High Phosphorus Conditions Research Articles

OsPHR2-mediated recruitment of Pseudomonadaceae enhances rice phosphorus uptake

Plants can shape their root microbiome to promote growth and nutrient uptake. PHOSPHATE STARVATION RESPONSE 2 (OsPHR2) is a central regulator of phosphate signaling in rice, but whether OsPHR2 can shape the root microbiome to promote phosphorus uptake is unclear. Here, we investigate the role of OsPHR2 in recruiting microbiota for phosphorus uptake using high-throughput sequencing and metabolite analysis. OsPHR2-overexpressing (OsPHR2 OE) rice showed 69.8% greater shoot P uptake in natural soil compared with sterilized soil under high-phosphorus (HP) conditions, but there was only a 54.8% increase in the wild-type (WT). The abundance of the family Pseudomonadaceae was significantly enriched in OsPHR2 OE roots relative to those of WT rice. Compared with the WT, OsPHR2 OE rice had a relatively higher abundance of succinic acid and methylmalonic acid, which could stimulate the growth of Pseudomonas sp. (P6). After inoculation with P6, phosphorus uptake in WT and OsPHR2 OE rice was higher than that in uninoculated rice under low-phosphorus (LP) conditions. Taken together, our results suggest that OsPHR2 can increase phosphorus use in rice through root exudate-mediated recruitment of Pseudomonas. This finding reveals a cooperative contribution of the OsPHR2-modulated root microbiome, which is important for improving phosphorus use in agriculture.

Dependence of evolution of Cyanobacteria superiority on temperature and nutrient use efficiency in a meso-eutrophic plateau lake

Algal blooms in lakes have been a challenging environmental issue globally under the dual influence of human activity and climate change. Considerable progress has been made in the study of phytoplankton dynamics in lakes; The long-term in situ evolution of dominant bloom-forming cyanobacteria in meso-eutrophic plateau lakes, however, lacks systematic research. Here, the monthly parameters from 12 sampling sites during the period of 1997–2022 were utilized to investigate the underlying mechanisms driving the superiority of bloom-forming cyanobacteria in Erhai, a representative meso-eutrophic plateau lake. The findings indicate that global warming will intensify the risk of cynaobacteria blooms, prolong Microcystis blooms in autumn to winter or even into the following year, and increase the superiority of filamentous Planktothrix and Cylindrospermum in summer and autumn. High RUETN (1.52 Biomass/TN, 0.95–3.04 times higher than other species) under N limitation (TN < 0.5 mg/L, TN/TP < 22.6) in the meso-eutrophic Lake Erhai facilitates the superiority of Dolichospermum. High RUETP (43.8 Biomass/TP, 2.1–10.2 times higher than others) in TP of 0.03–0.05 mg/L promotes the superiority of Planktothrix and Cylindrospermum. We provided a novel insight into the formation of Planktothrix and Cylindrospermum superiority in meso-eutrophic plateau lake with low TP (0.005–0.07 mg/L), which is mainly influenced by warming, high RUETP and their vertical migration characteristics. Therefore, we posit that although the obvious improvement of lake water quality is not directly proportional to the control efficacy of cyanobacterial blooms, the evolutionary shift in cyanobacteria population structure from Microcystis, which thrives under high nitrogen and phosphorus conditions, to filamentous cyanobacteria adapted to low nitrogen and phosphorus levels may serve as a significant indicator of water quality amelioration. Therefore, we suggest that the risk of filamentous cyanobacteria blooms in the meso-eutrophic plateau lake should be given attention, particularly in light of improving water quality and global warming, to ensure drinking water safety.

Grafted Tomatoes Removed More Soil Phosphorus than Nongrafted Tomatoes under High-phosphorus Conditions

Nonpoint-source phosphorus (P) from agricultural fields is a contaminant of surface waters, and high soil P fertility exacerbates this problem. Many vegetable growers and gardeners have a history of applying more P than is necessary for optimum plant growth. Avoiding unnecessary P applications is an important part of the long-term solution to reducing P loading in water. When soil P levels are very high, management practices that result in more intense P removal are recommended to reduce these levels and the potential for aquatic ecosystem contamination with P. Growers may apply soluble starter fertilizer containing P to encourage rapid transplant establishment; however, the effectiveness of this practice is unknown for soil P levels considered high or very high. Grafting tomatoes (Solanum lycopersicum L.) onto vigorous rootstocks may help the plant remove more P from the soil than nongrafted plants. This study investigated the effects of organic starter P fertilizers applied to three hybrids of nongrafted tomato and the same hybrids grafted onto ‘Estamino’ rootstock in field-grown conditions during three site-years with high preplant P fertility. The yield, fruit P concentration, and amount of P removed from the field were measured to elucidate starter P and grafting impacts on P removal. Starter P was not impactful on all responses. Grafting increased the total yield by 11.6%, fruit P concentration in a genotype-dependent manner (average of 12.6%), and net P removal from the field by 28.4% (6.0 kg P/ha). Net P removal was positively correlated with the total yield (r = 0.821) and fruit P concentration (r = 0.502), suggesting that practices to increase the yield or P concentration independently increase net P removal.

Changes in nitrogen metabolism of phosphorus-starved bloom-forming cyanobacterium Microcystis aeruginosa: Implications for nutrient management

The surplus of nitrogen plays a key role in the maintenance of cyanobacterial bloom when phosphorus has already been limited. However, the interplay between high nitrogen and low phosphorus conditions is not fully understood. Nitrogen metabolism is critical for the metabolism of cyanobacteria. Transcriptomic analysis in the present study suggested that nitrogen metabolism and ribosome biogenesis were the two most significantly changed pathways in long-term phosphorus-starved bloom-forming cyanobacteria Microcystis aeruginosa FACHB-905. Notably, the primary glutamine synthetase/glutamate synthase cycle, crucial for nitrogen metabolism, was significantly downregulated. Concurrently, nitrogen uptake showed a marked decrease due to reduced expression of nitrogen source transporters. The content of intracellular nitrogen reservoir phycocyanin also showed a drastic decrease upon phosphorus starvation. Our study demonstrated that long-term phosphorus-starved cells also suffered from nitrogen deficiency because of the reduction in nitrogen assimilation, which might be limited by the reduced ribosome biogenesis and the shortage of adenosine triphosphate. External nitrogen supply will not change the transcriptions of nitrogen metabolism-related genes significantly like that under phosphorus-rich conditions, but still help to maintain the survival of phosphorus-starved cells. The study deepens our understanding about the survival strategies of Microcystis cells under phosphorus starvation and the mutual dependence between nitrogen and phosphorus, which would provide valuable information for nutrient management in the eutrophicated water body.

Influence of Phosphorus and Sulphur Application on Sesame Yield in High P Soils of Telangana, India

The present study in pot experiments was conducted on “Influence of phosphorus and sulphur application on sesame yield in high P soils of Telangana”. The experiment was conducted in two different levels of high phosphorus status soils with 67.29 kg P2O5 ha-1 in soil 1 (S1) and 83.46 kg P2O5 ha-1 in soil 2 (S2). The treatments were taken in factorial completely randomized design in combination of five levels of phosphorus (P0-0, P25- 5, P50-10,P75-15 and P100-20 kg ha-1 of soil) four levels of sulphur (S0-0,S1-10,S2-20 and S3-30 kg ha-1 of soil). A significant increase in seed yield of sesame crop could be achieved by combined application of P75 (15 kg P2O5 ha-1) + S20 (20 kg S ha-1) in high available phosphorus soils. Among the various treatments tested within two high P soils, in S1 maximum seed (11.89 g pot-1) and stalk yield (21.98 g pot-1) was obtained with combined application of P75 (15 kg P2O5 ha-1) + S20 (20 kg S ha-1) while in S2 maximum seed (11.92 g pot-1) and stalk yield (21.89 g pot-1) was obtained with combined application of P50 (10 kg P2O5 ha-1) + S20 (20 kg S ha-1).

Characterization of young biofilm morphology, disinfection byproduct formation potential and toxicity of renewed water supply pipelines by phosphorus release from corroded pipes

The deterioration of drinking water quality due to corrosion of the water supply network has become inevitable and regular renewal of pipes has become a common means of doing so. Severely corroded pipes release certain nutrients (e.g., elemental phosphorus), however, little has been reported on the effect of old pipes on the young biofilm of new pipe sections and on ensuring water safety in the early stages of the water supply. The aim of our study was to model the effect of key phosphorus nutrients released from corroded old pipes on the morphological characteristics of young biofilms in new pipe sections, mediated disinfection byproducts (DBPs) production and their combined toxicity. Based on the experimental results, phosphorus showed significant differences in the morphological characteristics, spatial structure of extracellular polymers (EPS), functional abundance, disinfection byproduct formation potential (DBPsFP) and toxicity of young biofilms. Under residual chlorine (1.0 ± 0.2 mg/L) incubation, the functional abundance of young biofilm metabolism was dominant, particularly amino acid metabolism and carbohydrate metabolism. There is a dynamic balance between the trophic and shedding effects of phosphorus, where concentration changes affect young biofilm morphology and DBPFP. Relatively moderate phosphorus concentrations resulted in the highest density of PN/PS organic precursors in EPS and a clear advantage of DBPFP; relatively high phosphorus conditions had limited promotion of young biofilm, while membrane structure shedding was more pronounced, increasing young biofilm-mediated DBPs production. Nitrogen-containing disinfection byproducts (N-DBPs) in young biofilms had a clear toxicity advantage, with HANs and HNMs being key to controlling cytotoxicity and genotoxicity, respectively.

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

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

Spatial distribution of soil nutrient content for sustainable rice agriculture using geographic information system and Naïve Bayes classifier

Abstract This study aims to assist farmers in monitoring soil nutrients, especially phosphorus. To measure the phosphorus content of paddy soil, the TCS3200 converter, as an intelligent sensor, was applied. The geographical information system (GIS) was also involved in this research to map the phosphorus content. In addition, the Naïve Bayes method was applied to classify lowland soil phosphorus status. The result of this study indicated that the Naïve Bayes algorithm could classify lowland soil phosphorus status with a probability of 0.34 for moderate phosphorus conditions and 0.66 for high phosphorus conditions. The sample testing results showed that the error rate was 3% and the success rate was 97%. Testing with a phosphorus-measuring instrument can be carried out by mapping the soil phosphorus status with the ArcGIS software, whereby seven points of medium-phosphorus-status paddy soil and 13 locations of high-phosphorus-status soil samples were determined. This research thus successfully mapped the soil phosphorus.

Lessons from linking bio- and ecological traits to stoichiometric traits in stream macroinvertebrates.

Ecologists rely on various functional traits when investigating the functioning of ecological systems and its responses to global changes. Changing nutrient levels, for example, can affect taxa expressing different trait combinations in various ways, e.g., favoring small, fast-growing species under high phosphorus conditions. Stoichiometric traits, describing the elemental composition of organism body tissues, can help in understanding the mechanisms behind such functional shifts. So far, mainly life-history traits have been related to body stoichiometry (e.g., the growth rate hypothesis) on a limited number of taxa, and there is little knowledge of the general link between stoichiometric and other functional traits on a taxonomically large scale. Here, we highlight this link in the freshwater macroinvertebrates, testing predictions from underlying trait-based and Ecological Stoichiometry Theory (EST) in >200 taxa belonging to eight larger taxonomic groups. We applied a series of multivariate analyses on six of their stoichiometric traits (%C, %N, %P, C:N, C:P, and N:P) and 23 biological and ecological traits. We found significant relationships between stoichiometric traits and other types of traits when analyzing single-trait and multi-trait profiles. Patterns found within traits related to organism development or nutrient cycling were in line with our assumptions based on EST, e.g., traits describing predators were associated with high %N; traits suggesting a fast development (small maximum body size and high molting frequency) with high %P. Associations between ecological traits and body stoichiometry could be explained by the longitudinal stream gradient: Taxa preferring headwater habitats (i.e., high altitude, coarse substrate, and cold temperature) exhibited high %N and %P. Demonstrating the link between stoichiometric and both bio- and ecological traits on a large diversity of taxa underlines the potential of integrating stoichiometric traits into ecological analyses to improve our understanding of taxonomic and functional responses of communities-and ecosystems-to changing environmental conditions worldwide.

TbasCO: trait-based comparative ‘omics identifies ecosystem-level and niche-differentiating adaptations of an engineered microbiome

A grand challenge in microbial ecology is disentangling the traits of individual populations within complex communities. Various cultivation-independent approaches have been used to infer traits based on the presence of marker genes. However, marker genes are not linked to traits with complete fidelity, nor do they capture important attributes, such as the timing of gene expression or coordination among traits. To address this, we present an approach for assessing the trait landscape of microbial communities by statistically defining a trait attribute as a shared transcriptional pattern across multiple organisms. Leveraging the KEGG pathway database as a trait library and the Enhanced Biological Phosphorus Removal (EBPR) model microbial ecosystem, we demonstrate that a majority (65%) of traits present in 10 or more genomes have niche-differentiating expression attributes. For example, while many genomes containing high-affinity phosphorus transporter pstABCS display a canonical attribute (e.g. up-regulation under phosphorus starvation), we identified another attribute shared by many genomes where transcription was highest under high phosphorus conditions. Taken together, we provide a novel framework for unravelling the functional dynamics of uncultivated microorganisms by assigning trait-attributes through genome-resolved time-series metatranscriptomics.

Exosomal STAT1 derived from high phosphorus‑stimulated vascular endothelial cells induces vascular smooth muscle cell calcification via the Wnt/β‑catenin signaling pathway.

Vascular calcification is commonly observed in chronic kidney disease. The mechanism of how the calcification signal from endothelial cells is transmitted to vascular smooth muscle cells (VSMCs) remains unknown. The aim of the present study was to investigate whether exosomes from HUVECs (HUVEC‑Exos) could regulate VSMC calcification and its potential signaling pathway. HUVEC‑Exos were isolated from HUVECs under no phosphorus (NP) and high phosphorus (HP) conditions. Alizarin Red S staining and calcium (Ca) content analysis were carried out to detect calcification in VSMCs. Proteomics analysis was carried out to detect the differential expression of exosomal proteins. Protein and mRNA levels were measured by western blot analysis and reverse transcription‑quantitative PCR (RT‑qPCR). Exosomes derived from HP‑HUVECs promoted the calcification of VSMCs, as assessed by Alizarin Red S staining, alkaline phosphatase activity assays, Ca content measurements and the increased expression of runt‑related transcription factor 2 and osteopontin. Proteomic analysis detected the upregulation of STAT1 in HP‑exosomes from HUVECs (HUVEC‑Exos) compared with NP‑HUVEC‑Exos, which was also confirmed by western blot analysis and RT‑qPCR. Inhibition of STAT1 expression in VSMCs using fludarabine or knockdown of STAT1 expression using small interfering RNA alleviated the calcification of VSMCs. Furthermore, lithium chloride (Wnt activator) reversed the protective effect of STAT1 inhibition on VSMC calcification, while Dickkopf‑1 (Wnt inhibitor) exerted the opposite effect, suggesting that activation of the Wnt/β‑catenin signaling pathway was involved in STAT1‑mediated VSMC calcification. In conclusion, the present results indicated that exosomal STAT1 derived from HP‑treated HUVECs could promote VSMC calcification, and activation of the Wnt/β‑catenin pathway may be a potential mechanism of the VSMC calcification promoted by exosomes.

MicroRNA-103a regulates the calcification of vascular smooth muscle cells by targeting runt-related transcription factor 2 in high phosphorus conditions.

Vascular calcification, such as atherosclerosis, is a serious complication of chronic kidney disease that is characterized by tunica media calcification, and has gained increasing attention from researchers. The commonly observed association between vascular calcification and osteoporosis suggests a link between bone and vascular disorders. As microRNAs (miRNAs) have a wide range of gene regulation functions, such as cell proliferation, apoptosis, stress and transdifferentiation, the current study aimed to determine whether miRNAs play a vital role in the calcification and osteoblastic differentiation of rat thoracic aorta vascular smooth muscle cells (VSMCs). Gene expression analysis was performed on seven miRNAs (miR-29a, -30b, -103a, -125b, -133a, -143 and -211) that maybe potentially involved in the differentiation of smooth muscle cells into osteoblastic cells. The results showed that the levels of miR-29a, -30b, -103a, -125b and -143 were markedly reduced in the VSMC calcification model, particularly miR-103a, whereas runt-related transcription factor 2 (RUNX2) expression was increased. Furthermore, it was found that the expression of RUNX2 was significantly decreased following the upregulation of miR-103a, and that the expression of RUNX2 was significantly increased by downregulating miR-103a in VSMCs. Therefore, it was concluded that miR-103a plays a notable role in the transdifferentiation of the VSMCs in high phosphorus-induced calcification by targeting the regulation of RUNX2, and may therefore constitute a new target for the diagnosis and treatment of vascular calcification.

Analyzing Algae Growth and Oil Production in a Batch Reactor under High Nitrogen and Phosphorus Conditions

The feasibility for simultaneous local fresh water oleaginous algae cultivation and wastewater nitrogen removal were discussed in this study. The operation factors including illumination intensities, carbon source, initial nitrogen source, and retention time were fixed. The results indicated that the algae biomass increased from 28.3 mg/L to 254 mg/L at the 7th day. The oil weight increased from 5.75 mg/L to 85.34 mg/L at the 7th day. The percentage of algae oil increased from 20.4 % to 33.6 %, or by 13.2 %. The first-order equation was found to be the excellent fit model for describing the growth of algae biomass and production of oil content. The values of growth rate constant of algae and production rate constant were 0.30951/day and 0.37381/day, respectively. The value of production rate constant was about 1.2 times as that of the value of growth rate constant of algae, indicating an unbalance growth of algae biomass and oil content. The removal efficiency for ammonia nitrogen and phosphate was 84.8 % and 36.2 %, respectively.

Heavy grazing disrupts positive effects of arbuscular mycorrhizae symbiosis on community productivity and stability under low and high phosphorus conditions

We quantified the potential influence of arbuscular mycorrhizal fungi (AMF) on primary productivity and community stability and tested whether the effects of AMF depend on soil phosphorus (P) availability and grazing intensity in a semiarid grassland. We manipulated the abundance of AMF and soil P availability (P addition and no P addition) under four levels of grazing intensity. The aboveground biomass of plant species, functional groups and community, as well as community temporal stability were examined under these conditions. Under no to moderate grazing, benomyl decreased the aboveground biomass in C4 grasses and forbs, but increased the aboveground biomass in C3 grasses under low P conditions; thus no obvious changes in community primary productivity were observed. These results indicated that the mycorrhizal dependency of C4 grasses and forbs is higher than that of C3 grasses under low P conditions. However, community primary productivity was greatly enhanced by benomyl due to the increased biomasses of C3 grasses and forbs under high P conditions. Under heavy grazing conditions, benomyl increased community primary productivity under both low and high P conditions. AMF presence increased the community temporal stability by promoting the compensatory effects between plant species under no to moderate grazing conditions; whereas AMF decreased the community stability by forming a parasitic symbiosis with their plant hosts under heavy grazing conditions. Our findings demonstrate that the effects of benomyl application to suppress AMF on primary productivity and community stability are strongly mediated by soil P availability and grazing intensity, which improves our understanding for the roles of AMF-plant symbiosis on ecosystem functioning in grazed systems.

Changes in the mycorrhizal fungal community in host roots over five host generations under low and high phosphorus conditions

We tested whether arbuscular mycorrhizal fungal (AMF) community might shift as host plant generations advance under a low phosphorus (P) soil. Two greenhouse experiments were conducted using Medicago truncatula as the host plant, six AMF species, and two soil P levels. Experiment 1 assessed changes in AMF composition in roots and soil during five generations of host plant grown in low-P (5.7 mg kg−1) and high-P soil (24.0 mg kg−1). Experiment 2 tested the effects of single AMF species on host plant growth in low-P and high-P soil. Experiment 1 showed that AMF species composition at the OTU level in roots and soil significantly changed as host generations advanced, and that the pattern of change differed in low-P vs. high-P soil. In low-P soil, the dominant OTU in both roots and soil shifted from OTU-50 (Glomus tortuosum) to OTU-49 (Funneliformis geosporum) as host generations advanced. In high-P soil, the AMF community in roots and soil was dominated by OTU-50 in first two generations but OTU-49 and OTU-50 were co-dominant in the last three generations. Experiment 2 showed that mycorrhizal dependency indices based on plant biomass and P content in plant biomass, and spore numbers were higher in host plants with F. geosporum than other AMF fungal treatments in low-P soil. As the host M. truncatula grew in a low-P soil over five generations, AMF community in root and soil shifted to a composition with F. geosporum as dominant species who was effective in foraging for P.

P-limitation drives changes in DOM production by aquatic bacteria

Heterotrophic bacteria are key biogeochemical regulators in freshwater systems. Through both decomposition and production of organic matter, bacteria link multiple biogeochemical cycles together. While there has been a significant amount of work done on understanding the role of microbes in the aquatic carbon cycle, important linkages with other biogeochemical cycles will require more information about how organic matter transformations impact other nutrients, such as phosphorus. In this study, we conducted a culture-based laboratory experiment to examine the production of dissolved organic matter (DOM) by heterotrophic bacteria under varied nutrient conditions. In addition to quantifying the production of dissolved organic carbon (DOC), we also measured the production of dissolved organic phosphorus (DOP) and characterized the microbially produced organic matter using optical properties. Results demonstrated that measurable amounts of DOC and DOP were produced by heterotrophic bacteria under nutrient regimes ranging from carbon-limitation to strong phosphorus-limitation. Additionally, optical characterization of DOM revealed that the organic matter produced by bacteria grown under high phosphorus conditions was highly aromatic with similar optical properties to terrestrially derived organic matter. Overall, these findings suggest that heterotrophic bacteria can be important producers of organic matter in freshwaters and that continued trends of increased nutrient concentrations (eutrophication) may fundamentally change the composition of microbially produced organic matter in freshwater systems.

Inoculation of arbuscular mycorrhizal fungi and phosphorus addition increase coarse mint (Plectranthus amboinicus Lour.) plant growth and essential oil content

The coarse mint (Plectranthus amboinicus Lour.) is a medicinal plant that produces essential oil; however, it is still little studied the effects of effects of arbuscular mycorrhizal fungi species on growth and essential oil content and its composition in P. amboinicus. Therefore, this study aimed to evaluate Rhizophagus clarus and Claroideoglomus etunicatum under low and high phosphorus conditions and its effects in plant growth and the essential oil content and chemical composition in coarse mint. The experimental design was completely randomized with 8 replicates per treatment in a 3 × 2 factorial (without and with two arbuscular mycorrhizal fungi, two levels of phosphorus (at 20 or 200 mg dm−3 of substrate). We evaluated spore density in the substrate and root colonization by arbuscular mycorrhizal fungi, an also shoot and root phosphorus content and nitrogen in the shoots, plant growth, essential oil content and its chemical composition. Spore density and root colonization by arbuscular mycorrhizal fungi were higher in the inoculated treatments. The shoot dry matter, root dry matter and total dry matter increased with arbuscular mycorrhizal fungi inoculation, mainly with the inoculation of R. clarus and high addition of phosphorus to the substrate. Inoculation of arbuscular mycorrhizal fungi and/or the addition of phosphorus in the substrate increased phosphorus and nitrogen content in the plant. The essential oil content was higher with R. clarus and with low phosphorus addition (0.61%) and 18 compounds were identified in essential oil, being carvacrol (38.48–51.07%), followed by trans-Caryophyllene, α-Bergamotene and α-Humulene the major constituents. It was concluded that plant growth increased with R. clarus inoculation and high phosphorus condition and R. clarus inoculation increased essential oil content.

Nitrogen and phosphorus influence Acacia saligna invasiveness in the fynbos biome

This study attempts to understand how invasive legumes such as Acacia saligna may compete with indigenous legumes such as Virgilia divaricata. The two species are trees with similar growth forms. We studied the competitive ability of invasive and indigenous seedlings under variations in soil phosphorus availability. South African fynbos vegetation is threatened by invasive Acacia. The indigenous tree legume, Virgilia, grows in similar phosphorus soil conditions as Acacia although there is a gap in the knowledge of their physiology. We investigated the utilization of different inorganic P sources by the invasive A. saligna and the native V. divaricata in the presence and absence of root nodules in each species. Plant performance in terms of photosynthesis and biomass production was also analysed. Plants were cultivated in silica sand supplied with Long Ashton nutrient solution, modified to contain either 50 μM P or 500 μM P applied as NaH2PO4·2H2O. Rate of growth was estimated as the increase in mass in plants harvested after 4 and 8 weeks of growth. After 4 weeks of growth, the seedlings of Virgilia grew quicker and produced more biomass than Acacia, under both phosphorus conditions. However, this was reversed after 8 weeks of growth, with Acacia out-competing Virgilia. Increased growth of the invasive legumes was achieved by relying on soil nitrogen under high phosphorus conditions and shifting to atmospheric sources under lower phosphorus levels. The strategies of altering photosynthetic carbon balance and nitrogen acquisition under varying soil phosphorus conditions potentially underpin the invasive potential of Acacia in fynbos soils.

Strategies of phosphorus utilization in an astaxanthin-producing green alga Haematococcus pluvialis, a comparison with a bloom-forming cyanobacterium Microcystis wesenbergii

Haematococcus pluvialis is a unicellular green alga with great commercial value, due to its synthesis of powerful antioxidant astaxanthin. H. pluvialis was mainly distributed in small water bodies but was also observed in eutrophicated lakes, and even coexisted with Microcystis. However, Haematococcus cells never prevail in eutrophicated water bodies. Phosphorus is the main limiting factor in most aquatic ecosystems and may have a role in the distribution of H. pluvialis. Here, we focused on the physiological responses of H. pluvialis to various phosphorus conditions (0.002, 0.02, 0.2, and 2 mM), and compared with a bloom-forming cyanobacterium Microcystis wesenbergii. Growth determination suggested that high phosphorus conditions (0.2 mM and 2 mM) favor the growth of H. pluvialis cells, but H. pluvialis cells have a shorter duration of log phase than M. wesenbergii cells. Growth determination also indicated H. pluvialis cells had lower tolerability to low phosphorus (0.002 mM). Qualitative comparisons from long-term and short-term phosphorus uptake experiments, polyphosphate accumulation and extracellular alkaline phosphatase expression analysis suggested two different phosphorus utilization strategies in the two species. H. pluvialis cells were characterized with the induction of extracellular alkaline phosphatase to survive phosphorus-deficient condition, while M. wesenbergii cells were characterized with quick uptake of phosphorus and accumulation more of polyphosphate in phosphorus-replete conditions. To our knowledge, this is the first study to demonstrate features of phosphorus uptake and utilization in H. pluvialis, which will increase our understanding in the distribution of H. pluvialis.

Impacts of soil nitrogen and phosphorus levels on cytotype performance of the circumboreal herb Chamerion angustifolium: implications for polyploid establishment.

Although polyploidy commonly occurs in angiosperms, not all polyploidization events lead to successful lineages, and environmental conditions could influence cytotype dynamics and polyploid success. Low soil nitrogen and/or phosphorus concentrations often limit ecosystem primary productivity, and changes in these nutrients might differentially favor some cytotypes over others, thereby influencing polyploid establishment. We grew diploid, established tetraploid, and neotetraploid Chamerion angustifolium (fireweed) in a greenhouse under low and high soil nitrogen and phosphorus conditions and different competition treatments and measured plant performance (height, biomass, flower production, and root bud production) and insect damage responses. By comparing neotetraploids to established tetraploids, we were able to examine traits and responses that might directly arise from polyploidization before they are modified by natural selection and/or genetic drift. We found that (1) neopolyploids were the least likely to survive and flower and experienced the most herbivore damage, regardless of nutrient conditions; (2) both neo- and established tetraploids had greater biomass and root bud production under nutrient-enriched conditions, whereas diploid biomass and root bud production was not significantly affected by nutrients; and (3) intra-cytotype competition more negatively affected diploids and established tetraploids than it did neotetraploids. Following polyploidization, biomass and clonal growth might be more immediately affected by environmental nutrient availabilities than plant survival, flowering, and/or responses to herbivory, which could influence competitive dynamics. Specifically, polyploids might have competitive and colonizing advantages over diploids under nutrient-enriched conditions favoring their establishment, although establishment may also depend upon the density and occurrences of other related cytotypes in a population.