Combining the critical nitrogen concentration and machine learning algorithms to estimate nitrogen deficiency in rice from UAV hyperspectral data

Rapid and large area acquisition of nitrogen(N)deficiency status is important for achieving the optimal fertilization of rice.Most existing studies,however,focus on the use of unmanned aerial vehicle(UAV)remote sensing to diagnose N nutrition in rice,while there are fewer studies on the quantitative description of the degree of N deficiency in rice,and the effects of the critical N concentration on the spectral changes in rice have rarely been explored.Therefore,based on the canopy spectral data obtained by remotely-sensed UAV hyperspectral images,the N content in rice was obtained through field sampling.The construction method of the rice curve for the northeastern critical N concentration was studied,and on this basis,N deficiency was determined.Taking the spectrum of the critical N concentration state as the standard spectrum,the spectral reflectivity data were transformed by the ratios and differences,and the feature extraction of the spectral data was carried out by the successive projections algorithm(SPA).Finally,by taking the characteristic band as the input variable and N deficiency as the output variable,a set of multivariate linear regression(MLR),long short-term memory(LSTM)inversion models based on extreme learning machine(ELM),and the nondominated sorting genetic algorithmⅢextreme learning machine(NSGA-Ⅲ-ELM)were constructed.The results showed two key aspects of this system:1)The correlation between the N deficiency data and original spectrum was poor,but the correlation between the N deficiency data and N deficiency could be improved by a difference change and ratio transformation;2)The inversion results based on the ratio spectrum and NSGA-Ⅲ-ELM algorithm were the best,as the R2values of the training set and validation set were 0.852 and 0.810,and the root mean square error(RMSE)values were 0.291 and 0.308,respectively.From the perspective of the spectral data,the inversion accuracy of the ratio spectrum was better than the accuracy of the original spectrum or difference spectrum.At the algorithm level,the model inversion results based on LSTM algorithms showed a serious overfitting phenomenon and poor inversion effect.The inversion accuracy based on the NSGA-Ⅲ-ELM algorithm was better than the accuracy of the MLR algorithm or the ELM algorithm.Therefore,the inversion model based on the ratio spectrum and NSGA-Ⅲ-ELM algorithm could effectively invert the N deficiency in rice and provide critical technical support for accurate topdressing based on the N status in the rice.

Effect of nitrogen concentration in culture mediums on growth and enzyme production of Phanerochaete chrysosporium

Effect of different nitrogen concentration in the mediums on growth and enzyme production of Phanerochaete chrysosporium was studied when glucose concentration was 10 g/L. The results showed that the medium contained 0.8 g/L ammonium tartrate is the best. It not only supply abundant nutrients for the growth of Phanerochaete chrysosporium, which make mycelia the best grow compared with the other medium, but also produce higher manganese-dependent peroxidase(Mnp) and laccase(Lac) activity. In addition, it is observed that the variation of mycelia surface is related to ligninolytic enzyme secreted by Phanerochaete chrysosporium. When the surface of mycelium pellets appeared burs, it predicts secondary metabolism begin. This experimentation demonstrated that when the ratio of carbon and nitrogen in nitrogen limited medium is equal to 100∶8, growth and enzyme production of Phanerochaete chrysosporium is the best, it could achieve the maximum Mnp and Lac activity.

Effects of Nitrogen Concentration on Microstructure and Antibacterial Property of Copper-Bearing Austenite Stainless Steels

Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food industries. In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much research interest due to its antibacterial action. The objective of this study was to determine the effects of nitrogen concentration on the precipitation of epsilon copper and antibacterial property. Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentration （0.02 and 0.08 wt pct, respectively） were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis. A mathematical expression was deduced to predict the effect of nitrogen concentration on the activity coefficient of copper, In（fCu/f^0cu）=0.53524＋4.11xN-0.48x^2N. Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix, stimulate the aggregation of copper atoms from austenite, increase the precipitation amount and consequently enhance the antibacterial property of steel.

MATHEMATICAL MODELS OF NITROGEN CONCENTRATION PROFILE OF ION NITRIDED LAYERS AND COMPUTER SIMULATION

The mathematical models of the kinetics of the layer growth at different ion nitriding condi- tions of armco iron.steels 45,40Cr,42CrMo and 38CrMoAl have been established.Based on these models the expression of nitrogen concentration profile of ion nitrided layers have been deduced with profile simulating method.They are C_=C_(min)^+(P_4)/(ξ_1-x)+(P_5)/(ξ_(10)~2)(ξ_1-x)~2 C_(γ′)=C_(min)^(γ′)+(P_1)/(ξ_(21))(ξ_2-x)+(P_2)/(ξ_(21)~2)(ξ_2-x)~2 C_α=C_(min)~α+(C_(33))/(C_(33))/(ξ_(32))(ξ_3-x)~3 Using these models,the kinetics of layer growth and the nitrogen concentration profile of ion nitrided layers were sinulated on Apple-Ⅱ computer.Results show that the simulated curves coincide quite well with the experimental data.

Synthesis and characterization of a single diamond crystal with a high nitrogen concentration

In this paper, we explore diamond synthesis with a series of experiments using an Fe-Ni catalyst and a P3N5 additive in the temperature range of 1250-1550 ℃ and the pressure range of 5.0-6.3 GPa. We also investigate the influence of nitrogen on diamond crystallization. Our results show that the synthesis conditions （temperature and pressure） increase with the amount of P3N5 additive increasing. The nitrogen impurity can significantly influence the diamond morphology. The diamonds stably grow into strip and lamellar shapes in the nitrogen-rich environment. The Fourier-transform infrared spectrum shows that the nitrogen concentration increases rapidly with the content of P3N5 additive increasing. By spectrum analysis, we find that with the increase of the nitrogen concentration, the Ib-type nitrogen atoms can aggregate in the A-centre form. The highest A-centre nitrogen concentration is approximately 840 ppm.

Variation of bacterial community associated with Phaeodactylum tricornutum in response to different inorganic nitrogen concentrations

Specific bacterial communities interact with phytoplankton in laboratory algal cultures. These communities influence phytoplankton physiology and metabolism by transforming and exchanging phytoplankton-derived organic matter. Functional bacterial groups may participate in various critical nutrients fluxes within these associations, including nitrogen(N) metabolism. However, it is unclear how bacterial communities and the associated algae respond to changes of phycosphere N conditions. This response may have far-reaching implications for global nutrient cycling, algal bloom formation, and ecosystem function. Here, we identified changes in the bacterial communities associated with Phaeodactylum tricornutum when co-cultured with different forms and concentrations of N based on the Illumina HiSeq sequencing of 16 S rRNA amplicons.Phylogenetic analysis identified Proteobacteria and Bacteroidetes as the dominant phyla, accounting for 99.5% of all sequences. Importantly, bacterial abundance and community structure were more affected by algal abundance than by the form or concentration of inorganic N. The relative abundance of three gammaproteobacterial genera(Marinobacter, Algiphilus and Methylophaga) markedly increased in N-deficient cultures. Thus, some bacterial groups may play a role in the regulation of N metabolism when co-cultured with P.tricornutum.

Mathematical Models and Computer Simulation of Nitrogen Concentration Profiles in Pulse Ion Nitrided Layers

The nitrogen concentration profiles in surface layers and surface phase structures were accurately measured respectively using the glow discharge spectrometry and X-ray Diffractometer after the specimens had been pulse ion nitrided at 500℃ for 0.2-8h The results show that the compound layer growth, which is different from that of conventional DC nitriding, conforms to parabolic law At the same time the surface nitrogen concentration change little with increasing the nitriding time, at least it is so when the treating time is longer than 0.2h In addition, the mathematical models of nitrogen concentration profiles in ε -Fe2~3N,γ-Fe4N and α -Fe phases have been established. Using them the nitrogen concentration profiles in nitrided layers were simulated. Results show that the simulated curves coincide quite well with the experimental data.

Nitrogen Concentration in Subtending Cotton Leaves in Relation to Fiber Strength in Different Fruiting Branches

Nitrogen（N） fertilizer experiments were conducted to investigate the optimal subtending leaf N concentration for fiber strength,and its relationship with activities of key enzymes（sucrose synthase and β-1,3-glucanase） and contents of key constituents（sucrose and β-1,3-glucan） involved in fiber strength development in the lower,middle and upper fruiting branches of two cotton cultivars（Kemian 1 and NuCOTN 33B）.For each sampling day,we simulated changes in fiber strength,activity of sucrose synthase and β-1,3-glucanase and levels of sucrose and β-1,3-glucan in response to leaf N concentration using quadratic eqs.;the optimal subtending leaf N concentrations were deduced from the eqs.For the same fruiting branch,changes in the optimal leaf N concentration based on fiber development（DPA） could be simulated by power functions.From these functions,the average optimal subtending leaf N concentrations during fiber development for the cultivar,Kemian 1,were 2.84% in the lower fruiting branches,3.15% in the middle fruiting branches and 3.04% in the upper fruiting branches.For the cultivar,NuCOTN 33B,the optimum concentrations were 3.04,3.28 and 3.18% in the lower,middle and upper fruiting branches,respectively.This quantification may be used as a monitoring index for evaluating fiber strength and its related key enzymes and constituents during fiber formation at the lower,middle and upper fruiting branches.

An Evaluation of Spaceborne Imaging Spectrometry for Estimation of Forest Canopy Nitrogen Concentration in a Subtropical Conifer Plantation of Southern China

Canopy foliar Nitrogen Concentration （CNC） is one of the most important parameters influencing vegetation productivity in forest ecosystems. In this study, we explored the potential of imaging spectrometry （hyperspectral） remote sensing of CNC in conifer plantations in China’s subtropical red soil hilly region. Our analysis included data from 57 field plots scattered across two transects covered by Hyperion images. Single regression and partial least squares regression （PLSR） were used to explore the relationships between CNC and hyperspectral data. The correlations between CNC and nearinfrared relfectance （NIR） were consistent in three data subsets （subsets A-C）. For all subsets, CNC was signiifcantly positively correlated with NIR in the two transects （R2=0.29, 0.33 and 0.36, P＆lt;0.05 or P＆lt;0.01, respectively）. It suggested that the NIR-CNC relationship exist despite a weak one, and the relationship may be weakened by the single canopy structure. Besides, we also applied a shortwave infrared （SWIR） index - Normalized Difference Nitrogen Index （NDNI） to estimate CNC variation. NDNI presented a signiifcant positive correlation with CNC in different subsets, but like NIR, it was also with low coefifcient of determination （R2=0.38, 0.20 and 0.17, P＆lt;0.01, respectively）. Also, the correlations between CNC and the entire spectrum reflectance （or its derivative and logarithmic transformation） by PLSR owned different signiifcance in various subsets. We did not ifnd the very robust relationship like previous literatures, so the data we used were checked again. The paired T-test was applied to estimate the inlfuence of inter-annual variability of FNC on the relationships between CNC and Hyperion data. The inter-annual mismatch between period of ifeldwork and Hyperion acquisition had no inlfuence on the correlations of CNC-Hyperion data. Meanwhile, we pointed out that the lack of the canopy structure variation in conifer plantation area may lead to these weak relationships.

Seasonal variation of nitrogen-concentration in the surface water and its relationship with land use in a catchment of northern China

Surface waters can be contaminated by human activities in two ways: (1) by point sources, such as sewage treatment discharge and storm-water runoff; and (2) by non-point sources, such as runoff from urban and agricultural areas. With point-source pollution effectively controlled, non-point source pollution has become the most important environmental concern in the world. The formation of non-point source pollution is related to both the sources such as soil nutrient, the amount of fertilizer and pesticide applied, the amount of refuse, and the spatial complex combination of land uses within a heterogeneous landscape. Land-use change, dominated by human activities, has a significant impact on water resources and quality. In this study, fifteen surface water monitoring points in the Yuqiao Reservoir Basin, Zunhua, Hebei Province, northern China, were chosen to study the seasonal variation of nitrogen concentration in the surface water. Water samples were collected in low-flow period(June), high-flow period(July) and mean-flow period(October) from 1999 to 2000. The results indicated that the seasonal variation of nitrogen concentration in the surface water among the fifteen monitoring points in the rainfall-rich year is more complex than that in the rainfall-deficit year. It was found that the land use, the characteristics of the surface river system, rainfall, and human activities play an important role in the seasonal variation of N-concentration in surface water.

Effects of different nitrogen forms and concentrations on seedling growth traits and physiological characteristics of Populus simonii × P. nigra

Numerous growth and physiological variables of 3-week-old Populus simonii × P.nigra seedlings were assessed after treatment with either nitrate nitrogen(NO_(3)^(−)--N)(0.1,0.5,1,5,or 10 mmol·L^(−1)) or ammonium nitrogen(NH_(4)^(+)+-N)(0.1,0.5,1,5,or 10 mmol·L^(−1)) to determine the best nitrogen form and concentration to optimize growth,biomass allocation,pigment content,and photosynthetic capacity.The results of combining membership function and an evaluation index suggested that,5 mmol·L^(−1) nitrogen,regardless of the form,yielded the highest comprehensive evaluation index and good growth.In addition,a Pearson correlation analysis and network visualization revealed that the total mass,shoot mass,root mass,leaf dry mass,plant height,leaf area,chlorophyll a and total chlorophyll had a physiological index connectivity degree≥15 for both nitrogen forms.Net photosynthetic rate,stomatal conductance,transpiration rate,maximum photochemical efficiency of PSII,total nitrogen content,ground diameter,chlorophyll b,and carotenoid were unique indices for evaluating NH_(4)^(+)+-N-based nutrition,which could provide a theoretical basis for evaluating the effects of nitrogen fertilizer on seedlings,cultivation periods,and stress tolerance in P.simonii× P.nigra.

Monitoring nitrogen concentration of oilseed rape from hyperspectral data using radial basis function

Remote sensing technology is the important tool of digital earth,it can facilitate nutrient management in sustainable cropping systems.In the study,two types of radial basis function(RBF)neural network approaches,the standard radial basis function(SRBF)neural networks and the modified type of RBF,generalized regression neural networks(GRNN),were investigated in estimating the nitrogen concentrations of oilseed rape canopy using vegetation indices(VIs)and hyperspectral reflectance.Comparison analyses were performed to the spectral variables and the approaches.The Root Mean Square Error(RMSE)and determination coefficients(R2)were used to assess their predictability of nitrogen concentrations.For all spectral variables(VIs and hyperspectral reflectance),the GRNN method produced more accurate estimates of nitrogen concentrations than did the SRBF method at all ranges of nitrogen concentrations,and the better agreements between the measured and the predicted nitrogen concentration were obtained with the GRNN method.This indicated that the GRNN method is prior to the SRBF method in estimation of nitrogen concentrations.Among the VIs,the Modified Chlorophyll Absorption in Reflectance Index(MCARI),MCARI1510,and Transformed Chlorophyll Absorption in Reflectance Index are better than the others in estimating oilseed rape canopy nitrogen concentrations.Compared to the results from VIs,the hyperspectral reflectance data also gave an acceptable estimation.The study showed that nitrogen concentrations of oilseed rape canopy could be monitored using remotely sensed data and the RBF method,especially the GRNN method,is a useful explorative tool for oilseed rape nitrogen concentration monitoring when applied on hyperspectral data.

Influence of the concentration ratio of nitrogen to phosphorus on the growth and interspecies competition of two red tide algae

The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp. were studied under different concentration ratios of nitrogen to phosphorus, and the algal hatch culture experiments were conducted. The physiological and biochemical indexes were measured periodically, including the maximum comparing growth rate, relative growth rate, average double time and chlorophyll a concentration. The results showed that when the concentration ratio of nitrogen to phosphorus was 16： 1, the maximum comparing growth rate, relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest. This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16： 1. When the concentration ratio of nitrogen to phosphorus was 6：1, the maximum comparing growth rate, relative growth rate and the chlorophyll a concentration of Gymnodinium sp. reached the highest, and average double time was the shortest, so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp. is 6： 1. From the growth curves as indicated both in the cell density and the chlorophyll a concentration, it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same. Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae. Gymnodinium sp. may use the phosphorus in vivo for growth, so it is important to pay attention to the concealment of phosphorus, in order to avoid the outbreak of red tide. On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration, the possible outbreak mechanism of red tide of the two algae was also discussed.

Study on Nitrogen Distribution in Leaf, Stem and Sheathat Different Layers in Winter Wheat Canopyand Their Influence on Grain Quality

Vertical distribution of nitrogen in wheat canopy, nitrogen remobilization and their influence on grain quality of winter wheat were studied. Two winter wheat cultivars, Jingdong8, a common cultivar, and Zhongyou9507, a high quality cultivar, were selected. Leaf nitrogen showed an obvious decreasing trend from the canopy top to the ground surface for all treatments in growth duration. There was no apparent vertical nitrogen gradient in stem and sheath of Zhongyou9507 compared with Jingdong8. Zhongyou9507 had more nitrogen remobilization from leaf, stem and sheath than Jingdong8 from middle grain filling to waxening, especially the nitrogen remobilization amount in stem and sheath, which was higher than that in Jingdong8 during growth duration. Higher vertical nitrogen gradients in Jingdong8 at anthesis had disadvantages on its grain quality. But higher vertical nitrogen gradients between middle and lower layers of Jingdong8 at grain filling stage enhanced its grain quality. Higher vertical nitrogen gradients in upper layer at anthesis and upper layer leaf and middle layer stem and sheath at grain filling stage had advantages on protein accumulation in grain of Zhongyou9507. There were positive correlations between foliar nitrogen remobilization amount and grain quality at later growth stage for the two cultivars. There was a positive correlation between quality of Jingdong8 and stem and sheath nitrogen remobilization amount from anthesis to early grain filling, and that of Zhongyou9507 emerged from anthesis to early grain filling and from middle grain filling to waxening. Contribution of leaf nitrogen to the quality of Jingdong8 was larger than nitrogen from stem and sheath. High protein content of Zhongyou9507 was attributed to the nitrogen condition in its leaf, stem and sheath. Nitrogen in stem and sheath played a more important role on the grain quality of Zhongyou9507 than on that of Jingdong8.

Determining nitrogen status and quantifying nitrogen fertilizer requirement using a critical nitrogen dilution curve for hybrid indica rice under mechanical pot-seedling transplanting pattern

Field experiments of nitrogen(N)treatment at five different application rates(0,75,150,225,and 300 kg ha^(-1))were conducted under pot-seedling mechanical transplanting(PMT)in 2018 and 2019.Two high-quality and high-yielding hybrids of indica rice,Huiliangyou 898 and Y Liangyou 900,were used in this study.The N nutrition index(NNI)and accumulated N deficit(N_(and)),used to assess the N nutrition status in real-time,were calculated for the indica cultivars under PMT with a critical nitrogen concentration(N_(c))dilution model based on shoot dry matter(DM)during the whole rice growth stage.The relationships between NNI and N_(and) with relative yield(RY)were determined,and accurate N application schemes were developed for hybrids indica rice under PMT.The results indicated that high application rate of N-fertilizer significantly increased the concentrations of shoot DM and N in aboveground organs during the observed stages in the two cultivars for two years(P<0.05).The N_(c) dilution model of hybrid indica cultivars was N_(c)=4.02 DM^(-0.42)(R^(2)=0.97)combining the two cultivars under PMT.Root-mean-square error and normalized root-mean-square error of the curve verification were 0.23 and 10.61%,respectively.The NNI and Nand ranged from 0.58 to 1.31 and 109 to–55 kg ha^(-1),respectively,in the two cultivars for all N treatments.NNI showed a linear relationship with Nand during the entire growth stage(0.53<R^(2)<0.99,P<0.01).In addition,NNI showed a linear-plateau relationship with RY(0.73<R<0.92,P<0.01)throughout the observed stages.These results suggest that the models can accurately diagnose the N-nutrition status and support effective N-fertilizer management in real-time for hybrid indica rice under PMT.

Characterization of the Growth,Chlorophyll Content and Lipid Accumulation in a Marine Microalgae Dunaliella tertiolecta under Different Nitrogen to Phosphorus Ratios

Microalgal lipids are regarded as main future feedstock of biofuels for its higher efficiency of accumulation and sus- tainable production. In order to investigate the effect of various nitrogen to phosphorus ratios on cells growth, chlorophyll content and accumulation of lipids in Dunaliella tertiolecta, experiments were carried out in modified microalgal medium with inorganic nitrogen （nitrate-nitrogen） or organic nitrogen （urea-nitrogen） as the sole nitrogen source at initial N：P ratios ranging from 1：1 to 32：1. The favorable N：P of 16：1 in the nitrate-N or urea-N medium yielded the maximum cell density and specific growth rate. Decrease in chlorophyll content were observed at the N：P of 4：1 in both nitrate-N and urea-N cultures. It was also observed that the maximum lipids concentration was obtained at the N：P of 4：1 in both nitrate and urea nutrient medium. The lipid productivity and lipid content of cultures in the urea-N medium at the N：P of 4： lwere markedly higher than those from cultures with other N：P ratios （p〈 0.05）. The results of this work illustrate the possibility that higher ratios of nitrogen to phosphorus have enhancing effect on cells growth of D. tertiolecta. Conversely, higher lipid accumulation is associated with a decrease in chlorophyll content under lower ratios of nitro- gen to phosphorus. The results confirm the hypothesis of this study that a larger metabolic flux has been channeled to lipid accumu- lation in D. tertiolecta cells when the ratios of nitrogen to phosphorus drop below a critical level.

Sedimentary record of climate change in a high latitude fjord—Kongsfjord

The sedimentary record of climate change in the Arctic region is useful for understanding global warming.Kongsfjord is located in the subpolar region of the Arctic and is a suitable site for studying climate change.Glacier retreat is occurring in this region due to climate change,leading to an increase in meltwater outflow with a high debris content.In August 2017,we collected a sediment Core Z3 from the central fjord near the Yellow River Station.Then,we used the widely used chronology method of 210Pb,^(137)Cs,and other parameters to reflect the climate change record in the sedimentary environment of Kongsfjord.The results showed that after the mid-late 1990s,the mass accumulation rate of this core increased from 0.10 g/(cm^(2)·a)to 0.34 g/(cm^(2)·a),while the flux of^(210)Pb_(ex)increased from 125 Bq/(m^(2)·a)to 316 Bq/(m^(2)·a).The higher sedimentary inventory of^(210)Pb_(ex)in Kongsfjord compared to global fallout might have been caused by sediment focusing,boundary scavenging,and riverine input.Similarities between the inventory of^(137)Cs and global fallout indicated that terrestrial particulate matter was the main source of^(137)Cs in fjord sediments.The sedimentation rate increased after 1997,possibly due to the increased influx of glacial meltwater containing debris.In addition,the^(137)Cs activity,percentage of organic carbon(OC),and OC/total nitrogen concentration ratio showed increasing trends toward the top of the core since 1997,corresponding to a decrease in the mass balance of glaciers in the region.The results ofδ^(13)C,δ^(15)N and OC/TN concentration ratio showed both terrestrial and marine sources contributed to the organic matter in Core Z3.The relative contribution of terrestrial organic matter which was calculated by a two-endmember model showed an increased trend since mid-1990s.All these data indicate that global climate change has a significant impact on Arctic glaciers.

Tree-ring δ^(15)N of Qinghai spruce in the central Qilian Mountains of China:Is pre-treatment of wood samples necessary?

A knowledge of the tree-ring stable nitrogen isotope ratio(δ^(15)N)can deepen our understanding of forest ecosystem dynamics by indicating the long-term availability,cycling and sources of nitrogen(N).However,the radial mobility of N blurs the interannual variations in the long-term N records.Previous studies of the chemical extraction of tree rings before analysis had produced inconsistent results and it is still unclear whether it is necessary to pre-treat wood samples from specific tree species to remove soluble N compounds before determining theδ^(15)N values.We compared the effects of pre-treatment with organic solvents and hot ultrapure water on the N concentration andδ^(15)N of tree rings from endemic Qinghai spruce(Picea crassifolia)growing in the interior of the central Qilian Mountains,China,during the last 60 a.We assessed the effects of different preparation protocols on the removal of the labile N compounds and investigated the need to pre-treat wood samples before determining theδ^(15)N values of tree rings.Increasing trends of the tree-ring N concentration were consistently observed in both the extracted and unextracted wood samples.The total N removed by extraction with organic solvents was about 17.60%,with a significantly higher amount in the sapwood section(P<0.01).Theδ^(15)N values of tree rings decreased consistently from 1960 to 2019 in both the extracted and unextracted wood samples.Extraction with organic solvents increased theδ^(15)N values markedly by about 5.2‰and reduced the variations in theδ^(15)N series.However,extraction with hot ultrapure water had little effect,with only a slight decrease in theδ^(15)N values of about 0.5‰.Our results showed that the radial pattern in the inter-ring movement of N in Qinghai spruce was not minimized by extraction with either organic solvents or hot ultrapure water.It is unnecessary to conduct hot ultrapure water extraction for the wood samples from Qinghai spruce because of its negligible effect on the removal of the labile N.Theδ^(15)N variation trend of tree rings in the unextracted wood samples was not influenced by the heartwood-sapwood transition zone.We suggest that theδ^(15)N values of the unextracted wood samples of the climate-sensitive Qinghai spruce could be used to explore the ecophysiological dynamics while focusing on the long-term variations.

Effect of the codoping of N-H-O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N-H-O at 5.5 GPa-7.1 GPa and 1370℃-1450℃. With the increase in the N-H-O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds;surface morphology became block-like;and growth texture,stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N-H-O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N-H-O impurity contents of the synthesis system.

Effects of nitrogen addition on plant biomass and tissue elemental content in different degradation stages of temperate steppe in northern China

Aims Grassland degradation has become a common problem worldwide.Several studies have analyzed the effects of nitrogen(N)addition on plant growth in grasslands,but few have considered its effects on plant growth in degraded grasslands.The aim of this study was to evaluate the effects of N addition on plant growth in grasslands with different levels of degradation in Inner Mongolia,China.Methods A 2-year field experiment was conducted to evaluate plant growth response to N addition in degraded grasslands on the Inner Mongolian Steppe.Grasslands with four levels of degradation were selected for N-addition treatments(0,10,20,30,40,50 g N m−2 year−1).Important Findings Aboveground biomass was increased by N fertilization in degraded grasslands,and N addition was significantly related to increased biomass in grasslands with severe degradation.However,N fertilization did not significantly affect belowground biomass.The effects of N addition on foliar nutrient concentrations in the same species differed among grasslands with different degradation lev-els.There was an inconsistent response to N addition between Sanguisorba officinalis and Vicia sepium in non-degraded grassland.There was a significant positive correlation between foliar N content and aboveground biomass in grasslands with different levels of deg-radation.Our results indicate that the effects of N addition on plant growth in grasslands differ according to the severity of degradation.We conclude that N fertilization may be an effective management technique for degraded grasslands in this area and may improve for-age productivity in the short term.