Biotic and abiotic pathways of phosphorus cycling in minerals and sediments: insights from oxygen isotope ratios in phosphate

A key question to address in the development of oxygen isotope ratios in phosphate (δ(18)O(p)) as a tracer of biogeochemical cycling of phosphorus in ancient and modern environments is the nature of isotopic signatures associated with uptake and cycling of mineral-bound phosphate by microorganisms. Here, we present experimental results aimed at understanding the biotic and abiotic pathways of P cycling during biological uptake of phosphate sorbed to ferrihydrite and the selective uptake of sedimentary phosphate phases by Escherichia coli and Marinobacter aquaeolei. Results indicate that a significant fraction of ferrihydrite-bound phosphate is biologically available. The fraction of phosphate taken up by E. coli attained an equilibrium isotopic composition in a short time (<50 h) due to efficient O-isotope exchange (between O in PO(4) and O in water; that is, actual breaking and reforming of P-O bonds) (biotic pathway). The difference in isotopic composition between newly equilibrated aqueous and residual sorbed phosphate groups promoted the ion exchange (analogous to isotopic mixing) of intact phosphate ions (abiotic pathway) so that this difference gradually became negligible. In sediment containing different P phases, E. coli extracted loosely sorbed phosphate first, whereas M. aquaeolei preferred Fe-oxide-bound phosphate. The presence of bacteria always imprinted a biotic isotopic signature on the P phase that was taken up and cycled. For example, the δ(18)O(p) value of loosely sorbed phosphate shifted gradually toward equilibrium isotopic composition. The δ(18)O(p) value of Fe-oxide-bound phosphate, however, showed only slight changes initially but, when new Fe-oxides were formed, coprecipitated/occluded phosphate retained δ(18)O values of the aqueous phosphate at the time of formation of new Fe oxides. Concentrations and isotopic compositions of authigenic and detrital phosphates did not change, suggesting that these phosphate phases were not utilized by bacteria. These findings support burgeoning applications of δ(18)O(p) as a tracer of phosphorus cycling in sediments, soils, and aquatic environments and as an indicator of paleo- environmental conditions.     

Organic phosphorus in some northern nigerian soils in relation to soil organic carbon and as influenced by parent rock and vegetation

The distribution of organic phosphorus in relation to soil organic matter and the influence of parent material and vegetation of organic P level was studied in a number of soil profiles in the northern half of Nigeria. There was a close relationship between soil organic carbon and organic phosphorus contents of these soils. The ratios of these two ingredients were all less than 200:1. This fact suggests that organic P is likely to be mineralised. The effect of parent rock on organic P contents was slight, but there was an indication that soil profiles on metamorphic parent rocks contained more organic phosphorus than those on sedimentary parent material. Vegetation had a great influence on organic P as shown by the relatively higher organic phosphorus contents of profiles from southern Guinea savanna and the lower contents of the Sudan vegetation zone. The profiles from impeded drainage sites (fadamas) were generally richer in organic phosphorus than were those from comparable vegetation zones on well drained sites.     

Impact of transgenic tobacco on trinitrotoluene (TNT) contaminated soil community

Environmental contamination with recalcitrant toxic chemicals presents a serious and widespread problem to the functional capacity of soil. Soil bacteria play an essential role in ecosystem processes, such as nutrient cycling and decomposition; thus a decrease in their biomass and community diversity, resulting from exposure to toxic chemicals, negatively affects the functioning of soil. Plants provide the primary energy source to soil microorganisms and affect the size and composition of microbial communities, which in turn have an effect on vegetation dynamics. We have found that transgenic tobacco plants overexpressing a bacterial nitroreductase gene detoxify soil contaminated with the high explosive 2,4,6-trinitrotoluene (TNT), with a significantly increased microbial community biomass and metabolic activity in the rhizosphere of transgenic plants compared with wild type plants. This is the first report to demonstrate that transgenic plants engineered for the phytoremediation of organic pollutants can increase the functional and genetic diversity of the rhizosphere bacterial community in acutely polluted soil compared to wild type plants.     

解磷细菌肥对烤烟磷素吸收和磷肥利用率的影响

为探究解磷细菌肥对烤烟磷素吸收和磷肥利用率的影响,以云烟87为供试品种,设置解磷细菌肥（0、75 kg/hm²）与磷肥（0、1250 kg/hm²）的双因素随机区组试验,分析了烤烟根际土壤有效磷、微生物、根系活力、干物质积累量和各器官磷素吸收的变化。结果表明,解磷细菌肥配施磷肥可极显著提高烤烟根际土壤有效磷含量,显著提高烤烟根际土壤可培养细菌数量,提高烤烟根际土壤微生物AWCD,极显著提高土壤微生物对碳水化合物、氨基酸和胺类碳源的利用能力,改变微生物群落碳源代谢特征;显著提高了烤烟根系活力,促进了干物质量积累和磷素吸收,磷肥利用率显著提高了4.89%。     

Do earthworms mobilize fixed zinc from ingested soil?

A wide range of organisms inhabit the soil and has to deal with soil-bound metals. The bioavailable fraction of metals may be estimated explicitly using the isotopic dilution technique. In the present paper, we evaluated the isotopic exchange technique for assessing the bioavailability of soil Zn (using 65Zn) to earthworms. To validate the technique, the worms were first exposed to various 65Zn levels, and errors due to soil entrained in the gut were evaluated. This exposure indicated no effect of gamma-radiation on growth (wet weight gain) of the organisms and that depuration of the earthworms minimized errors in labile pools determined by isotopic dilution. Our study further showed that the earthworms accessed 55-65% of the total Zn in the soil. The labile pool for the earthworms Eisenia andrei was similar to that for the plant Lactuca sativa, indicating that earthworms and plants to a large extent access the same fraction of soil Zn. Hence, the isotopic dilution technique has the potential to assess biologically available pool of Zn in soils. As lettuce is not known to significantly mobilize nonlabile metals in soil, this study indicates that Zn uptake by E. andrei is predominantly via the exchangeable pools (possibly the soil pore water) rather than dissolution of Zn held within soil particles or within soil organic matter or other food sources.     

NanoSIMS study of organic matter associated with soil aggregates: advantages, limitations, and combination with STXM

Direct observations of processes occurring at the mineral-organic interface are increasingly seen as relevant for the cycling of both natural soil organic matter and organic contaminants in soils and sediments. Advanced analytical tools with the capability to visualize and characterize organic matter at the submicrometer scale, such as Nano Secondary Ion Mass Spectrometry (NanoSIMS) and Scanning Transmission X-ray Microscopy (STXM) coupled to Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS), may be combined to locate and characterize mineral-associated organic matter. Taking advantage of samples collected from a decadal (15)N litter labeling experiment in a temperate forest, we demonstrate the potential of NanoSIMS to image intact soil particles and to detect spots of isotopic enrichment even at low levels of (15)N application. We show how microsites of isotopic enrichment detected by NanoSIMS can be speciated by STXM-NEXAFS performed on the same particle. Finally, by showing how (15)N enrichment at one microsite could be linked to the presence of microbial metabolites, we emphasize the potential of this combined imaging and spectroscopic approach to link microenvironment with geochemical process and/or location with ecological function.     

有机物料对植烟土壤养分、酶活性和微生物群落功能多样性的影响

  目的  为探究有机物料施用对土壤养分和生物学特性的影响。  方法  采用盆栽试验,研究了草炭、花生壳炭、蒸汽爆破烟梗和玉米秸秆对植烟土壤的影响,采用BIOLOG ECO平板培养技术分析了土壤微生物群落功能多样性。  结果  施用有机物料能够显著提高土壤有机碳、速效氮、速效磷和速效钾含量;汽爆玉米秸秆处理土壤MBC、MBN含量及脲酶、蔗糖酶活性提高幅度最大。BIOLOG分析结果表明,有机物料提高了土壤微生物AWCD和多样性指数。主成分分析结果表明,生物炭促进了以羧酸类和多聚物类物质为碳源的微生物的生长,汽爆玉米秸秆有利于以碳水化合物类、氨基酸类、酚酸类和胺类物质为碳源微生物的生长。  结论  施用有机物料可提高植烟土壤养分含量,改善土壤微生态环境,其中以汽爆玉米秸秆效果最好。      

Online stable isotope analysis of dissolved organic carbon size classes using size exclusion chromatography coupled to an isotope ratio mass spectrometer

Stable isotopic content of dissolved organic carbon (δ(13)C-DOC) provides valuable information on its origin and fate. In an attempt to get additional insights into DOC cycling, we developed a method for δ(13)C measurement of DOC size classes by coupling high-performance liquid chromatography (HPLC)-size exclusion chromatography (SEC) to online isotope ratio mass spectrometry (IRMS). This represents a significant methodological contribution to DOC research. The interface was evaluated using various organic compounds, thoroughly tested with soil-water from a C3-C4 vegetation change experiment, and also applied to riverine and marine DOC. δ(13)C analysis of standard compounds resulted in excellent analytical precision (≤0.3‰). Chromatography resolved soil DOC into 3 fractions: high molecular weight (HMW; 0.4-10 kDa), low molecular weight (LMW; 50-400 Da), and retained (R) fraction. Sample reproducibility for measurement of δ(13)C-DOC size classes was ±0.25‰ for HMW fraction, ± 0.54‰ for LMW fraction, and ±1.3‰ for R fraction. The greater variance in δ(13)C values of the latter fractions was due to their lower concentrations. The limit of quantification (SD ≤0.6‰) for each size fraction measured as a peak is 200 ng C (2 mg C/L). δ(13)C-DOC values obtained in SEC mode correlated significantly with those obtained without column in the μEA mode (p < 0.001, intercept 0.17‰), which rules out SEC-associated isotopic effects or DOC loss. In the vegetation change experiment, fractions revealed a clear trend in plant contribution to DOC; those in deeper soils and smaller size fractions had less plant material. It was also demonstrated that the technique can be successfully applied to marine and riverine DOC without further sample pretreatment.     

施用等碳量生物炭和腐熟秸秆对土壤养分及有机碳库的影响

为明确生物炭和秸秆对植烟土壤养分和有机碳库的关系,采用田间定位试验,研究了等碳量的生物炭、腐熟秸秆、生物炭与腐熟秸秆配施对不同耕层土壤养分及有机碳库的影响。结果表明,施用等碳量的生物炭和腐熟秸秆处理后,不同耕层土壤除碱解氮外其他速效养分及碳库指标较常规化肥对照(CK)明显增加。单施生物炭处理对0~30 cm耕层土壤有机质含量(质量分数)的提升效果大于腐熟秸秆,而单施腐熟秸秆处理的不同耕层土壤可溶性有机碳及微生物量碳含量较单施生物炭处理均有所提高;生物炭与腐熟秸秆混施处理的10~20 cm耕层土壤速效磷、速效钾、有机质和总有机碳含量较单施腐熟秸秆处理分别提高22.26%、6.08%、8.68%和9.20%,且差异均达显著水平。可见,单施生物炭和单施腐熟秸秆对植烟土壤均有一定的改良作用,但二者混施的改良效果更好。     

化肥连续施用条件下植烟土壤微生物群落响应特征

【目的】为探索土壤微生物对化肥连续施用的响应特征。【方法】选择烟草生产中常用的9种化学肥料,设置减少50%、常规施肥量和增加50%施用量3个肥料浓度梯度,采用土柱模拟系统结合微生物高通量测序、Biolog表型芯片等技术,研究长期不同施肥处理条件下土壤微生物群落的结构、功能基因、生态多样性的变化情况,并构建化肥与土壤微生物关联网络。【结果】（1）连续施用9种化学肥料后土壤微生物群落结构多样性中放线菌门（Actinobacteria）和变形菌门（Proteobacteria）变化幅度较大,磷肥和复合肥增加放线菌门相对丰度,磷肥减少变形菌门相对丰度。（2）连续施肥条件下,尿素施用量减少50%处理的Shannon指数比初期增加1.77%,氯化钾减少50%处理和常规施肥处理在初期明显提高土壤微生物多样性,后期Shannon指数略有下降,与不施肥空白对照之间无显著差异,烤烟专用复合肥常规施肥处理Shannon指数后期较初期下降35.01%。（3）常规施肥浓度下钙镁磷肥处理的氨基酸与核苷酸运输和代谢基因表达较空白对照增多,氯化钾处理的碳水化合物运输和代谢、转录功能、次生代谢产物合成基因明显高于其他处...     

The cation exchange properties and microbial carbon,nitrogen and phosphorus in savanna Alfisol under continuous cultivation

The study reports on the impact of inorganic fertilisers with or without farmyard manure on the cation exchange capacity (CEC), cationic balance and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a savanna Alfisol after 45 years of cultivation. Soils for the study were fertilised with N or N+P+K, cow dung (D), D+N and D+N+P+K for 45 years. Inorganic fertiliser significantly reduced CEC, exchangeable cations and upset the cationic balance. The reduction in CEC and exchangeable cations seemed to operate via organic matter depletion and pH reduction. Similarly inorganic fertiliser stressed microbial activity evidenced by the low amounts of microbial biomass C, N and P compared to the soil under native vegetation and the soils fertilised with D+N and D+N+P+K. From the perspective of the flows of C, N and P through soil microbial biomass, and cation exchange properties and prevention of nutritional imbalances involving basic cations, a rational fertilisation program for savanna Alfisols is one that combines inorganic fertilisers with farmyard manures. ©1997 SCI     

Interactions between elevated CO2 and warming could amplify DOC exports from peatland catchments

Peatlands export more dissolved organic carbon (DOC) than any other biome, contributing 20% of all terrestrial DOC exported to the oceans. Both warming and elevated atmospheric CO2 (eCO2) can increase DOC exports, but their interaction is poorly understood. Peat monoliths were, therefore, exposed to eCO2, warming and eCO2 + warming (combined). The combined treatment produced a synergistic (i.e., significant interaction) rise in DOC concentrations available for export (119% higher than the control, interaction P < 0.05) and enriched this pool with phenolic compounds (284%). We attribute this to increased plant inputs, coupled with impaired microbial degradation induced by competition with the vegetation for nutrients and inhibitory phenolics. Root biomass showed a synergistic increase (407% relative to the control, P < 0.1 only), while exudate inputs increased additively. Phenol oxidase was suppressed synergistically (58%, interaction P < 0.1 only) and beta-glucosidase (27%) additively, while microbial nutritional stress increased (51%) additively. Such results suggest intensified carbon exports from peatlands, with potentially widespread ramifications for aquatic processes in the receiving waters.     

生物炭与有机肥配施对褐土烟田微生物功能多样性的影响

为实现褐土烟田土壤改良的目标,通过大田试验,以施用化肥为对照,研究了生物炭与芝麻饼肥、生物有机肥、动植物有机肥配施后土壤养分、微生物代谢功能和微生物数量的变化。结果表明,生物炭与有机肥配施能提高土壤碱解氮、速效磷、速效钾和有机碳含量,其中以配施生物有机肥提升作用最为明显,分别较对照提高28.18%、54.81%、46.72%和31.12%。与对照相比,生物炭配施3种有机肥均可以增强微生物的代谢活性,提升其对酚酸类、碳水化合物类碳源的利用能力。此外,生物炭与有机肥配施还降低了真菌数量,增加了土壤细菌、放线菌数量及细菌/真菌、放线菌/真菌比值。其中配施生物有机肥土壤细菌和放线菌数量分别较对照增加了192.45%、45.77%。因此,生物炭与有机肥配施能提高褐土土壤速效养分和有机碳含量,改善土壤微生物群落结构。综合来看,以生物炭与生物有机肥配施效果最好。     

Phosphorus status on Canadian organic farms

In eastern North America, many conventional livestock farms, especially dairy farms with high inputs of feed and fertiliser have excess soil phosphorus levels and an annual phosphorus surplus. However, a Canadian dairy farm in transition to organic, without fertiliser inputs reduced its farm P surplus to a marginal level. On long‐term organic dairy farms in Ontario, most soils tested low to very low in available P as measured by a standard soil test. Canadian Prairie organic grain farms also consistently demonstrate deficiencies in available soil P. Organic producers have few viable alternatives for P management. Phosphate rock can be acceptable to organic standards (provided they are low in heavy metals, and not processed synthetically), but the P in these becomes available slowly, especially in high pH soils common on most organic farms in Canada. An alternative is to increase soil P availability. Enhanced microbial activity in organically managed soils may make P more available. Livestock manures are rich sources of available phosphorus, but a majority of organic farmers in Canada do not keep livestock. Off‐farm manure sources are subject to organic regulations and hauling costs, both of which may be prohibitive. Furthermore, manure from conventional farms in Canada may be contaminated by genetically modified material from corn and soybean feed. Additional research is required to improve short‐term availability of soil P and long‐term replacement. Copyright © 2007 Society of Chemical Industry     

Microbially derived inputs to soil organic matter: are current estimates too low?

Soil microbes are central to many soil processes, but due to the structural complexity of soil organic matter, the accurate quantification of microbial biomass contributions continues to pose a significant analytical challenge. In this study, microbes from a range of soils were cultured such that their molecular profile could be compared to that of soil organic matter and native vegetation. With the use of modern NMR spectroscopy, the contributions from microbial species can be discerned in soil organic matter and quantified. On the basis of these studies, the contributions of microbial biomass to soil organic matter appear to be much higher than the 1-5% reported by other researchers. In some soils, microbial biomass was found to contribute >50% of the extractable soil organic matter fractions and approximately 45% of the humin fraction and accounted for >80% of the soil nitrogen. These findings are significant because organic matter is intimately linked to nutrient release and transport in soils, nitrogen turnover rates, contaminant fate, soil quality, and fertility. Therefore, if in some cases soil organic matter and soil organic nitrogen are predominately of microbial origin, it is likely that this fraction, whether in the form of preserved material or living cells, plays an underestimated role in several soil processes.     

Microbial respiration and diffusive transport of O2, 16O2, and 18O15O in unsaturated soils and geologic sediments

Molecular oxygen (O2) in unsaturated geologic sediments plays an important role in soil respiration, biodegradation of organic contaminants, metal oxidation, and global oxygen and carbon cycling, yet little is known about oxygen isotope fractionation during the consumption and transport of O2 in unsaturated zones. We used a laboratory kinetic cell technique to quantify isotope fractionation due to respiration and a numerical model to quantify both consumptive and diffusive fractionation of O2 isotopes at a field site comprised of unsaturated lacustrine sandy materials. The combined use of laboratory-based kinetic cell experiments and field-based isotope transport modeling provided an effective tool to characterize microbial respiration in unsaturated media. Based on results from the closed-system kinetic cells, O2 consumption and isotope fractionation were attributed to the alternative cyanide-resistant respiration pathway. At the field site, the modeled depth profiles for O2 and delta18O matched the measured in situ data and confirmed that the consumption of O2 was via the alternative respiration pathway. If the cyanide-resistant respiration pathway is indeed widespread in soils, its high oxygen isotope enrichment factor could help to explain the discrepancy between the predicted present-day Dole effect (+20.8/1000) and the observed Dole effect (+23.5/1000). Thus, further soil O2 isotope studies are needed to better characterize and model the fractionation of oxygen isotopes during subsurface respiration and the potential impact on the isotopic content of atmospheric O2.     

不同施肥措施对植烟土壤生物学特性和速效养分的影响

通过两年盆栽试验,研究增施不同有机物料对植烟土壤生物学特性和速效养分的影响。结果表明,与纯施化肥相比,增施芝麻饼肥显著增加土壤碱解氮和速效磷含量,增施生物炭显著增加速效钾含量;增施腐熟秸秆土壤蔗糖酶活性显著提升12%,芝麻饼肥和生物炭处理脲酶活性均显著增加19%,生物炭处理过氧化氢酶活性显著增加27%。增施腐熟秸秆土壤微生物生物量碳最高,达到234.52 mg/kg,生物炭处理土壤微生物生物量氮最高,达到35.29 mg/kg。细菌为植烟土壤可培养菌中的优势菌,增施生物炭显著提升可培养细菌数量,增施腐熟秸秆显著提升可培养真菌和放线菌数量。总体来看,增施不同有机物料能改善土壤生物学特性,增加速效养分含量,从而改善植烟土壤质量。     

Linking phosphorus sequestration to carbon humification in wetland soils by 31P and 13C NMR spectroscopy

Phosphorus sequestration in wetland soils is a prerequisite for long-term maintenance of water quality in downstream aquatic systems, but can be compromised if phosphorus is released following changes in nutrient status or hydrological regimen. The association of phosphorus with relatively refractory natural organic matter (e.g., humic substances) might protect soil phosphorus from such changes. Here we used hydrofluoric acid (HF) pretreatment to remove phosphorus associated with metals or anionic sorption sites, allowing us to isolate a pool of phosphorus associated with the soil organic fraction. Solution (31)P and solid state (13)C NMR spectra for wetland soils were acquired before and after hydrofluoric acid pretreatment to assess quantitatively and qualitatively the changes in phosphorus and carbon functional groups. Organic phosphorus was largely unaffected by HF treatment in soils dominated by refractory alkyl and aromatic carbon groups, indicating association of organic phosphorus with stable, humified soil organic matter. Conversely, a considerable decrease in organic phosphorus following HF pretreatment was detected in soils where O-alkyl groups represented the major fraction of the soil carbon. These correlations suggest that HF treatment can be used as a method to distinguish phosphorus fractions that are bound to the inorganic soil components from those fractions that are stabilized by incorporation into soil organic matter.     

秸秆还田对植烟土壤中微生物结构和数量的影响

测定了施加小麦秆糖、玉米秆糠后植烟土壤中细菌、霉菌、施线菌、解磷菌、解钾菌、硝化细菌和反硝化细菌７类菌群的分布及数量;应用生物统计分析法比较了施加不同秸秆对烤烟试验田土壤微生物结构和数量的影响。结果表明,施加７５００ｋｇ／ｈｍ＾２的小麦秆糠、９０００ｋｇ／ｈｍ＾２的玉米秆糠和１５０００ｋｇ／ｈｍ＾２的玉米秆糠都能显著或极显著地增加２０～４０ｃｍ耕作层中微生物的数据。