Cropland (CP),native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L.) (ST),and branchytamarisk (Tamarix ramosissima) (BT) were investigated...Cropland (CP),native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L.) (ST),and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China.Total organic carbon (TOC),light fraction organic carbon (LFOC),heavy fraction organic carbon (HFOC),total N (TN),nitrate nitrogen (NO 3-N) and nitrite nitrogen (NO 2-N),ammonium nitrogen (NH + 4-N),total P,and available P (AP) were measured.The results showed that SOC in NG,ST and BT were 12.7%,27.7% and 34.8% higher than that of the cropland,respectively.LFOC,light fraction (LF) dry matter,ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland.Cropland had the highest TN,the sum of NO 3-N and NO 2-N,TP and AP due to the use of chemical fertilizers.TOC significantly correlated with LFOC,HFOC and C/N.LFOC significantly correlated with dry matter of the LF and C/N.TN,the sum of NO 3-N and NO 2-N and AP were significantly negatively correlated with TOC and LFOC.Therefore,land use conversion from cropland to shrub land,or maybe grassland,contributed to SOC sequestration and improved soil nutrients stabilization.展开更多
We studied the uptake of ammonium, nitrate, and a variety of amino acids by alpine plant species in the Kobresia humil alpine meadow ecosystem in situ. We examined the extent of niche separation in uptake of N source ...We studied the uptake of ammonium, nitrate, and a variety of amino acids by alpine plant species in the Kobresia humil alpine meadow ecosystem in situ. We examined the extent of niche separation in uptake of N source by different plant species in alpine communities, and investigated the contribution of symbiotically fixed N to the total N in alpine meadow. The results are （1） δ15N natural abundance values of 13 plant species lie between -2.680‰ and 5.169‰, and the scope is 7.849‰. （2） Le- guminous plants, such as Trigonella ruthenica, Gueldenstaedtia diversiffolia, and Oxytyopis ochrocephala, and non-legumi- nous plant Gentiana straminea uptake low amounts of 15N labeled ammonium, nitrate, glycine or aspartate in soil. （3） As far as the plant uptake of organic N is concerned, Kobresia humilis, Poa pratensis, and Gentiuna spathutifolta can effectively uptake organic nitrogen, and about 37%-40% of the nitrogen of these species comes from soil organic nitrogen sources （such as glycine and aspartate）. Stipa aliena can effectively uptake nitrate, and 60% of its nitrogen comes from soil nitrate. Potentilla anserina, Poa pratensis, and Thalictrum alpinum can effectively absorb ammonium in comparason to other plant species in the meadow, and about 25%-27% of the nitrogen in these plants comes from soil ammonium. （4） The contribution of leguminous fixed N to total N is 7.48%-9.26% in Kobresia humilis alpine meadow. （5） These data show many plant species of alpine meadow may effectively utilize dissolved organic nitrogen such as amino acids, and these plants have diverse ways to uptake soil nitrogen in alpine meadows. Based on the results we can partly explain why there are abundant biodiversities and how plants at alpine habitat utilize the limited soil N sources.展开更多
Because laboratory tests are expensive and time-consuming and may not be available to farmers, soil nitrate quick tests are required for optimal nitrogen management strategies in China to increase nitrogen use efficie...Because laboratory tests are expensive and time-consuming and may not be available to farmers, soil nitrate quick tests are required for optimal nitrogen management strategies in China to increase nitrogen use efficiency and to reduce nitrogen losses. A total of 328 soil samples were collected at different soil depths from 225 sites in China, which covered a wide range of climatic and geographic regions, soil types, croplands and soil textures, to evaluate the suitability of a quick reflectometer test method for analysing soil NO3-N in a wide range of soil NO3 concentrations, soil types and cropping systems in China, mainly by comparison of soil NO3-N assessed by a quick-test method （a reflectometer） and a standard laboratory method, i.e., high-performance liquid chromatography （HPLC）. The reflectometer showed excellent agreement with the laboratory HPLC method with regard to soil nitrate contents for all analysed soil samples. The linear regression had slopes of 1 ± 0.08 and intercepts of ± 1.38 mg NO（-,3）-N L^（-1） among different soil types and croplands. Compared with the 1：1 lines, the regression analysis for each soil type showed statistically significant but small differences in slope; the relative difference between the values measured using the two analytical systems varied from -8% to 6%, and there were no differences in intercept except for paddy soil. The reflectometer showed adequate, statistically significant precision in determining soil nitrate contents, and it could therefore be directly used instead of the laboratory methods for soil NO（-,3）-N measurement in China.展开更多
基金Project supported by the National Basic Research Program (973 Program) of China (No. 2007CB106804)the International S&T Cooperation Program (ISTCP) of China (No. 2006DFA31070)the International Foundation for Sciences(No. C/3313-2)
文摘Cropland (CP),native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L.) (ST),and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China.Total organic carbon (TOC),light fraction organic carbon (LFOC),heavy fraction organic carbon (HFOC),total N (TN),nitrate nitrogen (NO 3-N) and nitrite nitrogen (NO 2-N),ammonium nitrogen (NH + 4-N),total P,and available P (AP) were measured.The results showed that SOC in NG,ST and BT were 12.7%,27.7% and 34.8% higher than that of the cropland,respectively.LFOC,light fraction (LF) dry matter,ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland.Cropland had the highest TN,the sum of NO 3-N and NO 2-N,TP and AP due to the use of chemical fertilizers.TOC significantly correlated with LFOC,HFOC and C/N.LFOC significantly correlated with dry matter of the LF and C/N.TN,the sum of NO 3-N and NO 2-N and AP were significantly negatively correlated with TOC and LFOC.Therefore,land use conversion from cropland to shrub land,or maybe grassland,contributed to SOC sequestration and improved soil nutrients stabilization.
基金supported by National Natural Science Foundation of China(Grant Nos.30660120 and 41030105)National Basic Research Program of China (Grant No. 2009CB421102)International Cooperation Program of Science and Technology Department of Qinghai Province (Grant No. 2010-H-809)
文摘We studied the uptake of ammonium, nitrate, and a variety of amino acids by alpine plant species in the Kobresia humil alpine meadow ecosystem in situ. We examined the extent of niche separation in uptake of N source by different plant species in alpine communities, and investigated the contribution of symbiotically fixed N to the total N in alpine meadow. The results are （1） δ15N natural abundance values of 13 plant species lie between -2.680‰ and 5.169‰, and the scope is 7.849‰. （2） Le- guminous plants, such as Trigonella ruthenica, Gueldenstaedtia diversiffolia, and Oxytyopis ochrocephala, and non-legumi- nous plant Gentiana straminea uptake low amounts of 15N labeled ammonium, nitrate, glycine or aspartate in soil. （3） As far as the plant uptake of organic N is concerned, Kobresia humilis, Poa pratensis, and Gentiuna spathutifolta can effectively uptake organic nitrogen, and about 37%-40% of the nitrogen of these species comes from soil organic nitrogen sources （such as glycine and aspartate）. Stipa aliena can effectively uptake nitrate, and 60% of its nitrogen comes from soil nitrate. Potentilla anserina, Poa pratensis, and Thalictrum alpinum can effectively absorb ammonium in comparason to other plant species in the meadow, and about 25%-27% of the nitrogen in these plants comes from soil ammonium. （4） The contribution of leguminous fixed N to total N is 7.48%-9.26% in Kobresia humilis alpine meadow. （5） These data show many plant species of alpine meadow may effectively utilize dissolved organic nitrogen such as amino acids, and these plants have diverse ways to uptake soil nitrogen in alpine meadows. Based on the results we can partly explain why there are abundant biodiversities and how plants at alpine habitat utilize the limited soil N sources.
基金the German Federal Ministry of Education and Research (BMBF) (No.00330800A)
文摘Because laboratory tests are expensive and time-consuming and may not be available to farmers, soil nitrate quick tests are required for optimal nitrogen management strategies in China to increase nitrogen use efficiency and to reduce nitrogen losses. A total of 328 soil samples were collected at different soil depths from 225 sites in China, which covered a wide range of climatic and geographic regions, soil types, croplands and soil textures, to evaluate the suitability of a quick reflectometer test method for analysing soil NO3-N in a wide range of soil NO3 concentrations, soil types and cropping systems in China, mainly by comparison of soil NO3-N assessed by a quick-test method （a reflectometer） and a standard laboratory method, i.e., high-performance liquid chromatography （HPLC）. The reflectometer showed excellent agreement with the laboratory HPLC method with regard to soil nitrate contents for all analysed soil samples. The linear regression had slopes of 1 ± 0.08 and intercepts of ± 1.38 mg NO（-,3）-N L^（-1） among different soil types and croplands. Compared with the 1：1 lines, the regression analysis for each soil type showed statistically significant but small differences in slope; the relative difference between the values measured using the two analytical systems varied from -8% to 6%, and there were no differences in intercept except for paddy soil. The reflectometer showed adequate, statistically significant precision in determining soil nitrate contents, and it could therefore be directly used instead of the laboratory methods for soil NO（-,3）-N measurement in China.
