low-P Availability Research Articles

Multi-trait association mapping for phosphorous efficiency reveals flexible root architectures in sorghum

BackgroundOn tropical regions, phosphorus (P) fixation onto aluminum and iron oxides in soil clays restricts P diffusion from the soil to the root surface, limiting crop yields. While increased root surface area favors P uptake under low-P availability, the relationship between the three-dimensional arrangement of the root system and P efficiency remains elusive. Here, we simultaneously assessed allelic effects of loci associated with a variety of root and P efficiency traits, in addition to grain yield under low-P availability, using multi-trait genome-wide association. We also set out to establish the relationship between root architectural traits assessed in hydroponics and in a low-P soil. Our goal was to better understand the influence of root morphology and architecture in sorghum performance under low-P availability.ResultIn general, the same alleles of associated SNPs increased root and P efficiency traits including grain yield in a low-P soil. We found that sorghum P efficiency relies on pleiotropic loci affecting root traits, which enhance grain yield under low-P availability. Root systems with enhanced surface area stemming from lateral root proliferation mostly up to 40 cm soil depth are important for sorghum adaptation to low-P soils, indicating that differences in root morphology leading to enhanced P uptake occur exactly in the soil layer where P is found at the highest concentration.ConclusionIntegrated QTLs detected in different mapping populations now provide a comprehensive molecular genetic framework for P efficiency studies in sorghum. This indicated extensive conservation of P efficiency QTL across populations and emphasized the terminal portion of chromosome 3 as an important region for P efficiency in sorghum. Increases in root surface area via enhancement of lateral root development is a relevant trait for sorghum low-P soil adaptation, impacting the overall architecture of the sorghum root system. In turn, particularly concerning the critical trait for water and nutrient uptake, root surface area, root system development in deeper soil layers does not occur at the expense of shallow rooting, which may be a key reason leading to the distinctive sorghum adaptation to tropical soils with multiple abiotic stresses including low P availability and drought.

Drought-tolerant rhizobacteria with predicted functional traits enhanced wheat growth and P uptake under moderate drought and low P-availability

This study aims to investigate the effect of isolated drought-tolerant rhizobacteria, spanning various groups, such as nitrogen-fixing bacteria (NFB), phosphate solubilizing bacteria (PSB), and other plant growth promoting rhizobacteria (PGPR), on the growth of wheat (Triticum durum) plants, focusing on various morphological and physiological responses under moderate drought and low-P availability. Among 343 rhizobacterial morphotypes, 16 exhibited tolerance to NaCl and PEG-6000. These included 8 PSB, 4 NFB, and 4 osmotolerant-PGPR groups, distributed across 14 different genera. Biochemical characterization showcased diverse PGP capabilities, particularly in P solubilization. The dynamic responses of drought-tolerant PSB to salt and PEG-6000-induced drought stress involved variations in organic acid (OA) secretion, with specific acids, including palmitic, lactic, and stearic, playing crucial roles in enhancing available P fractions. Inoculation with rhizobacteria significantly increased both shoot (SDW) and root (RDW) dry weights of wheat plants, as well as rhizosphere available P. PSB11 (Arthrobacter oryzae) emerged as the most effective strain, plausibly due to its positive impact on root morphological traits (length, surface, and volume). Other isolates, PSB10 (Priestia flexa), PSB13 (Bacillus haynesii), and particularly PGPR2 (Arthrobacter pascens) significantly increased shoot P content (up to 68.91 %), with a 2-fold increase in chlorophyll content. The correlation analysis highlighted positive associations between SDW, shoot P content, chlorophyll content index (CCI), and leaf area. Additionally, a negative correlation emerged between microbial biomass P and root morphophysiological parameters. This pattern could be explained by reduced competition between plants and rhizobacteria for accessible P, as indicated by low microbial biomass P and strong plant growth. Our investigation reveals the potential of drought-tolerant rhizobacteria in enhancing wheat resilience to moderate drought and low-P conditions. This is demonstrated through exceptional performance in influencing root architecture, P utilization efficiency, and overall plant physiological parameters. Beyond these outcomes, the innovative isolation procedure employed, targeting rhizobacteria from diverse groups, opens new avenues for targeted isolation techniques. This unique approach contributes to the novelty of our study, offering promising prospects for targeted bioinoculants in mitigating the challenges of drought and P deficiency in wheat cultivation.

Eucalypt species drive rhizosphere bacterial and fungal community assembly but soil phosphorus availability rearranges the microbiome.

Soil phosphorus (P) availability may limit plant growth and alter root-soil interactions and rhizosphere microbial community composition. The composition of the rhizosphere microbial community can also be shaped by plant genotype. In this study, we examined the rhizosphere microbial communities of young plants of 24 species of eucalypts (22 Eucalyptus and two Corymbia species) under low or sufficient soil P availability. The taxonomic diversity of the rhizosphere bacterial and fungal communities was assessed by 16S and 18S rRNA gene amplicon sequencing. The taxonomic modifications in response to low P availability were evaluated by principal component analysis, and co-inertia analysis was performed to identify associations between bacterial and fungal community structures and parameters related to plant growth and nutritional status under low and sufficient soil P availability. The sequencing results showed that while both soil P availability and eucalypt species influenced the microbial community assembly, eucalypt species was the stronger determinant. However, when the plants are subjected to low P-availability, the rhizosphere selection became strongest. In response to low P, the bacterial and fungal communities in the rhizosphere of some species showed significant changes, whereas in others remained relatively constant under low and sufficient P. Co-inertia analyses revealed a significant co-dependence between plant nutrient contents and bacterial and fungal community composition only under sufficient P. By contrast, under low P, bacterial community composition was related to plant biomass production. In conclusion, our study shows that eucalypt species identity was the main factor modulating rhizosphere microbial community composition; significant shifts due to P availability were observed only for some eucalypt species.

Genotypic variability for tolerance to low soil phosphorus availability in faba bean (Vicia faba L.)

The capacity of legumes to fix atmospheric dinitrogen in partnership with rhizobia provides an input-saving and resource-conserving alternative, thereby reducing the need for chemical fertilizers while enhancing overall crop productivity. However, low soil nutrient availability, notably phosphorus (P), is among the most nutrient limitations for legumes, since legume nodules responsible for N2 fixation have a high P requirement. In order to explore the genetic variability for P uptake and use efficiency in low-P availability in soils, three faba bean genotypes namely Sidi Aich, Castel and Diva were studied in two field sites (S1 and S2) over two growing seasons 2018 and 2019. At flowering stage, plants were harvested and analyzed for their nodulation, growth, P content and yield. Results indicate that low-P availability in the soil of S1 significantly limited plant growth, nodulation, and grain yield for all genotypes though with highest extent for Diva and Castel. We found a significant correlation between nodule growth of all genotypes and Olsen-P content in the rhizosphere soil during two growing seasons. It is concluded that the genotypes selected for their P uptake and use efficiency had a higher yield and could best adapt to low-P availability under field conditions.

Silicon- and Phosphate-Solubilizing Pseudomonas alkylphenolica PF9 Alleviate Low Phosphorus Availability Stress in Alfalfa (Medicago sativa L.)

Low phosphorus (P) availability is a major limiting factor facing current agriculture in several agricultural areas. Many P fertilizers are applied to enhance P availability; however, the major part is likely to lose due to various processes related to P cycle. Silicon (Si) treatment and P-solubilizing bacteria inoculation have been emerged as a promising way to improve plant P nutrition. This study aimed to investigate the synergistic effects of Si treatment and Pseudomonas alkylphenolica PF9 strain inoculation on plant growth, P nutrition, acid phosphatase (APase) activity, oxidative stress markers, and antioxidant metabolism in the Moroccan alfalfa population Oued Lmalah (OL) under low P availability. Results revealed a significant reduction in dry biomass, plant height, leaf number, and area under low P conditions. P deficiency also altered P nutrition and chlorophyll (Chl) content. However, P-deficient alfalfa plants treated with Si or inoculated with PF9 strain displayed higher plant growth, Chl content, and remarkably the effect was much higher when Si was applied together with PF9 strain. Moreover, the simultaneous application of Si and PF9 strain to the P-deficient alfalfa plants improved APase activity and as a result, P contents in both the shoots and roots. Results also showed that the application of both the Si and PF9 counteracted the low P availability stress-induced oxidative damage by lowering the accumulation of reactive oxygen species (ROS), electrolyte leakage, and lipid peroxidation. This seems to be related to the ability of both the Si and PF9 strain to modulate both the enzymatic and non-enzymatic antioxidant molecules including superoxide dismutase activity, total polyphenols, flavonoids, and proline contents. Our findings suggest that the combined application of Si and P. alkylphenolica PF9 strain could be a promising way for improving growth of alfalfa under low-P availability.

Effects of Scion Variety on the Phosphorus Efficiency of Grafted Camellia oleifera Seedlings

Grafting provides a way to improve tolerance to low phosphorus (P) stress for plants, and has been extensively applied in commercial cultivars grafted onto appropriate rootstocks. However, little literature is available concerning the scion-mediated effect on P efficiency in grafted plants. In this study, three different Camellia oleifera Abel. scion cultivars (G8, G83-1, and W2) were grafted onto the same rootstock (W2) under controls (0.5 mM) and low-P (0 mM) availability for eight months. The results showed that the scions significantly affected root-to-shoot weight ratios, the root morphology with a diameter larger than 1 mm, P accumulation, and the P utilization efficiency (PUE) of the root. A higher increase in the root-to-shoot weight ratio under the low-P supply was observed in the G83-1/W2 (26.15%) than in the G8/W2 (0%) and the W2/W2 (5.32%). Root PUE of the scion G8, G83-1, and W2 was improved by up to 113.73%, 45.46%, and 20.97% under the low-P supply. Moreover, G8/W2 exhibited higher shoot P accumulation and the highest root PUE under the low-P supply, indicating a high capability to tolerate P deficiency by maximizing the cost-effectiveness of P remobilization to photosynthetic organs. This suggested the vigorous variety of G8 could be a promising scion to improve grafted C. oleifera tolerance to low-P stress. Our results would have important implications for exploration and identification of a superior scion variety to enhance the ability of resistance concerning P deficiency stress in C. oleifera.

Farmyard manure application increases spikelet fertility and grain yield of lowland rice on phosphorus-deficient and cool-climate conditions in Madagascar highlands

ABSTRACT Phosphorus (P) deficiency is a major yield constraint for lowland rice production in the tropics. As P-fertilizer resources are finite, alternative fertilizer management is needed for sustainable rice production. We examined whether farmyard manure (FYM), a major nutrient source for smallholder farms, can overcome issue in typical P-deficient lowlands in the central highlands of Madagascar. A multi-location trial in sites varying in altitude and soil P availability, clarified that the effect of both FYM and mineral P fertilizer application on grain yield greatly increased at higher elevation and when the soil oxalate-extractable P content was <100 mg kg−1. The yield increase was attributable to improved grain fertility, probably because FYM and mineral P applications decreased days to flowering and avoided low temperatures at late growth stages. Nutrient uptake assessment clarified that despite its relatively low P content, FYM had an equivalent effect on plant P uptake to those of mineral P fertilizer. We concluded that FYM application was effective in low-P availability soils at high altitude, as alternative of mineral P fertilizer. Further monitoring is required to assess the effect of consecutive FYM use on grain yield and plant nutrient uptake in the context of cold stress induced by P deficiency.

Synergistic effect of Pseudomonas alkylphenolica PF9 and Sinorhizobium meliloti Rm41 on Moroccan alfalfa population grown under limited phosphorus availability.

This study looked at the synergistic effect of Pseudomonas alkylphenolica PF9 and Sinorhizobium meliloti Rm41 on the Moroccan alfalfa population (Oued Lmaleh) grown under symbiotic nitrogen fixation and limited phosphorus (P) availability. The experiment was conducted in a growth chamber and after two weeks of sowing, the young seedlings were inoculated with Sinorhizobium meliloti Rm41 alone or combined with a suspension of Pseudomonas alkylphenolica PF9. Then, the seedlings were submitted to limited available P (insoluble P using Ca3HPO4) versus a soluble P form (KH2PO4) at a final concentration of 250 μmol P·plant−1·week−1. After two months of P stress, the experiment was evaluated through some agro-physiological and biochemical parameters. The results indicated that the inoculation of alfalfa plants with Sinorhizobium strain alone or combined with Pseudomonas strain significantly (p < 0.001) improved the plant growth, the physiological and the biochemical traits focused in comparison to the uninoculated and P-stressed plants. For most sets of parameters, the improvement was more obvious in plants co-inoculated with both strains than in those inoculated with Sinorhizobium meliloti Rm41 alone. In fact, under limited P-availability, the co-inoculation with two strains significantly (p < 0.01) enhanced the growth of alfalfa plants evaluated by fresh and dry biomasses, plant height and leaf area. The results indicated also that the enhancement noted in plant growth was positively correlated with the shoot and root P contents. Furthermore, the incensement in plant P contents in response to bacterial inoculation improved cell membrane stability, reflected by low malonyldialdehyde (MDA) and electrolyte leakage (EL) contents, and photosynthetic-related parameters such as chlorophyll contents, the maximum quantum yield of PS II (Fv/Fm) and stomatal conductance (gs). Our findings suggest that Pseudomonas alkylphenolica PF9 can act synergistically with Sinorhizobium meliloti Rm41 in promoting alfalfa growth under low-P availability.

Drainage class and soil phosphorus availability shape microbial communities in Irish grasslands

Soil drainage and phosphorus (P) availability are considered indicators of management intensity in pasture-based agriculture supporting livestock. However, microbial adaptations to P-availability according to soil drainage class are rarely investigated. We hypothesized that well-drained grasslands with high P-availability will sustain a distinctive soil microbiota when compared to poorly-drained grasslands with low-P availability. The relationship between soil drainage, plant available P and grassland microbial communities was evaluated among well-drained sites with high- or low-P and poorly-drained sites with high- or low-P, using fingerprinting, next-generation sequencing and quantitative PCR. Bacterial community structures were primarily affected by drainage as well as significantly separated between a combination of drainage and P availability i.e. low-P and poorly drained versus high-P and well drained. Abundance of the bacterial phylum Actinobacteria was significantly higher in well-drained high-P soils while Firmicutes were more abundant in well-drained low-P soils. Soil fungal communities responded to both drainage status and plant available P. Fungal phyla such as Basidiomycota responded strongly towards availability of P, while Glomeromycota were most abundant in poorly drained low-P soils. The diversity of the alkaline phosphatase gene phoD responded more clearly to drainage than availability of P. Of the other environmental factors, soil pH significantly affected the bacterial and fungal communities structure analyzed. This study suggests that while bacteria and fungi are affected by a combination of soil drainage and P availability in Irish grassland soils, drainage has a more profound influence on bacterial communities than P availability.

Divergent root P uptake strategies of three temperate grassland forage species

Temperate grasslands are affected by nutrient deficiency and this deficiency is one of the main limiting factors for forage production, such as the grasslands of the Salado River Basin (Argentina), which exhibit low-P availability for plant growth. Alternatives to increase forage production include the selection of plant species adapted to grow under P deficiency, P fertilization, and arbuscular mycorrhizal (AM) fungi. In a pot experiment, we investigated the effect of low and high-P doses and AM fungi on the development of three forage species. The interaction of P addition and AM fungi increased L. tenuis (legume) biomass production and improve P nutrition, even with high-P dose, because of its higher P requirement to grow and lower ability for P uptake than grasses. High-P increased the biomass of S. arundinaceus (C3 grass) and P. coloratum (C4 grass), and AM fungi did not directly impact on plant growth of grasses, but did impact on P nutrition at either level of P fertilization. The specific P uptake of non-fertilized L. tenuis plants increased 97% due to AM inoculation and was the highest value among the three non-fertilized species. Furthermore, the specific P uptake of non-fertilized grasses was similar, despite the C metabolic pathway and AM fungi, but the specific root length was 70.88% lower for P. coloratum than for S. arundinaceus. Thus, the main strategy of L. tenuis was AM association, whereas that of S. arundinaceus was the highest ability of the root system to explore the soil. In P. coloratum, the strategy could not be explained by changes in specific root length or AM association. Our results would be an advantageous first step to promote better management of forage land sustainably while increasing forage production and preserve the beneficial effects of native AM communities in the Salado River Basin.

Coffee seedling growthafter legume cultivation in soils with contrasting phosphorus contents

Coffee seedling growth depends on soil phosphorus (P) availability and may be influenced by from pre-cultivation with legumes. Efficient and sustainable ways to increase the bioavailability of P through the recovery of P adsorbed by the soil matrix should be sought. This study proposed to evaluate the growth and P-use efficiency of coffee seedlings cultivated in soils with different P availability after cultivation with legumes. The experiment was carried out in a fully randomized design. Treatments were arranged in a factorial scheme [(2 x 4) + 1]: two soil types, pre-cultivation with four legume species, and one control (withoutpre-cultivation). The studied soils comprised a Typical Acriferic Red Oxisol (LVwf) with low-P availability and a Typical Chernossolic Litholytic Entisol (RLm) with high-P availability. The legume species Crotalaria juncea, Cajanus cajan, Canavalia ensiformis, and Mucuna aterrima were previously cultivated for 45 days. Afterwards, coffee seedlings were transplanted to the pots, which were then grown for 120 days until evaluations. We assessed the following parameters: plant height (H), stem diameter (SD), shoot dry matter (SDM), root dry matter (RDM), total dry matter (TDM), and shoot contents of macronutrients. Our results showed that coffee seedlings grew more when cultivated in the high-P availability soil, with increments of 13.05% in H, 4.86% in SD, 46.98% in SDM, 17.61% in RDM, and 41.80% in TDM.We also observed an increase of 28.09% in shoot P contents for coffee seedlings grown in RLm. Moreover, pre-cultivationwith C. juncea provided the largest increases in coffee seedling growth compared to the control. When grown after C. ensiformis cultivation, coffee seedlings had the highest shoot contents of P, Ca, Mg, and S, which, compared to control, increased by 45%, 39%, 18%, and 17%, respectively. Keywords: Canavalia ensiformis; Crotalaria juncea; Coffea arabica; phosphate fertilization; nutritional efficiency.

Response of foliar functional traits to experimental N and P addition among overstory and understory species in a tropical secondary forest

The plasticity of morphological, physiological and developmental traits can reflect the plant adaptation to diverse environmental changes. How the foliar morphological and physiological traits with different functional groups in response to N and P fertilization is still unclear in tropical forests. Here, we employed a nine-year manipulative field experiment with nitrogen (N) and phosphorus (P) addition to investigate the foliar morphological and physiological traits as well as the N and P stoichiometry within the overstory and understory species in a tropical secondary forest of southern China. Our results showed that the N and P addition did not significantly change leaf morphological traits (leaf length, width, and ratios of length:width, leaf mass per area, LMA) in most of the studied species. The effects of N and/or P addition on leaf photosynthetic pigments were species-specific variation regardless of the overstory and understory species. However, the leaf N:P ratios of two understory species were significantly influenced by P addition while leaf N:P ratios in all overstory plants were not affected by P fertilization. Combined with the change of leaf N:P ratios under nine-year fertilization experiment, the understory plants were primarily limited by P availability, while the overstroy trees were co-limited by N and P availability in this tropical forest. Given that, we recommend that the constant leaf morphological traits of overstory and understory species in response to exogenous long-term N and P addition may be an important mechanism for adapting to low-P availability soil.

Eucalypts and low phosphorus availability: between responsiveness and efficiency

Twenty-four species of eucalypts were studied regarding their ability to grow under low P and their responsiveness to P inputs. Growth and photosynthesis-related parameters were evaluated. Growth of all species was influenced by low P availability. No significant correlation was found between leaf P concentration and biomass, indicating that P concentrations in leaves cannot be solely considered an indication of the responsiveness to P in eucalypts. Species responsive to P-input (high agronomic P efficiency values, APE) were those with low P use efficiency - PUE (here assessed as relative efficiency of P-use, REP) and low P uptake efficiency (PUpE). But, non-responsive species were related to higher P-efficiency under low soil P-availability. Eucalyptus tereticornis, E. cladocalyx, E. globulus and E. camaldulensis were efficient under low-P availability. Whereas, E. crebra and E acmenoides were the most responsive species, with high APE, suggesting that for these species P-inputs are needed to guarantee plant growth. The root:shoot ratio remained constant at different P availabilities, suggesting that biomass allocation towards the root in response to P and greater investment in roots were not correlated with greater PUE. Under limited P, E. robusta and E. botryoides exhibited low foliar P contents and higher root:shoot ratios than those of other species with higher P contents, indicating that greater root investment does not necessarily result in greater PUE. The results suggest that the divergence among species is probably related to different mechanisms, which may improve P-use efficiency.

The genetic architecture of phosphorus efficiency in sorghum involves pleiotropic QTL for root morphology and grain yield under low phosphorus availability in the soil

BackgroundPhosphorus (P) fixation on aluminum (Al) and iron (Fe) oxides in soil clays restricts P availability for crops cultivated on highly weathered tropical soils, which are common in developing countries. Hence, P deficiency becomes a major obstacle for global food security. We used multi-trait quantitative trait loci (QTL) mapping to study the genetic architecture of P efficiency and to explore the importance of root traits on sorghum grain yield on a tropical low-P soil.ResultsP acquisition efficiency was the most important component of P efficiency, and both traits were highly correlated with grain yield under low P availability. Root surface area was positively associated with grain yield. The guinea parent, SC283, contributed 58% of all favorable alleles detected by single-trait mapping. Multi-trait mapping detected 14 grain yield and/or root morphology QTLs. Tightly linked or pleiotropic QTL underlying the surface area of fine roots (1–2 mm in diameter) and grain yield were detected at positions 1–7 megabase pairs (Mb) and 71 Mb on chromosome 3, respectively, and a root diameter/grain yield QTL was detected at 7 Mb on chromosome 7. All these QTLs were near sorghum homologs of the rice serine/threonine kinase, OsPSTOL1. The SbPSTOL1 genes on chromosome 3, Sb03g006765 at 7 Mb and Sb03g031690 at 60 Mb were more highly expressed in SC283, which donated the favorable alleles at all QTLs found nearby SbPSTOL1 genes. The Al tolerance gene, SbMATE, may also influence a grain yield QTL on chromosome 3. Another PSTOL1-like gene, Sb07g02840, appears to enhance grain yield via small increases in root diameter. Co-localization analyses suggested a role for other genes, such as a sorghum homolog of the Arabidopsis ubiquitin-conjugating E2 enzyme, phosphate 2 (PHO2), on grain yield advantage conferred by the elite parent, BR007 allele.ConclusionsGenetic determinants conferring higher root surface area and slight increases in fine root diameter may favor P uptake, thereby enhancing grain yield under low-P availability in the soil. Molecular markers for SbPSTOL1 genes and for QTL increasing grain yield by non-root morphology-based mechanisms hold promise in breeding strategies aimed at developing sorghum cultivars adapted to low-P soils.

High yields in a low-P tolerant recombinant inbred line of common bean under field conditions

Low phosphorus (P) availability is a primary factor that limits the production of common bean (Phaseolus vulgaris L.) in many parts of the world, especially when plant growth depends on N2 fixation. In order to understand how common bean copes with this nutritional constraint, two recombinant inbred lines (RILs) of common bean namely RILs 115 and 147 were studied in the field conditions during three growing seasons from 2012 to 2014. At flowering stage, plants were harvested and analyzed for their nodulation, growth, P content and yield. Results showed that for RIL115, the nodulation (43%), shoot (28%) and root growth (32%) was higher than for RIL147 in a low-P availability soil whatever the growing season. In addition, RIL115 had better growth and efficiency in use of P for the rhizobial symbiosis (7.29 mg nodule dry weight mg−1 nodule P) about twice higher may be involved in tolerance to low-P, and to be a useful marker for field data. At harvest, the RIL115 showed higher grain yield (1146 kg ha−1) than the RIL147 (1045 kg ha−1). It is concluded that the genotype of RIL 115 had a higher yield and could best adapt to low-P availability under field condition.

Calcium and iron as key drivers of brown moss composition through differential effects on phosphorus availability

Brown moss-dominated rich fens are characterized by minerotrophic conditions, in which calcium (Ca) and iron (Fe) concentrations show large variations. We examined the relative importance of Ca and Fe in relation to the occurrence of three typical brown moss species: Scorpidium scorpioides, Scorpidium cossonii, and Hamatocaulis vernicosus. Peat chemistry was examined in 24 stands of brown moss-dominated rich fens: 12 in the Netherlands and 12 in central Sweden. Ca and Fe turned out to be important drivers of brown moss composition. Fens dominated by Scorpidium scorpioides or Scorpidium cossonii were characterized by high pore water Ca-concentrations and total soil Ca-contents, but low P-availability. In these Ca-rich, but Fe-poor fens, foliar N:P ratios of vascular vegetation exceeded 20 g g−1, indicating phosphorus (P)-limitation due to Ca-P precipitation or low P-sorption capacity due to low Fe-levels. In contrast, fens dominated by Hamatocaulis vernicosus were characterized by high pore water Fe-concentrations and total soil Fe-contents, but also relatively high P-availability. N:P ratios in these fens were below 13.5 g g−1, indicating potential nitrogen (N)-limitation. We conclude that the relative roles of Ca and Fe, as related to the geohydrological conditions present, strongly determine the brown moss composition in rich fens through their differential effects on plant P-availability.

Role of acid phosphatase in the tolerance of the rhizobial symbiosis with legumes to phosphorus deficiency

Phosphorus (P) deficiency initiates a myriad of transcriptional, biochemical and physiological responses stimulating either the root’s extracellular abilities to acquire soil P in the rhizosphere or optimize its intracellular use efficiency and allocation through all plant organs. Enhancing activity of acid phosphatase (APase) to acquire and remobilize Pi from organic P compounds is one important strategy for improving plant P nutrition. The release of APase to the rhizosphere is a typical and almost universal P-starvation response in higher plants. However, relatively little is known about the functions of intracellular APase in legume nodules. The aim of this review was to track the enzyme activity along with the intra-nodular localization of APase, and its contribution in the rhizobial symbiosis tolerance to P-deficiency. Our findings have revealed that expression of APase and phytases genes and activities of the corresponding enzymes were positively correlated with increases both of the P use efficiency for N2 fixation and nodule O2 permeability in the rhizobial symbiosis with legumes. The induced enzyme activity and the marked transcripts localization of APase and phytase in nodule cortex would control nodule respiration and contribute to adaptation of nodulated legumes to low-P availability. Thus, the increase of APase and phytase activities in legume nodules supports a physiological role of these enzymes in the regulation of nitrogenase activity in connection with the nodule-P status, and opens up a new scenario for a better understanding of the regulation of N2 fixation in legumes.

Phosphorus-nutrition of European beech (Fagus sylvatica L.) during annual growth depends on tree age and P-availability in the soil

Forest ecosystems have often developed on phosphorus (P) −limited soils and, thus, are thought to require an efficient P-nutrition strategy during annual growth to sustain sufficient P-supply for growth and development. The present study was aimed at characterizing seasonal changes in P-composition and concentrations in different organs and transport tissues of mature and young European beech (Fagus sylvatica L.) trees growing at different soil-P availability. From these changes, a model of tree internal P-cycling strategy as dependent on tree age and P-availability was developed. For this purpose, leaves, stem tissues and roots, as well as xylem sap and phloem exudate were collected from adult trees and their progeny at two field sites in southern Germany, one with low but sufficient (Conventwald field site), and one with extremely low (Tuttlingen field site) P-availability in the soil. P-cycling during annual growth with bark and wood as the main P-storage tissues in winter is strongly indicated and was much more pronounced in adult beeches compared to its progeny, and of higher significance at extremely low soil-P. The re-use of stored organic phosphorus containing compounds (Porg) from bark and wood during spring and the resorption of Porg from senescing leaves can be seen as a strategy to enhance tree internal P-cycling efficiency, especially in adult trees growing at extremely low P-availability. The consequences of tree internal P-cycling for ecosystem P-losses and its dependency on tree age and soil P-availability are discussed.

Nitrogen deposition and grass encroachment in calcareous and acidic Grey dunes (H2130) in NW-Europe

We present an overview of high nitrogen deposition effects on coastal dune grasslands in NW-Europe (H2130), especially concerning grass encroachment in calcareous and acidic Grey Dunes. The problem is larger than previously assumed, because critical loads are still too high, and extra N-input from the sea may amount to 10kgha−1yr−1. Grass encroachment clearly leads to loss of characteristic plant species, from approximately 16 in open dune grassland to 2 in tall-grass vegetation. Dune zones differ in grass encroachment, due to the chemical status of the soil. In calcareous and iron-rich dunes (Renodunal district), grass encroachment showed a clear gradient over the dune area. Grass encroachment is low in calcareous foredunes, due to low P-availability, and large grazers were not needed to counteract grass encroachment after 2001. In partly decalcified middle dunes, P-availability and grass encroachment are high due to dissolution of calcium phosphates, and grazing only partially helped to control this. In acidic, iron-rich hinterdunes, grass encroachment gradually increased between 1990 and 2014, possibly because P-availability increased with time due to increased soil organic matter content. In acidic, iron-poor dunes (Wadden district), grass encroachment is a large problem, because chemical P-fixation with Ca or Fe does not occur. Large grazers may however reduce tall-grass cover. High cumulative N-deposition could theoretically lead to increased N-storage and N-mineralization in the soil. Mineralization indeed increased with N-deposition, but in 15N experiments, most ammonium was converted to nitrate, and storage in soil organic matter was low. Soil N-storage is probably reduced by high nitrate leaching, which will favour dune restoration when N-deposition levels decrease.

Multiple interval QTL mapping and searching for PSTOL1 homologs associated with root morphology, biomass accumulation and phosphorus content in maize seedlings under low-P.

BackgroundModifications in root morphology are important strategies to maximize soil exploitation under phosphorus starvation in plants. Here, we used two multiple interval models to map QTLs related to root traits, biomass accumulation and P content in a maize RIL population cultivated in nutrient solution. In addition, we searched for putative maize homologs to PSTOL1, a gene responsible to enhance early root growth, P uptake and grain yield in rice and sorghum.ResultsBased on path analysis, root surface area was the root morphology component that most strongly contributed to total dry weight and to P content in maize seedling under low-P availability. Multiple interval mapping models for single (MIM) and multiple traits (MT-MIM) were combined and revealed 13 genomic regions significantly associated with the target traits in a complementary way. The phenotypic variances explained by all QTLs and their epistatic interactions using MT-MIM (23.4 to 35.5 %) were higher than in previous studies, and presented superior statistical power. Some of these QTLs were coincident with QTLs for root morphology traits and grain yield previously mapped, whereas others harbored ZmPSTOL candidate genes, which shared more than 55 % of amino acid sequence identity and a conserved serine/threonine kinase domain with OsPSTOL1. Additionally, four ZmPSTOL candidate genes co-localized with QTLs for root morphology, biomass accumulation and/or P content were preferentially expressed in roots of the parental lines that contributed the alleles enhancing the respective phenotypes.ConclusionsQTL mapping strategies adopted in this study revealed complementary results for single and multiple traits with high accuracy. Some QTLs, mainly the ones that were also associated with yield performance in other studies, can be good targets for marker-assisted selection to improve P-use efficiency in maize. Based on the co-localization with QTLs, the protein domain conservation and the coincidence of gene expression, we selected novel maize genes as putative homologs to PSTOL1 that will require further validation studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0561-y) contains supplementary material, which is available to authorized users.