Phosphorus and nitrogen physiology of two contrasting poplar genotypes when exposed to phosphorus and/or nitrogen starvation

Metabolism Plasticity on Account of Aspartate aminotransferase 10 Promotes Poplar Growth under Altered Nitrogen Regimes

Improving poplar productivity across a wide spectrum of nitrogen conditions is a primary objective in poplar breeding. In this research, we engineered transgenic poplars to overexpress the aspartate aminotransferase 10 (AspAT10) gene. The results showed that these transgenic plantlets significantly outperformed the wild-type control in terms of growth under both nitrogen-poor and nitrogen-rich conditions, exhibiting increased biomass, height, and root development. This improvement was linked to changes in internal nitrogen pools (including NO3-, NH4+, and total free amino acids) and sugar content. In line with the metabolic results, notable alterations in genes related to nitrogen and carbon metabolism as well as hormone signaling pathways were identified. Our findings highlight the versatile role of AspAT10 in regulating poplar's adaptation to variable nitrogen availability, attributed to the reversible nature of its catalytic reaction, which allows for the flexible reprogramming of nitrogen and carbon metabolism to align nitrogen supply with plant demand.

High concentration of phosphate treatment increased the tolerance of Robinia pseudoacacia roots to salt stress

KEY MESSAGE

High P increased the tolerance of R. pseudoacacia roots to salt stress. Salt is an important abiotic factor that restricts plant growth and development in soil. An appropriate concentration of P can increase plant tolerance to salt stress. We investigated the physiological and transcriptional regulatory effects of high P (HP) or low P (LP) on the response of R. pseudoacacia roots to salt stress. A pot experiment was carried out to grow R. pseudoacacia seedlings in vermiculite media supplemented with 0 mM, 150 mM or 300 mM NaCl under HP or LP conditions. The root dry weight and concentrations of free proline, P, ions, and phytohormones were measured, and the transcription of the genes was analyzed under NaCl stress under HP or LP conditions. The results revealed that R. pseudoacacia responds to NaCl stress by regulating the absorption and utilization of P and the levels of free proline, phytohormones and Na+, K+, Ca2+, and Mg2+ as well as changing the expression levels of key genes. Compared with those under the LP condition, the roots of the R. pseudoacacia under the HP condition presented greater P concentrations, lower JA concentrations, and more stable K+ levels when subjected to NaCl stress, which increased their tolerance to NaCl stress. Moreover, genes involved in the cell wall, root growth, root architecture regulation, biomass accumulation, stress response, osmotic regulation and ion balance maintenance were upregulated under NaCl stress under HP conditions. In addition, NaCl stress impairs N metabolism under LP conditions. Our findings provide new insights into the response of woody plants to salt stress under different P conditions and contribute to the development of scientific afforestation in saline-alkali areas.

Flavones enrich rhizosphere Pseudomonas to enhance nitrogen utilization and secondary root growth in Populus

Plant growth behavior is a function of genetic network architecture. The importance of root microbiome variation driving plant functional traits is increasingly recognized, but the genetic mechanisms governing this variation are less studied. Here, we collect roots and rhizosphere soils from nine Populus species belonging to four sections (Leuce, Aigeiros, Tacamahaca, and Turanga), generate metabolite and transcription data for roots and microbiota data for rhizospheres, and conduct comprehensive multi-omics analyses. We demonstrate that the roots of vigorous Leuce poplar enrich more Pseudomonas, compared with the poorly performing poplar. Moreover, we confirm that Pseudomonas is strongly associated with tricin and apigenin biosynthesis and identify that gene GLABRA3 (GL3) is critical for tricin secretion. The elevated tricin secretion via constitutive transcription of PopGL3 and Chalcone synthase (PopCHS4) can drive Pseudomonas colonization in the rhizosphere and further enhance poplar growth, nitrogen acquisition, and secondary root development in nitrogen-poor soil. This study reveals that plant-metabolite-microbe regulation patterns contribute to the poplar fitness and thoroughly decodes the key regulatory mechanisms of tricin, and provides insights into the interactions of the plant's key metabolites with its transcriptome and rhizosphere microbes.

Proteomic reprogramming underlying anatomical and physiological characteristics of poplar wood in acclimation to changing light and nitrogen availabilities

To explore the proteomic regulation that underlies the physiological, anatomical, and chemical characteristics of wood in acclimation to changing light and nitrogen (N), saplings of Populus × canescens were treated with control or high irradiance in combination with low, control or high N for 4 months. High irradiance led to elevated levels of starch, sucrose, glucose, and fructose, decreased concentrations of ammonium, nitrate, most amino acids and total N, wider xylem, more xylem cell layers, narrower vessel lumina, longer fiber cells, greater fiber wall thickness, and more cellulose and hemicellulose but less lignin deposition in poplar wood. Limiting N resulted in increased levels of starch and sucrose, reduced levels of glucose, fructose, ammonium, nitrate, amino acids and total N, narrower xylem, fewer xylem cell layers, reduced vessel lumen diameter, thicker fiber walls, and less cellulose and more hemicellulose and lignin accumulation, whereas high N had the opposite effects on poplar wood. Correspondingly, numerous differentially abundant proteins, which are related mainly to the metabolism of carbohydrates and amino acids, cell division and expansion, and deposition of secondary cell walls, such as sucrose synthase 6 (SUS6), cell division cycle protein 48 (CDC48) and laccases (LACs), were identified in poplar cambiums in response to changes in light intensity and N availability. These results suggest that proteomic relays play essential roles in regulating the physiological characteristics and anatomical and chemical properties of poplar wood in acclimation to changing light and N availabilities.

Genome-Wide Identification of the CAT Genes and Molecular Characterization of Their Transcriptional Responses to Various Nutrient Stresses in Allotetraploid Rapeseed

Brassica napus is an important oil crop in China and has a great demand for nitrogen nutrients. Cationic amino acid transporters (CAT) play a key role in amino acid absorption and transport in plants. However, the CATs family has not been reported in B. napus so far. In this study, genome-wide analysis identified 22 CAT members in the B. napus genome. Based on phylogenetic and synteny analysis, BnaCATs were classified into four groups (Group I-Group IV). The members in the same subgroups showed similar physiochemical characteristics and intron/exon and motif patterns. By evaluating cis-elements in the promoter regions, we identified some cis-elements related to hormones, stress and plant development. Darwin's evolutionary analysis indicated that BnaCATs might have experienced strong purifying selection pressure. The BnaCAT family may have undergone gene expansion; the chromosomal location of BnaCATs indicated that whole-genome replication or segmental replication may play a major driving role. Differential expression patterns of BnaCATs under nitrate limitation, phosphate shortage, potassium shortage, cadmium toxicity, ammonium excess and salt stress conditions indicated that they were responsive to different nutrient stresses. In summary, these findings provide a comprehensive survey of the BnaCAT family and lay a foundation for the further functional analysis of family members.

Integrated small RNA, transcriptome and physiological approaches provide insight into Taxodium hybrid 'Zhongshanshan' roots in acclimation to prolonged flooding

Although Taxodium hybrid 'Zhongshanshan' 406 (Taxodium mucronatum Tenore × Taxodium distichum; Taxodium 406) is an extremely flooding-tolerant woody plant, the physiological and molecular mechanisms underlying acclimation of its roots to long-term flooding remain largely unknown. Thus, we exposed saplings of Taxodium 406 to either non-flooding (control) or flooding for 2 months. Flooding resulted in reduced root biomass, which is in line with lower concentrations of citrate, α-ketoglutaric acid, fumaric acid, malic acid and adenosine triphosphate (ATP) in Taxodium 406 roots. Flooding led to elevated activities of pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, which is consistent with higher lactate concentration in the roots of Taxodium 406. Flooding brought about stimulated activities of superoxide dismutase and catalase and elevated reduced glutathione (GSH) concentration and GSH/oxidized glutathione, which is in agreement with reduced concentrations of O2- and H2O2 in Taxodium 406 roots. The levels of starch, soluble protein, indole-3-acetic acid, gibberellin A4 and jasmonate were decreased, whereas the concentrations of glucose, total non-structural carbohydrates, most amino acids and 1-aminocyclopropane-1-carboxylate (ACC) were improved in the roots of flooding-treated Taxodium 406. Underlying these changes in growth and physiological characteristics, 12,420 mRNAs and 42 miRNAs were significantly differentially expressed, and 886 miRNA-mRNA pairs were identified in the roots of flooding-exposed Taxodium 406. For instance, 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8) was a target of Th-miR162-3p and 1-aminocyclopropane-1-carboxylate oxidase 4 (ACO4) was a target of Th-miR166i, and the downregulation of Th-miR162-3p and Th-miR166i results in the upregulation of ACS8 and ACO4, probably bringing about higher ACC content in flooding-treated roots. Overall, these results indicate that differentially expressed mRNA and miRNAs are involved in regulating tricarboxylic acid cycle, ATP production, fermentation, and metabolism of carbohydrates, amino acids and phytohormones, as well as reactive oxygen species detoxification of Taxodium 406 roots. These processes play pivotal roles in acclimation to flooding stress. These results will improve our understanding of the molecular and physiological bases underlying woody plant flooding acclimation and provide valuable insights into breeding-flooding tolerant trees.

The mechanism of melatonin promotion on cucumber seedling growth at different nitrogen levels

The supply level of exogenous nitrogen has a very important influence on the growth and development of cucumber. Insufficient or excessive nitrogen application will lead to metabolic disorders in the body and affect the formation of yield. Therefore, it is of great scientific and practical significance to explore the corresponding mitigation measures. Melatonin (MT) is a multi-regulatory molecule with pleiotropic effects on plant growth and development. A large number of studies have shown that the appropriate amount of melatonin supplementation is beneficial to plant growth and development by promoting root development, delaying leaf senescence, and improving fruit yield. However, the study of MT function combined with a detailed physiological analysis of nitrogen (N) absorption and metabolism in cucumber plants needs further strengthening. We performed hydroponic tests at different nitrogen levels to determine the metabolic processes associated with the enhanced tolerance to nitrogen in melatonin-treated cucumber (Cucucumis sativus L.) seedlings. Cucumber seedlings were sprayed with 100 μM melatonin or water and treated with different nitrogen in the growth chamber for 7 days. Nitrogen deficiency significantly inhibited seedling growth, and this growth inhibition was partially alleviated by melatonin. The expression analysis of related carbon and nitrogen genes showed that the genes whose expression was significantly altered by melatonin were mainly related to carbon (C) and nitrogen (N) metabolism. By enzyme activity and reactive oxygen content data analysis, melatonin-treated cucumber seedlings showed relatively stable carbon and nitrogen levels compared to untreated ones. In conclusion, MT can repair the impaired growth and development situation by regulating the nitrogen assimilation capacity and the balance between oxidation and oxidative metabolism and carbon metabolism in the cucumber under different nitrogen levels.

Nutrient conditions mediate mycorrhizal effects on biomass production and cell wall chemistry in poplar

Large-scale biofuel production from lignocellulosic feedstock is limited by the financial and environmental costs associated with growing and processing lignocellulosic material and the resilience of these plants to environmental stress. Symbiotic associations with arbuscular (AM) and ectomycorrhizal (EM) fungi represent a potential strategy for expanding feedstock production while reducing nutrient inputs. Comparing AM and EM effects on wood production and chemical composition is a necessary step in developing biofuel feedstocks. Here, we assessed the productivity, biomass allocation and secondary cell wall (SCW) composition of greenhouse-grown Populus tremuloidesMichx. inoculated with either AM or EM fungi. Given the long-term goal of reducing nutrient inputs for biofuel production, we further tested the effects of nutrient availability and nitrogen:phosphorus stoichiometry on mycorrhizal responses. Associations with both AM and EM fungi increased plant biomass by 14-74% depending on the nutrient conditions but had minimal effects on SCW composition. Mycorrhizal plants, especially those inoculated with EM fungi, also allocated a greater portion of their biomass to roots, which could be beneficial in the field where plants are likely to experience both water and nutrient stress. Leaf nutrient content was weakly but positively correlated with wood production in mycorrhizal plants. Surprisingly, phosphorus played a larger role in EM plants compared with AM plants. Relative nitrogen and phosphorus availability were correlated with shifts in SCW composition. For AM associations, the benefit of increased wood biomass may be partially offset by increased lignin content, a trait that affects downstream processing of lignocellulosic tissue for biofuels. By comparing AM and EM effects on the productivity and chemical composition of lignocellulosic tissue, this work links broad functional diversity in mycorrhizal associations to key biofuel traits and highlights the importance of considering both biotic and abiotic factors when developing strategies for sustainable biofuel production.

Influence of nitrogen and phosphorus additions on parameters of photosynthesis and chlorophyll fluorescence in Cyclocarya paliurus seedlings

Cyclocarya paliurus has been traditionally used as a functional food in China. A hydroponic experiment was conducted to determine the effects of N and P additions on photosynthesis and chlorophyll fluorescence (ChlF) of C. paliurus seedlings. N and P additions significantly altered photosynthesis and ChlF in the seedlings, but responses of these parameters to the N and P concentrations varied at different developmental stages. The greatest net photosynthetic rate (P N) and actual photochemical efficiency of PSII (ФPSII) occurred in the treatment of 150.0 mg(N) L-1 and 25.0 mg(P) L-1 addition, whereas the highest maximum quantum yield of PSII (Fv/Fm) and water-use efficiency (WUE) were recorded with 150.0 mg(N) L-1 and 15.0 mg(P) L-1 on the 60th day after treatment. Significantly positive correlations of P N with leaf relative chlorophyll content, transpiration rate, WUE, Fv/Fm, and ΦPSII, as well as the ФPSII with the Fv/Fm, were found. Our results indicated that an optimal addition of N and P nutrients depends on their coupling effects on the photosynthetic capacity and PSII photochemistry.

Comparative physiological, metabolomic, and transcriptomic analyses reveal mechanisms of apple dwarfing rootstock root morphogenesis under nitrogen and/or phosphorus deficient conditions

Nitrogen (N) and phosphorus (P) are essential phytomacronutrients, and deficiencies in these two elements limit growth and yield in apple (Malus domestica Borkh.). The rootstock plays a key role in the nutrient uptake and environmental adaptation of apple. The objective of this study was to investigate the effects of N and/or P deficiency on hydroponically-grown dwarfing rootstock 'M9-T337' seedlings, particularly the roots, by performing an integrated physiological, transcriptomics-, and metabolomics-based analyses. Compared to N and P sufficiency, N and/or P deficiency inhibited aboveground growth, increased the partitioning of total N and total P in roots, enhanced the total number of tips, length, volume, and surface area of roots, and improved the root-to-shoot ratio. P and/or N deficiency inhibited NO3 - influx into roots, and H⁺ pumps played a important role in the response to P and/or N deficiency. Conjoint analysis of differentially expressed genes and differentially accumulated metabolites in roots revealed that N and/or P deficiency altered the biosynthesis of cell wall components such as cellulose, hemicellulose, lignin, and pectin. The expression of MdEXPA4 and MdEXLB1, two cell wall expansin genes, were shown to be induced by N and/or P deficiency. Overexpression of MdEXPA4 enhanced root development and improved tolerance to N and/or P deficiency in transgenic Arabidopsis thaliana plants. In addition, overexpression of MdEXLB1 in transgenic Solanum lycopersicum seedlings increased the root surface area and promoted acquisition of N and P, thereby facilitating plant growth and adaptation to N and/or P deficiency. Collectively, these results provided a reference for improving root architecture in dwarfing rootstock and furthering our understanding of integration between N and P signaling pathways.

Exploring the Potential of Heterosis to Improve Nitrogen Use Efficiency in Popcorn Plants

Nitrogen is crucial for plant growth and development, and improving nitrogen use efficiency (NUE) is a viable strategy for reducing dependence on nitrogen inputs and promoting sustainability. While the benefits of heterosis in corn are well known, the physiological mechanisms underlying this phenomenon in popcorn are less understood. We aimed to investigate the effects of heterosis on growth and physiological traits in four popcorn lines and their hybrids under two contrasting nitrogen conditions. We evaluated morpho-agronomic and physiological traits such as leaf pigments, the maximum photochemical efficiency of PSII, and leaf gas exchange. Components associated with NUE were also evaluated. N deprivation caused reductions of up to 65% in terms of plant architecture, 37% in terms of leaf pigments, and 42% in terms of photosynthesis-related traits. Heterosis had significant effects on growth traits, NUE, and foliar pigments, particularly under low soil nitrogen conditions. N-utilization efficiency was found to be the mechanism favoring superior hybrid performance for NUE. Non-additive genetic effects were predominant in controlling the studied traits, indicating that exploring heterosis is the most effective strategy for obtaining superior hybrids to promote NUE. The findings are relevant and beneficial for agro farmers seeking sustainable agricultural practices and improved crop productivity through the optimization of nitrogen utilization.

Combining GS-assisted GWAS and transcriptome analysis to mine candidate genes for nitrogen utilization efficiency in Populus cathayana

BACKGROUND

Forest trees such as poplar, shrub willow, et al. are essential natural resources for sustainable and renewable energy production, and their wood can reduce dependence on fossil fuels and reduce environmental pollution. However, the productivity of forest trees is often limited by the availability of nitrogen (N), improving nitrogen use efficiency (NUE) is an important way to address it. Currently, NUE genetic resources are scarce in forest tree research, and more genetic resources are urgently needed.

RESULTS

Here, we performed genome-wide association studies (GWAS) using the mixed linear model (MLM) to identify genetic loci regulating growth traits in Populus cathayana at two N levels, and attempted to enhance the signal strength of single nucleotide polymorphism (SNP) detection by performing genome selection (GS) assistance GWAS. The results of the two GWAS analyses identified 55 and 40 SNPs that were respectively associated with plant height (PH) and ground diameter (GD), and 92 and 69 candidate genes, including 30 overlapping genes. The prediction accuracy of the GS model (rrBLUP) for phenotype exceeds 0.9. Transcriptome analysis of 13 genotypes under two N levels showed that genes related to carbon and N metabolism, amino acid metabolism, energy metabolism, and signal transduction were differentially expressed in the xylem of P. cathayana under N treatment. Furthermore, we observed strong regional patterns in gene expression levels of P. cathayana, with significant differences between different regions. Among them, P. cathayana in Longquan region exhibited the highest response to N. Finally, through weighted gene co-expression network analysis (WGCNA), we identified a module closely related to the N metabolic process and eight hub genes.

CONCLUSIONS

Integrating the GWAS, RNA-seq and WGCNA data, we ultimately identified four key regulatory genes (PtrNAC123, PtrNAC025, Potri.002G233100, and Potri.006G236200) involved in the wood formation process, and they may affect P. cathayana growth and wood formation by regulating nitrogen metabolism. This study will provide strong evidence for N regulation mechanisms, and reliable genetic resources for growth and NUE genetic improvement in poplar.

Phosphorous fertilization alleviates shading stress by regulating leaf photosynthesis and the antioxidant system in mung bean (Vigna radiata L.)

Shading can limit photosynthesis and plant growth. Understanding how phosphorus (P) application mitigates the effects of shading stress on morphology and physiology of mung beans (Vigna radiata L.) is of great significance for the establishment of efficient planting structures and optimizing P-use management. The effects of various light environments (non-shading stress, S0; low light stress, S1; severe shading stress, S2) on the growth of two mung bean cultivars (Xilv1 and Yulv1) and the role of P application (0 kg ha^-1, P0; 90 kg ha^-1, P1; 150 kg ha^-1, P2) in such responses were investigated in a field experiment. Our results demonstrated that shading decreased the dry matter accumulation of mung bean markedly by limiting photosynthesis capacity and disrupting agronomic traits. For the leaf areas of the two cultivars, chlorophyll a+b, the net photosynthetic and electron transport rates were increased by 16.8%, 20.0%, 15.5%, and 12.5% under P1 treatment, and by 32.4%, 40.3%, 16.3% and 12.8% under P2 treatment, respectively, when compared to those for the non-fertilized plants under shading stress. These responses resulted in increased light capture and weak light utilization. Moreover, the activities of superoxide dismutase and peroxidase were enhanced by 20.9% and 43.7%, respectively; malondialdehyde and superoxide anion contents were reduced by 18.6% and 14.1%, respectively, under P application. These findings suggest that P application moderately mitigates the damage caused by shading stress and enhances tolerance by regulating mung bean growth. In addition, Xilv1 was more sensitive to P under shading stress than Yulv1.

Maize Breeding for Low Nitrogen Inputs in Agriculture: Mechanisms Underlying the Tolerance to the Abiotic Stress

Nitrogen (N) is essential for sustaining life on Earth and plays a vital role in plant growth and thus agricultural production. The excessive use of N fertilizers not only harms the economy, but also the environment. In the context of the environmental impacts caused by agriculture, global maize improvement programs aim to develop cultivars with high N-use efficiency (NUE) to reduce the use of N fertilizers. Since N is highly mobile in plants, NUE is related to numerous little-known morphophysiological and molecular mechanisms. In this review paper we present an overview of the morpho-physiological adaptations of shoot and root, molecular mechanisms involved in plant response to low nitrogen environment, and the genetic effects involved in the control of key traits for NUE. Some studies show that the efficiency of cultivars growing under low N is related to deep root architecture, more lateral roots (LR), and sparser branching of LR, resulting in lower metabolic costs. The NUE cultivars also exhibit more efficient photosynthesis, which affects plant growth under suboptimal nitrogen conditions. In this sense, obtaining superior genotypes for NUE can be achieved with the exploitation of heterosis, as non-additive effects are more important in the expression of traits associated with NUE.

Effects of Exogenous L-Asparagine on Poplar Biomass Partitioning and Root Morphology

L-Asparagine (Asn) has been regarded as one of the most economical molecules for nitrogen (N) storage and transport in plants due to its relatively high N-to-carbon (C) ratio (2:4) and stability. Although its internal function has been addressed, the biological role of exogenous Asn in plants remains elusive. In this study, different concentrations (0.5, 1, 2, or 5 mM) of Asn were added to the N-deficient hydroponic solution for poplar ‘Nanlin895’. Morphometric analyses showed that poplar height, biomass, and photosynthesis activities were significantly promoted by Asn treatment compared with the N-free control. Moreover, the amino acid content, total N and C content, and nitrate and ammonia content were dramatically altered by Asn treatment. Moreover, exogenous Asn elicited root growth inhibition, accompanied by complex changes in the transcriptional pattern of genes and activities of enzymes associated with N and C metabolism. Combined with the plant phenotype and the physiological and biochemical indexes, our data suggest that poplar is competent to take up and utilize exogenous Asn dose-dependently. It provides valuable information and insight on how different forms of N and concentrations of Asn influence poplar root and shoot growth and function, and roles of Asn engaged in protein homeostasis regulation.

The mechanism of arbuscular mycorrhizal enhancing cadmium uptake in Phragmites australis depends on the phosphorus concentration

Arbuscular mycorrhizal fungi (AMF) is a vital strategy to enhance the phytoremediation of cadmium (Cd) pollution. However, the function of AMF was influenced by phosphorus (P) concentration. To reveal the effect of AMF on the Cd accumulation of host plants under different P concentrations and how the AMF and P interact, this study comparatively analyzed the regulatory effects of AMF on the Cd response, extraction, and transportation processes of Phragmites australis (P. australis) under different P levels, and explored its physiological, biochemical and molecular biological mechanisms. The study showed that AMF could induce different growth allocation strategies in response to Cd stress. Moreover, AMF promoted plant Cd tolerance and detoxification by enhancing P uptake, Cd passivation, Cd retention in the cell wall, and functional group modulation. Under P starvation treatments, AMF promoted Cd uptake by inducing Cd to enter the iron pathway, increased the transport coefficient by 493.39%, and retained Cd in stems. However, these effects disappeared following the addition of P. Additionally, AMF up-regulated the expression of ZIP, ZIP, and NRAMP genes to promote cadmium uptake at low, medium, and high phosphorus levels, respectively. Thus, the Cd response mechanism of the AMF-P. australis symbiotic system was P dose-dependent.

Adaptive responses of carbon and nitrogen metabolisms to nitrogen-deficiency in Citrus sinensis seedlings

BACKGROUND

In China, nitrogen (N)-deficiency often occurs in Citrus orchards, which is one of the main causes of yield loss and fruit quality decline. Little information is known about the adaptive responses of Citrus carbon (C) and N metabolisms to N-deficiency. Seedlings of 'Xuegan' (Citrus sinensis (L.) Osbeck) were supplied with nutrient solution at an N concentration of 0 (N-deficiency), 5, 10, 15 or 20 mM for 10 weeks. Thereafter, we examined the effects of N supply on the levels of C and N in roots, stems and leaves, and the levels of organic acids, nonstructural carbohydrates, NH₄⁺-N, NO₃^--N, total soluble proteins, free amino acids (FAAs) and derivatives (FAADs), and the activities of key enzymes related to N assimilation and organic acid metabolism in roots and leaves.

RESULTS

N-deficiency elevated sucrose export from leaves to roots, C and N distributions in roots and C/N ratio in roots, stems and leaves, thus enhancing root dry weight/shoot dry weight ratio and N use efficiency. N-deficient leaves displayed decreased accumulation of starch and total nonstructural carbohydrates (TNC) and increased sucrose/starch ratio as well as a partitioning trend of assimilated C toward to sucrose, but N-deficient roots displayed elevated accumulation of starch and TNC and reduced sucrose/starch ratio as well as a partitioning trend of assimilated C toward to starch. N-deficiency reduced the concentrations of most FAADs and the ratios of total FAADs (TFAADs)/N in leaves and roots. N-deficiency reduced the demand for C skeleton precursors for amino acid biosynthesis, thus lowering TFAADs/C ratio in leaves and roots. N-deficiency increased (decreased) the relative amounts of C-rich (N-rich) FAADs, thus increasing the molar ratio of C/N in TFAADs in leaves and roots.

CONCLUSIONS

Our findings corroborated our hypothesis that C and N metabolisms displayed adaptive responses to N-deficiency in C. sinensis seedlings, and that some differences existed between roots and leaves in N-deficiency-induced alterations of and C and N metabolisms.

Multi-omics analysis of xylem sap uncovers dynamic modulation of poplar defenses by ammonium and nitrate

Xylem sap is the major transport route for nutrients from roots to shoots. In the present study, we investigated how variations in nitrogen (N) nutrition affected the metabolome and proteome of xylem sap and the growth of the xylem endophyte Brennaria salicis, and we also report transcriptional re-wiring of leaf defenses in poplar (Populus × canescens). We supplied poplars with high, intermediate or low concentrations of ammonium or nitrate. We identified 288 unique proteins in xylem sap. Approximately 85% of the xylem sap proteins were shared among ammonium- and nitrate-supplied plants. The number of proteins increased with increasing N supply but the major functional categories (catabolic processes, cell wall-related enzymes, defense) were unaffected. Ammonium nutrition caused higher abundances of amino acids and carbohydrates, whereas nitrate caused higher malate levels in xylem sap. Pipecolic acid and N-hydroxy-pipecolic acid increased, whereas salicylic acid and jasmonoyl-isoleucine decreased, with increasing N nutrition. Untargeted metabolome analyses revealed 2179 features in xylem sap, of which 863 were differentially affected by N treatments. We identified 124 metabolites, mainly from specialized metabolism of the groups of salicinoids, phenylpropanoids, phenolics, flavonoids, and benzoates. Their abundances increased with decreasing N, except coumarins. Brennaria salicis growth was reduced in nutrient-supplemented xylem sap of low- and high- NO₃^- -fed plants compared to that of NH₄⁺ -fed plants. The drastic changes in xylem sap composition caused massive changes in the transcriptional landscape of leaves and recruited defenses related to systemic acquired and induced systemic resistance. Our study uncovers unexpected complexity and variability of xylem composition with consequences for plant defenses.

Cultivar sensitivity of broomcorn millet (Panicum miliaceum L.) to nitrogen availability is associated with differences in photosynthetic physiology and nitrogen uptake

In order to explore the influences of low nitrogen (N) fertilizer on the growth performances of two broomcorn millet (Panicum miliaceum L.) cultivars with different N tolerances, the field experiment was carried out with a low-N-tolerant cultivar (BM 184) and a low-N-sensitive cultivar (BM 230) under three N levels (0, 75 and 150 kg N ha^-1) in the Loess Plateau, China. 150 kg N ha^-1 was conventional N application rate and considered as the control. Compared to typical N supply, low N fertilizer significantly weakened the photosynthetic capacity by increasing the light transmission ratio and decreasing leaf area index, resulting in reduced biomass accumulation. BM 184 held the longer duration of the biomass increase phase and larger relative growth rate than BM 230 as well as higher photosynthetic parameters (i.e., relative chlorophyll content, net photosynthetic rate, and transpiration rate) did under low N treatments. Such optimized physiological characteristics contributed to more effective N uptake and transportation from the stems, leaves, and sheaths to grains in the BM 184. Furthermore, compared with BM 230, BM 184 had higher rhizosphere soil fertility and soil enzyme activity under low N conditions; consequently, combined with the physiological characteristics for aboveground and soil nutrient status for belowground, higher productivity was obtained in BM 184 than that in BM 230 over the two years study. Overall, our results demonstrated that low-N-tolerant cultivar achieved reduced N fertilizer input with increased efficiency by optimizing growth performances in semi-arid cultivation areas.

FTIR-ATR based fingerprinting and chemometrics analysis of metabolites profile of Phyllanthus niruri L. affected by fertilization with NPK-chitosan nanopolymer and harvesting age

Introduction: Phyllanthus niruri L. (PnL) is a herbaceous plant containing flavonoid quercetin and can be used as an immunomodulator to prevent Covid-19. However, the flavonoid content and yield of herbs extract were not maximized. Therefore, PnL herbs were planted in various harvest periods and application of NPK-chitosan nanopolymer fertilizer to estimate these parameters.

Objectives: Determine the effect of NPK-chitosan nanopolymer fertilizer and harvesting age on herb extracts also determine the grouping pattern and correlation between responses based on FTIR-ATR spectral pattern using a chemometric approach.

Methods: Each group consisted of 50 plants. The formulation of NPK-chitosan nanopolymer fertilizer based on the dose of NPK consisting of the first dose is 15.5 grams/group, the second dose is 31 grams/group, and the third dose is 7.5 grams/group. Grouping of differences in harvesting age for plants consisted of 4, 6, and 8 weeks after the plant (WAP). Extraction used ultrasound-assisted extraction, and data were analyzed using a chemometric approach.

Results: Extract with the highest yield was found in second harvest time and third doses of fertilizer (W2D3) which is 9.73 %, and the highest TFC obtained in an extract with second harvest time and first doses of fertilizer (W2D1) is 17.34 mg QE/g. Total flavonoid content and extract yield were influenced by functional groups at wavenumbers 3486.77–3157.12 cm−1 (1); 1740.96–1670.34 cm-1 (3); 1425.02–1272.62 cm-1 (5); 1257,753–1138,81 cm−1 (6); 1131.38–945.53 cm-1 (7); 711.36–529.23 cm-1 (8).

Conclusions: The results showed that harvest time and fertilizer dose affected the growth parameters of PnL, total flavonoid content, and yield of extract. Functional groups in IR spectra also have positive and negative correlations with total flavonoid and yield extract responses.

Physiological Characteristics and Transcriptomic Dissection in Two Root Segments with Contrasting Net Fluxes of Ammonium and Nitrate of Poplar Under Low Nitrogen Availability

To investigate physiological and transcriptomic regulation mechanisms underlying the distinct net fluxes of NH4+ and NO3- in different root segments of Populus species under low nitrogen (N) conditions, we used saplings of Populus × canescens supplied with either 500 (normal N) or 50 (low N) μM NH4NO3. The net fluxes of NH4+ and NO3-, the concentrations of NH4+, amino acids and organic acids and the enzymatic activities of nitrite reductase (NiR) and glutamine synthetase (GS) in root segment II (SII, 35-70 mm to the apex) were lower than those in root segment I (SI, 0-35 mm to the apex). The net NH4+ influxes and the concentrations of organic acids were elevated, whereas the concentrations of NH4+ and NO3- and the activities of NiR and GS were reduced in SI and SII in response to low N. A number of genes were significantly differentially expressed in SII vs SI and in both segments grown under low vs normal N conditions, and these genes were mainly involved in the transport of NH4+ and NO3-, N metabolism and adenosine triphosphate synthesis. Moreover, the hub gene coexpression networks were dissected and correlated with N physiological processes in SI and SII under normal and low N conditions. These results suggest that the hub gene coexpression networks play pivotal roles in regulating N uptake and assimilation, amino acid metabolism and the levels of organic acids from the tricarboxylic acid cycle in the two root segments of poplars in acclimation to low N availability.

Experimental Approach Alters N and P Addition Effects on Leaf Traits and Growth Rate of Subtropical Schima superba (Reinw. ex Blume) Seedlings

Nitrogen (N) and/or phosphorus (P) addition has controversial effects on tree functional traits and growth; however, this experimental approach may clarify these controversial results. In this study, field and pot experiments were designed with +N (100 kg N ha−1 yr−1), +P (50 kg P ha−1 yr−1), +NP (100 kg N plus 50 kg P ha−1 yr−1), and a control (no N or P addition) to comparatively investigate the effects of N and P addition on 24 leaf traits and the growth rate of Schima superba (Reinw. ex Blume ) seedlings in subtropical China. We found that the experimental approach alters N and P addition effects on leaf traits and tree growth. Nitrogen addition strongly altered leaf biochemical and physiological traits and limited tree growth compared to P addition in the pot experiment, while the effects of N and P addition on leaf traits and tree growth were weaker in the field, since the seedlings might be mainly limited by light availability rather than nutrient supplies. The inference from the pot experiment might amplify the impact of N deposition on forest plants in complicated natural systems. These findings will help guide refining pot fertilization experiments to simulate trees in the field under environmental change. Future directions should consider reducing the confounding effects of biotic and abiotic factors on fertilization in the field, and refinement of the control seedlings’ genetic diversity, mycorrhizal symbiont, and root competition for long-term fertilization experiments are required.

Physiological and proteomic analyses reveal the effects of exogenous nitrogen in diminishing Cd detoxification in Acacia auriculiformis

Cadmium (Cd) has toxic effects on plants. Nitrogen (N), an essential element, is critical for plant growth, development and stress response. However, their combined effects on woody plants, especially in N-fixing tree species is still poorly understood. Our previous study revealed that the fast-growing Acacia auriculiformis showed strong Cd tolerance but the underlying mechanisms was not clear, which constrained its use in mine land reclamation. Herein, we investigated the physiological and proteomic changes in A. auriculiformis leaves to reveal the mechanisms of Cd tolerance and toxicity without N fertilizer (treatment Cd) and with excess N fertilizer (treatment CdN). Results showed that Cd tolerance in A. auriculiformis was closely associated with the coordinated gas exchange and antioxidant defense reactions under Cd treatment alone. Exogenous excessive N, however, inhibited plant growth, increased Cd concentrations, and weaken photosynthetic performance, thus, aggregated the toxicity under Cd stress. Furthermore, the aggregated Cd toxicity was attributed to the depression in the abundance of proteins, as well as their corresponding genes, involved in photosynthesis, energy metabolism (oxidative phosphorylation, carbon metabolism, etc.), defense and stress response (antioxidants, flavonoids, etc.), plant hormone signal transduction (MAPK, STN, etc.), and ABC transporters. Collectively, this study unveils a previously unknown physiological and proteomic network that explains N diminishes Cd detoxification in A. auriculiformis. It may be counterproductive to apply N fertilizer to fast-growing, N-fixing trees planted for phytoremediation of Cd-contaminated soils.

Comparing the Effects of N and P Deficiency on Physiology and Growth for Fast- and Slow-Growing Provenances of Fraxinus mandshurica

With the continuous increase in atmospheric carbon dioxide emissions, nitrogen (N) and phosphorus (P) as mineral elements increasingly restrict plant growth. To explore the effect of deficiency of P and N on growth and physiology, Fraxinus mandshurica (hereafter “F. mandshurica”) Rupr. annual seedlings of Wuchang (WC) provenance with fast growth and Dailing (DL) provenance with slow growth were treated with complete nutrition or starvation of N (N-), P (P-) or both elements (NP-). Although P- and N- increased the use efficiency of P (PUE) and N (NUE), respectively, they reduced the leaf area, chlorophyll content and activities of N assimilation enzymes (NR, GS, GOGAT), which decreased the dry weight and P or N amount. The free amino acid content and activities of Phosphoenolpyruvate carboxylase (PEPC) and acid phosphatase enzymes were reduced by N-. The transcript levels of NRT2.1, NRT2.4, NRT2.5, NRT2.7, AVT1, AAP3, NIA2, PHT1-3, PHT1-4 and PHT2-1 in roots were increased, but those of NRT2.1, NRT2.4, NRT2.5, PHT1-3, PHT1-4, PHT2-1 and AAP3 in leaves were reduced by P-. WC was significantly greater than DL under P- in dry weight, C amount, N amount, leaf area, PUE, NUE, which related to greater chlorophyll content, PEPC enzyme activity, N assimilation enzyme activities, and transcript levels of N and P transporter genes in roots and foliage, indicating a greater ability of WC to absorb, transport and utilize N and P under P-. WC was also greater than DL under N- in terms of the above indicators except the transcript levels of N and P assimilation genes, but most of the indicators did not reach a significant level, indicating that WC might be more tolerant to N- than DL, which requires further verification. In summary, WC was identified as a P-efficient provenance, as the growth rate was greater for the genetic type with high than low tolerance to P-.

Nitrogen fertilization stimulates nitrogen assimilation and modifies nitrogen partitioning in the spring shoot leaves of citrus (Citrus reticulata Blanco) trees

The spring shoot leaves are important sites of nitrogen (N) metabolism in citrus trees. Understanding the physiological and metabolic response of the spring shoot leaves under varying N fertilization is fundamental to the fertilization management in citrus orchards. Thus, the processes affecting N composition, the activities of N metabolism related enzymes, and the expression of relevant genes were explored in spring shoot leaves under four N levels (0, 207, 275, 413 g N tree^-1 y^-1, as N0, N207, N275, N413). The results showed that, compared with N0, N275 significantly increased total N by 24.81%, which was mainly attributed to enhancement of structural N by 30.92%, free amino acid N by 40.91% and nitrate N by 41.33%. The relative expression of nitrate reductase (NR) and glutamate dehydrogenase (GDH) under N275 increased by 19.32% and 73.48%, respectively, compared with that under N0 treatment. Compared with N0 treatment, the NR transcription level under N275 treatment increased by 381%. The relative transcription levels of NADP-GDH and GDH1 also increased with increasing N fertilization. However, compared with that under N275, the relative transcription of GDH2 under N413 treatment was inhibited. Therefore, the transcript abundance of NR, NADP-GDH,GDH1 and GDH2 affected the activities of NR and GDH and thereby contributed to the regulation of N composition in the leaves. In addition, the activities of glutamine synthetase and nitrite reductase were largely unaffected or even declined in the N207, N275 and N413 treatments compared with the N0. This study elucidated the mechanism of primary N metabolism and partitioning in citrus leaves and provided a theoretical basis for N management in citrus orchards.

Genomic identification of nitrogen assimilation-related genes and transcriptional characterization of their responses to nitrogen in allotetraploid rapeseed

BACKGROUND

Nitrogen (N) is an essential macronutrient to maintain plant growth and development. Plants absorb nitrate-N or ammonium-N in the environment and undergo reduction reactions catalyzed by nitrate reductase (NR), nitrite reductase (NIR), glutamine synthetase (GS), and glutamine oxoglutarate aminotransferase (GOGAT) within plants.

METHODS AND RESULTS

A total of 42 N assimilation-related genes (NAG) members were identified in rapeseed. Darwin's evolutionary pressure analysis showed that rapeseed NAGs underwent purification selection. Cis-element analysis revealed differences in the transcriptional regulation of NAGs between Arabidopsis and rapeseed. Expression analyses revealed that NRs were expressed mainly in old leaves, NIRs were expressed mainly in old leaves and lower stem peels, while the expression situation between different subfamilies of GSs and GOGATs was more complicated.

CONCLUSIONS

Differential expression of NAGs suggested that they might be involved in abiotic stresses. The above results greatly enriched our understanding of NAGs' molecular characteristics and provided central gene resources for NAGs-mediated NUE improvement in rapeseed.

Phylogeny, tissue-specific expression, and activities of root-secreted purple acid phosphatases for P uptake from ATP in P starved poplar

Plants secrete purple acid phosphatases (PAPs) under phosphorus (P) shortage but the contribution of plant PAPs to P acquisition is not well understood. The goals of this study were to investigate comprehensively the transcription patterns of PAPs under P shortage in poplar (Populus × canescens), to identify secreted PAPs and to characterize their contribution to mobilize organic P. Phylogenetic analyses of the PAP family revealed 33 putative members. In this study, distinct, tissue-specific P responsive expression patterns could be shown for 23 PAPs in roots and leaves. Root-associated PAP activities were localized on the root surface by in-vivo staining. The activities of root-surface PAPs increased significantly under low P availability, but were suppressed by a PAP inhibitor and corresponded to elevated P uptake from ATP as an organic P source. By proteomic analyses of the root apoplast, we identified three newly secreted proteins under P shortage: PtPAP1 (Potri.005G233400) and two proteins with unknown functions (Potri.013G100800 and Potri.001G209300). Our results, based on the combination of transcriptome and proteome analyses with phosphatase activity assays, support that PtPAP1 plays a central role in enhanced P acquisition from organic sources, when the phosphate concentrations in soil are limited.

Identification of a phosphorus-solubilizing Tsukamurella tyrosinosolvens strain and its effect on the bacterial diversity of the rhizosphere soil of peanuts growth-promoting

Phosphate solubilizing microorganisms widely exist in plant rhizosphere soil, but report about the P solubilization and multiple growth-promoting properties of rare actinomycetes are scarce. In this paper, a phosphate solubilizing Tsukamurella tyrosinosolvens P9 strain was isolated from the rhizosphere soil of tea plants. Phosphorus-dissolving abilities of this strain were different under different carbon and nitrogen sources, the soluble phosphorus content was 442.41 mg/L with glucose and potassium nitrate as nutrient sources. The secretion of various organic acids, such as lactic acid, maleic acid, oxalic acid, etc., was the main mechanism for P solubilization and pH value in culture was very significant negative correlation with soluble P content. In addition, this strain had multiple growth-promoting characteristics with 37.26 μg/mL of IAA and 72.01% of siderophore relative content. Under pot experiments, P9 strain improved obviously the growth of peanut seedlings. The bacterial communities of peanut rhizoshpere soil were assessed after inoculated with P9 strain. It showed that there was no significant difference in alpha-diversity indices between the inoculation and control groups, but the P9 treatment group changed the composition of bacterial communities, which increased the relative abundance of beneficial and functional microbes, which relative abundances of Chitinophagaceae at the family level, and of Flavihumibacter, Ramlibacter and Microvirga at the genus level, were all siginificant increased. Specially, Tsukamurella tyrosinosolvens were only detected in the rhizosphere of the inoculated group. This study not only founded growth-promoting properties of T. tyrosinosolvens P9 strain and its possible phosphate solublizing mechanism, but also expected to afford an excellent strain resource in biological fertilizers.

Wood properties and transcriptional responses of poplar hybrids in mixed cropping with the nitrogen-fixing species Robinia pseudoacacia

Cultivation of fast-growing tree species is often confined to marginal land. Mixed cropping with Robinia pseudoacacia, a legume tree species that forms a symbiosis with N2-fixing bacteria, has been proposed to be a measure to improve soil fertility and to achieve beneficial effects on the cocultivated tree species. The goal of our study was to examine the influence of a Robinia mixture on wood chemistry, anatomy and gene expression in poplar. We hypothesized that annual wood growth is stimulated in species mixtures due to the positive effects of Robinia on nitrogen availability and complementary resource use. Alternatively, we hypothesized that competition, especially for water, has negative effects on the wood growth of poplar. We used two commercial biomass clones, Hybride 275 (H275, Populus trichocarpa × Populus maximowiczii) and Max1 (Populus nigra × P. maximowiczii), which were planted at two locations with contrasting soil fertility in monoculture or mixed plots with Robinia to investigate the annual wood increment, wood nitrogen and δ13C, wood anatomy (length, cell wall thickness, lumina and frequencies of fibers and vessels) and transcriptional profiles in the developing xylem of 4-year-old stems. In a mixture with Robinia, the annual stem increment was reduced, nitrogen in wood was enhanced, δ13C in wood was decreased, vessel and fiber frequencies were increased and fiber lengths and fiber lumina were decreased. Transcriptional profiles showed stronger differences between the genotypes and sites than between mono and mixed cultivation. The transcriptional abundances of only one gene (the putative nitrate transporter, NRT1.2) and one gene ontology term ('immune system process') were significantly enriched in wood-forming tissues in response to the mixture, irrespective of the poplar genotype and growth location. Weighted gene coexpression network analyses extracted gene modules that linked wood nitrogen mainly to vessel traits and wood δ13C with fiber traits. Collectively, molecular and anatomical changes in poplar wood suggest beneficial effects on the water and N supply in response to the mixture with Robinia. These alterations may render poplars less drought-susceptible. However, these benefits are accompanied by a reduced wood increment, emphasizing that other critical factors, presumably light competition or allelopathic effects, overrule a potential growth stimulation.

New Functions of Ceriporia lacerata HG2011: Mobilization of Soil Nitrogen and Phosphorus and Enhancement of Yield and Quality of Ketchup-Processing Tomato

The overuse of chemical nitrogen (N) and phosphorus (P) fertilizers in tomato cultivation is common for high fruit yields to meet the ever-increasing industrial needs, resulting in poor fruit quality, fertilizer waste, and environmental pollution. Nutrient-mobilizing microbes increase soil nutrient supply and decrease fertilizer use without yield sacrifices. Thus, the influence of a new white-rot fungus Ceriporia lacerata HG2011 was studied on soil N and P mobilization in lab and ketchup tomato performances in field. Compared with noninoculation, soil pH decreased, while ammonia (NH₄⁺-N), available P, microbial biomass N and P, and activities of protease and phosphatase in the inoculated soil increased as the fungus grew on and in the sterile soil. Protease activity was positively correlated with NH₄⁺-N and phosphatase activity was with water-soluble P and Olsen P in the sterile soil. Soil pH showed an inverse correlation with available P. In the field experiment, the treatments included a blank control, C. lacerata, chemical fertilizers, and chemical fertilizers plus C. lacerata. Fungal inoculation enhanced the available N and P and the activities of protease and phosphatase in both fertilized and unfertilized soils, leading to the increment of plant nutrient uptake. Fungal application increased the fruit yield by 18.18-20.16%, soluble solids by 3.17-6.30%, soluble sugar by 10.67-43.33%, sugar-acid ratio 20.19-52.91%, and vitamin C by 8.83-34.90%. Therefore, our results first demonstrated the new functions of C. lacerata HG2011 in the mobilization of soil N and P and the improvement of plant nutrient uptake, yield, and quality, showing a potential use as biofertilizers in ketchup-processing tomato cultivation.

Carbohydrate depletion in roots impedes phosphorus nutrition in young forest trees

Nutrient imbalances cause the deterioration of tree health in European forests, but the underlying physiological mechanisms are unknown. Here, we investigated the consequences of decreasing root carbohydrate reserves for phosphorus (P) mobilisation and uptake by forest trees. In P-rich and P-poor beech (Fagus sylvatica) forests, naturally grown, young trees were girdled and used to determine root, ectomycorrhizal and microbial activities related to P mobilisation in the organic layer and mineral topsoil in comparison with those in nongirdled trees. After girdling, root carbohydrate reserves decreased. Root phosphoenolpyruvate carboxylase activities linking carbon and P metabolism increased. Root and ectomycorrhizal phosphatase activities and the abundances of bacterial genes catalysing major steps in P turnover increased, but soil enzymes involved in P mobilisation were unaffected. The physiological responses to girdling were stronger in P-poor than in P-rich forests. P uptake was decreased after girdling. The soluble and total P concentrations in roots were stable, but fine root biomass declined after girdling. Our results support that carbohydrate depletion results in reduced P uptake, enhanced internal P remobilisation and root biomass trade-off to compensate for the P shortage. As reductions in root biomass render trees more susceptible to drought, our results link tree deterioration with disturbances in the P supply as a consequence of decreased belowground carbohydrate allocation.

Metabolome adjustments in ectomycorrhizal Populus × canescens associated with strong promotion of plant growth by Paxillus involutus despite a very low root colonization rate

It is believed that resource exchange, which is responsible for intensified growth of ectomycorrhizal plants, occurs in the fungus-plant interface. However, increasing evidence indicates that such intensified plant growth, especially root growth promotion, may be independent of root colonization. Nevertheless, the molecular adjustments in low-colonized plants remain poorly understood. Here, we analysed the metabolome of Populus × canescens microcuttings characterized by significantly increased growth triggered by inoculation with Paxillus involutus, which successfully colonized only 2.1 ± 0.3% of root tips. High-throughput metabolomic analyses of leaves, stems and roots of Populus × canescens microcuttings supplemented with leaf proteome data were performed to determine ectomycorrhiza-triggered changes in N-, P- and C-compounds. The molecular adjustments were relatively low in low-colonized (M) plants. Nevertheless, the levels of foliar phenolic compounds were significantly increased in M plants. Increases of total soluble carbohydrates, starch as well as P concentrations were also observed in M leaves along with the increased abundance of the majority of glycerophosphocholines detected in M roots. However, compared with the leaves of the non-inoculated controls, M leaves presented lower concentrations of both N and most photosynthesis-related proteins and all individual mono- and disaccharides. In M stems, only a few compounds with different abundances were detected, including a decrease in carbohydrates, which was also detected in M roots. Thus, these results suggest that the growth improvement of low-colonized poplar trees is independent of an increased photosynthesis rate, massively increased resource (C:N) exchange and delivery of most nutrients to leaves. The mechanism responsible for poplar growth promotion remains unknown but may be related to increased P uptake, subtle leaf pigment changes, the abundance of certain photosynthetic proteins, slight increases in stem and root amino acid levels and the increase in flavonoids (increasing the antioxidant capacity in poplar), all of which improve the fitness of low-colonized poplars.

Exogenous GABA promotes adaptation and growth by altering the carbon and nitrogen metabolic flux in poplar seedlings under low nitrogen conditions

Nitrogen (N) deficiency adversely affects tree growth. Additionally, γ-aminobutyric acid (GABA) is closely associated with growth and stress responses because of its effects on carbon (C) and N metabolism. However, little is known about its roles related to plant adaptations to N-deficient conditions. In this study, we analyzed the effects of GABA (0, 2 and 10 mM) applications on the growth traits and physiological responses of poplar (Populus alba × P. glandulosa '84K') seedlings under high N (HN) and low N (LN) conditions. We found that the added GABA interacted with N to affect more than half of the studied parameters, with greater effects in LN plants than in HN plants. Under LN conditions, the GABA application tended to increase poplar growth, accompanied by increased xylem fiber cell length and xylem width. In stems, exogenous GABA increased the abundance of non-structural carbohydrates (starch and sugars) and tricarboxylic acid cycle intermediates (succinate, malate and citrate), but had the opposite effect on the structural C contents (hemicellulose and lignin). Meanwhile, exogenous GABA increased the total soluble protein contents in leaves and stems, accompanied by significant increases in nitrate reductase, nitrite reductase and glutamine synthetase activities in leaves, but significant decreases in those (except for the increased glutamate synthetase activity) in stems. A multiple factorial analysis indicated that the nitrate assimilation pathway substantially influences poplar survival and growth in the presence of GABA under LN conditions. Interestingly, GABA applications also considerably attenuated the LN-induced increase in the activities of leaf antioxidant enzymes, including peroxidase and catalase, implying that GABA may regulate the relative allocation of C and N for growth activities by decreasing the energy cost associated with stress defense. Our results suggest that GABA enhances poplar growth and adaptation by regulating the C and N metabolic flux under N-deficient conditions.

Phosphorus deficiency induces root proliferation and Cd absorption but inhibits Cd tolerance and Cd translocation in roots of Populus × euramericana

To disclose how phosphorus deficiency influence phytoremediation of Cd contamination using poplars, root architecture, Cd absorption, Cd translocation and antioxidant defense in poplar roots were investigated using a clone of Populus × euramericana. Root growth was unaltered by Cd exposure regardless of P conditions, while the degree of root proliferation upon P deficiency was changed by high level of Cd exposure. The concentration and content of Cd accumulation in roots were increased by P deficiency. This can be partially explained by the increased expression of genes encoding PM H + -ATPase under the combined conditions of P deficiency and high Cd exposure, which enhanced Cd²⁺-H⁺ exchanges and led to an increment of Cd uptake under P deficiency. Despite of the increasing Cd accumulation in roots, the translocation of Cd from roots to aerial tissues sharply decreased upon P deficiency. The relative expression of genes responsible for Cd translocation (HMA4) decreased upon P deficiency and thus inhibited Cd translocation via xylem. GR activity was decreased by P deficiency, which can inhibit the form of GSH and GSH-Cd complexes and decrease Cd translocation via GSH-Cd complexes. The transportation of PC-Cd complexes into vacuole decreased under P deficiency as a result of the low expression of PCS and ABCC1, and thus suppressed Cd tolerance and Cd detoxification in roots. Moreover, P deficiency decreased the levels of antioxidase (GR and CAT) and phytohormones including JA, ABA and GA₃, which synchronously reduced antioxidant capacity in roots.

Nitrogen and Phosphorus interactions in plants: from agronomic to physiological and molecular insights

Nitrogen (N) and Phosphorus (P) are the two most essential nutrients ensuring food production and security. The ever growing population demands more N and P-based fertilizers. Even though the N provision to the agricultural system is virtually infinite (Haber and Bosch process) it triggers pollution when it is not used by the plant and leaks into the environment. On the other hand, P is predicted to be a limited source worldwide. P use is also responsible for water eutrophication. Thus understanding plant response to combinations of N and P has clear implications for sustainable human development. Recent works have shed new light on how N and P closely interact to control plant responses. Several molecular actors have been revealed controlling the molecular interaction between these two essential elements drafting a working model of N and P interactions. We summarize here these new findings as well as several previous lines of evidence in agronomy and physiology studies preceding this new trend of investigation in the molecular world.

Mineral nutrient homeostasis, photosynthetic performance, and modulations of antioxidative defense components in two contrasting genotypes of Arachis hypogaea L. (peanut) for mitigation of nitrogen and/or phosphorus starvation

Arachis hypogaea L. (peanut) is a major oil yielding crop and its productivity is largely affected by the availability of nitrogen and phosphorus. The present study aims to elucidate the differential physiological and biochemical mechanisms involved in two contrasting genotypes of peanut for mitigation of N and/or P deficiency. The plants of two contrasting genotypes of peanut (GG7 and TG26) were subjected to N and/or P deficiency under hydroponic culture condition. After 15 d of N and/or P deficiency, various growth parameters, mineral nutrient status, nutrient use efficiency, photosynthesis, transpiration, water use efficiency, chlorophyll fluorescence, ROS level, and changes in enzymatic and non-enzymatic antioxidative components were measured in control and nutrient deficient plants. Our results showed that GG7 is fast-growing genotype than TG26 under control condition, whereas under N and/or P deficiency growth performance of GG7 was significantly declined as compared to TG26. The levels of photosynthetic pigments, net photosynthesis activity (P_N), and stomatal conductance (g_s) declined in N and/or P deficient plants of both the genotypes. However, quantum efficiency of photosystem II (Fv/Fm) did not change significantly under N and/or P starvation in both the genotypes. In the present investigation, most of the antioxidative enzymes either remained in steady state or downregulated in both the genotypes of peanut under N and/or P deficiency condition. N and/or P deficiency did not influence the levels of ROS and oxidative stress indicators such as O₂^·-, H₂O₂, and MDA in both the genotypes. In the present investigation, the decline in growth in both the genotypes under N and/or P deficiency might be due to the reduced photosynthetic performance. Our results suggest that TG26 is more resistant to N and P deficiency than GG7 genotype. Higher NUE value of GG7 as compared to TG26 suggests that GG7 can utilize N more efficiently to promote biomass production than TG26 under sufficient nutrient condition. On the other hand, mineral resource allocation to leaf and higher PUE are key adaptive features of the TG26 genotype under N, and P deficiency conditions. The differential regulations of various enzymatic and non-enzymatic antioxidative components in peanut genotypes maintain the cellular redox homeostasis under mineral deficiency conditions and prevent the peanut plants from oxidative stress, thereby maintaining PSII efficiency. The information from the present study can be useful for the improvement of traits in peanut that can maintain the productivity under N and P deficient environment with minimum input of fertilizers.

In Vivo Metabolic Regulation of Alternative Oxidase under Nutrient Deficiency-Interaction with Arbuscular Mycorrhizal Fungi and Rhizobium Bacteria

The interaction of the alternative oxidase (AOX) pathway with nutrient metabolism is important for understanding how respiration modulates ATP synthesis and carbon economy in plants under nutrient deficiency. Although AOX activity reduces the energy yield of respiration, this enzymatic activity is upregulated under stress conditions to maintain the functioning of primary metabolism. The in vivo metabolic regulation of AOX activity by phosphorus (P) and nitrogen (N) and during plant symbioses with Arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria is still not fully understood. We highlight several findings and open questions concerning the in vivo regulation of AOX activity and its impact on plant metabolism during P deficiency and symbiosis with AMF. We also highlight the need for the identification of which metabolic regulatory factors of AOX activity are related to N availability and nitrogen-fixing legume-rhizobia symbiosis in order to improve our understanding of N assimilation and biological nitrogen fixation.

Distinct physiological and transcriptional responses of leaves of paper mulberry (Broussonetia kazinoki × B. papyrifera) under different nitrogen supply levels

Paper mulberry, a vigorous pioneer species used for ecological reclamation and a high-protein forage plant for economic development, has been widely planted in China. To further develop its potential value, it is necessary to explore the regulatory mechanism of nitrogen metabolism for rational nitrogen utilization. In this study, we investigated the morphology, physiology and transcriptome of a paper mulberry hybrid (Broussonetia kazinoki × B. papyrifera) in response to different nitrogen concentrations. Moderate nitrogen promoted plant growth and biomass accumulation. Photosynthetic characteristics, concentration of nitrogenous compounds and activities of enzymes were stimulated under nitrogen treatment. However, these enhancements were slightly or severely inhibited under excessive nitrogen supply. Nitrite reductase and glutamate synthase were more sensitive than nitrate reductase and glutamine synthetase and more likely to be inhibited under high nitrogen concentrations. Transcriptome analysis of the leaf transcriptome identified 161,961 unigenes. The differentially expressed genes associated with metabolism of nitrogen, alanine, aspartate, glutamate and glycerophospholipid showed high transcript abundances after nitrogen application, whereas those associated with glycerophospholipid, glycerolipid, amino sugar and nucleotide sugar metabolism were down-regulated. Combined with weighted gene coexpression network analysis, we uncovered 16 modules according to similarity in expression patterns. Asparagine synthetase and inorganic pyrophosphatase were considered two hub genes in two modules, which were associated with nitrogen metabolism and phosphorus metabolism, respectively. The expression characteristics of these genes may explain the regulation of morphological, physiological and other related metabolic strategies harmoniously. This multifaceted study provides valuable insights to further understand the mechanism of nitrogen metabolism and to guide utilization of paper mulberry.

Growth and nitrogen metabolism are associated with nitrogen-use efficiency in cotton genotypes

Crops, including cotton, are sensitive to nitrogen (N) and excessive use can lead to an increase in production costs and environmental problems. We hypothesized that the use of cotton genotypes with substantial root systems and high genetic potentials for nitrogen-use efficiency (NUE) would best address these problems. Therefore, the interspecific variations and traits contributing to NUE in six cotton genotypes having contrasting NUEs were studied in response to various nitrate concentrations. Large genotypic variations were observed in morphophysiological and biochemical traits, especially shoot dry weight, root traits, and N-assimilating enzyme levels. The roots of all the cotton genotypes were more sensitive to low-than high-nitrate concentrations, and the genotype CCRI-69 had the largest root system irrespective of the nitrate concentration. The root morphological traits were positively correlated with N-utilization efficiency and were more affected by genotype than nitrate concentration. Conversely, growth and N-assimilating enzyme levels were more affected by nitrate concentration and were positively correlated with N-uptake efficiency. Based on shoot dry weight, CCRI-69 and XLZ-30 were identified as N-efficient and N-inefficient genotypes, respectively, and these results were confirmed by their contrasting root systems, N metabolism, and NUEs. In the future, multi-omics techniques will be performed to identify key genes/pathways involved in N metabolism, which may have the potential to improve root architecture and increase NUE.

Phosphoproteomic and Metabolomic Analyses Reveal Sexually Differential Regulatory Mechanisms in Poplar to Nitrogen Deficiency

Nitrogen (N) is a key factor impacting physiological processes in plants. Many proteins have been investigated in male and female poplars under N limitation. However, little is known about sex differences in the protein modifications and metabolites that occur in poplar leaves in response to N deficiency. In this study, as compared to N-deficient males, N-deficient females suffered greater damage from N deficiency, including chloroplast disorganization and lipid peroxidation of cellular membranes. Male poplars had greater osmotic adjustment ability than did females, allowing greater accumulation of soluble metabolites. In addition, as compared to that in N-deficient males, glycolysis was less suppressed in N-deficient females for increased enzyme activities to consume excess energy. Moreover, we found that pronounced protein phosphorylation occurred during carbon metabolism and substance transport processes in both sexes of poplar under N-limiting conditions. Sex-specific metabolites mainly included intermediates in glycolysis, amino acids, and phenylpropanoid-derived metabolites. This study provides new molecular evidence that female poplars suffer greater negative effects from N deficiency than do male poplars.

Phosphorus influence Cd phytoextraction in Populus stems via modulating xylem development, cell wall Cd storage and antioxidant defense

The soils in mining lands with cadmium (Cd) contamination usually are deficient in nutrients. Disclosing how P nutrition and N:P stoichiometric ratio influences Cd accumulation and stress tolerance in stems of Populus spp. will facilitate the phytoremediation of mining sites polluted by Cd. In this study, investigations at the anatomical and physiological levels were conducted using a clone of Populus × euramericana. Both phosphorus deficiency and cadmium exposure inhibited xylem development via reducing cell layers in the xylem. Under P-sufficient condition, appropriate P status and balanced N:P ratio in stem promoted xylem development under Cd exposure via stimulating cell division, which enhanced Cd accumulation in stems. Cd accumulation in cell walls of collenchyma tissues of the stem was enhanced by P application due to increased polysaccharide production and cell wall affinity for Cd. The low P concentrations (0.3-0.4 mg g^-1) and imbalanced N:P ratio under P deficiency inhibited the production of APX and ascorbate-GSH cycle, which increased oxidative stress and lipid peroxidation as indicated by high MDA concentration in stem. Under P-sufficient condition, the interactions between phytohormones and antioxidants play crucial roles in the process of antioxidant defense under Cd exposure. In conclusions, appropriate P addition and balanced N:P ratio enhanced secondary xylem development and promoted cadmium accumulation and stress tolerance in Populus stems, which can benefit the phytoextraction of Cd from Cd-contaminated soil.

Nitrate Transporter Gene Expression and Kinetics of Nitrate Uptake by Populus × canadensis 'Neva' in Relation to Arbuscular Mycorrhizal Fungi and Nitrogen Availability

Plants and other organisms in the ecosystem compete for the limited nitrogen (N) in the soil. Formation of a symbiotic relationship with arbuscular mycorrhizal fungi (AMF) may influence plant competitiveness for N. However, the effects of AMF on plant nitrate (NO3 -) uptake capacity remain unknown. In this study, a pot experiment was conducted to investigate the effects of N application and Rhizophagus irregularis inoculation on the root absorbing area, uptake kinetics of NO3 -, and the expression of NO3 - transporter (NRT) genes in Populus × canadensis 'Neva'. The results showed that R. irregularis colonized more than 70% of the roots of the poplar and increased root active absorbing area/total absorbing area. The uptake kinetics of NO3 - by poplar fitted the Michaelis-Menten equation. Mycorrhizal plants had a higher maximum uptake rate (V max) value than non-mycorrhizal plants, indicating that R. irregularis enhanced the NO3 - uptake capacity of poplar. The expression of NRTs in roots, namely, NRT1;2, NRT2;4B, NRT2;4C, NRT3;1A, NRT3;1B, and NRT3;1C, was decreased by R. irregularis under conditions of 0 and 1 mM NH4NO3. This study demonstrated that the improved NO3 - uptake capacity by R. irregularis was not achieved by up-regulating the expression of NRTs in roots. The mycorrhizal pathway might repress root direct pathway in the NO3 - uptake by mycorrhizal plants.

Variations in Nitrogen Metabolism are Closely Linked with Nitrogen Uptake and Utilization Efficiency in Cotton Genotypes under Various Nitrogen Supplies

Cotton production is highly sensitive to nitrogen (N) fertilization, whose excessive use is responsible for human and environmental problems. Lowering N supply together with the selection of N-efficient genotypes, more able to uptake, utilize, and remobilize the available N, could be a challenge to maintain high cotton production sustainably. The current study aimed to explore the intraspecific variation among four cotton genotypes in response to various N supplies, in order to identify the most distinct N-efficient genotypes and their nitrogen use efficiency (NUE)-related traits in hydroponic culture. On the basis of shoot dry matter, CCRI-69 and XLZ-30 were identified as N-efficient and N-inefficient genotypes, respectively, and these results were confirmed by their contrasting N metabolism, uptake (NUpE), and utilization efficiency (NUtE). Overall, our results indicated the key role of shoot glutamine synthetase (GS) and root total soluble protein in NUtE. Conversely, tissue N concentration and N-metabolizing enzymes were considered as the key traits in conferring high NUpE. The remobilization of N from the shoot to roots by high shoot GS activity may be a strategy to enhance root total soluble protein, which improves root growth for N uptake and NUE. In future, multi-omics studies will be employed to focus on the key genes and pathways involved in N metabolism and their role in improving NUE.

Metabolic and physiological analyses reveal that Populus cathayana males adopt an energy-saving strategy to cope with phosphorus deficiency

Dioecious trees have evolved sex-specific adaptation strategies to cope with inorganic phosphorus (Pi) limitation. Yet, little is known about the effects of Pi limitation on plant metabolism, particularly in dioecious woody plants. To identify potential gender-specific metabolites appearing in response to Pi limitation in poplars, we studied the metabolic and ionomic responses in the roots and leaves of Populus cathayana Rehd males and females exposed to a 60-day period of Pi deficiency. Besides significant decreases in phosphorus contents in both Pi-deficient roots and leaves, the calcium level decreased significantly and the sulfur content increased significantly in Pi-deficient male roots, while the zinc and ferrum contents increased significantly in Pi-deficient female roots. Inorganic P deficiency caused a smaller change in the abscisic acid content, but a significant increase in the jasmonic acid content was detected in both leaves and roots. Salicylic acid significantly decreased under Pi deficiency in male leaves and female roots. Changes were found in phospholipids and phosphorylated metabolites (e.g., fructose-6-phosphate, glycerol-3-phosphate, glucose-6-phosphate, phosphoric acid and inositol-1-phosphate) in roots and leaves. Both P. cathayana males and females relied on inorganic pyrophosphate-dependent but not on Pi-dependent glycolysis under Pi-deficient conditions. Sex-specific metabolites in leaves were primarily in the category of primary metabolites (e.g., amino acids), while in roots primarily in the category of secondary metabolites (e.g., organic acids) and sugars. The metabolome analysis revealed that sexually different pathways occurred mainly in amino acid metabolism, and the tissue-related differences were in the shikimate pathway and glycolysis. We observed changes in carbon flow, reduced root biomass and increased amino acid contents in P. cathayana males but not in females, which indicated that males have adopted an energy-saving strategy to adapt to Pi deficiency. Thus, this study provides new insights into sex-specific metabolic responses to Pi deficiency.

Physiological responses and small RNAs changes in maize under nitrogen deficiency and resupply

BACKGROUND

Maize is an important crop in the world, nitrogen stress severely reduces maize yield. Although a large number of studies have identified the expression changes of microRNAs (miRNAs) under N stress in several species, the miRNAs expression patterns of N-deficient plants under N resupply remain unclear.

OBJECTIVE

The primary objective of this study was to identify miRNAs in response to nitrogen stress and understand relevant physiological changes in nitrogen-deficient maize after nitrogen resupply.

METHODS

Physiological parameters were measured to study relevant physiological changes under different nitrogen conditions. Small RNA sequencing and qRT-PCR analysis were performed to understand the response of miRNAs under different nitrogen conditions.

RESULTS

The content of chlorophyll, soluble protein and nitrate nitrogen decreased than CK by 0.52, 0.49 and 0.82 times after N deficiency treatment and increased than ND by 0.52, 1.36 and 0.65 times after N resupply, respectively. Conversely, the activity of superoxide dismutase (SOD) and peroxidase (POD) increased by 0.67 and 1.64 times than CK after N deficiency, respectively, and decreased by 0.09 and 0.35 times than ND after N resupply. A total of 226 known miRNAs were identified by sRNA sequencing; 106 miRNAs were differentially expressed between the control and N-deficient groups, and 103 were differentially expressed between the N-deficient and N-resupply groups (P < 0.05). Real-time quantitative PCR (qPCR) was used to further validate and analyze the expression of the identified miRNAs. A total of 1609 target genes were identified by target prediction, and some differentially expressed miRNAs were predicted to target transcription factors and functional proteins. Gene Ontology (GO) analysis was used to determine the biological function of these targets and revealed that some miRNAs, such as miR169, miR1214, miR2199, miR398, miR408 and miR827 might be involved in nitrogen metabolism regulation.

CONCLUSION

Our study comprehensively provides important information on miRNA functions and molecular mechanisms in response to N stress. These findings may assist to improve nitrogen availability in plants.

Amelioration of nitrate uptake under salt stress by ectomycorrhiza with and without a Hartig net

Salt stress is an important environmental cue impeding poplar nitrogen nutrition. Here, we characterized the impact of salinity on proton-driven nitrate fluxes in ectomycorrhizal roots and the importance of a Hartig net for nitrate uptake. We employed two Paxillus involutus strains for root colonization: MAJ, which forms typical ectomycorrhizal structures (mantle and Hartig net), and NAU, colonizing roots with a thin, loose hyphal sheath. Fungus-colonized and noncolonized Populus × canescens were exposed to sodium chloride and used to measure root surface pH, nitrate (NO3- ) flux and transcription of NO3- transporters (NRTs; PcNRT1.1, -1.2, -2.1), and plasmalemma proton ATPases (HAs; PcHA4, -8, -11). Paxillus colonization enhanced root NO3- uptake, decreased surface pH, and stimulated NRTs and HA4 of the host regardless the presence or absence of a Hartig net. Under salt stress, noncolonized roots exhibited strong net NO3- efflux, whereas beneficial effects of fungal colonization on surface pH and HAs prevented NO3- loss. Inhibition of HAs abolished NO3- influx under all conditions. We found that stimulation of HAs was crucial for the beneficial influence of ectomycorrhiza on NO3- uptake, whereas the presence of a Hartig net was not required for improved NO3- translocation. Mycorrhizas may contribute to host adaptation to salt-affected environments by keeping up NO3- nutrition.

The Phosphorus Economy of Mediterranean Oak Saplings Under Global Change

While a severe decrease in phosphorus (P) availability is already taking place in a large number of ecosystems, drought and nitrogen (N) deposition will likely further decrease the availability of P under global change. Plants have developed physiological strategies to cope with decreasing P resources, but it is unclear how these strategies respond to elevated N deposition and summer droughts. We investigated the influence of N and P availability and soil drought on P uptake (H3 33PO4 feeding experiment) and use efficiencies in young Quercus calliprinos Webb. trees. We hypothesized that (H1) the expected increases in soil N:P ratios will increase the efficiencies of P uptake and use of oak saplings but will decrease the efficiencies of N uptake and use, whereas (H2) drought will affect P uptake efficiency more than N uptake efficiency. In confirmation of (H1) we found that a sharp increase of the soil N:P ratio from 4 to 42 g g-1 significantly increased the instantaneous 33P uptake efficiency (33PUptakeE) by five-fold and long-term P uptake efficiency (PUptakeE) by six-fold, while it decreased N uptake efficiency (NUptakeE) and N use efficiency (NUE). In contradiction to (H1), P use efficiency (PUE) did not respond to the simulated extended gradient of soil N:P ratios but remained relatively constant. (H2) was only partially confirmed as soil drought reduced PUptakeE by up to a fourth at high soil N:P ratios but had no significant effect on NUptakeE. As a consequence, increasing summer droughts may decrease the response of PUptakeE to increasing P limitation, which - in the absence of adjustments of the efficiency of P use - can aggravate growth reductions in this eastern Mediterranean tree species under global change.

The influence of nitrogen availability on anatomical and physiological responses of Populus alba × P. glandulosa to drought stress

BACKGROUND

Drought and nitrogen (N) deficiency are two major limiting factors for forest productivity in many ecosystems. Elucidating the mechanisms underlying the influence of soil N availability on drought responses of tree species is crucial to improve tree growth under drought.

RESULTS

The root proliferation under drought was enhanced by adequate N application. Vessel frequency in xylem increased upon drought, with more significant increase under adequate N conditions compared with that under low N conditions, possibly leading to increased hydraulic safety. Nitrogen application under drought increased indole acetic acid (IAA), which contributed to the adaptive changes of xylem. Nitrogen application increased leaf abscisic acid (ABA) concentration, therefore regulated stomata adjustment, and promoted intrinsic water use efficiency (WUE_i). Moreover, N application promoted antioxidant defense in leaves by showing increased level of free proline and carotenoid, which improved drought tolerance and growth performance of poplars.

CONCLUSIONS

Anatomical and physiological responses of Populus to drought were suppressed by N deficiency. Adequate N application promoted adaptive changes of root and xylem under drought and increased hydraulic safety. Nitrogen addition under drought also increased leaf ABA level which may regulate stomata adjustment and promote WUE_i. Moreover, nitrogen application improved antioxidant defense in leaves with increased levels of antioxidants. These positive regulations improved drought tolerance and growth performance of poplars.

Effects of Fertilization Ratios and Frequencies on the Growth and Nutrient Uptake of Magnolia wufengensis (Magnoliaceae)

Through this study, the most suitable fertilization ratio, amount and frequency were determined, providing a scientific reference for further fertilization management for Magnolia wufengensis (Magnoliaceae) seedlings. Fertilization is an important cultivation and management measure to maintain forest seedling health and rapid growth. However, improper fertilization can also have unexpected effects: inhibiting seedling growth, increasing the cost of production and contaminating the environment. Thus, to explore the most suitable fertilization treatment for Magnolia wufengensis growth, one-year-old Magnolia wufengensis seedlings and the orthogonal design method were used in this study. Three different fertilization frequencies were used combined with 9 NPK ratios. The growth index, chlorophyll content, nutrient content in tissues, nutrient transport efficiency, nutrient uptake, and soil properties were analyzed. Fertilization can increase chlorophyll content, promoting the vegetative growth and biomass accumulation of Magnolia wufengensis. Fertilization reduced the proportion of root biomass to whole plant biomass, resulting in an increase in stem biomass with little effect on leaf biomass. Additionally, fertilization also increased the proportion of N in roots, P in stems and K in leaves. Under fertilization, the K transport efficiency was higher than that of N and P. Furthermore, there was a positive correlation between the nutrient use efficiencies of N and K. Overall, the effects of six fertilizer applications were much better than those of four and eight fertilizer applications on the promotion of vegetative growth, biomass and nutrient accumulation, nutrient uptake and transport efficiency. The results showed that six fertilizer applications with an NPK ratio of 3:2:1 as follows: N application at 480 mg/plant, P application at 320 mg/plant, and K application at 160 mg/plant was the most suitable fertilization method for plant growth.

Integrated Transcriptome Analysis Reveals Plant Hormones Jasmonic Acid and Salicylic Acid Coordinate Growth and Defense Responses upon Fungal Infection in Poplar

Plants have evolved a sophisticated system to respond to various stresses. Fungal attack or infection is one of the most important biotic stresses for most plants. During the defense response to fungal infection, the plant hormones jasmonic acid (JA) and salicylic acid (SA) play critical roles. Here, gene expression data on JA/SA treatments and Melampsora larici-populina (MLP) infection were generated. Integrated transcriptome analyses of these data were performed, and 943 genes in total were identified as common responsive genes (CRG). Gene ontology (GO) term analysis revealed that the genes from CRG are generally involved in the processes of stress responses, metabolism, and growth and development. The further cluster analysis of the CRG identified a set of core genes that are involved in the JA/SA-mediated response to fungal defense with distinct gene expression profiles upon JA/SA treatment, which highlighted the different effects of these two hormones on plant fungal defenses. The modifications of several pathways relative to metabolism, biotic stress, and plant hormone signal pathways suggest the possible roles of JA/SA on the regulation of growth and defense responses. Co-expression modules (CMs) were also constructed using the poplar expression data on JA, SA, M. larici-populina, Septoria musiva, and Marssonina brunnea treatment or infection. A total of 23 CMs were constructed, and different CMs clearly exhibited distinct biological functions, which conformably regulated the concerted processes in response to fungal defense. Furthermore, the GO term analysis of different CMs confirmed the roles of JA and SA in regulating growth and defense responses, and their expression profiles suggested that the growth ability was reduced when poplar deployed defense responses. Several transcription factors (TFs) among the CRG in the co-expression network were proposed as hub genes in regulating these processes. According to this study, our data finely uncovered the possible roles of JA/SA in regulating the balance between growth and defense responses by integrating multiple hormone signaling pathways. We were also able to provide more knowledge on how the plant hormones JA/SA are involved in the regulation of the balance between growth and plant defense.