Low Phosphorus Conditions Research Articles

Growth Behavior, Biomass Composition and Fatty Acid Methyl Esters (FAMEs) Production Potential of Chlamydomonas reinhardtii, and Chlorella vulgaris Cultures.

The production of biomolecules by microalgae has a wide range of applications in the development of various materials and products, such as biodiesel, food supplements, and cosmetics. Microalgae biomass can be produced using waste and in a smaller space than other types of crops (e.g., soja, corn), which shows microalgae's great potential as a source of biomass. Among the produced biomolecules of greatest interest are carbohydrates, proteins, lipids, and fatty acids. In this study, the production of these biomolecules was determined in two strains of microalgae (Chlamydomonas reinhardtii and Chlorella vulgaris) when exposed to different concentrations of nitrogen, phosphorus, and sulfur. Results show a significant microalgal growth (3.69 g L-1) and carbohydrates (163 mg g-1) increase in C. reinhardtii under low nitrogen concentration. Also, higher lipids content was produced under low sulfur concentration (246 mg g-1). It was observed that sulfur variation could affect in a negative way proteins production in C. reinhardtii culture. In the case of C. vulgaris, a higher biomass production was obtained in the standard culture medium (1.37 g L-1), and under a low-phosphorus condition, C. vulgaris produced a higher lipids concentration (248 mg g-1). It was observed that a low concentration of nitrogen had a better effect on the accumulation of fatty acid methyl esters (FAMEs) (C16-C18) in both microalgae. These results lead us to visualize the effects that the variation in macronutrients can have on the growth of microalgae and their possible utility for the production of microalgae-based subproducts.

Aspergillus niger Fermentation Broth Promotes Maize Germination and Alleviates Low Phosphorus Stress.

Aspergillus niger is a type of soil fungus with the ability to dissolve insoluble phosphate and secrete organic metabolites such as citric acid. However, whether cell-free Aspergillus niger fermentation broth (AFB) promotes maize growth and alleviates low-phosphorus stress has not been reported. In this study, we explored their relationship through a hydroponics system. The results indicated that either too low or too high concentrations of AFB may inhibit seed germination potential and germination rate. Under low phosphorus conditions, all physiological indexes (biomass, soluble sugar content, root length, etc.) increased after AFB was applied. A qRT-PCR analysis revealed that the expression of the EXPB4 and KRP1 genes, which are involved in root development, was upregulated, while the expression of the CAT2 and SOD9 genes, which are keys to the synthesis of antioxidant enzymes, was downregulated. The expression of LOX3, a key gene in lipid peroxidation, was down-regulated, consistent with changes in the corresponding enzyme activity. These results indicate that the application of AFB may alleviate the oxidative stress in maize seedlings, reduce the oxidative damage caused by low P stress, and enhance the resistance to low P stress in maize seedlings. In addition, it reveals the potential of A. niger to promote growth and provides new avenues for research on beneficial plant-fungal interactions.

Evaluation of Inbred Maize (Zea mays L.) for Tolerance to Low Phosphorus at the Seedling Stage.

In underdeveloped nations where low-input agriculture is practiced, low phosphorus (LP) in the soil reduces the production of maize. In the present study, a total of 550 inbred maize lines were assessed for seedling traits under LP (2.5 × 10-6 mol L-1 of KH2PO4) and NP (2.5 × 10-4 mol L-1 of KH2PO4) hydroponic conditions. The purpose of this study was to quantify the amount of variation present in the measured traits, estimate the genetic involvement of these characteristics, examine the phenotypic correlation coefficients between traits, and to integrate this information to prepare a multi-trait selection index for LP tolerance in maize. A great deal of variability in the maize genotype panel was confirmed by descriptive statistics and analysis of variance (ANOVA). Estimated broad-sense heritability (h2) ranged from 0.7 to 0.91, indicating intermediate to high heritability values for the measured traits. A substantial connection between MSL and other root traits suggested that the direct selection of MSL (maximum shoot length) could be beneficial for the enhancement of other traits. The principal component analysis (PCA) of the first two main component axes explained approximately 81.27% of the variation between lines for the eight maize seedling variables. TDM (total dry matter), SDW (shoot dry weight), RDW (root dry weight), SFW (shoot fresh weight), RFW (root fresh weight), MRL (maximum root length), and MSL measurements accounted for the majority of the first principal component (59.35%). The multi-trait indices were calculated based on PCA using all the measured traits, and 30 genotypes were selected. These selected lines might be considered as the potential source for the improvement of LP tolerance in maize.

Proper Delay of Phosphorus Application Promotes Wheat Growth and Nutrient Uptake under Low Phosphorus Condition

It is widely known that root morphology has different response mechanisms at different phosphorus (P) levels. However, the effects of P application times on wheat (Triticum aestivum L.) root morphology and, therefore, on growth and nutrient uptake are still unclear. In this study, we investigated the feedback from the physiological indexes of wheat on different P application times after planting. Compared with the P application at planting, the shoot biomass with delayed P application for 21 days (d) increased by 11.8% (p < 0.05). Compared with the P application at planting, the shoot P uptake with delayed P application for 14–21 days increased by 38.4–71.2%, while the shoot N uptake and K uptake with delayed P application for 21 days increased by 16.0% and 14.1% (p < 0.05). Compared with the P application at planting, P use efficiency, N use efficiency, and K use efficiency with delayed P application for 21 days increased by 16.4%, 12.4%, and 12.4%. Delayed P application for 14–21 days promoted wheat shoot growth, nutrient (P, N, and K) uptake, and their use efficiencies. This is particularly important for optimizing the P fertilizer input and nutrient management for wheat growth.

Overexpression of the autophagy-related gene SiATG8a from foxtail millet (Setaria italica L.) in transgenic wheat confers tolerance to phosphorus starvation

In plants, autophagy plays an important role in regulating intracellular degradation and amino acid recycling in response to nutrient starvation, senescence, and other environmental stresses. Foxtail millet (Setaria italica) shows strong resistance to various abiotic stresses; however, current understanding of the regulation network of abiotic stress resistance in foxtail millet remains limited. In this study, we aimed to determine the autophagy-related gene SiATG8a in foxtail millet. We found that SiATG8a was mainly expressed in the stem and was induced by low-phosphorus (LP) stress. Overexpression of SiATG8a in wheat (Triticum aestivum) significantly increased the grain yield and spike number per m2 under LP treatment compared to those in the WT varieties S366 and S4056. There was no significant difference in the grain P content between SiATG8a-overexpressing wheat and WT wheat under normal phosphorus (NP) and LP treatments. However, the phosphorus (P) content in the roots, stems, and leaves of transgenic plants was significantly higher than that in WT plants under NP and LP conditions. Furthermore, the expression of P transporter genes, such as TaPHR1, TaPHR3, TaIPS1, and TaPT9, in SiATG8a-transgenic wheat was higher than that in WT under LP. Collectively, overexpression of SiATG8a increases the P content of roots, stems, and leaves of transgenic wheat under LP conditions by modulating the expression of P-related transporter gene, which may result in increased grain yield; thus, SiATG8a is a candidate gene for generating transgenic wheat with improved tolerance to LP stress in the field.

Low-phosphorus concentrations and important ferric hydroxide scavenging in Archean seawater.

The availability of nutrients in seawater, such as dissolved phosphorus (P), is thought to have regulated the evolution and activity of microbial life in Earth's early oceans. Marine concentrations of bioavailable phosphorus spanning the Archean Eon remain a topic of debate, with variable estimates indicating either low (0.04 to 0.13 μM P) or high (10 to 100 μM P) dissolved P in seawater. The large uncertainty on these estimates reflects in part a lack of clear proxy signals recorded in sedimentary rocks. Contrary to some recent views, we show here that iron formations (IFs) are reliable recorders of past phosphorus concentrations and preserved a primary seawater signature. Using measured P and iron (Fe) contents in Neoarchean IF from Carajás (Brazil), we demonstrate for the first time a clear partitioning coefficient relationship in the P-Fe systematics of this IF, which, in combination with experimental and Archean literature data, permits us to constrain Archean seawater to a mean value of 0.063 ± 0.05 μM dissolved phosphorus. Our data set suggests that low-phosphorus conditions prevailed throughout the first half of Earth's history, likely as the result of limited continental emergence and marine P removal by iron oxyhydroxide precipitation, supporting prior suggestions that changes in ancient marine P availability at the end of the Archean modulated marine productivity, and ultimately, the redox state of Earth's early oceans and atmosphere. Classification: Physical Sciences, Earth, Atmospheric and Planetary Sciences.

Diallel analysis of soybean (Glycine max L.) for biomass yield and root characteristics under low phosphorus soil conditions in Western Ethiopia.

Combining ability studies under low soil P conditions provides useful information on the inheritance of important traits to improve soybean for low P tolerance. The study aimed at determining the combining ability and gene actions of biomass yield and root traits in soybean under low phosphorus conditions. Nine parental genotypes and their 36 half diallel F2/F3 progenies were evaluated at two locations in Ethiopia on soils of low P availability. Highly significant (P<0.01) general combining ability (GCA) were found for all the traits and specific combining ability (SCA) for root dry weight and root fresh weight; while the SCA effects of all the rest of the traits were significant (P<0.05). The higher relative contributions of GCA over SCA revealed the preponderance of additive gene action in the inheritance of biomass yield, root dry weight, biomass dry weight, root volume, and root fresh weight with respective relative GCA:SCA contributions of (60.6, 39.4), (50.4, 49.6), (54.9, 45.1), (51.1, 48.9), and (52.1, 47.9); while the narrow-sense heritability was high (34.3%) only for biomass yield. Hardee-1 displayed significant (P<0.05) and positive GCA effects for most of the studied traits, and several crosses involving this parent showed superior performances. The traits i.e., biomass yield, biomass dry weight, root volume and root fresh weight showed highly (P<0.001) correlation with grain yield. Thus, breeding programs aiming to improve soybean for biomass yield and root traits under low-P condition can use Hardee-1 as a parent.

In-frame mutation in rice TEOSINTE BRANCHED1 (OsTB1) improves productivity under phosphorus deficiency

Tillering is an important trait in rice productivity. We introduced mutations into the coding region of rice TEOSINTE BRANCHED1 (OsTB1), which is a negative regulator of tillering, using CRISPR/Cas9. The frameshift mutants exhibited substantially enhanced tillering and produced 3.5 times more panicles than the non-mutated plants at maturity. This enhanced tillering resulted in increased spikelet number; however, grain yields did not increase due to substantially reduced filled grain rate and 1,000-grain weight. In contrast, in-frame mutations in OsTB1 had the effect of slightly increasing tiller numbers, and the in-frame mutants had 40% more panicles than non-mutated plants. The grain yield of in-frame mutants also did not increase on nutrient-rich soil; however, under phosphorus-deficient conditions, where tillering is constrained, the in-frame mutants gave a significantly higher grain yield than non-mutated plants due to higher spikelet number and maintained filled grain rate. Rice grassy tiller1 (OsGT1)/OsHox12, which is directly regulated by OsTB1 to suppress tillering, was moderately down-regulated in in-frame mutants, suggesting that OsTB1 with the in-frame mutation shows partial function of intact OsTB1 in regulating OsGT1/OsHox12. We propose that mildly enhanced tillering by in-frame mutation of OsTB1 can improve grain yield under low phosphorus conditions.

Comparative Non Participating Transcriptome Analysis Response to Low Phosphorus by CmPht1;2 in Chrysanthemum

Chrysanthemum morifolium Ramat is one of the four major cut flowers in the world. Pht1 family is focus on the uptake and transport of phosphate in plants. In our previous studies, CmPht1;2 overexpression line (Oe1) had higher phosphate contents both in roots and shoots, and its root development was significantly enhanced than wild type (WT) at low phosphorus conditions in chrysanthemum. Metabolomics analysis showed that several metabolites had a change in pyruvate metabolism and tricarboxylic acid (TCA) cycle pathway. To explore the gene difference expression and the change of metabolic pathway between CmPht1;2-Oe1 and WT, we conducted the transcriptome analysis. A total of 617,681 and 207,271 unigenes were obtained from roots and shoots, respectively. They were classified into biological process, cellular component and molecular function by Gene Ontology (GO). In addition, 450 different expression genes (DEGs) were found in the roots after 2 d treatment, and 1,787 DEGs were identified in shoots after 7 d treatment under LP condition between Oe1 and WT. From the top 20 pathways of DEGs assigned by Kyoto Encyclopedia of Genes and Genomes (KEGG), TCA cycle and pyruvate metabolism pathways mostly affected by overexpression of CmPht1;2 attracted our attention. This research will be helpful for elucidating the mechanism of effects by CmPht1;2 overexpression on growth, development and stress tolerance.

Differential Expression of Iron Deficiency Responsive Rice Genes under Low Phosphorus and Iron Toxicity Conditions and Association of OsIRO3 with Yield in Acidic Soils

With the hypothesis that iron (Fe) deficiency responsive genes may play a role in Fe toxicity conditions, we studied five such genes OsNAS1, OsNAS3, OsIRO2, OsIRO3 and OsYSL16 across six contrasting rice genotypes for expression under high Fe and low phosphorus (P) conditions, and sequence polymorphism. Genotypes Sahbhagi Dhan, Chakhao Poirieton and Shasharang were high yielders with no bronzing symptom visible under Fe toxic field conditions, and BAM350 and BAM811 were low yielders but did not show bronzing symptoms. Hydroponic screening revealed that the number of crown roots and root length can be traits for consideration for identifying Fe toxicity tolerance in rice genotypes. Fe contents in rice roots and shoots of a high-yielding genotype KMR3 showing leaf bronzing were significantly high. In response to 24 h high Fe stress, the expression levels of OsNAS3 were up-regulated in all genotypes except KMR3. In response to 48 h high Fe stress, the expression levels of OsNAS1 were 3-fold higher in tolerant Shasharang, whereas in KMR3, it was significantly down-regulated. Even in response to 7 d excess Fe stress, the transcript abundances of OsIRO2 and OsNAS3 were contrasting in genotypes Shasharang and KMR3. This suggested that the reported Fe deficiency genes had a role in Fe toxicity and that in genotype KMR3 under excess Fe stress, there was disruption of metal homeostasis. Under the 48 h low P conditions, OsIRO2 and OsYSL16 were significantly up-regulated in Fe tolerant genotype Shasharang and in low P tolerant genotype Chakhao Poirieton, respectively. In silico sequence analysis across 3 024 rice genotypes revealed polymorphism for 4 genes. Sequencing across OsIRO3 and OsNAS3 revealed nucleotide polymorphism between tolerant and susceptible genotypes for Fe toxicity. Non-synonymous single nucleotide polymorphisms and insertion/deletions (InDels) differing in tolerant and susceptible genotypes were identified. A marker targeting 25-bp InDel in OsIRO3, when run on a diverse panel of 43 rice genotypes and a biparental population, was associated with superior performance for yield under acidic lowland field conditions. This study highlights the potential of one of the vital genes involved in Fe homeostasis as a genic target for improving rice yield in acidic soils.

Soilborne bacterium Klebsiella pneumoniae promotes cluster root formation in white lupin through ethylene mediation.

Cluster roots of white lupin are induced by low phosphorus (LP) to efficiently access unavailable P, but how soilborne microbes are associated with cluster root formation (CRF) is unclear. We investigated the roles of soilborne bacteria in CRF response to LP by high-throughput sequencing and root-bacteria interactions. Cluster root number was significantly decreased in plants grown in sterilized soil compared with nonsterilized soil. Proteobacteria was enriched in CR, as shown by microbiome analysis of soil (bulk, rhizosphere, and rhizosheath) and roots (main, lateral, and CR). Large-scale gene expression level implicated ethylene mediation in CRF. Klebsiella pneumoniae (P7), a soilborne bacterium belonging to Proteobacteria, was isolated from CR. Among 11 isolated strains, P7 exhibited the highest 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity; this enzyme inhibits the biosynthesis of ethylene in plants by the cleavage of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid and promotes CRF under LP. We constructed an ACCD-deficit mutant accd in the P7 genetic background. The loss-of-function mutation failed to promote CRF under LP conditions. Also, auxin responses may be involved in K. pneumoniae-ethylene-mediated CRF. Overall, we propose that the soilborne bacterium K. pneumoniae promotes CRF of white lupin in response to LP by ethylene mediation.

Identification and validation of quantitative trait loci for chlorophyll content of flag leaf in wheat under different phosphorus treatments.

In wheat, the leaf chlorophyll content in flag leaves is closely related to the degree of phosphorus stress. Identifying major genes/loci associated with chlorophyll content in flag leaves under different phosphorus conditions is critical for breeding wheat varieties resistant to low phosphorus (P). Under normal, medium, and low phosphorus conditions, the chlorophyll content of flag leaves was investigated by a double haploid (DH) population derived from a cross between two popular wheat varieties Jinmai 47 and Jinmai 84, at different grain filling stages. Chlorophyll content of the DH population and parents decreased gradually during the S1 to the S3 stages and rapidly at the S4 stage. At the S4 stage, the chlorophyll content of the DH population under low phosphorus conditions was significantly lower than under normal phosphate conditions. Using a wheat 15K single-nucleotide polymorphism (SNP) panel, a total of 157 QTLs were found to be associated with chlorophyll content in flag leaf and were identified under three phosphorus conditions. The phenotypic variation explained (PVE) ranged from 3.07 to 31.66%. Under three different phosphorus conditions, 36, 30, and 48 QTLs for chlorophyll content were identified, respectively. Six major QTLs Qchl.saw-2B.1, Qchl.saw-3B.1, Qchl.saw-4D.1, Qchl.saw-4D.2, Qchl.saw-5A.9 and Qchl.saw-6A.4 could be detected under multiple phosphorus conditions in which Qchl.saw-4D.1, Qchl.saw-4D.2, and Qchl.saw-6A.4 were revealed to be novel major QTLs. Moreover, the closely linked SNP markers of Qchl.saw-4D.1 and Qchl.saw-4D.2 were validated as KASP markers in a DH population sharing the common parent Jinmai 84, showed extreme significance (P <0.01) in more than three environments under different phosphorus conditions, which has the potential to be utilized in molecular marker-assisted breeding for low phosphorus tolerance in wheat.

Transcription Factor IAA27 Positively Regulates P Uptake through Promoted Adventitious Root Development in Apple Plants.

Phosphate (P) deficiency severely limits the growth and production of plants. Adventitious root development plays an essential role in responding to low phosphorus stress for apple plants. However, the molecular mechanisms regulating adventitious root growth and development in response to low phosphorus stress have remained elusive. In this study, a mutation (C-T) in the coding region of the apple AUXIN/INDOLE-3-ACETIC ACID 27 (IAA27) gene was identified. MdIAA27T-overexpressing transgenic apple improved the tolerance to phosphorus deficiency, which grew longer and denser adventitious roots and presented higher phosphorous content than the control plants under low phosphorus conditions, while the overexpression of MdIAA27C displayed the opposite trend. Moreover, the heterologous overexpression of MdIAA27 in tobacco yielded the same results, supporting the aforementioned findings. In vitro and in vivo assays showed that MdIAA27 directly interacted with AUXIN RESPONSE FACTOR (ARF8), ARF26 and ARF27, which regulated Small Auxin-Up RNA 76 (MdSAUR76) and lateral organ boundaries domain 16 (MdLBD16) transcription. The mutation in IAA27 resulted in altered interaction modes, which in turn promoted the release of positive ARFs to upregulate SAUR76 and LBD16 expression in low phosphorus conditions. Altogether, our studies provide insights into how the allelic variation of IAA27 affects adventitious root development in response to low phosphorus stress.

Ectopic expression of GmNF-YA8 in Arabidopsis delays flowering via modulating the expression of gibberellic acid biosynthesis- and flowering-related genes and promotes lateral root emergence in low phosphorus conditions.

NUCLEAR FACTOR Y subunit alpha (NF-YA), together with NF-YB and NF-YC, regulates plant growth and development, as well as plant responses to biotic and abiotic stresses. Although extensive studies have examined the functions of NF-YAs in Arabidopsis thaliana, the roles of NF- YAs in Glycinme max are poorly understood. In this study, we identified a phosphorus (P) starvation-responsive NF-YA8 in soybean. The expression of GmNF-YA8 is induced by low P or low nitrogen in leaves, but not by potassium or iron starvation, respectively. GmNF-YA8 is localized in the nucleus and plasma membrane. Ectopic expression of GmNF-YA8 inhibits plant growth and delayed flowering in Arabidopsis. Exogenous application of gibberellic acid (GA) rescues the delayed flowering phenotype in Arabidopsis overexpressing GmNF-YA8 lines GmNF-YA8OE-05 and GmNF-YA8OE-20. Moreover, quantitative real time PCR (qRT-PCR) verified that overexpression of GmNF-YA8 downregulates GA20ox2 and GA3ox2 expression, but upregulates GA2ox2 and GA2ox3 that encode enzymes, which inactive bioactive GAs. Consistent with the late flowering phenotype of Arabidopsis trangenic lines that overexpress GmNF-YA8, the transcript levels of flowering-promoting genes AP1, CO, LFY, and SOC1 are reduced. In addition, overexpression of GmNF-YA8 promotes the emergence of lateral root (LR) primordium from epidermis rather than the initiation of LR in low P, and increases the LR density in low nitrogen. Our results provide insights into the roles of GmNF-YA8.

Detection of Candidate Loci and Genes Related to Phosphorus Efficiency at Maturity through a Genome-Wide Association Study in Soybean

Phosphorus (P) deficiency is one of the major factors limiting soybean production, and approximately 90% of P absorbed by plants occurs during the reproductive stage. Thus, it is important to understand the genetic mechanism underlying soybean low-P tolerance, especially in the mature period. Here, we evaluated six P-efficiency-related traits at maturity of 219 soybean accessions, namely, plant height (PH), node number of the main shoot (NN), branch number of the main shoot (BN), pod number per plant (PN), 100-seed weight (100SW), and seed yield per plant (SY), under normal-phosphorus (NP) and low-phosphorus (LP) conditions across two environments. Then, a genome-wide association study (GWAS) in conjunction with a high-density NJAU 355 K SoySNP array was performed. As a result, 27 P-efficiency-related single nucleotide polymorphisms (SNPs) were identified. Furthermore, two repeated SNPs, AX-93897192 and AX-93897200, located on chromosome 19 that were associated with both PH and NN were considered as stable SNPs associated with P deficiency, and the candidate gene GmABCG39 was identified. This work will be helpful in breeding high-P-efficiency soybean varieties.

The pho1;2a'-m1.1 allele of Phosphate1 conditions misregulation of the phosphorus starvation response in maize (Zea mays ssp. mays L.).

Plant PHO1 proteins play a central role in the translocation and sensing of inorganic phosphate. The maize ( Zea mays ssp. mays ) genome encodes two co‐orthologs of the Arabidopsis PHO1 gene, designated ZmPho1;2a and ZmPho1;2b. Here, we report the characterization of the transposon footprint allele Zmpho1;2a′‐m1.1, which we refer to hereafter as pho1;2a. The pho1;2a allele is a stable derivative formed by excision of an Activator transposable element from the ZmPho1;2a gene. The pho1;2a allele contains an 8‐bp insertion at the point of transposon excision that disrupts the reading frame and is predicted to generate a premature translational stop. We show that the pho1;2a allele is linked to a dosage‐dependent reduction in Pho1;2a transcript accumulation and a mild reduction in seedling growth. Characterization of shoot and root transcriptomes under full nutrient, low nitrogen, low phosphorus, and combined low nitrogen and low phosphorus conditions identified 1100 differentially expressed genes between wild‐type plants and plants carrying the pho1;2a mutation. Of these 1100 genes, 966 were upregulated in plants carrying pho1;2a, indicating the wild‐type PHO1;2a to predominantly impact negative gene regulation. Gene set enrichment analysis of the pho1;2a‐misregulated genes revealed associations with phytohormone signaling and the phosphate starvation response. In roots, differential expression was broadly consistent across all nutrient conditions. In leaves, differential expression was largely specific to low phosphorus and combined low nitrogen and low phosphorus conditions. Of 276 genes upregulated in the leaves of pho1;2a mutants in the low phosphorus condition, 153 were themselves induced in wild‐type plants with respect to the full nutrient condition. Our observations suggest that Pho1;2a functions in the fine‐tuning of the transcriptional response to phosphate starvation through maintenance and/or sensing of plant phosphate status.

Soil biota is decisive for overyielding in intercropping under low phosphorus conditions

Abstract Cereal/legume intercropping typically increases crop yield; however, the mechanisms through which soil microbes mediate overyielding in intercropping under different nutrient availability remain elusive. Here we examined the effect of soil biota and phosphate (P) availability on intercropping advantages in wheat Triticum aestivum/faba bean Vicia faba systems using a pot experiment consisting of soil sterilization treatment and different P supply levels. A complementary experiment on the contribution of different microbial groups was also included using the removal method. Intercropping advantage was observed only in the presence of microbes and was mainly associated with increase in wheat biomass. Overyielding effect was stronger under low‐P than high‐P conditions, and was negatively correlated with P availability and the effect of soil biota in the monoculture. The effect was likely related to the enlarged active P pools and modified microbial communities associated with the alteration of rhizosphere traits (protons and carboxylates) by the neighbouring faba bean. Similarly, simplification of soil microbes significantly increased the growth and P uptake of wheat plants while faba bean growth was less affected. Synthesis and applications. Our research provides compelling evidence that soil microbiome is important in driving intercropping overyielding by regulating interspecific interactions under nutrient‐limited conditions. These findings have important implications for crop species choice in designing and managing intercropping systems where crop functional traits, soil microbiome and nutrient management should be integrated in pursuit of sustainable agriculture.

Local and systemic responses conferring acclimation of Brassica napus roots to low phosphorus conditions.

Due to the non-uniform distribution of inorganic phosphate (Pi) in the soil, plants modify their root architecture to improve acquisition of this nutrient. In this study, a split-root system was employed to assess the nature of local and systemic signals that modulate root architecture of Brassica napus grown with non-uniform Pi availability. Lateral root (LR) growth was regulated systemically by non-uniform Pi distribution, by increasing the second-order LR (2°LR) density in compartments with high Pi supply but decreasing it in compartments with low Pi availability. Transcriptomic profiling identified groups of genes regulated, both locally and systemically, by Pi starvation. The number of systemically induced genes was greater than the number of genes locally induced, and included genes related to abscisic acid (ABA) and jasmonic acid (JA) signalling pathways, reactive oxygen species (ROS) metabolism, sucrose, and starch metabolism. Physiological studies confirmed the involvement of ABA, JA, sugars, and ROS in the systemic Pi starvation response. Our results reveal the mechanistic basis of local and systemic responses of B. napus to Pi starvation and provide new insights into the molecular and physiological basis of root plasticity.

Genome-wide association analysis discovered new loci and candidate genes associated with low-phosphorus tolerance based on shoot mineral elements concentrations in soybean.

Phosphorus (P) deficiency is one of the major limitations for soybean production. Moreover, it has been well reported P and other mineral elements function interdependently or antagonistically to control nutrients homeostasis in plants. Thus, it is urgently needed to understand the genetic mechanism of the accumulation of mineral elements in response to low-P stress. In this study, to identify single nucleotide polymorphisms (SNPs) and candidate genes controlling the accumulation of mineral elements suffering low-P stress in seedling stage of soybean plants, we measured concentrations of mineral elements, including P, Zn, Fe, Mn, Mg and Ca, in shoots of 211 soybean accessions under normal phosphorus (+P) and low phosphorus (-P) conditions in two hydroponic experiments. And genome-wide association study (GWAS) using high density NJAU 355K SoySNP array and concentrations of five of these mineral elements except P was performed. A total of 36 SNPs distributed on 13 chromosomes were identified to be significantly associated with low-P tolerance, and nine SNPs on chromosome 10 formed a SNP cluster. Meanwhile, the candidate gene GmFeB1 was found to serve as a negative regulator element involved in soybean P metabolism and the haplotype1 (Hap1) of GmFeB1 showed significantly higher shoot Fe concentration under -P condition than that of Hap2. In summary, we uncover 36 SNPs significantly associated with shoot mineral elements concentrations under different P conditions and a soybean low-P related gene GmFeB1, which will provide additional genetic information for soybean low-P tolerance and new gene resources for P-efficient soybean varieties breeding.

Antagonistic effect of copper and zinc in fertilization of spring wheat under low soil phosphorus conditions

Sound micronutrient management requires an understanding of nutrient interactions and transformation processes in soil–plant systems which can regulate bioavailability and plant uptake. A series of studies were conducted under controlled environment and field conditions to evaluate wheat response to Cu and Zn fertilization on P-deficient soils from western Canada. The grain and straw yields of wheat were reduced in two (Waskada and Tisdale) of three soils used in the controlled environment study, while yield was not affected at the Echo field site in 2016 when both Cu and Zn sulfate fertilizer were applied at 5 kg·ha–1 rates. Zinc concentration in soil and plant tissues was increased to apparent toxic levels with fertilizer addition in Waskada soils. An imbalance in tissue P:Zn concentration related to micronutrient fertilization was observed in Waskada and Tisdale soils. The availability of Cu and Zn in post-harvest soils was increased with increasing rate of these fertilizers' addition. Chemical and spectroscopic speciation using sequential extraction and X-ray absorption near edge structure, respectively, revealed that Cu and Zn were mostly speciated as carbonate phases, and complexation of these elements with carbonate and phyllosilicate minerals is likely the process controlling bioavailability in the soils.