Po Content Research Articles

High-rate nitrogen loading accelerates organic phosphorus loss through enzymatic and non-enzymatic processes in a semi-arid grassland

Semi-arid grasslands suffer from increased nitrogen (N) loading, which affects phosphorus (P) cycling. Phosphorus is essential but limited for all living organisms. Organic P (Po) is crucial for P supply in grasslands response to N loading, but its transformation process remains unclear. To elucidate P cycling, we evaluated P fractions, phosphatase activities, and their coding genes (pho genes phoD, phoX, and phoC) at both DNA and RNA levels in response to a nitrogen loading gradient. The results showed that the total P and Po contents significantly decreased with increasing N loading rates. In contrast, plant and litter biomass P exhibited an opposite trend but were insufficient to offset soil P loss. Unexpectedly, neither the phosphatase activities nor microbial biomass increased with increasing N loading rates, although the DNA abundance of pho genes responded positively to N enrichment. A partial correlation network indicated that N loading rates decreased Po levels through phosphatase activities, which were significantly associated with soil pH and the RNA abundance of pho genes. Moreover, non-enzymatic mineralization may be enhanced in Po cycling in semi-arid grasslands undergoing high N loading, especially following the initial stage of enzymatic mineralization. Although the activity of phosphatases did not continue to rise with increased N loading, the strategy for addressing N-induced P limitation through overconsumption of Po via non-enzymatic processes would accelerate the degradation of the ecosystem in the future.

Rare and Abundant phoD‐Harboring Bacteria Mediate the Mineralization of Organic Phosphorus Fractions in Soil Aggregates During Cut Slope Restoration

ABSTRACTPhosphorus (P) is the key nutritional element in the soil of cut road slopes undergoing ecological restoration, and the transformation of organic P (Po) is a crucial part of the P cycle. However, the role of phoD‐harboring bacteria in driving the mineralization of Po fractions in road slope soil aggregates is unclear. This study analyzed road slope soils that had undergone 7, 11, and 14 years of restoration in the western Sichuan Plateau of China. We examined the differences and associations between the Po fraction content, alkaline phosphatase (ALP) activity, and community composition of rare and abundant phoD‐harboring bacteria in soil aggregates of four particle sizes (0.053–0.25, 0.25–2, 0.053–0.25, and, > 2 mm). The results showed that NaHCO3‐extracted Po (NaHCO3‐Po) content in soil aggregates increased with restoration years, while NaOH‐extracted Po (NaOH‐Po) content decreased. ALP activity in soil aggregates increased with restoration years, but there was no significant relationship between ALP activity with the phoD‐harboring bacterial community. There were significant differences in the composition of rare and abundant phoD‐harboring bacterial communities during slope restoration. Soil moisture, pH, organic carbon, and the C:P ratio in soil aggregates were the primary factors affecting the distribution of the Po fractions and the phoD‐harboring bacterial community. NaHCO3‐Po and NaOH‐Po in soil aggregates were likely the main substrates for ALP‐mediated Po mineralization. More genera were involved in Po mineralization in slope soils restored for 14 years than in soils restored for 7 and 11 years, and rare phoD‐harboring genera were more actively involved in Po mineralization than abundant phoD‐harboring genera. This study provides some theoretical basis for P effectiveness enhancement and P management during slope soil restoration.

Impact of freeze-thaw cycles on the physicochemical properties and structure-function relationship of potato starch with varying granule sizes in frozen dough

Starch, as a critical component of dough, significantly influences quality preservation during the freezing process. In particular, the fine structure of potato (B-type) starch in frozen processing is a subject of considerable interest. This study aims to investigate the intrinsic differences of B-type starch and the impact of freeze-thaw (F/T) treatment on its molecular structure and physicochemical properties. Chain length distribution and X-ray photoelectron spectroscopy were utilized to examine the structural characteristics of natural potato starch with different granule sizes. Furthermore, the fine structure, thermal properties, and rheological properties of the isolated starches after F/T treatment were analyzed. The results indicate that potato starch with smaller particle sizes exhibits higher surface CC and PO content along with a higher proportion of very short chains (DP < 6, 8.17 %) and long B chains (DP > 25, 20.68 %). The study found that after F/T treatment, the surface of small-sized starch granules was initially damaged, exhibiting threads on the surface centered on the umbilical point. Following F/T treatment, both the crystallinity (very large (VL): 24.52–18.36 %; small (S): 17.03–16.69 %) and short-range order (VL: 2.97–2.61; S: 2.71–2.35) of starch particle size decreased. Both the amylose content (20.88–14.57 %) and ΔH (10.15–8.62 J/g) of isolated starch after freeze-thaw-treated dough exhibited a decrease to varying degrees. With the exception of the fifth cycle, small-size starch particles exhibited relatively higher G' and G" values and showed significant changes as a result of F/T treatment, demonstrating high hardness and complex viscosity. Clarifying the physicochemical properties of potato starches with different granule sizes is expected to expand their applications in frozen dough.

Effects of forest regeneration types on phosphorus fractions of soil aggregates in subtropical forest.

Soil aggregates are important for the storage and availability of phosphorus in the soil. However, how forest regeneration types affect phosphorus fractions of soil aggregates remains unclear. In this study, we examined the composition of aggregate particle size, phosphorus fractions, phosphorus sorption capacity index (PSOR), legacy phosphorus index (PLGC) and degree of phosphorus saturation by Mehlich 3 (DPSM3) in bulk soils and soil aggregates of Castanopsis carlesii secondary forest (slight disturbance), C. carlesii human-assisted regeneration forest (moderate disturbance), and Cunninghamia lanceolata plantation (severe disturbance), aiming to explore the impact of forest regeneration types on phosphorus availability and supply potential of bulk soils and soil aggregates. The results showed that forest regeneration types significantly influenced the composition of soil aggregates. The proportion of coarse macroaggregates (>2 mm) in the soil of C. carlesii secondary forest and human-assisted regeneration forest was significantly higher than that in the C. lanceolata plantation, while the proportion of silt and clay fraction (<0.053 mm) showed an opposite trend. The composition of soil aggregates significantly affected the contents of different phosphorus fractions. The contents of soil labile phosphorus fractions (PSOL and PM3) decreased as aggregate particle size decreased. The contents of soil total phosphorus (TP), total organic phosphorus (Po), mode-rately labile phosphorus fractions (PiOH and PoOH), and occluded phosphorus (POCL), as well as PSOR and PLGC, exhibited a trend of decreasing at the beginning and then increasing as particle size decreased. The contents of TP, Po, and PiOH in coarse and silt macroaggregates was significantly higher than that in fine macroaggregates (0.25-2 mm) and microaggregates (0.053-0.25 mm). Forest regeneration types significantly influenced the contents of phosphorus fractions of bulk soils and soil aggregates. The contents of TP, Po, PSOL, and PM3 in the soil of C. carlesii secondary forests was significantly higher than that in C. carlesii human-assisted regeneration forest and C. lanceolata plantation. The contents of PSOL and PM3 in different-sized aggregates of C. carlesii secondary forests were significantly higher than that in the C. lanceolata plantation. Forest regeneration types significantly influenced the composition and supply potential of phosphorus fractions in soil aggregates. The proportions of PSOL, and PM3 to TP in different-sized soil aggregates were significantly lower in C. carlesii human-assisted regeneration forest compared with C. carlesii secondary forest. PSOR and DPSM3 in different-sized soil aggregates were significantly lower in C. lanceolata plantation than that in C. carlesii secondary forest. Overall, our results indicated that natural regeneration is more favorable for maintaining soil phosphorus availability, and that forest regeneration affects soil phosphorus availa-bility and its supply potential by altering the composition of soil aggregates.

Disentangling the relative importance of precipitation, biocrust succession, and shrub cover in mediating soil phoD-harbouring communities and organic phosphorus mineralisation

Biological soil crusts (biocrusts) are crucial components of dryland ecosystems worldwide; however, their roles in phosphorus (P) transformation and associated functional communities have received less scientific attention compared with carbon (C) and nitrogen (N) cycling. Currently, little is known about the relative importance of precipitation, biocrust succession, and shrub cover in mediating soil P transformation. Here, we conducted a broad field survey across deserts in Northern China to investigate the roles of these factors in soil organic P (Po) mineralisation. We examined various P mineralisation parameters, including soil C:P ratio, soil Po content, bioavailable P, alkaline phosphatase (ALP)-encoding gene phoD abundance, and ALP activity. Additionally, we investigated the diversity and composition of soil phoD-harbouring communities and their relationships with Po mineralisation. Overall, the P mineralisation parameters increased with biocrust succession, and their responses to precipitation levels varied and were contingent upon the biocrust successional stages, while less significant differences were observed between the presence and absence of shrub cover. Most P mineralisation parameters were positively correlated within individual deserts or across all deserts studied. Moreover, the beta diversity, rather than the alpha diversity, of soil phoD-harbouring communities predominantly drove Po mineralisation. The abundance of certain genera (Actinoplanes and Micromonospora) that were relatively less dominant but showed significant positive correlations with P mineralisation parameters. By highlighting biocrust succession as the key determinant of soil Po mineralisation, the significance of precipitation and biocrust succession on phoD-harbouring communities, as well as the prevalence of community beta diversity in driving soil Po mineralisation, this study provides novel insights into the mechanisms underlying the transformation of Po into bioavailable P in biocrust systems.

Variation of 210-polonium in the cephalopod community from the Bay of Biscay, North-East Atlantic

Among natural radionuclides, 210Po is the major contributor to the radiation dose received by marine organisms. In cephalopods, 210Po is concentrated in the digestive gland, which contains over 90% of the whole-body burden of the nuclide. Although previous studies showed that 210Po was taken up independently of 210Pb, its parent nuclide, very little is known about the factors influencing its levels in cephalopods. To the best of our knowledge, no studies investigated 210Po levels in different species at the same time. In the present study, 210Po was analysed in the digestive gland of 62 individuals from 11 species representing a large range of feeding ecologies and habitats, including squids, cuttlefish and octopus species from coastal to deep-oceanic habitats. Among species, the highest activity was measured in Loligo vulgaris (5720 ± 3606 Bq/kg) and the lowest in T. megalops (188 Bq/kg). However, considering the habitats (benthic vs pelagic and neritic vs oceanic), no significant differences appeared. At the species level, no differences between sexes were found so both sexes were plotted together to test the size effect for species with at least 8 individuals (i.e., Eledone cirrhosa, L. vulgaris, L. forbesi and Sepia officinalis). In the first three species, 210Po levels decreased significantly with increasing size or weight but not in S. officinalis. In squid, this could be related to ontogenetic changes in diet from a high proportion of crustaceans (high Po content) in small individuals to fish (low Po content) in larger individuals, while the high dietary plasticity of S. officinalis at all stages of its life cycle could explain the lack of decrease in 210Po with size. In comparison to the few data from the literature, the levels of 210Po concentrations in the cephalopod community of the Bay of Biscay were overall in the same range than those reported in other cephalopods, varying across 4 orders of magnitude. Further studies are needed to understand the mechanism of retention in the cephalopod digestive gland.

Time‐dependent effects of ecological rehabilitation on soil phosphorus fractions on cut slopes in the mountains of Southwest China

AbstractWhen a cut slope is excavated, the ecological environment in the footprint is destroyed. Soil spray seeding technique is used for the ecological rehabilitation of cut slopes in the mountain areas of Southwest China. However, there have been few studies of the temporal variation in soil phosphorus (P) fractions during the rehabilitation of the cut slopes. In this study, time‐dependent changes in soil inorganic P (Pi) and organic P (Po) fractions of the cut slopes were assessed at selected post‐rehabilitation ages (i.e., 1 year, 1a; 3 years, 3a; 5 years, 5a; and 11 years, 11a). The results showed that the amounts of Pi and Po fractions in soils on rehabilitated cut slopes varied with time. The reduction in the total Po (TPo) content was mainly caused by the change in high concentration hydrochloric acid‐soluble Po (HHCl‐Po) in the soil. The reason for the highest TP content in 3a was the addition of inorganic fertilizer and straw in the artificial soil. The analyses of Pearson correlation and multiple stepwise linear regression showed that TPo and N:P were the main factors affecting the availability of soil P. With the increase in the post‐rehabilitation age, the limitation of soil P gradually weakened, but nitrogen became one of the limiting factors for plant growth. Overall, soil nutrient monitoring is very important for vegetation restoration of the cut slopes. Applying organic fertilizer after 5 years of ecological rehabilitation is conducive to long‐term supply of nutrients required for plant growth.

Long-term cattle manure addition enhances soil-available phosphorus fractions in subtropical open-field rotated vegetable systems.

Evaluation of the changes in phosphorus (P) fractions (various P forms) and their availability at different soil layers is critical for enhancing P resource use efficiency, mitigating subsequent environmental pollution, and establishing a suitable manure application strategy. However, changes in P fractions at different soil layers in response to cattle manure (M), as well as a combined cattle manure and chemical fertilizer application (M+F), remain unclear in open-field vegetable systems. If the amount of annual P input remains the same, identifying which treatment would cause a higher phosphate fertilizer use efficiency (PUE) and vegetable yield while simultaneously reducing the P surplus is especially warranted. Based on a long-term manure experiment that started in 2008, we used a modified P fractionation scheme to analyze P fractions at two soil layers for three treatments (M, M+F, and control without fertilizer application) in an open-field cabbage (Brassica oleracea) and lettuce (Lactuca sativa) system, and assessed the PUE and accumulated P surplus. The concentrations of the soil P fractions were higher in the 0-20-cm soil layer compared to the 20-40-cm layer, except for organic P (Po) and residual-P. M application significantly increased the inorganic P (Pi) (by 8.92%-72.26%) and the Po content (by 5.01%-61.23%) at the two soil layers. Compared with the control and M+F treatments, M significantly increased residual-P, Resin-P, and NaHCO3-Pi at both soil layers (by 31.9%-32.95%, 68.40%-72.60%, and 48.22%-61.04%), whereas NaOH-Pi and HCl-Pi at 0-20 cm were positively correlated with available P. Soil moderately labile-P was the predominant P component in the two soil layers (accounting for 59%-70%). With the same annual P input amount, M+CF created the highest vegetable yield (117.86 t ha-1), and PUE (37.88%) and M created the highest accumulated P surplus (128.80 kg ha-1yr-1). Collectively, a combined manure-chemical fertilizer application has great potential to yield a long-term positive outcome both in terms of vegetable productivity and environmental health in open-field vegetable systems. This highlights the methods' benefits as a sustainable practice in subtropical vegetable systems. Specific attention should be given to a P balance to avoid excessive P input if a rational strategy for manure application is to be attained. This is especially the case for stem vegetables that require manure application and decreases the environmental risk of P loss in vegetable systems.

Soil organic carbon stability mediate soil phosphorus in greenhouse vegetable soil by shifting phoD-harboring bacterial communities and keystone taxa

Addition of organic amendments, such as manure and straw, to arable fields as a partial substitute for mineral phosphorus (P), are a sustainable practice in high-efficiency agricultural production. Different organic inputs may induce varied soil organic carbon (OC) stability and phoD harboring microbes, subsequently regulate P behavior, but the underlying mechanisms are poorly understood. A 11-year field experiment examined P forms by 31P-nuclear magnetic resonance (NMR), OC chemical composition by 13C NMR, and biologically-based P availability methods, phoD bacterial communities, and their co-occurrence in soils amended with chemical P fertilizer (CF), chemical P partly substituted by organic amendments including pig manure (CM), a mixture of pig manure and corn straw (CMS), and corn straw (CS), with equal P input in all treatments. Organic amendments significantly increased soil labile Pi (CaCl2-P, citrate-P, 2.91–3.26 and 1.16–1.32 times higher than CF) and Po (enzyme-P, diesters, 4.08–7.47 and 1.71–2.14 times higher than CF) contents and phosphatase activities, while significantly decreased aromaticity (AI) and recalcitrance indexes (RI) of soil C, compared with CF. The keystone genera in manured soils (Alienimomas and Streptomyces) and straw-applied soils (Janthinobacterium and Caulobacter) were significantly correlated with soil enzyme-P, microbial biomass P (MBP), diesters, and citrate-P. Soil AI and RI were significantly correlated with the phoD keystone and soil P species. It suggested that the keystone was impacted by soil OC stability and play a role in regulating P redistribution in amended soils. This study highlights how manure and straw incorporation altered soil OC stability, shaped the phoD harboring community, and enhanced soil P biological processes promoted by the keystone taxa. The partial substitution of mineral P by mixture of manure and straw is effectively promote soil P availability and beneficial for environmental sustainability.

Rheological behavior with time dependence and fresh slurry liquidity of cemented aeolian sand backfill based on response surface method

Slurry transportation in pipelines is the key link in the filling process. Liquidity and rheological behavior are important bases for evaluating the feasibility and stability of slurry pipeline transportation and the rheological behavior is time-dependent. Research on the performance and application of cemented aeolian sand (AS) backfill (CASB) is in the preliminary stage, and the time effect and continuous response of various factors to the rheological behavior of CASB slurry have not been studied. Here, the CASB slurry contained AS as an aggregate, fly ash (FA) as an auxiliary material, ordinary Portland cement (PO) as a cementitious material, and water. The response surface method (RSM) was adopted to analyze the influence of PO content (x1), FA–AS ratio (x2), concentration (x3), and their interaction terms (x1x2, x1x3, and x2x3) on the rheological parameters (yield stress (τ0) and viscosity coefficient (η)) of slurry at 0, 40, 80 and 120 min. Additionally, liquidity (slump flow (Sf) and bleeding rate (Br)) of fresh slurry was evaluated. The rheological parameters increased with PO content, FA–AS ratio, and concentration, except that the bleeding rate first decreased and then increased with PO content, the slump flow and bleeding rate decreased with each response factor. The interaction term, x2x3 had a significant influence on τ0 and η at each curing time and Sf and Br, x1x3 had a significant influence on the τ0 and η at 40, 80, and 120 min, and x1x2 influenced τ0 and η at 80 and 120 min significantly. An improvement in one factor promoted the strengthening of another factor. τ0 increased as a quadratic function, and η increased as a primary or quadratic function with curing time. The fitting degree between τ0, η, and curing time was > 0.9, indicating that the rheological parameters of the slurry had a strong time dependence. In conclusion, this study determined the influence and mechanisms of PO content, FA-AS rate, concentration, and their interaction terms on the rheological behavior with time dependence and fresh slurry liquidity of CASB, thereby providing theoretical and engineering guidance for CASB filling.

Effect of Al(PO3)3, NaF, and SrF2 on structure and properties of fluorophosphate glass

The thermal stability and structural evolution of (55-x-y)Al(PO3)3-xNaF-8MgF2-10CaF2-ySrF2-17BaF2-10LiF (mol%) glasses were investigated. The thermal stability of the fluorophosphate glass system was characterized by DSC. As the content of metaphosphate increased, the thermal stability was strengthened. Besides, the thermal stability reached the strongest at alkaline metal and alkaline earth metal fluoride contents converged. On the one hand, according to Raman and FT-IR spectra, it was demonstrated that the intensity of OPO vibration in the glass structure was strengthened with the increase of Al (PO3)3 and NaF. On the other hand, 31P NMR results indicated that the POP bond was also enhancing when the Al (PO3)3 content increased. In summary, OPO and POP bonds were components of [PO4] units, and their increase signified that the structural stability of glass was enhanced. During the process of expanding the content of Al(PO3)3, deconvolution of O 1s and F 1s in XPS spectrum revealed that the increase of PO and FP bond content resulted in the structural distortion of polyhedral P[O, F]4 in glass structure and enhanced the disorder of glass.

Spatiotemporal distributions and relationships of phosphorus content, phosphomonoesterase activity, and bacterial phosphomonoesterase genes in sediments from a eutrophic brackish water lake in Chile

Phosphorus (P) cycling by microbial activity is highly relevant in the eutrophication of lakes. In this context, the contents of organic (Po) and inorganic (Pi) phosphorus, the activity of acid (ACP) and alkaline (ALP) phosphomonoesterase (Pase), and the abundances of bacterial Pase genes (phoD, phoC, and phoX) were studied in sediments from Budi Lake, a eutrophic coastal brackish water lake in Chile. Our results showed spatiotemporal variations in P fractions, Pase activities, and Pase gene abundances. In general, our results showed higher contents of Pi (110–144 mg kg−1), Po (512–576 mg kg−1), and total P (647–721 mg kg−1) in sediments from the more anthropogenized sampling sites in summer compared with those values of Pi (86–127 mg kg−1), Po (363–491 mg kg−1) and total P (449–618 mg kg−1) in less anthropogenized sampling sites in winter. In concordance, sediments showed higher Pase activities (μg nitrophenyl phosphate g−1 h−1) in sediments from the more anthropogenized sampling sites (9.7–22.7 for ACP and 5.9 to 9.6 for ALP) compared with those observed in less anthropogenized sampling sites in winter (4.2–12.9 for ACP and 0.3 to 6.7 for ALP). Higher abundances (gene copy g−1 sediment) of phoC (8.5–19 × 108), phoD (9.2–47 × 106), and phoX (8.5–26 × 106) genes were also found in sediments from the more anthropogenized sampling sites in summer compared with those values of phoC (0.1–1.1 × 108), phoD (1.4–2.4 × 106) and phoX (0.7–1.2 × 106) genes in the less anthropogenized sites in winter. Our results also showed a positive correlation between P contents, Pase activities, and abundances of bacterial Pase genes, independent of seasonality. The present study provided information on the microbial activity involved in P cycling in sediments of Budi Lake, which may be used in further research as indicators for the monitoring of eutrophication of lakes.

Straw returning mediates soil microbial biomass carbon and phosphorus turnover to enhance soil phosphorus availability in a rice-oilseed rape rotation with different soil phosphorus levels

The alleviation of phosphorus (P) limitation by increasing carbon (C) input is an effective strategy for improving crop production and P uptake efficiency. However, the effects of straw returning on soil microbial biomass P (MBP) turnover and P fractions in paddy-upland rotation remain poorly understood. Soil MBP turnover involves the mineralization and immobilization of organic P (Po), potentially altering P fractions and reducing the risk of P loss. The effects of straw returning on soil MBP turnover, P fractions and crop P utilization during the rice-oilseed rape rotation were evaluated in two field experiments with different soil Po levels. The treatments included no P fertilizer (-P), P fertilizer (+P) and P fertilizer plus straw returning (+P + S). The crop P uptake and cumulative P utilization efficiency were increased by straw returning. Straw addition promoted microbial biomass, decreased the MBC:MBP ratio in Po-high soil, increased the MBC:MBP ratio in Po-low soil, and increased the MBP turnover rates and fluxes in both soils. According to structural equation modeling (SEM), soil MBC and MBP had significant effects on crop P uptake directly or via P fractions. In Po-high soil, straw addition increased inorganic P (Pi) (NaHCO3 and NaOH) and decreased Po content by increasing the MBP turnover, while the Po-low soil mainly increased Po content. Among multiple observed variables, MBP was the most important driving factor controlling P uptake in Po-high soil, while MBC and NaOH-Pi were the best driving factors in Po-low soil. Additionally, the soil MBC, MBP and MBC:MBP ratios were higher in the oilseed rape season than in the rice season. Consequently, straw returning improves soil P availability by increasing MBP turnover, which is beneficial for improving P utilization.

A meta-analysis of arable soil phosphorus pools response to manure application as influenced by manure types, soil properties, and climate

Manure amendments to agricultural soils is an excellent opportunity for sustainable utilization of agricultural waste while providing multiple benefits to improve soil quality and increase the availability of nutrients to plants, including phosphorus (P). In this study, a meta-analysis of published data from 411 independent observations based on 133 peer-reviewed papers was performed for an in depth understanding of various factors affecting the transformation of soil P pools with manure application. Manure application increased all soil inorganic P (Pi) by 58.0%–282% and organic P (Po) by 65.0%–105%, while decreasing Po/total P (TP), compared to those in unamended soils. Manure types, soil TP, and manure application rates were the important factors that influenced soil P fractions. Elevation of soil labile Pi was more pronounced with compost application, while poultry and pig manure were more beneficial for promoting soil Pi fractions and stable Po contents compared with other manure types. The manure application rate had pronounced effect on increasing the stable Po fractions. The effects of manure application on increasing soil P fractions were greater in soils with lower TP contents as compared to that in high TP soils. Manure effects on enhancing soil labile Pi and moderately labile Pi were greater in acidic soil than that in neutral and alkaline soils. In addition, soil P fractions showed significant correlation with latitude and mean annual precipitation (MAP). By integrating the impacts of manure types, soil properties, and climate, this meta-analysis would help to develop the management of manure application in a specific region of agriculture as well as promote the interpretation of the interfering factors on the soil P fractions changes in the manure-amended soils.

No Tillage Increases SOM in Labile Fraction but Not Stable Fraction of Andosols from a Long-Term Experiment in Japan

No tillage (NT) fosters carbon (C) sequestration, increases soil organic matter (SOM) stock, and improves soil health. However, its effect on SOM accumulation in Andosol, which has high OM stabilization characteristics due to its specific mineral properties, remains unclear. In this study, we evaluated the effect of NT on SOM content and its distribution by the physical fractionation method and assessed the quality of accumulated SOM in each fraction. We collected soil samples at 0–2.5, 2.5–7.5, and 7.5–15 cm depths from NT and conventional tillage (CT) plots in a long-term (19 years) field experiment of Andosols in Ibaraki, Japan. The soil samples were separated into light fraction (LF), coarse-POM (cPOM: 0.25–2 mm), fine-POM (fPOM: 0.053–0.25 mm), and silt + clay (mOM: &lt;0.053 mm). The C, nitrogen (N), and organic phosphorus (Po) contents of each fraction were analyzed. The C content of cPOM and fPOM in NT at 0–7.5 cm was higher than in CT, while there was no clear difference in the mOM fraction or deeper layer (7.5–15 cm). NT increased the C, N, and Po contents in the labile POM fractions at the surface layers but did not increase the stable fraction or change the quality.

Phytorestoration of Sewage Sludge from the Mangrove Landfill of «Bois des Singes» by Planted Filters of &amp;lt;i&amp;gt;Pennisetum purpureum&amp;lt;/i&amp;gt; (Douala, Cameroon)

Human activities are causing wetland degradation. Macrophytes play an important role in the management of hydrosystems. They can therefore be used to restore a polluted environment. The aim of the study is to contribute to the phytorestoration of sewage sludge in nitrates, phosphates, cadmium, iron and lead from the Mangrove landfill of "Bois des singes" by planted filters of <i>Pennisetum purpureum</i>. A planted filter of <i>P. purpureum</i> was constructed. Sewages sludges samples were introduced into the device. Nitrates (NO₃), phosphates (PO₄), cadmium (Cd), iron (Fe) and lead (Pb) assays were carried out in water and plants at different levels of the filter (Settling basin B1, basin B2, basin B3, negative control and positive control) by absorption spectrophotometry flame atomic. The bioaccumulation and translocation factors as well as the bioaccumulation coefficient have been determined. The high contents of PO₄ (4000 mg/l), NO₃ (89 mg/l), Fe (5000 mg/l), Pb (20 mg/l) and Cd (0.08 mg/l) are greatly reduced by the filters at values below the tolerance threshold in B3 of 0.01 mg/l, 0.14 mg/l, 0.0002 mg/l, 0.0003 mg/l and 0.0003 mg/l respectively. The bioaccumulation factor shows that <i>P. purpureum</i> contained in barrels where the parameters are high is lead accumulator with a value of 1.305 (B2), hyperaccumulator of Fe and Cd with values of 10.05 (B2) and 13, 23 (B3). The leaf translocation is greater than 1 with Fe and Pb in the leaves of the boles. <i>P. purpureum</i> transfers Fe and Pb to the leaves. The planted filter of <i>P. purpureum</i> allows a restoration of this sewage sludge. This macrophyte extracts NO₃, PO₄, Cd, Fe and Pb and accumulates them in its vegetative system. <i>P. purpureum</i> cant be use to to restore the environment stressed by faecal sludge in the city of Douala.

Synergistic consortium of beneficial microorganisms in rice rhizosphere promotes host defense to blight-causing Xanthomonas oryzae pv. oryzae.

Rice plants primed with beneficial microbes Bacillus amyloliquefaciens and Aspergillus spinulosporus with biocontrol potential against Xanthomonas oryzae pv. oryzae, provided protection from disease by reprogramming host defence response under pathogen challenge. Plant-beneficial microbe interactions taking place in the rhizosphere are widely used for growth promotion and mitigation of biotic stresses in plants. The present study aims to evaluate the defense network induced by beneficial microorganisms in the rice rhizosphere, and the three-way interaction involved upon inoculation with dreadful bacteria Xanthomonas oryzae pv. oryzae (Xoo). Differential expression of defense-related enzymes, proteins, and genes in rice variety Swarna primed with a microbial consortium of Bacillus amyloliquefaciens and Aspergillus spinulosporus were quantified in the presence and absence of Xoo. The time-based expression profile alterations in leaves under the five distinct treatments "(unprimed unchallenged, unprimed Xoo challenged, B. amyloliquefaciens primed and challenged, A. spinulosporus primed and challenged, B. amyloliquefaciens and A. spinulosporus consortium primed and challenged)" revealed differential early upregulation of SOD, PAL, PO, PPO activities and TPC content in beneficial microbes primed plants in comparison to unprimed challenged plants. The enhanced defense response in all the rice plants recruited with beneficial microbe was also reflected by reduced plant mortality and an increased plant dry biomass and chlorophyll content. Also, more than 550 protein spots were observed per gel by PD Quest software, a total of 55 differentially expressed protein spots were analysed used MALDI-TOF MS, out of which 48 spots were recognized with a significant score with direct or supporting roles in stress alleviation and disease resistance. qRT-PCR was carried out to compare the biochemical and proteomic data to mRNA levels. We conclude that protein biogenesis and alleviated resistance response may contribute to improved biotic stress adaptation. These results might accelerate the functional regulation of the Xoo-receptive proteins in the presence of beneficial rhizospheric microbes and their computation as promising molecular markers for superior disease management.

Acid phosphomonoesterase and β-glucosidase activities in volcanic soils under permanent fertilized pastures: distribution profile and microbial effort toward P acquisition

ABSTRACT This work focused on the amounts and distribution of organic C (OC), organic phosphorus (Po), and acid phosphomonoesterase (AcP) and β-glucosidase (βG) activities in volcanic soils, as well as on the effect of inorganic P (Pi) on potential P-acquiring effort. The OC and Po contents are correlated with the active aluminum (Alox) and iron (Feox) and with the stratified gradients of the enzyme activities. The AcP activity does not seem to be suppressed by soil Pi content, showing a positive linear relationship with Pi. High values for the AcP:βG activity ratio are observed, which suggests a high energy allocation (C consumption) to ensure P demand. With the increase of Alox and Feox, the AcP:βG ratios increase and the potential C:P acquisition (ln(βG):ln(AcP)) values decrease. Nevertheless, the average C:P molar ratio of the six soils (115) are below the critical value, above which soils may present low P bioavailability. The results suggest that the effort for P acquisition (AcP:βG) and the potential C:P acquisition are both affected by the size of the Pi pools and by Alox and Feox contents. If Pi retention increases due to high contents of Alox and Feox, energy allocation shifts toward AcP production, in detriment of microbial population and plant nutrition. Considering the OC accumulation in the studied soils, several hypotheses may be considered such as the energy demand toward P acquisition, and the ability of Alox and Feox metal complexes to protect organic molecules to depress βG activity.

Distribution Characteristics of Soil Organic Phosphorus Fractions in the Inner Mongolia Steppe

Phosphorus (P) is one of the limiting nutrients in Inner Mongolia steppe soil, which seriously affect steppe productivity. Therefore, it is necessary to understand the distribution characteristics of organic P (Po) fractions and their influencing factors in Inner Mongolia steppe soil and to identify the contribution of Po fractions to soil available P (AP) to maintain the sustainable development of the Inner Mongolia steppe by improving the utilization rate of Po. The contents of soil Po fractions such as H2O-extractable Po (H2O-Po), NaHCO3-extractable Po (NaHCO3-Po), HCl-extractable Po (HCl-Po), NaOH-extractable Po (NaOH-Po), and phytate P (Phyt-P) were determined in soil samples (0–15 cm) from 15 sampling sites representing three types of grassland (i.e., desert steppe, typical steppe, and meadow steppe) in Inner Mongolia. The influencing factors of the soil Po fractions were determined by redundancy analysis (RDA). Soil Po content accounted for 61.0% of the total P (TP) on average. NaOH-Po was the main fraction of Po, accounting for 49.1% of Po on average; H2O-Po content accounted for the least amount of Po (mean 1.3 mg kg−1). H2O-Po and HCl-Po were not significantly different among the three steppes. The contents of NaHCO3-Po increased in the order of desert steppe < typical steppe < meadow steppe, and the trend of NaOH-Po and Phyt-P contents were desert steppe < meadow steppe < typical steppe. Pearson correlation analysis showed that NaHCO3-Po was positively correlated with AP (r = 0.86, p < 0.01). HCl-Po was negatively correlated with AP (r = − 0.56, p < 0.05). NaOH-Po and Phyt-P were significantly positively correlated with NaHCO3-extractable inorganic P (NaHCO3-Pi); Phyt-P was also negatively correlated with HCl-extractable Pi (HCl-Pi) (r = − 0.61, p < 0.05). These correlations were mainly caused by differences in steppe types and soil properties caused by climatic conditions, as shown by the result of RDA analysis. Soil Po plays an indispensable role in the supply of soil P in the semi-arid steppe of Inner Mongolia, where NaHCO3-Po and HCl-Po strongly contributed to AP. In addition, NaOH-Po and Phyt-P as a part of stable pools are important for providing P to other P pools. Po fractions in steppe soils were mainly regulated by climatic conditions and are closely related to the soil organic matter and pH.

Soil phosphorus accumulation changes with decreasing temperature along a 2300 m altitude gradient

Understanding the abundance of organic P in soil is a prerequisite for predicting the effects of climate change on P dynamics and availability in cold alpine regions. We sampled plant roots (up to 40 cm depth) and soils (100 cm depth) in grasslands along a 2300 m altitude gradient (1286–3589 m above sea level, mean annual temperature (MAT) from 9 to 0.3 °C) between alpine steppes on the Loess Plateau and alpine meadows on the Tibetan Plateau. A modified Hedley P fractionation in combination with root and microbial P, alongside phosphatase activity, was used to characterize P transformations depending on climate. Both the roots and microorganisms stored more P and produced higher phosphatase activity in cold meadow than in warm steppe soils. Total inorganic P (Pi) content decreased in cold meadow (MAT < 3 °C) compared with warm steppe soils because of the decrease of moderately labile Pi (extracted with diluted HCl) in cold meadow soils. Available P (NaHCO3) and labile Pi (NaOH) contents increased upslope, whereas the recalcitrant Pi (concentrated HCl) contents remained stable at all sites down to 100 cm soil depth. Labile (NaHCO3), moderately labile (NaOH) and recalcitrant (concentrated HCl) organic P (Po) contents sharply increased in cold meadow compared with warm steppe soils. The residue P in the 0–100 cm along the temperature gradient was similar to that of all Po fractions. The Po proportion in the total P was less than 10 % at sites with a MAT above 3 °C, but sharply increased up to 50 % at sites with a MAT below 0.7 °C. The greater root and microbial P uptake versus slower Po mineralization in cold meadows than in warm steppes increase the incorporation of Pi into organic pools in cold alpine areas. This accumulation of Po forms is a mechanism to prevent P losses by leaching as inorganic forms. The increased plant available P in cold meadows was associated with the increased phosphatase activity and Po contents compared with warm steppe soils. We conclude that the on-going climate warming could stimulate P cycling more in cold meadows than in warm steppe regions because Po dominated the total soil P in cold areas.