Forms of phosphorus in bacteria and fungi isolated from two Australian soils

To understand the origin of organic and condensed forms of phosphorus (P) in soils, detailed information about P forms in microorganisms is required. We isolated 7 bacteria and 8 fungi from two Australian soils and analyzed the P forms in their pure cultures by extraction with NaOH-EDTA followed by ³¹P solution nuclear magnetic (NMR) spectroscopy. The bacteria belonged to the actinobacteria and the fungi to the ascomycota, as determined by rDNA sequencing. The proportions of broad forms of P were significantly different between the bacterial and fungal isolates (analysis of similarities, p = 0.001). Ortho-, pyro- and polyphosphate were present in higher proportions in fungi, while monoester and diester P were present in higher proportions in bacteria. Spectral deconvolution of the monoester region revealed 15 distinct resonances. The three major ones, which were identified by spiking experiments as glycerol 1-phosphate, glycerol 2-phosphate and adenosine-5′-monophosphate (AMP), comprised 56–74% of P in the monoester region. Ordination by principal component analysis and testing for treatment effects using analysis of similarities showed significant separation of P distribution in the monoester region between bacterial and fungal isolates (p = 0.007). However, neither group of microorganisms had a specific single P form which might be considered characteristic. As such, it may be difficult to distinguish soil P from bacterial or fungal origins, with the possible exception of a predominantly fungal origin of pyro- and polyphosphate. The identification of three major resonances in the monoester region of microorganisms is important, since the same resonances are found in ³¹P NMR spectra of soil extracts.     

Evenness and plant species identity affect earthworm diversity and community structure in grassland soils

Diversity of plant species and the species composition (identity) are known to influence below-ground diversity. In this paper we examine the effects of plant species diversity (richness and evenness), rates of nitrogen application and planting density, on earthworm community structure in grassland. The study was carried out at three sites in Ireland using a Simplex experimental design to define the compositions of the experimental plant communities used.A negative relationship was detected between diversity (evenness) of plant species and diversity of earthworms in the soils. However, plant species identity also affected the structure of the earthworm assemblage. In particular, the legume, Trifolium repens had a strong effect but this was conditional on the rate of nitrogen application. No earthworm species favoured communities dominated by slow growing grasses (Phleum pratense and Dactylis glomerata) (P = 0.02).Higher N inputs reduced earthworm abundance and biomass under T. repens. Earthworm richness, was negatively influenced by elevated amounts of N inputs. No effect of planting density was detected but this factor also did not affect plant biomass production.     

Influence of conifers on the forms of phosphorus in selected New Zealand grassland soils

We examined the effects of conifers on the forms of P in low-fertility tussock grassland soils using ³¹P nuclear magnetic resonance (NMR) and soil P fractionation. Results from field and glasshouse experiments clearly demonstrated that conifers enhanced the mineralization of labile (and to a lesser extent more resistant) forms of soil organic P which, in turn, increased amounts of labile inorganic P in the soil. These findings have important implications for P availability and long-term sustainable management of grassland soils in New Zealand.     

Effect of water composition on phosphorus concentration in runoff and water-soluble phosphate in two grassland soils

Many irrigation experiments determine phosphorus (P) losses from soil. Often, these studies cannot be compared, because the irrigation water was not characterized. We used calcium‐rich tap water and deionized water to investigate the influence of water composition on P concentrations in induced runoff. We irrigated two grassland sites: one acid and one calcareous. Less P was measured in runoff from tap water irrigation than from deionized water, especially for the acid soil. Batch experiments confirmed the findings of the field experiments. Tap water decreased water‐soluble phosphate and increased calcium in the solid phase. This interaction increased with decreasing soil:water ratio. Water of low ionic strength gave results comparable to rainwater. Our findings demonstrate that solution chemistry and the soil:water ratio can strongly influence the availability of P for transport. We recommend that P tests or irrigation experiments should use water resembling that of the system of interest. Irrigation experiments aiming to simulate P losses by surface runoff should be carried out with water having a composition comparable to rainwater.     

Relationship of soil phosphorus with uranium in grassland mineral soils in Ireland using soils from a long‐term phosphorus experiment and a National Soil Database

Phosphorus fertilizer contains contaminants that may increase the content in the soil and in plants. The relationship between soil P and soil uranium (U) was investigated to determine potential effects of P‐fertilizer use. This study is based on a long‐term experiment (38 years with 0, 15, and 30 kg fertilizer P ha^–1 y^–1) for beef production on grassland at Teagasc, Johnstown Castle, Wexford, Ireland and also on soils from a National Soil Database (NSD). The NSD soils were taken at fixed locations on a predetermined grid system at the density of one sample every 50 km². Of the 1310 samples in the NSD, the 760 grassland mineral soils were selected for this study. The aim was to determine to what extent P fertilizer increases the content of U in the soil. The results showed that there was a small but significant increase in soil U in the high‐P treatments, which contained high levels of soil P, in the long‐term field experiment. The results from the NSD showed that there was not a significant relationship between extractable (Morgan's) soil test P (STP) and U. It is concluded that the use of chemical P fertilizer at normal rates used in agriculture in Ireland is not a major threat to U content of soil based on the results of this study. There was a significant relationship between total P and STP, in the NSD, with the latter making up approx. 1% of the former. Soil available P increased with soil pH, probably reflecting the use of chemical P fertilizer and lime on agricultural soils.     

The effect of soil type on phosphorus sorption capacity and desorption dynamics in Irish grassland soils

Abstract. The phosphorus (P) sorption and desorption dynamics of eleven major agricultural grassland soil types in Ireland were examined using laboratory techniques, so that soils vulnerable to P loss might be identified. Desorption of P from soil using the iron-oxide paper strip test (Pfeo), water extractable P (Pw) and calcium chloride extractable P (Pcacl₂) depended on soil P status in all soils. However, soil types with high organic matter levels (OM), namely peat soils (%OM >30), had lower Pfeo and Pw but higher Pcacl₂ values compared to mineral soils at similar soil test P levels. Phosphorus sorption capacity remaining (PSCr) was measured using a single addition of P to soils and used to calculate total P sorption capacities (PSCt) and degree of P saturation (DPS). Phosphorus sorption capacities correlated negatively with % OM in soils indicating that OM may inhibit P sorption from solution to soil. High organic matter soils exhibited low P sorption capacities and poor P reserves (total P, oxalate extractable P) compared to mineral soils. Low P sorption capacities (PSCt) in peat soils were attributed to OM, which blocked or eliminated sorption sites with organic acids, therefore, P remained in the soil solution phase (Pcacl₂). In this work, peat and high organic matter soils exhibited P sorption and desorption characteristics which suggest that these soils may not be suitable for heavy applications of manure or fertilizer P owing to their low capacities for P sorption and storage.     

Anion and cation exchange resin membranes to assess the phosphorus status of some Portuguese soils

Abstract

Ion exchange resin methods were applied to 78 different soils to assess their phosphorus (P) status for predicting their response to P fertilization. The techniques used were anion exchange resin membranes eluted with hydrochloric acid (HCl) (AEM) and cation‐anion exchange resin membranes eluted with HCl (CAEM‐HC1), sodium chloride (NaCl) (CAEM‐NaCl) or water with directly color development (CAEM‐H₂O). Greenhouse studies were conducted with the same soils in order to validate laboratory data. Ryegrass was grown with two levels of P: nil and 150 mg P kg^‐1 of soil. Results indicate that soil P levels are significantly correlated (p<0.001) if extracted with AEM or CAEM, both eluted with HCl, although the CAEM technique had extracted larger amounts of P. Concerning the type of elution, results did not show significant differences (p<0.05) between CAEM‐HC1 and CAEM‐NaCl, but both were significantly correlated (p<0.001) with the results obtained with CAEM‐H₂O. All the techniques used to measure extractable P correlated significantly with relative yield and P uptake by ryegrass, showing their ability to predict soil P availability. Nevertheless, CAEM extraction had higher values of r². Among the three techniques for elution, the levels of correlation with the biological parameters were equivalent. From these results, it was concluded that: (i) exchange resins, specially CAEM, is an accurate method to assess the P fertility status of soils, and (ii) the traditional step of elution can be avoided, allowing the process to be less time consuming, thus more suitable for routine use.     

Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils

Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine.     

磷细菌在复垦土壤上生长规律及对磷解析特性的影响

为了解磷细菌在山西采煤塌陷复垦土壤上的应用效果,以采煤塌陷复垦土壤为研究对象,通过室内培养方法,设空白对照,探索了施有机肥(M)、磷细菌(B)、磷细菌+葡萄糖(BG)、磷细菌+尿素(BU)、磷细菌+葡萄糖+尿素(BGU)、磷细菌+葡萄糖+尿素+有机肥(BGUM)对磷细菌生长和土壤养分、磷吸附解吸的影响,其中磷细菌菌液浓度为1.2×108 CFU·m L?1,接种量为5 m L·盆?1。结果表明:在培养周期内各处理磷细菌数量呈先增加后减少的趋势,BGUM处理磷细菌数量远高于其他处理;培养的60 d内BGUM处理土壤磷细菌数量由最初的1.0×106 CFU·g?1降到3.3×104 CFU·g?1,60 d后,BGUM处理磷细菌数量分别是BGU、BG、BU、B处理的300倍、367倍、1 650倍、3 300倍。M、B和BGUM处理复垦土壤有效磷含量分别比CK处理增加172.27 mg·kg?1、3.00 mg·kg?1和188.9 mg·kg?1,施用有机肥或者接种磷细菌可以显著增加土壤有效磷含量,葡萄糖、尿素、有机肥与磷细菌配合施用对复垦土壤有效磷增加的效果更显著。随着外加磷源浓度的增加,各处理复垦土壤吸磷量和解吸磷量都呈现增加的趋势,Langmuir等温吸附方程是描述各处理等温吸附特征的最佳方法;与CK相比,BGUM处理土壤最大吸磷量降低幅度最大,减少119.05 mg·kg?1,吸附常数也显著降低,BGUM处理复垦土壤磷的平均解吸率为33.20%,显著高于其他处理(P0.05)。因此,在各处理中,BGUM处理土壤磷细菌数量最多,对复垦土壤有效磷的增加效果最显著,对土壤最大缓冲容量和平均解吸率影响最大。BGUM处理是磷细菌在复垦土壤上应用的最佳选择,即在复垦土壤上施用磷细菌时,应该与合适的碳源、氮源及有机肥共同配合施用。     

同位素动力学方法评价中国亚热带地区主要酸性土壤磷状况及生物有效性的适用性

A ^32P isotope kinetic approach was used to describe the chemical status and bioavailability of phosphorus in 32 acidic soils from subtropical China.By determining the residual radoactivity,rt,in soil solution at different time,t,after introduction of the isotope in an amount of R into the steady soil-water system,a well-defined isotope kinetic model was established,and upon this model the decrease rate ,n,of log(rt/R) with respect to logt,the mean sojourn time of phosphate ions in solution,the mean exchange rate and the mean flux of phosphate ions between soil solid and solution phases were calculated.Other parameters,such as the exchangeable P within the first minute of isotope exchange(E1),and P in various compartments that could be exchanged with solution phosphte ions at different perods of time,were also obtained.For these acidic soils,the r1/R had a significant correlation with the contents of clay and free Al2O3 where r1 is the radioactivity in solution 1 minute after introduction of the isotope into the system.Parameter n also had a significant correlation with clay content and a neagtive correlation with soil pH,E1 values and Cp,the P concentration in soil solution,also Significantly correlated with clay and sesquioxide contents of the soils.these indicated that these isotope kinetic parameters were largely influenced by P-fixing components of the soils.For the soils with strong P-fixing ability,the E1 values overestimated labile P pools and hence their correlations with A values and plant P uptake were not significant .The other iostope kinetic parameters also had no significant correlation with plant P uptak.On the other hand,the convetional chemical-extracted p correlated better with plant P uptake .It was concluded that the iostope kinetic method could assess the p chemical status yet it would inappropriate in predicting plant available P for soils with a high P-fixing ability as the problem of an overestimation of soil lable P in these soils was inevitable.     

EDTA extractable phosphorus in soils as related to available and inorganic phosphorus forms

Abstract

Twenty surface soil samples, representing two major soil orders alfisols and vertisols were extracted with 0.01N Na₂ EDTA solution (pH 4.8) at a soil/solution ratio of 1:25. Phosphorus in the extract was determined following ammonium molybdate‐stannous chloride colorimetric method. The EDTA extractable P showed significant positive correlations with extractable P according to the Olsen, Morgan, Bray 1 and 2 and also with inorganic phosphorus fractions associated with Al, Ca and Fe.     

Long-term phosphorus fertilisation increased the diversity of the total bacterial community and the phoD phosphorus mineraliser group in pasture soils

Fertilisers, especially nitrogen (N) and phosphorus (P) supplies, are frequently used in agricultural soil management to attain high crop yields. However, the intensive application of these chemical inputs can decrease the quality of agricultural soils and increase the probability of environmental pollution. In this study, the impact of P fertilisation on the diversity of the soil bacterial community was assessed. For this, a culture-independent approach targeting 16 rRNA and phoD genes was used on DNA extracted from pasture soils subjected to three different P fertilisation regimes for a long-term (42 years). As alkaline phosphomonoesterase (ALP) is necessary for mineralisation of organic P, an inverse relationship between the level of potential ALP activity and soil available P was expected. Indeed, a lower ALP activity was observed in soil subjected to higher chemical P fertiliser input. Analysis of the prevalence of three divergent families of ALP (PhoA, PhoD and PhoX) in metagenomic datasets revealed that PhoD is the most frequent ALP in soil samples and was selected as the most representative ALP possessed by the soil bacterial communities. Diversity of the phoD phosphorus mineraliser group, as well as the total bacterial community, was both increased in response to long-term P fertilisation. Specifically, phosphorus fertilisation decreased the relative abundance of certain taxa, including Acidobacteria and Pseudomonas fluorescens. In conclusion, this study shows that P fertilisation affects the microbial diversity of soil ecosystems, which might potentially modulate the soil biogeochemical cycle.     

Abundance and diversity of sulphur-oxidising bacteria and their role in oxidising elemental sulphur in cropping soils

There is an increasing interest in elemental S as a S fertiliser source, but to be available to plants, elemental S has to be oxidised to sulphate. Elemental S oxidation is known to be affected by soil properties and environmental conditions, but it is still unclear if elemental S oxidation is related to the abundance and diversity of S-oxidising bacteria in cropping soils. In this study, we investigated the abundance and diversity of S-oxidising bacteria by targeting a functional gene (soxB) and assessed their relationship with elemental S oxidation in ten cropping soils. Positive correlations between soil C, N and S contents on the one hand and the abundances of soxB and 16S ribosomal deoxyribonucleic acid (rRNA) genes on the other suggested that the abundances of S oxidising bacteria in particular and of bacteria in general depend on soil C and nutrient supply. Both soxB and 16S rRNA gene abundances were significantly correlated with the oxidation rate of elemental S (P < 0.05). In addition, more than 80% of the variation in the oxidation rate of elemental S could be explained by the combination of soxB or 16S rRNA gene abundances and soil pH, suggesting that pH not only affected bacterial abundances but also their activity during elemental S oxidation. Clone libraries constructed with the soxB primers showed genera belonging to Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria and Actinobacteria. The phylogenetic diversity and relative distribution of soxB clones revealed great differences across soils. However, no direct linkage was found between the diversity of S-oxidising bacteria and elemental S oxidation rate.     

Effects of land-use on the activity and diversity of methane oxidizing bacteria in forest soils

Methane is an important greenhouse gas and CH₄ oxidation in soil represents a significant sink for this gas. High capacity CH₄ oxidation potentials and molecular profiles of CH₄ oxidizing bacteria in soil were compared for five land-use treatments at a fully replicated experimental site within the Gisburn Forest Experiment, to assess the effects of land-use on both the potential activity of CH₄ oxidizing bacteria and their diversity. Forestry land-use was found to have a highly significant effect on CH₄ oxidation potentials. Highest CH₄ oxidation potentials were found in soils collected under stands of oak, in grassland plots, and in one soil under Norway spruce. A negative relationship between soil water nitrate concentration and CH₄ oxidation capacity was evident across the experimental site, with the high nitrate soils under stands of alder exhibiting little or no capacity for CH₄ oxidation even at optimal temperature and water content. Molecular profiles indicated that a diverse range of bacteria with the potential to oxidize CH₄ were present in all soils, however no clear correlation with CH₄ oxidation potential was identified.     

农作措施对集约化土壤中磷形态变化的影响

Phosphorus (P) in agricultural soils is an important factor for soil quality and environmental protection. Understanding of P and its fractions in soils on a regional scale is imperative for effective management or utilization of P and the improvement of P availability in soils. To study spatial variability and changes of soil P and its fractions as affected by farming practices, soil samples were taken in Rugao County, Jiangsu Province of China, an intensive agricultural area in the Yangtze River Delta region, in years of 1982 (n = 1 514), 1997 (n = 1 651), and 2002 (n = 342). High spatial variabilities of Olsen P and total P (TP) were observed throughout the study area. Loamy Stagnic Anthrosols and clay or loamy Aquic Cambosols had significantly higher concentrations of Olsen P and TP than sandy Ustic Cambosols and Aquic Cambosols. Olsen P and TP were increased from 1982 to 2002. The accumulations of Olsen P and TP in the cultivated soils were likely related to the increased application of P fertilizer, organic input, and soil incorporation of crop residues as well as conversion of soil use. Accumulated soil P was dominantly in labile and semi-labile P fractions. These P fractions may be utilized by future crop production by adjusting management practices, but they also pose a serious threat to nearby water bodies. Future strategies should include decreasing P fertilization in soils and supporting sustainable management. The information from this study can be used to monitor changes in soil fertility and environmental risks so that the use of fertilizers can become more rational.     

Characterization of phosphorus in sub-alpine forest and adjacent grassland soils by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy

We used chemical extraction methods and ³¹P-nuclear magnetic resonance (NMR) to investigate the effects of vegetation on the amount and structural composition of phosphorous (P) in the sub-alpine soils of central Taiwan. Chemical extraction methods were used to measure inorganic P (Pi) and organic P (Po) in main soil horizons. The soil P composition was assessed by ³¹P-NMR spectroscopy on alkaline EDTA–NaOH extracts. According to the results of chemical extractions, the forest soil had a higher amount of Pi than the grassland soil, which might be a result of the mineralization of Po. ³¹P-NMR spectra showed inorganic orthophosphate (up to 67%) and orthophosphate monoesters (up to 75%) as the major forms of P extracted in forest and grassland soils, respectively. Smaller proportions of orthophosphate diesters and trace amounts of phosphonates and pyrophosphate were found. With possible hydrolysis of P compounds during chemical extraction and slight systemic error in the processes of extraction with NMR, the results from NMR analysis are, in general, consistent with those of chemical extraction.     

Microbial biomass phosphorus contributions to phosphorus solubility in riparian vegetated buffer strip soils

This study tests the hypothesis that microbial biomass phosphorus (P) makes a significant contribution to P solubility in riparian buffer strip soils. In 36 soils collected from buffer strips within three UK soil associations, water-extractable inorganic P solubility was most strongly related to NaHCO₃ extractable inorganic P. However, within individual soil associations where soil pedological properties and management were similar, water-extractable inorganic P was most strongly related to microbial biomass P. These results highlight the difficulty in predicting dissolved P leaching risk based on agronomic soil P tests alone and the dissolved P leaching risk presented by having soils high in organic matter and microbial biomass P in close proximity to surface waters.     

Carbon pulses but not phosphorus pulses are related to decreases in microbial biomass during repeated drying and rewetting of soils

Drying and rewetting cycles are known to be important for the turnover of carbon (C) in soil, but less is known about the turnover of phosphorus (P) and its relation to C cycling. In this study the effects of repeated drying-rewetting (DRW) cycles on phosphorus (P) and carbon (C) pulses and microbial biomass were investigated. Soil (Chromic Luvisol) was amended with different C substrates (glucose, cellulose, starch; 2.5 g C kg⁻¹) to manipulate the size and community composition of the microbial biomass, thereby altering P mineralisation and immobilisation and the forms and availability of P. Subsequently, soils were either subjected to three DRW cycles (1 week dry/1 week moist) or incubated at constant water content (70% water filled pore space). Rewetting dry soil always produced an immediate pulse in respiration, between 2 and 10 times the basal rates of the moist incubated controls, but respiration pulses decreased with consecutive DRW cycles. DRW increased total CO₂ production in glucose and starch amended and non-amended soils, but decreased it in cellulose amended soil. Large differences between the soils persisted when respiration was expressed per unit of microbial biomass. In all soils, a large reduction in microbial biomass (C and P) occurred after the first DRW event, and microbial C and P remained lower than in the moist control. Pulses in extractable organic C (EOC) after rewetting were related to changes in microbial C only during the first DRW cycle; EOC concentrations were similar in all soils despite large differences in microbial C and respiration rates. Up to 7 mg kg⁻¹ of resin extractable P (P_resin) was released after rewetting, representing a 35-40% increase in P availability. However, the pulse in P_resin had disappeared after 7 d of moist incubation. Unlike respiration and reductions in microbial P due to DRW, pulses in P_resin increased during subsequent DRW cycles, indicating that the source of the P pulse was probably not the microbial biomass. Microbial community composition as indicated by fatty acid methyl ester (FAME) analysis showed that in amended soils, DRW resulted in a reduction in fungi and an increase in Gram-positive bacteria. In contrast, the microbial community in the non-amended soil was not altered by DRW. The non-selective reduction in the microbial community in the non-amended soil suggests that indigenous microbial communities may be more resilient to DRW. In conclusion, DRW cycles result in C and P pulses and alter the microbial community composition. Carbon pulses but not phosphorus pulses are related to changes in microbial biomass. The transient pulses in available P could be important for P availability in soils under Mediterranean climates.