Elevated CO₂ concentration and nitrogen fertilisation effects on N₂O and CH₄ fluxes and biomass production of Phleum pratense on farmed peat soil     

Riitta Kettunen  Sanna Saarnio  Jouko Silvola 《Soil biology & biochemistry》2005,37(4):739-750

The effects of elevated CO₂ supply on N₂O and CH₄ fluxes and biomass production of Phleum pratense were studied in a greenhouse experiment. Three sets of 12 farmed peat soil mesocosms (10 cm dia, 47 cm long) sown with P. pratense and equally distributed in four thermo-controlled greenhouses were fertilised with a commercial fertiliser in order to add 2, 6 or 10 g N m⁻². In two of the greenhouses, CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹) and in the other two at doubled concentration (720 μmol mol⁻¹). Soil temperature was kept at 15 °C and air temperature at 20 °C. Natural lighting was supported by artificial light and deionized water was used to regulate soil moisture. Forage was harvested and the plants fertilised three times during the basic experiment, followed by an extra fertilisations and harvests. At the end of the experiment CH₄ production and CH₄ oxidation potentials were determined; roots were collected and the biomass was determined. From the three first harvests the amount of total N in the aboveground biomass was determined. N₂O and CH₄ exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N₂O fluxes (on average, 255 μg N₂O m⁻² h⁻¹ during period IV) occurred just after fertilisation at high water contents, and especially at the beginning of the growing season (on average, 490 μg N₂O m⁻² h⁻¹ during period I) when the competition of vegetation for N was low. CH₄ fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH₄ were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO₂ increased above- and below-ground biomass production, but both at the highest and lowest rates of fertilisation, decreased the total amount of N in the aboveground dry biomass. N₂O fluxes tended to be higher under doubled CO₂ concentrations, indicating that increasing atmospheric CO₂ concentration may affect N and C dynamics in farmed peat soil.  相似文献   

CO₂ and inorganic N supply modify competition for N between co-occurring grass plants, tree seedlings and soil microorganisms     

Juliette M.G. Bloor  Audrey Niboyet  Paul W. Leadley  Laure Barthes 《Soil biology & biochemistry》2009,41(3):544-552

Plant-plant and plant-soil interactions play a key role in determining plant community structure and ecosystem function. However, the effects of global change on the interplay between co-occurring plants and soil microbes in successional communities are poorly understood. In this study, we investigated competition for nitrogen (N) between soil microorganisms, grass plants and establishing tree seedlings under factorial carbon dioxide (CO₂) and N treatments. Fraxinus excelsior seedlings were germinated in the presence or absence of grass competition (Dactylis glomerata) at low (380 μmol mol⁻¹) or high (645 μmol mol⁻¹) CO₂ and at two levels of N nutrition in a mesocosm experiment. Pulse ¹⁵N labelling was used to examine N partitioning among plant and soil compartments. Dactylis exerted a strong negative effect on Fraxinus biomass, N capture and ¹⁵N recovery irrespective of N and CO₂ treatment. In contrast, the presence of Dactylis had a positive effect on the microbial N pool. Plant and soil responses to N treatment were of a greater magnitude compared with responses to elevated CO₂, but the pattern of Fraxinus- and microbial-N pool response to N and CO₂ varied depending on grass competition treatment. Within the Dactylis competition treatment, decreases in Fraxinus biomass in response to N were not mirrored by decreases in tree seedling N content, suggesting a shift from below- to above-ground competition. In the Dactylis-sown pots, ¹⁵N recovery could be ranked Dactylis > microbial pool > Fraxinus in all N and CO₂ treatment combinations. Inequalities between Fraxinus and soil microorganisms in terms of ¹⁵N recovery were exacerbated by N addition. Contrary to expectations, elevated CO₂ did not increase plant-microbe competition. Nevertheless, microbial ¹⁵N recovery showed a small positive increase in the high CO₂ treatment. Overall, elevated CO₂ and N supply did not interact on plant/soil N partitioning. Our data suggest that the competitive balance between establishing tree seedlings and grass plants in an undisturbed sward is relatively insensitive to CO₂ or N-induced modifications in N competition between plant and soil compartments.  相似文献   

CH₄ oxidation and emissions of CH₄ and N₂O from Lolium perenne swards under elevated atmospheric CO₂     

E.M Baggs  H Blum 《Soil biology & biochemistry》2004,36(4):713-723

Emissions of N₂O and CH₄ and CH₄ oxidation rates were measured from Lolium perenne swards in a short-term study under ambient (36 Pa) and elevated (60 Pa) atmospheric CO₂ at the Free Air Carbon dioxide Enrichment experiment, Eschikon, Switzerland. Elevated pCO₂ increased (P<0.05) N₂O emissions from high N fertilised (11.2 g N m⁻²) swards by 69%, but had no significant effect on net emissions of CH₄. Application of ¹³C-CH₄ (11 μl l⁻¹; 11 at.% excess ¹³C) to closed chamber headspaces in microplots enabled determination of rates of ¹³C-CH₄ oxidation even when net CH₄ fluxes from main plots were positive. We found a significant interaction between fertiliser application rate and atmospheric pCO₂ on ¹³C-CH₄ oxidation rates that was attributed to differences in gross nitrification rates and C and N availability. CH₄ oxidation was slower and thought to be temporarily inhibited in the high N ambient pCO₂ sward. The most rapid CH₄ oxidation of 14.6 μg ¹³C-CH₄ m⁻² h⁻¹ was measured in the high fertilised elevated pCO₂ sward, and we concluded that either elevated pCO₂ had a stimulatory effect on CH₄ oxidation or inhibition of oxidation following fertiliser application was lowered under elevated pCO₂. Application of ¹⁴NH₄¹⁵NO₃ and ¹⁵NH₄¹⁵NO₃ (10 at.% excess ¹⁵N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N₂O emissions. Inhibition of CH₄ oxidation in the high fertilised ambient pCO₂ sward, due to competition between NH₃ and CH₄ for methane monooxygenase enzymes or toxic effects of NH₂OH or NO₂⁻ produced during nitrification, was hypothesised to increase gross nitrification (12.0 mg N kg dry soil⁻¹) and N₂O emissions during nitrification (327 mg ¹⁵N-N₂O m⁻² over 11 d). Our results indicate that increasing atmospheric concentrations of CO₂ may increase emissions of N₂O by denitrification, lower nitrification rates and either increase or decrease the ability of soil to act as a sink for atmospheric CH₄ depending on fertiliser management.  相似文献   

Elevation of atmospheric CO₂ and N-nutritional status modify nodulation, nodule-carbon supply, and root exudation of Phaseolus vulgaris L.     

Susan Haase  Angelika Kania  Volker Römheld 《Soil biology & biochemistry》2007,39(9):2208-2221

Increased root exudation and a related stimulation of rhizosphere-microbial growth have been hypothesised as possible explanations for a lower nitrogen- (N-) nutritional status of plants grown under elevated atmospheric CO₂ concentrations, due to enhanced plant-microbial N competition in the rhizosphere. Leguminous plants may be able to counterbalance the enhanced N requirement by increased symbiotic N₂ fixation. Only limited information is available about the factors determining the stimulation of symbiotic N₂ fixation in response to elevated CO₂.In this study, short-term effects of elevated CO₂ on quality and quantity of root exudation, and on carbon supply to the nodules were assessed in Phaseolus vulgaris, grown in soil culture with limited (30 mg N kg⁻¹ soil) and sufficient N supply (200 mg N kg⁻¹ soil), at ambient (400 μmol mol⁻¹) and elevated (800 μmol mol⁻¹) atmospheric CO₂ concentrations.Elevated CO₂ reduced N tissue concentrations in both N treatments, accelerated the expression of N deficiency symptoms in the N-limited variant, but did not affect plant biomass production. ¹⁴CO₂ pulse-chase labelling revealed no indication for a general increase in root exudation with subsequent stimulation of rhizosphere microbial growth, resulting in increased N-competition in the rhizosphere at elevated CO₂. However, a CO₂-induced stimulation in root exudation of sugars and malate as a chemo-attractant for rhizobia was detected in 0.5-1.5 cm apical root zones as potential infection sites. Particularly in nodules, elevated CO₂ increased the accumulation of malate as a major carbon source for the microsymbiont and of malonate with essential functions for nodule development. Nodule number, biomass and the proportion of leghaemoglobin-producing nodules were also enhanced. The release of nod-gene-inducing flavonoids (genistein, daidzein and coumestrol) was stimulated under elevated CO₂, independent of the N supply, and was already detectable at early stages of seedling development at 6 days after sowing.  相似文献   

Long-term N addition effects on the C mineralization and DOC production in mor humus under spruce     

G. Sjöberg  B. BergkvistD. Berggren  S.I. Nilsson 《Soil biology & biochemistry》2003,35(10):1305-1315

This study was based on laboratory incubations of mor humus from two N fertilized stands of Norway spruce in Sweden (Skogaby and Stråsan), which had received repeated N additions (100 kg N ha⁻¹ yr⁻¹ as (NH₄)₂SO₄ at Skogaby and 35, 73 and 108 kg ha⁻¹ yr⁻¹ as NH₄NO₃ at Stråsan) during 8 and 24-29 years, respectively. The aim was to investigate long-term N effects on the mineralization of C and production of DOC. Mor humus (Oe and Oa) was incubated in columns at 20 °C for 49 days. Columns were leached once a week with artificial throughfall solution, which was analyzed for DOC, total N, NH₄⁺-N and NO₃⁻-N. Prior to each leaching event, CO₂ evolution from the columns was determined. C-to-N ratios in the N-treated Oe layers at Stråsan (21-24) and Skogaby (24) were significantly lower than those of the controls (Stråsan, 32; Skogaby, 28). The cumulative amount of CO₂-C showed a significant treatment effect in the Oe layer at Skogaby, i.e. 18 and 29 mg C g⁻¹ C in the N treatment and control, respectively. At Stråsan, the cumulative CO₂-C was significantly lower in the N3 treatment compared to the control in both layers (33 compared to 74 mg C g⁻¹ C in the Oe layer and 16 compared to 35 mg C g⁻¹ C in the Oa layer). Neither the DOC nor the DON production showed any significant treatment effects at the two sites. However, DOC was lower in the fertilized Oe layer at Skogaby throughout the incubation. The leaching of DON was highest in the Oe layers at both sites, and DON increased with time at Skogaby while there was a decreasing trend at Stråsan. The DOC-to-DON ratio tended to be lower in the fertilized Oe layers at both sites. The NH₄⁺ leaching at Skogaby decreased in the N-treated Oe and Oa layers. At Stråsan, NH₄⁺ from the Oe layer increased in N2 and control. The NO₃⁻ leaching was low and constant in both Skogaby layers. At Stråsan, NO₃⁻ increased in the Oe layer of N1. Cumulative CO₂ was positively correlated to C-to-N ratio (r2=0.71,p<0.01) and to cumulative DOC (r2=0.63,p<0.05) in the Oe layer at Stråsan. Our conclusion was that long-term N additions caused decreased C-to-N ratios and decreased CO₂ evolution rates. The correlation between CO₂ and C-to-N ratio in the Oe layers at Stråsan may be due to a changed quality of the fertilized forest floor material and presence of more N efficient microorganisms.  相似文献   

Temporal change in spatial variability of soil respiration on a slope of Japanese cedar (Cryptomeria japonica D. Don) forest     

Mizue Ohashi  Koichiro Gyokusen 《Soil biology & biochemistry》2007,39(5):1130-1138

Although information regarding the spatial variability of soil respiration is important for understanding carbon cycling and developing a suitable sampling design for estimating average soil respiration, it remains relatively understudied compared to temporal changes. In this study, soil respiration was measured at 35 locations by season on a slope of Japanese cedar forest in order to examine temporal changes in the spatial distribution of soil respiration. Spatial variability of soil respiration varied between seasons, with the highest coefficient variation in winter (42%) and lowest in summer (26%). Semivariogram analysis and kriged maps revealed different patterns of spatial distribution in each season. Factors affecting the spatial variability were relief index (autumn), soil hardness of the A layer (winter), soil hardness at 50 cm depth (spring) and the altitude and relief index (summer). Annual soil respiration (average: 39 mol m⁻² y⁻¹) varied from 26 mol m⁻² y⁻¹ to 55 mol m⁻² y⁻¹ between the 35 locations and was higher in the upper part of the slope and lower in the lower part. The average Q₁₀ value was 2.3, varying from 1.3 to 3.0 among the locations. These findings suggest that insufficient information on the spatial variability of soil respiration and imbalanced sampling could bias estimates of current and future carbon budgets.  相似文献   

Nitrate leaching in soil: Tracing the NO₃ sources with the help of stable N and O isotopes     

Yvonne Oelmann  Yvonne Kreutziger  Wolfgang Wilcke 《Soil biology & biochemistry》2007,39(12):3024-3033

Legumes increase the plant-available N pool in soil, but might also increase NO₃⁻ leaching to groundwater. To minimize NO₃⁻ leaching, N-release processes and the contribution of legumes to NO₃⁻ concentrations in soil must be known. Our objectives were (1) to quantify NO₃⁻-N export to >0.3 m soil depth from three legume monocultures (Medicago x varia Martyn, Onobrychis viciifolia Scop., Lathyrus pratensis L.) and from three bare ground plots. Furthermore, we (2) tested if it is possible to apply a mixing model for NO₃⁻ in soil solution based on its dual isotope signals, and (3) estimated the contribution of legume mineralization to NO₃⁻ concentrations in soil solution under field conditions. We collected rainfall and soil solution at 0.3 m soil depth during 1 year, and determined NO₃⁻ concentrations and δ¹⁵N and δ¹⁸O of NO₃⁻ for >11.5 mg NO₃⁻-N l⁻¹. We incubated soil samples to assess potential N release by mineralization and determined δ¹⁵N and δ¹⁸O signals of NO₃⁻ derived from mineralization of non-leguminous and leguminous organic matter.Mean annual N export to >0.3 m soil depth was highest in bare ground plots (9.7 g NO₃⁻-N m⁻²; the SD reflects the spatial variation) followed by Medicago x varia monoculture (6.0 g NO₃⁻-N m⁻²). The O. viciifolia and L. pratensis monocultures had a much lower mean annual N export (0.5 and 0.3 g NO₃⁻-N m⁻²). The averaged NO₃⁻-N leaching during 70 days was not significantly different between field estimates and incubation for the Medicago x varia Martyn monoculture.The δ¹⁵N and δ¹⁸O values in NO₃⁻ of rainfall (δ¹⁵N: 3.3±0.8‰; δ¹⁸O: 30.8±4.7‰), mineralization of non-leguminous SOM (9.3±0.9‰; 6.7±0.8‰), and mineralization of leguminous SOM (1.5±0.6‰; 5.1±0.9‰) were markedly different. Applying a linear mixing model based on these three sources to δ¹⁵N and δ¹⁸O values in NO₃⁻ of soil solution during winter 2003, we calculated 18-41% to originate from rainfall, 38-57% from mineralization of non-leguminous SOM, and 18-40% from mineralization of leguminous SOM.Our results demonstrate that (1) even under legumes NO₃⁻-N leaching was reduced compared to bare ground, (2) the application of a three-end-member mixing model for NO₃⁻ based on its dual isotope signals produced plausible results and suggests that under particular circumstances such models can be used to estimate the contributions of different NO₃⁻ sources in soil solution, and (3) in the 2nd year after establishment of legumes, they contributed approximately one-fourth to NO₃⁻-N loss.  相似文献   

Carbon dynamics in a temperate grassland soil after 9 years exposure to elevated CO₂ (Swiss FACE)     

Zubin Xie  Georg Cadisch  Grant Edwards  Elizabeth M. Baggs 《Soil biology & biochemistry》2005,37(7):1387-1395

Elevated pCO₂ increases the net primary production, C/N ratio, and C input to the soil and hence provides opportunities to sequester CO₂-C in soils to mitigate anthropogenic CO₂. The Swiss 9 y grassland FACE (free air carbon-dioxide enrichment) experiment enabled us to explore the potential of elevated pCO₂ (60 Pa), plant species (Lolium perenne L. and Trifolium repens L.) and nitrogen fertilization (140 and 540 kg ha⁻¹ y⁻¹) on carbon sequestration and mineralization by a temperate grassland soil. Use of ¹³C in combination with respired CO₂ enabled the identification of the origins of active fractions of soil organic carbon. Elevated pCO₂ had no significant effect on total soil carbon, and total soil carbon was also independent of plant species and nitrogen fertilization. However, new (FACE-derived depleted ¹³C) input of carbon into the soil in the elevated pCO₂ treatments was dependent on nitrogen fertilization and plant species. New carbon input into the top 15 cm of soil from L. perennne high nitrogen (LPH), L. perenne low nitrogen (LPL) and T. repens low nitrogen (TRL) treatments during the 9 y elevated pCO₂ experiment was 9.3±2.0, 12.1±1.8 and 6.8±2.7 Mg C ha⁻¹, respectively. Fractions of FACE-derived carbon in less protected soil particles >53 μm in size were higher than in <53 μm particles. In addition, elevated pCO₂ increased CO₂ emission over the 118 d incubation by 55, 61 and 13% from undisturbed soil from LPH, LPL and TRL treatments, respectively; but only by 13, 36, and 18%, respectively, from disturbed soil (without roots). Higher input of new carbon led to increased decomposition of older soil organic matter (priming effect), which was driven by the quantity (mainly roots) of newly input carbon (L. perenne) as well as the quality of old soil carbon (e.g. higher recalcitrance in T. repens). Based on these results, the potential of well managed and established temperate grassland soils to sequester carbon under continued increasing concentrations of atmospheric CO₂ appears to be rather limited.  相似文献   

Rhizospheric influence on soil respiration and decomposition in a temperate Norway spruce stand     

Anna Ekberg  Gerd Gleixner 《Soil biology & biochemistry》2007,39(8):2103-2110

Assessments of terrestrial carbon fluxes require a thorough understanding of links between primary production, soil respiration and carbon loss through drainage. In this study, stem girdling was used to terminate autotrophic soil respiration including rhizosphere respiration and root exudation in a temperate Norway spruce stand. Rates of soil respiration and dissolved organic carbon (DOC) formation were measured in the second year after girdling, comparing an intact plant-rhizosphere continuum with an exclusive decomposer system. The molecular and isotopic composition of DOC in the soil solution was analysed with a coupled Py-GC/MS-C-IRMS system to distinguish between the carbon sources of dissolved carbon. Pyrolysis products were grouped according to their precursor origins: polysaccharides, proteins or of mixed origin (mainly derivates of lignins and proteins). When dead roots became available for decomposition, rates of heterotrophic soil respiration in girdling plots peaked at 6.5 μmol m⁻² s⁻¹, comparable to peak rates of total soil respiration (autotrophic and heterotrophic) in control plots, 6.1 μmol m⁻² s⁻¹. A significant response of soil respiration to temperature was found in control plots only, showing that an unlimiting supply of organic substrates for microbial respiration may mask any temperature effects. The enhanced decomposition in girdled plots was further supported by the isotopic composition of DOC in soil solution; all three precursor groups became isotopically enriched as the growing season progressed (polysaccharides by 2.3‰, proteins by 1.9‰, mixed origin group by 2.2‰). This indicates a trophic level shift due to incorporation of organic substrate into the microbial food chain. In the control plots’ mixed origin fraction, the isotopic composition changed over time from a signature resembling that of lignin (−28.9‰) to one similar of the protein fraction (−25.7‰). Significant temporal changes of structural DOC composition occurred in the girdling plots only. These results suggest that changes in the microbial community and in decomposition rates occurred in both girdled and control plots in the following ways: (i) increased substrate availability (dead roots) gave rise to generally enhanced performance of the decomposer community in girdled plots, (ii) root-derived exudates probably contributed to enhanced decomposition of recalcitrant lignin in the control plots and (iii) the structural composition of DOC seemed to be more a result of decomposition than of plant root exudation in all plots.  相似文献   

Compaction effects on CO₂ and N₂O production during drying and rewetting of soil   总被引：1，自引：0，他引：1  

M.H. Beare  E.G. Gregorich 《Soil biology & biochemistry》2009,41(3):611-621

The effects of compaction on soil porosity and soil water relations are likely to influence substrate availability and microbial activity under fluctuating soil moisture conditions. We conducted a short laboratory incubation to investigate the effects of soil compaction on substrate availability and biogenic gas (CO₂ and N₂O) production during the drying and rewetting of a fine-loamy soil. Prior to initiating the drying and wetting treatments, CO₂ production (−10 kPa soil water content) from uncompacted soil was 2.3 times that of compacted soil and corresponded with higher concentrations of microbial biomass C (MBC) and dissolved organic C (DOC). In contrast, N₂O production was 67 times higher in compacted than uncompacted soil at field capacity. Soil aeration rather than substrate availability (e.g. NO₃⁻ and DOC) appeared to be the most important factor affecting N₂O production during this phase. The drying of compacted soil resulted in an initial increase in CO₂ production and a nearly two-fold higher average rate of C mineralization at maximum dryness (owing to a higher water-filled pore space [WFPS]) compared to uncompacted soil. During the drying phase, N₂O production was markedly reduced (by 93-96%) in both soils, though total N₂O production remained slightly higher in compacted than uncompacted soil. The increase in CO₂ production during the first 24 h following rewetting of dry soil was about 2.5 times higher in uncompacted soil and corresponded with a much greater release of DOC than in compacted soil. MBC appeared to be the source of the DOC released from uncompacted soil but not from compacted soil. The production of N₂O during the first 24 h following rewetting of dry soil was nearly 20 times higher in compacted than uncompacted soil. Our results suggest that N₂O production from compacted soil was primarily the result of denitrification, which was limited by substrates (especially NO₃⁻) made available during drying and rewetting and occurred rapidly after the onset of anoxic conditions during the rewetting phase. In contrast, N₂O production from uncompacted soil appeared to be primarily the product of nitrification that was largely associated with an accumulation of NO₃⁻ following rewetting of dry soil. Irrespective of compaction, the response to drying and rewetting was greater for N₂O production than for CO₂ production.  相似文献   

Loss of low molecular weight dissolved organic carbon (DOC) and nitrogen (DON) in H₂O and 0.5 M K₂SO₄ soil extracts     

Johannes Rousk  Davey L. Jones 《Soil biology & biochemistry》2010,42(12):2331-2335

Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (¹⁴C-glucose, 1 and 100 μM) and DON (¹⁴C-amino acid mixture, 1 and 100 μM) during extraction of soil (0-6 h) with either distilled water or 0.5 M K₂SO₄. The extractions were performed at 20 °C, at 4 °C, or in the presence of an inhibitor of microbial activity (HgCl₂ and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H₂O extracts at 1 μM for both substances (>90% loss after 15 min). Lower temperature (4 °C) and presence of K₂SO₄ both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H₂O or K₂SO₄ extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON.  相似文献   

Denitrification in grass swards is increased under elevated atmospheric CO₂     

E.M Baggs  M RichterG Cadisch  U.A Hartwig 《Soil biology & biochemistry》2003,35(5):729-732

Emissions of N₂O and N₂ were measured from Lolium perenne L. swards under ambient (36 Pa) and elevated (60 Pa) atmospheric CO₂ at the Swiss free air carbon dioxide enrichment experiment following application of 11.2 g N m⁻² as ¹⁵NH₄¹⁵NO₃ or ¹⁴NH₄¹⁵NO₃ (1 at.% excess ¹⁵N). Total denitrification (N₂O+N₂) was increased under elevated pCO₂ with emissions of 6.2 and 19.5 mg ¹⁵N m⁻² measured over 22 d from ambient and elevated pCO₂ swards, respectively, supporting the hypothesis that increased belowground C allocation under elevated pCO₂ provides the energy for denitrification. Nitrification was the predominant N₂O producing process under ambient pCO₂ whereas denitrification was predominant under elevated pCO₂. The N₂-to-N₂O ratio was often higher under elevated pCO₂ suggesting that previous estimates of gaseous N losses based only on N₂O emissions have greatly underestimated the loss of N by denitrification.  相似文献   

Rhizodeposition-induced decomposition increases N availability to wild and cultivated wheat genotypes under elevated CO₂     

Marie-Anne de Graaff  Chris Van Kessel 《Soil biology & biochemistry》2009,41(6):1094-1103

Elevated CO₂ may increase nutrient availability in the rhizosphere by stimulating N release from recalcitrant soil organic matter (SOM) pools through enhanced rhizodeposition. We aimed to elucidate how CO₂-induced increases in rhizodeposition affect N release from recalcitrant SOM, and how wild versus cultivated genotypes of wheat mediated differential responses in soil N cycling under elevated CO₂. To quantify root-derived soil carbon (C) input and release of N from stable SOM pools, plants were grown for 1 month in microcosms, exposed to ¹³C labeling at ambient (392 μmol mol⁻¹) and elevated (792 μmol mol⁻¹) CO₂ concentrations, in soil containing ¹⁵N predominantly incorporated into recalcitrant SOM pools. Decomposition of stable soil C increased by 43%, root-derived soil C increased by 59%, and microbial-¹³C was enhanced by 50% under elevated compared to ambient CO₂. Concurrently, plant ¹⁵N uptake increased (+7%) under elevated CO₂ while ¹⁵N contents in the microbial biomass and mineral N pool decreased. Wild genotypes allocated more C to their roots, while cultivated genotypes allocated more C to their shoots under ambient and elevated CO₂. This led to increased stable C decomposition, but not to increased N acquisition for the wild genotypes. Data suggest that increased rhizodeposition under elevated CO₂ can stimulate mineralization of N from recalcitrant SOM pools and that contrasting C allocation patterns cannot fully explain plant mediated differential responses in soil N cycling to elevated CO₂.  相似文献   

Dynamics of labile and recalcitrant soil carbon pools in a sorghum free-air CO₂ enrichment (FACE) agroecosystem     

L. Cheng  S.W. Leavitt  P.J. Pinter Jr.  A. Matthias  T. Brooks  T.L. Thompson 《Soil biology & biochemistry》2007,39(9):2250-2263

Experimentation with dynamics of soil carbon pools as affected by elevated CO₂ can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis (δ¹³C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998-1999 Arizona Maricopa free air CO₂ enrichment (FACE) experiment, in which elevated CO₂ (FACE: 560 μmol mol⁻¹) and ambient CO₂ (Control: 360 μmol mol⁻¹) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO₂ transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0-30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO₂ was higher than that under ambient CO₂, indicating that elevated CO₂ reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0-30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO₂ enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO₂ and mitigating harmful CO₂ under future atmospheric conditions.  相似文献   

Emission of CO₂, CH₄ and N₂O from lakeshore soils in an Antarctic dry valley     

E.G. Gregorich  D.W. Hopkins  A.D. Sparrow  P. Novis  P. Rochette 《Soil biology & biochemistry》2006,38(10):3120-3129

We measured soil profile concentrations and emission of CO₂, CH₄ and N₂O from soils along a lakeshore in Garwood Valley, Antarctica, to assess the extent and biogeochemical significance of biogenic gas emission to C and N cycling processes. Simultaneous emission of all three gases from the same site indicated that aerobic and anaerobic processes occurred in different layers or different parts of each soil profile. The day and location of high gas concentrations in the soil profile corresponded to those having high gas emission, but the pattern of concentration with depth in the soil profile was not consistent across sites. That the highest gas concentrations were not always in the deepest soil layer suggests either limited production or gas diffusion in the deeper layers. Emission of CO₂ was as high as 47 μmol m⁻² min⁻¹ and was strongly related to soil temperature. Soil respiration differed significantly according to location on the lakeshore, suggesting that factors other than environmental variables, such as the amount and availability of O₂ and nutrients, play an important role in C mineralization processes in these soils. High surface emission (maximum: 15 μmol m⁻² min⁻¹) and profile gas concentration (maximum: 5780 μL L⁻¹) of CH₄ were at levels comparable to those in resource-rich temperate ecosystems, indicating an active indigenous population of methanogenic organisms. Emission of N₂O was low and highly variable, but the presence of this gas and NO₃ in some of the soils suggest that denitrification and nitrification occur there. No significant relationships between N₂O emission and environmental variables were found. It appears that considerable C and N turnover occurs in the lakeshore soils, and accurate accounting will require measurements of aerobic and anaerobic mineralization. The production and emission of biogenic gases confirm the importance of these soils as hotspots of biological activity in the dry valleys and probable reservoirs of biological diversity.  相似文献   

Short-term effects of clearfelling on soil CO₂, CH₄, and N₂O fluxes in a Sitka spruce plantation     

Argyro Zerva 《Soil biology & biochemistry》2005,37(11):2025-2036

We examined the effects of forest clearfelling on the fluxes of soil CO₂, CH₄, and N₂O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO₂, CH₄, N₂O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO₂ efflux, with an average efflux rate of 4.0 g m⁻² d⁻¹ in the mature stand (40-year) and 2.7 g m⁻² d⁻¹ in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m⁻² d⁻¹) for CH₄ to a net source (2.01 mg m⁻² d⁻¹). For the same period, soil N₂O fluxes averaged 0.57 mg m⁻² d⁻¹ in the CF and 0.23 mg m⁻² d⁻¹ in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO₂ remained the dominant greenhouse gas in terms of its greenhouse warming potential.  相似文献   

Can a mixed stand of N₂-fixing and non-fixing plants restrict N₂O emissions with increasing CO₂ concentration?     

Riitta Kettunen  Sanna Saarnio  Jouko Silvola 《Soil biology & biochemistry》2007,39(10):2538-2546

Initial effects of elevated atmospheric CO₂ concentration on N₂O fluxes and biomass production of timothy/red clover were studied in the laboratory. The experimental design consisted of two levels of atmospheric CO₂ (ca. 360 and 720 μmol CO₂ mol⁻¹) and two N fertilisation levels (5 and 10 g N m⁻²). There was a total of 36 mesocosms comprising sandy loam soil, which were equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at ambient concentration and in the other two at doubled concentration. Forage was harvested and the plants fertilised three times during the basic experiment, followed by harvest, a fertilisation with the double amount of nitrogen and rise of water level. Under elevated CO₂, harvestable and total aboveground dry biomass production of a mixed Trifolium/Phleum stand was increased at both N treatments compared to ambient CO₂. The N₂O flux rates under ambient CO₂ were significantly higher at both N treatments during the early growth of mixed Phleum/Trifolium mesocosms compared to the N₂O flux rate under elevated CO₂. However, when the conditions were favourable for denitrification at the end of the experiment, i.e. N availability and soil moisture were high enough, the elevated CO₂ concentration enhanced the N₂O efflux.  相似文献   

Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil   总被引：1，自引：0，他引：1  

D.L. Jones  V.B. Willett 《Soil biology & biochemistry》2006,38(5):991-999

A significant proportion of the total nutrient in soil solution can be bound to organic molecules and these often constitute a major loss from soil to freshwater. Our purpose was to determine whether chemical extractants used for measuring inorganic N could also be used to quantify dissolved organic nitrogen (DON) and carbon (DOC) in soil. In a range of soils, DOC and DON were extracted with either distilled water or 2 M KCl and the amount recovered compared with that present in soil solution recovered by centrifugal-drainage. The recovery of DON and DOC from soil was highly dependent upon the method of extraction. Factors such as soil sampling strategy (number of samples over space and time), sample preparation (sieving and drying), soil storage, extraction temperature, shaking time, and soil-to-extractant volume ratio all significantly affected the amount of DOC and DON extracted from soil. To allow direct comparison between independent studies we therefore propose the introduction of a standardized extraction procedure: Replicate samples of unsieved, field-moist soil extracted as soon as possible after collection with distilled water, 0.5 M K₂SO₄ or 2 M KCl at a 1:5 w/v ratio for 1 h at 20 °C.  相似文献   

Controls on soil nitrogen cycling and microbial community composition across land use and incubation temperature     

W.R. Cookson  M. Osman  D.A. Abaye  D.V. Murphy  C.A. Watson 《Soil biology & biochemistry》2007,39(3):744-756

We conducted a laboratory incubation of forest (Scots pine (Pinus sylvestris) or beech (Fagus sylvatica)), grassland (Trifolium repens/Lolium perenne) and arable (organic and conventional) soils at 5 and 25 °C. We aimed to clarify the mechanisms of short-term (2-weeks) nitrogen (N) cycling processes and microbial community composition in relation to dissolved organic carbon (DOC) and N (DON) availability and selected soil properties. N cycling was measured by ¹⁵N pool dilution and microbial community composition by denaturing gradient gel electrophoresis (DGGE), phospholipid fatty acid (PLFA) and community level physiological profiles (CLPP). Soil DOC increased in the order of arable<grassland<forest soil while DON and gross N fluxes increased in the order of forest<arable<grassland soil; land use had no affect on respiration rate. Soil DOC was lower, while respiration, DON and gross N fluxes were higher at 25 than 5 °C. Gross N fluxes, respiration and bacterial biomass were all positively correlated with each other. Gross N fluxes were positively correlated with pH and DON, and negatively correlated with organic matter, fungal biomass, DOC and DOC/DON ratio. Respiration rate was positively correlated with bacterial biomass, DON and DOC/DON ratio. Multiple linear modelling indicated that soil pH, organic matter, bacterial biomass, DON and DOC/DON ratio were important in predicting gross N mineralization. Incubation temperature, pH and total-C were important in predicting gross nitrification, while gross N mineralization, gross nitrification and pH were important in predicting gross N immobilization. Permutation multivariate analysis of variance indicated that DGGE, CLPP and PLFA profiles were all significantly (P<0.05) affected by land use and incubation temperature. Multivariate regressions indicated that incubation temperature, pH and organic matter content were important in predicting DGGE, CLPP and PLFA profiles. PLFA and CLPP were also related to DON, DOC, ammonium and nitrate contents. Canonical correlation analysis showed that PLFA and CLPP were related to differences in the rates of gross N mineralization, gross nitrification and soil respiration. Our study indicates that vegetation type and/or management practices which control soil pH and mediate dissolved organic matter availability were important predictors of gross N fluxes and microbial composition in this short-term experiment.  相似文献   

CO₂ emissions from subtropical arable soils of China     

Yunsheng Lou  Zhongpei Li  Taolin Zhang 《Soil biology & biochemistry》2004,36(11):1835-1842

CO₂ efflux plays a key role in carbon exchange between the biosphere and atmosphere, but our understanding of the mechanism controlling its temporal and spatial variations is limited. The purpose of this study is to determine annual soil CO₂ flux and assess its variations in arable subtropical soils of China in relation to soil temperature, moisture, rainfall, microbial biomass carbon (MBC) and dissolved organic carbon (DOC) using the closed chamber method. Soils were derived from three parent materials including granite (G), tertiary red sandstone (T) and quaternary red clay (Q). The experiment was conducted at the Ecological Station of Red Soil, The Chinese Academy of Sciences, in a subtropical region of China. The results showed that soil CO₂ flux had clear seasonal fluctuations with the maximum value in summer, the minimum in winter and intermediate in spring and autumn. Further, significant differences in soil CO₂ flux were found among the three red soils, generally in the order of G>T>Q. The average annual fluxes were estimated as 2.84, 2.13 and 1.41 kg CO₂ m⁻² year⁻¹ for red soils derived from G, T and Q, respectively. Soil temperature strongly affects the seasonal variability of soil CO₂ flux (85.0-88.5% of the variability), followed by DOC (55.8-84.4%) and rainfall (43.0-55.8%). The differences in soil CO₂ flux among the three red soils were partly explained by MBC (33.7-58.9% of the variability) and DOC (23.8-33.6%).  相似文献