Changes in Phosphorus Fractions and Nitrogen Forms During Composting of Pig Manure with Rice Straw

The study was conducted to reveal P fractions and N forms changing characters during composting of pig manure with rice straw.During composting,the NH 4 ＋-N concentration decreased and reached at a relatively low value（〈400 mg kg-1） in the final compost,while the NO 3--N concentration increased.Total N losses mainly occurred during thermophilic phase due to the high temperature,the high NH 4 ＋-N concentration and the increase of pH value.Labile inorganic P was dominated in the pig manure and initial compost mixture.During composting,the proportion of labile inorganic P of total extracted P decreased,while the proportion of Fe＋Al-bound P,Ca＋Mg-bound P and residual P increased.The evolutions of the proportion of labile inorganic P,Fe＋Al-bound P and Ca＋Mg-bound P were well correlated with the changes of pH value,organic matter and C/N ratio.Therefore,composting could increase the concentration of N and P and decrease the presence of NH 4 ＋-N and labile P fractions which might cause environmental issues following land application.

Variations in nitrogen isotopic values among various particle-sized fractions in modern soil in northwestern China

Ratios of stable nitrogen isotopes in organic matter derived from plants and preserved in soil are potential tracers for nitrogen cycles in natural ecosystems and valuable for evaluation of climate change. However, the rela-tionship between nitrogen isotopic compositions in surface soil and in plant litter during the decomposition process from plant litter to soil organic matter is not well understood. By using nitrogen isotopic analysis of soil parti-cle-sized fractions, nitrogen isotope discrimination between plant litter and surface soil organic matter in various modern ecosystems in northwestern China was conducted. The results of our study indicate that: (1) in general, the nitrogen isotopic compositions of particle-sized fractions from surface soil are different, and δ15N values increase from plant litter to fine soil organic matter; (2) the δ15N values in the soil particle-sized fractions become larger with increasing relative humidity and temperature, and the largest variation in the δ15N values is from -5.9‰ to -0.3‰; and (3) under a controlled climate, significant nitrogen isotope differences in δ15N values (Δδ15Nplant-soil) between plant litter and bulk soil organic matter were observed, with the values of 1.52 to 4.75 at various sites. Our results suggested that comparisons of Δδ15N values between bulk soil and the particle-sized fractions of soil could reveal the effect of humidity on transferring process of nitrogen from plant to soil in arid and semi-arid ecosystems.

Response of nitrogen fractions in the rhizosphere and bulk soil to organic mulching in an urban forest plantation

Nitrogen is an essential component in forest ecosystem nutrient cycling.Nitrogen fractions,such as dissolved nitrogen,ammonium,nitrate,and microbial biomass nitrogen,are sensitive indicators of soil nitrogen pools which affect soil fertility and nutrient cycling.However,the responses of nitrogen fractions in forest soils to organic mulching are less well understood.The rhizosphere is an important micro-region that must be considered to better understand element cycling between plants and the soil.A field investigation was carried out on the effect of mulching soil in a 15-year-old Ligustrum lucidum urban plantation.Changes in total nitrogen and nitrogen fractions in rhizosphere and bulk soil in the topsoil(upper 20 cm)and in the subsoil(20-40 cm)were evaluated following different levels of mulching,in addition to nitrogen contents in fine roots,leaves,and organic mulch.The relationships between nitrogen fractions and other measured variables were analysed.Organic mulching had no significant effect on most nitrogen fractions except for the rhizosphere microbial biomass nitrogen(MBN),and the thinnest(5 cm)mulching layer showed greater effects than other treatments.Rhizosphere MBN was more sensitive to mulching compared to bulk soil,and was more affected by soil environmental changes.Season and soil depth had more pronounced effects on nitrogen fractions than mulching.Total nitrogen and dissolved nitrogen were correlated to soil phosphorus,whereas other nitrogen fractions were strongly affected by soil physical properties(temperature,water content,bulk density).Mulching also decreased leaf nitrogen content,which was more related to soil nitrogen fractions(except for MBN)than nitrogen contents in either fine roots or organic mulch.Frequent applications of small quantities of organic mulch contribute to nitrogen transformation and utilization in urban forests.

Determination of Atomic Fractions of Isotopes Carbon-13 and Nitrogen-15 Directly in Glicine, L-Leucine, Isoleucine and Alanine

Using compounds modified by the isotopes carbon-13 and nitrogen-15 helps conduct research in various fields of science, such as medicine, pharmacology, pharmacokinetics, metabolism, agriculture, and others. In the case of the availability of reliable, express, and cheap methods, the area of their use will gradually expand. A determination of the atomic fraction of the isotopes carbon-13 and nitrogen-15 directly in glycine, leucine, isoleucine, and alanine is proposed;the modification concerns all centers or one or more identical carbon and nitrogen centers separately, as well as both isotopes at the same time. There are defined mass lines of the mass spectrum of each amino acid, through which the isotopic content of carbon and nitrogen is calculated. The processes that must be taken into account for the determination of the isotopic content are also established. Isotopic analysis of these compounds until now was carried out by transforming them into carbon oxide, dioxide, and molecular nitrogen, and determination of their content in individual centers was impossible.

Charactering protein fraction concentrations as influenced by nitrogen application in low-glutelin rice cultivars

To optimize both grain yield and quality of low-glutelin rice cultivars under N-fertilizer strategies, two-year field experiments involving three low-glutelin rice cultivars（W1240, W1721, W025） and an ordinary rice cultivar（H9405） with five N treatments were carried out to determine the effects of N application rate and genotype on protein fractions contents and Glutelin/Prolamin ratio（Glu/Pro）. The difference of protein fraction concentrations affected by N application rate existed in genotypes. Ordinary rice cultivar had a larger increase in glutlein concentration affected by N application rate than low-glutelin rice cultivars did. Glutelin in H9405 had a increase of 30.6 and 41.0% under the N4 treatment（360 kg N ha^（–1）） when compared with N0 treatment（no fertilizer N） in 2010 and 2011 respectively, while all the low-glutelin rice cultivars showed relatively smaller increases for two years. Variance analysis showed no significant effect of N application rate on glutelin in W1240 and W025 while the effects on albumin, globulin and prolamin were significant in low-glutelin rice. What＇s more, N treatment had no significant i nfluence on Glu/Pro ratios in low-glutelin rice cultivars while a significant increase in Glu/Pro ratio was observed in ordinary rice cultivar. So low-gultelin rice cultivars showed a different pattern from ordinary rice cultivars when influenced by N application rate.

Migration Fractionation of Neutral Nitrogen Compounds of Crude Oils from Tabei Oilfield in the Tarim Basin, China

The absolute amounts and relative distributions of neutral nitrogen compounds in the Tabei oilfield (e.g. blocks Ln1-Ln11) showed remarkable migration fractionation in the vertical direction. From Ordovician reservoirs (O) to oil legs T-Ⅲ and T-Ⅰ of Triassic reservoirs in blocks LN1-LN11, the concentrations of + decreased from {1.59}μg/g, {0.49}μg/g to {0.17}μg/g (oil). The ratios of various alkylcarbazole isomers, such as 1,8-dimethylcarbazole/nitrogen-partially shielded isomers and 1,8-dimethylcarbazole/nitrogen-exposed isomers, were adopted as the indicators of petroleum migration. The ratios increased from {0.13}, {0.20} to {0.67} and from {0.42}, {0.87} to {3.30}, corresponding to those of Ordovician oil leg and oil legs T-Ⅲ and T-Ⅰ. In going from the south to the north of the Tabei oilfield, the absolute concentrations of neutral nitrogen compounds decreased drastically, and the nitrogen-shielded isomers were enriched relative to nitrogen-exposed isomers and nitrogen-partially shielded isomers. Crude oils in the Tabei oilfield migrated laterally from the Jilake structure to the Sangtamu fault uplift and Lunnan fault uplift, and crude oils in the same fault uplift migrated and remigrated vertically from Ordovician reservoirs, to oil legs T-Ⅲ to T-Ⅰ of Triassic reservoirs.

Soil Organic Fractions in Cultivated and Uncultivated Soils of Costal Area in Bangladesh

Assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus soil fertility restoration. A study was conducted in cultivated and uncultivated saline soil, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on cultivation and soil fertility at Sundarbans costal area in Bangladesh. Soil samples were taken from the 0 - 15 and 15 - 30 cm depths from four cultivated fields and from four nearby sites in a native mangrove forest as references. Soil samples were physically fractionated into sand (2000-50 μm), silt (50-2 μm) and clay (<2 μm). Total SOC and N were analyzed in bulk samples and each size fraction, and the Carbon Management Index (CMI), a widely used indicator of soil quality, was calculated for each field. The CMI in cultivated soils was far below the 100% in reference soils, reaching 38.16%, 25.70%, 32.21% and 34.43% in Field 1, Field 2, Field 3 and Field 4 respectively. SOC and N concentrations decreased in particle size separates in the order clay > silt > sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt + clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in cultivated soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated soils.

Does Soil Disturbance Affect Soil Phosphorus Fractions?

Increased turnover of organic matter as a result of soil disturbance (e.g. by soil tillage) is described in principle, but the direct influence of soil disturbance on soil P turnover especially for organic farming systems has not been sufficiently proven. The objective of the study was to evaluate the short term effect of soil disturbance on different soil P fractions in a soil shaking experiment. Four soils were incubated for 10 days in the dark with three different disturbance treatments: 1) no disturbance, 2) overhead shaking for 2 h at the beginning of the experiment and 3) continuous overhead shaking at 5 r. p. m. The four investigated soils were: 1) a silty loam soil with long term bio-compost application and 2) the corresponding soil without bio-compost application, 3) a long-term organically managed clay loam soil and 4) a clay loam soil with long time application of pig manure, all not and from Baden-Württemberg, Germany. We determined NaHCO3-, NaOH- and H2SO4-extractable inorganic and organic P fractions (Pi and Po, resp.) in a sequential extraction. Furthermore, the potentially plant available P as Calcium-acetate-lactate-extractable P (CAL-P) and P extractable by electro-ultra-filtration (EUF-P), and aqua regia extractable total P (PT) were determined. Furthermore, we determined microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), and acid phosphatase activity in soil. The organically managed soil had the highest PT contents (1300 mg·kg-1). The soil with pig manure application had the smallest potentially labile P fractions (NaHCO3-Pi and -Po and NaOH-Pi). The ecologically managed soil had the biggest organic P fractions (114 mg·kg-1 NaHCO3-Po and 463 mg·kg-1 NaOH-Po), but, this soil was the lowest in CAL-P (5 mg·kg-1). Short term soil disturbance had effects on labile organic P fractions of two of the four analyzed soils, but inorganic P was rather unaffected. In the compost amended COMP(+) soil, there was an incorporation of P from the less available NaOH-P fractions into the more available NaHCO3-Po fraction. However, if taking all investigated soils and treatments into account, the effects of soil disturbance were limited and not consistent.

Assessment of Soil C and N Stocks and Fractions across 11 European Soils under Varying Land Uses

In this study, we measured the stocks and pool sizes of soil organic carbon (SOC) and total soil nitrogen (TN), and their natural 13C and 15N abundance across a wide range of temperate European ecosystems. The objectives were to examine any distinct isotope patterns with land use or climate, and how C and N in these different ecosystems are distributed among soil organic matter (SOM) fractions to better predict soil C and N dynamics and longer term persistence. Soils were sampled to 30 cm depth at 11 sites of the Nitro Europe (NEU) network and included four forests, three grasslands and four croplands. Surface soil samples were fractionated using a combined size-density fractionation protocol separating light (LF) from heavy particulate organic matter (hPOM) by density and silt-from-clay-associated SOM by size. Down-profile natural abundance 15N patterns pointed towards a closed N cycle in the forest sites, while 13C patterns suggested differences in plant water use efficiency across the C3 grassland sites. The forests and grassland sites stored the majority of surface SOC and TN in the LF and hPOM pools. Sustained sequestration of C and N in these rather labile pools will rely on management practices that minimize soil disturbance and increase C input. We also found that the mineral fraction (silt and clay) in the cropland soils stored less C and N per unit of fraction mass compared to the forests and grasslands, which points towards a lower mineral-OM stabilization efficiency of cropland soils. Finally, our study revealed total POM (LF plus hPOM) as a strong predictor of SOC and TN differences, particularly among the non-cropped sites. This study shows that these sites, independent of soil type and climate, store a large fraction of C and N in POM pools that are particularly vulnerable to soil disturbance such as caused by land use change.

The Effects of Three Mineral Nitrogen Sources and Zinc on Maize and Wheat Straw Decomposition and Soil Organic Carbon

The incorporation of straw in cultivated ifelds can potentially improve soil quality and crop yield. However, the presence of recalcitrant carbon compounds in straw slow its decomposition rate. The objective of this study was to determine the effects of different nitrogen sources, with and without the application of zinc, on straw decomposition and soil quality. Soils were treated with three different nitrogen sources, with and without zinc： urea （CO（NH2）2）, ammonium sulfate （（NH4）2SO4）, and ammonium chloride （NH4Cl）. The combined treatments were as follows：maize （M） and wheat （W） straw incorporated into urea-, ammonium sulfate-, or ammonium chloride-treated soil （U, S, and C, respectively） with and without zinc （Z） （MU, MUZ, WU, WUZ;MS, MSZ, WS, WSZ;MC, MCZ, WC, WCZ, respectively）;straw with zinc only （MZ, WZ）;straw with untreated soil （MS, WS）;and soil-only or control conditions （NT）. The experiment consisted of 17 treatments with four replications. Each pot contained 150 g soil and 1.125 g straw, had a moisture content of 80%of the ifeld capacity, and was incubated for 53 days at 25°C. The rates of CO2-C emission, cumulative CO2-C evolution, total CO2 production in the soils of different treatments were measured to infer decomposition rates. The total organic carbon （TOC）, labile organic carbon （LOC）, and soil microbial biomass in the soils of different treatments were measured to infer soil quality. All results were signiifcantly different （P〈0.05） with the exception of the labile organic carbon （LOC）. The maize and wheat straw showed different patterns in CO2 evolution rates. For both straw types, Zn had a synergic effect with U, but an antagonistic effect with the other N sources as determined by the total CO2 produced. The MUZ treatment showed the highest decomposition rate and cumulative CO2 concentration （1 120.29 mg/pot）, whereas the WACZ treatment had the lowest cumulative CO2 concentration （1 040.57 mg/pot）. The addition of NH4Cl resulted in the highest total organic carbon （TOC） concentration （11.59 mg kg-1）. The incorporation of wheat straw resulted in higher microbial biomass accumulation in soils relative to that of the maize straw application. The results demonstrate that mineral N sources can affect the ability of microorganisms to decompose straw, as well as the soil carbon concentrations.

Effect of six years of nitrogen additions on soil chemistry in a subtropical Pleioblastus amarus forest, Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen(N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels(0, 50, 150,and300 kg N ha-1a-1,applied monthly, expressed as CK,LN,MN, HN,respectively) in three replicates. After6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity(EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK,LN,MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al3+,EA, and Al/Ca,and exchangeable Al3+ in HN increased by 70%compared to CK. Soil base cations(Ca2+, Mg2+, K+, and Na+) did not respond to N additions. Nitrogen treatments significantly increased soil NO3--N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH4~+-N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon,incorporated organic carbon, or particulate organic carbon.This study suggests that increasing N deposition could increase soil NO3--N, reduce soil pH, and increase mobilization of Al3+. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen（N） deposition are likely to change soil microbial properties, and ultimately to affect soil carbon（C） storage.Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch（Larix gmelinii） plantation. In a 9-year experiment in the plantation, N was applied at100 kg N ha-1 a-1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However,soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However,microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, d13 C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition（1） altered microbial biomass and activity without affecting soil C in light fractions and（2） resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Application of Stable Isotope Techniques in Studies of Carbon and Nitrogen Biogeochemical Cycles of Ecosystem

Stable isotope techniques have been proved useful as tools for studying the carbon (C) and nitrogen (N) biogeochemical cycles of ecosystem. This paper firstly introduced the basic principles and the distribution characteristics of stable isotope, then reviewed the recent advances and applications of stable isotope in the C and N biogeochemical cycles of ecosystem. By applying the 13 C natural abundance technique, ecologists are able to understand the photosynthetic path and CO 2 fixation of plants, the CO 2 exchange and C balance status of ecosystem, the composition, distribution and turnover of soil organic C and the sources of organic matter in food webs, while by using the 13 C labeled technique, the effects of elevated CO 2 on the C processes of ecosystem and the sources and fate of organic matter in ecosystem can be revealed in detail. Differently, by applying the 15 N natural abundance technique, ecologists are able to analyze the biological N 2 -fixation, the N sources of ecosystem, the N transformation processes of ecosystem and the N trophic status in food webs, while by using the 15 N labeled technique, the sources, transformation and fate of N in ecosystem and the effects of N input on the ecosystem can be investigated in depth. The applications of both C and N isotope natural abundance and labeled techniques, combined with the elemental, other isotope ( 34 S) and molecular biomarker information, will be more propitious to the investigation of C and N cycle mechanisms. Finally, this paper concluded the problems existed in current researches, and put forward the perspective of stable isotope techniques in the studies on C and N biogeochemical cycles of ecosystem in the future.

Dynamics of organic carbon and nitrogen in deep soil profile and crop yields under long-term fertilization in wheat-maize cropping system

Soil organic carbon(SOC)and nitrogen(N)are two of the most important indicators for agricultural productivity.The primary objective of this study was to investigate the changes in SOC and N in the deep soil profile(up to 100 cm)and their relationships with crop productivity under the influence of long-term(since 1990)fertilization in the wheat-maize cropping system.Treatments included CK(control),NP(inorganic N and phosphorus(P)fertilizers),NPK(inorganic N,P and potassium fertilizers),NPKM(NPK plus manure),and M(manure).Crop yield and the properties of topsoil were measured yearly from 2001 to 2009.C and N contents were measured at five different depths in 2001 and 2009.The results showed that wheat and maize yields decreased between 2001 and 2009 under the inorganic fertilizer(NP and NPK)treatments.The average yield between 2001 and 2009 under the NP,NPK,NPKM,and M treatments(compared with the CK treatment)increased by 38,115,383,and 381%,respectively,for wheat and 348,891,2738,and 1845%,respectively,for maize.Different long-term fertilization treatments significantly changed coarse free particulate(cf POC),fine free particulate(ff POC),intramicroaggregate particulate(i POC),and mineral-associated(m SOC)organic carbon fractions.In the experimental years of 2001 and 2009,soil fractions occurred in the following order for all treatments:m SOC>cf POC>i POC>ff POC.All fractions were higher under the manure application treatments than under the inorganic fertilization treatments.Compared to the inorganic fertilization treatments,manure input enhanced the stocks of SOC and total N in the surface layer(0–20 cm)but decreased SOC and N in the deep soil layer(80–100 cm).This reveals the efficiency of manure in increasing yield productivity and decreasing risk of vertical loss of nutrients,especially N,compared to inorganic fertilization treatments.The findings provide opportunities for understanding deep soil C and N dynamics,which could help mitigate climate change impact on agricultural production and maintain soil health.

Air pollution and heart failure: Relationship with the ejection fraction

AIM: To study whether the concentrations of particulate matter in ambient air are associated with hospitaladmission due to heart failure in patients with heart failure with preserved ejection fraction and reduced ejection fraction. METHODS: We studied 353 consecutive patients admitted into a tertiary care hospital with a diagnosis of heart failure. Patients with ejection fraction of ≥ 45% were classified as having heart failure with preserved ejection fraction and those with an ejection fraction of < 45% were classified as having heart failure with reduced ejection fraction. We determined the average concentrations of different sizes of particulate matter (< 10, < 2.5, and < 1 μm) and the concentrations of gaseous pollutants (carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone) from 1 d up to 7 d prior to admission. RESULTS: The heart failure with preserved ejection fraction population was exposed to higher nitrogen dioxide concentrations compared to the heart failure with reduced ejection fraction population (12.95 ± 8.22 μg/m 3 vs 4.50 ± 2.34 μg/m 3 , P < 0.0001). Multivariate analysis showed that nitrogen dioxide was a significant predictor of heart failure with preserved ejection fraction (odds ratio ranging from (1.403, 95%CI: 1.003-2.007, P = 0.04) to (1.669, 95%CI: 1.043-2.671, P = 0.03). CONCLUSION: This study demonstrates that shortterm nitrogen dioxide exposure is independently associated with admission in the heart failure with preserved ejection fraction population.

Land use effects on soil organic carbon, nitrogen and salinity in saline-alkaline wetland

Land-use and soil management affects soil organic carbon （SOC） pools, nitrogen, salinity and the depth distribution. The objective of this study was to estimate land-use effects on the distribution of SOC, labile fractions C, nitrogen （N） and salinity in saline-alkaline wetlands in the middle reaches of the Heihe River Basin. Three land-use types were selected： intact saline-alkaline meadow wetland, artificial shrubbery （planting Tamarix） and farmland （cultivated for 18 years） of soils previously under meadow wetland. SOC, easily oxidized carbon, microbial biomass carbon, total N, NO3--N and salinity concentrations were measured. The results show that SOC and labile fraction carbon contents decreased significantly with increasing soil depth in the three land-use wetlands. The labile fraction carbon contents in the topsoil （0-20cm） in cultivated soils were significantly higher than that in intact meadow wetland and artificial shrubbery soil. The aboveground biomass and soil permeability were the primary influencing factors on the contents of SOC and the labile carbon in the intact meadow wetland and artificial shrubbery soil, however, the farming practice was a factor in cultivated soil. Agricultural measures can effectively reduce the salinity contents; however, it caused a significant increase of NO 3--N concentrations which posed a threat to groundwater quality in the study area.

Mass-Spectrometric Method of Measurement of Isotopic Content of Nitrogen in Organic Compounds

Nitrogen-15 isotope-modified compounds are widely used in medicine, pharmacology, agriculture and various fields of science and their nomenclature is gradually increasing. Their widespread use depends on the availability of inexpensive and simple isotope analysis methods. The present article is an attempt to determine the nitrogen-15 isotope content directly in organic compounds without their conversion. The general principle of possibility of determination of the isotopes of nitrogen directly in organic compounds is proposed. Based on the study of mass-spectra of Carbamide Carbonyldiamide, isocyanic acid and nitrobenzene the mass peaks are selected, by which it is possible to determine the atomic fraction of the isotopes of nitrogen. The respective formulas are proposed.

氮的地球生物学循环:生物与地质演化的耦联

氮的地球生物学循环是氮的生物地球化学循环与地质循环的耦合,是探讨生物与环境相互作用,进而了解地球系统演化的重要窗口。大气中氮气分压(pN_(2))是认识氮的地球生物学循环的重要抓手,也是地外生命探测的潜在生命标识。因而,深入认识pN_(2)的地质演化具有重要意义。本文围绕深时大气pN_(2)的变化,简要总结了地球上主要的氮储库特征,从氮的生物地球化学循环和氮的地质循环两方面探讨了氮的地球生物循环过程、影响因素、可能的演化阶段,总结了当前对深时pN_(2)变化总体过程及影响因素的认识,提出了未来亟需解决的一些关键科学问题。

长期不同施肥模式对大麦–双季稻田根际土壤有机氮组分的影响

根际土壤有机氮组分在土壤养分和作物氮素营养中具有重要作用。本研究依托长期(37年)定位施肥试验田,设置4个施肥处理:不施肥对照(CK)、单独施用化肥(CF)、秸秆还田+化肥(RF)和30%有机肥+70%化肥(OM),于晚稻成熟期测定大麦–双季稻田根际土壤基础理化性质、微生物生物量氮和有机氮组分(氨基酸态氮、氨基糖态氮、酸解氨态氮、酸解未知态氮、非酸解性氮)含量。研究表明:相对CK处理,RF和OM处理显著增加了稻田根际土壤有机碳、全氮、铵态氮和硝态氮的含量。RF和OM处理土壤微生物生物量氮含量分别比CK处理增加了19.8%和30.7%。酸解性氮作为根际土壤全氮的主体部分,占全氮的59.61%~72.06%;各处理根际土壤酸解性氮含量大小顺序表现为OM>RF>CF>CK。各施肥处理中,酸解有机氮中的氨基糖态氮、氨基酸态氮和酸解未知态氮含量均以OM处理最大,分别比CK处理增加139.3%、47.9%和110.0%;酸解氨态氮以RF处理最大,比CK处理增加69.9%。土壤有机碳、全氮、铵态氮、硝态氮与土壤氨基酸态氮、氨基糖态氮、酸解未知态氮以及微生物生物量氮均呈极显著(P<0.01)正相关。因此,秸秆、有机肥配施化肥均能有效提高大麦–双季稻田根际土壤的供氮能力,是改善稻田土壤肥力的有效手段。

长期种植紫花苜蓿对复垦土壤碳氮磷养分转化的影响

为研究长期种植紫花苜蓿对复垦土壤质量改善和生物改土的效果,以种植作物地和撂荒地为对照,分析建筑复垦地多年种植紫花苜蓿土壤有机碳(SOC)、全氮(TN)和全磷(TP)含量的化学计量特征变化。结果表明,长期种植紫花苜蓿显著降低土壤电导率(EC),对表层土壤保水效果较好,显著提升土壤有效养分含量(P<0.05);与作物地和撂荒地相比,苜蓿地土壤SOC和TN含量显著提高(P<0.05),但0~20 cm土壤TP含量显著低于作物地。3种土地利用类型0~20 cm土壤化学计量差异显著,苜蓿地土壤C/N显著低于作物地和撂荒地(P<0.05),而土壤C/P和N/P则表现为苜蓿地显著高于作物地和撂荒地(P<0.05)。种植紫花苜蓿有助于提升土壤有机碳氮活性组分,0~20 cm土层苜蓿地颗粒有机碳(POC)、易氧化有机碳(ROC)和微生物生物量碳(MBC)含量较作物地分别提高88.38%、17.24%和39.16%(P<0.05),苜蓿地颗粒有机氮(PON)、微生物生物量氮(MBN)和酸解有机氮组分含量最高,PON和MBN比作物地显著提高135.29%和17.39%,较撂荒地显著提高207.69%和28.41%。因此,长期种植紫花苜蓿对土壤质量和有机碳氮活性组分均有改善作用,研究结果可为退化土壤修复和复垦土壤生物改土效果提供参考。