Phosphate Supply Research Articles

Cycling of reduced phosphorus compounds in soil and potential impacts of climate change

AbstractSoil phosphorus (P) remains an ever‐increasing topic of importance, notably for its key role as a nutrient for driving food production but with parallel concerns over damaging water quality, all against a backdrop of uncertainty of long‐term rock phosphate supplies. Soil is a key interface that holds P and regulates its onward flow to plants or leakage to waters. Often overlooked are a ubiquitous group of P compounds that exist in alternative oxidation states to that of phosphate (+5). Redox cycling, and the behaviour that chemically reduced P compounds exhibit in soils, introduces alternative routes of cycling P that may become more important as the soil system itself alters, especially due to the external pressures of climate change, bringing about critical dynamics in rainfall and runoff and also wetting and drying. All of these factors are known to affect soil redox potential and consequently the oxidation state of soil P. This review considers the chemically reduced species in the P cycle, exploring their sources and sinks, while considering their importance within the primary global biogeochemical cycling of P and how this may be impacted by climate change in the temperate climate of the northern hemisphere.Highlights This paper addresses how climate change will affect soil phosphorus cycling. This review is novel as it considers the reduced phosphorus forms when discussing P transfer in soils. Climate change is likely to increase prevalence of reduced P and free phosphate in northern hemisphere temperate soils. Phosphorus cycling relies partly on redox P processes. Their importance will increase as climate alters soils.

Enhanced production of L-arginine by improving carbamoyl phosphate supply in metabolically engineered Corynebacterium crenatum

Carbamoyl phosphate is an important precursor for L-arginine and pyrimidines biosynthesis. In view of this importance, the cell factory should enhance carbamoyl phosphate synthesis to improve related compound production. In this work, we verified that carbamoyl phosphate is essential for L-arginine production in Corynebacterium sp., followed by engineering of carbamoyl phosphate synthesis for further strain improvement. First, carAB encoding carbamoyl phosphate synthetase II was overexpressed to improve the synthesis of carbamoyl phosphate. Second, the regulation of glutamine synthetase increases the supply of L-glutamine, providing an effective substrate for carbamoyl phosphate synthetase II. Third, carbamate kinase, which catalyzes inorganic ammonia synthesis carbamoyl phosphate, was screened and selected to assist in carbamoyl phosphate supply. Finally, we disrupted ldh (encoding lactate dehydrogenase) to decrease by-production formation and save NADH to regenerate ATP through the electron transport chain. Subsequently, the resulting strain allowed a dramatically increased L-arginine production of 68.6 ± 1.2 g∙L-1, with an overall productivity of 0.71 ± 0.01 g∙L-1∙h-1 in 5-L bioreactor. Stepwise rational metabolic engineering based on an increase in the supply of carbamoyl phosphate resulted in a gradual increase in L-arginine production. The strategy described here can also be implemented to improve L-arginine and pyrimidine derivatives. KEY POINTS: • The L-arginine production strongly depended on the supply of carbamoyl phosphate. • The novel carbamoyl phosphate synthesis pathway for C. crenatum based on carbamate kinase was first applied to L-arginine synthesis. • ATP was regenerated followed with the disruption of lactate formation.

Anthropogenic influences on the distribution of the Casuarina-Frankia symbiosis

Casuarina species are evergreen angiosperm trees native to Australia, South East Asia and the Pacific archipelagos. The genus comprises 14 confirmed species that are able to grow on a wide range of soils. Casuarina spp. are able to enter into an actinorhizal root nodule symbiosis with Frankia casuarinae, nitrogen-fixing soil actinobacteria; the symbiosis renders them independent of soil nitrogen sources. Casuarina spp. can also form symbiotic associations with ectomycorrhizal fungi (EMF) and/or arbuscular mycorrhizal fungi (AMF) for better phosphate supply. Under severe deficiency of phosphate and iron, several Casuarina spp. can form cluster roots. These trees are highly tolerant to salinity, drought, flooding and heavy metal pollution and are extensively used for the rehabilitation of degraded sites. Casuarina spp. plantations also play a significant role in prevention of soil erosion, coastal reclamation, dune stabilization, and as windbreaks in agricultural lands. Due to their multipurpose applications in agriculture and forestry, they have been widely introduced outside their native habitat especially in tropical, arid and semiarid countries across the globe. Therefore, the global distribution of Casuarina spp. has been significantly affected by anthropogenic influences. While in most of these countries, Casuarina spp. have become well-integrated into the regional farming systems, they have become invasive in other regions.

PE_PGRS3 ensures provision of the vital phospholipids cardiolipin and phosphatidylinositols by promoting the interaction between M. tuberculosis and host cells

ABSTRACT PE_PGRS proteins of Mycobacterium tuberculosis (Mtb) constitute a large family of complex modular proteins whose role is still unclear. Among those, we have previously shown, using the heterologous expression in Mycobacterium smegmatis, that PE_PGRS3 containing a unique arginine-rich C-terminal domain, promotes adhesion to host cells. In this study, we investigate the role of PE_PGRS3 and its C-terminal domain directly in Mtb using functional deletion mutants. The results obtained here show that PE_PGRS3 is localized on the mycobacterial cell wall and its arginine-rich C-terminal region protrudes from the mycobacterial membrane and mediates Mtb entry into epithelial cells. Most importantly, this positively charged helical domain specifically binds phosphorylated phosphatidylinositols and cardiolipin, whereas it is unable to bind other phospholipids. Interestingly, administration of cardiolipin and phosphatidylinositol but no other phospholipids was able to turn-off expression of pe_pgrs3 activated by phosphate starvation conditions. These findings suggest that PE_PGRS3 has the key role to serve as a bridge between mycobacteria and host cells by interacting with specific host phospholipids and extracting them from host cells, for their direct integration or as a source of phosphate, during phases of TB pathogenesis when Mtb is short of phosphate supply.

The Phosin PptA Plays a Negative Role in the Regulation of Antibiotic Production in Streptomyces lividans.

In Streptomyces, antibiotic biosynthesis is triggered in phosphate limitation that is usually correlated with energetic stress. Polyphosphates constitute an important reservoir of phosphate and energy and a better understanding of their role in the regulation of antibiotic biosynthesis is of crucial importance. We previously characterized a gene, SLI_4384/ppk, encoding a polyphosphate kinase, whose disruption greatly enhanced the weak antibiotic production of Streptomyces lividans. In the condition of energetic stress, Ppk utilizes polyP as phosphate and energy donor, to generate ATP from ADP. In this paper, we established that ppk is co-transcribed with its two downstream genes, SLI_4383, encoding a phosin called PptA possessing a CHAD domain constituting a polyphosphate binding module and SLI_4382 encoding a nudix hydrolase. The expression of the ppk/pptA/SLI_4382 operon was shown to be under the positive control of the two-component system PhoR/PhoP and thus mainly expressed in condition of phosphate limitation. However, pptA and SLI_4382 can also be transcribed alone from their own promoter. The deletion of pptA resulted into earlier and stronger actinorhodin production and lower lipid content than the disruption of ppk, whereas the deletion of SLI_4382 had no obvious phenotypical consequences. The disruption of ppk was shown to have a polar effect on the expression of pptA, suggesting that the phenotype of the ppk mutant might be linked, at least in part, to the weak expression of pptA in this strain. Interestingly, the expression of phoR/phoP and that of the genes of the pho regulon involved in phosphate supply or saving were strongly up-regulated in pptA and ppk mutants, revealing that both mutants suffer from phosphate stress. Considering the presence of a polyphosphate binding module in PptA, but absence of similarities between PptA and known exo-polyphosphatases, we proposed that PptA constitutes an accessory factor for exopolyphosphatases or general phosphatases involved in the degradation of polyphosphates into phosphate.

Phosphorous Supply to a Eutrophic Artificial Lake: Sedimentary versus Groundwater Sources

The eutrophic Lake Eichbaumsee, a ~1 km long and 280 m wide (maximum water depth 16 m) dredging lake southeast of Hamburg (Germany), has been treated for water quality improvements using various techniques (i.e., aeration plants, removal of dissolved phosphorous by aluminum phosphorous precipitation, and by Bentophos® (Phoslock Environmental Technologies, Sydney, Australia), adsorption) during the past ~15 years. Despite these treatments, no long-term improvement of the water quality has been observed and the lake water phosphorous content has continued to increase by e.g., ~670 kg phosphorous between autumn 2014 and autumn 2019. As no creeks or rivers drain into the lake and hydrological groundwater models do not suggest any major groundwater discharge into the lake, sources of phosphorous (and other nutrients) are unknown. We investigated the phosphorous fluxes from sediment pore water and from groundwater in the water body of the lake. Sediment pore water was extracted from sediment cores recovered by divers in August 2018 and February 2019. Diffusive phosphorous fluxes from pore water were calculated based on phosphorus gradients. Stable water isotopes (δ2H, δ18O) were measured in the lake water, in interstitial waters in the banks surrounding the lake, in the Elbe River, and in three groundwater wells close to the lake. Stable isotope (δ2H, δ18O) water mass balance models were used to compute water inflow/outflow to/from the lake. Our results revealed pore-water borne phosphorous fluxes between 0.2 mg/m2/d and 1.9 mg/m2/d. Assuming that the measured phosphorous fluxes are temporarily and spatially representative for the whole lake, about 11 kg/a to 110 kg/a of phosphorous is released from sediments. This amount is lower than the observed lake water phosphorous increase of ~344 kg between April 2018 and November 2018. Water stable isotope (δ2H, δ18O) compositions indicate a water exchange between an aquifer and the lake water. Based on stable isotope mass balances we estimated an inflow of phosphorous from the aquifer to the lake of between ~150 kg/a and ~390 kg/a. This result suggests that groundwater-borne phosphorous is a significant phosphorous source for the Eichbaumsee and highlights the importance of groundwater for lake water phosphorous balances.

Impact of Phosphate Availability on Membrane Lipid Content of the Model Strains, Streptomyces lividans and Streptomyces coelicolor.

In this issue we demonstrated that the phospholipid content of Streptomyces lividans varies greatly with Pi availability being was much lower in Pi limitation than in Pi proficiency whereas that of Streptomyces coelicolor varied little with Pi availability. In contrast the content in phosphate free ornithine lipids was enhanced in both strains in condition of phosphate limitation. Ornithine lipids biosynthesis starts with the N-acylation of ornithine to form lyso-ornithine that is then O-acylated to yield ornithine lipid. The operon sco1222-23 was proposed to be involved in the conversion of specific amino acids into ornithine in condition of phosphate limitation whereas the sco0921-20 operon encoding N- and O-acyltransferase, respectively, was shown to be involved in the biosynthesis of these lipids. The expression of these two operons was shown to be under the positive control of the two components system PhoR/PhoP and thus induced in phosphate limitation. The expression of phoR/phoP being weak in S. coelicolor, the poor expression of these operons resulted into a fivefold lower ornithine lipids content in this strain compared to S. lividans. In the deletion mutant of the sco0921-20 operon of S. lividans, lyso-ornithine and ornithine lipids were barely detectable and TAG content was enhanced. The complementation of this mutant by the sco0921-20 operon or by sco0920 alone restored ornithine lipids and TAG content to wild type level and was correlated with a twofold increase in the cardiolipin content. This suggested that SCO0920 bears, besides its broad O-acyltransferase activity, an N-acyltransferase activity and this was confirmed by the detection of lyso-ornithine in this strain. In contrast, the complementation of the mutant by sco0921 alone had no impact on ornithine lipids, TAG nor cardiolipin content but was correlated with a high lyso-ornithine content. This confirmed that SCO0921 is a strict N-acyltransferase. However, interestingly, the over-expression of the sco0921-20 operon or of sco0921 alone in S. coelicolor, led to an almost total disappearance of phosphatidylinositol that was correlated with an enhanced DAG and TAG content. This suggested that SCO0921 also acts as a phospholipase C, degrading phosphatidylinositol to indirectly supply of phosphate in condition of phosphate limitation.

Sustentabilidade do cultivo de mandioca em comunidades indígenas do Pantanal Brasileiro

We aimed with this study to help maximizing cassava production for subsistence in indigenous communities at the Brazilian Pantanal, by introducing minimal changes to the usual indigenous way of cultivation aiming to reduce human labor in weed management in this crop. For that, we tested distinct intercrops and phosphate sources, taking the Babassu Indigenous Village, located in Miranda‑MS, Brazil, as a reference. The experiment involved the intercrop of cassava with pigeon pea (Cajanus cajan), jack‑bean (Canavalia ensiformis) and millet (Pennisetum americanum) and the source of phosphate fertilizer (mycorrhizal inoculants, P2O5 and without fertilization / mycorrhizal inoculum). Soil samples were collected to study the soil seed bank of spontaneous species. We adopted the phytosociological method to assess the absolute level of infestation, its composition density, frequency, dominance and importance value, and diversity coefficients of Simpson and Shannon-Weiner, as well as the Shannon Evenness Proportion (a sustainability coefficient) for all treatments. Areas were also grouped by similarity of plant species. Cultivation of cassava for subsistence in indigenous areas also selects certain spontaneous species, and management should focus in removing mostly by hand those established in the crop row; the damage to the crop may be higher in years of high abiotic stresses. There is no effect of phosphate supply source (P) in the level or composition of spontaneous species. There is clear evidence that the continued cultivation of cassava for subsistence in indigenous areas of the Brazilian Pantanal is sustainable over time, mainly when intercropped with other food species.

5. Exploring conditions that promote phosphate supply

5. Exploring conditions that promote phosphate supply

Detection about fungal contamination in products milk in local and manufacturing yogurt and cheese in Al-Diwaniya city

This study included random examination of milk products such as yogurt and cheese in both types the local and manufacturing milk product, to detect the fungal contamination in these products. Yogurt was a well source of essential nutrients such as protein, essential minerals (Ca, P, Mg, Zn, K) and vitamins such as B1, B9, B2 B12, B3. Yogurt increase the body product of cytokine, activity of phagocytic cell, antibodies, T- cell and natural killer cell, also it induced immune system against other diseases such as cancer, gastrointestinal and allergic syndrome. Caseins are the main protein in cheese; which exist in the form of aggregates after combination with colloidal calcium phosphate common knowledge as micelles of casein. Caseins in cheese are nutritionally rich due to the high supply of essential amino acids, phosphate and calcium. Samples taken from market of al-Diwaniya city about ten samples for each type, these samples cultured on SDA by use dilution method and after incubated found several types of fungi were appeared, such as Candida albicans the general average for it cell in 1 ml about 2.7×10^2(cell/ml) in samples of local yogurt, 7.6×10 (cell/ml) in samples of manufacturing yogurt, in cheese; about 1.8×10(cell/ml) in samples of local cheese and 1.3×10 in manufacturing cheese. The fungi also appeared in samples such as Penicillium notatum, Aspergillus flavus, Fusarium oxysporium, Trichoderma harzianum, the higher frequency rate was recorded in samples of local yogurt about 13.7%, 25.4%, 19.6%, 11.3% respectively.

Triose phosphate utilization limitation: an unnecessary complexity in terrestrial biosphere model representation of photosynthesis

Triose phosphates are the principal product of photosynthesis. They are used within the chloroplast for starch synthesis, or translocated to the cytosol where they are used to fuel sucrose synthesis. Use of triose phosphate releases inorganic phosphate, and is under strict metabolic control that matches the supply of triose phosphate from the Calvin-Benson cycle to the demand for carbon by sinks (Heldt & Heldt, 2011; McClain & Sharkey, 2019). However, a low rate of triose phosphate utilization (TPU) can deplete the phosphate pool, restrict ATP synthesis and reduce the availability of ATP to power the Calvin-Benson cycle, thereby limiting photosynthesis (Sharkey, 1985).

A Kinetic Study on Selective Leaching of Phosphorus from Dephosphorization Slag

Phosphorus recovery from dephosphorization slag generated during steelmaking has enormous potential to secure a stable supply of phosphate. Because P and Fe in slag are concentrated in different mineral phases, P can be recovered by separation of the P-bearing phase, and the residue can be reutilized in steel plant at the same time. In the present study, we adopted selective leaching of P and investigated the effects of leaching parameters on the dissolution behavior of slag. It was determined that with the decrease in particle size and increase in stirring speed, the P dissolution ratio increased significantly. When particle size was less than 53 μm and stirring speed exceeded 200 rpm, most of the P-bearing C2S−C3P solid solution was dissolved and separated. Increasing temperature and decreasing the mass ratio of slag to liquid had a slight influence on promoting P dissolution, while the Si dissolution was significantly suppressed in the case of high temperature and mass ratio due to the formation of silica gel. The P dissolution ratio reached 84.9%, and the Fe dissolution was negligible. Through selective leaching, the residue primarily consisting of magnesioferrite could be used as a flux in steelmaking process. The shrinking core model was successfully used to describe the dissolution kinetics of P. As temperature increased, apparent rate constant increased slightly. The calculated activation energy was 9.23 kJ/mol, demonstrating that the P dissolution was controlled by diffusion in the residue layer. Most of the P-bearing solid solution in dephosphorization slag was dissolved and the dissolution of Fe-bearing phase was negligible, achieving selective leaching of P. The P dissolution from slag was controlled by diffusion in the residue layer.

Flexibility of dynamic blending with alternative routings combined with security stocks: a new approach in a mining supply chain

ABSTRACT In the OCP phosphate supply chain, source ores (SOs) are extracted according to a tactical extraction programme, constrained by geological conditions that constantly limit and modify the variety of available SOs. Then SOs are blended to get merchantable ores (MOs) respecting composition constraints and ordered by internal (phosphoric acid plant) or external (export) customers. The blending process is performed in a dry blending plant, possibly followed by treatments in a washing plant which modifies the SOs weights and compositions. The choice of alternative routings and blends depends on orders book and SOs availability in the dry blending area or present on mine. To improve the performance in meeting a rolling 4-weeks orders book, a quadratic model was created and implemented. It optimises jointly: (i) for each order, the routing and the SOs quantities used in the dry blending plant; (ii) the SOs quantities transferred from the mine; (iii) security stocks to face some unforeseen change in the MO book order, and the slight instability of the SO chemical composition that triggers a SO multiplication to be contained. The performance of the linearised model has led the relevant OCP site to develop and use an extended version of this model.

Rich dynamics of a simple delay host-pathogen model of cell-to-cell infection for plant virus

Viral dynamics within plant hosts can be important for understanding plant disease prevalence and impacts. However, few mathematical modeling efforts aim to characterize within-plant viral dynamics. In this paper, we derive a simple system of delay differential equations that describes the spread of infection throughout the plant by barley and cereal yellow dwarf viruses via the cell-to-cell mechanism. By incorporating ratio-dependent incidence function and logistic growth of the healthy cells, the model can capture a wide range of biologically relevant phenomena via the disease-free, endemic, mutual extinction steady states, and a stable periodic orbit. We show that when the basic reproduction number is less than \begin{document}$ 1 $\end{document} ( \begin{document}$ R_0 ), the disease-free steady state is asymptotically stable. When \begin{document}$ R_0>1 $\end{document} , the dynamics either converge to the endemic equilibrium or enter a periodic orbit. Using a ratio-dependent transformation, we show that if the infection rate is very high relative to the growth rate of healthy cells, then the system collapses to the mutual extinction steady state. Numerical and bifurcation simulations are provided to demonstrate our theoretical results. Finally, we carry out parameter estimation using experimental data to characterize the effects of varying nutrients on the dynamics of the system. Our parameter estimates suggest that varying the nutrient supply of nitrogen and phosphorous can alter the dynamics of the infection in plants, specifically reducing the rate of viral production and the rate of infection in certain cases.

Scion genotypes exert long distance control over rootstock transcriptome responses to low phosphate in grafted grapevine

BackgroundGrafting is widely used in horticulture and rootstocks are known to modify scion growth and adaptation to soil conditions. However, the role of scion genotype in regulating rootstock development and functioning has remained largely unexplored. In this study, reciprocal grafts of two grapevine genotypes were produced as well as the corresponding homo-graft controls. These plants were subjected to a low phosphate (LP) treatment and transcriptome profiling by RNA sequencing was done on root samples collected 27 h after the onset of the LP treatment.ResultsA set of transcripts responsive to the LP treatment in all scion/rootstock combinations was identified. Gene expression patterns associated with genetic variation in response to LP were identified by comparing the response of the two homo-grafts. In addition, the scion was shown to modify root transcriptome responses to LP in a rootstock dependent manner. A weighted gene co-expression network analysis identified modules of correlated genes; the analysis of the association of these modules with the phosphate treatment, and the scion and rootstock genotype identified potential hub genes.ConclusionsThis study provides insights into the response of grafted grapevine to phosphate supply and identifies potential shoot-to-root signals that could vary between different grapevine genotypes.

Genetic variation associated with the shoot biomass of upland cotton seedlings under contrasting phosphate supplies

As over-fertilization leads to environmental concerns, selecting cultivars that can produce high yields on phosphorus (P)-deficient soils and understanding the genetic basis underlying P-starved tolerance have become crucially important. In this study, we evaluated the variation of ten P deficiency-related traits at the seedling stage of 419 core accessions in two different environments. The results showed that the shoot dry weight (SDW) could be considered an indicator for screening P-tolerant germplasm resources. A genome-wide association study (GWAS) was performed for two SDW-related traits using 3.66 million high-quality single-nucleotide polymorphisms (SNPs). A total of 102 significantly associated SNPs were located within or near 137 genes, of which, 27 of the SNPs were consistently detected for multiple traits or multiple environments. We further identified and validated a novel candidate gene, Gh_D11G2219, by qRT-PCR analysis and virus-induced gene silencing (VIGS), and the results suggested that Gh_D11G2219 plays a role in the positive regulation of tolerance to P deficiency stress in cotton. In addition, the elite SNPs linked to tolerance to P-starved stress have undergone negative selection pressure during the cotton breeding process. This is the first GWAS of P deficiency tolerance, and the identified SNPs and candidate genes provide valuable information for breeding highly P-efficient varieties.

Managing agricultural vulnerability to phosphorus scarcity through bottom-up assessment of regional-scale opportunities

Many developing countries are dependent on imported phosphorus (P) fertilizers and therefore increasingly vulnerable to scarcity of non-renewable global phosphate supplies, including short-term disruptions. A combination of participatory approach with quantitative substance flow analysis was used for identifying strategies for strengthening preparedness of regional food systems towards potential P scarcity. A P vulnerability index (PVI) – the lower its value, the higher the vulnerability (or P insecurity) – was defined on a regional scale in consultation with local stakeholders including government officials and experts and with farmers seriously affected by relevant policies and programmes. Potential mitigation and adaptation strategies were developed based on the estimated PVI and regional P flows. Regional policy planning and implementation with participatory approach are critical, because national, top-down policies may not cater to local and regional challenges and aspirations. The participatory approach offered fresh insights hitherto unidentified in top-down approaches. The study region, Sonipat in Haryana, India, is highly vulnerable to potential P scarcity (PVI of 38.68) but can theoretically reduce its P requirements by 11,574 t annually (about 85% of the current requirements) through recovery and recycling of P from human waste and by adjusting the fertilizer dose. Crop diversification combined with recycling and recovery of P and better governance can increase the PVI to 60 and above, implying adequate P security. Soil fertility, farmers' income, and access to institutional credit had the maximum impact on P vulnerability. The proposed framework can be applied in other countries to contextualize challenges related to P management and to devise strategies for building P security at regional scale.

Phosphate Homeostasis − A Vital Metabolic Equilibrium Maintained Through the INPHORS Signaling Pathway

Cells face major changes in demand for and supply of inorganic phosphate (Pi). Pi is often a limiting nutrient in the environment, particularly for plants and microorganisms. At the same time, the need for phosphate varies, establishing conflicts of goals. Cells experience strong peaks of Pi demand, e.g., during the S-phase, when DNA, a highly abundant and phosphate-rich compound, is duplicated. While cells must satisfy these Pi demands, they must safeguard themselves against an excess of Pi in the cytosol. This is necessary because Pi is a product of all nucleotide-hydrolyzing reactions. An accumulation of Pi shifts the equilibria of these reactions and reduces the free energy that they can provide to drive endergonic metabolic reactions. Thus, while Pi starvation may simply retard growth and division, an elevated cytosolic Pi concentration is potentially dangerous for cells because it might stall metabolism. Accordingly, the consequences of perturbed cellular Pi homeostasis are severe. In eukaryotes, they range from lethality in microorganisms such as yeast (Sethuraman et al., 2001; Hürlimann, 2009), severe growth retardation and dwarfism in plants (Puga et al., 2014; Liu et al., 2015; Wild et al., 2016) to neurodegeneration or renal Fanconi syndrome in humans (Legati et al., 2015; Ansermet et al., 2017). Intracellular Pi homeostasis is thus not only a fundamental topic of cell biology but also of growing interest for medicine and agriculture.

Trophic degradation predispositions and intensity in a high-flow, silted reservoir.

The objective of the work was to demonstrate the relationship between the natural environmental characteristics of a reservoir and its catchment and severity of trophic degradation. The shallow, highly-silted Rzeszów Reservoir (SE Poland) was the object of study. The impact on degradation of internal supply from accumulated bottom sediments was also assessed, using water and sediment sampled in 2013 and 2014. A high value for trophic state was identified for the reservoir on the basis of TSI indexes, while assessed natural resilience to degradation and analysis of the catchment as a supplier of biogenic and organic matter both indicate high susceptibility to cultural eutrophication. Obtained values for equilibrium phosphate concentrations under anoxic conditions (EPC-0) point to the possibility of a more intensive process of internal supply in phosphorus. However, the presence of sediments poor in organic matter suggest no major threat of ongoing eutrophication. Desludging and/or dredging are likely to entail elimination from the ecosystem of a large part of the pollutants accumulated in sediments, as well as the internal supply of phosphate to the water column. However, as external sources are responsible for the advanced degradation of Rzeszów Reservoir, any attempts at reclamation within the water will fail to yield persistent effects if appropriate protective procedures in the catchment are not implemented.

Neighboring plants divergently modulate effects of loss-of-function in maize mycorrhizal phosphate uptake on host physiology and root fungal microbiota.

Maize, a main crop worldwide, establishes a mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi providing nutrients to the roots from soil volumes which are normally not in reach of the non-colonized root. The mycorrhizal phosphate uptake pathway (MPU) spans from extraradical hyphae to root cortex cells housing fungal arbuscules and promotes the supply of phosphate to the mycorrhizal host in exchange for photosynthetic carbon. This symbiotic association with the mycobiont has been shown to affect plant host nutritional status and growth performance. However, whether and how the MPU affects the root microbial community associated with mycorrhizal hosts in association with neighboring plants, remains to be demonstrated. Here the maize germinal Mu transposon insertion mutant pht1;6, defective in mycorrhiza-specific Pi transporter PHT1;6 gene, and wild type B73 (wt) plants were grown in mono- and mixed culture and examined under greenhouse and field conditions. Disruption of the MPU in pht1;6 resulted in strongly diminished growth performance, in reduced P allocation to photosynthetic source leaves, and in imbalances in leaf elemental composition beyond P. At the microbial community level a loss of MPU activity had a minor effect on the root-associated fungal microbiome which was almost fully restricted to AM fungi of the Glomeromycotina. Moreover, while wt grew better in presence of pht1;6, pht1;6 accumulated little biomass irrespective of whether it was grown in mono- or mixed culture and despite of an enhanced fungal colonization of its roots in co-culture with wt. This suggested that a functional MPU is prerequisite to maintain maize growth and that neighboring plants competed for AM fungal Pi in low P soil. Thus future strategies towards improving yield in maize populations on soils with low inputs of P fertilizer could be realized by enhancing MPU at the individual plant level while leaving the root-associated fungal community largely unaffected.