Soil microbial community responses to dairy manure or ammonium nitrate applications

Soil management practices that result in increased soil C also impact soil microbial biomass and community structure. In this study, the effects of dairy manure applications and inorganic N fertilizer on microbial biomass and microbial community composition were determined. Treatments examined were a control with no nutrient additions (CT), ammonium nitrate at 218 kg N ha⁻¹ (AN), and manure N rates of 252 kg manure-N ha⁻¹ (LM) and 504 kg manure-N ha⁻¹ (HM). All plots were no-till cropped to silage corn (Zea mays, L. Merr) followed by a Crimson clover (Trifolium incarnatum, L.)/annual ryegrass (Lolium multiflorum, Lam.) winter cover crop. Treatments were applied yearly, with two-thirds of the N applied in late April or early May, and the remainder applied in September. Soil samples (0–5, 5–10, and 10–15 cm) were taken in March 1996, prior to the spring nutrient application. Polar lipid fatty acid (PLFA) analysis was used to assess changes in microbial biomass and community structure. Significantly greater soil C, N and microbial biomass in the 0–5 cm depth were observed under both manure treatments than in the CT and AN treatments. There was also a definable shift in the microbial community composition of the surface soils (0–5cm). Typical Gram-negative bacteria PLFA biomarkers were 15 and 27% higher in the LM and HM treatments than in the control. The AN treatment resulted in a 15% decrease in these PLFA compared with the control. Factor analysis of the polar lipid fatty acid profiles from all treatments revealed that the two manure amendments were correlated and could be described by a single factor comprised of typical Gram-negative bacterial biomarkers. The AN treatments from all three depths were also correlated and were described by a second factor comprised of typical Gram-positive bacterial biomarkers. These results demonstrate that soil management practices, such as manuring, that result in accumulations of organic carbon will result in increased microbial biomass and changes in community structure.     

施用铵态氮对森林土壤硝态氮和铵态氮的影响

对取自武夷山的红壤、黄壤、黄壤性草甸土分别在对照(CK,N 0 mg/kg)、低氮(LN,N 50 mg/kg)、高氮(HN,N 100 mg/kg)3种氮(N)水平处理下开展培养实验,研究施加NH4+-N对森林土壤N转化的短期影响.结果表明,添加NH4+-N可显著(p＜0.05)降低土壤NO3--N含量4.5％～25.7％,但LN与HN处理差异不显著,NO3--N降低可能与NO3--N反硝化和异氧还原有关;然而,黄壤性草甸土NO3--N没有降低.与培养前比较,在第56天红壤NO3--N含量显著增加5倍左右;桐木关黄壤增加40％左右,而黄冈山25 km黄壤仅在CK处理下增加16％,但是黄壤性草甸土显著降低;结果显示LN与HN处理土壤NO3--N含量变化幅度小于CK.与CK相比,LN和HN处理红壤NH4+-N分别显著(p＜0.05)升高24.1％ ～ 96.5％和68.7％～114.1％,且随培养进行没有累积,可能与微生物固N有关;桐木关NH4+-N分别升高17.6％ ～ 39.6％和37.6％～95.8％ (p＜0.05),LN处理黄冈山25 km黄壤NH4+-N只有第7天升高17.8％ (p＜0.05),HN处理第7、14、28、42天显著升高17.5％～48.6％(p＜0.05).LN处理黄壤性草甸土的NH4+-N在前3周显著降低11.6％～28.5％ (p＜0.01); HN处理在第7天和14天分别降低10.8％(p＜0.01)和7.5％,但是在第28～56天显著增加17.6％～20.4％(p=0.002).随着培养进行,CK处理红壤NH4+-N逐渐降低,桐木关黄壤、黄冈山25 km黄壤和黄壤性草甸土升高;LN和HN处理黄壤和黄壤性草甸土NH4+-N逐渐升高.可见,不同海拔土壤类型对NH4+-N添加响应存在差异.     

冬小麦对铵态氮和硝态氮的响应

在陕西省永寿县和河南省洛阳市分别设置了11和7处大田试验,分5层采集0~100 cm土壤样品并测定其起始硝态氮含量。永寿试验设7个处理,分别为不施氮,硝态氮、铵态氮品种、硝态氮与铵态氮2∶1组合各2个处理;洛阳试验设6个处理(硝态氮肥只有1个品种),施氮处理均施N 150 kg hm-2,研究小麦对铵态氮和硝态氮肥响应的差异及其与不同深度土层硝态氮累积量的关系。试验表明,同一形态不同氮肥品种之间的增产差异显著低于不同形态之间的差异。比较不同形态氮肥的小麦产量、增产量和增产率的平均值,硝态氮肥最高,硝态氮、铵态氮组合次之,铵态氮最低。氮肥增产量和增产率随土壤累积硝态氮量增加而显著下降;累积量越低,氮肥增产效果越突出,硝态氮的效果也越显著。由此可见,土壤累积的硝态氮量是决定氮肥肥效的主要因子,也是决定不同形态氮素效果的主要因子。只有在硝态氮累积量低的土壤上,氮肥才能充分发挥作用,硝态氮也才能表现出明显的优势。     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

Accompanying ions of ammonium sources and nitrate : ammonium ratios in tomato plants

The tomato (Solanum lycopersicum L.) cultivar Micro‐Tom (MT) is widely used in physiological studies, but the effects of nitrate ( ) and ammonium ( ) ratios ( : ratios) and, in particular, the effects of the accompanying ions in sources are unknown. To determine whether the accompanying ions in sources influence toxicity, the effects of : ratios on the physiology, electrolyte leakage index, nutrition, and dry weight were studied using hydroponics. The sources were ammonium chloride (NH₄Cl) or ammonium sulfate [(NH₄)₂SO₄], and five : ratios were used: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. The source was calcium nitrate [Ca(NO₃)₂], and the nitrogen (N) concentration was 15 mmol L^?1. The results indicate that NH₄Cl or (NH₄)₂SO₄ can be used in studies on toxicity because the accompanying ions did not influence the tomato plants. In addition, : ratios of 100 : 0 and 75 : 25 resulted in the highest dry weight of tomato plants, whereas ratios of 25 : 75 or 0 : 100 were toxic.     

几种蔬菜对硝态氮、铵态氮的相对吸收能力

采用溶液培养方法探讨了莴笋、菠菜、小白菜和大青菜 4种蔬菜作物对硝、铵态氮的相对吸收能力以及这两种氮源对它们生长发育的影响。结果表明 ,单独供给NO3-N ,4种作物均生长发育良好 ;供给NO3--N +NH4+-N(NO3-∶NH4+=1∶1) ,生长量均有所下降 ,而单独供给NH4+-N时 ,生长量则大幅度下降。莴笋单独供给NO3--N时 ,其吸氮量显著高于供给NO3--N +NH4+-N的处理 ,大青菜、菠菜供给NO3--N +NH4+-N与单独供给NO3--N相比吸氮量大体相当 ;小白菜同时供应NO3--N +NH4+N时吸氮量最高 ,供给NO3--N时次之 ,供给NH4+-N时显著降低。供给NH4+-N时 4种作物吸氮量均比其它氮源显著降低。 4种作物对NO3--N与NH4+-N的吸收具有明显的偏向性。供给等氮量铵、硝态氮 (NO3--N +NH4+-N处理 )时 ,菠菜、小白菜吸收的NO3-N显著多于NH4+-N ,表现出喜硝性 ,莴笋则与此相反 ,表现出喜铵性 ;而大青菜对两种形态氮素的吸收量相差不多 ,表现出兼性吸收的特点。但上述偏向性具有阶段特点 ,即喜硝作物可能在某一阶段表现出喜铵性状     

磷酸二氢钙和氯化钾对氯化铵处理黄泥土水溶性铵态氮和硝态氮的影响

氮磷钾是农业生产中大量施用并且经常共同施用的肥料,三者在土壤中的相互作用对养分的迁移转化、吸收和代谢有着深远影响.本文模拟生产中氮磷钾肥料同施,研究了田间持水量条件下磷酸二氢钙、氯化钾对氯化铵处理土壤水溶性铵态氮和硝态氮的影响.结果表明,铵态氮施入土壤后,随着培养时间的延长,土壤中水溶性铵态氮含量下降,硝态氮含量升高,两者之间存在着显著相关性.磷酸二氢钙延缓了铵态氮向其他形态氮的转变,使培养中期土壤水溶性铵态氮显著高于氯化铵处理土壤,并对培养中后期硝态氮的增加有抑制作用.氯化钾增加了培养前中期氯化铵处理土壤铵态含量,但显著抑制了氯化铵处理土壤培养后期硝态氮的含量.因此,农业生产中氯化铵和氯化钾共施,氯化铵和磷酸二氢钙共施,氯化铵、氯化钾和磷酸二氢钙共施,对提高氮肥利用率,降低硝态氮淋失损失均有重要作用.     

Potato uptake and recovery of nitrogen 15N-enriched ammonium nitrate

Tuber yield and nitrogen uptake in potatoes were recorded during 1996 and 1997 in Southern Bavaria. Recovery of applied fertilizer nitrogen was measured by using ¹⁵N (¹⁵NH₄¹⁵NO₃). Nitrogen fertilizer was brought out either broadcast or in the ridge; 150 kg N ha⁻¹ were applied either at planting or in split doses of 50 kg N ha⁻¹ (at planting, emergence and at 20-cm plant height). Due to unfavorable conditions, tuber yield and fertilizer N recovery were lower in 1996 as compared with 1997. Fertilizer N recovery in plant biomass (tuber and foliage) ranged from 35.9% to 68.5% at growth stage EC 79; the main fraction was allocated to tubers. Placement of fertilizer N in the ridge had a positive effect on N recovery, when the total N amount was applied at planting. In broadcast application, fertilizer N recovery was higher when the fertilizer doses were split, as compared with a single broadcast application at planting. When fertilizer N was applied in split doses, the effect of N placement became negligibly small. Fertilizer N recovery in soil ranged from 19.5% to 24.6%, and total recovery ranged from 60.1% to 88.0%. Rainfall between planting and plant emergence, and conditions restricting plant development in early developmental stages were related with unaccounted fertilizer N losses. Therefore, the positive effects of split N applications or fertilizer placement are most likely to occur under unfavorable growing conditions.     

Agronomical and physiological aspects of ammonium and nitrate nutrition of plants

Field studies comparing yield responses of crops treated with different nitrogen fertilizer types have led to very contradictory results. This can be explained by the fact that the application of different forms of nitrogen may affect plant growth via numerous processes in the soil and within the plant. In this review the significance of these processes for nutrient availability in soil are briefly outlined. Then, data from literature and own results are used to show that an enhanced ammonium supply may promote certain yield components such as the number of ears per plant in wheat or the number of kernels per plant in maize whereas other yield components such as the number of grains per ear in cereals or the number of tillers in linseed may be adversely affected by ammonium supply. These different effects of ammonium and nitrate supply on yield structure of plants are related to physiological changes in the plant using a model.     

Immobilization of ammonium and nitrate and their interaction with native N in three Illinois Mollisols

Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or ¹⁵N-labelled (NH₄)₂SO₄ or ¹⁵N-labelled KNO₃. The objectives were: (1) to compare the immobilization and interaction of NH _inf4 ^sup+ –N and NO _inf3 ^sup- –N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized ¹⁵N+clay-fixed ¹⁵NH _inf4 ^sup+ ). In all cases, both NH _inf4 ^sup+ –N and NO _inf3 ^sup- –N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH _inf4 ^sup+ than NO _inf3 ^sup- was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH _inf4 ^sup+ than NO _inf3 ^sup- , whereas there was very little difference between NH _inf4 ^sup+ and NO _inf3 ^sup- in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH _inf4 ^sup+ and NO _inf3 ^sup- will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH _inf4 ^sup+ than with NO _inf3 ^sup- . Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content.     

Effects of acetylene on nitrification and denitrification in two soils during incubation with ammonium nitrate

A loam from the Frilsham and one from the Wickham Series were incubated at 50 and 90 per cent of their water contents at saturation with 100 μg NH₄NO₃-N_g^?1 soil in the presence and absence of C₂H₂ (0.5 per cent, v/v). Acetylene inhibited nitrification in both soils, but had no effect on mineralization of N. No denitrification (measured as the production of N₂O in the presence of C₂H₂) occurred during incubation at 50 per cent saturation. At 90 per cent saturation, denitrification resulted in a loss of 28.4 and 36.7 μg N_g^?1 after 48 h from the Frilsham and Wickham soils, respectively. The concurrent inhibition of nitrification had no effect on the extent of denitrification at this time. In the Wickham soil, NO₃^? was exhausted after 168 h incubation in the presence of C₂H₂ and denitrification was underestimated by 13 μg N_g^?. The data suggested that concurrent inhibition of nitrification during measurement of denitrification using the C₂H₂ inhibition technique is most likely to affect the estimate of denitrification loss when NO₃^?supply is limited by the inhibition of nitrification.     

Induction of high affinity nitrate and ammonium uptake systems in wheat

Abstract

The ability of 7 day old wheat seedlings to take up nitrate or ammonium from hydroponic solution was measured. Seedlings were grown under fully aerated hydroponic conditions. The growth solution consisted of either 0.5 mM CaSO₄ alone or in combination with high nitrate (5 mM NO₃ ^‐ ), high ammonium (2 mM NH₄ ⁺) or modified 1/10 Hoaglands solution with nitrate N only (14 mM) or ammonium N only (2 mM). After washing the roots for one hour in CaSO₄, nitrate or ammonium uptake was measured with an ion selective electrode. Plants grown in high nitrate were unable to take up nitrate from a 0.1 mM external solution. Those grown in CaSO₄ were able to take up nitrate at the same external concentration (flux = 10.2 +/‐ 3.0 μmol nitrate/g dry wtlbh). The same result was seen for plants grown in high ammonium vs those grown in CaSO₄ (flux = 21.0 +/‐ 10.0 μmol/g dry wtlbh). Similar results were obtained when modified Hoagland's solution was substituted for the high N solutions. These data indicate that wheat roots possess both high and low affinity nitrate and ammonium uptake systems. The data further indicate that, for a given ion, the high and low affinity systems do not operate simultaneously under high N conditions. The high affinity system is switched off in the range of 1 mM for both ionic forms of N. Developmental studies show that the expression of the high affinity trait is reversible and may be induced (repressed) by conditioning for 24 h in low (high) N media. Plants grown in high N solutions showed efflux of the ion under assay conditions. Neither ion interfered with the induction/repression of the high affinity trait for the other under the conditions used in this study.     

Tomato responses to ammonium and nitrate nutrition under controlled root-zone pH

Tomato (Lycopersicon esculentum L. Mill. 'Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO3- or 1.0 mM NH4+. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO3- or NH4+ can be used efficiently by tomato. Uptake of K+ and Ca2+ were not altered by N source, but uptake of Mg2+ was reduced in NH4(+)-fed plants. This indicates that uptake of Mg2+ was regulated at least partially by ionic balance within the plant.     

不同处理对河套灌区玉米土壤硝态氮和铵态氮动态及氮肥利用率的影响

为了探讨内蒙古河套灌区农业化肥面源污染检测和治理措施,采用大田土壤淋溶试验,分析了河套灌区农田在缓控释尿素、活性炭、生物菌肥处理下,玉米生育期内土壤硝态氮、铵态氮动态变化特征及氮肥利用情况。结果表明,缓控释尿素、活性炭、微生物菌肥处理与常规处理相比,在玉米拔节期、大喇叭口期土壤NO-3-N、NH+4-N含量变化不太显著,而苗期土壤NO-3-N含量平均分别提高24.76%、18.36%、4.31%,收获期平均分别降低23.98%、12.53%、5.47%;苗期土壤中NH+4-N含量较常规处理分别平均提高28.21%、15.47%、5.24%,收获期平均分别降低26.33%、16.93%、7.37%;氮肥利用率分别较常规处理提高15.71%、10.65%和5.16%。     

Soil nitrate sources and nitrate leaching losses, Slapton, South Devon

Abstract. Concentrations of soil nitrate were measured in areas of different land use within a small drainage basin. From previous work on nitrate losses from subcatchments, soil nitrate levels were expected in the order arable > grassland > woodland. Although differences were detected, they were not consistent and seasonal variations in soil nitrate for the same land use were greater than those between land uses. Seasonal fluctuations in stream nitrate loads were not strongly related to the seasonal differences in soil nitrate levels but were more closely related to stream discharge and antecedent climatic conditions. Losses of nitrate from the catchment seemed to be transport limited and independent of variations in soil nitrate supply; the implication is that water quality control by land use manipulation will only be successful in supply limited situations when leaching losses are sensitive to variations in soil nitrate supply.     

Effect of sodium chloride on denitrification in glucose amended soil treated with ammonium and nitrate nitrogen

Laboratory incubations were conducted to study the effect of sodium chloride (NaCl) on denitrification and respiratory gases (CO₂, O₂) from soil treated with ammonium or nitrate and incubated at 20 % moisture. The same samples were assayed for denitrifying enzyme activity (DEA) after incubation at 40 % moisture with glucose and NO₃^–. Under aerobic conditions (20 % water content), a flush of activity was observed at 6 hours after start of incubation and subsided to negligible levels at 12 hours. Sodium chloride significantly depressed N₂O and CO₂ emissions and O₂ consumption. Significantly more loss of N₂O occurred from NH₄⁺‐ than NO₃^–‐treated soil at all NaCl levels and was attributed to higher microbial activity. A highly significant positive correlation was obtained between N₂O emission and respiratory gases. The respiratory quotient (CO₂ evolved/O₂) was higher for NH₄⁺‐treated soil and decreased with the amount of NaCl. At 40 % moisture, N₂O emissions were higher than at 20 % and peaked at 37 hours followed by a sharp decrease. Short‐term incubations of soil with NH₄⁺ or NO₃^– did not have an effect on denitrifying enzyme activity (DEA) while NaCl had a positive effect, particularly in previously NO₃^–‐treated soil.     

Glucose metabolism in detached leaves of tomato plants grown with ammonium and nitrate as nitrogen sources

The metabolism of exogenous glucose-¹⁴C in the light and the dark was studied in the detached leaves of tomato plants grown with ammonium nitrogen and nitrate nitrogen. In the light, ¹⁴CO₂, release and incorporation of glucose into insoluble materials were hardly affected at all by the nitrogen sources. Among the soluble labelled amino acids, serine had the greatest amount of label in the ammonium-plants while aspartate had the greatest amount in the nitrate-plants. This aspartate was synthesized from C₃-compounds by carboxylation. During dark-light transition, the change in the composition of soluble amino acids was more rapid in the ammonium-plants than in the nitrate-plants. In the dark, ¹⁴CO₂-release, which was ten times as much as in the light, was larger in the ammonium-plants than in the nitrate-plants; but the synthesis of high molecular compounds from glucose in the ammonium-plants was about half that in the nitrate-plants. So, it is considered that respiration operates sufficiently in the ammonium-plants. The effects of DCMU and a 100% O₂ atmosphere on glucose metabolism in both groups of plants were studied and the respiration of leaves in the light was discussed.     

Effects of ammonium nitrate encapsulated with coal combustion byproducts on nutrient accumulation by corn and rye

Ammonium nitrate is a fertilizer and an explosive. Encapsulation of ammonium nitrate (NH₄NO₃) with coal combustion byproducts (fly ash or flue gas desulfurization gypsum) reduces the explosiveness of NH₄NO₃. A field study was conducted to determine the effects of encapsulated NH₄NO₃ on corn (Zea mays L.) and rye (Secale cereal L.) yield and accumulation of nitrogen (N), arsenic (As), cadmium (Cd), iron (Pb), copper (Cu), manganese (Mn), and zinc (Zn). Nitrogen rates were 56 and 112 kg ha^?1. Yields and concentrations of N and metals in corn grain, ear-leaf, and stover and in rye shoots were not affected by N source. Increased N rate resulted in increased corn ear-leaf, grain, and stover N, ear-leaf Cu, Mn, and Zn, and rye shoot yield, Cu, and Zn. For both species, metal levels did not exceed normal ranges. Coal byproduct-encapsulated NH₄NO₃ is as effective as non-encapsulated NH₄NO₃ for corn or rye production, without increasing plant metal concentrations above normal levels.     

丛枝菌根根外菌丝对铵态氮和硝态氮吸收能力的比较

采用空气隔板分室法并结合15N标记技术,以玉米为宿主植物并接种Glomus mosseae和Glomus intraradices,比较了这两种真菌根外菌丝对铵态氮和硝态氮吸收传递能力的差异。结果表明,丛枝菌根根外菌丝吸收传递氮的能力因菌种和氮素形态而异。两种真菌根外菌丝吸收传递NH4+-N能力均高于NO3--N;G. intraradices根外菌丝吸收传递氮的能力高于G. mosseae,这可能与两种真菌根外菌丝生长量有关。     

Effects of ammonium and nitrate additions on carbon mineralization in wetland soils

Wetlands have been recognized as a soil carbon (C) sink due to low decomposition. As decomposition is largely controlled by the availability of soil nitrogen (N), an elevated anthropogenic N input could influence the C balance in wetlands. However, the effects of the form of N on decomposition are poorly understood. Here, a 54-day laboratory incubation experiment was conducted, with a diel cycle (day: 22 °C for 13 h; night: 17 °C for 11 h) in order to determine how the dominant N form influences the mineralization of soil C in two adjacent wetland soils, with distinct physicochemical characteristics. Three combinations of N compounds were added at three different rates (0, 30, 60 kg N ha⁻¹ yr⁻¹): Ammonium dominant (NH₄Cl + NH₄NO₃); nitrate dominant (NH₄NO₃ + NaNO₃); and ammonium nitrate treatments (NH₄NO₃). In the acidic soil, the CO₂ efflux was reduced with N additions, especially with NH₄NO₃ treatment. In addition, decreases in the microbial enzyme activities (β-glucosidase, N-acetyl-glucosaminidase, phosphatase, and phenol oxidase) and soil pH were observed with NH₄NO₃ and -dominant treatment. Under alkaline conditions, marginal changes in response to N additions were observed in the soil CO₂ efflux, extractable DOC, simple substrate utilization, enzyme activities and pH. A regression analysis revealed that the changes in pH and enzyme activities after fertilization significantly influenced the soil CO₂ efflux. Our findings suggest that the form of N additions could influence the rate of C cycling in wetland soils via biological (enzyme activities) and chemical (pH) changes.