马占相思近熟林养分循环研究

研究了广西高峰林场11年生（近熟林）马占相思人工林10种营养元素生物循环的特点。结果表明：（1）马占相思不同器官营养元素含量以树叶（叶状柄）为最高,树干最低;各器官中大量营养元素含量以N最高,其次是Ca或K,然后是Mg,P最低;微量元素含量则以Mn和Fe最高,其次是Zn和B,Cu最低;（2）林分营养元素贮存量为2609．28kg／hm^2,乔木层、灌木层、草本层和凋落物层分别占83．95％、4．43％、1．71％和9．91％,林木中不同器官营养元素贮存量排序为干材〉树枝〉树根〉干皮〉树叶．（3）林分年吸收量、归还量、存留量分别为388．47、195．51和192．96kg／（hm^2·a）,10种元素的循环系数为0．39～0．78,循环速率依次为Mn〉Zn〉Mg〉P〉Ca〉Fe〉N〉Cu〉K〉B。     

马占相思人工林不同年龄阶段水源涵养功能及其价值研究

对马占相思人工林3个不同年龄阶段（4，7a和11a）的林冠层、林下植被层、枯枝落叶层、林地土壤持水量和渗透性能以及它们随林分年龄的变化规律进行了比较分析。研究结果表明，林分地上部分持水量的大小顺序为11a生（52．86t／hm^2）〉7a生（41．90t／hm^2）〉4a生（25．78t／hm^2），其趋势是随林龄的增大而增加，林地土壤（0～40cm）持水量和渗透性能也有相同的变化趋势；4，7a和11a林分的总持水量即地上部分与林地土壤的持水总量分别为2048．8，2200．3，2313．3t／hm^2，林分水源涵养总价值分别为1372．70，1474．42元／hm^2和1549．91元／hm^2。因此，马占相思人工林对改善土壤结构、提高水源涵养功能都有良好的作用。     

Carbon-iron coupling reduced N2O emissions via promoting the conversion to N2 in paddy soils

The influence of redox reactions involving carbon-iron coupling (organic carbon and iron oxides) on nitrous oxide (N₂O) production in paddy soils remains poorly understood. In this study, two microcosm experiments were conducted to investigate the effects of carbon-iron coupling on N₂O emissions, and the underlying mechanisms were verified using quantitative denitrification functional genes (nirS, nirK, nosZI and nosZII) and high-throughput sequencing. The results showed that ferrihydrite (iron) significantly promoted N₂O-N emissions (p < 0.05) after adding ammonium nitrogen, while glucose (carbon) significantly inhibited N₂O-N emissions (p < 0.05). Carbon-iron coupling significantly decreased N₂O-N emissions (p < 0.05) but did not affect soil total nitrogen loss and increased nitrogen (N₂) emissions. After adding high concentrations of acetylene (10% C₂H₂), the N₂O-N emissions from carbon-iron coupling treatment increased significantly from 6.4 to 11.9 mg N kg⁻¹ (p < 0.05), which confirmed that the carbon-iron coupling reduced the N₂O emissions by promoting the conversion of N₂O to N₂. The mechanisms behind carbon-iron coupling promoting complete denitrification and reducing N₂O emissions were attributed to glucose promoting iron reduction and carbon-iron coupling enhancing the abundance of nosZI (42.7%) and nosZII (16.6%).     

马占相思木材解剖特性研究

对采自广西国营高峰林场9.5年生的马占相思木材解剖构造特征进行研究。结果表明:心边材区别明显,心材率高,全树平均55.6%;生材绝对含水率为96.9%;树皮率为12.99%;生长轮宽度平均为22.82mm。木纤维长度、直径、双壁厚、长径比均随着树龄的增加而增加,其平均值分别为891.2μm、20.34μm、6.05μm和46.0。微纤丝角随着树龄的增大变化不大,平均值为9.8°。木纤维比量、木射线比量、导管比量、薄壁组织比量的平均值分别为:70.2%、14.3%、9.9%、5.6%,各组织比量随着树龄的增加变化较小。     

Tea plantation destroys soil retention of NO3− and increases N2O emissions in subtropical China

The intensive conversion from woodland to tea plantation in subtropical China might significantly change the potential supply processes and cycling of inorganic Nitrogen (N). However, few studies have been conducted to investigate the internal N transformations involved in the production and consumption of inorganic N and N₂O emissions in subtropical soils under tea plantations. In a ¹⁵N tracing experiment, nine tea fields with different plantation ages (1-y, 5-y and 30-y) and three adjacent woodlands were sampled to investigate changes in soil gross N transformation rates in humid subtropical China. Conversion of woodland to tea plantation significantly altered soil gross N transformation rates. The mineralization rate (M_Norg) was much lower in soils under tea plantation (0.53–0.75 mg N kg⁻¹ d⁻¹) than in soil sampled from woodland (1.71 mg N kg⁻¹ d⁻¹), while the biological inorganic N supply (INS), defined as the sum of organic N mineralized into NH₄⁺ (M_Norg) and heterotrophic nitrification (O_Nrec), was not significantly different between soils under woodland and tea plantation, apart from soil under 30-y tea plantation which had the largest INS. Interestingly, the contribution of O_Nrec to INS increased from 19.6% in soil under woodland to 65.0–82.4% in tea-planted soils, suggesting O_Nrec is the dominant process producing inorganic N in tea-planted soils. Meanwhile, the conversion from woodland to tea plantation destroyed soil NO₃⁻ retention by increasing O_Nrec, autotrophic nitrification (O_NH4) and abiotic release of stored NO₃⁻ while decreasing microbial NO₃⁻ immobilization (I_NO3), resulting in greater NO₃⁻ production in soil. In addition, long-term tea plantation significantly enhanced the potential release of N₂O. Soil C/N was positively correlated with M_Norg and I_NO3, suggesting that an increase in soil C/N from added organic materials (e.g. rice hull) is likely to reduce the increased production of NO₃⁻ in the soils under tea plantation.     

农田土壤N2O和NO排放的影响因素及其作用机制

农田土壤作为N2O和NO的重要排放源而备受关注。硝化和反硝化是土壤N2O和NO产生的两个主要微生物过程,环境因子和农田管理措施等因素强烈影响着这两个过程以及N2O和NO的排放。本文重点论述了土壤水热状况、土壤质地、pH、肥料施用、耕作措施变更等关键性影响因素对农田土壤N2O和NO排放的影响及其影响机制。     

表面风速和模拟降水对奶牛粪便堆放过程中N2O排放的影响

奶牛场粪便的自然堆放过程中会造成大量的温室气体排放,排放过程和排放量受表面风速和自然降水等环境因素的影响显著。该文针对中国常用的奶牛粪便管理方式,采用动态箱法研究了不同表面风速(0.5、0.8、1.2、1.6 m/s)和模拟降水(降水量9.9 mm)对奶牛粪便自然堆放过程中典型的温室气体氧化亚氮(N2O)排放的影响。结果表明,在0.5~1.2 m/s风速范围内,奶牛粪便自然堆放过程中的N2O排放量随风速升高逐渐增加,1.2 m/s达到最大值,且不同风速下N2O的排放量存在显著差异。模拟降水后N2O排放量在短时间内急剧升高,之后迅速下降至降水前的排放水平,整个过程持续约10 h。由于降低了二氧化碳(CO2)和甲烷(CH4)的排放,与降水前一天相比2次降水分别降低了12.9%和10.9%的温室气体排放量。     

Effects of soil type and nitrate concentration on denitrification products (N2O and N2) under flooded conditions in laboratory microcosms

Abstract

Denitrification products nitrous oxide ((N₂O) and nitrogen (N₂)) were measured in three flooded soils (paddy soil from Vietnam, PV; mangrove soil from Vietnam, MV; paddy soil from Japan, PJ) with different nitrate (NO₃^–) concentrations. Closed incubation experiments were conducted in 100-mL bottles for 7 d at 25°C. Each bottle contained 2 g of air-dried soil and 25 mL solution with NO₃^– (concentration 0, 5 or 10 mg N L^?1) with or without acetylene (C₂H₂). The N₂O + N₂ emissions were estimated by the C₂H₂ inhibition method. Results showed that N₂O + N₂ emissions for 7 d were positively correlated with those of NO₃^– removal from solution with C₂H₂ (R² = 0.9872), indicating that most removed NO₃^– was transformed to N₂O and N₂ by denitrification. In PJ soil, N₂O and N₂ emissions were increased significantly (P < 0.05) by the addition of greater NO₃^– concentrations. However, N₂O and N₂ emissions from PV and MV soils were increased by the addition of 0 to 5 mg N L^?1, but not by 5 to 10 mg N L^?1. At 10 mg N L^?1, N₂ emissions for 7 d were greater in PJ soil (pH 7.0) than in PV (pH 5.8) or MV (pH 4.3) soils, while N₂O emissions were higher in PV and MV soils than in PJ soil. In MV soil, N₂O was the main product throughout the experiment. In conclusion, NO₃^– concentration and soil pH affected N₂O and N₂ emissions from three flooded soils.     

Time-lagged induction of N2O emission and its trade-off with NO emission from a nitrogen fertilized Andisol

Abstract

To understand the influence of basal application of N fertilizer on nitrification potential and N₂O and NO emissions, four soil samples were collected from an upland Andisol field just before (sample 1) and 4 (sample 2), 36 (sample 3) and 72 (sample 4) days after the basal application of N fertilizer during the Chinese cabbage growing season from 12 September to 30 November 2005. The potentials of N₂O production and nitrification of the soils were determined using a ¹⁵N tracer technique and the soils were incubated for 25 days at 25°C and 60% water-filled pore space (WFPS). The results revealed that as much as 84–97% N₂O and almost all NO were produced by nitrification. The ¹⁵N₂O emission peak occurred approximately 350 h after the beginning of incubation for samples 1 and 2, but just 48 h later in samples 3 and 4. Total ¹⁵N₂O emission during the 25-day incubation of samples 3 and 4 ranged from 190 to 198 µg N kg^?1 soil, which was significantly higher than the 99–108 µg N kg^?1 soil recorded in samples 1 and 2. Basal application of N fertilizer did not immediately increase the nitrification potential and the ratio of N₂O to N added, but did dramatically increase the nitrification potential and the ratio of N₂O to N added as (¹⁵NH₄)₂SO₄ 36–72 days after the basal N fertilizer was added. In contrast, NO emission was negatively correlated with nitrification potential and total N₂O emission. As a result, a trade-off relationship between total NO and N₂O emissions was identified. The results indicated that there was a time-lagged induction of the change of N turnover in the soil, which was possibly caused by slow population growth of the nitrifiers and/or a slow shift in the microbial community in the soil.     

A new approach to enhance growth and nodulation of Acacia mangium through aeroponic culture

This work was designed to determine whether a plant culture method on non-solid media could be used as an alternative for inoculation of Acacia mangium with selected strains of Bradyrhizobium spp. A. mangium seedlings were grown and inoculated with Bradyrhizobium strain Aust13c and strain Tel2 in hydroponics, aeroponics and sand. Aeroponics was found to be the best system of the three, allowing the production of tree saplings 1 m in height after only 4 months in culture. Moreover, compared to plants grown in liquid or sand media, aeroponically grown saplings inoculated with Bradyrhizobium spp. developed a very high number of small nodules distributed all along the root system, resulting in an increase in nitrogen and chlorophyll content in plant tissues. We propose aeroponics as an alternative method to classical soil inoculation procedures for the production of hypernodulated legume tree saplings. Received: 18 July 1996     

Effect of different biochar and fertilizer types on N2O and NO emissions

The use of biochar as soil improver and climate change mitigation strategy has gained much attention, although at present the effects of biochar on soil properties and greenhouse gas emissions are not completely understood. The objective of our incubation study was to investigate biochar's effect on N₂O and NO emissions from an agricultural Luvisol upon fertilizer (urea, NH₄Cl or KNO₃) application. Seven biochar types were used, which were produced from four different feedstocks pyrolyzed at various temperatures. At the end of the experiment, after 14 days of incubation, soil nitrate concentrations were decreased upon biochar addition in all fertilizer treatments by 6–16%. Biochar application decreased both cumulative N₂O (52–84%) and NO (47–67%) emissions compared to a corresponding treatment without biochar after urea and nitrate fertilizer application, and only NO emissions after ammonium application. N₂O emissions were more decreased at high compared to low pyrolysis temperature.Several hypotheses for our observations exist, which were assessed against current literature and discussed thoroughly. In our study, the decreased N₂O and NO emissions are expected to be mediated by multiple interacting phenomena such as stimulated NH₃ volatilization, microbial N immobilization, non-electrostatic sorption of NH₄⁺ and NO₃⁻, and biochar pH effects.     

Combined effects of nitrogen deposition and biochar application on emissions of N2O,CO2 and NH3 from agricultural and forest soils

Abstract

Both nitrogen (N) deposition and biochar can affect the emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and ammonia (NH₃) from different soils. Here, we have established a simulated wet N deposition experiment to investigate the effects of N deposition and biochar addition on N₂O and CO₂ emissions and NH₃ volatilization from agricultural and forest soils. Repacked soil columns were subjected to six N deposition events over a 1-year period. N was applied at rates of 0 (N0), 60 (N60), and 120 (N120) kg Nh a^?1 yr^?1 without or with biochar (0 and 30 t ha^?1 yr^?1). For agricultural soil, adding N increased cumulative N₂O emissions by 29.8% and 99.1% (p < 0.05) from the N60 and N120 treatments, respectively as compared to without N treatments, and N120 emitted 53.4% more (p < 0.05) N₂O than the N60 treatment; NH₃ volatilization increased by 33.6% and 91.9% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 43.6% more (p < 0.05) NH₃ than N60; cumulative CO₂ emissions were not influenced by N addition. For forest soil, adding N significantly increased cumulative N₂O emissions by 141.2% (p < 0.05) and 323.0% (p < 0.05) from N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 75.4% more (p < 0.05) N₂O than N60; NH₃ volatilization increased by 39.0% (p < 0.05) and 56.1% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and there was no obvious difference between N120 and N60 treatments; cumulative CO₂ emissions were not influenced by N addition. Biochar amendment significantly (p < 0.05) decreased cumulative N₂O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively, and increased CO₂ emissions slightly by 7.2% and NH₃ volatilization obviously by 21.0% in the agricultural soil, while significantly decreasing CO₂ emissions by 31.5% and NH₃ volatilization by 22.5% in the forest soil. These results suggest that N deposition would strengthen N₂O and NH₃ emissions and have no effect on CO₂ emissions in both soils, and treatments receiving the higher N rate at N120 emitted obviously more N₂O and NH₃ than the lower rate at N60. Under the simulated N deposition circumstances, biochar incorporation suppressed N₂O emissions in both soils, and produced contrasting effects on CO₂ and NH₃ emissions, being enhanced in the agricultural soil while suppressed in the forest soil.     

Variability of CO2 and N2O emissions during freeze‐thaw cycles: results of model experiments on undisturbed forest‐soil cores

The amounts of N₂O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N₂O emissions. However, quantitative information on the N₂O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO₂ and N₂O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO₂ emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N₂O emissions during thawing differed considerably. Large N₂O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N₂O emission of 1200 μg N m^–2 h^–1 and a cumulative emission of 0.15 g N m^–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N₂O‐N m^–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N₂O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m^–2 in the two thawing periods) with a maximum emission of 150 μg N m^–2 h^–1 while insignificant N₂O emissions were found on the silty soil under spruce (0.2 mg N m^–2 in the two thawing periods). The cumulative N₂O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N₂O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N₂O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer.     

Lime-nitrogen application reduces N2O emission from a vegetable field with imperfectly-drained sandy clay-loam soil

Abstract

We studied the effect of lime-nitrogen (calcium cyanamide, CaCN₂) application on the emission of nitrous oxide (N₂O) from a vegetable field with imperfectly-drained sandy clay-loam soil. Lime-nitrogen acts as both a pesticide and a fertilizer. During the decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed, and as a result lime-nitrogen application may mitigate N₂O emission from the soil. The study design consisted of three different nitrogen-application treatments in field plots with a randomized block design. The nitrogen application treatments were: CF (chemical fertilizer), LN (all nitrogen fertilizer applied as lime-nitrogen), and CFD (chemical fertilizer containing DCD). Soil nitrification activity was lower in the LN and CFD plots than in the CF plots, and nitrification was inhibited for a longer period in the LN plots than in the CFD plots. In the LN plots, N₂O emission was lower than those of other treatments from 20 to 40 days after fertilization, a period when large peaks of N₂O emission were observed after rainfall in the CF and CFD plots. Cumulative N₂O emission over 63 days in the CF plots (mean ± standard deviation: 30.2 ± 14.4 mg N₂O m^?2) and CFD plots (24.3 ± 10.8 mg N₂O m^?2) was significantly higher than that in the LN plots (10.7 ± 1.2 mg N₂O m^?2; P < 0.05). Our results suggested that lime-nitrogen application decreased N₂O emission by inhibiting both nitrification and denitrification.     

Formation of hybrid N2O in a suspended soil due to co‐denitrification of NH2OH

A few studies have shown that amine compounds (e.g., hydroxylamine) can be co‐metabolically introduced into the reaction pathway of denitrification. During this microbial process, the N atom of the amine species is bound to a N atom of nitrite. In case of hydroxylamine, this concomitant reaction ultimately results in the formation of hybrid N₂O. Due to its co‐metabolic character the process has been termed co‐denitrification. Hybrid N₂O production during co‐denitrification has been proven to occur in prokaryotic (e.g., Pseudomonas sp.) as well as eukaryotic (e.g., Fusarium sp.) species. Many of them are already well‐known as common denitrifiers. However, until now no clear evidence has been provided to show that N₂O production by co‐denitrification really takes place in a soil. In the present study, a formation of hybrid N₂O was revealed by an adapted ¹⁵N‐tracer model, when both hydroxylamine and ¹⁵N‐nitrate were applied (mol ratio 10:1) to an anaerobically incubated soil suspension from a Haplic Chernozem. The presence of hybrid N₂O was also indicated by a novel characteristic factor (R_binom) developed for a hybrid‐N‐N‐gas detection. By contrast, no hybrid N₂O was found when either an autoclaved soil suspension, only nitrate or only hydroxylamine was used. Thus, it appears that hybrid‐N₂O formation occurred due to co‐denitrification of hydroxylamine. Hence, this is the first study which demonstrates hybrid‐N₂O production by co‐denitrification beyond a microbial species level. The ¹⁵N‐tracer model revealed that under the given experimental conditions N₂O production by co‐denitrification prevailed against N₂O from denitrification and abiotic hydroxylamine decomposition. In addition, a formation of hybrid N₂ was also calculated by the model. However, the experimental results lead to the conclusion that it was most likely caused by a reduction of hybrid N₂O due to conventional denitrification.     

Effects of N placement,carbon distribution and temperature on N2O emissions in clay loam and loamy sand soils

Changes in the profile distribution of soil C stocks for conventional versus no‐tillage can affect N₂O losses. Uncertainty remains whether deep N placement into a wetter layer in humid areas would affect N₂O losses. This study evaluated the effects of soil carbon profile distribution (inverted, normal), depth of nitrogen placement (5 cm, 15 cm), temperature (10, 20 and 30 °C) and soil texture (clay loam, loamy sand) on N₂O emissions from soil cores in a 216‐h incubation after simulated rainfall. N₂O losses were larger from the clay loam than from the loamy sand, and cumulative N₂O emissions from the inverted profile, with greater C levels at depth, were more than those from the profile with more C near the upper surface. Cumulative N₂O losses from the inverted clay loam profile with deep N placement (1.16 mg N per kg dry soil; 0.71% of applied N) on average were almost double those in the loamy sand (0.62 mg N per kg dry soil; 0.42%). The smallest N₂O losses were measured from the profiles with more C close to the upper surface with a shallow placement of N for the clay loam (0.19 mg N per kg dry soil; 0.12%) and loamy sand (0.33 mg N per kg dry soil; 0.23%). An exponential relationship between N₂O fluxes and temperature was measured. We conclude that large N₂O losses may occur under the combination of greater soil C content at deeper layers (ploughed soils) and moist profiles after N application (humid regions). Deep N placement appears to aggravate rather than ameliorate these concerns.     

Effect of mineral nitrogen fertilizer forms on N2O emissions from arable soils in winter wheat production

Nitrogen fertilizers are supposed to be a major source of nitrous oxide (N₂O) emissions from arable soils. The objective of this study was to compare the effect of N forms on N₂O emissions from arable fields cropped with winter wheat (Triticum aestivum L.). In three field trials in North‐West Germany (two trials in 2011/2012, one trial in 2012/2013), direct N₂O emissions during a one‐year measurement period, starting after application of either urea, ammonium sulfate (AS) or calcium ammonium nitrate (CAN), were compared at an application rate of 220 kg N ha^?1. During the growth season (March to August) of winter wheat, N₂O emission rates were significantly higher in all three field experiments and in all treatments receiving N fertilizer than from the non‐fertilized treatments (control). At two of the three sites, cumulative N₂O emissions from N fertilizer decreased in the order of urea > AS > CAN, with emissions ranging from 522–617 g N ha^?1 (0.24–0.28% of applied fertilizer) for urea, 368–554 g N ha^?1 (0.17–0.25%) for AS, and 242–264 g N ha^?1 (0.11–0.12%) for CAN during March to August. These results suggest that mineral nitrogen forms can differ in N₂O emissions during the growth period of winter wheat. Strong variations in the seasonal dynamics of N₂O emissions between sites were observed which could partly be related to weather events (e.g., precipitation). Between harvest and the following spring (post‐harvest period) no significant differences in N₂O emissions between fertilized and non‐fertilized treatments were detected on two of three fields. Only on one site post‐harvest emissions from the AS treatment were significantly higher than all other fertilizer forms as well as compared to the control treatment. The cumulative one‐year emissions varied depending on fertilizer form across the three field sites from 0.05% to 0.51% with one exception at one field site (AS: 0.94%). The calculated overall fertilizer induced emission averaged for the three fields was 0.38% which was only about 1/3 of the IPCC default value of 1.0%.