Experiments were carried out on a vegetable field with Peking cabbage(Brassica pekinensis (Lour.) Rupr.), cabbage (Brassica, chinensis var. oleifcra Makino and nemoto),green cabbage (Brassica chinensis L.), spinach (S...Experiments were carried out on a vegetable field with Peking cabbage(Brassica pekinensis (Lour.) Rupr.), cabbage (Brassica, chinensis var. oleifcra Makino and nemoto),green cabbage (Brassica chinensis L.), spinach (Spinacia oleracea L.) and rape(Brassica campestrisL.) to study the effects of N forms and N rates on their growth and nitrate accumulation. Theresults indicated that application of ammonium chloride, ammonium nitrate, sodium nitrate and ureasignificantly increased the yields and nitrate concentrations of Peking cabbage and spinach.Although no significant difference was found in the yields after application of the 4 N forms,nitrate N increased nitrate accumulation in vegetables much more than ammonium N. The vegetableyields were not increased continuously with N rate increase, and oversupply of N reduced the plantgrowth, leading to a yield decline. This trend was also true for nitrate concentrations in somevegetables and at some sampling times. However, as a whole, the nitrate concentrations in vegetableswere positively correlated with N rates. Thus, addition of N fertilizer to soil was the major causefor increases in nitrate concentrations in vegetables. Nitrate concentrations were much higher inroots, stems and petioles than in blades at any N rate.展开更多
Changes of soil organic nitrogen forms and soil nitrogen supply under continuous rice cropping system were investigated in a long-term fertilization experiment in Jinhua, Zhejiang Province, China. The fertilizer treat...Changes of soil organic nitrogen forms and soil nitrogen supply under continuous rice cropping system were investigated in a long-term fertilization experiment in Jinhua, Zhejiang Province, China. The fertilizer treatments included combination of P-K, N-K, N-P, and N-P-K as well as the control. After six years of continuous double-rice cropping, total soil N and hydrolysable N contents remained stable in plots with N treatments, while the hydrolysable N contents were substantially reduced in those plots without N application. Compared to the unbalanced fertilization treatments, P and K increased the percentage of hydrolysable ammonium N in the total soil N with the balanced application of N, and also maintained higher rice grain yields and nitrogen uptake. Grain yield was positively correlated with total N uptake (r = 0.875**), hydrolysable N (r = 0.608**), hydrolysable ammonium N (r = 0.560**) and the hydrolysable unknown N (r = 0.417**). Total N uptake was positively correlated with hydrolysable N (r = 0.608**), hydrolysable ammonium N (r = 0.440**) and hydrolysable unknown N (r = 0.431**). Soil nutrient depletion and/or unbalanced fertilization to rice crop reduced N content in soil microbial biomass, and therefore increased C/N ratio, suggesting a negative effect on the total microbial biomass in the soil.展开更多
Effects of different levels of compost application on the amounts and percentage distribution of organic N forms in whole soils and particle size fractions were investigated. Soil samples were collected from three plo...Effects of different levels of compost application on the amounts and percentage distribution of organic N forms in whole soils and particle size fractions were investigated. Soil samples were collected from three plots: (a) F, only chemical fertilizers;(b) F+LC, chemical fertilizers plus low level of compost;(c) F+HC, chemical fertilizers plus high level of compost. Each soil sample was divided into five fractions: coarse sand-sized aggregate (CSA), medium sand-sized aggregate (MSA), fine sand-sized aggregate (FSA), silt-sized aggregate (SIA) and clay-sized aggregate (CLA) fractions. The sand fractions were subdivided into decayed plants (DP) and mineral particles (MP). The amounts of total N and different organic N forms in the whole soils as well as size fractions generally increased with increasing the amount of compost. In the whole soils, percentage distribution of non-hydrolysable-N and amino sugar-N increased by compost application while the distribution values of the hydrolysable ammonium- N and unidentified-N decreased. The application did not affect the distribution degree of amino acid-N. In the size fractions, the distribution values of most organic N forms increased in the CSA-DP, MSA-DP and FSA-DP fractions by compost application. In the CLA fractions, the amounts and percentage distribution of organic N forms were the highest, although the application caused decreases in their distribution values. These findings indicate that the CLA fraction merit close attention as an important reservoir of various organic N.展开更多
Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-pola...Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. Of the detectable 15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups, 10%-18% to aromatic/aliphatic amines and 6%~11% to indole- and pyrrole-like N. Whereas in the spectrum of the fulvic acid from weathered coal 46%, at least, of the total 15N-signal intensity might be assigned to pyrrole-like N, 14% to aromatic/aliphatic ammes, and the remaining intensities could not be assigned with certainty. Data on nonhydrolyzable residue of protein-sugar mixture and a 15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis. Project (No. 39790100) supported by the National Natural Science Foundation of China.展开更多
The growth, chlorophyll composition, photosynthesis, respiration, K uptake and root K+ secretion offlue-cured tobacco as thected by different concentrations of N supplied as urea, NaNO3 and NH4NO3 werestudied under th...The growth, chlorophyll composition, photosynthesis, respiration, K uptake and root K+ secretion offlue-cured tobacco as thected by different concentrations of N supplied as urea, NaNO3 and NH4NO3 werestudied under the experimental condition of sand culture. The results showed that the content of K in thefiue-cured tobacco was not merely related with root vitality and uptake but also closely related with root cellmembrane structure and K+ secretion.展开更多
Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-m...Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-mechanical modeling tests. And the flow stress curves of the steel were obtained for various combinations of the temperature and strain rate. Based on the results of the tests, the complex forming process of a retaining ring including punching, expanding and extrusion with an enclosure was put forward and simulated by means of numerical simulation method. The results indicate that the process is a novel and force-saved practical technology for manufacturing heavy retaining rings.展开更多
Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ...Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ranging from 0.028 to 0.074. The mineralization rate under waterlogged conditions was higher than that under upland conditions. The proportion of α-amino acid N in humus newly-formed under waterlogged conditions was slightly higher than that under upland conditions. It decreased gradually with time, while the proportion of nonhydrolyzable N showed no consistent trend, irrespective of the water regimes for decomposition. The distribution of amino acids in humus newly- formed from different plant materials under various water regimes was quite similar with that in original plant materials, and only minor differences could be found among them. For example, in comparison to original plant materials, the newly-formed humus contained higher proportions of isoleucine, cystine, γ-amino-butync acid and ornithine, and lower proportions of phenylalanine and proline. Moreover the proportion of phenylalanine was higher in the humus newly-formed under waterlogged conditions than that under upland conditions.展开更多
In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemic...In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemical approaches.Results show that the majority of nitrogen in HA,FA and HAI was in the amide form with some presented as aliphatic and/ or aromatic amines and some as pyrrole type nitrogen,although the contents of nonhydrolyzable nitrogen in them differed greatly from each other (15-55%).展开更多
In the hot forming of Mn18Cr18N steel, such problems as easy cracking, difficult controlling of forming paramenters often occur. In this paper,the variation rule of the plasticity of the steel, the starting mechanis...In the hot forming of Mn18Cr18N steel, such problems as easy cracking, difficult controlling of forming paramenters often occur. In this paper,the variation rule of the plasticity of the steel, the starting mechanism of micro-crack and its generating characteristics were studied with the combination of thermodynamic simulation test, micro-simulation and FEM, the related data of microstructure change and hot forming parameters were produced. The hot forming process of 600MW generator retaining ring was analyzed as an example.展开更多
The atmosphere is an evolutionary agent essential to the shaping of a planet,while in oceanic science and daily life,liquids are commonly seen.In this paper,we investigate a generalized variable-coefficient Korteweg-d...The atmosphere is an evolutionary agent essential to the shaping of a planet,while in oceanic science and daily life,liquids are commonly seen.In this paper,we investigate a generalized variable-coefficient Korteweg-de Vriesmodified Korteweg-de Vries equation for the atmosphere,oceanic fluids and plasmas.With symbolic computation,beginning with a presumption,we work out certain scaling transformations,bilinear forms through the binary Bell polynomials and our scaling transformations,N solitons(with N being a positive integer)via the aforementioned bilinear forms and bilinear auto-Bäcklund transformations through the Hirota method with some solitons.In addition,Painlevé-type auto-Bäcklund transformations with some solitons are symbolically computed out.Respective dependences and constraints on the variable/constant coefficients are discussed,while those coefficients correspond to the quadratic-nonlinear,cubic-nonlinear,dispersive,dissipative and line-damping effects in the atmosphere,oceanic fluids and plasmas.展开更多
Water-soluble, nondialyzable Maillard polymers were prepared by reacting D-xylose with 15N-glycine (and/or glycine) at 68 ℃ and pH 8.0 at equimolar concentrations of 1, 0.5 and 0.1 mol L-1, respectively,for 13 days a...Water-soluble, nondialyzable Maillard polymers were prepared by reacting D-xylose with 15N-glycine (and/or glycine) at 68 ℃ and pH 8.0 at equimolar concentrations of 1, 0.5 and 0.1 mol L-1, respectively,for 13 days and partitioned into acid-insoluble (MHA) and acid-soluble (MFA) fractions. The nitrogen forms in these polymers were studied by using the 15N cross polarization-magic angle spinning nuclear magnetic resonance (CPMAS NMR) technique in combination with chemical methods. The 15N nuclear magnetic resonance (NMR) data showed that while the yield, especially the MHA/MFA ratio, varied considerably with the concentrations of the reactants, the nitrogen distribution patterns of these polymers were quite similar.From 65% to 70% of nitrogen in them was in the secondary amide and/or indole form with 24%~25% present as aliphatic and/or aromatic ammes and 5% to 11% as pyrrole and/or pyrrole-like nitrogen. More than half (50%~77%) of the N in these polymers were nonhydrolyzable. The role of Maillard reaction in the formation of nonhydrolyzable nitrogen in soil organic matter is discussed.展开更多
of 是个含义丰富的常用介词,可放在两个名词(代词)之间,表示两者是所属、主谓、动宾、同位等关系。但 of 放在形容词和名词(代词)之间,表示修饰与被修饰关系的用法却不为人们所注意。这种结构有如下几种情况:1.of 用在表示“摆脱”、“...of 是个含义丰富的常用介词,可放在两个名词(代词)之间,表示两者是所属、主谓、动宾、同位等关系。但 of 放在形容词和名词(代词)之间,表示修饰与被修饰关系的用法却不为人们所注意。这种结构有如下几种情况:1.of 用在表示“摆脱”、“缺少”、“解脱”等含义的形容词后,表示“分离”,展开更多
Distribution of different forms of sulphur(S)and carbon-nitrogen-sulphur relationships were studied in surface and subsurface soils of some tea growing areas of Northeastern India.The soils were strongly acidic in rea...Distribution of different forms of sulphur(S)and carbon-nitrogen-sulphur relationships were studied in surface and subsurface soils of some tea growing areas of Northeastern India.The soils were strongly acidic in reaction(pH-4.0 to 5.5),low to very high in organic carbon(4 to 54 g kg^-1),with cation exchange capacity(8.8 to 19.2 cmol(p+)kg^-1)and base saturation(50 to 77%).Organic S mostly contributed to the total-sulphur(62 to 77%)followed by Non sulphate S(28.8 to 37.2%)and sulphate S(0.7 to 1.4%).Except sulphate S,other forms of sulphur showed significant positive correlation among themselves as well as with organic carbon and total nitrogen.The C:N,C:S,N:S and C:N:S ratio varied from 8.2 to 10.0,6.18 to 71.57,0.62 to 7.26 and 100:10.1:1.4 to 100:12.2:16.2 respectively.Wider C:N:S ratios in all the surface and sub-surface soils indicated that the major portion of nitrogen and sulphur in tea growing soils of Northeastern India is locked up in organic combination which might pose as a potential threat towards tea plantation if application of sulphur is continuously ignored.展开更多
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...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.展开更多
基金Project supported by the National Key Basic Research Support Foundation (No. G1999011707)the National Natural Science Foundation of China (Nos. 39970429, 49890330, 30070429 and 40201028).
文摘Experiments were carried out on a vegetable field with Peking cabbage(Brassica pekinensis (Lour.) Rupr.), cabbage (Brassica, chinensis var. oleifcra Makino and nemoto),green cabbage (Brassica chinensis L.), spinach (Spinacia oleracea L.) and rape(Brassica campestrisL.) to study the effects of N forms and N rates on their growth and nitrate accumulation. Theresults indicated that application of ammonium chloride, ammonium nitrate, sodium nitrate and ureasignificantly increased the yields and nitrate concentrations of Peking cabbage and spinach.Although no significant difference was found in the yields after application of the 4 N forms,nitrate N increased nitrate accumulation in vegetables much more than ammonium N. The vegetableyields were not increased continuously with N rate increase, and oversupply of N reduced the plantgrowth, leading to a yield decline. This trend was also true for nitrate concentrations in somevegetables and at some sampling times. However, as a whole, the nitrate concentrations in vegetableswere positively correlated with N rates. Thus, addition of N fertilizer to soil was the major causefor increases in nitrate concentrations in vegetables. Nitrate concentrations were much higher inroots, stems and petioles than in blades at any N rate.
基金Project supported by the International Fertilizer Industry Association (IFI), Francethe Potast & Phosphate Institute (PPI), USA and Canadathe International Potassium Institute (IPI), Switzerland
文摘Changes of soil organic nitrogen forms and soil nitrogen supply under continuous rice cropping system were investigated in a long-term fertilization experiment in Jinhua, Zhejiang Province, China. The fertilizer treatments included combination of P-K, N-K, N-P, and N-P-K as well as the control. After six years of continuous double-rice cropping, total soil N and hydrolysable N contents remained stable in plots with N treatments, while the hydrolysable N contents were substantially reduced in those plots without N application. Compared to the unbalanced fertilization treatments, P and K increased the percentage of hydrolysable ammonium N in the total soil N with the balanced application of N, and also maintained higher rice grain yields and nitrogen uptake. Grain yield was positively correlated with total N uptake (r = 0.875**), hydrolysable N (r = 0.608**), hydrolysable ammonium N (r = 0.560**) and the hydrolysable unknown N (r = 0.417**). Total N uptake was positively correlated with hydrolysable N (r = 0.608**), hydrolysable ammonium N (r = 0.440**) and hydrolysable unknown N (r = 0.431**). Soil nutrient depletion and/or unbalanced fertilization to rice crop reduced N content in soil microbial biomass, and therefore increased C/N ratio, suggesting a negative effect on the total microbial biomass in the soil.
文摘Effects of different levels of compost application on the amounts and percentage distribution of organic N forms in whole soils and particle size fractions were investigated. Soil samples were collected from three plots: (a) F, only chemical fertilizers;(b) F+LC, chemical fertilizers plus low level of compost;(c) F+HC, chemical fertilizers plus high level of compost. Each soil sample was divided into five fractions: coarse sand-sized aggregate (CSA), medium sand-sized aggregate (MSA), fine sand-sized aggregate (FSA), silt-sized aggregate (SIA) and clay-sized aggregate (CLA) fractions. The sand fractions were subdivided into decayed plants (DP) and mineral particles (MP). The amounts of total N and different organic N forms in the whole soils as well as size fractions generally increased with increasing the amount of compost. In the whole soils, percentage distribution of non-hydrolysable-N and amino sugar-N increased by compost application while the distribution values of the hydrolysable ammonium- N and unidentified-N decreased. The application did not affect the distribution degree of amino acid-N. In the size fractions, the distribution values of most organic N forms increased in the CSA-DP, MSA-DP and FSA-DP fractions by compost application. In the CLA fractions, the amounts and percentage distribution of organic N forms were the highest, although the application caused decreases in their distribution values. These findings indicate that the CLA fraction merit close attention as an important reservoir of various organic N.
基金supported by the National Natural science Foundation of China.(No.39790100)
文摘Nitrogen forms of humic substances from a subalpine meadow soil, a latentic red soil and a weathered coal and the effect of acid hydrolysis on N structures of soil humic substances were studied by using 15N cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy. Of the detectable 15N-signal intensity in the spectra of soil humic substances 71%-79% may be attributed to amide groups, 10%-18% to aromatic/aliphatic amines and 6%~11% to indole- and pyrrole-like N. Whereas in the spectrum of the fulvic acid from weathered coal 46%, at least, of the total 15N-signal intensity might be assigned to pyrrole-like N, 14% to aromatic/aliphatic ammes, and the remaining intensities could not be assigned with certainty. Data on nonhydrolyzable residue of protein-sugar mixture and a 15N-labelled soil fulvic acid confirm the formation of nonhydrolyzable heterocyclic N during acid hydrolysis. Project (No. 39790100) supported by the National Natural Science Foundation of China.
文摘The growth, chlorophyll composition, photosynthesis, respiration, K uptake and root K+ secretion offlue-cured tobacco as thected by different concentrations of N supplied as urea, NaNO3 and NH4NO3 werestudied under the experimental condition of sand culture. The results showed that the content of K in thefiue-cured tobacco was not merely related with root vitality and uptake but also closely related with root cellmembrane structure and K+ secretion.
文摘Mn18Cr18N, the high-nitrogen steel, is the 2nd generation material for manufacturing the retaining ring of firepower generators. In this paper, the hot deformation behavior of the material was investigated by thermo-mechanical modeling tests. And the flow stress curves of the steel were obtained for various combinations of the temperature and strain rate. Based on the results of the tests, the complex forming process of a retaining ring including punching, expanding and extrusion with an enclosure was put forward and simulated by means of numerical simulation method. The results indicate that the process is a novel and force-saved practical technology for manufacturing heavy retaining rings.
基金Project supported by the National Natural Science Foundation of China.
文摘Results of a 10-year decomposition experiment indicated that the annual mineralization rate of organic N in newly-formed humus varied with the type of original plant materials and the water regimes for decomposition, ranging from 0.028 to 0.074. The mineralization rate under waterlogged conditions was higher than that under upland conditions. The proportion of α-amino acid N in humus newly-formed under waterlogged conditions was slightly higher than that under upland conditions. It decreased gradually with time, while the proportion of nonhydrolyzable N showed no consistent trend, irrespective of the water regimes for decomposition. The distribution of amino acids in humus newly- formed from different plant materials under various water regimes was quite similar with that in original plant materials, and only minor differences could be found among them. For example, in comparison to original plant materials, the newly-formed humus contained higher proportions of isoleucine, cystine, γ-amino-butync acid and ornithine, and lower proportions of phenylalanine and proline. Moreover the proportion of phenylalanine was higher in the humus newly-formed under waterlogged conditions than that under upland conditions.
基金Project supported by the National Natural Science Foundation of China
文摘In this paper,the nitrogen forms in newly-formed humic substances,including humic acid (HA),fulvic acid (FA) and humic acid in humin (HAI),were studied by using the ^15N CP-MAS NMR technique in combination with chemical approaches.Results show that the majority of nitrogen in HA,FA and HAI was in the amide form with some presented as aliphatic and/ or aromatic amines and some as pyrrole type nitrogen,although the contents of nonhydrolyzable nitrogen in them differed greatly from each other (15-55%).
文摘In the hot forming of Mn18Cr18N steel, such problems as easy cracking, difficult controlling of forming paramenters often occur. In this paper,the variation rule of the plasticity of the steel, the starting mechanism of micro-crack and its generating characteristics were studied with the combination of thermodynamic simulation test, micro-simulation and FEM, the related data of microstructure change and hot forming parameters were produced. The hot forming process of 600MW generator retaining ring was analyzed as an example.
基金the National Natural Science Foundation of China(Grant No.11871116)the Fundamental Research Funds for the Central Universities of China(Grant No.2019XD-A11)the BUPT Innovation and Entrepreneurship Support Program,Beijing University of Posts and Telecommunications,and the National Scholarship for Doctoral Students of China.
文摘The atmosphere is an evolutionary agent essential to the shaping of a planet,while in oceanic science and daily life,liquids are commonly seen.In this paper,we investigate a generalized variable-coefficient Korteweg-de Vriesmodified Korteweg-de Vries equation for the atmosphere,oceanic fluids and plasmas.With symbolic computation,beginning with a presumption,we work out certain scaling transformations,bilinear forms through the binary Bell polynomials and our scaling transformations,N solitons(with N being a positive integer)via the aforementioned bilinear forms and bilinear auto-Bäcklund transformations through the Hirota method with some solitons.In addition,Painlevé-type auto-Bäcklund transformations with some solitons are symbolically computed out.Respective dependences and constraints on the variable/constant coefficients are discussed,while those coefficients correspond to the quadratic-nonlinear,cubic-nonlinear,dispersive,dissipative and line-damping effects in the atmosphere,oceanic fluids and plasmas.
文摘Water-soluble, nondialyzable Maillard polymers were prepared by reacting D-xylose with 15N-glycine (and/or glycine) at 68 ℃ and pH 8.0 at equimolar concentrations of 1, 0.5 and 0.1 mol L-1, respectively,for 13 days and partitioned into acid-insoluble (MHA) and acid-soluble (MFA) fractions. The nitrogen forms in these polymers were studied by using the 15N cross polarization-magic angle spinning nuclear magnetic resonance (CPMAS NMR) technique in combination with chemical methods. The 15N nuclear magnetic resonance (NMR) data showed that while the yield, especially the MHA/MFA ratio, varied considerably with the concentrations of the reactants, the nitrogen distribution patterns of these polymers were quite similar.From 65% to 70% of nitrogen in them was in the secondary amide and/or indole form with 24%~25% present as aliphatic and/or aromatic ammes and 5% to 11% as pyrrole and/or pyrrole-like nitrogen. More than half (50%~77%) of the N in these polymers were nonhydrolyzable. The role of Maillard reaction in the formation of nonhydrolyzable nitrogen in soil organic matter is discussed.
文摘Distribution of different forms of sulphur(S)and carbon-nitrogen-sulphur relationships were studied in surface and subsurface soils of some tea growing areas of Northeastern India.The soils were strongly acidic in reaction(pH-4.0 to 5.5),low to very high in organic carbon(4 to 54 g kg^-1),with cation exchange capacity(8.8 to 19.2 cmol(p+)kg^-1)and base saturation(50 to 77%).Organic S mostly contributed to the total-sulphur(62 to 77%)followed by Non sulphate S(28.8 to 37.2%)and sulphate S(0.7 to 1.4%).Except sulphate S,other forms of sulphur showed significant positive correlation among themselves as well as with organic carbon and total nitrogen.The C:N,C:S,N:S and C:N:S ratio varied from 8.2 to 10.0,6.18 to 71.57,0.62 to 7.26 and 100:10.1:1.4 to 100:12.2:16.2 respectively.Wider C:N:S ratios in all the surface and sub-surface soils indicated that the major portion of nitrogen and sulphur in tea growing soils of Northeastern India is locked up in organic combination which might pose as a potential threat towards tea plantation if application of sulphur is continuously ignored.
基金supported by the National Natural Science Foundation of China(Nos.31800369,32271686,U1904204)the State Scholarship Fund of Chinathe Innovation Scientists and Technicians Troop Construction Projects of Henan Province(No.182101510005)。
文摘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.