Phosphorus Demand Research Articles

Assessing phosphorus fluxes in Portugal

Phosphorus (P) has been shown essential in the food sector. Due to the global shortage of P nutrients and the dependence on imports of phosphorus products and by-products, many countries have developed strategies to track the flows of this nutrient in their national territory. This comprises assessing which sectors and subsectors are the most relevant and identifying potential interventions for its recovery with consequent reduction of imports. Previous studies estimated that the circularity of the supply chain offers the possibility of satisfying the demand for phosphorus and reduce significantly the European Union's dependence on imports. The present research focuses on estimating the value of P fluxes in the Portuguese territory through Substance Flow Analysis (SFA) methodology to evaluate phosphorus's circularity within its production/consumption chain, collecting demographic, spatial, and economic data. Due to the great diversity of information and sources, the accuracy and reliability of the calculated fluxes were evaluated. P flows were compared through indicators that measure the effectiveness of use, accumulation, and losses of P nutrients among other countries (the UK, USA, Australia, New Zealand, France, Finland, and Japan) that have assessed the chain of this nutrient. The results show that soil nutrient management in Portugal in 2013 was considerably efficient (Soil out/ Soil in = 79 %). However, the urban system appears with a high amount of P in landfills (35.38 kt) and in treated wastewater (0.87 kt). The solid waste sector has ongoing P recovery measures, as it already has organic material recovery activities and indirect P recovery (1.39kt). In the influent wastewater, there is a possibility of recovering 8.2 kt of P, however there are no efforts or policies aimed at valuing this nutrient, as the same time that infrastructure improvements are needed to reduce P discharges into water body.

Phosphorus dynamics and sustainable agriculture: The role of microbial solubilization and innovations in nutrient management

Phosphorus (P) is an essential element for plant growth, playing a crucial role in various metabolic processes. Despite its importance, phosphorus availability in soils is often restricted due to its tendency to form insoluble complexes, limiting plant uptake. The increasing demand for phosphorus in agriculture, combined with limited global reserves of phosphate rock, has created challenges for sustainable plant production. Additionally, the overuse of chemical phosphorus fertilizers has resulted in environmental degradation, such as eutrophication of water bodies. Increasing agronomic phosphorus (P) efficiency is crucial because of population growth and increased food demand. Hence, microorganisms involved in the P cycle are a promising biotechnological strategy that has gained global interest in recent decades. Microorganisms' solubilization of phosphate rock (PR) is an environmentally sustainable alternative to chemical processing for producing phosphate fertilizers. Phosphorus-solubilizing microorganisms (PSMs), including bacteria and fungi, and their enzymatic processes offer an eco-friendly and sustainable alternative to chemical inputs by converting insoluble phosphorus into forms readily available for plant uptake. Integrating PSMs into agricultural systems presents a promising strategy to reduce dependence on chemical fertilizers, enhance soil health, and contribute to the transition toward more sustainable and resilient agricultural practices. It can be an alternative that reduces the loss of phosphorus in the environment, especially the eutrophication of aquatic systems. This paper explores the challenges of phosphorus availability in agriculture and the potential of microbial phosphorus solubilization as a sustainable alternative to conventional practices.

Calculating the effect of intensive use of urban organic waste on soil concentrations of potentially toxic elements in a peri-urban agriculture context in Norway

BackgroundRecycling nutrients and organic matter available as waste in urban areas may close nutrient gaps and improve soil quality, but the concentrations of potentially toxic elements (PTEs) are commonly higher than in mineral fertilisers. How quickly may the limits for soil quality be exceeded, and for which elements, if such materials are applied intensively? For a rough answer to this question, we used soil data from ten case farms near Oslo and Bergen (Norway) to estimate how PTE concentrations increased when the demand for nitrogen (N), phosphorus (P) and potassium (K) in a theoretical carrot crop produced every year was covered by compost or digestate from source-separated food waste, or composted garden waste, compared with manure from horses and poultry which are often kept in peri-urban areas.ResultsWith the intensive fertilisation assumed here, the Norwegian soil quality limits for PTEs were reached within 20–85 years, and faster for soil with more organic matter since regulatory limits set by weight discriminate soils with low bulk density. The limits were reached first for Cu and Zn, which are both essential micronutrients for crop plants. The concentrations of macronutrients in the urban waste-based fertilisers were not well balanced. Rates covering the K demand would lead to high surpluses of P and N. In peri-urban vegetable growing, high applications of compost are not unusual, but more balanced fertilisation is required.ConclusionsThe Norwegian regulations for PTEs in organic soil amendments and agricultural soil are stricter than in the EU, and do not support recycling of organic matter and nutrients from urban waste. Many materials which can only be applied with restricted amounts to Norwegian agricultural soil, may be applied according to crop demand in the EU. Growers utilising urban waste-based fertilisers intensively should monitor the soil regularly, including PTE analyses. Soil sampling should occur on fixed sampling points to reveal changes in concentrations over time. Norwegian authorities should consider a revision of the organic fertiliser regulation to support recycling of valuable organic materials. There is a need for more data on the PTE concentrations in agricultural soil and organic fertiliser materials.

Is the response of plant root systems to precipitation primarily driven by the rhizosphere soil?

BackgroundChanges in precipitation alter soil moisture, thereby affecting the aboveground and belowground ecological processes. However, it remains unclear whether plant root systems alter these effects through rhizospheric processes. In this study, a precipitation control experiment was conducted in the alpine grassland of northern Tibet to simulate precipitation changes with a 50% decrease and 50% increase in precipitation. Nutrient and microbial biomass, root traits, and survival strategies in the rhizosphere and bulk soils of the dominant plant, Stipa purpurea, were analyzed for alterations under precipitation changes.ResultsIncreased precipitation (IP) significantly decreased the rhizosphere soil total phosphorus and bulk soil ammonium nitrogen and increased the rhizosphere soil total potassium. Decreasing precipitation (DP) significantly increased the rhizosphere soil total potassium and decreased the bulk soil total potassium. DP significantly reduced microbial biomass carbon, nitrogen and phosphorus in rhizosphere soil, while IP significantly increased the bulk soil MBC:MBP, soil C:P imbalance, and soil N:P imbalance. Along the PC1 axis, where the contribution of the traits was relatively large, it was possible to define the root economic spectrum. The root system of Stipa purpurea from the DP treatment was distributed on the conservative side of the economic spectrum, whereas that from the control and IP treatments were clustered on the acquisition side.ConclusionsIncreasing and decreasing precipitation mainly affected the contents of total phosphorus and total potassium in rhizosphere soil and the contents of ammonium nitrogen and total potassium in bulk soil of Stipa purpurea. The microbial biomass carbon, nitrogen and phosphorus were mainly affected by a decrease in precipitation. Decreasing precipitation significantly reduced microbial biomass carbon, nitrogen and phosphorus, but the rhizosphere MBC:MBN, MBC:MBP and MBN:MBP remained stable under the change of precipitation. Increasing precipitation exacerbated the C:P imbalance and N:P imbalance in bulk soil, and increased the demand for phosphorus by bulk microorganisms. Increased precipitation promoted root access to resources. The root system of Stipa purpurea in the context of precipitation changes was driven by rhizosphere nutrients and bulk microorganisms. This study is important for revealing plant–microbe–soil interactions in terrestrial ecosystems.

AZNEK FOSFORITLARIDAN ODDIY FOSFORLI O‘G‘ITLAR OLISH ASOSLARI VA FIZIK-KIMYOVIY TEXNOLOGIYASI

The article examines the basics of the physico-chemical technology of obtaining simple phosphorus fertilizers from aznekic phosphorites, which is becoming more and more relevant in the context of the growing demand for phosphorus for agriculture. The chemical composition and mineralogy of aznekic phosphorites, as well as their role in the production of phosphorus fertilizers, are discussed. We analyze the main stages of the technological process, including the preparation, extraction and conversion of raw materials into phosphorus compounds. The available methods of obtaining phosphoric acid and phosphoric fertilizers such as superphosphate and ammophos are highlighted, as well as the economic and ecological aspects of the use of aznekic phosphorites in agronomy are considered. At the end of the article, it is emphasized the need to continue research and development of new technologies that will increase the stability of agriculture and increase the efficiency of resource use.

Bigger genomes provide environment-dependent growth benefits in grasses.

Increasing genome size (GS) has been associated with slower rates of DNA replication and greater cellular nitrogen (N) and phosphorus demands. Despite most plant species having small genomes, the existence of larger GS species suggests that such costs may be negligible or represent benefits under certain conditions. Focussing on the widespread and diverse grass family (Poaceae), we used data on species' climatic niches and growth rates under different environmental conditions to test for growth costs or benefits associated with GS. The influence of photosynthetic pathway, life history and evolutionary history on grass GS was also explored. We found that evolutionary history, photosynthetic pathway and life history all influence the distribution of grass species' GS. Genomes were smaller in annual and C4 species, the latter allowing for small cells necessary for C4 leaf anatomy. We found larger GS were associated with high N availability and, for perennial species, low growth-season temperature. Our findings reveal that GS is a globally important predictor of grass performance dependent on environmental conditions. The benefits for species with larger GS are likely due to associated larger cell sizes, allowing rapid biomass production where soil fertility meets N demands and/or when growth occurs via temperature-independent cell expansion.

Phosphorus Adsorption as Affected by Concretionary Nodules of Oxic Rhodustalf in Southern Guinea Savannah Agroecological Zone of Nigeria

Hard, rounded masses of mineral matter, known as concretionary nodules, can be found in soil or sedimentary rock. These nodules are typically made up of minerals like iron oxides, hydroxides, and carbonates that have been deposited in groundwater. Their sizes can range from small pebbles to large boulders, and they often differ in composition or hardness compared to the surrounding rock or soil. Nodules act as a highly effective storage space for extra P, leading to a significant increase in overall P requirements. Phosphorus, although an essential element for all living organisms, including plants and animals, is scarce. Despite its importance, only a small fraction of the total phosphorus available can be readily absorbed by plants. Given the worldwide demand for phosphorus in food production, it is crucial to devise techniques for extracting it from different sources. However, there has been limited research on the understanding of phosphorus availability and adsorption mechanisms in these areas. Therefore, the study focused on exploring the impact of concretionary nodules on phosphorus sorption and the characteristics of low-activity clay soil in the Guinea savannah of Nigeria. Soil samples collected from the study area were used to investigate the soil’s ability to absorb phosphorus at depths ranging from 0 to 30-60-90-120-150 cm in different soil and concretion locations. Various soil and concretion types demonstrated distinct capacities for phosphorus adsorption, as indicated by the adsorption isotherm. The maximum monolayer adsorption capacities (Qmax values) were 161.0, 154.5, 149.6, 141.7, 139.8, and 139.3 mg/g for OBC, OBS, OC, OIS, OS, and OIC, respectively. At equilibrium with a 50-ppm solution, the pseudo-second-order rate constants for P sorption were 1.180 x 10<sup>–4</sup>, 9.740 x 10<sup>–5</sup>, 1.120 x 10<sup>–4</sup>, 1.140 x 10<sup>–4</sup>, 1.000 x 10<sup>–4</sup>, and 8.010 x 10<sup>–5</sup> g mg<sup>–1</sup> min<sup>–1</sup> for OIS, OIC, OBS, OBC, OS, and OC, in that order. In the 300-ppm equilibrium solution, the OIS, OIC, OBS, OBC, OS, and OC pseudo-second-order rate constants were 1.250 x 10<sup>–4</sup>, 1.130 x 10<sup>–4</sup>, 9.550 x 10<sup>–5</sup>, 1.040 x 10<sup>–4</sup>, 2.750 x 10<sup>–4</sup>, and 1.420 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. At the 500-ppm equilibrium, the pseudo-second-order rate constants for OIS, OIC, OBS, OBC, OS, and OC were 1.240 x 10<sup>–4</sup>, 1.090 x 10<sup>–4</sup>, 1.020 x 10<sup>–5</sup>, 1.100 x 10<sup>–4</sup>, 2.730 x 10<sup>–4</sup>, and 1.180 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. Consequently, the soil adsorption capacity increased with higher pseudo-second-order rate constants.

Assessment of pilot-scale sewage sludge pelletization for non-food crop fertilization: nutrient content, pathogenicity, and growth performance.

Application of sewage sludge as fertilizer can be beneficial for sustainable agriculture as it could largely account for nitrogen and phosphorus demand for crops and has lower costs compared to other disposal routes, e.g., incineration, and sanitary landfills. This study evaluates the feasibility of pilot-scale pelletization of sewage sludge for non-food crops (e.g., ornamental plants). The co-pelletization method was designed by mixing sewage sludge and binder (tapioca starch) at a 9:1 sludge-to-starch weight ratio. The amount of nitrogen (N), phosphorus (P), and potassium (K) of the resultant pellets were determined at 5.7%, 4.9%, and 0.2%, respectively. Following Malaysian and US Standards, non-essential elements and pathogenicity of the pelletized sewage sludge were measured below the predetermined limits and hence safe for agricultural application. The planting trial using 50% inorganic fertilizer + 50% sewage sludge pellets exhibited a promising result on the growth of the flowering plant Celosia plumosa, with having better dimension and color, 20% higher in height, 4% more chlorophyll content, 54% more leaf, 43% greater stem growth, and 27% more flowers compared to control. Likewise, the planting trial on Tagetes erecta resulted in 10.5% wider leaf, 10.6% heavier leaf dry weight, and 12.5% more chlorophyll content compared to control with full usage of inorganic fertilizer. By considering liquidities to operate the production facility, the economic analysis estimated that the production cost per ton of pelletized sewage sludge produced was USD 0.98.

Impact of Phosphorus and Sulphur Levels on Growth Parameters of Groundnut (Arachis hypogaea L.)

Background: Groundnut, a well-recognized oilseed crop belonging to the Leguminosae family, faces several challenges in India that results in lesser productivity compared to the global average. The principal underlying cause of India’s diminished groundnut production lies in the irregular and inadequate utilization of essential nutrients. Given its status as a leguminous oilseed crop, it exhibits a heightened demand for phosphorus, calcium and sulphur, which often remains unmet, further exacerbating the problem. Methods: In a field experiment, split-plot design was employed to investigate the impact of four phosphorus levels (Control, 40, 50 and 60 kg P2O5 ha-1) and four sulphur levels (Control, 25, 50 and 75 kg S ha-1) on the growth parameters of groundnut. Results: The findings demonstrate that the utilization of phosphorus and sulphur fertilizers yielded significant improvements in various aspects of groundnut growth parameters. These improvements encompassed increased plant height, root length, improved root-to-shoot ratio on a length and weight basis, greater numbers of root nodules per plant and dry weight of root nodules per plant.

Numerical Variables Analysis and Improving Phosphorus Use Efficiency in Groundnut with Microbial Cultures in Coastal Zone of Puducherry

Background: The precise application of phosphorus fertilizer is pivotal in determining Groundnut (Arachis hypogaea L.) productivity. The high demand of phosphorus for energy transfer molecules involved in nitrogen fixation makes it essential for leguminous crop. A field experiment was conducted at Perunthalaivar Kamaraj Krishi Vigyan Kendra, Puducherry during 2021 to 2023 to explore the performance of groundnut by employing an optimal combination of microbial culture alongside varying levels of phosphorus. Methods: The experiment was laid out in randomized block design with 10 treatments and replicated thrice. The treatments consisted of different doses of phosphorus (@ 20, 40 and 60 kg/ha) with and without seed treatment with DGRC culture. Result: The experiment results of the three years study revealed that a variable response of groundnut to P fertilizer rates and rhizobium inoculant on sandy loam soil in puducherry. P fertilizer rates combined with DGRC inoculant had a significant influence on growth, root nodule, nodule dry weight, pod and kernel yield. From this study, it may concluded that combined application of P fertilizer @ 60 kg/ha and seed treatment of DGRC culture inoculants @ 20 g/kg seed have the potential to increase the productivity and profitability of groundnut. Correlation and Regression analysis also indicated that the yield attributes had a positive impact on groundnut yield.

Assessment of Inter- and Intraspecific P Efficiency in Forage Legumes as Affected by Recycling Fertiliser

Legumes have a high demand for phosphorus (P) due to energetically costly biological nitrogen fixation, but they also have effective physiological and morphological strategies for P mobilization. To evaluate the inter- and intraspecific P efficiency of small-grain legumes supplied with different P recycling fertilisers, eight accessions each of alfalfa (Medicago sativa L.) and red clover (Trifolium pratense L.) were cultivated in two pot experiments under greenhouse conditions until the flowering stage. To substantiate the results, some accessions were used in both experiments. Five treatments (no P, triple-superphosphate (TSP), sewage sludge ash (SSA), biowaste compost (compost), and struvite) were considered P sources. In addition to plant P uptake, the soil P pools were analysed in detail. Red clover showed higher yields and nutrient uptakes compared to alfalfa, but intraspecific effects were marginal. The addition of P resulted only partly in an increase in yield, despite the low P content in the soil. While struvite application clearly enhanced the P uptake of the plants in both experiments, SSA application had no effect compared to the control. The same treatment effect occurs with the bio-available soil P contents, which were on average 72.6 mg kg−1 after struvite and 44.3 mg kg−1 after SSA addition. Struvite as a P source was especially effective when applied to red clover. Our study aligns with previous field results and underscores the high potential of P mobilization of small-grain legumes without pronounced inter- or intraspecific differences. While struvite is suitable as a P fertiliser, the application of SSA to legumes is not recommended.

Global emergent responses of stream microbial metabolism to glacier shrinkage

Most cryospheric ecosystems are energy limited. How their energetics will respond to climate change remains largely unknown. This is particularly true for glacier-fed streams, which interface with the cryosphere and initiate some of Earth’s largest river systems. Here, by studying resource stoichiometry and microbial energetics in 154 glacier-fed streams sampled by the Vanishing Glaciers project across Earth’s major mountain ranges, we show that these ecosystems and their benthic microbiome are overall carbon and phosphorus limited. Threshold elemental ratios and low carbon use efficiencies (median: 0.15) modelled from extracellular enzymatic activities corroborate resource limitation in agreement with maintenance metabolism of benthic microorganisms. Space-for-time substitution analyses suggest that glacier shrinkage will stimulate benthic primary production in glacier-fed streams, thereby relieving microbial metabolism from carbon limitation. Concomitantly, we find that increasing streamwater temperature will probably stimulate microbial growth (temperature sensitivity: 0.62 eV). Consequently, elevated microbial demands for phosphorus, but diminishing inputs from subglacial sources, may intensify phosphorus limitation as glaciers shrink. Our study thus unveils a ‘green transition’ towards autotrophy in the world’s glacier-fed streams, entailing shifts in the energetics of their microorganisms.

Transition to cellular agriculture reduces agriculture land use and greenhouse gas emissions but increases demand for critical materials

Cellular agriculture, that is, the production of cultured meat and microbial proteins, has been developed to provide food security for a growing world population. The use of green energy technologies is recommended to ensure the sustainability of changing traditional agriculture to a cellular one. Here, we use a global dynamic model and life-cycle assessment to analyze scenarios of replacing traditional livestock products with cellular agriculture from 2020 to 2050. Our findings indicate that a transition to cellular agriculture by 2050 could reduce annual greenhouse gas emissions by 52%, compared to current agriculture emissions, reduce demand for phosphorus by 53%, and use 83% less land than traditional agriculture. A maximum 72% replacement of livestock products with cellular agriculture using renewable energy is possible based on the 2050 regional green energy capacities. A complete transition can be achieved but requires 33% of the global green energy capacities in 2050. Further, the accelerated demand for critical materials will not exceed their primary production capacities, except for tellurium. We conclude that a transition to cellular agriculture is possible with environmental benefits and provide a benchmark to study different alternatives to animal-based diets.

A Battery of Simple Bioassays for Domestic and Industrial Wastewater Treatment Plants in Konya, Turkey

Wastewater ingredients present risks to the environment and can cause health problems. The aim of this study was to identify the toxicological effects of influent and effluent wastewater from Konya Urban Wastewater Treatment Plant (KU WWTP) and Konya Organized Industrial Zone Wastewater Treatment Plant (KOI WWTP). Three different trophic level toxicity tests were conducted to determine the possible harmful effects of wastewater on the environment. The base toxic unit values of the Lepidium sativum toxicity test for the inlet and outlet samples of KU WWTP were found to be 1.43 and 1.10, respectively. Both values classified the analyzed wastewater into the “toxic” category. Wastewater entering the KU wastewater treatment facility was classified as “toxic” for the presence of toxic substances according to the Vibrio fischeri toxicity testing. Influent samples from the KOI wastewater treatment plant were classified as “toxic” with the Vibrio fischeri toxicity test. In addition, based on the fish bioassay value (TDF), wastewater from the KOI treatment facility was also classified as “toxic”. It was concluded that increased chemical oxygen demand and concentrations of total nitrogen and phosphorus and of certain heavy metals above the limits played a decisive role in classifying the samples as “toxic”. The results of this study suggest that all three tests have the potential to assess wastewater toxicity and that changes in wastewater properties may result in differences in test sensitivity.

Cover crops impact phosphorus cycling and environmental efficiency in a corn–soybean system

AbstractSolutions to simultaneously meet crop phosphorus (P) demand and reduce P loss from agricultural systems are required to improve the sustainability of our production. Our objective was to determine the effect of cover crop addition (with cover crop [CC], and without cover crop [NC]) and P fertilizer management (zero P control [CN], fall broadcast [FB], and spring injected [SI]) on P cycling, agronomic P use efficiency (PUE), and environmental P use efficiency (EPUE), measured as the percent of P lost in runoff water, in a no‐till corn (Zea mays)–soybean [Glycine max (L.) Merr.] rotation. The experiment was a 2 × 3 factorial. Both FB and SI increased P cycling through the main crop and cover crop tissue, compared to the CN. Cover crop did not affect main crop P uptake, removal in grain, or return to soil in crop residue, but CC treatment increased total P uptake and return in the system. Cover crop effects on P uptake, removal, and return were the same regardless of P fertilization treatments. Phosphorus fertilizer and CC treatments did not affect PUE. Both FB and SI P fertilizer management decreased EPUE, although SI tended to decrease EPUE less than FB. Cover crop significantly improved EPUE only in 2019, when CC reduced erosion losses. Therefore, cover crops were not consistently beneficial for reducing the environmental effects of P fertilization, and their use cannot replace the importance of sound P fertilizer stewardship, including sub‐surface P placement. However, cover crops play an important role in improving EPUE in years with high erosion loss potential.

Soil Enzyme Activity Differs among Native Species and Continuously Planted Eucalyptus Plantations

In recent years, monoculture and multi-rotation successional Eucalyptus plantations have given rise to several environmental issues, including the degradation of soil quality and nutrient imbalance, and the conversion of logging sites to multi-rotation Eucalyptus plantations has attracted considerable attention from the scientists involved. However, the effects of different management strategies on soil extracellular enzyme activities (EEAs) and enzyme stoichiometry (ES) in degraded Eucalyptus plantations are not clear. In this study, we investigated the responses and mechanisms of soil physicochemical properties, microbial biomass, carbon, and nitrogen- and phosphorus-acquiring enzyme activities, as well as the microbial resource requirements of Eucalyptus plantations, under different management strategies. The findings revealed that second-rotation (TWE) and third-rotation (THE) continuous plantings of pure Eucalyptus plantations resulted in significant decreases in soil organic carbon (SOC), total nitrogen (TN) and effective available phosphorus (AP) contents, while soil nutrient contents increased after the introduction of Manglietia glauca to form mixed forests (EM) with Eucalyptus or pure Manglietia glauca (M). Meanwhile, phosphorus-acquiring enzymes significantly increased with successive rotations of Eucalyptus (TWE and THE), while EEAC:P and EEAN:P gradually decreased and phosphorus limitation gradually increased compared to that of a native-species-mixed plantation (CK). After the introduction of Manglietia glauca (EM and M), phosphorus-acquiring enzyme activities showed lower levels and there were significant increases in EEAC:P and EEAN:P compared to those of continuous plantings of pure Eucalyptus plantations, which reduced microbial phosphorus demand. Moreover, soil nutrients played a more significant role in altering the EEAs and ES than did microbial biomass (0–10 cm: 72.7% > 53.3%, 10–20 cm: 54.5% > 32.6%). The results showed that EM and M improved soil fertility quality conditions and alleviated soil nutrient phosphorus limitations for soil microorganisms. Therefore, the introduction of Manglietia glauca, either to form mixed forests with Eucalyptus or in rotation with Eucalyptus, can be used as technical means for the conversion of multi-rotation successive Eucalyptus plantations.

Spatial Distribution of Nutrient Loads Based on Mineral Fertilizers Applied to Crops: Case Study of the Lobo Basin in Côte d’Ivoire (West Africa)

Eutrophication in the Lobo watershed remains a major problem. The work carried out has focused on chemical and biological analyses in the lake or in its immediate environment: they did not sufficiently take into account the diffuse transfer of nutrients over the entire watershed. This study aims to assess the nutrient (N and P) loads in the Lobo watershed, an agricultural area, to understand the spatio-temporal impacts of land management practices on eutrophication. The methodology uses two steps: streamflow calibration and nutrient (N and P) estimation using the Soil and Water Assessment Tool (SWAT) watershed model. Thus, the nutrient inputs were estimated based on the levels of N and P in every kilogram of Nitrogen-phosphorus-Potassium (NPK) type fertilizers applied by farmers. The average quantities of N and P applied to the crops were 47.24 kg ha−1 and 21.25 kg ha−1. Results show a good performance on flow calibration as evidenced using evaluation criteria R2, Nash–Sutcliffe Efficiency (NSE), and Percent Bias (PBIAS) of 0.63, 0.62, and −8.1, respectively. The yields of inorganic N and soluble P varied from 0 to 0.049 kg ha−1 and from 0 to 0.31 kg ha−1. These results show that the crops’ inorganic nitrogen requirements were higher than the demands for soluble phosphorus. Simulations relating to the organic N transfer revealed values ranging from 0.2 to 5 kg ha−1, while the transport of organic phosphorus was estimated to vary from 0.3 to 1.3 kg ha−1.

Effect of Elevated CO2 and Temperature on Phosphorus Harvest Index of Wheat (Triticum aestivum L.) at Various Levels of Phosphorus Fertilization

The possible alteration in plant growth, productivity and phosphorus (P) demand of wheat under rising atmospheric CO2 and temperature is expected to influence the partitioning of P to different plant parts of wheat. A phytotron experiment was conducted to study the effects of elevated atmospheric CO2 (650 µmol mol-1) and elevated temperature (ambient + 3 °C) on phosphorus harvest index of wheat at various levels (control, 100% and 200% of recommended P) of P fertilization. While there was a slight increase (5.6%) in P harvest index of wheat under elevated CO2, the reverse trend (12.7% decline) was observed under elevated temperature with no consistent effect at various levels of P fertilization. Interestingly, there was a moderate decline (7.7%) in P harvest index of wheat under combined elevation of CO2 and temperature as compared to their ambient combination. The results suggest that temperature could be the dominant factor as compared to the atmospheric CO2 in deciding the overall impact of projected increase in atmospheric CO2 and temperature on P harvest index of wheat. As there is logically possible relationship between P harvest index of wheat and various physical and nutritional qualities of wheat grains such as grain Zn and Fe content and their bio-availability, grain protein content, seedling vigour, etc., the decline in wheat’s P harvest index under projected levels of CO2 and temperature in our study underscores the need of undertaking elaborate experimentations to investigate the probable effects of climate change on quality parameters associated with P harvest index of wheat.

Endofungal Bacterial Microbiota Promotes the Absorption of Chelated Inorganic Phosphorus by Host Pine through the Ectomycorrhizal System.

Ectomycorrhizal fungi play an irreplaceable role in phosphorus cycling. However, ectomycorrhizal fungi have a limited ability to dissolve chelated inorganic phosphorus, which is the main component of soil phosphorus. Endofungal bacteria in ectomycorrhizal fruiting bodies are always closely related to the ecological function of ectomycorrhizal fungi. In this study, we explore endofungal bacteria in the fruiting body of Tylopilus neofelleus and their function during the absorption of chelated inorganic phosphorus by host pine through the ectomycorrhizal system. The results showed that the endofungal bacterial microbiota in the fruiting body of T. neofelleus might be related to the dissolution of chelated inorganic phosphorus in soil. The soluble phosphorus content in the combined system of T. neofelleus and endofungal bacteria Bacillus sp. strain B5 was five times higher than the sum of T. neofelleus-only treatment and Bacillus sp. strain B5-only treatment in the dissolution experiment of chelated inorganic phosphorus. The results showed that T. neofelleus not only promoted the proliferation of Bacillus sp. strain B5 in the combined system but also improved the expression of genes related to organic acid metabolism, as assesed by transcriptomic analysis. Lactic acid content was five times higher in the combined system than the sum of T. neofelleus-only treatment and Bacillus sp. strain B5-only treatment. Two essential genes related to lactate metabolism of Bacillus sp. strain B5, gapA and pckA, were significantly upregulated. Finally, in a pot experiment, we verified that T. neofelleus and Bacillus sp. strain B5 could synergistically promote the absorption of chelated inorganic phosphorus by Pinus sylvestris in a ternary symbiotic system. IMPORTANCE Ectomycorrhizal fungi (ECMF) have a limited ability to dissolve chelated inorganic phosphorus, which is the main component of soil phosphorus. In the natural environment, the extraradical hyphae of ECMF alone may not satisfy the phosphorus demand of the plant ectomycorrhizal system. In this study, our results innovatively show that the ectomycorrhizal system might be a ternary symbiont in which ectomycorrhizal fungi might recruit endofungal bacteria that could synergistically promote the mineralization of chelated inorganic phosphorus, which ultimately promotes plant phosphorus absorption by the ectomycorrhizal system.

Eighteen‐year nitrogen addition does not increase plant phosphorus demand in a nitrogen‐saturated tropical forest

Abstract Nitrogen (N) deposition usually increases plant tissue N concentrations and thus phosphorus (P) demand in young and/or N‐limited forests, but the N deposition effect on plant P demand has rarely been assessed in N‐saturated forests. Impacts of 18‐year external N additions (Control: 0, Low N: 50, Moderate N:100 and High N: 150 kg N ha−1 year−1) on leaf P of four plant life‐forms (tree, shrub, herb and liana), P fractions of bulk and rhizosphere soils were examined in a N‐saturated mature tropical forest in southern China. Leaf N, P and N: P ratios of all plant life‐forms remained stable under three N additions. Among soil P fractions, moderate labile organic P increased by 25%–33% across three N additions; and soil total P was increased by 11.76% under Low N, and 8.87% under High N, compared with the control. The PLS‐PM results showed that path coefficient of microbial community to available P significantly increased and of inorganic P to available P significantly decreased under N additions than control. N additions improved soil P availability through microbe‐mediated P transformation: Low N significantly increased soil microbial taxonomic diversity, and a higher microbial diversity could enlarge the sources of nutrient acquisition and stimulate decomposition of recalcitrant organic matters; while High N significantly decreased soil microbial taxonomic diversity, the remaining microorganisms that were screened by N‐rich environments had the characteristics of resisting the N addition effects and maintained efficient P acquisition. Synthesis. Our findings provide a novel line of evidence that long‐term N deposition did not increase plant P demand in a N‐saturated mature tropical forest. The underlying mechanism is that plants did not increase N uptakes therefore nor increase P uptakes (a stable leaf N: P stoichiometry) in an already N‐saturated ecosystem. Different N addition rates regulated soil P transformation via microbial community transition. These findings help improve the understanding of plant P acquisition and modelling of biogeochemical N–P cycling and vegetation productivity in N‐rich forest ecosystems, particularly considering the fact that chronic N deposition may likely lead to soil N richness and even saturation of many forests in the future.