Phosphorus Accumulation Research Articles

Twice-Split Phosphorus Application Alleviates Low Temperature Stress by Improving Root Physiology and Phosphorus Accumulation, Translocation, and Partitioning in Wheat

In the context of global warming, low temperature (LT) disasters in major crops are also becoming more common. LT stress in the Huang-Huai-Hai Plain, the central wheat region in China, caused a massive reduction in wheat yields. A step towards ensuring wheat yield stability and food security, this study investigated the effects of optimizing phosphorus application on the root physiology, dry matter phosphorus accumulation, translocation, and partitioning of wheat under LT stress, using the representative cultivar Yannong 19 as the test material. The treatments included conventional phosphorus application (R1) and twice-split phosphorus application (R2), followed by −4 °C LT treatment and normal temperature (NT) treatment during the anther interval stage. Analysis of the root physiology (enzymatic activities and acid phosphatase, contents of malondialdehyde, soluble sugar, and soluble protein), phosphorus and dry matter accumulation, translocation, partitioning, and agronomic and yield-related components was carried during this research study. The results showed that the wheat root activity was significantly reduced and the antioxidant enzyme activities were increased to mitigate the damage of LT stress. Moreover, LT treatments damaged root function. The root activity and antioxidant properties were significantly lower than those of the NT treatment at the flowering stage. The dry matter and phosphorus accumulations were reduced by 30.6~33.6% and 15.1~21.3% at the flowering and maturity stages, resulting in final yield losses of 10.3~13.0%. In contrast, root activity increased by 16.1~27.2% in the twice-split phosphorus application treatments, and the root antioxidant characteristics were higher. As a result, dry matter and phosphorus accumulation increased after twice-split phosphorus application and their translocation to the grains was more; the final yield increased by 5.5~7.3%. Overall, the twice-split phosphorus application enhanced the physiological function of the root system and promoted the accumulation of nutrients and their transport to the grain, and alleviated the yield loss of wheat caused by LT stress.

Co-inoculation of phosphate-solubilizing bacteria and phosphate accumulating bacteria in phosphorus-enriched composting regulates phosphorus transformation by facilitating polyphosphate formation

This study aimed to explore the impact of co-inoculating phosphate-solubilizing bacteria (PSB) and phosphate accumulating bacteria (PAB) on phosphorus forms transformation, microbial biomass phosphorus (MBP) and polyphosphate (Poly-P) accumulation, bacterial community composition in composting, using high throughput sequencing, PICRUSt 2, network analysis, structural equation model (SEM) and random forest (RF) analysis. The results demonstrated PSB-PAB co-inoculation (T1) reduced Olsen-P content (1.4 g) but had higher levels of MBP (74.2 mg/kg) and Poly-P (419 A.U.) compared to PSB-only (T0). The mantel test revealed a significantly positive correlation between bacterial diversity and both bioavailable P and MBP. Halocella was identified as a key genus related to Poly-P synthesis by network analysis. SEM and RF analysis showed that pH and bacterial community had the most influence on Poly-P synthesis, and PICRUSt 2 analysis revealed inoculation of PAB increased ppk gene abundance in T1. Thus, PSB-PAB co-inoculation provides a new idea for phosphorus management.

Effects of tea application on cadmium, phosphorus, and iron accumulations in rice (Oryza sativa L.) seedlings

AbstractTo decrease the cadmium (Cd) uptake in rice and study the relationships of phosphorus (P), iron (Fe), and Cd uptakes in rice, the effects of four different tea types (green, black, dark, and white teas) on the P, Fe, and Cd accumulation in rice seedlings were studied. The results showed that only the black and dark teas increased the biomass of rice seedlings. The application of green, black, dark, and white teas increased the photosynthetic pigment content to some extent. Only the black tea increased the shoot P content, and the black, dark, and white teas increased the shoot Fe content. Compared with the control, only the black and dark teas decreased the shoot Cd content by 9.51% and 25.02%. Correlation and gray relational analyses showed that the root Cd content, soil pH value and soil exchangeable Cd concentration were the most closely associated with the shoot Cd content. The principal component and cluster analyses also showed the top three close cluster categories with shoot Cd content were root Cd content, soil exchangeable Cd concentration, and soil pH value. These findings indicate that the application of black and dark teas can promote the growth and decrease the Cd uptake of rice.

Isolation of euryhaline microalgal strains from tropical waters of Brunei Darussalam for potential biomass production

Abstract. Roseli W, Tanaka Y, Taha H. 2023. Isolation of euryhaline microalgal strains from tropical waters of Brunei Darussalam for potential biomass production. Biodiversitas 24: 4651-4660. Rapid urbanization has increased the accumulation of excess nitrogen (N) and phosphorus (P) in natural water bodies (eutrophication). Microalgae are seen as a viable candidate to resolve the problem due to their ability to absorb nutrients from the eutrophicated water (phycoremediation). Euryhaline microalgae could significantly benefit because they can tolerate various salinities while maintaining high biomass productivity. This study aimed to isolate euryhaline microalgae from tropical waters and evaluate the algae's potential to produce biomass and absorb nutrients in a wide range of salinities. Three strains labeled W1, W2, and W3 were isolated from Brunei waters and confirmed by DNA barcoding as Desmodesmus sp., Micractinium sp., and Chlorococcum sp., respectively. These strains were screened for salinity tolerance by exposing them to eight conditions (salinity 0, 5, 10, 15, 20, 25, 30, and 35) and evaluated for their high growth performance based on optical density. While the growth of Desmodesmus sp. and Chlorococcum sp. decreased from its highest value by 51% and 45%, respectively, the growth of Micractinium sp. was only reduced by 30%, and therefore, Micractinium sp. was considered to be the most euryhaline species and studied further in the next scale-up experiment. Micractinium sp. was cultivated at salinities of 0, 15, and 30 and recorded the highest biomass production of 54.1 ± 6.0 mg L?1 d?1 at salinity 15. Furthermore, they produced high amounts of N and P in their biomass, indicating that they are suitable for the phycoremediation of eutrophic water bodies. Therefore, Micractinium sp. is a potential candidate for open-pond cultivation because of its tolerance to a wide range of salinities and high biomass productivity.

Application of flocculated sewage sludge for growing miscanthus on post-mining lands

ABSTRACT Miscanthus yields well on raw subsoil where organic matter and nutrients are supplied by sewage sludge; the yield is directly dependent on the amount of sludge applied; the greatest productivity (12.9t/ha) was achieved by adding 60t/ha of flocculated sludge. Among the macronutrients, nitrogen is most actively absorbed, the intensity of biomass accumulation of phosphorus and potassium is much lower; other essential elements can be ranked as Fe → Zn → Mn → Cu. Cobalt, nickel and cadmium do not accumulate in biomass but chromium does. The introduction of sewage sludge affects the thermal characteristics of the miscanthus biomass. The proportion of incombustible residue increases when sludge is applied at high doses. Application of 20t/ha flocculated sludge appears to be optimal for ensuring environmental safety and suitability as a fuel.

Optimising fertigation of hydroponically grown sowthistle (Sonchus oleraceus L.): The impact of the nitrogen source and supply concentration

The efficient use of water and nutrients in leafy vegetable crops can be improved by effective water management, whereas the form of the supplied nitrogen may affect their quality and productivity. Sowthistle (Sonchus oleraceus L.), a widespread weed collected and consumed as a wild vegetable in the past, currently attracts a high interest for commercial cultivation due to its high nutritional value. The present study evaluated the effects of different nitrogen concentrations: N50: 50 mg L−1; (N 3.6 mmol L−1), N100: 100 mg L−1; (N 7.1 mmol L−1), N200: 200 mg L−1; (N 14.3 mmol L−1), and N300: 300 mg L−1; (N 21.4 mmol L−1) and different ammonium/total-N ratios (Nr: 0.01, 0.05, 0.10, 0.15) on growth, physiological parameters, antioxidant capacity and nutrient accumulation in the different plant parts of sowthistle, grown in Nutrient Film Technique hydroponic system. Total N was ammonium N plus nitrate N. Plant growth, total phenols, and antioxidant capacity were higher at the two intermediate N concentrations, whereas flavonoid and nitrogen content, as well as irrigation water productivity increased only with 200 mg N L−1 (N 14.3 mmol L−1), compared to the other three N concentrations. The accumulation of nitrogen in leaves and roots was lower, while leaf stomatal conductance was enhanced by increased N concentrations in the nutrient solution. Higher Nr ratios than ≥ 0.05 decreased plant dry matter, total phenols, flavonoids, and antioxidant capacity in leaf extracts, and negatively affected nitrogen translocation from roots to leaves. Sowthistle plants treated with a Nr of 0.05 exhibited a less intense oxidative stress, with decreased lipid peroxidation and hydrogen peroxide production, and increased superoxide dismutase and catalase activities, compared to those treated with higher Nr ratios. Increased Nr resulted in the accumulation of phosphorus and magnesium in leaves while the highest irrigation water productivity was obtained in plants grown with a Nr of 0.05. In conclusion, to increase yield, nutritional value and efficiency of water and nitrogen use in sowthistle grown in closed hydroponic systems, a N concentration of 200 mg L−1 of N (N 14.3 mmol L−1) and a Nr of 0.05 are suggested.

Phosphorus accumulation aggravates potato common scab and to be controlled by phosphorus-solubilizing bacteria

Phosphorus accumulation aggravates potato common scab and to be controlled by phosphorus-solubilizing bacteria

Salinity and nitrogen source affect productivity and nutritional value of edible halophytes.

Saline agriculture may contribute to food production in the face of the declining availability of fresh water and an expanding area of salinized soils worldwide. However, there is currently little known about the biomass and nutrient/antinutrient accumulation response of many edible halophytes to increasing levels of salinity and nitrogen source. To address this, two glass house experiments were carried out. The first to study the shoot biomass, and nutrient accumulation response, measured by ICP-MS analysis, of edible halophyte species, including Mesembryanthemum crystallinum (ice plant), Salsola komarovii (Land seaweed), Enchylaena tomentosa (Ruby Saltbush), Crithmum maritimum (Rock Samphire), Crambe maritima (Sea Kale) and Mertensia maritima (Oyster Plant), under increasing levels of salinity (0 to 800 mM). The second experiment studied the effects of nitrogen source combined with salinity, on levels of oxalate, measured by HPLC, in ice plant and ruby saltbush. Species differences for biomass and sodium (Na), potassium (K), chloride (Cl), nitrogen (N) and phosphorus (P) accumulation were observed across the range of salt treatments (0 to 800mM). Shoot concentrations of the anti-nutrient oxalate decreased significantly in ice plant and ruby saltbush with an increase in the proportion of N provided as NH4+ (up to 100%), while shoot oxalate concentrations in ice plant and ruby saltbush grown in the absence of NaCl were not significantly different to oxalate concentrations in plants treated with 200 mM or 400 mM NaCl. However, the lower shoot oxalate concentrations observed with the increase in NH4+ came with concurrent reductions in shoot biomass. Results suggest that there will need to be a calculated tradeoff between oxalate levels and biomass when growing these plants for commercial purposes.

Post-agricultural succession affects the accumulation and enzymatic transformation of organic phosphorus in a karst area, southwest China

Post-agricultural succession affects the accumulation and enzymatic transformation of organic phosphorus in a karst area, southwest China

Different cover crops have a limited impact on marketable yields and biogeochemical cycling but secondary effects on pollinators and plant-parasitic nematodes in Florida organic vegetable systems

Cover crops are typically grown during the summer in Florida’s organic vegetable systems, where they can affect nutrient cycling, soil health, and pests/pollinators. We compared the effects of five summer cover crops and a weedy fallow on marketable yields and the cycling of phosphorus, potassium, and carbon. Weed, nematode, and insect pollinator abundance were also monitored to measure any secondary impacts of cover cropping. Cover crops included monocultures of sunn hemp or sorghum sudangrass, a sunn hemp and sorghum sudangrass biculture, a three species mixture (biculture plus buckwheat), and a five species mixture (three species mixture plus cowpea and sunflower). In both 2018 and 2019, cover crops were planted in June and terminated in August, and bell peppers were grown from August until December. Marketable yields were greater with the tree and five species mixtures relative to the biculture in 2018, with no effects of cover crops on yields in 2019. Phosphorus and potassium accumulation was typically greater with cover crops than in the weedy fallow, but cover crops did not affect pepper nutrient accumulation or soil concentrations. Similarly, differences in carbon accumulation (lowest in sorghum sudangrass monoculture and weedy fallow) did not affect soil organic matter, soil total carbon or permanganate-oxidizable carbon. When analyzed as part of a radar plot analysis, cover crops helped manage summer weeds and root-knot nematodes in 2019, but the sorghum sudangrass monoculture increased sting nematodes; only the three and five species mixtures benefitted pollinators as buckwheat was the only cover crop that flowered in this study. Overall, cover crops had a limited effect on marketable yields and biogeochemical cycling but had more important secondary effects on pests and pollinators.

Microalgae-mediated tandem culture of shrimp and bivalve: an environmental and health co-benefits solution for phosphorus recovery and emission reduction

Phosphorus (P) accumulation in aquaculture systems is damaging our environment beyond acceptable levels. Devising strategies to potentially recover P from aquaculture systems in a reusable bioresource form is paramount and aligns with circular economy policies. In this study, we constructed two culture models, monoculture (Mon) and tandem culture (Tan), using Exopalaemon carinicauda and Mercenaria mercenaria. By monitoring the performance of rearing organisms, P dynamic patterns, and pollutant emissions, we found that: i) Compared to the Mon system, the Tan system demonstrated no differences in the performance of E. carinicauda and M. mercenaria, suggesting that the Tan model was viable in terms of fishery yield; ii) P in the Tan system could be efficiently recovered and removed from water and sediment, as indicated by the lower phosphate concentration in water (0.01 mg L−1), and the decrease in labile P in surface sediment (from 0.04 to 0.02 mg L−1). A combination of assimilatory and dissimilatory processes, mediated by phototrophic (bait-microalgae) and heterotrophic organisms (bivalves), appeared to be the primary mechanism for P utilization and removal; iii) The Tan system reduced pollutant emissions four times lower than the Mon system due to its minimal tailwater discharge (10%, 230 L). The emissions of total P, phosphate, total organic carbon, ammonium, and chemical oxygen demand from the Tan systems were 19 mg m−2 d−1, 2 mg m−2 d−1, 2 g m−2 d−1, 38 mg m−2 d−1, and 11 g m−2 d−1, respectively, 1.3, 1.7, 1.4, 1.3, and 1.2 times lower than those from the Mon systems. The eco-friendly Tan culture model fully exploited the resources of pond culture, a solution with environmental and health co-benefits for P recovery and emission reduction.

Responses of total, reactive and dissolved phosphorus pools and crop yields to long-term fertilization

Maintaining an appropriate soil phosphorus level is key to ensure sustainable phosphorus management for crop production and to minimise phosphorus losses to water bodies. However, the effects of long-term fertilization on different soil phosphorus pools, crop yields and phosphorus loss risk remain unclear. This requires insights into the responses of soil phosphorus pools, crop phosphorus uptake with related crop yields and phosphorus loss to long-term phosphorus inputs. Changes in four soil phosphorus pools (PCACL2, POLSEN, POX and PTOTAL, respectively) and crop yield responses to various fertilization rates were examined in a 29-year long-term phosphorus fertilization experiment in China. Results showed that the increase in the four soil phosphorus pools was proportional to the accumulated phosphorus surplus, i.e., the input minus uptake. POLSEN and POX increased linearly with continuous phosphorus application and peaked at a phosphorus accumulation near 3200 kg P ha−1. Beyond this threshold, continuous phosphorus application caused a gradual increase in PTOTAL and a linear increase in PCACL2, which implies an increasing risk for leaching. The POX pool accounted for 87% of the accumulated phosphorus surplus until soil phosphorus saturation occurred. The crop yields of wheat and maize responded clearly to changes in PTOTAL, POX, POLSEN and PCACL2, with POX explaining most of the yield variation. Furthermore, POX was highly correlated with PCACL2, being a risk indicator for phosphorus leaching. Given that POX explains best how much of phosphorus surplus accumulates in soil, the variation in crop yield, and the risk for P leaching, it can be used as a valuable and reliable indicator to manage phosphorus sustainably.

The effectiveness of forms of mineral fertilisers and productivity of winter wheat on grey-meadow soils of Kyrgyzstan

Fertilisation of winter wheat is necessary to provide the crop with nutrients for optimal growth, development, and formation of the crop. However, the effectiveness of fertilisers may depend on their shape, soil conditions, and climate. The purpose of the study is to examine the effectiveness of using various forms of mineral fertilisers on the formation of productivity of winter wheat on grey-meadow soils of Kyrgyzstan. In 2019-2021, field experiment was conducted in the Educational-experimental Farm of the Kyrgyz National Agrarian University, named after K.I. Skryabin to achieve this goal. As a result of the study, it was identified that the formation of high yields of winter wheat is closely related to the use of nitrogen-containing fertilisers in crop rotation, which contributes to the accumulation of nitrate nitrogen in the soil. The substantial effect of ammonium nitrate and granulated superphosphate on the nitrogen regime of the soil was also noted. The concentration of carbon-ammonium-soluble phosphates is determined by the actions of ammonium sulphate, ammonium nitrate, and all forms of phosphorus fertilisers, but no special changes in the phosphate regime of the soil under the influence of forms of phosphorus fertilisers were identified. However, when using complex fertilisers, a slight accumulation of mobile phosphorus in the soil was noted. The introduction of ammonium nitrate ensures the yield of winter wheat grain at the level of 56 centner/ha, ammonium sulphate – 53.1 centner/ha. granulated superphosphate provided the highest level of winter wheat yield – 55.5 centner/ha and the highest increase in yield against the background of nitrogen-potassium nutrition – 8.7 centner/ha. Therefore, for winter wheat, after rowed precursors, it is preferable to apply ammonium nitrate from nitrogen forms of fertilisers. As an alternative to it – ammonium sulphate or urea, from phosphorus forms of fertilisers – granular superphosphate. The practical importance of the results of the study allows for developing more effective methods of using fertilisers and increasing the productivity of grain crops on grey-meadow soils of Kyrgyzstan and in other regions with similar soil and climatic conditions

Accumulation and composition characteristics of organic phosphorus in sediments from the Yangtze River–connected lakes, China

Accumulation and composition characteristics of organic phosphorus in sediments from the Yangtze River–connected lakes, China

Tomato performance and changes in soil chemistry in response to salinity and Na/Ca ratio of irrigation water

Although unconventional water can be applied as an alternative for agricultural production, inappropriate irrigation water quality may adversely affect the soil crop system. Thus, field experiments under mulched drip irrigation were performed over three years (2017–2019) to investigate the impacts of three salinity (1, 2 and 3 g·L−1) with five Na:Ca molar ratios (1, 3, 5, 7 and 9) of irrigation water on tomato plant growth, fruit development, soil salt accumulation and soil sodium adsorption ratio. The results showed that, with irrigation water salinity of 1 g·L−1, the critical value of irrigation water Na:Ca molar ratio for the high yield and dry matter accumulation was 3 and 5, respectively, while the threshold for high concentration of vitamin C and lycopene was 7. With the irrigation water salinity of 2 g·L−1 and 3 g·L−1, the Na:Ca molar ratio threshold for a high concentration of soluble solids, vitamin C and lycopene was 5. Moreover, considering the increase of plant nitrogen and phosphorus accumulation, the decrease of sodium adsorption ratio at 40–100 cm soil layer inside the film, and the diminution of soil salt accumulation at 0–100 cm layer, irrigation water with higher salinity and lower Na:Ca molar ratio was more proper than that with lower salinity and higher Na:Ca molar ratio. Based on the multi-objective optimization with entropy-weight TOPSIS method, irrigation water with a salinity level at 2 g·L−1 and the Na:Ca molar ratio at 5 was suggested for tomato planting in the Yinbei Yellow River Irrigation District, China.

Inference of Rock Phosphate, Phosphorus Solubilizing Bacteria and Lime on Phosphorus Content and Economic Yield of Green Gram

Aim: To study the effect of Rock Phosphate, Phosphorus Solubilizing Bacteria, and Lime on phosphorus content in the soil, Phosphorus Uptake, and Economic yield of green gram (var. DGGS-4).
 Study Design: This experiment was conducted through a completely randomized design with 10 treatments and 3 replications.
 Place and Duration of Study: The research was conducted at the Department of Soil Science and Agricultural Chemistry, Central Agricultural University, Imphal between February 2019- November 2019.
 Methodology: Available phosphorus content in soil was estimated spectrophotometrically by Bray and Kurtz No. 1 method, the Active Phosphorus was determined by the addition of Saloid-bound phosphate, Aluminum phosphate, iron phosphate, and calcium phosphate, and total Inorganic P is the summation of all the inorganic forms of P. Total Phosphorus (Total P) in Soil was estimated by using Murphy-Riley solution and 5M NaOH and the intensity of yellow color was read at 730 nm in a spectrophotometer, organic P was calculated from the difference between total phosphorus and total mineral P, and the uptake of phosphorus was computed from the data on P concentration and dry matter yield.
 Results: The release and fixation pattern of different forms of phosphorus, its uptake, and the economic yield of green gram were significantly affected by the application of rock phosphate singly or combination with PSB and lime. Comparing among the different treatments, significantly higher accumulation of available Phosphorus, Phosphorus uptake, and economic yield were recorded in soil treated with Rock phosphate in combination with Phosphocare, Bacillus megatherium, and lime which is at par with treatment with Rock phosphate in combination with Bacillus megatherium and lime.
 Conclusion: The investigation revealed that the release and fixation pattern of different forms of phosphorus, its uptake, and the yield of green gram are significantly affected by the application of RP singly or combination with PSB and lime.

A Geospatial Modelling Approach to Assess the Capability of High-Country Stations in Delivering Ecosystem Services

The creation of more sustainable land use strategies is paramount to designing multifunctional agricultural landscapes that allow grasslands to continually deliver multiple ecosystem services. A mapping modelling approach would provide us with a tool for system diagnosis to better assess the value of a landscape and define place-based practices for designing more context-adjusted systems that are in synergy with the complexity of grasslands. To assess the potential capability of a high-country pastoral livestock production system in New Zealand in delivering ecosystem services, this work uses a geospatial model as a decision support tool to identify management practices that enhance grassland health. The model uses national, climatic, soil, and landcover data to assess the agricultural productivity, flood mitigation, C sequestration, erosion, and sediment delivery capacity of a case study high-country station in New Zealand. Model outcomes suggest that the station has the potential for increased agricultural productivity although varying spatially, a high flood mitigation capacity, a high capacity for C sequestration, a moderate risk of erosion, a capacity to reduce sediment delivery to streams, and overall, a low to moderate nitrogen and phosphorus accumulation. Output maps display a spatial visualisation of ecosystem services associated with the landscape topography, soil, and vegetation patterns that allow the identification of neglected areas and planning of best place-based management practices strategies to enhance the health of grasslands.

Effect of ecological restoration on topsoil phosphorus following afforestation on abandoned ponds in northern Chaohu Lake, China

Afforestation is an approach for ecological restoration. Soil total phosphorus is one of the important ecological and evolutionary elements for carbon cycles and plant growth following afforestation. However, studies on soil total phosphorus of afforestation on abandoned ponds with different slopes are still lacking. Soil total phosphorus and other soil properties from afforestation sites with different slopes were investigated. Soil total phosphorus, total nitrogen, bulk density, soil water contents and pH of poplar (Populus spp.) plantation sites (Slope 1) with a steep slope and pond cypress (Taxodium spp.) plantation sites (Slope 2) with a flat slope were determined. Soil total nitrogen stocks, soil total phosphorus stocks and the ratio of soil total nitrogen to total phosphorus (N:P) were calculated. Results showed that soil bulk density, soil water content, total phosphorus, total phosphorus stocks and total nitrogen stocks of three soil layers at Slope 1 were significantly lower than those of Slope 2. N:P of Slope 1 was significantly higher, but no significant difference of total nitrogen and pH were found between the two sampling sites. Soil bulk density, soil water content and total nitrogen had significant positive relationships with both total phosphorus and total phosphorus stocks. No obvious correlation was found between pH and total phosphorus or total phosphorus stocks. Redundancy analysis (RDA analysis) suggested that soil water content and bulk density had the most important individual effect on total phosphorus and total phosphorus stocks with values at 59.3% and 59.5%, respectively. It is recommended that afforestation on a flat or gentle slope rather than on a steep gradient could be helpful for accumulation of soil total phosphorus and phosphorus stocks and could decrease the risk of soil phosphorus loss, when afforestation is used for ecological restoration.

Overexpression of the HcPT1.1 transporter in Hebeloma cylindrosporum alters the phosphorus accumulation of Pinus pinaster and the distribution of HcPT2 in ectomycorrhizae.

Ectomycorrhizal (ECM) fungi are associated with the roots of woody plants in temperate and boreal forests and help them to acquire water and nutrients, particularly phosphorus (P). However, the molecular mechanisms responsible for the transfer of P from the fungus to the plant in ectomycorrhizae are still poorly understood. In the model association between the ECM fungus Hebeloma cylindrosporum and its host plant Pinus pinaster, we have shown that the fungus, which possesses three H+:Pi symporters (HcPT1.1, HcPT1.2 and HcPT2), expresses mainly HcPT1.1 and HcPT2 in the extraradical and intraradical hyphae of ectomycorrhizae to transport P from the soil to colonized roots. The present study focuses on the role of the HcPT1.1 protein in plant P nutrition, in function of P availability. We artificially overexpressed this P transporter by fungal Agrotransformation and investigated the effect of the different lines, wild-type and transformed ones, on plant P accumulation, the distribution of HcPT1.1 and HcPT2 proteins in ectomycorrhizae by immunolocalization, and 32P efflux in an experimental system mimicking intraradical hyphae. Surprisingly, we showed that plants interacting with transgenic fungal lines overexpressing HcPT1.1 did not accumulate more P in their shoots than plants colonized with the control ones. Although the overexpression of HcPT1.1 did not affect the expression levels of the other two P transporters in pure cultures, it induced a strong reduction in HcPT2 proteins in ectomycorrhizae, particularly in intraradical hyphae, but still improved the P status of host plant shoots compared with non-mycorrhizal plants. Finally, 32P efflux from hyphae was higher in lines overexpressing HcPT1.1 than in the control ones. These results suggest that a tight regulation and/or a functional redundancy between the H+:Pi symporters of H. cylindrosporum might exist to ensure a sustainable P delivery to P. pinaster roots.

Speciation and microscale distribution of phosphorus compounds accumulated in continuously fertilized greenhouse soils

AbstractThe overuse of phosphate fertilizer results in the accumulation of surplus phosphorus (P) compounds in soil, and this trend is particularly intense in greenhouse farming. We aimed to characterize P compounds in greenhouse soils by comparing their speciation in soil samples collected from greenhouses and an open field. Two soil types with different phosphate sorption abilities, namely, Ultisol and Andisol, were considered. Phosphorus compounds in the soil were characterized by bulk soil analysis via acid extraction; molecular‐scale analyses by solid‐state 31P nuclear magnetic resonance and P K‐edge X‐ray absorption near edge structure and spatially resolved analyses by electron probe microanalyzer and micro‐X‐ray absorption near edge structure. Spectroscopic results showed that a larger proportion of P compounds associated with inorganic P compounds associated with calcium (Ca‐P) was present in the greenhouse soil than in the open‐field soil. Some P compounds in the greenhouse Andisol were Ca‐P, even though Andisol has a high phosphate sorption ability due to an abundance of aluminum‐bearing sorbents. Heterogeneously distributed spots of Calcium phosphate, most likely hydroxyapatite or tricalcium phosphate, were found at the microscale in the greenhouse Ultisol soil grain. In addition to the detection of poorly‐soluble Ca‐P, a larger proportion of Ca‐P was potentially plant available. Spatially resolved analyses showed that organic amendments containing Ca‐P were incorporated into the Andisol soil grains. Our study demonstrated that Ca‐P with different solubilities can serve as a source of phosphate even in soils of high phosphate sorption ability under greenhouse conditions.