Effect of simulated acid precipitation on nitrogen mineralization and nitrification in forest soils

After exposure of samples of three forest soils (pH 3.4 to 3.9) from the Adirondacks region of New York to 60, 230, or 400 cm of simulated rain of pH 3.5 or 5.6 in 4, 14, or 24 weeks, respectively, the soil samples were separated into the 0 to 2 and 2 to 5 cm organic layers and further incubated. The rates of N mineralization in Woods soil exposed to the simulated precipitation were less for rain at pH 3.5 than at pH 5.6, but the inhibition decreased with increasing exposure of the 0 to 2 cm layer. In Panther soil, the rates of mineralization were usually not affected by the acidity of the simulated rain. In the upper layer of Sagamore soil, mineralization was not influenced by pH of the simulated rain, but the transformation was faster in the bottom layer of soil after prolonged exposure to simulated rain at pH 3.5 than at pH 5.6. The rate of nitrate formation in Panther and Woods soil amended with ammonium was inhibited by the more acid rain. Studies with ¹⁵NH₄ indicated that ammonium was oxidized to nitrate even though ammonium levels did not decline or declined only slightly after prolonged exposure of Panther or Woods soil to rain at pH 3.5. The growth of orchardgrass in Panther and Woods soil was inhibited by the more acid simulated rain.     

红壤氮素的矿化和硝化作用特征

采用培养试验研究了侵蚀红壤,培肥后的红壤以及不同利用方式红壤氮素的矿化和硝化作用特征.结果表明,侵蚀红壤的矿化作用和硝化作用都很微弱,采用适宜的施肥措施培肥后氮素的矿化和硝化速率都有很大提高;红壤氮素的矿化和硝化速率与土壤pH、速效磷含量和有机质含量呈显著正相关.     

添加碳源、磷和石灰对红壤氮素矿化和硝化作用的影响

用培养试验研究了添加碳源、磷和石灰石粉对第四纪红色粘土及红砂岩母质上发育的不同侵蚀程度的红壤以及经培肥后红壤的矿化和硝化作用的影响。结果表明 :上述 3个因子对矿化作用的影响较大 ,添加碳源表现出土壤矿质氮的净生物固持 ;在低磷红壤上增施磷能有效地促进红壤氮素的矿化 ;添加石灰石粉也能有效地促进 pH较低的红壤氮素的矿化。培肥后的红壤矿化和硝化作用明显增强 ,添加磷和石灰石粉进一步促进了培肥红壤矿化率和硝化率的提高。但施用石灰石粉和磷并未提高未经培肥的侵蚀红壤的硝化作用     

Net nitrogen mineralization and nitrification rates in forest soil in northeastern Taiwan

We used a laboratory incubation approach to measure rates of net N mineralization and nitrification in forest soils from Fu-shan Experimental Forest WS1 in northern Taiwan. Net mineralization rates in the O horizon ranged from 4.0 to 13.8 mg N kg⁻¹ day⁻¹, and net nitrification rates ranged from 2.2 to 11.6 mg N kg⁻¹ day⁻¹. For mineral (10–20 cm depth) soil, net mineralization ranged from 0.06 to 2.8 mg N kg⁻¹ day⁻¹ and net nitrification rates ranged from 0.02 to 2.8 mg N kg⁻¹ day⁻¹. We did not find any consistent differences in N mineralization or nitrification rates in soils from the upper and lower part of the watershed. We compared the rates of these processes in three soil horizons (to a soil depth of 30 cm) on a single sampling date and found a large decrease in both net N mineralization and nitrification with depth. We estimated that the soil total N pool was 6,909 kg N ha⁻¹. The present study demonstrates the importance of the stock of mineral soil N in WS1, mostly organic N, which can be transformed to inorganic N and potentially exported to surface and ground water from this watershed. Additional studies quantifying the rates of soil N cycling, particularly multi-site comparisons within Taiwan and the East Asia–Pacific region, will greatly improve our understanding of regional patterns in nitrogen cycling.     

Factors controlling nitrogen mineralization and nitrification in forest ecosystems in New Mexico

Summary Forest floor and mineral soil from ponderosa-pine, Douglas-fir, aspen and spruce-fir ecosystems located along a rising gradient in New Mexico were tested with laboratory assays for factors controlling N mineralization and nitrification. We concluded that low pH in combination with factors associated with organic quality controlled N mineralization and almost completely limited nitrification in spruce-fir soils, while N mineralization in the forest floor of ponderosa-pine was limited by low nutrient availability (other than N). Organic quality of the substrate and temporal changes in organic quality appeared to control N-mineralization and nitrification processes in forest-floor and mineral soils from all other sites.     

Carbon and nitrogen mineralization in subarctic agricultural and forest soils

Summary C and N mineralization potentials were determined, in a 12-week laboratory incubation study, on soil samples obtained from recently cleared land which had been cropped to barley for 4 years (field soils) and from nearby undisturbed taiga (forest soils). Treatments for the cropped soils were conventional and no-tillage with and without crop residues removed. An average of about 3% of the total C was evolved as CO₂ from the field soils compared with > 10% and 4% for the upper (Oie) and lower (Oa) forest-floor horizons, respectively. Significantly more C was mineralized from the Ap of the no-till treatment with residue left on the surface than from the other field Ap horizons. Both forest-floor horizons showed rather long lag periods for net mineralization compared with the field soils, but at the end of the incubation, more mineral N was recovered from the forest Oie despite a rather wide C:N ratio, than from the field soils. After 12 weeks about 115, 200 and 20 g mineral N/g soil were recovered from the field Ap, the forest Oie and the forest Oa horizons, respectively. Very little C or N was mineralized from the B horizon of the forest or the field soils. Nitrification was rapid and virtually complete for the field soils but was negligible for both forest-floor O horizons.Paper no J-188 of the Journal Series of the Alaska Agricultural and Forestry Experiment Station     

Low levels of nitrogen addition stimulate decomposition by boreal forest fungi

Climate warming and associated increases in nutrient mineralization may increase the availability of soil nitrogen (N) in high latitude ecosystems, such as boreal forests. These changes in N availability could feed back to affect the decomposition of litter and organic matter by soil microbes. Since fungi are important decomposers in boreal forest ecosystems, we conducted a 69-day incubation study to examine N constraints on fungal decomposition of organic substrates common in boreal ecosystems, including cellulose, lignin, spruce wood, spruce needle litter, and moss litter. We added 0, 20, or 200 μg N to vials containing 200 mg substrate in factorial combination with five fungal species isolated from boreal soil, including an Ascomycete, a Zygomycete, and three Basidiomycetes. We hypothesized that N addition would increase CO₂ mineralization from the substrates, particularly those with low N concentrations. In addition we predicted that Basidiomycetes would be more effective decomposers than the other fungi, but would respond weakly or negatively to N additions. In support of the first hypothesis, cumulative CO₂ mineralization increased from 635 ± 117 to 806 + 108 μg C across all fungal species and substrates in response to 20 μg added N; however, there was no significant increase at the highest level of N addition. The positive effect of N addition was only significant on cellulose and wood substrates which contained very little N. We also observed clear differences in the substrate preferences of the fungal species. The Zygomycete mineralized little CO₂ from any of the substrates, while the Basidiomycetes mineralized all of the substrates except spruce needles. However, the Ascomycete (Penicillium) was surprisingly efficient at mineralizing spruce wood and was the only species that substantially mineralized spruce litter. The activities of β-glucosidase and N-acetyl-glucosaminidase were strongly correlated with cumulative respiration (r = 0.78 and 0.74, respectively), and Penicillium was particularly effective at producing these enzymes. On moss litter, the different fungal species produced enzymes that targeted different chemical components. Overall, our results suggest that fungal species specialize on different organic substrates, and only respond to N addition on low N substrates, such as wood. Furthermore, the response to N addition is non-linear, with the greatest substrate mineralization at intermediate N levels.     

Effects of nitrification inhibitors on transformations of urea nitrogen in soils

The effects of three patented nitrification inhibitors on transformations of urea N in soils were studied by determining the effects of these compounds (10 μg/g of soil) on urea hydrolysis, ammonia volatilization. and production of ammonium, nitrite, and nitrate in soils incubated under aerobic conditions (30°C, 60% WHC) after treatment with urea (400 μg of urea N/g of soil). The inhibitors used (N-Serve, ATC, and CL-1580) had little, if any, effect on urea hydrolysis, but they retarded nitrification of the ammonium formed by urea hydrolysis and increased gaseous loss of urea N as ammonia. They also decreased the amount of (urea + exchangeable ammonium + nitrite + nitrate) — N found in urea-treated soils after various times.Two of the soils used accumulated substantial amounts of nitrite(> 160 μg of nitrite N/g of soil) when incubated under aerobic conditions after treatment with urea. Addition of nitrification inhibitors to these soils eliminated or substantially reduced nitrite accumulation and greatly retarded nitrate formation, but had little, if any, effect on the recovery of urea N as (urea + exchangeable ammonium + nitrite + nitrate + ammonia) — N after various times. This finding and other observations reported indicate that the “nitrogen deficits” observed in studies of urea N transformations in soils may not largely be due to gaseous loss of urea N through chemodenitrification and are at least partly due to volatilization and fixation of the ammonium formed by urea hydrolysis in soils. The work reported also indicates that N-Serve and other nitrification inhibitors may prove useful for reduction of the nitrite toxicity problems associated with the use of urea as a fertilizer but that application of such inhibitors in conjunction with fertilizer urea, when surface applied, may promote gaseous loss of urea N as ammonia.     

Impact of anthropogenic induced nitrogen input and liming on phosphorus leaching in forest soils

Phosphorus (P) is essential for sustainable forest growth, yet the impact of anthropogenic impacts on P leaching losses from forest soils is hardly known. We conducted an irrigation experiment with 128 mesocosms from three forest sites representing a gradient of resin extractable P of the A‐horizon. On each site we selected a Fagus sylvatica and a Picea abies managed subsite. We simulated ambient rain (AR), anthropogenic nitrogen input (NI) of 100 kg (ha · a)^?1 and forest liming (FL) with a dolomite input of 0.3 Mg (ha · a)^?1. Soil solution was extracted from the organic layer, 10 cm depth and 20 cm depth of the mesocosms, and analyzed for molybdate reactive phosphorus (MRP) and molybdate unreactive phosphorus (MUP). Additionally, we separated colloids from the soil solution using Asymmetric Field Flow Fractionation for assessing the colloidal fraction of total element concentrations. NI increased MRP and MUP concentrations for all plots with one exception, while FL decreased MRP and MUP with the exception of another plot. While the irrigation treatments had little impact on the P‐richest site, MRP and MUP concentrations changed strongly at the poorer sites. The colloidal fraction of P in the soil solution equaled 38–47% of the total P load. Nitrogen input and liming also affected the Fe, Al, Ca, and Corg contents of the colloidal fraction.     

酸雨对土壤有机碳氮潜在矿化的影响

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain （SAR） for 42 months compared to a control ofpH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg^-1 dry soil, net production of available N from 17.37 to 48.95 mg kg^-1 dry soil, and net production of NO3-N from 9.09 to 46.23 mg kg^-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher （P 〈 0.05） than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.     

Effects of soil,grass and legume root extracts on heterotrophic bacteria,nitrogen mineralization and nitrification in soil

The effects of root extracts of four grasses and two legumes and extracts of soils supporting these plants on the growth of five strains of heterotrophic soil bacteria, and on the rate of nitrogen mineralization and nitrification were measured in culture and in soil. All the root extracts inhibited the growth in culture of the five bacteria by 9–98 per cent. The legume-soil and one of the grass-soil extracts did not inhibit bacterial growth. Only two of the grass-soils, Andropogon lectorum and Pennisetum purpureum markedly inhibited the five bacteria. Incubation of soils with extracts of grass roots or grass-soil increased the rates of nitrogen mineralization and nitrification and incubation with legume root and soil extracts increased the rates of nitrogen mineralization and nitrification even further.     

Mineralization and nitrification in three Malaysian forest soils

Examination of three forest soils from Malaysia using the soil incubation technique suggests that nitrification was not inhibited in these oligotrophic soils. Nitrification rates were between 40 and 750 ngN produced g^?1 dry weight soil day^?1 of incubation. Addition of phenolic metabolites (tannic acid) and leaf filtrates from hill and lowland forest litter did not significantly inhibit nitrification. Addition of sucrose (1% w/w carbon source) decreased nitrification but not ammonification.     

外加氮源在Cd超标菜地上的应用效果

探讨外加氮源对Cd超标菜地不同叶菜吸收Cd及土壤Cd有效性的影响,以明确施氮对土壤Cd的影响效应,并试图对不同氮源的应用效果进行综合评价,为合理利用氮肥来降低叶菜Cd含量提供参考。在Cd含量为0.628 mg·kg?1的Cd超标菜地上,试验研究了氮用量水平为150 kg·hm?2时,4种氮肥(尿素、硝酸钙、硝酸铵、碳酸氢铵)对矮脚葵扇黑叶白菜(Brassica chinensis L.)和白梗尖叶苋菜(Amaranthus mangostanus L.)Cd含量、品质及土壤Cd有效性的效应。结果表明,田间条件下,与不施氮处理相比,4种氮肥均不同程度地增加了Cd超标菜地上2种叶菜产量,降低了其地上部和根系Cd含量。4种氮肥中,尿素对白梗尖叶苋菜的增产效果最好,增产幅度达47.5%;碳酸氢铵对葵扇黑叶白菜的增产效果最好,增幅达59.7%;硝酸钙降低2种叶菜地上部和根系Cd含量的效果均优于其他氮肥,该处理的白梗尖叶苋菜地上部和根系Cd含量分别比对照降低41.6%和24.1%,葵扇黑叶白菜降低32.2%和25.9%。4种氮源对2种叶菜地上部Cd吸收总量、NO3?-N、NO2?-N、维生素C及可溶性糖含量等的影响各异,对土壤p H和DTPA-Cd含量影响也不同。其中,硝酸铵处理的土壤p H分别比对照降低0.12和0.25个单位,而土壤DTPA-Cd含量则显著增加15.3%和14.6%;碳酸氢铵处理则呈相反变化趋势。综合评价结果显示,4种氮肥的综合加权平均值均高于对照处理,以硝酸钙相对最高,表明硝酸钙在Cd超标菜地上的综合应用效果相对最好。因此,在Cd超标土壤上,硝酸钙可作为优选氮源使用。     

不同施肥措施对稻田土壤氮矿化的影响

采集田间通过不同施肥处理的水稻土为研究对象,在室内采用淹水培养方法,研究不同施肥措施对水稻土氮矿化的影响。结果表明:与不施肥处理相比,施加氮肥和饼肥能提高土壤的氮矿化能力;与常规施氮处理相比,采用新型施肥措施,氮肥+木质素、一次施用的水稻缓释肥、氮肥+有机碳源均降低土壤的氮矿化作用,其中氮肥+有机碳源处理与常规施氮处理相比,土壤全氮增加了16.7%,但淹水培养期间土壤的氮矿化量却减少了18.5%,这一结果说明,采用这些新型施肥措施有利于增加土壤对氮的固持,降低氮素向环境损失的风险。     

Potential mineralization and nitrification in volcanic grassland soils in Chile

Abstract

A proportion of the nitrogen (N) applied to grasslands as organic or inorganic fertilizers can be lost to water courses as nitrate and to the atmosphere as nitrous and nitric oxides. Volcanic soils from Chile are not generally prone to leaching, possibly due to net immobilization of nitrate and/or ammonium, and/or due to inhibition of nitrification by either chemical or physical processes. In laboratory studies we found large mineralization potentials in soils from three different Chilean soils after 17 weeks of incubation, totalling 215 and 254 mg kg^?1 dry soil for two Andisols and 127 mg kg^?1 dry soil in an Ultisol. Nitrification occurred after a short period, and was lowest in the Ultisol. In addition, microbial analysis showed nitrifiers to be present in all three soils. Adsorption of ammonium was two-fold stronger than for nitrate, ranging from 29 to 180 kg N ha^?1. The highest potential for N adsorption in the 0–60 cm soil profile was with the Ultisol (398 kg N ha^?1), but was similar in both Andisols (193 and 172 kg N ha^?1, respectively). The combination of ammonium retention together with delayed nitrification could account for the low leaching rates in these soils.     

Effects of plants on net mineralization of nitrogen in forest soil microcosms

Summary The effects of plant roots on net N mineralization were examined by comparing soil microcosms with and without plants. Additionally, inorganic N amendments were used to test for competition for N between plants and microorganisms. Daily watering and the application of suction to microcosms eliminated the effects of transpiration on soil moisture content. Monthly litter collections reduced the influence of the aboveground portions of plants. Plants decreased net N mineralization by 23% during days 0–114 and then increased net mineralization by the same amount during days 144–124. Root-free soil collected from with-plant microcosms on day 244 evolved 24% more CO₂ in laboratory incubations than soil from without-plant microcosms. This indicates that plants had increased substrate availability to soil microorganisms. Inorganic N amendments had no significant effects on the microcosms or on laboratory soil incubations. Evidence is most consistent with the hypothesis that plant roots increased microbial activity due to the increased substrate availability. Different net N mineralization rates probably resulted from changes in the substrate C : N ratio.     

Nitrogen mineralization in boreal forest stands of isle royale,Northern Michigan

The correlation of soil temperature and moisture with inorganic N concentrations and net mineralization beneath major species types in mature boreal and northern hardwood forests was examined over a two year period. Soils beneath species types where the canopy was dominated byBetula papyrifera, Picea glauca, Alnus rugosa or, in northern hardwoods,Acer saccharum were studied. Net NO₃ ^? mineralization varied by species type and net total inorganic nitrogen (N) mineralization varied by month and the interaction of species type with month. Soil NO₃ ^? concentration and NO₃ ^? mineralization were correlated for spruce, and inversely correlated for alder and maple. Soil NH₄ ⁺ concentration and NH₄ ⁺ mineralization were inversely correlated for alder and maple. In laboratory temperature and moisture treatments of birch, spruce and maple soils, NH₄ ⁺ and total inorganic N-mineralization increased with temperature. The response to moisture was most evident for NO₃ ^? mineralization in maple soils.     

Effects of soil texture and structure on carbon and nitrogen mineralization in grassland soils

Summary The hypotheses that disruption of soil structure increases mineralization rates in loams and clays more than in sandy soils and that this increase can be used to estimate the fraction of physically protected organic matter were tested. C and N mineralization was measured in undisturbed, and in finely and coarsely sieved moist or dried/remoistened soil. Fine sieving caused a temporary increase in mineralization. The relative increase in mineralization was much larger in loams and clays than in sandy soils and much larger for N than for C. The combination of remoistening and sieving of the soil gave a further increase in the mineralization flush after the disturbance. Again, the extra flush was larger in loams and clays than in sandy soils, and larger for N than for C. In loams and clays, small pores constituted a higher percentage of the total pore space than in sandy soils. The fraction of small pores explained more than 50% of the variation in the N mineralization rate between soils. There was also a good correlation between the small-pore fraction and the relative increase in N mineralization with fine sieving. For C, these relations were not clear. It is suggested that a large part of the organic matter that was present in the small pores could not be reached by microorganisms, and was therefore physically protected against decomposition. Fine sieving exposed part of this fraction to decomposition. This physically protected organic matter had a lower C: N ratio than the rest of the soil organic matter. The increase in N mineralization after fine sieving can be regarded as a measure of physically protected organic matter.