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1.
Soil organic carbon dynamics in cleared temperate forest spodosols converted to maize cropping 总被引:5,自引:0,他引:5
In southwest France, sandy spodosols have developed from Quaternary sandy eolian deposits. On these soils, numerous forest lands have been converted to continuous intensive maize cropping. A chronosequence study is realized by comparing organic C pools and 13C natural abundance of one forested and 6 agricultural sites, whose ages of cultivation range from 4 to 32 yr. 13C ratio is found to increase with time of cultivation. After 3 decades of intensive maize cropping, about half of the initial organic C content in the forest topsoil layer has disappeared. The fraction of C derived from maize crop increases during the first decades of cultivation, but its level is significantly lower than those observed in other soils, which indicates a high mineralization rate of organic C. In this context, soil characteristics associated to intensive agricultural practices lead to a rapid and large loss of C, whereas inputs from maize seem to have only a very small long-term contribution. 相似文献
2.
Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France 总被引:3,自引:0,他引:3
Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect
of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content.
Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation,
texture, soil type, vegetation).
Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites.
The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm
layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given
depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same
soil mass rather than the same depth.
The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic
carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can
be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile
pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow
depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in
under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon
average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m-2. Carbon release to the atmosphere averaged 0.8 kg m-2 yr-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important
source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic
matter management. 相似文献
3.
Short-term mineralization of maize residues in soils as determined by carbon-13 natural abundance 总被引:2,自引:0,他引:2
Studies of soil organic matter equilibria must include estimates of C turnover. The objective of this study was to provide
data on how the natural 13C abundance method can be used to determine the flow of C from C4 residues and soil organic matter (C3-source) in a short-term incubation. Corn residue was added at a rate of 5.7 mg C g−1 soil to two soils, a clay and a sandy clay loam. During the course of a 35-day incubation in a CO2-free system, CO2-C and 13C natural abundance of the respired CO2 were measured. About 20% of the corn residue-C added was mineralized in both soils as determined from the CO2 respired and the 13C natural abundance of the respired CO2. Mineralization of the added residues was also calculated as the difference of the total amount of the respired CO2-C between the control and the corn residue-treated soils divided by the total amount of corn residue-C. Values were 35% for
the clay soil, and 30% for the sandy clay loam soil. The difference in values calculated from the 13 C natural abundance and the difference method was due to mineralization of the indigenous soil organic C resulting from the
addition of corn residues. Use of the natural 13C abundance method could determine the degree of ‘priming effect’ in soils amended with C4-C residues.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
Changes in soil organic matter with cropping as measured by organic carbon fractions and 13C natural isotope abundance 总被引:15,自引:0,他引:15
The decline in soil organic matter with cropping is a major factor affecting the sustainability of cropping systems. Changes in total C levels are relativelyinsensitive as a sustainability measure. Oxidation with different strength KMnO4 has been shown to be a more sensitive indicator of change. The relative size of soil C fractions oxidised by 333 mM KMnO4 declined with cropping, whilst the relative size of the unoxidised fraction increased. Changes in 13C ratio have been used to measure C turnover in systems which include C3 and C4 species. 相似文献
5.
Weixin Cheng 《Plant and Soil》1996,183(2):263-268
Due to the limitations in methodology it has been a difficult task to measure rhizosphere respiration and original soil carbon decomposition under the influence of living roots. 14C-labeling has been widely used for this purpose in spite of numerous problems associated with the labeling method. In this paper, a natural 13C method was used to measure rhizosphere respiration and original soil carbon decomposition in a short-term growth chamber experiment. The main objective of the experiment was to validate a key assumption of this method: the 13C value of the roots represents the 13C value of the rhizosphere respired CO2. Results from plants grown in inoculated carbon-free medium indicated that this assumption was valid. This natural 13C method was demonstrated to be advantageous for studying rhizosphere respiration and the effects of living roots on original soil carbon decomposition. 相似文献
6.
The objective of this study was to examine the chemical structure of the organic matter (SOM) of Oxisols soils in slash and
burn agriculture, in relation to its biological properties and soil fertility. The CP/MAS 13C technique was used to identify the main structural groups in litter and fine roots as SOM precursors; to identify the changes
on the nature of the SOM upon cultivation and the proportion of labile and stable components; and to identify the nature of
the organics present in water extracts (DOC).
Carbohydrates were the main structural components in litter whereas components such as carbonyl C, carboxyl C,O-alkyl C and
alkyl C were more common in SOM. Phenolic C and the degree of aromaticity were similar in litter and SOM. Cultivation resulted
in a small decrease in the relative proportion of carbohydrates in SOM, little change in the levels of O-alkyl C and carbonyl
C, but an increase in carboxyl C, phenolic C and aromaticity of the SOM. The level of alkyl C in soil was higher than the
level of O-alkyl C, indicating the importance of long-chain aliphatics along with lignins in the stabilization of the SOM
in Oxisols. The SOM of Mollisols from the Canadian Prairies differed from the Oxisol, with a generally stronger expression
of aromatic structures, particularly in a cultivated soil in relation to a native equivalent. Carbohydrate components were
the predominant structures in the DOC, indicating their importance in nutrient cycling and vertical translocations in the
Oxisol. 相似文献
7.
13C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland
watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated
wetland with δ13C values as low as -97 ‰ in carbonate minerals found in floating peat mats. It is postulated that13C depleted CH4 is oxidized in the mat and reacts with calcium ions to form calcite (identified through x-ray diffraction). Methane flux
measurements during the summer of 1992 showed much lower fluxes in areas with floating peat mats relative to open water. Secondary
carbonates in the basin peat have isotope compositions close to the δ13C values of the peat organic carbon (-25 ‰), indicating their origin from fermentation and possibly from sulfate-reduction.
In the upland basin peat deposits, the δ13CPDB values of organic C were constant with depth, while the permanently saturated mire had localities of13C enrichment in deeper layers of the peat. The13C enrichment may reflect areas of intense CH4 production in which13C enriched residual substrate is left behind during the production of highly13C depleted CH4. 相似文献
8.
Coupling 13C natural abundance and 14C pulse labelling enabled us to investigate the dependence of 13C fractionation on assimilate partitioning between shoots, roots, exudates, and CO2 respired by maize roots. The amount of recently assimilated C in these four pools was controlled by three levels of nutrient
supply: full nutrient supply (NS), 10 times diluted nutrient supply (DNS), and deionised water (DW). After pulse labelling
of maize shoots in a 14CO2 atmosphere, 14C was traced to determine the amounts of recently assimilated C in the four pools and the δ13C values of the four pools were measured. Increasing amounts of recently assimilated C in the roots (from 8% to 10% of recovered
14C in NS and DNS treatments) led to a 0.3‰ 13C enrichment from NS to DNS treatments. A further increase of C allocation in the roots (from 10% to 13% of recovered 14C in DNS and DW treatments) resulted in an additional enrichment of the roots from DNS to DW treatments by 0.3‰. These findings
support the hypothesis that 13C enrichment in a pool increases with an increasing amount of C transferred into that pool. δ13C of CO2 evolved by root respiration was similar to that of the roots in DNS and DW treatments. However, if the amount of recently
assimilated C in root respiration was reduced (NS treatment), the respired CO2 became 0.7‰ 13C depleted compared to roots. Increasing amounts of recently assimilated C in the CO2 from NS via DNS to DW treatments resulted in a 1.6‰ δ13C increase of root respired CO2 from NS to DW treatments. Thus, for both pools, i.e. roots and root respiration, increasing amounts of recently assimilated
C in the pool led to a δ13C increase. In DW and DNS plants there was no 13C fractionation between roots and exudates. However, high nutrient supply decreased the amount of recently assimilated C in
exudates compared to the other two treatments and led to a 5.3‰ 13C enrichment in exudates compared to roots. We conclude that 13C discrimination between plant pools and within processes such as exudation and root respiration is not constant but strongly
depends on the amount of C in the respective pool and on partitioning of recently assimilated C between plant pools.
Section Editor: H. Lambers 相似文献
9.
Soil organic carbon dynamics: variability with depth in forested and deforested soils under pasture in Costa Rica 总被引:5,自引:2,他引:5
Dynamics of soil organic carbon (SOC) inchronosequences of soils below forests that had beenreplaced by grazed pastures 3–25 years ago, wereinvestigated for two contrasting soil types (AndicHumitropept and Eutric Hapludand) in the Atlantic Zoneof Costa Rica. By forest clearing and subsequentestablishment of pastures, photosynthesis changes froma C-3 to a C-4 pathway. The accompanying changes inC-input and its 13C and 14Csignals, were used to quantify SOC dynamics. C-input from rootturnover at a pasture site was measured by sequentialharvesting and 14C-pulse labelling. With aspatial resolution of 5 cm, data on total SOC,13C and 14C of soil profileswere interpreted with a model that distinguishes threepools of SOC: active C, slow C and passive C,each with a 1-st order decomposition rate(ka, ks and kp). The modelincludes carbon isotope fractionation and depth-dependentdecomposition rates. Transport of C between soillayers was described as a diffusion process, whichaccounts for physical and biotic mixing processes.Calibrated diffusion coefficients were 0.42 cm2yr-1 for the Humitropept and 3.97 cm2yr-1 for the Hapludand chronosequence.Diffusional transport alone was insufficient foroptimal simulation; it had to be augmented bydepth-dependent decomposition rates to explain thedynamics of SOC, 13C and14C. Decomposition rates decreasedstrongly with depth. Upon increased diffusion,differences between calibrated decomposition rates ofSOC fractions between surface soils and subsoilsdiminished, but the concept of depth-dependentdecomposition had to be retained, to obtain smallresiduals between observed and simulated data. At areference depth of 15–20 cm ks was 90 yr-1in the Humitropept and 146 yr-1 in the Hapludand.Slow C contributed most to total organic C in surfacesoils, whereas passive C contributed most below 40 cmdepth. After 18–25 years of pasture, net loss of C was2180 g C m-2 for the Hapludand and 150 g m-2for the Humitropept soil. 相似文献
10.
Carbon sequestration and turnover in soil under the energy crop Miscanthus: repeated 13C natural abundance approach and literature synthesis
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Huadong Zang Evgenia Blagodatskaya Yuan Wen Xingliang Xu Jens Dyckmans Yakov Kuzyakov 《Global Change Biology Bioenergy》2018,10(4):262-271
The stability and turnover of soil organic matter (SOM) are a very important but poorly understood part of carbon (C) cycling. Conversion of C3 grassland to the C4 energy crop Miscanthus provides an ideal opportunity to quantify medium‐term SOM dynamics without disturbance (e.g., plowing), due to the natural shift in the δ13C signature of soil C. For the first time, we used a repeated 13C natural abundance approach to measure C turnover in a loamy Gleyic Cambisol after 9 and 21 years of Miscanthus cultivation. This is the longest C3–C4 vegetation change study on C turnover in soil under energy crops. SOM stocks under Miscanthus and reference grassland were similar down to 1 m depth. However, both increased between 9 and 21 years from 105 to 140 mg C ha?1 (P < 0.05), indicating nonsteady state of SOM. This calls for caution when estimating SOM turnover based on a single sampling. The mean residence time (MRT) of old C (>9 years) increased with depth from 19 years (0–10 cm) to 30–152 years (10–50 cm), and remained stable below 50 cm. From 41 literature observations, the average SOM increase after conversion from cropland or grassland to Miscanthus was 6.4 and 0.4 mg C ha?1, respectively. The MRT of total C in topsoil under Miscanthus remained stable at ~60 years, independent of plantation age, corroborating the idea that C dynamics are dominated by recycling processes rather than by C stabilization. In conclusion, growing Miscanthus on C‐poor arable soils caused immediate C sequestration because of higher C input and decreased SOM decomposition. However, after replacing grasslands with Miscanthus, SOM stocks remained stable and the MRT of old C3‐C increased strongly with depth. 相似文献
11.
12.
The dynamics of threonine side chains of the Tenebrio molitor antifreeze protein (TmAFP) were investigated using natural abundance (13)C NMR. In TmAFP, the array of threonine residues on one face of the protein is responsible for conferring its ability to bind crystalline ice and inhibit its growth. Heteronuclear longitudinal and transverse relaxation rates and the [(1)H]-(13)C NOE were determined in this study. The C alpha H relaxation measurements were compared to the previously measured (15)N backbone parameters and these are found to be in agreement. For the analysis of the threonine side chain motions, the model of restricted rotational diffusion about the chi(1) dihedral angle was employed [London and Avitabile (1978) J. Am. Chem. Soc., 100, 7159-7165]. We demonstrate that the motion experienced by the ice binding threonine side chains is highly restricted, with an approximate upper limit of less than +/-25 degrees. 相似文献
13.
亚热带不同林分土壤表层有机碳组成及其稳定性 总被引:5,自引:0,他引:5
在浙江临安玲珑山选取了常绿阔叶林、马尾松林、板栗林和雷竹林4种林分,采用传统的化学方法与固态13C核磁共振(NMR)技术研究其土壤有机碳在不同粒径土壤颗粒中的分布规律和结构特征,探讨林分类别和管理措施对土壤有机碳含量及其结构的影响,为亚热带地区森林固碳和土壤碳库管理提供科学依据。结果显示:(1)土壤表层(0—20 cm)有机碳含量按以下次序递减:雷竹林>常绿阔叶林>马尾松林>板栗林,且板栗林以粉黏粒结合态碳为主,其他林分土壤则以粗砂结合态碳为主;(2)13C NMR结果表明,阔叶林和马尾松林土壤有机碳中烷基碳所占比例最大,而雷竹林和板栗林则是烷氧碳比例最大,表明人工经营措施改变了土壤有机碳的成分组成;(3)随着土壤颗粒变细,有机碳中烷基碳比例增加,烷氧碳比例减少,A/O-A值和疏水碳/亲水碳值逐渐增大,表明颗粒越细,其结合的有机碳结构稳定性越高。 相似文献
14.
用天然13C丰度法评估贵州茂兰喀斯特森林区玉米地土壤中有机碳的来源 总被引:23,自引:0,他引:23
当森林生态系统转变成农田生态系统时,会把C4植物有机质导入到曾在C3植被下发育的土训中去,使土壤中含有来源不同的土壤有机质,引起碳同位素组成变化。因此,可以利用碳同位素来区分土壤有机质来源,实验结果表明,耕作几十年后原森林土壤有机质的含量仍占有主要地位,来源于原始C3植被的有机碳的比例为66.7%,但容易矿化的、对植物营养有效的有机质含量较低,这与当地的耕作方式有关,需要加强对植物残留物返回土壤工作的管理。 相似文献
15.
C4-derived soil organic carbon decomposes faster than its C3 counterpart in mixed C3/C4 soils 总被引:1,自引:0,他引:1
The large difference in the degree of discrimination of stable carbon isotopes between C3 and C4 plants is widely exploited in global change and carbon cycle research, often with the assumption that carbon retains the carbon isotopic signature of its photosynthetic pathway during later stages of decomposition in soil and sediments. We applied long-term incubation experiments and natural 13 C-labelling of C3 and C4-derived soil organic carbon (SOC) collected from across major environmental gradients in Australia to elucidate a significant difference in the rate of decomposition of C3- and C4-derived SOC. We find that the active pool of SOC (ASOC) derived from C4 plants decomposes at over twice the rate of the total pool of ASOC. As a result, the proportion of C4 photosynthesis represented in the heterotrophic CO2 flux from soil must be over twice the proportional representation of C4-derived biomass in SOC. This observation has significant implications for much carbon cycle research that exploits the carbon isotopic difference in these two photosynthetic pathways. 相似文献
16.
Joël Mispelter Claudine Lefèvre Élisabeth Adjadj Éric Quiniou Vincent Favaudon 《Journal of biomolecular NMR》1995,5(3):233-244
Summary Dynamics of the backbone and some side chains of apo-neocarzinostatin, a 10.7 kDa carrier protein, have been studied from 13C relaxation rates R1, R2 and steady-state 13C-{1H} NOEs, measured at natural abundance. Relaxation data were obtained for 79 nonoverlapping C resonances and for 11 threonine C single resonances. Except for three C relaxation rates, all data were analysed from a simple two-parameter spectral density function using the model-free approach of Lipari and Szabo. The corresponding C–H fragments exhibit fast (e < 40 ps) restricted libration motions (S2=0.73 to 0.95). Global examination of the microdynamical parameters S2 and e along the amino acid sequence gives no immediate correlation with structural elements. However, different trends for the three loops involved in the binding site are revealed. The -ribbon comprising residues 37 to 47 is spatially restricted, with relatively large e values in its hairpin region. The other -ribbon (residues 72 to 87) and the large disordered loop ranging between residues 97–107 experience small-amplitude motions on a much faster (picosecond) time scale. The two N-terminal residues, Ala1 and Ala2, and the C-terminal residue Asn113, exhibit an additional slow motion on a subnanosecond time scale (400–500 ps). Similarly, the relaxation data for eight threonine side-chain C must be interpreted in terms of a three-parameter spectral density function. They exhibit slower motions, on the nanosecond time scale (500–3000 ps). Three threonine (Thr65, Thr68, Thr81) side chains do not display a slow component, but an exchange contribution to the observed transverse relaxation rate R2 could not be excluded at these sites. The microdynamical parameters (S2, e and R2ex) or (S
infslow
sup2
, S
inffast
sup2
and slow) were obtained from a straightforward solution of the equations describing the relaxation data. They were calculated assuming an overall isotropic rotational correlation time e for the protein of 5.7 ns, determined using standard procedures from R2/R1 ratios. However, it is shown that the product (1–S2)× e is nearly independent of e for residues not exhibiting slow motions on the nanosecond time scale. In addition, this parameter very closely follows the heteronuclear NOEs, which therefore could be good indices for local fast motions on the picosecond time scale. 相似文献
17.
Chen Meng-Chun Wang Ming-Kuang Chiu Chih-Yu Huang Pan-Ming King Hen-Biau 《Plant and Soil》2001,231(1):37-44
Low molecular weight organic acids (LMWOAs) derived from root exudates, decomposing organic matter, and other sources are important ligands. The species of these LMWOAs in the Tsuga rhizosphere soil (TRS), and Yushania rhizosphere soil (YRS), and bulk soil (BS) from an alpine forest region were identified. LMWOA and organic functional groups were used to those fresh twigs and leaves, litters, and roots as comparison. The objectives of this study were to (i) develop a method that could be used to determine LMWOAs in soil solution by gas chromatography (GC), (ii) assess methods for processing LMWOAs in soil samples, and (iii) determine the relative proportions of organic carbon functional groups in the TRS, YRS and BS, and fresh plant materials with13C nuclear magnetic resonance (13C NMR) analysis. The proportion of organic acid contents followed the order of YRS > TRS > BS, and also showed significant differences (P < 0.05) from GC analysis. The amounts of malonic, fumaric and succinic acids in the YRS samples were greater than in the TRS and BS. Samples analyzed after 1 month of deep freeze storage (–24°C) showed no signs of decomposition. The proportion of organic functional groups in the rhizosphere and bulk soils quantified by 13C NMR analyses followed the general order: alkyl-C > O-alkyl-C > N-alkyl-C > acetal-C > aromatic-C > carboxylic-C > phenolic-C. 相似文献
18.
凋落物是森林土壤有机碳(SOC)形成、稳定和周转的重要影响因子。目前针对亚热带不同类型森林地上和地下凋落物对新SOC累积和老SOC输出动态平衡的影响仍不清楚。本研究以中亚热带常绿阔叶天然林、马尾松人工林和杉木人工林为对象,基于C3/C4植物-土壤置换试验,利用稳定同位素13C示踪方法开展3年野外定位试验,分析了森林地上、地下凋落物输入对SOC周转的影响。结果表明: 森林类型、凋落物处理和时间均能显著影响SOC含量、土壤δ13C值、新SOC和老SOC含量,且存在显著的森林类型×凋落物处理交互效应。地上和地下凋落物输入均能显著提高SOC含量和净增量,与杉木人工林相比,天然林SOC对凋落物输入的响应更敏感。凋落物输入显著降低了土壤δ13C值,且天然林、马尾松人工林土壤δ13C显著低于杉木人工林。在马尾松人工林,地下凋落物处理的新SOC含量显著高于地上凋落物;在天然林和马尾松人工林,地下凋落物输入处理的老SOC含量显著低于地上凋落物处理。此外,地上凋落物归还量和地下根生物量与SOC含量和净增量呈显著正相关,而地下根凋落物量和C/N与新SOC含量呈显著正相关。森林地下凋落物比地上凋落物输入对SOC周转的影响更重要,且不同森林凋落物输入对SOC的影响存在差异性。本研究可为揭示亚热带典型森林土壤有机碳库的形成和可持续管理提供依据。 相似文献
19.
R. B. Thompson 《Plant and Soil》1996,180(1):49-55
A preliminary study was conducted using the stable isotope 13C to pulse label the cover crop phacelia (Phacelia tanacetifolia) to examine its decomposition in soil, under field conditions. Plants were grown, in pots, in the greenhouse and after four weeks of growth were labelled with 13CO2 six times, at 1–2 week intervals. A single chamber was placed over the pots, and 13CO2 was generated, inside the chamber, by injecting lactic acid into sodium carbonate (99 atom % 13C). For calculating the quantity of Na2CO3 required, a target enrichment of 5 atom% 13C within the shoots of plants, assuming no respiration losses, was used. When harvested, at flowering, the mean enrichment of the shoot material was 3.0466 atom% 13C, or 1.9654 atom% excess 13C. To assess uniformity of labelling within plants, the shoot of a single plant was divided into leaves and stem from three sections of equal length. Ninety-three percent of this plant's dry matter had a 13C enrichment within 20 % of the weighted mean. At a field site with sandy soil, 13C labelled shoot and root material were combined and mixed with soil (0–15 cm). The soil was sampled 16 and 179 days later to determine the recovery of the added excess 13C in soil total C. The recoveries in soil (0–30 cm) were, respectively, 78 and 40 % at 16 and 179 days; there was appreciable variation associated with the recovery data from day 16, much less so at day 179. Methodological procedures for (i) enhancing the uniformity of labelling with 13C within plants, and (ii) minimising variability in the recovery of 13C from soil are suggested. ei]R Merckx 相似文献
20.
Steven W. Leavitt Eldor A. Paul Abraham Galadima Francis S. Nakayama Shelley R. Danzer Hyrum Johnson Bruce A. Kimball 《Plant and Soil》1995,187(2):147-155
The Maricopa cotton and wheat FACE (free-air CO2 enrichment) experiments offer propitious opportunity to quantify carbon turnover. The commercial CO2 (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqiTdq2aaW% baaSqabeaacaaIXaGaaG4maaaakiaaboeacqGHijYUcqGHsislcaaI% ZaGaaG4naiaacwcaliaad+gaaaa!3FCB!\[\delta ^{13} {\text{C}} \approx - 37\% o\]) used to elevate CO2 concentration in field plots provided a strongly 13C-depleted tracer. Soil CO2 and 13C of soil organic carbon (SOC) in CO2-enriched and Control plots were measured between the final cotton FACE project (October 1991) and the end of the second wheat experiment (June 1994). The initial 13C-depletion in SOC of cotton FACE plots (measured by the difference in 13C between FACE and Control plots) persisted at the same level (1.9) 1.5 years after the experiment ended. A similar depletion was observed in soil CO2 evolved in the same plots, indicating ongoing decomposition of the new SOC. The SOC 13C of wheat plots before and after two growing seasons showed increasing 13C-depletion in FACE relative to Control. Isotopic mass balance was consistent with 5–6% new carbon input from the two wheat crops. This is lower than the 12–13% calculated for FACE cotton and perhaps a consequence of the larger root system of cotton or the 3-year duration of the cotton experiments versus 2 years for the wheat. 相似文献