Integrative multi-omics analyses of date palm (Phoenix dactylifera) roots and leaves reveal how the halophyte land plant copes with sea water.

Date palm (Phoenix dactylifera L.) is able to grow and complete its life cycle while being rooted in highly saline soils. Which of the many well-known salt-tolerance strategies are combined to fine-tune this remarkable resilience is unknown. The precise location, whether in the shoot or the root, where these strategies are employed remains uncertain, leaving us unaware of how the various known salt-tolerance mechanisms are integrated to fine-tune this remarkable resilience. To address this shortcoming, we exposed date palm to a salt stress dose equivalent to seawater for up to 4 weeks and applied integrative multi-omics analyses followed by targeted metabolomics, hormone, and ion analyses. Integration of proteomic into transcriptomic data allowed a view beyond simple correlation, revealing a remarkably high degree of convergence between gene expression and protein abundance. This sheds a clear light on the acclimatization mechanisms employed, which depend on reprogramming of protein biosynthesis. For growth in highly saline habitats, date palm effectively combines various salt-tolerance mechanisms found in both halophytes and glycophytes: "avoidance" by efficient sodium and chloride exclusion at the roots, and "acclimation" by osmotic adjustment, reactive oxygen species scavenging in leaves, and remodeling of the ribosome-associated proteome in salt-exposed root cells. Combined efficiently as in P. dactylifera L., these sets of mechanisms seem to explain the palm's excellent salt stress tolerance.

A critical review of plant adaptation to environmental boron stress: Uptake, utilization, and interplay with other abiotic and biotic factors.

Boron (B) is an indispensable mineral nutrient for plants and is primarily taken up by roots mainly in the form of boric acid (H3BO3). Recently, research shows that B has a significant impact on plant growth and productivity due to its narrow range between deficiency and toxicity. Fertilization and other procedures to address B stress (deficiency and toxicity) in soils are generally expensive and time-consuming. Over the past 20 years, substantial studies have been conducted to investigate the mechanisms underlying B acquisition and the molecular regulation of B stress in plants. In this review, we discuss the effects of B stress on plant growth, physiology, and biochemistry, and finding on enhancing plant tolerance from the perspective of plant B uptake, transport, and utilization. We also refer to recent results demonstrating the interactions among B and other biological and abiotic factors, including nitrogen, phosphorus, aluminum, and microorganisms. Finally, emerging trends in this field are discussed.

Integrating genome-wide association studies with selective sweep reveals genetic loci associated with tolerance to low phosphate availability in Brassica napus.

Oilseed rape (Brassica napus L.; B. napus) is an important oil crop worldwide. However, the genetic mechanisms of B. napus adaptations to low phosphate (P) stress are largely unknown. In this study, a genome-wide association study (GWAS) identified 68 SNPs significantly associated with seed yield (SY) under low P (LP) availability, and 7 SNPs significantly associated with phosphorus efficiency coefficient (PEC) in two trials. Among these SNPs, two, chrC07__39807169 and chrC09__14194798, were co-detected in two trials, and BnaC07.ARF9 and BnaC09.PHT1;2 were identified as candidate genes of them, respectively, by combining GWAS with quantitative reverse-transcription PCR (qRT-PCR). There were significant differences in the gene expression level of BnaC07.ARF9 and BnaC09.PHT1;2 between P-efficient and -inefficiency varieties at LP. SY_LP had a significant positive correlation with the gene expression level of both BnaC07.ARF9 and BnaC09.PHT1;2. BnaC07.ARF9 and BnaA01.PHR1 could directly bind the promoters of BnaA01.PHR1 and BnaC09.PHT1;2, respectively. Selective sweep analysis was conducted between ancient and derived B. napus, and detected 1280 putative selective signals. Within the selected region, a large number of genes related to P uptake, transport, and utilization were detected, such as purple acid phosphatase (PAP) family genes and phosphate transporter (PHT) family genes. These findings provide novel insights into the molecular targets for breeding P efficiency varieties in B. napus. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01399-9.

Potato root-associated microbiomes adapt to combined water and nutrient limitation and have a plant genotype-specific role for plant stress mitigation.

BACKGROUND: Due to climate change and reduced use of fertilizers combined stress scenarios are becoming increasingly frequent in crop production. In a field experiment we tested the effect of combined water and phosphorus limitation on the growth performance and plant traits of eight tetraploid and two diploid potato varieties as well as on root-associated microbiome diversity and functional potential. Microbiome and metagenome analysis targeted the diversity and potential functions of prokaryotes, fungi, plasmids, and bacteriophages and was linked to plant traits like tuber yield or timing of canopy closure. RESULTS: The different potato genotypes responded differently to the combined stress and hosted distinct microbiota in the rhizosphere and the root endosphere. Proximity to the root, stress and potato genotype had significant effects on bacteria, whereas fungi were only mildly affected. To address the involvement of microbial functions, we investigated well and poorly performing potato genotypes (Stirling and Desirée, respectively) under stress conditions and executed a metagenome analysis of rhizosphere microbiomes subjected to stress and no stress conditions. Functions like ROS detoxification, aromatic amino acid and terpene metabolism were enriched and in synchrony with the metabolism of stressed plants. In Desirée, Pseudonocardiales had the genetic potential to take up assimilates produced in the fast-growing canopy and to reduce plant stress-sensing by degrading ethylene, but overall yield losses were high. In Stirling, Xanthomonadales had the genetic potential to reduce oxidative stress and to produce biofilms, potentially around roots. Biofilm formation could be involved in drought resilience and nutrient accessibility of Stirling and explain the recorded low yield losses. In the rhizosphere exposed to combined stress, the relative abundance of plasmids was reduced, and the diversity of phages was enriched. Moreover, mobile elements like plasmids and phages were affected by combined stresses in a genotype-specific manner. CONCLUSION: Our study gives new insights into the interconnectedness of root-associated microbiota and plant stress responses in the field. Functional genes in the metagenome, phylogenetic composition and mobile elements play a role in potato stress adaption. In a poor and a well performing potato genotype grown under stress conditions, distinct functional genes pinpoint to a distinct stress sensing, water availability and compounds in the rhizospheres.

Chronic ozone exposure impairs the mineral nutrition of date palm (Phoenix dactylifera) seedlings.

Chronic ozone (O3) exposure in the atmosphere preferentially disturbs metabolic processes in the roots rather than the shoot as a consequence of reduced photosynthesis and carbohydrate allocation from the leaves to the roots. The aim of the present study was to elucidate if mineral nutrition is also impaired by chronic O3 exposure. For this purpose, date palm (Phoenix dactylifera) plants were fumigated with ambient, 1.5 × ambient and 2 × ambient O3 in a free air controlled exposure (FACE) system for one growing season and concentrations of major nutrients were analyzed in leaves and roots. In addition, concentrations of C and N and their partitioning between different metabolic C and N pools were determined in both organs. The results showed that calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), sodium (Na) and potassium (K) acquisition by roots was diminished by O3 exposure of the shoot. For Ca, Mg, Fe and Zn reduced uptake by the roots was combined with reduced allocation to the shoot, resulting in a decline of foliar concentrations; for Na and K, allocation to the shoot was maintained at the expense of the roots. Thus, elevated O3 impaired both mineral uptake by the roots and partitioning of minerals between roots and shoots, but in an element specific way. Thereby, elevated O3 affected roots and shoots differently already after one growing season. However, considerable changes in total C and N concentrations and their partitioning between different metabolic pools upon chronic O3 exposure were not observed in either leaves or roots, except for reduced foliar lignin concentrations at 2 × ambient O3. Significant differences in these parameters were shown between leaves and roots independent of O3 application. The physiological consequences of the effects of chronic O3 exposure on mineral acquisition and partitioning between leaves and roots are discussed.

Rhizosphere engineering for sustainable crop production: entropy-based insights.

There is a growing interest in exploring interactions at root-soil interface in natural and agricultural ecosystems, but an entropy-based understanding of these dynamic rhizosphere processes is lacking. We have developed a new conceptual model of rhizosphere regulation by localized nutrient supply using thermodynamic entropy. Increased nutrient-use efficiency is achieved by rhizosphere management based on self-organization and minimized entropy via equilibrium attractors comprising (i) optimized root strategies for nutrient acquisition and (ii) improved information exchange related to root-soil-microbe interactions. The cascading effects through different hierarchical levels amplify the underlying processes in plant-soil system. We propose a strategy for manipulating rhizosphere dynamics and improving nutrient-use efficiency by localized nutrient supply with minimization of entropy to underpin sustainable food/feed/fiber production.

Differences of nitrogen metabolism in date palm (Phoenix dactylifera) seedlings subjected to water deprivation and salt exposure.

Drought and salt exposure are among the most prevalent and severe abiotic stressors causing serious agricultural yield losses, alone and in combination. Little is known about differences and similarities in the effects of these two stress factors on plant metabolic regulation, particularly on nitrogen metabolism. Here, we studied the effects of water deprivation and salt exposure on water relations and nitrogen metabolites in leaves and roots of date palm seedlings. Both, water deprivation and salt exposure had no significant effects on plant water content or stable carbon (C) and nitrogen (N) isotope signatures. Significant effects of water deprivation on total C and N concentrations were only observed in roots, i.e., decreased total C and increased total N concentrations. Whereas salt exposure initially decreased total C and increased total N concentrations significantly in roots, foliar total C concentration was increased upon prolonged exposure. Initially C/N ratios declined in roots of plants from both treatments and upon prolonged salt exposure also in the leaves. Neither treatment affected soluble protein and structural N concentrations in leaves or roots, but resulted in the accumulation of most amino acids, except for glutamate and tryptophan, which remained stable, and serine, which decreased, in roots. Accumulation of the most abundant amino acids, lysine and proline, was observed in roots under both treatments, but in leaves only upon salt exposure. This finding indicates a similar role of these amino acids as compatible solutes in the roots in response to salt und drought, but not in the leaves. Upon prolonged treatment, amino acid concentrations returned to levels found in unstressed plants in leaves of water deprived, but not salt exposed, plants. The present results show both water deprivation and salt exposure strongly impact N metabolism of date palm seedlings, but in a different manner in leaves and roots.

Identification of vacuolar phosphate influx transporters in Brassica napus.

Recent progress has shown that vacuolar Pi transporters (VPTs) are important for cellular Pi homoeostasis in Arabidopsis thaliana and Oryza sativa under fluctuating external Pi supply, but the identity and involvement of VPTs in cellular Pi homoeostasis in Brassica napus is poorly understood. Here, we identified two vacuolar Pi influx transporters B. napus, BnA09PHT5;1b and BnCnPHT5;1b, and uncovered their necessity for cellular Pi homoeostasis through functional analysis. Both Brassica proteins are homologs of Arabidopsis AtPHT5;1 with a similar sequence, structure, tonoplast localization, and VPT activity. Brassica pht5;1b double mutants had smaller shoots and larger shoot cellular Pi concentrations than wild-type B. napus, which contrasts with a previous study of the Arabidopsis pht5;1 mutant, suggesting that PHT5;1-VPTs play different roles in cellular Pi homoeostasis in seedlings of B. napus and A. thaliana. Disruption of BnPHT5;1b genes also caused Pi toxicity in floral organs, reduced seed yield and impacted seed traits, consistent with the proposed role of AtPHT5;1 in floral Pi homoeostasis in Arabidopsis. Taken together, our studies identified two vacuolar Pi influx transporters in B. napus and revealed the distinct and conserved roles of BnPHT5;1bs in cellular Pi homoeostasis in this plant species.

Synchrotron X-ray Fluorescence Technique Identifies Contribution of Node Iron and Zinc Accumulations to the Grain of Wheat.

Increasing iron (Fe) and zinc (Zn) concentrations in crop grains with high yield is an effective measure to ensure food supply and alleviate mineral malnutrition in humans. Micronutrient concentrations in grains depend on not only their availability in soils but also their uptake in roots and translocation to shoots and grains. In this three-year field study, we investigated genotypic variation in Fe and Zn uptake and translocation within six wheat cultivars and examined in detail Fe and Zn distributions in various tissues of two cultivars with similar high yield but different grain Fe and Zn concentrations using synchrotron micro-X-ray fluorescence. Results revealed that root Fe and Zn concentrations were 11 and 44% greater in high-nutrient (HN) than in low-nutrient (LN) concentration cultivar. Although both cultivars accumulated similar amounts of Fe in shoots, HN cultivar had greater accumulation of Fe in grain and greater accumulation of Zn in both shoots and grain. Grain Zn concentration was positively correlated with shoot Zn accumulation, and grain Fe concentration was positively correlated with the ability to translocate Fe from leaves/stem to grains. In the first nodes of shoots, HN cultivar had 482% greater Fe and 36% greater Zn concentrations in the enlarged vascular bundle (EVB) than LN cultivar. In top nodes, HN cultivar had 225 and 116% greater Fe and Zn concentrations in the transit vascular bundle and 77 and 71% greater in the EVB when compared to LN cultivar. HN cultivar also had a greater ability to allocate Fe and Zn to the grain than LN cultivar. In conclusion, HN cultivar had greater capacity of Fe and Zn acquirement by roots and translocation and partitioning from shoots into grains. Screening wheat cultivars for larger Fe and Zn concentrations in shoot nodes could be a novel strategy for breeding crops with greater grain Fe and Zn concentrations.

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.

The exacerbation of soil acidification correlates with structural and functional succession of the soil microbiome upon agricultural intensification.

Agricultural intensification driven by land-use changes has caused continuous and cumulative soil acidification (SA) throughout the global agroecosystem. Microorganisms mediate acid-generating reactions; however, the microbial mechanisms responsible for exacerbating SA feedback remain largely unknown. To determine the microbial community composition and putative function associated with SA, we conducted a metagenomic analysis of soils across a chronosequence that has elapsed since the conversion of rice-wheat (RW) to rice-vegetable (RV) rotations. Compared to RW rotations, soil pH decreased by 0.50 and 1.56 units (p < 0.05) in response to 10-year and 20-year RV rotations, respectively. Additionally, acid saturation ratios were increased by 7.3% and 36.2% (p < 0.05), respectively. The loss of microbial beta-diversity was a key element that contributed to the exacerbation of SA in the RV. Notably, the 20-year RV-enriched microbial taxa were more hydrogen (H+)-, aluminium (Al3+)-, and nitrate nitrogen (NO3--N) -dependent and contained more genera exhibiting dehydrogenation functions than did RW-enriched taxa. "M00115, M00151, M00417, and M00004" and "M00531 and M00135" that are the "proton-pumping" and "proton-consuming" gene modules, respectively, were linked to the massive recruitment of acid-dependent biomarkers in 20-year RV soils, particularly Rhodanobacter, Gemmatirosa, Sphingomonas, and Streptomyces. Collectively, soils in long-term RV rotations were highly acidified and acid-sensitive, as the enrichment of microbial dehydrogenation genes allowing for soil buffering capacity is more vulnerable to H+ loading and consequently promotes the colonization of more acid-tolerant and acidogenic microbes, and ultimately provide new clues for researchers to elucidate the interaction between SA and the soil microbiome.

Mechanisms for improving phosphorus utilization efficiency in plants.

BACKGROUND: Limitation of plant productivity by phosphorus (P) supply is widespread and will probably increase in the future. Relatively large amounts of P fertilizer are applied to sustain crop growth and development and to achieve high yields. However, with increasing P application, plant P efficiency generally declines, which results in greater losses of P to the environment with detrimental consequences for ecosystems. SCOPE: A strategy for reducing P input and environmental losses while maintaining or increasing plant performance is the development of crops that take up P effectively from the soil (P acquisition efficiency) or promote productivity per unit of P taken up (P utilization efficiency). In this review, we describe current research on P metabolism and transport and its relevance for improving P utilization efficiency. CONCLUSIONS: Enhanced P utilization efficiency can be achieved by optimal partitioning of cellular P and distributing P effectively between tissues, allowing maximum growth and biomass of harvestable plant parts. Knowledge of the mechanisms involved could help design and breed crops with greater P utilization efficiency.

Sodium hyperaccumulators in the Caryophyllales are characterized by both abnormally large shoot sodium concentrations and [Na]shoot/[Na]root quotients greater than unity.

BACKGROUND AND AIMS: Some Caryophyllales species accumulate abnormally large shoot sodium (Na) concentrations in non-saline environments. It is not known whether this is a consequence of altered Na partitioning between roots and shoots. This paper tests the hypotheses (1) that Na concentrations in shoots ([Na]shoot) and in roots ([Na]root) are positively correlated among Caryophyllales, and (2) that shoot Na hyperaccumulation is correlated with [Na]shoot/[Na]root quotients. METHODS: Fifty two genotypes, representing 45 Caryophyllales species and 4 species from other angiosperm orders, were grown hydroponically in a non-saline, complete nutrient solution. Concentrations of Na in shoots and in roots were determined using inductively coupled plasma mass spectrometry (ICP-MS). KEY RESULTS: Sodium concentrations in shoots and roots were not correlated among Caryophyllales species with normal [Na]shoot, but were positively correlated among Caryophyllales species with abnormally large [Na]shoot. In addition, Caryophyllales species with abnormally large [Na]shoot had greater [Na]shoot/[Na]root than Caryophyllales species with normal [Na]shoot. CONCLUSIONS: Sodium hyperaccumulators in the Caryophyllales are characterized by abnormally large [Na]shoot, a positive correlation between [Na]shoot and [Na]root, and [Na]shoot/[Na]root quotients greater than unity.

Linking root exudation to belowground economic traits for resource acquisition.

The concept of a root economics space (RES) is increasingly adopted to explore root trait variation and belowground resource-acquisition strategies. Much progress has been made on interactions of root morphology and mycorrhizal symbioses. However, root exudation, with a significant carbon (C) cost (c. 5-21% of total photosynthetically fixed C) to enhance resource acquisition, remains a missing link in this RES. Here, we argue that incorporating root exudation into the structure of RES is key to a holistic understanding of soil nutrient acquisition. We highlight the different functional roles of root exudates in soil phosphorus (P) and nitrogen (N) acquisition. Thereafter, we synthesize emerging evidence that illustrates how root exudation interacts with root morphology and mycorrhizal symbioses at the level of species and individual plant and argue contrasting patterns in species evolved in P-impoverished vs N-limited environments. Finally, we propose a new conceptual framework, integrating three groups of root functional traits to better capture the complexity of belowground resource-acquisition strategies. Such a deeper understanding of the integrated and dynamic interactions of root morphology, root exudation, and mycorrhizal symbioses will provide valuable insights into the mechanisms underlying species coexistence and how to explore belowground interactions for sustainable managed systems.

Genetic Dissection of Root Angle of Brassica napus in Response to Low Phosphorus.

Plant root angle determines the vertical and horizontal distribution of roots in the soil layer, which further influences the acquisition of phosphorus (P) in topsoil. Large genetic variability for the lateral root angle (root angle) was observed in a linkage mapping population (BnaTNDH population) and an association panel of Brassica napus whether at a low P (LP) or at an optimal P (OP). At LP, the average root angle of both populations became smaller. Nine quantitative trait loci (QTLs) at LP and three QTLs at OP for the root angle and five QTLs for the relative root angle (RRA) were identified by the linkage mapping analysis in the BnaTNDH population. Genome-wide association studies (GWASs) revealed 11 single-nucleotide polymorphisms (SNPs) significantly associated with the root angle at LP (LPRA). The interval of a QTL for LPRA on A06 (qLPRA-A06c) overlapped with the confidence region of the leading SNP (Bn-A06-p14439400) significantly associated with LPRA. In addition, a QTL cluster on chromosome C01 associated with the root angle and the primary root length (PRL) in the "pouch and wick" high-throughput phenotyping (HTP) system, the root P concentration in the agar system, and the seed yield in the field was identified in the BnaTNDH population at LP. A total of 87 genes on A06 and 192 genes on C01 were identified within the confidence interval, and 14 genes related to auxin asymmetric redistribution and root developmental process were predicted to be candidate genes. The identification and functional analyses of these genes affecting LPRA are of benefit to the cultivar selection with optimal root system architecture (RSA) under P deficiency in Brassica napus.

Unravelling homeostasis effects of phosphorus and zinc nutrition by leaf photochemistry and metabolic adjustment in cotton plants.

Phosphorus (P) and zinc (Zn) uptake and its physiological use in plants are interconnected and are tightly controlled. However, there is still conflicting information about the interactions of these two nutrients, thus a better understanding of nutritional homeostasis is needed. The objective of this work was to evaluate responses of photosynthesis parameters, P-Zn nutritional homeostasis and antioxidant metabolism to variation in the P × Zn supply of cotton (Gossypium hirsutum L.). Plants were grown in pots and watered with nutrient solution containing combinations of P and Zn supply. An excess of either P or Zn limited plant growth, reduced photosynthesis-related parameters, and antioxidant scavenging enzymes. Phosphorus uptake favoured photochemical dissipation of energy decreasing oxidative stress, notably on Zn-well-nourished plants. On the other hand, excessive P uptake reduces Zn-shoot concentration and decreasing carbonic anhydrase activity. Adequate Zn supply facilitated adaptation responses to P deficiency, upregulating acid phosphatase activity, whereas Zn and P excess were alleviated by increasing P and Zn supply, respectively. Collectively, the results showed that inter ionic effects of P and Zn uptake affected light use and CO2 assimilation rate on photosynthesis, activation of antioxidant metabolism, acid phosphatase and carbonic anhydrase activities, and plant growth-related responses to different extents.

Relationships Between Leaf Carbon and Macronutrients Across Woody Species and Forest Ecosystems Highlight How Carbon Is Allocated to Leaf Structural Function.

Stoichiometry of leaf macronutrients can provide insight into the tradeoffs between leaf structural and metabolic investments. Structural carbon (C) in cell walls is contained in lignin and polysaccharides (cellulose, hemicellulose, and pectins). Much of leaf calcium (Ca) and a fraction of magnesium (Mg) were further bounded with cell wall pectins. The macronutrients phosphorus (P), potassium (K), and nitrogen (N) are primarily involved in cell metabolic functions. There is limited information on the functional interrelations among leaf C and macronutrients, and the functional dimensions characterizing the leaf structural and metabolic tradeoffs are not widely appreciated. We investigated the relationships between leaf C and macronutrient (N, P, K, Ca, Mg) concentrations in two widespread broad-leaved deciduous woody species Quercus wutaishanica (90 individuals) and Betula platyphylla (47 individuals), and further tested the generality of the observed relationships in 222 woody eudicots from 15 forest ecosystems. In a subsample of 20 broad-leaved species, we also analyzed the relationships among C, Ca, lignin, and pectin concentrations in leaf cell walls. We found a significant leaf C-Ca tradeoff operating within and across species and across ecosystems. This basic relationship was explained by variations in the share of cell wall lignin and pectin investments at the cell scale. The C-Ca tradeoffs were mainly driven by soil pH and mean annual temperature and precipitation, suggesting that leaves were more economically built with less C and more Ca as soil pH increased and at lower temperature and lower precipitation. However, we did not detect consistent patterns among C-N, and C-Mg at different levels of biological organization, suggesting substantial plasticity in N and Mg distribution among cell organelles and cell protoplast and cell wall. We observed two major axes of macronutrient differentiation: the cell-wall structural axis consisting of protein-free C and Ca and the protoplasm metabolic axis consisting of P and K, underscoring the decoupling of structural and metabolic elements inherently linked with cell wall from protoplasm investment strategies. We conclude that the tradeoffs between leaf C and Ca highlight how carbon is allocated to leaf structural function and suggest that this might indicate biogeochemical niche differentiation of species.

Application of sodium selenate to cowpea (Vigna unguiculata L.) increases shoot and grain Se partitioning with strong genotypic interactions.

BACKGORUND: Cowpea is a crop widely used in developing countries due its rusticity. Besides its rich genotypic variability, most breeding programs do not explore its potential to improve elements uptake. Selenium (Se) is a scarce element in most soils, resulting in its deficiency being common in human diets. This study aimed to evaluate the interaction between biofortification with Se and genotypic variation in cowpea, on the concentrations of Se in roots, leaves + stem and grains. METHODS: Twenty-nine cowpea genotypes were grown in a greenhouse in the absence (control) and presence of Se (12.5 µg Se kg-1 soil) as sodium selenate, in fully randomized scheme. The plants were cultivated until grains harvest. The following variables were determined: roots dry weight (g), leaves + stems dry weight (g), grains dry weight (g), Se concentration (mg kg-1) in roots, leaves + stems and grains, and Se partitioning to shoots and grains. RESULTS: Selenium application increased the Se concentration in roots, leaves + stems and grains in all genotypes. At least twofold variation in grain Se concentration was observed among genotypes. Selenium application did not impair biomass accumulation, including grain dry weight. Genotype "BRS Guariba" had the largest Se concentration in grains and leaves + stems. Genotype MNC04-795 F-158 had the largest partitioning of Se to shoots and grain, due to elevated dry weights of leaves + stems and grain, and high Se concentrations in these tissues. CONCLUSION: This information might be valuable in future breeding programs to select for genotypes with better abilities to accumulate Se in grain to reduce widespread human Se undernutrition.

Loss of organic carbon in suburban soil upon urbanization of Chengdu megacity, China.

Urbanization is progressing rapidly. It can affect soils ecosystem services directly through land management and indirectly through changes in the socioeconomic environment, which eventually leads to an increase in emissions of greenhouse gases. Soil carbon (C) sequestration plays an important role in offsetting the anthropogenic C emissions. However, there is limited knowledge of how urbanization affects the soil C especially that in suburban. In this study, we studied changes in easily oxidizable organic C (EOC) and total organic C (TOC) of suburban soils (0-100 cm) in the rapid urbanising megacity Chengdu, China. The EOC stock and TOC stock decreased from the outer-suburb to the inner-suburb by 17.8-28.2% and 5.4-13.5%, respectively; particularly, the inner-suburb EOC decreased by 31.4-38.6% during the past 10 years. The quotient of EOC/TOC in the soil profile, reflecting the stability of soil C, declined from the outer-suburb (0.78) to the inner-suburb (0.20). Factors that influenced the EOC and TOC included the changes in economics (economic density, industrialization), farmland (cultivated area, farmland structure), urbanization (city size, population growth) and traffic flow. Among which, economic density growth was the primarily driver of the loss in TOC, explaining 31.6% of the variation in soil surface TOC and 16.0% of the variation in subsoil TOC; changes in farmland and urban expansion were the main factors contributing to the loss of subsoil EOC, with 40.4% explanatory ability. In addition, traffic flow also has contribution to the subsoil EOC loss. We concluded that the increasing soil C loss with decreasing distance from the city centre has a continuous contribution to C emission, and the C loss will persist until the suburbs are fully urbanized. The large losses of EOC and TOC caused by urbanization, and their contribution to global warming, necessitate their consideration in future appraisals of climate change and urban planning projects.