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1.
Chemical composition of fog and rain water was studied during a 47-day experimental period. The differences between the fog and rain water were found to be significantly for most analyzed ions. H+, NH4 +, NO3 ?, and SO4 2? made up 85% of the total median ion concentration in fog and 84% in rain water. The total mean equivalent concentration was 15 times higher in the fog than in the rain water. The fog water samples were classified according to their air mass history. The analysis of the 120 h backward trajectory led to the identification of three advection regimes. Significant differences of ion concentrations between the respective classes were found. Air masses of class I travelled exclusively over the Pacific Ocean, class II were carried over the Philippines, and class III were advected from mainland China. The turbulent fog water deposition was determined by the means of the eddy covariance method. The total (turbulent plus gravitational) fog water fluxes ranged between +31.7 mg m?2 s?1 and ?56.6 mg m?2 s?1. Fog water droplets with mean diameters between 15 μm and 25 μm contributed most to the liquid water flux. The sample based nutrient input was calculated on the basis of the occult and wet deposition, and the concentrations of the simultaneously collected fog and rainwater samples, respectively. The nutrient input through wet deposition was about 13 times higher than through occult deposition.  相似文献   

2.
Measurements of the chemical composition of fog water at Murododaira (altitude, 2,450 m), on the western slope of Mt. Tateyama near the coast of the Japan Sea, were performed each autumn from 2004 through 2007. Strong acidic fogs (pH?<?4) containing high concentrations of nssSO 4 2? were frequently observed in the autumn of 2005, when the air mass at Mt. Tateyama originated mainly from the polluted regions of Asia. The ratio of NO 3 ? /nssSO 4 2? in fog water was relatively high in 2004 and 2007. High concentrations of nssCa2+ derived from dust particles were detected in 2006. Background Kosa particles might have been predominant in the free troposphere and could have neutralized acidic fogs in the autumn of 2006. High concentrations of sea-salt components were also observed in October 2005. The sea-salt particles might have been transported from the Pacific Ocean by a strong typhoon, and significant Mg2+ loss was observed. Peroxides higher than 100 μM, which are seriously harmful to vegetation were sometimes detected.  相似文献   

3.
Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N2O, and N2 emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO 3 ? -rich (340 mg N?kg?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C2H2, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg?1 (equivalent to 2.5 t?C ha?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N2 production (398–524 μg N?kg?1) was significantly higher than N2O (84.6–190 μg N?kg?1) and NO (196–224 μg N?kg?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO 3 ? in vegetable soil but enhanced N2O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N2O production reached 13,645–45,224 μg N?kg?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.  相似文献   

4.
Fogwater, fog drip and rainwater chemistry were examined at a tropical seasonal rain forest in Xishuangbanna, southwest China between November 2001 and October 2002. During the period of observation, 204 days with the occurrence of radiation fog were observed and the total duration of fog was 1949 h, of which 1618 h occurred in the dry season (November to April), accounting for 37.0% of the time during the season. The mean pH of fogwater, fog drip and rainwater were 6.78, 7.30, and 6.13, respectively. The ion with the highest concentration for fog- and rainwater was HCO3 ?, which amounted to 85.2 and 37.3 μeq l?1, followed by Ca2+, Mg2+ and NH4 +. Concentrations of NO3 ?, HCO3 ?, NH4 +, Ca2+, and K+ in fogwater samples collected in the dry season were significantly greater when compared to those collected in the rainy season. It was found that the ionic concentrations in fog drip were higher than those in fogwater, except for NH4 + and H+, which was attributed to the washout of the soil- and ash-oriented ions deposited on the leaves and the alkaline ionic emissions by the leaves, since biomass burns are very common in the region and nearby road was widening.  相似文献   

5.
Dry and wet deposition of atmospheric nitrogen species (NO2 and HNO3) coming from nitrogen oxides emissions in Buenos Aires city to surface waters of de la Plata River were estimated. Atmospheric dispersion models DAUMOD-RD (v.2) and CALPUFF were applied to area and point sources, respectively. These models were run considering 1 year of hourly meteorological data. Emission information included a typical diurnal variation of area source emissions. Annual atmospheric nitrogen (N–NO2?+?N–HNO3) deposition to 1,763 km2 of the river was 35,600 kg-N year?1. Dry deposition processes accounted for 89% of this value. The small contribution of wet deposition was a consequence of the very few cases (5%) of rain events during offshore wind conditions. Monthly dry deposition to 1,763 km2 of the river varied from 1,628 kg-N month?1 in February to 3,799 kg-N month?1 in December, following the monthly occurrence of offshore winds. Monthly wet deposition varied from 1 kg-N month?1 in June to 1,162 kg-N month?1 in February. These results came from the combination of favorable conditions for formation of HNO3 and the occurrence of precipitation during offshore wind situations. Spatial distribution of annual atmospheric N deposition showed a strong coastal gradient. Deposition values reached a maximum of 137.1 kg-N km?2 year?1 near the shoreline, which was reduced to the half at 4 km from the coast.  相似文献   

6.
A composting experiment was carried out to study changes in physical [color, odor, temperature, organic matter (OM) loss], chemical [C:N ratio, water-soluble organic carbon (Cw):organic N (Norg) ratio, NH4 +-N and NO3 ?-N, humic acid (HA):fulvic acid (FA) ratio, humification index (HI) and cation-exchange capacity (CEC):total organic carbon (TOC) ratio)] and biological [seed germination index (GI)] parameters to assess compost maturity and stability over a period of 150 days. Five composts were prepared using a mixture of different farm wastes with or without enrichment of N, rock phosphate (RP) and microorganism (MO) inoculation. All the composts appeared to change to a granular and dark grey color without foul odor, and attained a constant temperature with no measurable changes (ambient level) at 120 days of composting. Correlation analysis showed that the optimal values of the selected parameters for our experimental conditions are as follows: organic matter loss > 42%, C:N ratio < 15, HA:FA ratio > 1.9, HI > 30%, CEC:TOC ratio > 1.7 and Cw:Norg ratio < 0.55. Composts enriched with N + RP or N + RP + MO matured at 150 and 120 days, respectively, whereas composts without any enrichment or enrichment with N or RP + MO did not mature even at 150 days of composting.  相似文献   

7.
Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO3-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L?1 K2SO4 extractable N (extractable N), NO3-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha?1 containing 158 kg N ha?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO3-N leaching were monitored in soil treated with SDC (20 Mg ha?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha?1 containing 0, 15, 29, 44 and 59 kg N ha?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH4)2SO4 at rates of 220 kg N ha?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO3-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO3-N leaching in the CF treatment was 146 kg N ha?1, which was equal to half of the applied N, but only 53 kg N ha?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO3-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO3-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO3-N leaching without impacting negatively on N uptake by plants.  相似文献   

8.
Abstract

Nitrite (NO2 ?‐N) toxicity symptoms have been observed on lettuce (Lactuca sativa) at various locations in California. The objective was to evaluate the symptoms of ammonium (NH4 +‐N) and nitrite (NO2 ?‐N) toxicity on Sundevil iceberg lettuce and Paragon romaine lettuce and to determine lettuce growth and biomass production under different levels of NO2 ?‐N. Hydroponic studies under greenhouse conditions were conducted using nutrient solutions containing nitrate (NO3 ?‐N) and two other forms of nitrogen (NO2 ?‐N and NH4 +‐N) applied at a constant concentration (50 mg NL?1) or using different NO2 ?‐N levels (0, 5, 10, 20, 30, and 40 mg N L?1) and a constant NO3 ?‐N level (30 mg N L?1). Crown discoloration (brownish color) was observed for lettuce grown in both NO2 ?‐N and NH4 +‐N solutions approximately 3 weeks after transplanting into the hydroponic systems. Lettuce grown in NO3 ?‐N solution produced larger biomass and greater number of leaves per plant than lettuce grown in NO2 ?‐N or NH4 +‐N solutions. Increasing the concentration of NO2 ?‐N suppressed plant height, fresh and dry biomass yield, and number of leaves and increased the root vascular discoloration. Lettuce growth was reduced more than 50% at NO2 ?‐N concentrations greater than 30 mg N L?1. Even at 5 mg NO2 ?‐N L?1, growth was reduced 14 and 24% for romaine and iceberg lettuce, respectively, relative to that obtained in nitrate solution. Although concentrations between 5 and 40 mg NO2 ?‐N L ?1 reduced dry biomass similarly for both lettuce types, toxicity symptoms were more severe in iceberg lettuce than in romaine.  相似文献   

9.
Atmospheric gases and particulates were collected using four-stage filter-pack in Chunchon from January through December in 1999. Particulate SO4 2? and NO3 ?, and gaseous HNO3, SO2 and NH3 were analyzed. Annual average concentration of SO4 2?(S), NO3 ?(S), HNO3 (g), SO2(g) and NH3(g) were 5.75µg/m3, 4.98µg/m3, 0.33ppb, 1.52ppb and 7.25ppb, respectively. Annual dry deposition fluxes were estimated using the measured concentration and dry deposition velocity published by other research group. Annual dry deposition of S was 287kg · (km)?2·y?1, which accounted for about 30% of total S deposition. For N deposition, dry deposition is predominant; about 70% of total N deposition was through dry process mostly as forms of NH3 and HNO3.  相似文献   

10.
One aluminum (Al)-sensitive (B-73) and two Al-tolerant (F-2 and L-2039) maize genotypes were subjected to Al stress (100 μM Al) under two nitrogen (N) treatments [13.2 mM nitrate (NO3?) and 8.3 mM NO3? + 4.9 mM ammonium (NH4+)]. Growth parameters, chlorophyll, root N and NO3? contents, root nicotinamide adenine dinucleotide (NADH-) and nicotinamide adenine dinucleotide phosphate (NADPH)-nitrate reductase, glutamine synthetase, and glutamate dehydrogenase activities were determined. Aluminum significantly decreased growth and chlorophyll content in Al-sensitive genotype. Nitrate accumulation in roots was increased by Al in tolerant plants. In the sensitive genotype, Al suppressed all enzymes in NO3? plants, while in NO3?/NH4+ plants the suppression was less severe, and NADPH-nitrate reductase was even stimulated. In tolerant NO3?plants, glutamate dehydrogenase was stimulated in F-2 and glutamine synthetase suppressed in L-2039 genotype. In tolerant NO3?/NH4+- plants, all enzymes were stimulated by Al, which may be attributed to their participation in defense mechanisms.  相似文献   

11.

Purpose

Mounting evidence has indicated that there was dramatic increase in atmospheric nitrogen (N) deposition. The objectives of this study were to characterize how soil carbon dioxide (CO2) flux responds to different forms and levels of N addition in 5 years. We hope to provide further understanding and detailed information of the impact of N addition on CO2 flux in temperate forests in North China.

Materials and methods

A 5-year field experiment was conducted at the Xi Mountain Research Station of Beijing Forestry University, northern China, from 2011 to 2016. Multiple levels and forms of N addition experiment included control with no N added, NH4NO3, NaNO3, and (NH4)2SO4 at two levels (low N (L) 50 kg N ha?1 year?1 and high N (H) 150 kg N ha?1 year?1). Additional N was administered equally once per month during the growing season (March to October), and CO2 flux was measured three times every month. Soil temperature, water-filled pore space, and NO3 ?-N and NH4 +-N concentrations were measured monthly to determine the relationships between CO2 flux and soil physicochemical variables.

Results and discussion

Cumulative CO2 flux increased by more than 50% under all high-level N addition and by 27% under L-NH4NO3 addition, while other N additions had no significant effect. H-NaNO3 and H-NH4NO3 exerted stronger effects on cumulative CO2 flux in initial years, especially the second year when maximum increases were 99 and 129%, respectively. Increasing inorganic N concentration could change soil from N-limited to N-rich, and then N-saturated, and so the promotion increased and then decreased. The effect of high-level N addition was stronger than that of low-level, and exhibited a general order: NH4NO3 > (NH4)2SO4. Considering the amount and decrease in NH4 +-N/NO3 ?-N in local actual N deposition, there might be an increase in soil CO2 flux in our study area in the future.

Conclusions

The performance of N addition on cumulative CO2 flux depended on N forms and levels. If the experimental period had been less than 3 years, the effect of N addition on temperate forest soil would be overestimated. Our findings highlighted the importance of experimental time and multiple forms and levels of N addition with regard to the response of soil CO2 flux to N deposition.
  相似文献   

12.
A 12-week incubation experiment was conducted to determine the pattern and rate of N mineralized from organic materials. Treatments consisted of sheep manure (SM), cattle manure (CM), poultry manure (PM), sewage sludge (SS) at 1% (W/W) level, and unfertilized treatment with three replications. The concentrations of nitrate (NO3)- nitrogen (N) and ammonium (NH4)-N were determined in day 1 and 1, 2, 4, 8, and 12 weeks after the beginning of incubation. Results indicated that the magnitude of N mineralized during the incubation time periods was in the order of CM (134 mg kg?1) > PM (83 mg kg?1) > SS (56 mg kg?1) > SM (55 mg kg?1), and different management is required for obtaining optimum N-use efficiency. In conclusion, improving N-uptake efficiency in manure- and SS-amended soils depends on the pattern and rate of N mineralization to synchronize N released with crop N demand periods.  相似文献   

13.
Brassica alboglabra plants were first grown aeroponically with full nutrients under full sunlight with average midday photosynthetic photon flux density (PPFD) of 1200 μmol m?2 s?1. Thirty days after transplanting, plants were respectively, subjected to 10 days of average midday PPFD of 1200 (control, L1), 600 (L2) and 300 μmol m?2 s?1 (L3). Productivity, photosynthetic CO2 assimilation and stomatal conductance were significantly lower in low-light (L2 and L3) plants than in high-light (L1) plants. Low light plants had the highest nitrate (NO3?) accumulation in the petioles. Low light also had an inverse effect total reduced N content. After different light treatments, all plants were re-exposed to another 10 days of full sunlight. Low-light plants demonstrated their ability to recover their photosynthetic rate, enhance productivity and reduce the NO3? concentration. These results have led to the recommendation of not harvesting this popular vegetable during or immediately after cloudy weather conditions.  相似文献   

14.

Purpose

Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg?ha–1?year–1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water.

Materials and methods

The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N2 fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N2/Ar technique. A suite of parameters known to influence denitrification were also measured.

Results and discussion

Net denitrification rates ranged between 28.2?±?18.2 and 674.3?±?314.5 μmol N2–N?m–2?h–1 for the streams, 23.7?±?23.9 and 121.2?±?38.7 μmol N2–N?m–2?h–1 for the ponds, and 41.8?±?17.7 and 239.3?±?49.8 μmol N2–N?m–2?h–1 for the reservoir. The mean net denitrification rate of the stream sites (173.2?±?248.4 μmol N2–N?m–2?h–1) was significantly higher (p?<?0.001) than that of the pond sites (48.3?±?44.5 μmol N2–N?m–2?h–1), and the three types of waterways all had significantly higher (p?<?0.01) mean net denitrification rates in summer than in other seasons. Linear regression and linear mixed effect model analysis showed that nitrate (NO3 ?–N) concentration in surface water was the primary controlling factor for net sediment denitrification, followed by water temperature. Using monitoring data on NO3 ?–N concentrations and temperature of the surface water of waterways and an established linear mixed effect model, total N removed through net sediment denitrification in the pond–stream–reservoir continuum was estimated at 46.8?±?24.0 t?year–1 from July 2007 to June 2009, which was comparable with earlier estimates based on the mass balance method (34.3?±?12.7 t?year–1), and accounted for 83.4 % of the total aquatic N. However, the total aquatic N was only 4.4 % of the total N input to the watershed, and thus most of the surplus N in the watershed was likely to be either denitrified or stored in soil.

Conclusions

High doses of N in a rice-paddy-dominated watershed did not lead to high stream N concentrations due to limited input of N into waterways and the high efficiency of waterways in removing N through denitrification.  相似文献   

15.
This study determines the seasonal variability of metal partition coefficients [aluminium (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn)] and analyses the importance of suspended sediments (SS), dissolved organic carbon (DOC) concentrations, pH, and discharge (Q) on the seasonal variability of metal partition coefficients (KDs) in the headwaters of the Mero River catchment, which drains an agroforestry area in northwestern Spain. Metal partition coefficients were used as an approach to relate dissolved and particulate fractions. Water samples were collected over 3 years (2005–2008) at the catchment outlet. The mean metal dissolved concentrations were: Fe (43.5 μg L?1) > Al (23.3 μg L?1) > Zn (1.8 μg L?1) > Mn (1.2 μg L?1) > Cu (0.3 μg L?1). Partition coefficients followed the order Mn > Al > Fe > Zn > Cu, and their values exhibited low variability. Al, Cu, and Zn partition coefficients presented the greatest values in summer, except during 2007–2008, when the greatest KDs value was observed in autumn, whereas the KDs of Fe showed the greatest values in winter. The KD of Mn has no seasonality. For Al, Cu, and Zn, the seasonal SS concentrations were closely related to Kd. For Fe, Kd was more closely related to DOC concentration than to SS concentration.  相似文献   

16.
Abstract

The rate and timing of manure application when used as nitrogen (N) fertilizer depend on N‐releasing capacity (mineralization) of manures. A soil incubation study was undertaken to establish relative potential rates of mineralization of three organic manures to estimate the value of manure as N fertilizer. Surface soil samples of 0–15 cm were collected and amended with cattle manure (CM), sheep manure (SM), and poultry manure (PM) at a rate equivalent to 200 mg N kg?1 soil. Soil without any amendment was used as a check (control). Nitrogen‐release potential of organic manures was determined by measuring changes in total mineral N [ammonium‐N+nitrate‐N (NH4 +–N+NO3 ?–N)], NH4 +–N, and accumulation of NO3 ?–N periodically over 120 days. Results indicated that the control soil (without any amendment) released a maximum of 33 mg N kg?1soil at day 90, a fourfold increase (significant) over initial concentration, indicating that soil had substantial potential for mineralization. Soil with CM, SM, and PM released a maximum of 50, 40, and 52 mg N kg?1 soil, respectively. Addition of organic manures (i.e., CM, SM, and PM) increased net N released by 42, 25, and 43% over the control (average). No significant differences were observed among manures. Net mineralization of organic N was observed for all manures, and the net rates varied between 0.01 and 0.74 mg N kg?1 soil day?1. Net N released, as percent of organic N added, was 9, 10, and 8% for CM, SM, and PM. Four phases of mineralization were observed; initial rapid release phase in 10–20 days followed by slow phase in 30–40 days, a maximum mineralization in 55–90 days, and finally a declined phase in 120 days. Accumulation of NO3 ?–N was 13.2, 10.6, and 14.6 mg kg?1 soil relative to 7.4 mg NO3 ?–N kg?1 in the control soil, indicating that manures accumulated NO3 ?–N almost double than the control. The proportion of total mineral N to NO3 ?–N revealed that a total of 44–61% of mineral N is converted into NO3 ?–N, indicating that nitrifiers were unable to completely oxidize the available NH4 +. The net rates of mineralization were highest during the initial 10–20 days, showing that application of manures 1–2 months before sowing generally practiced in the field may cause a substantial loss of mineralized N. The rates of mineralization and nitrification in the present study indicated that release of inorganic N from the organic pool of manures was very low; therefore, manures have a low N fertilizer effect in our conditions.  相似文献   

17.
The different responses of two populations of Suaeda salsa (Linn.) Pall. (saline seepweed) from an intertidal zone and a saline inland zone to salinity [1 or 500 mM sodium chloride (NaCl)] and nitrogen [N; 0.05, 1, or 10 mM nitrate (NO3 ?)‐N] were investigated. Greater NO3 ?‐N supply (10 mM) increased shoot dry weight for the two populations of S. salsa, especially for S. salsa from the saline inland zone. Greater NO3 ?‐N supply (10 mM) increased the concentrations of chlorophyll and carotenoid in leaves and the NO3 ? and potassium (K+) concentrations in shoots for both populations. Greater NO3 ?‐N supply (10 mM) increased shoot Na+ in S. salsa from the intertidal zone. In conclusion, S. salsa from the saline inland zone is more responsive to NO3 ?‐N supply than the intertidal population. Greater NO3 ?‐N supply can help the species, especially the intertidal population, to grow and to mediate ion homeostasis under high salinity.  相似文献   

18.
ABSTRACT

Understanding how plants use of various nitrogen (N) sources is important for improving plant N use efficiency in organic farming systems. This study investigated the effects of farming management practices (organic and conventional) on pakchoi short-term uptake of glycine (Gly), nitrate (NO3 ?) and ammonium (NH4 +) under two N level conditions. Results showed that plant N uptake rates and N contributions from the three N forms in the low N (0.15 μg N g?1 dry soil) treatment did not significantly differ between the organic and conventional soils, except the significantly greater Gly contribution in organic soil at 24 h after tracer addition. Under high N (15 μg N g?1 dry soil) conditions, the N uptake rates, uptake efficiencies, and N contributions of Gly and NH4 +-N were significantly greater in pakchoi cultivated in the organic soil compared to conventional soil, whereas the N uptake rates and N contributions from NO3 –-N decreased in pakchoi cultivated in the organic soil. The greater Gly-N uptake in plants grown in high-N treated organic soil may be related to the greater gross N transformation, Gly turnover rate and the increased expression of an amino acid transporter gene BcLHT1. Intact Gly contributed at most 6% to Gly-derived N at 24 h after tracer additions, which accounting for about 1.24% of the total N uptake in organic soil. Our study suggested that Gly-N and other organic source N might serve as a more important compensatory N source for plants in organic farming.  相似文献   

19.
Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH4 +-N, NO3 ?-N, and NH4NO3-N) and rates (1.5 and 7.5 g N m?2 year?1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.  相似文献   

20.
Our understanding of leaf litter carbon (C) and nitrogen (N) cycling and its effects on N management of deciduous permanent crops is limited. In a 30-day laboratory incubation, we compared soil respiration and changes in mineral N [ammonium (NH4+-N) + nitrate (NO3–-N)], microbial biomass nitrogen (MBN), total organic carbon (TOC) and total non-extractable organic nitrogen (TON) between a control soil at 15N natural abundance (δ15N = 1.08‰) without leaf litter and a treatment with the same soil, but with almond (Prunus dulcis (Mill.) D.A. Webb) leaf litter that was also enriched in 15N (δ15N = 213‰). Furthermore, a two-end member isotope mixing model was used to identify the source of N in mineral N, MBN and TON pools as either soil or leaf litter. Over 30 d, control and treatment TOC pools decreased while the TON pool increased for the treatment and decreased for the control. Greater soil respiration and significantly lower (p < 0.05) mineral N from 3 to 15 d and significantly greater MBN from 10 to 30 d were observed for the treatment compared to the control. After 30 d, soil-sourced mineral N was significantly greater for the treatment compared to the control. Combined mineral N and MBN pools derived from leaf litter followed a positive linear trend (R2 = 0.75) at a rate of 1.39 μg N g?1 soil day?1. These results suggest early-stage decomposition of leaf litter leads to N immobilization followed by greater N mineralization during later stages of decomposition. Direct observations of leaf litter C and N cycling assists with quantifying soil N retention and availability in orchard N budgets.  相似文献   

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