2, OsPT4, and OsPHO1;1. Disruption of OsHHO3 increased Pi uptake and Pi contents in shoots and roots, while overexpression of OsHHO3 caused the opposite effects. Furthermore, phosphorus (P) deficiency slightly decreased OsHHO3 expression, up-regulating a specific subset of PT genes. However, N deficiency was more effective than P deficiency in suppressing OsHHO3 expression in roots, and unlike N deficiency-dependent activation of PT genes under the control of OsHHO3, the P deficiency-dependent activation of OsAMT1 genes was minimal. Interestingly, the simultaneous deficiency of both N and P promoted the OsHHO3-regulated expression of PT genes more significantly than the deficiency of either N or P, but diminished the expression of genes regulated by OsPHR2, a master regulator of Pi starvation-responsive transcriptional activation. Phenotypic analysis revealed that the inactivation and overexpression of OsHHO3 improved and reduced plant growth, respectively, under N-deficient and P-deficient conditions. These results indicate that OsHHO3 regulates a specific subset of PT genes independently of OsPHR2-mediated regulation and plays a critical role in the adaptation to diverse N and P environments.

Melatonin Increases Root Cell Wall Phosphorus Reutilization via an NODependent Pathway in Rice (Oryza sativa).

Melatonin (MT) has been implicated in the plant response to phosphorus (P) stress; however, the precise molecular mechanisms involved remain unclear. This study investigated whether MT controls internal P distribution and root cell wall P remobilization in rice. Rice was treated with varying MT and P levels and analyzed using biochemical and molecular techniques to study phosphorus utilization. The results demonstrated that low P levels lead to a rapid increase in endogenous MT levels in rice roots. Furthermore, the exogenous application of MT significantly improved rice tolerance to P deficiency, as evidenced by the increased biomass and reduced proportion of roots to shoots under P-deficient conditions. MT application also mitigated the decrease in P content regardless in both the roots and shoots. Mechanistically, MT accelerated the reutilization of P, particularly in the root pectin fraction, leading to increased soluble P liberation. In addition, MT enhanced the expression of OsPT8, a gene involved in root-to-shoot P translocation. Furthermore, we observed that MT induced the production of nitric oxide (NO) in P-deficient rice roots and that the mitigating effect of MT on P deficiency was compromised in the presence of the NO inhibitor, c-PTIO, implying that NO is involved in the MT-facilitated mitigation of P deficiency in rice. Overall, our findings highlight the potential of MT as a promising strategy for enhancing rice tolerance to P deficiency and improving P use efficiency in agricultural practices.

Comparative Analysis of Hulless Barley Transcriptomes to Regulatory Effects of Phosphorous Deficiency.

Hulless barley is a cold-resistant crop widely planted in the northwest plateau of China. It is also the main food crop in this region. Phosphorus (P), as one of the important essential nutrient elements, regulates plant growth and defense. This study aimed to analyze the development and related molecular mechanisms of hulless barley under P deficiency and explore the regulatory genes so as to provide a basis for subsequent molecular breeding research. Transcriptome analysis was performed on the root and leaf samples of hulless barley cultured with different concentrations of KH2PO4 (1 mM and 10 μM) Hoagland solution. A total of 46,439 genes were finally obtained by the combined analysis of leaf and root samples. Among them, 325 and 453 genes had more than twofold differences in expression. These differentially expressed genes (DEGs) mainly participated in the abiotic stress biosynthetic process through Gene Ontology prediction. Moreover, the Kyoto Encyclopedia of Genes and Genomes showed that DEGs were mainly involved in photosynthesis, plant hormone signal transduction, glycolysis, phenylpropanoid biosynthesis, and synthesis of metabolites. These pathways also appeared in other abiotic stresses. Plants initiated multiple hormone synergistic regulatory mechanisms to maintain growth under P-deficient conditions. Transcription factors (TFs) also proved these predictions. The enrichment of ARR-B TFs, which positively regulated the phosphorelay-mediated cytokinin signal transduction, and some other TFs (AP2, GRAS, and ARF) was related to plant hormone regulation. Some DEGs showed different values in their FPKM (fragment per kilobase of transcript per million mapped reads), but the expression trends of genes responding to stress and phosphorylation remained highly consistent. Therefore, in the case of P deficiency, the first response of plants was the expression of stress-related genes. The effects of this stress on plant metabolites need to be further studied to improve the relevant regulatory mechanisms so as to further understand the importance of P in the development and stress resistance of hulless barley.

Root growth dynamics, nutrient uptake and use efficiency of Grevillea robusta grown under nitrogen and phosphorus deficiency

Root growth, nutrient uptake, and nutrient use efficiency of a plant is influenced by the nutrient availability in its growing environment. The aim of this study was to investigate the root morphology, nutrient uptake and use efficiency of Grevillea robusta grown in nitrogen (N)- and phosphorus (P)-limited conditions. A hydroponic experiment was conducted for three months in a glasshouse with four nutrient treatments; (i) N-deficient, (ii) P-deficient, (iii) N/P-deficient (co-limitation of N and P), and (iv) control (sufficient amounts of N, P, and other nutrients in the growth medium). The composition and the concentration of each nutrient in the control solution were custom-made based on the growth requirement of G. robusta. N and P concentration in nutrient-deficient media were maintained at 2 ppm. The impact of N- or P-deficiency and their co-limitation on cluster root formation, organ-specific dry matter and nutrient accumulation, N and P uptake and their use efficiencies were measured. P-deficient conditions produced the highest number of cluster roots (24 ± 4) which was comparatively lower than those of N- and N/P-deficient conditions indicating that P-deficiency is the primary factor influencing the formation of cluster roots in G. robusta. The use efficiency of N and P in biomass formation was significantly (p < 0.05) enhanced when their uptake was reduced in response to N- and P-limitation. The efficient internal use of P by G. robusta under N- and N/P-deficiency is indicated by the significant increase in P-remobilization efficiency under these nutrient-deficient conditions.

Comparative physiological and transcriptomic characterization of rice (Oryza Sativa L.) root seedlings under phosphorus deficiency

Phosphorus (P) is essential for optimal growth, development, and metabolic functioning in rice. In this research study, we compared the physiologies and transcriptomes of root seedlings of two rice varieties, upland rice (LH1) and lowland rice (IR26), under the treatments of normal P application (NP: 300 μM) and low P application (LP: 10 μM). The results demonstrated that the plant biomass of LH1 and IR26 was reduced by 10.0% and 27.8% in the LP treatment compared to the NP treatment (control), respectively. The P deficiency substantially affected the enzymatic activities in the roots of LH1 and IR26, which are vital for carbon and energy metabolism. Transcriptomic results identified 24,193 genes in all samples, and over 5000 differentially expressed genes (DEGs) were identified in both varieties under LP compared with their controls. KEGG analysis showed the functional categories for DEGs, which mainly included phenylpropanoid biosynthesis, glutathione metabolism, plant hormone signal transduction, photosynthesis, and carbon fixation in photosynthetic organisms. The DEGs involved in the glutathione metabolism, carbon fixation, and photosynthesis in photosynthetic pathways were downregulated by P deficiency. The DEGs involved in the metabolism of plant hormone signal transduction and carbohydrate transition for LH1 and IR26 exhibited different defense responses to the P deficiency in upland and lowland rice. The genes engaged in plant hormone signal transduction and carbohydrate fixation are anticipated to play key roles in improving the upland and lowland rice adaptation to P-deficient conditions. The results of this investigation have established a theoretical basis for strengthening our insight into the P tolerance mechanism in lowland and upland rice.

Interactions between Root Hair Development and Arbuscular Mycorrhizal Fungal Colonization in Trifoliate Orange Seedlings in Response to P Levels

Both arbuscular mycorrhizal (AM) fungi and root hairs are crucial in facilitating plant uptake of phosphorus (P), while it is unclear whether and how they respond to varying P supplies. In order to explore how AM fungal colonization and root hair development are affected by substrate P supply, trifoliate orange (Poncirus trifoliata) seedlings were inoculated with AM fungus Rhizophagus intraradices and grown under low, moderate, and high P conditions; then, root hair morphological features and AM fungal colonization were measured. Following 120 days of AM fungal inoculation, root hair density, root hair length, AM fungal colonization rate, arbuscule colonization rate, and AM fungal colonization frequency all increased significantly under P-deficient conditions but decreased under high P conditions. Moreover, the colonization of AM fungi had a major impact on root hair formation by altering the expression of related genes and the growth of epidermal cells. The effect of AM fungi was dependent on P supply levels, as evidenced by the fact that root hair density and length increased at high P levels but decreased at low P levels. As a result, root hairs may serve as a preferential site for AM fungal colonization, and their morphology could influence the early stage of AM symbiosis establishment.

Overexpression of GmPAP4 Enhances Symbiotic Nitrogen Fixation and Seed Yield in Soybean under Phosphorus-Deficient Condition.

Legume crops establish symbiosis with nitrogen-fixing rhizobia for biological nitrogen fixation (BNF), a process that provides a prominent natural nitrogen source in agroecosystems; and efficient nodulation and nitrogen fixation processes require a large amount of phosphorus (P). Here, a role of GmPAP4, a nodule-localized purple acid phosphatase, in BNF and seed yield was functionally characterized in whole transgenic soybean (Glycine max) plants under a P-limited condition. GmPAP4 was specifically expressed in the infection zones of soybean nodules and its expression was greatly induced in low P stress. Altered expression of GmPAP4 significantly affected soybean nodulation, BNF, and yield under the P-deficient condition. Nodule number, nodule fresh weight, nodule nitrogenase, APase activities, and nodule total P content were significantly increased in GmPAP4 overexpression (OE) lines. Structural characteristics revealed by toluidine blue staining showed that overexpression of GmPAP4 resulted in a larger infection area than wild-type (WT) control. Moreover, the plant biomass and N and P content of shoot and root in GmPAP4 OE lines were also greatly improved, resulting in increased soybean yield in the P-deficient condition. Taken together, our results demonstrated that GmPAP4, a purple acid phosphatase, increased P utilization efficiency in nodules under a P-deficient condition and, subsequently, enhanced symbiotic BNF and seed yield of soybean.

Trade-offs between root-secreted acid phosphatase and root morphology traits, and their contribution to phosphorus acquisition in Brassica napus.

Oilseed rape (Brassica napus) is one of the most important oil crops in the world and shows sensitivity to low phosphorus (P) availability. In many soils, organic P (Po) is the main component of the soil P pool. Po must be mineralised to Pi through phosphatases, and then taken up by plants. However, the relationship between root-secreted acid phosphatases (APase) and root morphology traits, two important P-acquisition strategies in response to P deficiency, is unclear among B. napus genotypes. This study aimed to understand their relationship and how they affect P acquisition, which is crucial for the sustainable utilisation of agricultural P resources. This study showed significant genotypic variations in root-secreted APase activity per unit root fresh weight (SAP) and total root-secreted APase activity per plant (total SAP) among 350 B. napus genotypes. Seed yield was positively correlated with total SAP but not significantly correlated with SAP. Six root traits of 18 B. napus genotypes with contrasting root biomass were compared under normal Pi, low Pi and Po. Genotypes with longer total root length (TRL) reduced SAP, but those with shorter TRL increased SAP under P deficiency. Additionally, TRL was important in P-acquisition under three P treatments, and total SAP was also important in P-acquisition under Po treatment. In conclusion, trade-offs existed between the two P-acquisition strategies among B. napus genotypes under P-deficient conditions. Total SAP was an important root trait under Po conditions. These results might help to breed B. napus with greater P-acquisition ability under low P availability conditions.

Lanthanum Significantly Contributes to the Growth of the Fine Roots' Morphology and Phosphorus Uptake Efficiency by Increasing the Yield and Quality of Glycyrrhiza uralensis Taproots.

The occurrence of different degrees of phosphorus deficiency in the vast majority of G. uralensis cultivation regions worldwide is common. There is a pressing need within the cultivated G. uralensis industry to identify appropriate exogenous substances that can enhance the uptake of phosphorus and improve both the yield and quality of the taproots of G. uralensis. This study was conducted to investigate the fine root and taproot morphology, physiological characteristics, and secondary metabolite accumulation in response to the supply of varying concentrations of LaCl3 to G. uralensis, to determine the optimal concentration of LaCl3 that can effectively enhance the yield and quality of G. uralensis's taproots, while also alleviating its reliance on soil phosphate fertilizer. The findings indicate that the foliar application of lanthanum enhanced root activity and increased APase activity, eliciting alterations in the fine root morphology, leading to promoting the accumulation of biomass in grown G. uralensis when subjected to P-deficient conditions. Furthermore, it was observed that the nutrient uptake of G. uralensis was significantly improved when subjected to P-deficient conditions but treated with LaCl3. Additionally, the yield and quality of the medicinal organs of G. uralensis were significantly enhanced.

Strigolactone GR24-mediated mitigation of phosphorus deficiency through mycorrhization in aerobic rice

Strigolactones (SLs) are a new class of plant hormones that play a significant role in regulating various aspects of plant growth promotion, stress tolerance and influence the rhizospheric microbiome. GR24 is a synthetic SL analog used in scientific research to understand the effects of SL on plants and to act as a plant growth promoter. This study aimed to conduct hormonal seed priming at different concentrations of GR24 (0.1, 0.5, 1.0, 5.0 and 10.0 µM with and without arbuscular mycorrhizal fungi (AMF) inoculation in selected aerobic rice varieties (CR Dhan 201, CR Dhan 204, CR Dhan 205, and CR Dhan 207), Kasalath-IC459373 (P-tolerant check), and IR-36 (P-susceptible check) under phosphorus (P)-deficient conditions to understand the enhancement of growth and priming effects in mycorrhization. Our findings showed that seed priming with 5.0 µM SL GR24 enhanced the performance of mycorrhization in CR Dhan 205 (88.91 %), followed by CR Dhan 204 and 207, and AMF sporulation in CR Dhan 201 (31.98 spores / 10 gm soil) and CR Dhan 207 (30.29 spores / 10 g soil), as well as rice growth. The study showed that the highly responsive variety CR Dhan 207 followed by CR Dhan 204, 205, 201, and Kasalath IC459373 showed higher P uptake than the control, and AMF treated with 5.0 µM SL GR24 varieties CR Dhan 205 followed by CR Dhan 207 and 204 showed the best performance in plant growth, chlorophyll content, and soil functional properties, such as acid and alkaline phosphatase activity, soil microbial biomass carbon (MBC), dehydrogenase activity (DHA), and fluorescein diacetate activity (FDA). Overall, AMF intervention with SL GR24 significantly increased plant growth, soil enzyme activity, and uptake of P compared to the control. Under P-deficient conditions, seed priming with 5.0 µM strigolactone GR24 and AMF inoculum significantly increased selected aerobic rice growth, P uptake, and soil enzyme activities. Application of SLs formulations with AMF inoculum in selected aerobic rice varieties, CR Dhan 207, CR Dhan 204, and CR Dhan 205, will play an important role in mycorrhization, growth, and enhancement of P utilization under P- nutrient deficient conditions.

Phosphorus absorption kinetics and exudation strategies of roots developed by three lupin species to tackle P deficiency.

Different lupin species exhibited varied biomass, P allocation, and physiological responses to P-deprivation. White and yellow lupins had higher carboxylate exudation rates, while blue lupin showed the highest phosphatase activity. White lupin (Lupinus albus) can produce specialized root structures, called cluster roots, which are adapted to low-phosphorus (P) soil. Blue lupin (L. angustifolius) and yellow lupin (L. luteus), which are two close relatives of white lupin, do not produce cluster roots. This study characterized plant responses to nutrient limitation by analyzing biomass accumulation and P distribution, absorption kinetics and root exudation in white, blue, and yellow lupins. Plants were grown in hydroponic culture with (64µM NaH2PO4) or without P for 31days. Under P limitation, more biomass was allocated to roots to improve P absorption. Furthermore, the relative growth rate of blue lupin showed the strongest inhibition. Under + P conditions, the plant total-P contents of blue lupin and yellow lupin were higher than that of white lupin. To elucidate the responses of lupins via the perspective of absorption kinetics and secretion analysis, blue and yellow lupins were confirmed to have stronger affinity and absorption capacity for orthophosphate after P-deprivation cultivation, whereas white lupin and yellow lupin had greater ability to secrete organic acids. The exudation of blue lupin had higher acid phosphatase activity. This study elucidated that blue lupin was more sensitive to P-scarcity stress and yellow had the greater tolerance of P-deficient condition than either of the other two lupin species. The three lupin species have evolved different adaptation strategies to cope with P deficiency.

Low phosphorus impact on Moso bamboo (Phyllostachys edulis) root morphological polymorphism and expression pattern of the related genes.

Moso bamboo typically grows in phosphorus (P)-deficient soil that limits its growth and development. In this study, 10 Moso bamboo genotypes (Ph-1 to Ph-10) were evaluated for their responses to P deficiency during the seedling stage by growing them in both P-sufficient and P-deficient conditions. Adaptive responses to low P (LP) conditions were observed in the majority of genotypes. Under P deficiency conditions, the total biomass decreased in several genotypes, but at the same time, the root-to-shoot ratio increased. Principal component analysis identified two main comprehensive traits (PC1 and PC2) related to the root volume and surface area and P concentration and accumulation. Based on the analysis, two genotypes (Ph-6 and Ph-10) were identified with significantly different levels of tolerance to P deficiency. The results revealed that the genotype Ph-10 responded to P deficiency by significantly increasing the root surface area and volume, while simultaneously reducing the number of root cortex cells when compared with the genotype Ph-6, which showed the lowest tolerance (intolerant). The genotype Ph-10 exhibited a robust response to external LP conditions, marked by elevated expression levels of PHOSPHATE TRANSPORTERs and SYG1/PHO81/XPR1s. In situ Polymerase Chain Reaction (PCR) analysis also revealed distinct tissue-specific expression patterns of the genes in the roots, particularly highlighting the differences between Ph-6 and Ph-10. The results provide a foundation for elucidating the mechanism of LP tolerance, thus potentially contributing to developing high P-use efficiency in Moso bamboo species.

Enhancing phosphorus use efficiency in wheat grown on alkaline calcareous soils

Phosphorus (P) use efficiency is crucial for sustainable wheat production, particularly on alkaline calcareous soils. This study investigates the relative importance of two factors; P acquisition efficiency (PAE) and P utilization efficiency (PUtE), in determining P use efficiency (PUE) in wheat. A field trial with ten wheat genotypes was conducted under two P levels (no P application and P application at 110 kg P2O5 ha−1). Results revealed significant genetic variability in PUE, PAE, and PUtE among wheat genotypes under varying P availabilities. Genotypes MK-4 and MK-8 exhibited superior PUE, making them ideal candidates for soils with differing P levels. PAE played a more substantial role in influencing PUE, with PUtE contributing less to the variability. The findings underscore the importance of improving PAE, particularly for wheat genotypes grown in P-deficient conditions. Moreover, selecting genotypes with lower grain P concentration can enhance PUtE, contributing to improved PUE. These insights can improve breeding efforts and crop management practices to enhance P use efficiency in wheat, ultimately reducing production costs and fertilizer demand, especially in P-limited alkaline calcareous soils.

Changes in Phosphorus Fractions Upon Inoculation of Pseudomonas sp. and Nano Phosphorus Application in Wheat Rhizosphere

ABSTRACT The decreased availability of phosphorus (P) in Indian soils including the soils of Bihar can be attributed to its affinity to the formation of complex compounds. This study is undertaken to investigate the interactive effect of mineral P, nano P and phosphate-solubilizing bacteria (PSBs) for different inorganic and organic P fractions in an alluvial soil with seven treatments in triplicates viz. control (T1); 100% RDF (120:60:40 N:P:K) (T2); 100% recommended dose of P (RDP) through nano P as soil application (T3); 50% nano-P soil application + 50% nano P as foliar application at flowering stage (T4); 50% RDP + 25% P (nano P) soil application + PSB at the rate of 0.335 µl kg−1 soil (T5); 50% RDP + 25% P (nano P) foliar spray + PSB at the rate of 0.335 µl kg−1 soil (T6) and application of 100% P through FYM at the rate of 10.71 g kg−1 + PSB at the rate of 0.335 µl kg−1 soil (T7). The application of treatment T7 yielded highest soluble P, Al-P and Fe 2 P while Fe 1 P, Ca-P and residual P were found to be greatest in case of treatment T5. Soluble P fraction had established significant positive correlation with Fe1-P (p ≤ .836), Ca-P (p ≤ .842) and Fe2-P (p ≤ .822). Hence, the application of mineral P in combination with nano P as soil application and conjugative application of FYM along with PSB could be very helpful in increasing the availability of soluble P by increasing its release and availability under naturally P-deficient conditions.

Rice straw-derived smoke water promotes rice root growth under phosphorus deficiency by modulating oxidative stress and photosynthetic gene expression

Plant-derived smoke has been shown to promote plant growth and seed germination, but its roles and mechanisms in response to nutrient deficiency stress remain unclear. Plants respond to phosphorus (P) deficiency by undergoing morphological, physiological, and transcriptional changes in order to improve nutrient uptake efficiency. Here, we showed that rice straw-derived smoke water could promote root growth in rice (Oryza sativa cv. Nipponbare) grown under P-sufficient and P-deficient conditions. Transcriptome analysis of the root tissues identified 1309 genes up-regulated and 1311 genes down-regulated by smoke water under P-deficient conditions. The GO terms ‘glutathione transferase activity’ and ‘photosynthesis—light reaction’ were found to be significantly enriched among the genes that were up- and down-regulated by smoke water, respectively. Biochemical analysis showed that smoke water reduced P-deficient-induced accumulation of H2O2 and malondialdehyde (MDA), a lipid peroxidation marker, reduced sucrose contents, but increased Fe accumulation. Furthermore, smoke water suppressed the expression of strigolactone biosynthesis genes, which were strongly induced by P deficiency as an adaptive strategy to improve root P uptake. These results revealed a potential mechanism by which smoke water promotes root growth and interacts with P deficiency-induced transcriptional regulation to mitigate P deficiency stress in rice.

Transcriptomic Analysis of the Response of the Toxic Dinoflagellate Prorocentrum lima to Phosphorous Limitation.

Some dinoflagellates cause harmful algal blooms, releasing toxic secondary metabolites, to the detriment of marine ecosystems and human health. Phosphorus (P) is a limiting macronutrient for dinoflagellate growth in the ocean. Previous studies have been focused on the physiological response of dinoflagellates to ambient P changes. However, the whole-genome's molecular mechanisms are poorly understood. In this study, RNA-Seq was utilized to compare the global gene expression patterns of a marine diarrheic shellfish poisoning (DSP) toxin-producing dinoflagellate, Prorocentrum lima, grown in inorganic P-replete and P-deficient conditions. A total of 148 unigenes were significantly up-regulated, and 30 unigenes were down-regulated under 1/4 P-limited conditions, while 2708 unigenes were significantly up-regulated, and 284 unigenes were down-regulated under 1/16 P-limited conditions. KEGG enrichment analysis of the differentially expressed genes shows that genes related to ribosomal proteins, glycolysis, fatty acid biosynthesis, phagosome formation, and ubiquitin-mediated proteolysis are found to be up-regulated, while most of the genes related to photosynthesis are down-regulated. Further analysis shows that genes encoding P transporters, organic P utilization, and endocytosis are significantly up-regulated in the P-limited cells, indicating a strong ability of P. lima to utilize dissolved inorganic P as well as intracellular organic P. These transcriptomic data are further corroborated by biochemical and physiological analyses, which reveals that under P deficiency, cellular contents of starch, lipid, and toxin increase, while photosynthetic efficiency declines. Our results indicate that has P. lima evolved diverse strategies to acclimatize to low P environments. The accumulation of carbon sources and DSP toxins could provide protection for P. lima to cope with adverse environmental conditions.

Transcriptional responses of the marine diatom Chaetoceros tenuissimus to phosphate deficiency

The planktonic diatom Chaetoceros tenuissimus sometimes forms blooms in coastal surface waters where dissolved inorganic phosphorus (P) is typically deficient. To understand the molecular mechanisms for survival under P-deficient conditions, we compared whole transcripts and metabolites with P-sufficient conditions using stationary growth cells. Under P-deficient conditions, cell numbers and photosynthetic activities decreased as cells entered the stationary growth phase, with downregulation of transcripts related to the Calvin cycle and glycolysis/gluconeogenesis. Therefore, metabolites varied across nutritional conditions. Alkaline phosphatase, phosphodiesterase, phytase, phosphate transporter, and transcription factor genes were drastically upregulated under dissolved inorganic P deficiency. Genes related to phospholipid degradation and nonphospholipid synthesis were also upregulated. These results indicate that C. tenuissimus rearranges its membrane composition from phospholipids to nonphospholipids to conserve phosphate. To endure in P-deficient conditions, C. tenuissimus modifies its gene responses, suggesting a potential survival strategy in nature.

Abundance of colloidal organic phosphorus in the Taiwan Strait

The Taiwan Strait is a coastal sea with dynamic hydrologic condition and dissolved organic matter (DOM) cycling. To better understand its phosphorus (P) transformation, phosphate and bulk dissolved organic phosphorus (DOP) concentrations were determined in the surface water of the Taiwan Strait during 2010 and 2011 summers. The bulk DOP was further fractionated into the low molecular weight (LMW) DOP and colloidal organic phosphorus (COP) with the application of the cross-flow ultrafiltration technique at a size cut-off of 10 kDa. The surface water in the Taiwan Strait generally showed higher bulk DOP concentration than phosphate excluding estuarine stations. This is similar to the surface waters in the subtropical gyres, implying a P-deficient condition in the Taiwan Strait. The LMW-DOP followed a constant permeation behavior in the ultrafiltration experiments, allowing the quantification of LMW-DOP and COP concentrations with the ultrafiltration permeation model. The average COP concentration was 0.044 ± 0.022 μmol/L and 0.042 ± 0.027 μmol/L during 2010 and 2011 summers, respectively. Accordingly, COP accounted for 35 ± 13% and 34 ± 16% of bulk DOP during 2010 and 2011 summers, respectively, suggesting a substantial occurrence of organic phosphorus in the colloidal fraction. The C/P ratio decreased from LMW-DOM to bulk DOM and to colloidal organic matter (COM), supporting the degradation pathway of bulk DOM from colloidal to LMW fractions and the lability of COP in the Taiwan Strait. The fractionation of C/P ratio between bulk DOM and COM in the Taiwan Strait, denoted by the fractionation factor (FC/D), was comparable to the open oceans, but significantly stronger than rivers and estuaries. It might indicate an autochthonous input and rapid turnover of bulk DOP pool in the Taiwan Strait in the context of low phosphate concentration. The FC/D also showed a spatial variability in the Taiwan Strait, high in the South China Sea Warm Current and upwelling occupied stations and low in inshore areas influenced by terrestrial input. This further supports the FC/D as an indicator of bulk DOM sources besides its application to decipher the diagenetic status of bulk DOM and biogeochemical cycles of bulk DOP in the coastal oceans.

Arbuscular Mycorrhizal Fungi Response on Soil Phosphorus Utilization and Enzymes Activities in Aerobic Rice under Phosphorus-Deficient Conditions.

The prominence of arbuscular mycorrhizal fungi (AMF) in sustainable rice production has long been recognized. However, there is little information about AMF response in aerobic rice cultivation under phosphorus (P)-deficient conditions. The aim of this experiment was to compare and determine the preeminent AMF effects on rice mycorrhizal colonization, responsiveness, P utilization, and different growth-promoting traits under P-deficient conditions. Different AMF genera viz. (Funneliformis sp., Rhizophagus sp., Glomus sp., Acaulospora sp., and Claroideoglomus sp.) in four different aerobic rice varieties developed by ICAR-NRRI, India (CR Dhan 201, CR Dhan 204, CR Dhan 205, and CR Dhan 207) were investigated using the check P-susceptible variety (IR 36) and the P-tolerant variety (Kasalath IC459373). Data analyzed through linear modeling approaches and bivariate associations found that AMF colonization was highly correlated with soil enzymes, particularly fluorescein diacetate (FDA) and plant P uptake. The microbial biomass carbon (MBC) and FDA content were significantly changed among rice varieties treated with AMF compared to uninoculated control. Out of four different rice varieties, CR Dhan 207 inoculated with AMF showed higher plant P uptake compared to other varieties. In all the rice varieties, AMF colonization had higher correlation coefficients with soil enzymes (FDA), MBC, and plant P uptake than uninoculated control. The present study indicates that AMF intervention in aerobic rice cultivation under P-deficient conditions significantly increased plant P uptake, soil enzymes activities and plant growth promotion. Thus, the information gathered from this study will help us to develop a viable AMF package for sustainable aerobic rice cultivation.