共查询到20条相似文献,搜索用时 15 毫秒
1.
《Communications in Soil Science and Plant Analysis》2012,43(1):72-87
Recycling organic waste in agricultural soils is a valid solution. We performed short‐term experiments to investigate the fate of urban sludge and composts, in mine spoils, cultivated or uncultivated, and reclaimed soils located in Florence and Milan, Italy. The samples, either treated or untreated, were fractionated by density into light (<1.63 Mg m?3) and heavy (>1.63 Mg m?3) fractions. The fractions were analyzed for total carbon (C) and nitrogen (N) contents and for δ 13C and δ 15N isotopes, and they were characterized by 13C NMR spectroscopy. Treatment increased the heavy fraction. The addition of sludge in the Florence area acts in synergy with the cultivation, increasing the light fraction (LF). In the Milan area, the LF tends to be decomposed and apparently transformed into HF. The addition of amendments or cultivation enhances the decomposition with release of carbon dioxide. For future research, we suggest lengthening the time of the experiments to integrate climatic variations. 相似文献
2.
后续施肥措施改变对水稻土团聚体有机碳分布及其周转的影响 总被引:5,自引:1,他引:5
利用一个长达30 a且已进行适当变更的长期定位施肥试验,改施C4玉米秸秆以替代C3水稻秸秆,运用δ~(13)C自然丰度方法,研究长期施用高量有机肥、常量有机肥、化肥及当其施肥措施改变(化肥改为常量有机肥、常量有机肥改为高量有机肥、高量有机肥改为化肥、常量有机肥改为化肥)3 a后对红壤性水稻土团聚体有机碳分布及其周转的影响。结果表明:在所有施肥处理条件下红壤性水稻土团聚体分布以大团聚体(0.25 mm)为主,占72.48%~86.33%。与施用化肥30 a相比,长期施用常量有机肥、高量有机肥有利于促进红壤性水稻土粗大团聚体(2 mm)的形成,并提高团聚体平均重量直径(MWD)。团聚体中有机碳含量随着团聚体粒径的增大而增大,大团聚体更有利于有机碳富集。长期常量有机肥、高量有机肥处理下红壤性水稻土中有机碳主要贮存在粗大团聚体(2 mm)中,而长期化肥处理下以细大团聚体(2~0.25 mm)对土壤有机碳贡献率最高。外源新碳施入量越多,全土和各粒径团聚体新碳含量越高,且外源新碳主要分布在大团聚中。在后续施肥措施改变3年后,增加有机肥施入量(化改常、常改高)2 mm粗大团聚体、MWD、全土及各粒径团聚体中有机碳含量将分别显著提高7.08%~73.13%、5.38%~44.22%、14.53%~38.50%、0.70%~35.86%;而减少有机肥施入量(高改化、常改化)则与之相反,分别降低28.17%~43.20%、21.17%~31.54%、17.54%~27.30%、11.49%~29.77%。因此,在我国南方红壤性稻作区的农业生产过程中应继续或加大施用有机肥,从而进一步维持或改善土壤结构,提高土壤有机碳含量。 相似文献
3.
Kinetic Parameters of Gross N Mineralization of Peat Soils as Related to the Composition of Soil Organic Matter 总被引:1,自引:0,他引:1
Bentio Heru Purwanto Akira Watanabe Jong Foh Shoon Ken-ichi Kakuda Ho Ando 《Soil Science and Plant Nutrition》2005,51(1):109-115
Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using 13 C CPMAS NMR. Mineralization potential ( N 0 ), apparent activation energy ( E a ), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg−1 , 281–8,181 J mol−1 , and 0.009–0.020 d−1 , respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by 13 C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates. 相似文献
4.
Yasmmin Tadeu Costa Nilton Curi Geraldo César de Oliveira Luiz Roberto Guimarães Guilherme 《Communications in Soil Science and Plant Analysis》2019,50(6):673-681
Many factors can influence the results obtained by portable X-ray fluorescence analysis (pXRF). The effect of soil organic matter on pXRF results is not satisfactory understood. Thus, we conducted this study to verify the effect of organic matter removal on oxide determination by pXRF in Oxisols. To obtain soil material with different organic matter contents and maintaining the same elemental composition from soil minerals, six contrasting Oxisols were heated in a muffle furnace for 30 min at the following temperatures (°C): 100; 200; 300; 400; 500 and 600. After heating, the soil samples were scanned using a pXRF Bruker® S1 Titan LE model (Dual Soil mode) for 60 s and the contents of SiO2, Al2O3, Fe2O3, TiO2, P2O5, and MnO were recorded. The soil organic matter presence underestimated the pXRF results for lightest oxides (Si and Al) compared to heaviest oxides (Fe, Ti, and Mn). These oxides are important for tropical soils classification and for many soil-related studies and pXRF technology has been a useful tool for soil chemical characterization. Our findings contribute to more suitable use of pXRF highlighting the possible effect of organic matter. 相似文献
5.
María del Mar Montiel‐Rozas Marco Panettieri Paula Madejn Engracia Madejn 《Land Degradation \u0026amp; Development》2016,27(3):620-629
The study of different natural carbon sinks has become especially important because of climate change effects. The restoration of contaminated areas can be an ideal strategy for carbon sequestration. The studied area was affected by toxic Aznalcóllar mine spill in 1998. Restoration process of the contaminated area was based, mainly, on the use of two organic amendments: leonardite (LE) and biosolid compost (BC). The objective of this study was to verify whether the application of these amendments promotes the long‐term carbon sequestration in this soil. Five treatments were established: untreated control, biosolid compost (doses 4 and 2) and leonardite (doses 4 and 2). The addition of amendments implied an improvement in soil quality that was directly related to the amendment dose: decrease in bulk density, increase in pH, higher respiration rates and an improvement in the stratification ratio. Dose‐dependent changes in the molecular composition of soil organic matter were shown by nuclear magnetic resonance analysis. Both amendments promoted carbon retention, although because of the low mineralization rates of soil organic matter in LE treatments, the carbon storage was higher. The dosage effect on the carbon balance was more important in LE treatments, whereas in the BC treatments, the balance was similar for both doses. Our findings suggest that LE4 significantly increased the total organic carbon and it was the most suitable treatment for long‐term carbon storage, because of its molecular composition rich in relatively stable aromatic and lignin‐derived compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
《Communications in Soil Science and Plant Analysis》2012,43(7-8):1295-1321
The potential of Nostoc 9v for improving the nitrogen (N)2–fixing capacity and nutrient status of semi‐arid soils from Tanzania, Zimbabwe, and South Africa was studied in a laboratory experiment. Nostoc 9v was inoculated on nonsterilized and sterilized soils. Inoculum rates were 2.5 mg dry biomass g?1 soil and 5 mg dry biomass g?1 soil. The soils were incubated for 3 months at 27 °C under 22 W m2 illumination with a photoperiod of 16 h light and 8 h dark. The moisture was maintained at 60% of field capacity. In all soils, Nostoc 9v proliferated and colonized the soil surfaces very quickly and was tolerant to acidity and low nutrient availability. Cyanobacteria promoted soil N2 fixation and had a pronounced effect on total soil organic carbon (SOC), which increased by 30–100%. Total N also increased, but the enrichment was, in most soils, comparatively lower than for carbon (C). Nitrate and ammonium concentrations, in contrast, decreased in all the soils studied. Increases in the concentration of available macronutrients were produced in most soils and treatments, ranging from 3 to 20 mg phosphorus (P) kg?1 soil, from 5 to 58 mg potassium (K) kg?1 soil, from 4 to 285 mg calcium (Ca) kg?1, and from 12 to 90 mg magnesium (Mg) kg?1 soil. Positive effects on the levels of available manganese (Mn) and zinc (Zn) were also observed. 相似文献
7.
Forest soils contain about 30% of terrestrial carbon (C) and so knowledge of the influence of forest management on stability of soil C pools is important for understanding the global C cycle. Here we present the changes of soil C pools in the 0-5 cm layer in two second-rotation Pinus radiata (D.Don) plantations which were subjected to three contrasting harvest residue management treatments in New Zealand. These treatments included whole-tree harvest plus forest floor removal (defined as forest floor removal hereafter), whole-tree, and stem-only harvest. Soil samples were collected 5, 10 and 15 years after tree planting at Kinleith Forest (on sandy loam soils) and 4, 12 and 20 years after tree planting at Woodhill Forest (on sandy soils). These soils were then physically divided into light (labile) and heavy (stable) pools based on density fractionation (1.70 g cm−3). At Woodhill, soil C mass in the heavy fraction was significantly greater in the whole-tree and stem-only harvest plots than the forest floor removal plots in all sampling years. At Kinleith, the soil C mass in the heavy fraction was also greater in the stem-only harvest plots than the forest floor removal plots at year 15. The larger stable soil C pools with increased residue return was supported by analyses of the chemical composition and plant biomarkers in the soil organic matter (SOM) heavy fractions using NMR and GC/MS. At Woodhill, alkyl C, cutin-, suberin- and lignin-derived C contents in the SOM heavy fraction were significantly greater in the whole-tree and stem-only harvest plots than in the forest floor removal plots in all sampling years. At Kinleith, alkyl C (year 15), cutin-derived C (year 5 and 15) and lignin-derived C (Year 5 and 10) contents in the SOM heavy fraction were significantly greater in stem-only harvest plots than in plots where the forest floor was removed. The analyses of plant C biomarkers and soil δ13C in the light and heavy fractions of SOM indicate that the increased stable soil C in the heavy fraction with increased residue return might be derived from a greater input of recalcitrant C in the residue substrate. 相似文献
8.
后续施肥措施改变对红壤性水稻土团聚体有机碳组分的影响 总被引:5,自引:1,他引:5
利用一个长达30年且已进行适当变更的长期定位施肥试验,采用物理方法对团聚体有机碳进行分组,并运用δ13 C自然丰度方法,研究长期施用高量有机肥、常量有机肥、化肥及当其施肥措施改变(化改常、常改高、高改化、常改化)3年后红壤性水稻土团聚体有机碳组分含量及其分布比例的变化规律,以期为调控稻田土壤肥力及红壤性水稻土有机碳库的管理提供理论依据。结果表明:与施用化肥30年相比,长期施用有机肥显著提高了红壤性水稻土团聚体总有机碳、粗游离态颗粒有机碳(cfPOC)、细游离态颗粒有机碳(ffPOC)、闭蓄态颗粒有机碳(oPOC)及矿物结合态有机碳(MmMOC)的含量,其中以游离态颗粒有机碳变幅最大,达67.5%~150.0%,对施肥最敏感,能较好地反映长期施肥下土壤有机碳库的变化。在后续施肥过程中,增加有机肥施入量(化改常、常改高)团聚体总有机碳、粗游离态颗粒有机碳(cfPOC)、细游离态颗粒有机碳(ffPOC)、闭蓄态颗粒有机碳(oPOC)及矿物结合态有机碳(MmMOC)含量将分别显著提高5.2%~15.5%,2.8%~40.2%,18.9%~43.9%,2.8%~17.6%,5.1%~8.2%;而减少有机肥施入量(高改化、常改化)则与之相反,分别降低15.8%~20.9%,12.6%~26.9%,24.6%~48.4%,19.9%~23.9%,4.9%~21.9%。在所有施肥处理条件下闭蓄态颗粒有机碳(oPOC)分布比例最低,为11.3%~13.4%;矿物结合态有机碳(MmMOC)分布比例最高,为50.4%~59.0%,是红壤性水稻土固存有机碳的主要形式。外源新碳施入量越多,大团聚体及其各有机碳组分的新碳含量越高,且45.6%~50.1%进入矿物结合态有机碳组分,34.1%~42.3%进入游离态颗粒有机碳组分,11.8%~18.0%进入闭蓄态颗粒有机碳组分。因此,在我国南方红壤性稻作区的农业生产过程中应继续或加大施用有机肥,从而进一步维持或提升土壤不同组分有机碳库。 相似文献
9.
《Communications in Soil Science and Plant Analysis》2012,43(15-16):2221-2249
The worldwide production of rice husk, a by‐product and agrowaste that causes serious environmental problems, may reach 116 million t y?1. The objectives of this study were (i) to determine the physicochemical changes of rice husk and its structural chemistry during composting using 13carbon nuclear magnetic resonance (13C NMR) and (ii) to determine the effect of the composted rice husk (CRH) on the properties of Oxisol and cocoa (Theobroma cacao L.) growth under glasshouse conditions. Results showed an active composting phase occurred at the first 53 days as revealed by high carbon dioxide (CO2)‐C (40–71 µg g?1 h?1) production, followed by a matured composting phase occurring at 54–116 days as revealed by decreasing in CO2‐C production (10 µg g?1 h?1). The active composting was accompanied by increases in electrical conductivity (EC), pH, ammonium (NH4 +), and nitrate (NO3), whereas during the matured composting phase, the EC and cation exchange capacity increased but pH, NH4 +, and NO3 ?1 decreased. The ash of the produced compost contains mainly calcium (Ca), potassium (K), sulfur (S), magnesium (Mg), and phosphorus (P) as essential nutrients. The CP/MAS 13C NMR spectra before and after various composting times indicated the dominance of sharp and well‐resolved signal peaks at O‐alkyl C and di‐O‐alkyl C regions (67–73%), which are characteristic of cellulose. The percentage of N‐alky/methoxyl was 23–26% whereas phenolic, carboxyl, and alkyl C types were less than 3% each. The application of the CRH to an Oxisol significantly increased soil pH and Ca, Mg, K, sodium (Na), and silicon (Si) ions of in situ soil solution but decreased the amounts of toxic ions [aluminum (Al), manganese (Mn), and iron (Fe)]. The CRH was found to increase cocoa growth up to 37%. 相似文献
10.
Keke Hua Zhibin Guo 《Acta Agriculturae Scandinavica, Section B - Plant Soil Science》2018,68(6):505-514
Current understanding of the effects of long-term application of various organic amendments on soil particulate organic matter (POM) storage and chemical stabilisation remains limited. Therefore, we collected soil samples from the soil profile (0–100?cm) under six treatments in a 31-year long-term fertilisation experiment: no fertiliser (CK), mineral fertilisers (NPK), mineral fertilisers plus 3.8 or 7.5?t?ha?1?year?1 (fresh base) the amount of wheat straw (1/2SNPK and SNPK) and mineral fertilisers plus swine or cattle manure (PMNPK and CMNPK). Long-term incorporation of wheat straw and livestock manure amendments significantly (p?<?0.05) increased crop yield and sustainable yield index, and POM storage compared with CK and NPK treatments. The mole ratios of H/C in the POM under organic amendment treatments significantly (p?<?0.05) decreased by 13.8% and 37.1%, respectively, compared with the NPK treatment. Similarly, solid state NMR spectroscopy showed that the O–alkyl carbon content of POM was greatly decreased, whereas aromatic carbon contents and alkyl to O–alkyl carbon ratios were substantially increased under PMNPK and CMNPK treatments. In conclusion, we recommend long-term livestock manure application as a preferred strategy for enhancing POM quantity and quality (chemical stability), and crop yield of vertisol soil in northern China. 相似文献
11.
在典型的干旱区新疆,选取沿海拔分布的4类草地,使用固态13C核磁共振技术与热分析技术研究了灌丛化对草地土壤有机碳(SOC)化学结构和热稳定性的影响。结果表明:灌丛间的芳香碳比例沿海拔从温性荒漠到山地草甸逐渐降低。在温性荒漠、温性草原化荒漠、温性荒漠草原和山地草甸,灌丛下烷基碳/烷氧碳的比值相对于灌丛间分别增加了0.10、0.09、0.03、0.21。低海拔的温性荒漠和温性草原化荒漠的热易分解SOC质量(较低温度下分解的SOC)与SOC总质量的比值(%Exo1)、SOC分解一半时的温度(TG-T50)和SOC在能量释放一半时对应的温度(DSC-T50)显著低于高海拔的温性荒漠草原和山地草甸。在草原化荒漠、荒漠草原和山地草甸中,灌丛下的%Exo1和DSC-T50均高于灌丛间,而TG-T50低于灌丛间。在温性荒漠,从灌丛间到灌丛下,低温时SOC燃烧释放出的能量占总燃烧能量(Q)的比例减小,而高温时SOC燃烧释放出的能量增加。本研究结果表明灌... 相似文献
12.
13.
《Communications in Soil Science and Plant Analysis》2012,43(19-20):2767-2778
Abstract A study was carried out in the Argentine Pampa. Plots under continuous maize and maize–wheat/soybean–soybean rotation were used. Three control plots on grassland with different undisturbed periods were also used. The objective was to show that C3 and C4 plants have a different effect on the quantity of carbon retained in the soil when different crop sequences are used. Total organic carbon was determined, and mass spectrometry techniques were used to assess the natural variation of the abundance of 13C and 12C to trace carbon fate in the soil. No differences were observed in the carbon stock at 90 cm deep across cultivated plots. Maize monoculture represented an important contribution to the soil organic matter when compared to the grassland areas, but the comparison through the initial δ13C from reference plots did not allow an assessment of the original soil carbon in the plot under rotation. 相似文献
14.
《Soil Science and Plant Nutrition》2013,59(3):328-336
Abstract In determining the soil and ecosystem carbon balance, it is necessary to distinguish between autotrophic respiration and heterotrophic respiration. We attempted to measure the contribution of CO2 emissions from plant roots (RRHI), from soil organic matter (RSOM), and from litter (RL) to CO2 emissions from the forest floor (soil respiration; RS) in a deciduous forest of oak (Quercus serrata Thunb.) and hornbeams (Carpinus laxiflora Sieb. et Zucc. Bl., Carpinus tschonoskii Maxim. and Carpinus japonica Bl.) on Andosols in Japan, using a 13C natural abundance technique. The 13C natural abundances of roots (δRHI), litter (δL) and SOM (δSOM) in the surface soil were ?28.9, ?30.1 and ?24.3‰, respectively. This means that the differences between δSOM and δRHI are large enough to calculate the contributions of RRHI, RSOM and RL to RS based on the mass balance of the CO2 isotope ratios. RRHI and RSOM had close relationships with soil temperature, and RL was influenced by soil temperature and moisture. In summer, under high soil temperatures, RRHI and RSOM were the predominant sources of RS and the proportion of RRHI to RSOM to RL was 51:44:5. In winter, RL was predominant and the proportion of RRHI to RSOM to RL was 20:11:69. The estimated annual emissions of RRHI, RSOM and RL were 1.45, 2.10 and 1.30 Mg C ha?1, respectively; thus, the proportion of RRHI to RSOM to RL was 30:43:27 on a whole-year basis. 相似文献
15.
《Communications in Soil Science and Plant Analysis》2012,43(5-6):787-796
Abstract Soil nitrogen (N) supply plays a dominant role in the N nutrition of wetland rice. Organic matter has been proposed as an index of soil N availability to wetland rice. This is based on the finding that mineralizable N produced under waterlogged conditions is related to soil organic carbon (C) and total N. The relationship between organic matter and mineralizable N is a prerequisite for determining the N requirement of wetland rice. However, no critical analysis of recent literature on organic matter–mineralizable N relationships has been made. This article evaluates current literature on the relationships of mineralizable N or ammonium N production with soil organic C in wetland rice soils. A number of studies with diverse wetland rice soils demonstrate a close relationship of N mineralized (ammonium‐N) under anaerobic conditions with organic C or total N. However, a few recent studies made on sites under long‐term intensive wetland rice cropping showed that strong positive relationships of mineralizable N with organic C or total N do not hold. Clearly, both quantity and quality of organic matter affect N mineralization in wetland rice soils. Future research is needed to clarify the role of quality of organic matter, especially its chemistry, as modified by the chemical environment of submerged soils, on the mineralization of organic N in wetland rice soils. 相似文献
16.
S. Paramananthan Pei-Xiong Lee Mum-Keng Wong E. Van Ranst R.A.J. Wüst J.R. Vijiandran 《Communications in Soil Science and Plant Analysis》2018,49(5):626-634
Organic soils or Histosols or peats as they are commonly referred to, are characterized by the presence of large amounts of organic soil materials (OSM), which is commonly quantified by the Walkley and Black (1934) (WB) method to determine the soil organic matter (SOM) using a correction factor of 1.724. SOM of Histosols is also identified through a combustion (loss on ignition, LOI) or elemental C-analysis (with a carbon-nitrogen-sulfur (CNS) analyzer with combustion and gas density detector). These methods were established using temperate and boreal peat deposits and here we demonstrate that tropical peat deposits require a modified approach. Typical SE-Asian tropical lowland peat pedons from rain forest and oil palm settings were sampled and the material analysed using a CNS analyzer, WB-C and LOI. The ratios for LOI:CNS-C for the 20 samples yielded values between 2.00–3.09 with a mean of 2.50 while the LOI:WB-C ratio yielded values from 1.75 to 2.58 with a mean of 1.94. A comparison of these values for topsoils and subsoils showed mean ratios (LOI:WB-C) of 1.94 and 1.89 for topsoils and subsoils, respectively. The forest samples had higher LOI:WB-C ratios than the subsoils from oil palm settings (1.94 vs 1.84). These values suggest that the standard factor of 1.724 to correct OSM to SOM for tropical soils is untenable. The values to convert CNS and WB-C values of tropical topsoils/subsoils to SOM or LOI should be 2.5 or 1.9, respectively. Our results indicate a significant difference in the soil organic carbon (SOC) of tropical lowland peats depending on the method used. 相似文献
17.
减氮配施有机物质对土壤氮素淋失的调控作用 总被引:2,自引:1,他引:1
采用室内土柱模拟试验方法,研究不同氮肥施用下1m土体中氮素的分布和移动特征,揭示土壤氮素动态变化规律。结果表明:FN(农民习惯施无机氮用量)、RN(根据土壤养分供应和作物需求确定的推荐无机氮用量)显著增加了土壤上层NH_4^+-N和NO_3^--N向下层淋失。RN+HA(与推荐无机氮纯养分相等的锌腐酸尿素)和RN40%+OMB(推荐无机氮肥减60%基础上配施自制有机调理物质)可延长上层土壤NH_4^+-N峰值出现时间,降低下层NH_4^+-N。淋溶结束后,等氮量下增施HA较RN降低60cm以下NH_4^+-N残留29.7%~54.2%;降低60—80cm NO_3^--N累积17.4%。RN40%+OMB处理无机氮肥用量最小,0—20cm的NH_4^+-N最高,40—100cm稳定在2.0mg/kg左右;0—20,20—40cm土层NO_3^--N较RN+HA增加12.3%和2.0%,显著降低40cm以下NO_3^--N残留。RN+HA和RN40%+OMB较RN的土壤总无机氮残留分别减少7.4%和20.2%,降低表观淋失率。因此,RN40%+OMB可较好地抑制氮素下移,降低氮素淋失风险,为减少氮素淋失、明确合理氮肥施用方式提供科学依据。 相似文献
18.
For a quantitative analysis of SOC dynamics it is necessary to trace the origins of the soil organic compounds and the pathways of their transformations. We used the 13C isotope to determine the incorporation of maize residues into the soil organic carbon (SOC), to trace the origin of the dissolved organic carbon (DOC), and to quantify the fraction of the maize C in the soil respiration. The maize‐derived SOC was quantified in soil samples collected to a depth of 65 cm from two plots, one ’︁continuous maize’ and the other ’︁continuous rye’ (reference site) from the long‐term field experiment ’︁Ewiger Roggen’ in Halle. This field trial was established in 1878 and was partly changed to a continuous maize cropping system in 1961. Production rates and δ13C of DOC and CO2 were determined for the Ap horizon in incubation experiments with undisturbed soil columns. After 37 years of continuous maize cropping, 15% of the total SOC in the topsoil originated from maize C. The fraction of the maize‐derived C below the ploughed horizon was only 5 to 3%. The total amount of maize C stored in the profile was 9080 kg ha−1 which was equal to about 31% of the estimated total C input via maize residues (roots and stubble). Total leaching of DOC during the incubation period of 16 weeks was 1.1 g m−2 and one third of the DOC derived from maize C. The specific DOC production rate from the maize‐derived SOC was 2.5 times higher than that from the older humus formed by C3 plants. The total CO2‐C emission for 16 weeks was 18 g m−2. Fifty‐eight percent of the soil respiration originated from maize C. The specific CO2 formation from maize‐derived SOC was 8 times higher than that from the older SOC formed by C3 plants. The ratio of DOC production to CO2‐C production was three times smaller for the young, maize‐derived SOC than for the older humus formed by C3 plants. 相似文献
19.
A theoretical approach to the partitioning of carbon dioxide (CO2) efflux from soil with a C3 vegetation history planted with maize (Zea mays), a C4 plant, into three sources, root respiration (RR), rhizomicrobial respiration (RMR), and microbial soil organic matter (SOM) decomposition (SOMD), was examined. The δ13C values of SOM, roots, microbial biomass, and total CO2 efflux were measured during a 40-day growing period. A three-source isotopic mass balance based on the measured δ13C values and on assumptions made in other studies showed that RR, RMR, and SOMD amounted to 91%, 4%, and 5%, respectively. Two assumptions were thoroughly examined in a sensitivity analysis: the absence of 13C fractionation and the conformity of δ13C of microbial CO2 and that of microbial biomass. This approach strongly overestimated RR and underestimated RMR and microbial SOMD. CO2 efflux from unplanted soil was enriched in 13C by 2.0‰ compared to microbial biomass. The consideration of this 13C fractionation in the mass balance equation changed the proportions of RR and RMR by only 4% and did not affect SOMD. A calculated δ13C value of microbial CO2 by a mass balance equation including active and inactive parts of microbial biomass was used to adjust a hypothetical below-ground CO2 partitioning to the measured and literature data. The active microbial biomass in the rhizosphere amounted to 37% to achieve an appropriate ratio between RR and RMR compared to measured data. Therefore, the three-source partitioning approach failed due to a low active portion of microbial biomass, which is the main microbial CO2 source controlling the δ13C value of total microbial biomass. Since fumigation-extraction reflects total microbial biomass, its δ13C value was unsuitable to predict δ13C of released microbial CO2 after a C3-C4 vegetation change. The second adjustment to the CO2 partitioning results in the literature showed that at least 71% of the active microbial biomass utilizing maize rhizodeposits would be necessary to achieve that proportion between RR and RMR observed by other approaches based on 14C labelling. The method for partitioning total below-ground CO2 efflux into three sources using a natural 13C labelling technique failed due to the small proportion of active microbial biomass in the rhizosphere. This small active fraction led to a discrepancy between δ13C values of microbial biomass and of microbially respired CO2. 相似文献