Effects of tree size and organ age on variations in carbon,nitrogen,and phosphorus stoichiometry in Pinus koraiensis

Carbon(C),nitrogen(N),and phosphorus(P)are of fundamental importance for growth and nutrient dynamics within plant organs and deserve more attention at regional to global scales.However,our knowledge of how these nutrients vary with tree size,organ age,or root order at the individual level remains limited.We determined C,N,and P contents and their stoichiometric ratios(i.e.,nutrient traits)in needles,branches,and fine roots at different organ ages(0-3-year-old needles and branches)and root orders(1st-4th order roots)from 64 Pinus koraiensis of varying size(Diameter at breast height ranged from 0.3 to 100 cm)in northeast China.Soil factors were also measured.The results show that nutrient traits were regulated by tree size,organ age,or root order rather than soil factors.At a whole-plant level,nutrient traits decreased in needles and fine roots but increased in branches with tree size.At the organ level,age or root order had a negative effect on C,N,and P and a positive effect on stoichiometric ratios.Our results demonstrate that nutrient variations are closely related to organ-specific functions and ecophysiological processes at an individual level.It is suggested that the nutrient acquisition strategy by younger trees and organ fractions with higher nutrient content is for survival.Conversely,nutrient storage strategy in older trees and organ fractions are mainly for steady growth.Our results clarified the nutrient utilization strategies during tree and organ ontogeny and suggest that tree size and organ age or root order should be simultaneously considered to understand the complexities of nutrient variations.

Atmospheric nitrogen deposition affects forest plant and soil system carbon:nitrogen:phosphorus stoichiometric flexibility:A meta-analysis

Background:Nitrogen(N)deposition affects forest stoichiometric flexibility through changing soil nutrient availability to influence plant uptake.However,the effect of N deposition on the flexibility of carbon(C),N,and phosphorus(P)in forest plant-soil-microbe systems remains unclear.Methods:We conducted a meta-analysis based on 751 pairs of observations to evaluate the responses of plant,soil and microbial biomass C,N and P nutrients and stoichiometry to N addition in different N intensity(050,50–100,>100 kg·ha^(-1)·year^(-1)of N),duration(0–5,>5 year),method(understory,canopy),and matter(ammonium N,nitrate N,organic N,mixed N).Results:N addition significantly increased plant N:P(leaf:14.98%,root:13.29%),plant C:P(leaf:6.8%,root:25.44%),soil N:P(13.94%),soil C:P(10.86%),microbial biomass N:P(23.58%),microbial biomass C:P(12.62%),but reduced plant C:N(leaf:6.49%,root:9.02%).Furthermore,plant C:N:P stoichiometry changed significantly under short-term N inputs,while soil and microorganisms changed drastically under high N addition.Canopy N addition primarily affected plant C:N:P stoichiometry through altering plant N content,while understory N inputs altered more by influencing soil C and P content.Organic N significantly influenced plant and soil C:N and C:P,while ammonia N changed plant N:P.Plant C:P and soil C:N were strongly correlated with mean annual precipitation(MAT),and the C:N:P stoichiometric flexibility in soil and plant under N addition connected with soil depth.Besides,N addition decoupled the correlations between soil microorganisms and the plant.Conclusions:N addition significantly increased the C:P and N:P in soil,plant,and microbial biomass,reducing plant C:N,and aggravated forest P limitations.Significantly,these impacts were contingent on climate types,soil layers,and N input forms.The findings enhance our comprehension of the plant-soil system nutrient cycling mechanisms in forest ecosystems and plant strategy responses to N deposition.

Effect of Different Fertilization Patterns on Carbon and Nitrogen Components of Tobacco Topsoil

In order to explore the fertilizing ways and dynamic changes of soil carbon and nitrogen in the main producing areas of tobacco in Guizhou,research was conducted to study the variations of dissolved organic carbon and nitrogen,total organic carbon and nitrogen and their ratio of tobacco-topsoil in organic fertilization pattern and conventional cultivation pattern （No fertilizer as control） by pot experiment.The results were as follows：（1） The effects of different fertilization patterns on soil dissolved organic carbon and nitrogen and total organic carbon and nitrogen were significantly different.The content of DOC,DON,TOC and TON in tobaccotopsoil was decreased with the advancing of growth period in conventional fertilization pattern.In the conventional fertilization pattern,the accumulation of DOC and TOC was increased first and then decreased,and the accumulation of DON and TON was decreased first and then increased.（2） The TOC content at the different growing stage and DOC content at the middle and later stage of tobacco were significantly improved in organic fertilization patterns.The accumulation of DON and TON in the conventional fertilization pattern was significantly higher than those in the organic fertilizer pattern and control at the rosette stage and vigorous stage.In the harvest period,the content of DOC,DON,TOC and TON of tobacco-topsoil in the conventional fertilization and organic fertilization pattern was significantly higher than those in the control.（3）The DOC/DON ratio and the TOC/TiON ratio was increased gradually with the advancing of growth period in conventional fertilization pattern,but they were increased first and then decreased in the organic fertilization pattern and CK.The DOC/DON and TOC/TON ratio of tobacco-topsoil in different fertilization patterns was showed as Y J＞ CK＞ CG at the different growing stage.The experiment results revealed that：The organic fertilization pattern may improve significantly the accumulation of DOC,DON,TOC and TON of tobacco-topsoil at the middle and later stage and the DOC/DON and TOC/TON ratio at the different growth stage.It contributed to the continuous and balanced supply of nutrients at the middle and later stage of tobacco and the soil fertility.

Transformation of Carbon and Nitrogen by Earthworms in the Decomposition Processes of Broad-leaved Litters

Earthworms are the important constituents in the decayed food web and the main ecological conditioners in the process of decomposition and nutrient mineralization. The transformation of organic carbon (C) and total nitrogen (N) in the broad-leaved litters ingested by earthworms was researched by means of a laboratory experiment. Experimental samples were collected from broad-leaved Korea Pine mixed forest in Liangshui National Natural Reserve (47°10′50″N, 128°53′20″E) in the northeastern Xiao Hinggan Mountains of Northeast China. The contents of organic C and total N in earthworms, leaf litters and earthworm faeces were analyzed. Results show that the organic C content was in the fol- lowing order: leaf litters>faeces>earthworms, while total N content was contrary to that of the organic C. The organic C contents in the different leaf litters were in the following order: Tilia amurensis>Betula costata>Acer mono, whereas the total N contents in the different leaf litters were: Betula costata>Tilia amurensis>Acer mono. The contents of organic C and total N in the faeces from the different leaf litters were almost consistent with the contents of the leaf litters. After the leaf litters were ingested by earthworms, the organic C, which was transformed to increase earthworms' weights, ac- counted for 3.90%-13.31% of the total ingestion by earthworms, while that in the earthworm faeces accounted for 6.14%-13.70%. The transformed organic C through the other metabolism (e.g., respiration) of earthworms accounted for 75.04%-89.92%. The ingested organic C by earthworms was mostly used for metabolic activities. The N ingested by earthworms was less than organic C. It is estimated that 37.08% of total N was transformed to increase the earthworm's weight, 19.97% into earthworm faeces and 47.86% for the consumption of the earthworm's activities. The earthworms not only increased the content of organic C and total N in the soil, but also decreased the values of C/N in the soil and leaf litters. Earthworms play a major role in the leaf litters' decomposition and transformation.

Dependence of Wheat and Rice Respiration on Tissue Nitrogen and the Corresponding Net Carbon Fixation Efficiency Under Different Rates of Nitrogen Application

To quantitatively address the role of tissue N in crop respiration under various agricultural practices, and to consequently evaluate the impact of synthetic fertilizer N application on biomass production and respiration, and hence net carbon fixation efficiency （Encf）, pot and field experiments were carried out for an annual rotation of a rice-wheat cropping system from 2001 to 2003. The treatments of the pot experiments included fertilizer N application, sowing date and planting density. Different rates of N application were tested in the field experiments. Static opaque chambers were used for sampling the gas. The respiration as CO2 emission was detected by a gas chromatograph. A successive biomass clipping method was employed to determine the crop autotrophic respiration coefficient （Ra）. Results from the pot experiments revealed a linear relationship between Ra and tissue N content as Ra = 4.74N-1.45 （R^2= 0.85, P 〈 0.001）. Measurements and calculations from the field experiments indicated that fertilizer N application promoted not only biomass production but also increased the respiration of crops. A further investigation showed that the increase of carbon loss in terms of respiration owing to fertilizer N application exceeded that of net carbon gain in terms of aboveground biomass when fertilizer N was applied over a certain rate. Consequently, the Encf declined as the N application rate increased.

Effects of Nitrogen Forms on Carbon and Nitrogen Accumulation in Tomato Seedling

Utilization of organic nitrogen （N） is an important aspect of plant N assimilation and has potential application in sustainable agriculture. The aim of this study was to investigate the plant growth, C and N accumulation in leaves and roots of tomato seedlings in response to inorganic （NH4^＋-N, NO3^-N） and organic nitrogen （Gly-N）. Different forms of nitrogen （NH4^＋-N, NO3^--N, Gly-N） were supplied to two tomato cultivars （Shenfen 918 and Huying 932） using a hydroponics system. The plant dry biomass, chlorophyll content, root activity, total carbon and nitrogen content in roots and leaves, and total N absorption, etc. were assayed during the cultivation. Our results showed that no significant differences in plant height, dry biomass, and total N content were found within the first 16 d among three treatments; however, significant differences in treatments on 24 d and 32 d were observed, and the order was NO3^--N 〉 Gly-N 〉 NH4^＋-N. Significant differences were also observed between the two tomato cultivars. Chlorophyll contents in the two cultivars were significantly increased by the Gly-N treatment, and root activity showed a significant decrease in NHa^＋-N treatment. Tomato leaf total carbon content was slightly affected by different N forms; however, total carbon in root and total nitrogen in root and leaf were promoted significantly by inorganic and organic N. Among the applied N forms, the increasing effects of the NH4^＋-N treatment were larger than that of the Gly-N. In a word, different N resources resulted in different physiological effects in tomatoes. Organic nitrogen （e.g., Gly-N） can be a proper resource of plant N nutrition. Tomatoes of different genotypes had different responses under organic nitrogen （e.g., Gly-N） supplies.

Characteristics of Soil Organic Carbon, Total Nitrogen, and C/N Ratio in Chinese Apple Orchards

Soil organic carbon and nitrogen are used as indexes of soil quality assessment and sustainable land use management. At the same time, soil C/N ratio is a sensitive indicator of soil quality and for assessing the carbon and nitrogen nutrition balance of soils. We studied the characteristics of soil organic carbon and total nitrogen by investigating a large number of apple orchards in major apple production areas in China. High apple orchard soil organic carbon content was observed in the provinces of Heilongjiang, Xinjiang, and Yunnan, whereas low content was found in the provinces of Shandong, Henan, Hebei, and Shaanxi, with the values ranging between 6.44 and 7.76 g·kg-1. Similar to soil organic carbon, soil total nitrogen content also exhibited obvious differences in the 12 major apple producing provinces. Shandong apple orchard soil had the highest total nitrogen content (1.26 g·kg-1), followed by Beijing (1.23 g·kg-1). No significant difference was noted between these two regions, but their total nitrogen content was significantly higher than the other nine provinces, excluding Yunnan. The soil total nitrogen content for Xinjiang, Heilongjiang, Hebei, Henan, and Gansu was between 0.87 and 1.03 g·kg-1, which was significantly lower than that in Shandong and Beijing, but significantly higher than that in Liaoning, Shanxi, and Shaanxi. Six provinces exhibited apple orchard soil C/N ratio higher than 10, including Heilongjiang (15.42), Xinjiang (13.38), Ningxia (14.45), Liaoning (12.24), Yunnan (11.03), and Gansu (10.63). The soil C/N ratio was below 10 in the remaining six provinces, in which the highest was found in Shaanxi (9.47), followed by Beijing (8.98), Henan (7.99), and Shanxi (7.62), and the lowest was found in Hebei (6.80) and Shandong (6.05). Therefore, the improvement of soil organic carbon should be given more attention to increase the steady growth of soil C/N ratio.

Maize straw application as an interlayer improves organic carbon and total nitrogen concentrations in the soil profile: A four-year experiment in a saline soil

Soil salinization is a critical environmental issue restricting agricultural production.Deep return of straw to the soil as an interlayer (at 40 cm depth) has been a popular practice to alleviate salt stress.However,the legacy effects of straw added as an interlayer at different rates on soil organic carbon (SOC) and total nitrogen (TN) in saline soils still remain inconclusive.Therefore,a four-year (2015–2018) field experiment was conducted with four levels (i.e.,0,6,12and 18 Mg ha~(–1)) of straw returned as an interlayer.Compared with no straw interlayer (CK),straw addition increased SOC concentration by 14–32 and 11–57%in the 20–40 and 40–60 cm soil layers,respectively.The increases in soil TN concentration (8–22 and 6–34%in the 20–40 and 40–60 cm soil layers,respectively) were lower than that for SOC concentration,which led to increased soil C:N ratio in the 20–60 cm soil depth.Increases in SOC and TN concentrations in the 20–60 cm soil layer with straw addition led to a decrease in stratification ratios (0–20 cm:20–60 cm),which promoted uniform distributions of SOC and TN in the soil profile.Increases in SOC and TN concentrations were associated with soil salinity and moisture regulation and improved sunflower yield.Generally,compared with other treatments,the application of 12 Mg ha~(–1) straw had higher SOC,TN and C:N ratio,and lower soil stratification ratio in the2015–2017 period.The results highlighted that legacy effects of straw application as an interlayer were maintained for at least four years,and demonstrated that deep soil straw application had a great potential for improving subsoil fertility in salt-affected soils.

Synergetic effect of nitrogen‐doped carbon catalysts for high‐efficiency electrochemical CO_(2) reduction

The use of carbon‐based materials is an appealing strategy to solve the issue of excessive CO_(2) emis‐sions.In particular,metal‐free nitrogen‐doped carbon materials(mf‐NCs)have the advantages of convenient synthesis,cost‐effectiveness,and high conductivity and are ideal electrocatalysts for the CO_(2) reduction reaction(CO_(2)RR).However,the unclear identification of the active N sites and the low intrinsic activity of mf‐NCs hinder the further development of high‐performance CO_(2)RR electrocat‐alysts.Achieving precise control over the synthesis of mf‐NC catalysts with well‐defined active N‐species sites is still challenging.To this end,we adopted a facile synthesis method to construct a set of mf‐NCs as robust catalysts for CO_(2)RR.The resulting best‐performing catalyst obtained a Far‐adaic efficiency of CO of approximately 90%at−0.55 V(vs.reversible hydrogen electrode)and good stability.The electrocatalytic performance and in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy measurements collectively revealed that graphitic and pyridinic N can synergistically adsorb CO_(2) and H_(2)O and thus promote CO_(2) activation and protonation.

The Effect of Nitrogen Gas Flow Rate on the Cr-Containing DLC (Diamond-Like Carbon) Coating by AEGD Hybrid-CVD Coating Process

The development of electric and hybrid automobiles has gained momentum with the growth of interest in the field of miniaturization of electrode materials. In particular, technologies that improve the electrical property of stainless steel, while maintaining corrosion resistance, are gaining interest in terms of maintaining specific resistivity. The study on metal doping in diamond-like carbon coating is currently in progress to enhance the characteristics of conductivity and corrosion resistance with excellent properties such as corrosion resistance and lubrication coating. It is the process of using Cr arc with DLC coating to actuate AEGD. The change of I(D)/I(G) (Graphite peak (G) and disordered bond peak (D)) ratio and G-peak position in Cr-containing DLC film causes graphitization and thus lowers the basic electric resistance. Simultaneous input of nitrogen gas leads to deposition of CrN by a specific ratio of Cr and N in the DLC coating, and the nitrogen atoms replace hydrogen in bonding to increase the sp3 bond structure in the DLC film, in which CrN is not deposited, to result in specific resistivity of a specific value or less.

Influences of nitrogen flow rate on the structures and properties of Ti and N co-doped diamond-like carbon films deposited by arc ion plating

In this paper, Ti-C-N nanocomposite films are deposited under different nitrogen flow rates by pulsed bias arc ion plating using Ti and graphite targets in the Ar/N2 mixture gas. The surface morphologies, compositions, microstructures, and mechanical properties of the Ti-C-N films are investigated systematically by field emission scanning electron mi- croscopy （FE-SEM）, x-ray photoelectron spectroscopy （XPS）, grazing incident x-ray diffraction （GIXRD）, Raman spectra, and nano-indentation. The results show that the nanocrystalline Ti（C,N） phase precipitates in the film from GIXRD and XPS analysis, and Raman spectra prove the presence of diamond-like carbon, indicating the formation of nanocomposite film with microstructures comprising nanocrystalline Ti（C,N） phase embedded into a diamond-like matrix. The nitrogen flow rate has a significant effect on the composition, structure, and properties of the film. The nano-hardness and elastic modulus first increase and then decrease as nitrogen flow rate increases, reaching a maximum of 34.3 GPa and 383.2 GPa, at a nitrogen flow rate of 90 sccm, respectively.

Soil Carbon Sequestration,Water Use Efficiency(WUE) and Biological Nitrogen Fixation(BNF) Under Conservation Agriculture in Rain-fed Dry Area of North-west Pakistan

Land degradation,unbalanced nutrition,change in climate and its extreme variability are the factors affecting the sustainability of agriculture and food security.In North-west Pakistan,more than 50%of the cultivated area is rain-fed and the crop productivity is low.Conservation agriculture reduces greenhouse gas emissions by enhancing soil carbon sequestration and then improved soil fertility,WUE and crop productivity.A field experiment

Simultaneous Carbon and Nitrogen Removal in Wastewater Treatment Using a Partially Packed Biological Aerated Filter （BAF） without Backwashing Process

Biological aerated filter （BAF） is an advanced oxidation process that can sustain high volumetric loads with high quality effluent. However, backwashing process needed for the system limits its applicability. This study is to investigate the possibility of removing carbon and nitrogen simultaneously in a biological aerated filter （BAF） with partially packed media without any backwashing process. The upper part of BAF up to 0.5 m depth is packed with plastic media （Kaldnes K1） with diameter and length of 10 mm and 7 mm respectively. This partially packed BAF creates a hybrid system of attached growth and suspended growth combined in a single reactor. Three C：N ratios, i.e. 15, 10 and 4, were compared during this study by varying the nitrogen loading while the carbon loading was kept constant at 1.0±0.54 kg COD/（m^3·d）. The organic loading rate （OLR） ratios were calculated based on carbon and TKN loading. The carbon removal percentage of 86.7±7.3%, 85.1±10.3%, and 91.0±5.6% and TKN removal percentage of 24.7±11.6%, 48.0±25.9% and 62.8±7.9% were achieved after steady-state for the C：N ratio of 15, 10, and 4 respectively. Suspended solid concentration in the effluent was found to be high throughout the treatment, but no clogging occurred during the 4 months of operation period even though backwashing was eliminated.

C/N对枸杞枝条粉发酵过程中堆体理化性状及微生物群落多样性的影响

为探讨C/N对枸杞枝条粉园艺基质化腐熟发酵过程中堆体理化性状及微生物群落多样性的影响,以宁夏枸杞枝条粉为研究材料,以尿素为氮源,分别设置C/N为15(W1)、20(W2)、25(W3)、30(W4)、35(W5)、43.75(W6)。结果表明:整个发酵过程中各处理的pH和电导率均呈现逐渐降低趋势,总氮含量逐渐升高,铵态氮含量呈现先增加后降低的总体变化规律,硝态氮含量各时期变化规律较为一致,均呈现出先增加、后降低、再升高的折线变化规律。在整个发酵过程中纤维素酶活性差异较大,C/N为20~35处理W2、W3、W4、W5在发酵过程中呈现出持续上升趋势,C/N过低(15)或过高(43.75)表现为发酵前期(0~15 d)呈小幅度上升趋势,在15~105 d时间内呈现缓慢下降趋势。发酵堆体中脲酶变化规律为先增加、后降低、再增加的变化规律。C/N为20时,纤维素、半纤维素降解率值最大,而木质素增加值最大。在属水平上草酸降解菌(Pandoraea)、亚硝基单胞菌(Nitrosomonas)、亚硝基螺旋体(Nitrosospira)、假单胞菌(Pseudomonas)、双球菌(Paracoccus)、陶厄氏菌(Thauera)、嗜酸盐杆菌(Acidihalobacter)、绵羊属(Ovis)、马赛菌属(Massilia)、硝化细菌(Nitrobacter)、游动放线菌属(Actinoplanes)、硫磺菌属(Sulfuritortus)均为优势菌群。C/N较高时(C/N≥25),枸杞枝条发酵堆体微生物群落物种数量、物种多样性、丰富度、物种均匀度均显著增加,基于PCA分析得出C/N值25为氨化作用和硝化作用临界值、C/N值35为反硝化作用临界值。因此,为加速枸杞枝条粉发酵过程并减少氮素流失,建议发酵堆体初始C/N保持在20~25之间。

人造沸石对低C/N污水中氮的去除性能及机理

以人造沸石为吸附剂,处理低C/N高速服务区污水。考察了沸石投加量对人造沸石去除污水中氮效果的影响,利用正交实验探讨了影响人造沸石吸附污水中NH_(3)-N效果的因素,并结合吸附动力学和热力学、比表面积分析(BET)、扫描电子显微镜(SEM)等手段探讨了人造沸石去除NH_(3)-N的机理。结果表明:人造沸石可在短时间内实现对污水中NH_(3)-N和TN的显著去除,并可有效提升污水C/N,反应24 h后,40 g/L人造沸石可使污水中NH_(3)-N和TN分别降至(13.45±0.39)、(19.23±0.21)mg/L,去除率分别达到(91.14±0.32)%和(87.12±0.10)%,C/N由1.30±0.01提升至5.47±0.07;正交实验表明各因素影响人造沸石脱氮效果的程度表现为沸石投加量>曝气量>NH_(3)-N初始浓度;人造沸石对NH_(3)-N的吸附过程符合准二级反应动力学模型(R^(2)=0.990),且该吸附行为是吸热过程;BET和SEM显示,人造沸石对NH_(3)-N的高效去除主要得益于其较大的比表面积(493.23 m^(2)/g)以及以介孔为主且分布范围较宽的孔道,吸附后沸石表面的颗粒变得光滑、紧密且数量减少。

凋落物C/N对土壤有机碳矿化的影响

凋落物输入会影响土壤有机碳(SOC)矿化过程,其影响程度主要受凋落物C/N、土壤肥力和温度条件的影响,然而,这三因素的综合影响仍不清楚。以低肥力土壤(LF)和高肥力土壤(HF)为研究对象,分别添加7种不同C/N的凋落物,并设置培养温度为23℃和33℃,进行恒温避光培养,期间动态监测CO_(2)排放的变化,以揭示SOC矿化过程应对三因子的响应机制。结果显示,凋落物添加显著增加CO_(2)峰值排放速率,且与C/N>30的凋落物相比,添加C/N<30的凋落物对CO_(2)的峰值排放速率的促进作用更显著。CO_(2)峰值排放速率同时受土壤肥力和培养温度影响,HF-33℃条件下的CO_(2)峰值排放速率最高。添加C/N<30的凋落物显著增加了CO_(2)累积排放量,在LF-23℃、LF-33℃、HF-23℃和HF-33℃条件下,最大增幅分别为407%、304%、345%和160%。相关分析显示,SOC矿化率与凋落物C/N间呈负相关关系,这说明低质量凋落物会抑制SOC矿化。在LF-23℃、LF-33℃、HF-23℃和HF-33℃处理下,与凋落物C/N最低的CN1相比,添加C/N最高的CN7后,SOC矿化率的降幅分别达3.53、3.04、1.71和2.06倍。土壤肥力影响SOC矿化,HF的SOC矿化率较LF高1.29-2.66倍。培养温度对SOC矿化的影响在HF中表现出显著差异,与CK相比,在HF中添加凋落物显著降低了SOC矿化温度敏感性(Q10)。综合PLS-PM模型可知,SOC矿化是凋落物C/N、土壤肥力和培养温度综合作用的结果。其中,凋落物的C/N比对SOC矿化产生显著的负效应,土壤肥力则对SOC矿化产生主要的正效应,而温度的正效应则相对较小。研究结果有助于进一步理解不同土壤肥力和温度背景下,C/N不同的外源有机物输入对SOC矿化的影响及其背后的综合效应。

不同C/N对高氮废水高效脱氮处理的影响

考察低C/N(质量比,0.03、0.17、0.27、0.33)对高氮废水脱氮过程及污染物降解的影响,同时结合高通量测序,探讨系统中微生物多样性和菌群结构。结果表明,低C/N条件下高氮废水仍能实现脱氮,当C/N为0.33时,总氮去除率达到83.01%,该条件下出现较高的亚硝酸盐氮积累现象,最高达到316.09 mg/L。高通量测序结果表明,特吕珀菌属(Truepera,相对丰度31.33%)、水微菌属(Aquamicrobium,相对丰度6.42%)等是C/N为0.33时系统能够维持较高脱氮效率的原因。在低C/N条件下对高氮废水进行高效脱氮处理是可行性的。

Relationship Between Soil Microbial Biomass C and N and Mineralizable Nitrogen in Some Arable Soils on Loess Plateau

The chloroform fumigation-incubation method was used to measure the soil microbial biomass C (SMBC)and N (SMBN) in 16 loessial soils sampled from Ausai, Yongshou and Yangling in Shaanxi Province. The SMBC contents in the soils ranged from 75.9 to 301.0 μg Cg-1 with an average of 206.1 μg C g-1, accounting for 1.36%～6.24% of the total soil organic C with an average of 3.07%, and the SMBN contents from 0.51 to 68.40 μg N g-1 with an average of 29.4 μg N g-1, accounting for 0.20%～5.65% of the total N in the soils with an average of 3.36%. A close relationship was found between SMBC and SMBN, and they both were positively correlated with total organic C, total N, NaOH hydrolizable N and mineralizable N. These results confirmed that soil microbial biomass had a comparative role in nutrient cycles of soils.

Profile Distribution and Storage of Soil Organic Carbon in an Aquic BrownSoil as Affected by Land Use

Many attempts have been made to estimate the soil organic carbon (SOC) storage under different land uses, especiallyfrom the conversion of forest land or grassland into cultivated field, but limited reports were found on the estimation ofthis storage after cultivated field converted into woodland or grassland, especially in small scales. This study is aimed toinvestigate the dynamics of SOC concentration, its storage and carbon /nitrogen (C/N) ratio in an aquic brown soil at theShenyang Experimental Station of Ecology, Chinese Academy of Sciences under four land use patterns over 14 years. Thefour land use patterns were paddy field (PF), maize field (MF), fallow field (FF) and woodland (WL). In each pedon at 0-150cm depth, soil samples were collected from ten layers. The results showed that the profile distribution of SOC was differentunder different land uses, indicating the effect of land use on SOC. Soil organic carbon was significantly related with soiltotal N, and the correlation was slightly closer in nature ecosystems (with R2=0.990 and P<0.001 in both WL and FF, n=30)than in agroecosystems (with R2=0.976 and P<0.001 in PF, and R2=0.980 and P<0.001 in MF, n=30). The C/N ratio in theprofiles decreased generally with depth under the four land use patterns, and was comparatively higher in WL and lowerin PF. The C/N ratio of the FF was closer to that in the same soil depths of MF than to that of PF. Within 100 cm depth, theannual sequestration of SOC was 4.25, 2.87, and 4.48 t ha-1 more in WL than in PF, MF and FF, the annual SOC increasingrate being 6.15, 3.26, and 5.09 % higher, respectively. As a result, the SOC storage was significantly greater in WL than inany of the other three land use patterns, P=0.001, 0.008, and 0.008 as compared with PF, MF, and FF, respectively, whilethere was no significant difference among the other three land uses. It is suggested that woodland has the potential tomake a significant contribution to C storage and environmental quality.

Microstructure and cutting performance of Ti(C, N)-based cermets heat-treated in nitrogen

Ti（C, N）-based cermets were treated using hot isostatic pressing （HIP） at 1423 K in nitrogen. The microstructures compared with the as-sintered cermets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and electron microprobe analysis. It was found that high nitrogen activity in the surface zone resulted in the formation of gradient structure. Approximately 20-1am-deep, nitrogen-rich and titanium-rich hard surface zone was introduced by the heat treatment. The nitrogen activity was the driving force that caused the transportation of the atoms through the binder, titanium towards the surface, and tungsten and molybdenum inwards. In the surface zone, the particle size became fine, the inner rim disappeared, and the volume fraction of the outer rim and the binder phase considerably reduced. Small grains of TiN, WC, Mo2C, and nitrogen-rich carbonitlide phases formed in the surface zone during the heat treatment, improving the tlibological property of the heat-treated cermet.