low-P Conditions Research Articles

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

Genetic Diversification and Selection Strategies for Improving Sorghum Grain Yield Under Phosphorous-Deficient Conditions in West Africa

Sorghum, a major crop for income generation and food security in West and Central Africa, is predominantly grown in low-input farming systems with serious soil phosphorus (P) deficiencies. This study (a) estimates genetic parameters needed to design selection protocols that optimize genetic gains for yield under low-phosphorus conditions and (b) examines the utility of introgressed backcross nested association mapping (BCNAM) populations for diversifying Malian breeding materials. A total of 1083 BC1F5 progenies derived from an elite hybrid restorer “Lata-3” and 13 diverse donor accessions were evaluated for yield and agronomic traits under contrasting soil P conditions in Mali in 2013. A subset of 298 progenies were further tested under low-P (LP) and high-P (HP) conditions in 2014 and 2015. Significant genetic variation for grain yield was observed under LP and HP conditions. Selection for grain yield under LP conditions was feasible and more efficient than the indirect selection under HP in all three years of testing. Several of the BCNAM populations exhibited yields under LP conditions that were superior to the elite restorer line used as a recurrent parent. The BCNAM approach appears promising for diversifying the male parent pool with introgression of diverse materials using both adapted Malian breed and unadapted landrace material from distant geographic origins as donors.

Sorghum Hybrids for Low‐Input Farming Systems in West Africa: Quantitative Genetic Parameters to Guide Hybrid Breeding

ABSTRACTThe development of sorghum [Sorghum bicolor (L.) Moench] hybrids with Guinea‐race parents is a promising approach to increase yields in West Africa (WA). There is heretofore no quantitative genetic information about the genetic value of new hybrids and their parents, or about the efficiency of alternative selection methods for targeting yield performance under the predominantly low‐input, P‐deficient production conditions. This study aims to estimate the heterosis levels attainable by new Guinea‐race hybrids and the combining abilities of the current suite of parents with partial‐ to full‐Guinea‐race backgrounds of contrasting geographic origins, and to determine the effectiveness of direct selection under low‐P (LP) relative to indirect selection under high‐P (HP) conditions. Single‐cross hybrids were evaluated in 2015 and 2016 for yield under both LP and HP conditions at two locations in Mali. The hybrid yields were substantially superior to farmers’ local Guinea‐race varieties, with 20 to 80% higher means in both LP and HP environments. Average midparent and better‐parent heterosis estimates were, respectively, 78 and 48% under HP, and 75 and 42% under LP. Direct selection for yield under LP was predicted to be 20 to 60% more effective than indirect selection under HP conditions. The combining ability estimates provided initial insights into the potential benefit of germplasm from more eastern and humid regions of WA for developing a restorer pool distinct and complementary to the female pool from Mali and surrounding countries. Substantial yield superiorities of hybrids over local varieties suggested that a hybrid breeding strategy based on Guinea germplasm could help improve WA smallholder farmers’ livelihood.

Dry matter and nutritive value responses of native, naturalised and sown pasture species to soil Olsen P

The soil phosphorus (P) requirements of 18 species that included native grasses and naturalised legumes were compared with the predominant sown species (Trifolium subterraneum, Lolium perenne and Phalaris aquatica) in a series of glasshouse and field experiments based on the Long-term Phosphate Experiment at Hamilton, Victoria. The native grasses Austrostipa scabra and Rytidosperma caespitosum had the lowest external P requirements, as measured by the Olsen P at which 90% of maximal dry matter (DM) production was obtained, but were of low nutrient value as livestock feed. The naturalised legume Lotus corniculatus had the lowest external P requirement of the legumes, but had low DM production. The highest legume DM production under low-P conditions in the field and one glasshouse experiment was obtained for T. subterraneum. This was attributed to its large seed, which enables rapid initial growth and thus captures light and nutrient resources early in the growing season. However, it forms a relatively low proportion of the pasture sward in low-P soil under grazed mixed pasture conditions in the field. This was attributed to its relatively high nutritive value, which leads to it being preferentially grazed, leaving species that are either less palatable or less accessible to grazing livestock. This work suggests that, in low-P environments, there is a much stronger selection pressure favouring low relative palatability over P efficiency. In conclusion, to maintain desirable species in temperate low-input pastures, sufficient P needs to be applied to maintain fertility above a threshold at which the less-palatable species begin to invade.

Petunia- and Arabidopsis-Specific Root Microbiota Responses to Phosphate Supplementation

Phosphorus (P) is a limiting element for plant growth. Several root microbes, including arbuscular mycorrhizal fungi (AMF), have the capacity to improve plant nutrition and their abundance is known to depend on P fertility. However, how complex root-associated bacterial and fungal communities respond to various levels of P supplementation remains ill-defined. Here we investigated the responses of the root-associated bacteria and fungi to varying levels of P supply using 16S rRNA gene and internal transcribed spacer amplicon sequencing. We grew Petunia, which forms symbiosis with AMF, and the nonmycorrhizal model species Arabidopsis as a control in a soil that is limiting in plant-available P and we then supplemented the plants with complete fertilizer solutions that varied only in their phosphate concentrations. We searched for microbes, whose abundances varied by P fertilization, tested whether a core microbiota responding to the P treatments could be identified and asked whether bacterial and fungal co-occurrence patterns change in response to the varying P levels. Root microbiota composition varied substantially in response to the varying P application. A core microbiota was not identified as different bacterial and fungal groups responded to low-P conditions in Arabidopsis and Petunia. Microbes with P-dependent abundance patterns included Mortierellomycotina in Arabidopsis, while in Petunia, they included AMF and their symbiotic endobacteria. Of note, the P-dependent root colonization by AMF was reliably quantified by sequencing. The fact that the root microbiotas of the two plant species responded differently to low-P conditions suggests that plant species specificity would need to be considered for the eventual development of microbial products that improve plant P nutrition. [Formula: see text]Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Sensitivity of different Lupinus species to calcium under a low phosphorus supply.

To study mechanism underpinning the calcifuge habit of some Lupinus species, especially under low-phosphorus (P) conditions, Lupinus species that were likely to respond differently to calcium (Ca) availability were assembled, and the sensitivity to Ca under a low-P supply was assessed. Seven Lupinus species (9 genotypes, L.albus L. cv Kiev, L.albus L. P26766, L.angustifolius L. cv Mandelup, L.angustifolius L. P26723, L.luteus L. cv Pootalong, L.hispanicus ssp. bicolor Boiss. and Reut. P22999, L.pilosus Murr. P27440, L.cosentinii Guss. P27225, and L.atlanticus Gladst. P27219) were grown hydroponically at 10 or 6000μM Ca. Leaf symptoms, gas exchange and biomass were recorded; leaf and root nutrient concentrations were analysed, and the leaf cell types in which Ca and P accumulated were determined using elemental X-ray microanalyses. Calcium toxicity was demonstrated for L.angustifolius P26723, L.hispanicus ssp. bicolor. P22999, and L.cosentinii P27225, whereas the other species were tolerant of a high Ca supply under low-P conditions. In addition, genotypic differences in Ca toxicity were found within L.angustifolius. Most Ca accumulated in the mesophyll cells in all species, whereas most P was located in epidermal cells.

Leaf transpiration plays a role in phosphorus acquisition among a large set of chickpea genotypes.

Low availability of inorganic phosphorus (P) is considered a major constraint for crop productivity worldwide. A unique set of 266 chickpea (Cicer arietinum L.) genotypes, originating from 29 countries and with diverse genetic background, were used to study P-use efficiency. Plants were grown in pots containing sterilized river sand supplied with P at a rate of 10μgPg-1 soil as FePO4 , a poorly soluble form of P. The results showed large genotypic variation in plant growth, shoot P content, physiological P-use efficiency, and P-utilization efficiency in response to low P supply. Further investigation of a subset of 100 chickpea genotypes with contrasting growth performance showed significant differences in photosynthetic rate and photosynthetic P-use efficiency. A positive correlation was found between leaf P concentration and transpiration rate of the young fully expanded leaves. For the first time, our study has suggested a role of leaf transpiration in P acquisition, consistent with transpiration-driven mass flow in chickpea grown in low-P sandy soils. The identification of 6 genotypes with high plant growth, P-acquisition, and P-utilization efficiency suggests that the chickpea reference set can be used in breeding programmes to improve both P-acquisition and P-utilization efficiency under low-P conditions.

Response of energy microalgae Chlamydomonas reinhardtii to nitrogen and phosphorus stress.

Microalgae can effectively absorb nitrogen (N) and phosphorus (P) in wastewater, while growth characteristics can be affected by such nutrients. The influences of the N and P concentration on growth, biomass yield, protein yield, and cell ultrastructure of Chlamydomonas reinhardtii (C. reinhardtii) were investigated in this study. The results showed that, in the optimum conditions (24-72mg/L for N and 4.5-13.5mg/L for P), the final biomass and protein content of C. reinhardtii could reach maximum value, and the cell organelles (chloroplast, mitochondria,etc.) showed good structures with larger chloroplasts, and more and neater thylakoids. However, if the concentration of nutrients was much higher or lower than the optimal value, it would cause adverse effects on the growth of C. reinhardtii, especially in high nitrogen (1000mg/L) and low phosphorus (0.5mg/L) conditions. Under these extreme conditions, the ultrastructure of the cells was also damaged significantly as follows: the majority of the organelles were deformed, the chloroplast membrane became shrunken, and the mitochondria became swollen, even partial disintegrated (differing slightly under high-N and low-P conditions); furthermore, it is found that C. reinhardtii was more sensitive to low-P stress. On the basis of these results, our findings have general implications in the application of wastewater treatment.

Identification of genomic regions associated with low phosphorus tolerance in japonica rice (Oryza sativa L.) by QTL-Seq

ABSTRACTPhosphorus (P) is a major nutrient supporting rice productivity. Improving low-P tolerance of rice is expected to reduce dependence on P fertilizer, thereby reducing rice production costs and environmental impacts. This report describes the mapping of quantitative trait loci (QTL) associated with P deficiency tolerance in japonica rice. An F5 population derived from a cross of the low-P tolerant cultivar Akamai (Yamagata) and the sensitive cultivar Koshihikari was evaluated for shoot growth under low-P conditions. Then single nucleotide polymorphism (SNP) profiles of the low-P tolerant and sensitive bulks were compared on a genome-wide scale by QTL-Seq, a rapid QTL mapping method using next-generation sequencing technology. Results show a major QTL associated with low-P tolerance located on the long arm of chromosome 12. It has been named QTL for low-P tolerance 1 or qLPT1. SNPs were detected in 45 genes of qLPT1 region and the 5 genes were harboring synonymous SNPs, although none of them had been reported as involved in low-P tolerance. This result implies that the novel gene responsible for low-P tolerance exists in qLPT1. This study will contribute to the elucidation of mechanisms underlying low-P tolerance of Akamai and will facilitate the breeding of rice with low-P tolerance.

Revealing new insights into different phosphorus-starving responses between two maize (Zea mays) inbred lines by transcriptomic and proteomic studies

Phosphorus (P) is an essential plant nutrient, and deficiency of P is one of the most important factors restricting maize yield. Therefore, it is necessary to develop a more efficient program of P fertilization and breeding crop varieties with enhanced Pi uptake and use efficiency, which required understanding how plants respond to Pi starvation. To understand how maize plants adapt to P-deficiency stress, we screened 116 inbred lines in the field and identified two lines, DSY2 and DSY79 that were extreme low-P resistant and sensitive, respectively. We further conducted physiological, transcriptomic, and proteomic studies using the roots of DSY2 and DSY79 under normal or low-P conditions. The results showed that the low-P resistant line, DSY2 had larger root length, surface area and volume, higher root vitality, as well as acid phosphatase activity as compared with the low-P sensitive line, DSY79 under the low-P condition. The transcriptomic and proteomic results suggest that dramatic more genes were induced in DSY2, including the plant hormone signaling, acid phosphatase, and metabolite genes, as compared with DSY79 after being challenged by low-P stress. The new insights generated in this study will be useful toward the improvement of P-utilize efficiency in maize.

Generation mean analysis of phosphorus-use efficiency in freely nodulating soybean crosses grown in low-phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P-use efficiency (PUE) in low-P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high-PUE genotypes, two moderate-PUE genotypes and two inefficient-PUE genotypes, and obtained F1, F2, BC1 and BC2 populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P-incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100-seed weight, root dry weight and shoot dry matter per unit P for populations grown under low-P conditions. Dominance effects were generally greater than additive effects on PUE-related indices. These PUE indices can be used to select P-efficient soybean genotypes from segregating populations.

Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas.

Capturing the full growth potential in crops under future elevated CO2 (eCO2) concentrations would be facilitated by improved understanding of eCO2 effects on uptake and use of mineral nutrients. This study investigates interactions of eCO2, soil phosphorus (P), and arbuscular mycorrhizal (AM) symbiosis in Medicago truncatula and Brachypodium distachyon grown under the same conditions. The focus was on eCO2 effects on vegetative growth, efficiency in acquisition and use of P, and expression of phosphate transporter (PT) genes. Growth responses to eCO2 were positive at P sufficiency, but under low-P conditions they ranged from non-significant in M. truncatula to highly significant in B. distachyon Growth of M. truncatula was increased by AM at low P conditions at both CO2 levels and eCO2×AM interactions were sparse. Elevated CO2 had small effects on P acquisition, but enhanced conversion of tissue P into biomass. Expression of PT genes was influenced by eCO2, but effects were inconsistent across genes and species. The ability of eCO2 to partly mitigate P limitation-induced growth reductions in B. distachyon was associated with enhanced P use efficiency, and requirements for P fertilizers may not increase in such species in future CO2-rich climates.

Overcoming Phosphorus Deficiency in West African Pearl Millet and Sorghum Production Systems: Promising Options for Crop Improvement.

West Africa (WA) is among the most food insecure regions. Rapid human population growth and stagnating crop yields greatly contribute to this fact. Poor soil fertility, especially low plant available phosphorus (P) is constraining food production in the region. P-fertilizer use in WA is among the lowest in the world due to inaccessibility and high prices, often unaffordable to resource-poor subsistence farmers. This article provides an overview of soil P-deficiency in WA and opportunities to overcome it by exploiting sorghum and pearl millet genetic diversity. The topic is examined from the perspectives of plant breeding, soil science, plant physiology, plant nutrition, and agronomy, thereby referring to recent results obtained in a joint interdisciplinary research project, and reported literature. Specific objectives are to summarize: (1) The global problem of P scarcity and how it will affect WA farmers; (2) Soil P dynamics in WA soils; (3) Plant responses to P deficiency; (4) Opportunities to breed for improved crop adaptation to P-limited conditions; (5) Challenges and trade-offs for improving sorghum and pearl millet adaptation to low-P conditions in WA; and (6) Systems approaches to address soil P-deficiency in WA. Sorghum and pearl millet in WA exhibit highly significant genetic variation for P-uptake efficiency, P-utilization efficiency, and grain yield under P-limited conditions indicating the possibility of breeding P-efficient varieties. Direct selection under P-limited conditions was more efficient than indirect selection under high-P conditions. Combining P-uptake and P-utilization efficiency is recommendable for WA to avoid further soil mining. Genomic regions responsible for P-uptake, P-utilization efficiency, and grain yield under low-P have been identified in WA sorghum and pearl millet, and marker-assisted selection could be possible once these genomic regions are validated. Developing P-efficient genotypes may not, however, be a sustainable solution in itself in the long-term without replenishing the P removed from the system in harvested produce. We therefore propose the use of integrated soil fertility management and systems-oriented management such as enhanced crop-tree-livestock integration in combination with P-use-efficiency-improved varieties. Recycling P from animal bones, human excreta and urine are also possible approaches toward a partially closed and efficient P cycle in WA.

Sensitivity to dietary phosphorus limitation in native vs. invasive lineages of a New Zealand freshwater snail

Why some species and lineages are more likely to be invasive than others is one of the most important unanswered questions in basic and applied biology. In particular, the relative contributions to the invasion process of factors like pre-adaptation to invasiveness in the native range, evolution post-colonization, and random vs. non-random sampling of colonist lineages remain unclear. We use a powerful common garden approach to address the potential for a role for sensitivity to nutrient limitation in determining the invasiveness of particular lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail that has become globally invasive. We quantified specific growth rate (SGR), an important fitness-related trait in this species, under high phosphorus (P) vs. low-P conditions for a diverse set of native and invasive P.antipodarum. This experiment revealed that native-range P.antipodarum experience a more severe decline in SGR in low-P conditions relative to SGR in high-P conditions than their invasive range counterparts. Although these results suggest resilience to P limitation in invasive lineages, the absence of significant absolute differences in SGR between native and invasive lineages indicates that a straightforward connection between response to P limitation and invasiveness in P.antipodarum is unlikely. Regardless, our data demonstrate that invasive vs. native lineages of P.antipodarum exhibit consistently different responses to an important environmental variable that is rarely studied in the context of invasion success. Further studies directed at exploring and disentangling the roles of sampling effects, selection on preexisting variation, and evolution after colonization will be required to provide a comprehensive picture of the role (or lack thereof) of nutrient limitation in the global invasion of P.antipodarum, as well for as other invasive taxa.

A genome-wide expression profile analysis reveals active genes and pathways coping with phosphate starvation in soybean.

BackgroundPhosphorus is one of the most important macronutrients that is required for plant growth and development. However, stress under low-P conditions has become a limiting factor that affects crop yields and qualities. Plants have developed strategies to cope with this, while few genes associated with low-P tolerance have been identified in soybean.ResultsGenome-wide analyses were performed on the roots and leaves of a low-P-tolerant accession and a low-P-sensitive accession which were identified by hydroponic experiments under different P treatments. Through comparative analyses on the differently expressed genes, we explored 42 common genes that were highly correlated to low-P stress. The functional classification of these genes revealed 24 Gene Ontology (GO) terms of biological process including response to oxidation reduction, hormone stimuli, and biotic and abiotic stimuli. Additionally, three common pathways were identified.ConclusionsThese results could not only promote the work on the molecular regulation mechanism under low-P stress in soybean, but also facilitate the cultivation of high-phosphorus-acquisition and high-phosphorus-utilization soybean varieties.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2558-9) contains supplementary material, which is available to authorized users.

Association analysis of low-phosphorus tolerance in West African pearl millet using DArT markers

Pearl millet [Pennisetum glaucum (L.) R. Br.] is a food security crop in the harshest agricultural regions of the world. While low soil phosphorus (P) availability is a big constraint on its production, especially in West Africa (WA), information on genomic regions responsible for low-P tolerance in pearl millet is generally lacking. We present the first report on genetic polymorphisms underlying several plant P-related parameters, flowering time (FLO) and grain yield (GY) under P-limiting conditions based on 285 diversity array technology markers and 151 West African pearl millet inbred lines phenotyped in six environments in WA under both high-P and low-P conditions. Nine markers were significantly associated with P-related traits, nine markers were associated with FLO, whereas 13 markers were associated with GY each explaining between 5.5 and 15.9 % of the observed variation. Both constitutive and adaptive associations were observed for FLO and GY, with markers PgPb11603 and PgPb12954 being associated with the most stable effects on FLO and GY, respectively, across locations. There were a few shared polymorphisms between traits, especially P-efficiency-related traits and GY, implying possible colocation of genomic regions responsible for these traits. Our findings help bridge the gap between quantitative and molecular methods of studying complex traits like low-P tolerance in WA. However, validation of these markers is necessary to determine their potential applicability in marker-assisted selection programs targeting low-P environments, which are especially important in WA where resource-poor farmers are expected to be the hardest hit by the approaching global P crisis.

Contrasting responses of root morphology and root-exuded organic acids to low phosphorus availability in three important food crops with divergent root traits.

Phosphorus (P) is an important element for crop productivity and is widely applied in fertilizers. Most P fertilizers applied to land are sorbed onto soil particles, so research on improving plant uptake of less easily available P is important. In the current study, we investigated the responses in root morphology and root-exuded organic acids (OAs) to low available P (1 μM P) and sufficient P (50 μM P) in barley, canola and micropropagated seedlings of potato-three important food crops with divergent root traits, using a hydroponic plant growth system. We hypothesized that the dicots canola and tuber-producing potato and the monocot barley would respond differently under various P availabilities. WinRHIZO and liquid chromatography triple quadrupole mass spectrometry results suggested that under low P availability, canola developed longer roots and exhibited the fastest root exudation rate for citric acid. Barley showed a reduction in root length and root surface area and an increase in root-exuded malic acid under low-P conditions. Potato exuded relatively small amounts of OAs under low P, while there was a marked increase in root tips. Based on the results, we conclude that different crops show divergent morphological and physiological responses to low P availability, having evolved specific traits of root morphology and root exudation that enhance their P-uptake capacity under low-P conditions. These results could underpin future efforts to improve P uptake of the three crops that are of importance for future sustainable crop production.

Duplicate and conquer: multiple homologs of PHOSPHORUS-STARVATION TOLERANCE1 enhance phosphorus acquisition and sorghum performance on low-phosphorus soils.

Low soil phosphorus (P) availability is a major constraint for crop production in tropical regions. The rice (Oryza sativa) protein kinase, PHOSPHORUS-STARVATION TOLERANCE1 (OsPSTOL1), was previously shown to enhance P acquisition and grain yield in rice under P deficiency. We investigated the role of homologs of OsPSTOL1 in sorghum (Sorghum bicolor) performance under low P. Association mapping was undertaken in two sorghum association panels phenotyped for P uptake, root system morphology and architecture in hydroponics and grain yield and biomass accumulation under low-P conditions, in Brazil and/or in Mali. Root length and root surface area were positively correlated with grain yield under low P in the soil, emphasizing the importance of P acquisition efficiency in sorghum adaptation to low-P availability. SbPSTOL1 alleles reducing root diameter were associated with enhanced P uptake under low P in hydroponics, whereas Sb03g006765 and Sb03g0031680 alleles increasing root surface area also increased grain yield in a low-P soil. SbPSTOL1 genes colocalized with quantitative trait loci for traits underlying root morphology and dry weight accumulation under low P via linkage mapping. Consistent allelic effects for enhanced sorghum performance under low P between association panels, including enhanced grain yield under low P in the soil in Brazil, point toward a relatively stable role for Sb03g006765 across genetic backgrounds and environmental conditions. This study indicates that multiple SbPSTOL1 genes have a more general role in the root system, not only enhancing root morphology traits but also changing root system architecture, which leads to grain yield gain under low-P availability in the soil.

Sm–Nd geochronology of the Erro-Tobbio gabbros (Ligurian Alps, Italy): Insights into the evolution of the Alpine Tethys

article The Alpine-Apennine ophiolites are considered analogs of the oceanic lithosphere formed at ocean-continent transition zones and very slow oceanic spreading centers. They are lithospheric remnants of the Jurassic Piedmont-Ligurian ocean, a branch of the Mesozoic Tethys separating the European and Adriatic continental margins. Previous geochronological studies on gabbroic rocks of the Alpine Tethys indicated a rather large time span of crust formation. In this paper, we present Sm-Nd geochronological data on well-preserved olivine gabbros intruded in mantle peridotites from the Erro-Tobbio ophiolitic unit (Ligurian Alps, Italy). Borghini et al. (2007) documented that these gabbros crystallized at low-P conditions (b5 kb) from primitive N-MORB melts, similar to many gabbroic rocks from Alpine-Apennine ophiolites. Here four plagioclase-clinopyroxene internal Sm-Nd isochrons are presented, yielding equivalent ages and initial eNd values. The ages are 177 ± 7 Ma, 179 ± 7 Ma, 178 ± 21 Ma and 182 ± 19 Ma, reflecting a weighted mean age of 178 ± 5 Ma with initial eNd of 9.2 ± 0.4 (2SD). Similar ages are only recorded in gabbroic rocks from the External Liguride Units (Northern Apennines) and represent the oldest ages available for the gabbroic crust of the Alpine Tethys. These Mg-rich gabbros can therefore be considered as representative of early (syn-rift) melt intrusions in thinned lithospheric mantle exhumed at ocean-continent transition domains, likely close to Adria's continental margin, similar to the hyper-extended Western Iberian Margin. Our new results together with previous ages of the Tethys oceanic crust allow for the reconstruction of the spatial distribution of oceanic gabbros over time, and evaluation of the spreading and propagation rates of this paleo-ocean. The northward propagation rifting velocity, estimated at ~5 cm/year, is presumably higher than the lateral spreading rate of ~2 cm/year. Our rate estimates suggest that the Red Sea is a present-day analog for the evolution of the Piedmont-Ligurian ocean. © 2014 Elsevier B.V. All rights reserved.

The involvement of expansins in responses to phosphorus availability in wheat, and its potentials in improving phosphorus efficiency of plants

Phosphorus (P) is a critical macronutrient required for numerous functions in plants and is one of the limiting factors for plant growth. Phosphate availability has a strong effect on root system architecture. Expansins are encoded by a superfamily of genes that are organized into four families, and growing evidence has demonstrated that expansins are involved in almost all aspects of plant development, especially root development. In the current study, we demonstrate that expansins may be involved in increasing phosphorus availability by regulating the growth and development of plant roots. Multiple expansins (five α- and nine β-expansin genes) were up- or down-regulated in response to phosphorus and showed different expression patterns in wheat. Meanwhile, the expression level of TaEXPB23 was up-regulated at excess-P condition, suggesting the involvement of TaEXPB23 in phosphorus adaptability. Overexpression of the TaEXPB23 resulted in improved phenotypes, particularly improved root system architecture, as indicated by the increased number of lateral roots in transgenic tobacco plants under excess-P and low-P conditions. Thus, these transgenic plants maintained better photosynthetic gas exchange ability than the control under both P-sufficient and P-deficient conditions.