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1.
Abstract

Nitrate (NO3 ?) meters have been used effectively for crop nitrogen (N) management in many crops, including corn and cabbage. The use of a Cardy NO3 ? meter to assess the N status of the carrot crop could improve the utilization of applied N, but critical NO3‐N concentrations are required. Two carrot cultivars were grown on mineral and organic soils over 3 years at five N application rates to establish critical sap and soil NO3‐N concentrations and to identify the effects of soil type and cultivar. Although a yield response to N application occurred on mineral soil in 2 of 3 years, consistent critical sap NO3‐N concentrations could not be established because of variability among years, cultivars, and soil types. Critical soil nitrate concentrations were highly variable, but values of 31 to 36 mg · L?1 NO3‐N could be established for the early sampling date to 30 cm deep. Sap NO3‐N concentrations cannot be used alone for N analysis of carrots, but early‐season soil NO3‐N assessment could be useful in adjusting N‐fertilization practices.  相似文献   

2.
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   

3.
ABSTRACT

A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO3 ?) accumulation, and macronutrient concentrations of pakchoi (Brassica chinensis L.) in hydroponics. Plants were supplied with NO3 ? and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO3 ?-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO3 ?-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO3 ?-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO3 ?-N/AA-N ratios reduced NO3 ? concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO3 ?-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO3 ? concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields.  相似文献   

4.
The soil nitrogen cycle was investigated for several watershed forests of which stream waters have distinctively different nitrate (NO3 ?) concentrations. In a watershed with stream water NO3 ? of more than 100 µM, soil NO3 ? content increased even beneath the rooting zone, revealing "nitrogen saturation" status. A laboratory soil experiment demonstrated that the proportion of net NO3 ? production to CO2 production was largely regulated by a soil C/N ratio, suggesting a key parameter for NO3 ? abundance. In the respective watershed soils, little nitrogen was actually present as NO3 ? above a soil C/N ratio of 20. The annual mean soil temperature recorded at the sites was correlated with a shift in the C/N ratio in watershed soils (a soil C/N ratio increase of 0.5 per 1°C decrease) along the stream NO3 ? gradient of 30 fold. The results suggest that soil microbial metabolisms affected by C/N ratio may be a direct agent regulating NO3 ? leaching from watersheds under the influence of an atmospheric nitrogen load and climate.  相似文献   

5.
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   

6.
Dentrification rates in two soils were assessed separately as a function of NO3? concentration while providing a constant initial glucose concentration, and as a function of glucose concentration while providing a constant initial NO3?-N concentration. Of the soils used, a Hanford sandy loam and a Coachella fine sand, the bacteria in the former produced higher rates of denitrification with a maximum loss of 1500 μg NO3?-N/ml day?1 as compared to a loss of 150 μg NO3?-N/ml day?1 from the latter. Rates of loss closely approximated Michaelis Menten kinetics in the Coachella sand, and Km values for glucose-C and NO3?-N were 500 μg/ml and 170 μg/ml, respectively. Rates of loss of NO3?-N from the Hanford soil did not approximate Michaelis-Menten kinetics, and this was attributed to failure to saturate enzyme systems in the denitrifying bacteria with glucose and nitrogen when each was held constant. C/N ratios around 2 appeared to provide the greatest rates of denitrification. High C/N ratios or high glucose concentrations (1.8 per cent) retarded denitrification, with fungal growth and a subsequent drop in pH occuring. A Pseudomonas was incubated aerobically for 24 h followed by a 72 h anaerobic incubation with nitrate as the sole nitrogen source at 0, 10, 50, 100, 250 and 500mg N/ml concentrations. Assimilatory nitrate reduction never exceeded 75 mg N/ml, and it was concluded that this mode of nitrate reduction is insignificant at higher nitrate concentrations by comparison to dissimilatory nitrate reduction, i.e. denitrification.  相似文献   

7.
Nitrate (NO3?) can contribute to surface water eutrophication and is deemed harmful to human health if present at high concentrations in the drinking water. In grazed grassland, most of the NO3?‐N leaching occurs from animal urine‐N returns. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3? leaching in three different soils from different regions of New Zealand under two different rainfall conditions (1260 mm and 2145 mm p.a.), and explore the relationships between NO3?‐N leaching loss and ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The DCD nitrification inhibitor was found to be highly effective in decreasing NO3?‐N leaching losses from all three soils under both rainfall conditions. Total NO3?‐N leaching losses from the urine patch areas were decreased from 67.7–457.0 kg NO3?‐N/ha to 29.7–257.4 kg NO3?‐N/ha by the DCD treatment, giving an average decrease of 59%. The total NO3?‐N leaching losses were not significantly affected by the two different rainfall treatments. The total NO3?‐N leaching loss was significantly related to the amoA gene copy numbers of the AOB DNA and to nitrification rate in the soil but not to that of the AOA. These results suggest that the DCD nitrification inhibitor is highly effective in decreasing NO3? leaching under these different soil and rainfall conditions and that the amount of NO3?‐N leached is mainly related to the growth of the AOB population in the nitrogen rich urine patch soils of grazed grassland.  相似文献   

8.
Mineral N accumulates in autumn under pastures in southeastern Australia and is at risk of leaching as nitrate during winter. Nitrate leaching loss and soil mineral N concentrations were measured under pastures grazed by sheep on a duplex (texture contrast) soil in southern New South Wales from 1994 to 1996. Legume (Trifolium subterraneum)‐based pastures contained either annual grass (Lolium rigidum) or perennial grasses (Phalaris aquatica and Dactylis glomerata), and had a control (soil pH 4.1 in 0.01 m CaCl2) or lime treatment (pH 5.5). One of the four replicates was monitored for surface runoff and subsurface flow (the top of the B horizon), and solution NO3– concentrations. The soil contained more mineral N in autumn (64–133 kg N ha?1 to 120 cm) than in spring (51–96 kg N ha?1), with NO3– comprising 70–77%. No NO3– leached in 1994 (475 mm rainfall). In 1995 (697 mm rainfall) and 1996 (666 mm rainfall), the solution at 20 cm depth and subsurface flow contained 20–50 mg N l?1 as NO3– initially but < 1 mg N l?1 by spring. Nitrate‐N concentrations at 120 cm ranged between 2 and 22 mg N l?1 during winter. Losses of NO3– were small in surface runoff (0–2 kg N ha?1 year?1). In 1995, 9–19 kg N ha?1 was lost in subsurface flow. Deep drainage losses were 3–12 kg N ha?1 in 1995 and 4–10 kg N ha?1 in 1996, with the most loss occurring under limed annual pasture. Averaged over 3 years, N losses were 9 and 15 kg N ha?1 year?1 under control and limed annual pastures, respectively, and 6 and 8 kg N ha?1 year?1 under control and limed perennial pastures. Nitrate losses in the wet year of 1995 were 22, 33, 13 and 19 kg N ha?1 under the four respective pastures. The increased loss of N caused by liming was of a similar amount to the decreased N loss by maintaining perennial pasture as distinct from an annual pasture.  相似文献   

9.
Two hydroponic experiments were carried out to investigate the effects of nitrogen (N) levels and forms on the oxalate concentrations of different form in edible parts of spinach. Nitrogen was supplied at five levels (4, 8, 12, 16, 20 mM) in Experiment 1 and five ratios of nitrate (NO3 ?) to ammonium (NH4 +) (100/0, 75/25, 50/50, 25/75, 0/100) at a total N of 8 mM in Experiment 2. Biomass of spinach increased markedly from 4 mM to 8 mM N and reached the flat with further increase in N. The total oxalate and soluble oxalate in leaves and shoots (edible parts) increased significantly with increasing N levels from 4 to 12 mM, while the total oxalate and insoluble oxalate decreased markedly when N level was further increased from 12 to 20 mM. Oxalates of different forms in petioles increased first and then decreased and elevated again with increasing nitrogen levels. In the second experiment, decreasing NO3 ?/NH4 + ratios markedly increased at first and then significantly decreased the biomass of spinach plants and the maximum biomass was recorded in the treatment of the NO3 ?/NH4 + ratio of 50:50. The oxalate concentrations of different form in leaves and shoots were all decreased obviously as the ratio of NO3 ?/NH4 + decreased from 100:0 to 0:100. Concentrations of total oxalate and soluble oxalate in petioles could be reduced by increasing ammonium proportion and were the lowest as the ratio of NO3 ?/NH4 + was 50:50 and insoluble oxalate decreased as nitrate/ammonium ratio decreased. The concentrations of oxalate forms in leaves were all higher than those in petioles and soluble oxalate was predominant form of oxalates in both trials. It is evident that high biomass of spinach can be achieved and oxalate concentrations of different forms can be reduced by modulating N levels and NO3 ?/NH4 + ratio, so this will benefit for human health especially for those people with a history of calcium oxalate kidney stones.  相似文献   

10.
The effects of different forms and concentrations of N in the rooting medium on the CO2/H2O gas exchange of leaves of the pedunculate oak (Quercus robur L.) were investigated. Two-year-old seedlings were grown in nutrient solutions containing low (1.8 mM) or high (4.8 mM) concentrations of NH4+, 3.6 mM NO3?, or both NH4+ and NO3? (1.8 mM + 1.8 mM). In various sets of plants subjected to these N treatments, the following parameters were determined: biomasses of leaves and fine roots, leaf area-related net photosynthesis at light saturation (A) and leaf conductance (g), foliar concentrations of chlorophylls, N, Ca2+, Mg2+ and K+ and the ash alkalinity of the leaves (as a measure of the carboxylate content). In all treatments, the leaves were equally well supplied with nutrients. Oaks grown in high NH4+ concentrations produced significantly smaller leaf and root biomasses. Compared to oaks cultivated with both N forms or with low NH4+ concentration, oaks grown with high NH4+ supply showed lower values of A and g, but no significant differences in ash alkalinity and leaf area-related chlorophyll concentrations. Oaks fed with NO3? as the only N form had an intermediate biomass production, but low values of A and g. The time courses of A in the different treatments closely followed the patterns of g. In all N treatments, the same linear relationship was found between A and g, indicating that, within a rather wide range, the variation in the form and amount of supplied N does not affect the instantaneous water use efficiency of young pedunculate oaks.  相似文献   

11.
《Journal of plant nutrition》2013,36(12):2503-2520
Abstract

Rooted cuttings of Rhododendron canescens “Brook” and Rhododendron austrinum were grown in sand culture with a modified Hoagland's solution under greenhouse conditions. The effect of varying ammonium:nitrate (NO3 ?:NH4 +) ratios (100:0, 75:25, 50:50, 25:75, 0:100) on growth, chlorophyll content, plant quality, and elemental tissue concentration were determined. With NO3 ? as the nitrogen (N) form, both azalea cultivars exhibited less vegetative growth, lower overall plant quality, with leaves showing visual chlorotic symptoms in comparison to plants receiving NH4 + as the N‐form. Leachate pH was highest with NO3 ? as the predominate N‐form and decreased significantly with each increment of NH4 +. With both azalea cultivars, N‐form significantly influenced uptake and utilization of essential plant nutrients. Leaf concentrations of N, potassium (K), calcium (Ca), sulfur (S), boron (B), and molybdenum (Mo) were highest with NO3 ?‐N. Leaf elemental concentrations of phosphorous (P), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) increased as NH4 + supplied more of the N‐ratio. Significant differences in Mg, Mn, and Zn were observed between species. Results from this study show that foliar N concentration is not an accurate indicator of plant growth response. Further investigations are needed to determine if foliarchlorosis and low growth rates observed with NO3 ? fed plants due to an Fe deficiency, to low nitrate reductase (NR) activity in the leaves, or to a combination of these factors.  相似文献   

12.
ABSTRACT

The present study was performed to characterize the interaction between nitrogen (N) form and availability with respect to growth, water relations, and mineral nutrition of wild swiss chard (Beta macrocarpa Guss). Plants were cultured hydroponically with two levels of N concentrations, high-N (2.5 mM) or low-N (0.5 mM), added as nitrate (NO? 3) or ammonium (NH+ 4). At high N, growth was affected significantly by N form. If the NO? 3 medium was considered as control, the use of NH+ 4 decreased dry matter production and leaf area by ca. 35%. Use of NH+ 4 led to water economy and did not affect the nutrient content of the plant tissues. Compared to growth with high N, plants growth fell in either low- NO? 3 or low- NH+ 4 medium. In this case, the difference between the two N sources was not significant. Our results showed that the replacement of NO? 3 by NH+ 4 as the N source decreased the NO? 3 concentration in consumable leaves and increased the water use efficiency.  相似文献   

13.
Nitrate-N (NO3 ?-N) is a ubiquitous pollutant in both surface and groundwater in many agro-ecosystems. This has elicited a concerted effort to identify management strategies that mitigate NO3 ?–N pollution, without compromising crop yield. This study was conducted on a field site located at the Bio-Environmental Engineering Centre (BEEC) in Truro, NS, Canada during 1999 and 2000. The site has been used since 1997 to investigate the relative effect of inorganic versus organic fertilizer (liquid hog manure; LHM) applied at rates (70 kg N ha?1) on NO3 ?-N leaching from a carrot rotation system. NO3 ?-N concentrations were monitored in both the soil profile and in tile drainage effluents from eight treatment plots. The LHM treatment elicited significantly (P < 0.01) higher soil NO3 ?-N concentrations than inorganic fertilizer (IF) in June and October during 1999, but not 2000. The sampling date and soil depth were significant in most cases. Annual flow weighted averages (FWA) of NO3 ?-N in drainage water were generally greater for plots receiving LHM (15.4 and 10.5 mg L?1 for 1999 and 2000, respectively), when compared to IF (8.9 and 6.0 mg L?1 for 1999 and 2000, respectively), but the difference was significant (P < 0.05) only in 1999. Maximum NO3 ?-N concentrations in drainage water were similar for both treatments, while the LHM treatment had a significantly higher percentage of samples that were > 10 mg L?1. The total NO3 ?-N load was greater for the LHM treatment when compared to the IF treatment in 1999. Barley and carrot yields were unaffected by treatment applications.  相似文献   

14.
A column lysimeter study was conducted under greenhouse conditions to determine the impact of moderately saline irrigation water on NO3 leaching from turfgrass. Bermudagrass (Cynodon dactylon L. ‘NuMex Sahara’) was fertilized at three N levels (25, 50 and 75 kg NH4NO3-N ha?1 month?1) and irrigated with saline water (0, 3.0 and 6.0 dS m?1) in a factorial arrangement. Leachate was analyzed for salinity and NO3, and clippings were collected and analyzed for total N. Nitrate leaching was not affected by either N level or salinity. Nitrate concentrations in the leachate were low, averaging approximately 0.3 mg N L?1; less than 1% of the applied N leached. Longer-term N allocation to leaf growth accounted for up to 98% of applied N, whereas short-term allocation, determined using 15N, ranged from 46–67%. Salinity had no affect on clipping yield, the biomass of root and verdure, or root distribution. These data indicate the potential for moderately saline irrigation water to be used on bermudagrass turf without increasing NO3 contamination of groundwater, as long as leaching is adequate to prevent rootzone salinity reaching damaging levels.  相似文献   

15.
Hydroponic production of rocket as a salad vegetable has become increasingly important in recent years. Rocket is known to be a high nitrate (NO3–)-accumulating vegetable, which can be grown throughout the year. In the present study, rocket was grown in a floating hydroponic system at three levels of nitrogen (N) and sodium chloride (NaCl). The highest yield was obtained at 14 mM N, whereas the yield was lower at 20 mM and 40 Mm NaCl. Leaf elongation was more sensitive to salinity than leaf differentiation. Adding NaCl to the nutrient solution increased the relative chlorophyll content. Na+ and Cl– concentrations increased as salinity increased. NO3? levels in fresh biomass increased with increased amounts of NO3? in the nutrient solution, and plants at 18 mM N were able to maintain a higher NO3? : Cl? ratio than those at 10 mM N.  相似文献   

16.
Denitrification was studied using samples of salt marsh soils collected from the New Jersey coast. The pH, organic matter content, NO3? and NO2? concentrations were determined on samples from marshes with and without grasses. Denitrification was measured in laboratory studies over a temperature range from 4° to 60°C and a pH range from 5.0 to 9.0 by monitoring NO3? reduction, NO2? reduction and N2 evolution. Optimum conditions were controlled by a temperature-pH interaction which caused shifts in the pH optima relative to the change in temperature. No3? and NO2? were reduced over a broad range of No3? concentration; whereas, 0.2 mg NO2?-N ml?1 completely inhibited denitrification. The presence of NO3? reverses this inhibition. N2O was produced only at low pH values and low NO3? concentrations. It was concluded that the NO2? reducing system was the most easily disrupted of the three main processes of denitrification.  相似文献   

17.
The objectives of this article were to analyze the evolution of the nutrient parameters of the leachates collected from Syngonium podophyllum var. Silver plants cultivated for 20 weeks in a buried greenhouse with four methods of fertilization. The treatments were T1, standard liquid feeding (SLF) [7.0 mmol L?1 nitrate (NO3 ?) nitrogen (N), 0.3 mmol L?1 phosphorus (P), and 3.5 mmol L?1 potassium (K)] after transplanting; T2, liquid feeding soluble fertilizer (LFSF) [6.9% NO3 ? N, 11.1% ammonium (NH4 +) N stabilized by 3,4-dimethylpyrazole phosphate, 8.0% P2O5, and 14.0% K2O] after transplanting; T3, controlled release fertilizer (CRF I) (7.4% NO3 ? N, 8.6% NH4 + N, 8.0% P2O5, and 12.0% K2O) applied before planting and half concentration of SLF from 45 days after transplanting; and T4, controlled release fertilizer (CRF II) (8.5% NO3 ? N, 7.5% NH4 + N, 8.0% P2O5, and 12.0% K2O) applied before planting and half concentration of SLF from 45 days after transplanting. Solution pH, electrical conductivity (EC), NO3 ? N, NH4 + N, K, and P concentrations in the leachate were analyzed weekly. Plant quality was assessed at the end of the trial through objective and subjective parameters. Significant differences among the different fertilization methods were observed. CRF treatments resulted in the greatest nutrient leachate concentration during the first 6 weeks of the study, and afterward it decreased gradually until the end of the cultivation. CRF I showed greater leachate concentrations of N, P, and K than the others during the first half of the study. The concentrations of NO3 ? N and P from all the fertilizer types were often above the permissible levels cited in the federal Clean Water Act. The best-quality plants were obtained with CRF II, whereas the greatest height and Aerial Dry Weight (ADW) were obtained with CRF treatments and the greatest Root Dry Weight (RDW) was obtained with the NH4 + N treatments.  相似文献   

18.
The temporal and vertical distributions of four N species, N03 ?, NO2 ?, total ammonia (T-NH3), and free ammonia (NH3), are documented for Onondaga Lake, an urban, polluted, hypereutrophic, dimictic, lake that receives a very high load of T-NH3. Nitrate and NO2 ? were lost rapidly from the hypolimnion, and T-NH3 accumulated to high concentrations (maximum > 10 mgN L?1), after the onset of anoxia, consistent with the lake's high level of productivity. The concentrations of T-NH3, NH3 and N03 ? that were maintained in the epilimnion (average concentrations at a depth of 1 m of 2.81, 0.16 and 0.91 mgN L?1, respectively), and concentrations of N02 ? that developed in the epilimnion (maximum of 0.48 mgN L?1), were high in comparison to levels reported in the literature. These elevated concentrations are largely a result of the extremely high loads of T-NH3, and its precursors, received by the lake. Water quality problems in the lake related to the prevailing high concentrations of N species include potential toxicity effects and severe lake-wide oxygen depletion during fall turnover.  相似文献   

19.
ABSTRACT

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the United States, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. The objective was to determine the N concentration and the nitrate (NO3 ??N):ammonium (NH4 +?N) ratio of N source that optimized bedding-plant impatiens growth and flower development. Four N concentrations (3.5, 7, 10.5, and 14 mmol N · L?1) were used in factorial combination with four ratios of NO3 ??N:NH4 +?N (4:0, 3:1, 1:1, and 1:3). Application of treatments was made for 30 d. Then for 10 d only deionized water was applied to reduce salt buildup. Substrate pH was lowest (4.9) with the NH4 +?N source and electrical conductivity (EC) highest, but never > 2.4 dS m?1. Nitrogen concentration and N source displayed an interaction for most growth parameters. Shoot fresh and dry weights and flower bud number were maximized at the 1:3 NO3 ??N:NH4 +?N ratio with a N concentration of 10.5 mmol L?1. However, plant diameter, leaf number, and leaf chlorophyll content responded quadratically to N form ratio, with the 1:1 ratio optimum at a concentration of 10.5 mmol N· L?1.  相似文献   

20.
Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH 4 + and NO 3 ? whereby higher values were reached at the end of spring–early summer, except at the easternmost coastal site of Begur. Weekly NH 4 + concentrations decreased with time at all sites (except at La Senia) whilst NO 3 ? concentrations increased at all sites during the same period. Rainfall SO 4 2? concentrations decreased with time at all sites. The opposite trends in NO 3 ? and SO 4 2? concentrations determined a shift in the relative acid contribution of those anions during the 12–13-year period. To interpret the increasing trend, mean annual NO 3 ? concentrations were regressed against NO2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha?1 year?1. When including estimates of dry deposition, total annual deposition rose up to 10–20 kg ha?1 year?1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems.  相似文献   

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