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1.
Withania somnifera is an important medicinal plant that contains withanolides and withaferins, both bioactive compounds. We have tested the effects of macroelements and nitrogen source in W. somnifera cell suspension cultures with the aim of optimizing the production of biomass and withanolide A. The effects of the macroelements NH4NO3, KNO3, CaCl2, MgSO4 and KH2PO4 at concentrations of 0.0, 0.5, 1.0, 1.5 and 2.0× strength and of the nitrogen source [NH4 +/NO3 (mM/mM) ratio of: 0.00/18.80, 7.19/18.80, 14.38/18.80, 21.57/18.80, 28.75/18.80, 14.38/0.00, 14.38/9.40, 14.38/18.80, 14.38/28.20, and 14.38/37.60 (mM)] in Murashige and Skoog medium were tested for biomass and withanolide A production. The highest accumulation of biomass [147.81 g l−1 fresh weight (FW) and 14.02 g l−1 (dry weight (DW)] was recorded in the medium containing a 0.5× concentration of NH4NO3, and the highest production of withanolide A content was recorded in the medium with 2.0× KNO3 (4.36 mg g−1 DW). The NH4 +/NO3 ratio also influenced cell growth and withanolide A production, with both parameters being larger when the NO3 concentration was higher than that of NH4 +. Maximum biomass growth (110.45 g l−1 FW and 9.29 g l−1 DW) was achieved at an NH4 +/NO3 ratio of 7.19/18.80, while withanolide A production was greatest (3.96 mg g−1 DW) when the NH4 +/NO3 ratio was 14.38/37.60 mM.  相似文献   

2.
Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan, USA. Biofilms were enriched with nitrate (NO3 ), phosphate (PO4 3−), ammonium (NH4 +), NO3  + PO4 3−, NH4 + + PO4 3−, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations. We found no difference between biofilm response to NH4 + versus NO3 enrichment, although the response to both N-species was positively related to water column PO4 3− concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient limitation, but the dominant members of the bacterial community on cellulose were different on NO3 , PO43, and NO3  + PO4 3− treatments relative to control, NH4 +, and NH4 + + PO4 3− treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function may be linked following nutrient enrichment in streams.  相似文献   

3.
An hydroponic experiment with a simulated water stress induced by PEG (6000) was conducted in a greenhouse to study the effects of nitrate (NO3 ), ammonium (NH4 +) and the mixture of NO3 and NH4 +, on water stress tolerance of rice seedlings. Rice (Shanyou 63) was grown under non- or simulated water stress condition (10% (w/v) PEG, MW6000) with the 3 different N forms during 4 weeks. Under non-stressed condition no difference was observed among the N treatments. Under simulated water stress, seedlings grown on N-NO3 were stunted. Addition of PEG did not affect rice seedling growth in the treatment of only NH4 + supply but slightly inhibited the rice seedling growth in the treatment of mixed supply of NO3 and NH4 +. Simulated water stress, when only N-NH4 + was present, did not affect leaf area and photosynthesis rate, however, both parameters decreased significantly in the NO3 containing solutions. Under water stress, Rubisco content in newly expanded leaves significantly increased in the sole NH4 + supplied plants as compared to that in plants of the other two N treatments. Under water stress, the ratio of carboxylation efficiency to Rubisco content was, respectively, decreased by 13 and 23% in NH4 + and NO3 treatments, respectively. It is concluded that, water stress influenced the Rubisco activity than stomatal limitation, and this effects could be regulated by N forms. Responsible Editor: Herbert Johannes Kronzucker. Shiwei Guo and Gui Chen contributed equally to this paper.  相似文献   

4.
Nutrient enrichment threatens river ecosystem health in urban watersheds, but the influence of urbanization on spatial variation in nutrient concentrations and nutrient limitation of biofilm activity are infrequently measured simultaneously. In summer 2009, we used synoptic sampling to measure spatial patterns of nitrate (NO3 ), ammonium (NH4 +), and soluble reactive phosphorus (SRP) concentration, flux, and instantaneous yield throughout the Bronx River watershed within New York City and adjacent suburbs. We also quantified biofilm response to addition of NO3 , phosphate (PO4 3−), and NO3  + PO4 3− on organic and inorganic surfaces in the river mainstem and tributaries. Longitudinal variation in NO3 was low and related to impervious surface cover across sub-watersheds, but spatial variation in NH4 + and SRP was higher and unrelated to sub-watershed land-use. Biofilm respiration on organic surfaces was frequently limited by PO4 3− or NO3  + PO4 3−, while primary production on organic and inorganic surfaces was nutrient-limited at just one site. Infrequent NO3 limitation and low spatial variability of NO3 throughout the watershed suggested saturation of biological N demand. For P, both higher biological demand and point-sources contributed to greater spatial variability. Finally, a comparison of our data to synoptic studies of forested, temperate watersheds showed lower spatial variation of N and P in urban watersheds. Reduced spatial variation in nutrients as a result of biological saturation may represent an overlooked effect of urbanization on watershed ecology, and may influence urban stream biota and downstream environments.  相似文献   

5.
The aim of this research was to test whether NH4 + and NO3 affect the growth, P demand, cell composition and N2 fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l−1 PO4-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l−1 NH4-N, 4,000 μg l−1 NO3-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH4 + and NO3 supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N2-grown culture was significantly lower. The maximum specific growth rate of N2-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the P and energy requirement for heterocyte formation, nitrogenase synthesis and N2 fixation. N2 fixation was partially inhibited by NO3 and completely inhibited by NH4 +. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH4 + or NO3 is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies. Handling editor: Luigi Naselli-Flores  相似文献   

6.
Fermentation of biomass derived synthesis gas to ethanol is a sustainable approach that can provide more usable energy and environmental benefits than food-based biofuels. The effects of various medium components on ethanol production by Clostridium ragsdalei utilizing syngas components (CO:CO2) were investigated, and corn steep liquor (CSL) was used as an inexpensive nutrient source for ethanol production by C. ragsdalei. Elimination of Mg2+, NH4 + and PO4 3− decreased ethanol production from 38 to 3.7, 23 and 5.93 mM, respectively. Eliminating Na+, Ca2+, and K+ or increasing Ca2+, Mg2+, K+, NH4 + and PO4 3− concentrations had no effect on ethanol production. However, increased Na+ concentration (171 mM) inhibited growth and ethanol production. Yeast extract (0.5 g l−1) and trace metals were necessary for growth of C. ragsdalei. CSL alone did not support growth and ethanol production. Nutrients limiting in CSL were trace metals, NH4 + and reducing agent (Cys: cysteine sulfide). Supplementation of trace metals, NH4 + and CyS to CSL (20 g l−1, wet weight basis) yielded better growth and similar ethanol production as compared to control medium. Using 10 g l−1, the nutritional limitation led to reduced ethanol production. Higher concentrations of CSL (50 and 100 g l−1) were inhibitory for cell growth and ethanol production. The CSL could replace yeast extract, vitamins and minerals (excluding NH4 +). The optimized CSL medium produced 120 and 50 mM of ethanol and acetate, respectively. The CSL could provide as an inexpensive source of most of the nutrients required for the syngas fermentation, and thus could improve the economics of ethanol production from biomass derived synthesis gas by C. ragsdalei.  相似文献   

7.
Zu-Hua Yin  John A. Raven 《Planta》1998,205(4):574-580
The impacts of various nitrogen sources, i.e. NO 3, NH4 + or NH4NO3 in combination with gaseous NH3, on nitrogen-, carbon- and water-use efficiency and 13C discrimination (δ13C) by plants of the C3 species Triticum aestivum L. (wheat) and the C4 species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m−3 of N supplied as NO 3, NH4 + or NH4NO3 for 21 and 18 d, respectively, and thereafter exposed to gaseous NH3 at 320 μg · m−3 or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH4NO3-N > NO 3-N > NH4 +-N and NO 3-N > NH4NO3-N > NH4 +-N, respectively. Fumigation with NH3 decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH4 +-N > NO 3-N≈NH4NO3-N in non-fumigated T. aestivum, while fumigation with NH3 increased the WUE of NO 3-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ13C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH4 +-grown plants of T. aestivum and Z. mays than in those supplied with NH4NO3 or NO 3. Regardless of the N-form supplied to the roots of the plant species, exposure to NH3 caused more-positive δ13C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ13C values in plants of T. aestivum and Z. mays. These differences in δ13C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source. Received: 12 September 1997 / Accepted: 13 January 1998  相似文献   

8.
The present work deals with optimization of adventitious shoot culture of Bacopa monnieri for the production of biomass and bacoside A and has investigated the effects of macro elements (NH4NO3, KNO3, CaCl2, MgSO4 and KH2PO4) and nitrogen source [NH4 +/NO3 ] of Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium (MS) on accumulation of biomass and bacoside A content. Optimum number of adventitious shoots (99.33 shoots explant−1), fresh weight (1.841 g) and dry weight (0.150 g) were obtained in the medium with 2.0× strength of NH4NO3. The highest production of bacoside A content was also recorded in the medium of 2.0× NH4NO3, which produced 17.935 mg g−1 DW. The number of adventitious shoot biomass and bacoside A content were optimum when the NO3 concentration was higher than that of NH4 +. Maximum number of shoots (70.00 shoots explant−1), biomass (fresh weight 1.137 g and dry weight 0.080 g) and also bacoside A content (27.106 mg g−1 DW) were obtained at NH4 +/NO3 ratio of 14.38/37.60 mM. Overall, MS medium supplemented with 2.0× NH4NO3 is recommended for most efficient bacoside A production.  相似文献   

9.
Supplying both N forms (NH4 ++NO3 ) to the maize (Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore, field and gravel hydroponic studies were conducted to examine the effect of N form (NH4 ++NO3 versus predominantly NO3 ) and exogenous cytokinin treatment (six foliar applications of 22 μM 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants, NH4 ++NO3 nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO3 . Cytokinin application to NO3 -grown field plants increased grain yield to that of NH4 ++NO3 -grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise, hydroponically grown maize supplied with NH4 ++NO3 doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH4 ++NO3 nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH4 ++NO3 plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO3 -grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH4 ++NO3 may be partly associated with an increased endogenous cytokinin supply.  相似文献   

10.
A thermotolerant bacterium, identified as Bacillus licheniformis, completely utilized 0.1% (w/v) NH4NO3 at 30 and 50°C under aerobic condition. The addition of 0.5 mM Fe2+ to the NH4NO3 medium markedly promoted the utilization of NH4+ and NO3. At 50°C, of total nitrogen originally provided, 24% was taken up into the cells and 20% remained in the culture supernatant. Residual nitrogen (56%) was probably removed into the atmosphere. The cell extracts contained enzymes involved in denitrification. GC-MS demonstrated that NH4 15NO3 had been converted to 15N2O. These results indicate that the strain has denitrification ability under aerobic condition.  相似文献   

11.
A mathematical computer-aided model CELLOP was constructed in which the desirability functions in a three-dimensional experimental design can be used to find the optimal growing conditions for plant cells. CELLOP is intended for the optimisation of 3 to 6 physical, chemical, or biological variables in the cultivation conditions of plant cell cultures. The model was used to optimise the culturing conditions (calcium, inorganic nitrogen, and sucrose concentrations) for coumarin-producing, spontaneously embryogenic cell lines of angelica Angelica archangelica L. subsp. archangelica and hogs fennel Peucedanum palustre (L.) Moench. For A. archangelica the overall optimum concentrations were 0.47 mM Ca2+, 5.06 mM NO3 , 0.40 mM NH4 +, and 96.25 mM sucrose. The dry mass was 24.7 % higher and the coumarin content 40.5 % higher than those achieved in the standard 75 % Gamborg B5 medium. For A. archangelica the highest embryogenic activity was reached in the media containing 1.25 mM Ca2+. In the case of P. palustre the overall optimum concentrations were 1.60 mM Ca2+, 2.84 mM NO3 , 0.23 mM NH4 +, and 85.10 mM sucrose. For P. palustre the dry mass production increased by 61.8 % and the coumarin content by 58.1 % compared to the values achieved in the Gamborg B5 medium. For P. palustre the highest embryogenic activity was reached in the presence of 50.0 mM NO3 and 4.01 mM NH4 +.  相似文献   

12.
Summary To improve proliferation of soybean cultures in liquid medium, the effects of sucrose; total inorganic nitrogen; content of No3 , NH4 +, Ca2+, PO4 3−, K+; NH4 +/NO3 ratio; and medium osmotic pressure were studied using cv. Jack. Sucrose concentration, osmotic pressure, total nitrogen content, and ammonium to nitrate ratio were found to be the major factors controlling proliferation of soybean embryogenic cultures. Growth decreased linearly as sucrose concentration increased from 29.7 mM to 175.3 mM. A sucrose concentration of 29.2 mM, a nitrogen content of 34.9 mM, at 1 to 4 ammonium to nitrate ratio were found to be optimal for the fastest proliferation of soybean embryogenic cultures. There was no significant effect on proliferation of cultures when concentrations of NH4 +, Ca2+, PO4 3−, and K+ were tested in the range of 3.50 to 10.50, 1.02 to 3.06, 0.68 to 2.04, and 22.30 to 36.70 mM, respectively. The relative proliferation of embryogenic cultures of four soybean genotypes was evaluated in Finer and Nagasawa medium and in the new medium formulation. Despite genotype-specific differences in growth, the genotypes tested showed a biomass increase in the new formulation equal to 278, 269, 170, and 251% for Chapman, F138, Jack, and Williams 82, respectively, relative to their growth on standard FN medium. Due to its lowered sucrose and nitrogen content, we are referring to the new medium as FN Lite.  相似文献   

13.
The objective of this study was to improve the growth of in vitro shoot cultures of Brugmansia × candida ‘Creamsickle’. Several mineral nutrient experiments were conducted to determine the effect of NH4+, NO3, K+, FeSO4/EDTA, ZnSO4, MnSO4, and CuSO4 on quality, leaf width and length, size and weight of shoot mass, and shoot number. The experiment to determine the levels of NH4+, NO3, and K+, was conducted as a 2-component NH4+: K+ mixture crossed by [NO3] and resulted in an experimental design free of ion confounding and capable of separating the effects of proportion and concentration. The results of the NH4+-K+-NO3 experiment revealed a region in the design space where growth was significantly improved; the region generally had lower total nitrogen and lower NH4+:K+ ratios than MS medium. The experiments to determine the appropriate levels of Fe, Zn, Mn, and Cu were conducted at six log levels ranging from 0 to 1 mM. Of the four metal salts tested, MnSO4 had the least effect on in vitro shoot growth and its concentration was reduced from 0.1 mM (MS level) to 0.001 mM. CuSO4 had large effects on in vitro shoot growth and was increased from 0.0001 mM to 0.001 mM. A 2-level factorial of NH4+-K+-NO3, FeSO4/EDTA, and ZnSO4 was conducted and several formulations identified for their improvements of quality and growth. In addition to the changes to MnSO4 and CuSO4, these formulations were characterized by lower levels of NH4+, K+, NO3 and Zn, and higher levels of FeSO4/EDTA. Overall, several nutrient formulations were identified as superior to MS medium for growth of in vitro shoot cultures of B. ‘Creamsickle’.  相似文献   

14.
Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms is limited. We fertilized 1-year-old, half-sib black walnut (Juglans nigra L.) seedlings with ammonium (NH4 +) [as (NH4)2SO4], nitrate (NO3 ) (as NaNO3), or a mixed N source (NH4NO3) at 0, 800, or 1,600 mg N plant−1 season−1. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed. Specific leaf NRA was higher in NO3 -fed and NH4NO3-fed plants compared to observed responses in NH4 +-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO3 -fed than in NH4 +-fed plants. Exogenous NO3 was assimilated in roots or stored, so no difference was observed in NO3 levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over NO3 or NH4 + alone, suggesting NH4NO3 is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms.  相似文献   

15.
Carbon-14 pulse labeling technique was used to study the effect of rooting medium salinity and form and availability of N on growth and rhizodeposition of wheat (Triticum aestivum L.). Thirty days old plants grown in continuously aerated Arnon and Hoagland nutrient solution were subjected to 14C pulse labeling for 24 h and transferred to aqueous rooting medium containing 0, 150, and 300 mM NaCl in all combinations with different forms (calcium nitrate, ammonium sulphate, and ammonium nitrate) and amounts (0.5, 1.0, 1.5, and 2.0 times the standard N concentration (150 ppm) of Arnon and Hoagland plant growth medium). Plant samples immediately after pulse labeling, following 7 days of growth under different rooting medium conditions, and the freeze-dried rooting medium were analyzed for total C and 14C. Length and fresh/dry weight of root and shoot portions and calculated values of unaccounted 14C were determined. Presence of NaCl in the rooting medium led to a decrease in root and shoot portions. However, NO3 -fed plants showed better growth than NH4 +-fed plants at all the three salinity levels. Salinity in rooting medium led to higher rhizodeposition and lower loss of 14C. Relatively higher proportion of 14C was released as rhizodeposits and retained in root/shoot portions of plants fed with NH4 + or NH4 ++NO3 , than those with NO3 , while less was respired. The specific activity of the rhizodeposits (kBq 14C g−1 C) was also higher under saline conditions. The rhizodeposits in NH4 +-fed plants were more highly labeled as compared to NO3 -plants.  相似文献   

16.
The kinetics of NH4 + and NO3 uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the Vmax of NH4 + uptake was higher than that of NO3 uptake. The Km of NH4 + uptake and Km of NO3 uptake differed not significantly. When both NH4 + and NO3 were present, the Vmax for NH4 + uptake became slightly higher, and the Km for NH4 + uptake remained in the same order. Under these conditions the NO3 uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4 + occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}  相似文献   

17.
The biodegradation potential of an innovative enclosed tubular biofilm photobioreactor inoculated with a Chlorella sorokiniana strain and an acclimated activated sludge consortium was evaluated under continuous illumination and increasing pretreated (centrifuged) swine slurry loading rates. This photobioreactor configuration provided simultaneous and efficient carbon, nitrogen, and phosphorous treatment in a single-stage process at sustained nitrogen and phosphorous removals efficiencies ranging from 94% to 100% and 70–90%, respectively. Maximum total organic carbon (TOC), NH4 +, and PO4 3− removal rates of 80 ± 5 g C mr −3 day−1, 89 ± 5 g N mr −3 day−1, and 13 ± 3 g P mr −3 day−1, respectively, were recorded at the highest swine slurry loadings (TOC of 1,247 ± 62 mg L−1, N–NH4 + of 656 ± 37 mg L−1, P–PO4 3+ of 117 ± 19 mg L−1, and 7 days of hydraulic retention time). The unusual substrates diffusional pathways established within the phototrophic biofilm (photosynthetic O2 and TOC/NH4 + diffusing from opposite sides of the biofilm) allowed both the occurrence of a simultaneous denitrification/nitrification process at the highest swine slurry loading rate and the protection of microalgae from any potential inhibitory effect mediated by the combination of high pH and high NH3 concentrations. In addition, this biofilm-based photobioreactor supported efficient biomass retention (>92% of the biomass generated during the pretreated swine slurry biodegradation).  相似文献   

18.
Using vegetative propagules (ramuli) of the iota carrageenan producing red seaweed Solieria chordalis, a maximum growth rate of 6.8% d−1 was achieved when cultured at 20 °C and 100 μmol photon m−2 s−1 in seawater supplemented with 20 μM NO3-N or 10 μM NO3-N plus 10 μM NH4-N. Ramuli grew less well when nitrogen was supplied solely as NH 4 + . Maximum carrageenan content was observed at the same temperature, irradiance and salinity as growth, but at lower nitrogen concentrations. These findings are discussed in relation to results obtained from studies on other iota-carrageenan producing carrageenophytes.  相似文献   

19.
20.
Spatial variability of soil total nitrogen (N), available N (KCl extractable NH4+ and NO3), and spatial patterns of N mineralization and nitrification at a stand scale were characterized with geostatistical and univariate analysis. Two extensive soil spatial samplings were conducted in an evergreen broadleaf forest in Sichuan province, southwestern China in June and August 2000. In a study area of 90 × 105 m2, three soil samples were collected from each 5 × 5 m2 plot (n = 378) in June and August, and were analyzed for total N and available N contents. Net N mineralization and nitrification were measured by in situ core incubation and the rates were estimated based on the difference of NH4+ and NO3 contents between the two sampling dates. Total N, NH4+, and NO3 were all spatially structured with different semivariogram ranges (from high to low: NH4+, NO3, and total N). The semivariograms of mineralization and nitrification were not as spatially structured as available N. NH4+ was the dominant soil inorganic N form in the system. Both NH4+ and NO3 affected spatial patterns of soil available N, but their relative importance switched in August, probably due to high nitrification as indicated by greatly increased soil NO3 content. High spatial auto-correlations (>0.7) were found between available N and NH4+, available N and NO3 on both sampling dates, as well as total N measurements between both sampling dates. Although significant, the spatial auto-correlation between NH4+ and NO3 were generally low. Topography had significant but low correlations with mineralization (r = −0.16) and nitrification (r = −0.14), while soil moisture did not. The large nugget values of the calculated semivariograms and high-semivariance values, particularly for mineralization and nitrification, indicate that some fine scale (<5 m) variability may lie below the threshold for detection in this study.  相似文献   

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