The soil carbon dilemma: Shall we hoard it or use it?     

H.H. Janzen 《Soil biology & biochemistry》2006,38(3):419-424

Rapidly rising concentrations of atmospheric CO₂ have prompted a flurry of studies on soils as potential carbon (C) ‘sinks’. Sequestering C in soils is often seen as a ‘win-win’ proposition; it not only removes excess CO₂ from the air, but also improves soils by augmenting organic matter, an energy and nutrient source for biota. But organic matter is most useful, biologically, when it decays. So we face a dilemma: can we both conserve organic matter and profit from its decay? Or must we choose one or the other? In this essay, I contemplate the merits, first of building soil C and then of decaying (losing) it, partly from a historical perspective. I then consider the apparent trade-off between accrual and decay, and reflect on how the dilemma might be resolved or assuaged. These fledgling thoughts, offered mostly to stir more fruitful debate, include: finding ways to increase C inputs to soil; seeking to optimize the timing of decay; and understanding better, from an ecosystem perspective, the flows of C, rather than only the stocks. Carbon sequestration is a sound and worthy goal. But soil organic matter is far more than a potential tank for impounding excess CO₂; it is a relentless flow of C atoms, through a myriad of streams—some fast, some slow—wending their way through the ecosystem, driving biotic processes along the way. Now, when we aim to regain some of the C lost, we may need new ways of thinking about soil C dynamics, and tuning them for the services expected of our ecosystems. This objective, perhaps demanding more biology along with other disciplines, is especially urgent when we contemplate the stresses soon to be imposed by coming global changes.  相似文献   

CN-SIM: a model for the turnover of soil organic matter. II. Short-term carbon and nitrogen development     

Bjørn M. Petersen  Lars S. Jensen  Anders Pedersen  Peter Sørensen  Jørgen Berntsen 《Soil biology & biochemistry》2005,37(2):375-393

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植被重建下露天煤矿排土场边坡土壤碳储量变化   总被引：5，自引：0，他引：5  

李俊超  党廷辉  薛江  唐骏  郭胜利  靳静静 《土壤学报》2015,52(2):453-460

植被重建是治理排土场边坡水土流失最直接也是最有效的生物措施,研究不同植被重建模式下土壤有机碳(SOC)和全氮(TN)含量的空间分布规律是筛选适宜排土场边坡生长的植被模式的重要条件。选取内蒙古黑岱沟露天煤矿治理15年的排土场边坡中4种植被重建模式(自然恢复地、草地、灌木林、乔木林),采集270个土壤剖面(0~100 cm)样品,研究不同重建模式下SOC储量的变化。结果表明:(1)植被重建模式显著影响剖面SOC、TN含量及分布(p0.05),0~10 cm和10~20 cm SOC、TN均呈草地灌木乔木自然恢复地,20 cm以下各土层SOC、TN虽然也表现相似的特征,但差异随土层深度增加越来越小。(2)剖面SOC密度和储量表现为原地貌区治理排土场新建排土场。经15年植被重建后,排土场边坡表现出巨大的固碳能力,1 m深度的林地和草地碳储量分别增加了5.38、11.85 t hm-2,但仅原地貌水平的1/2和3/5。(3)林地和草地的固碳速率分别为35.87、79.01 g m-2a-1,草地的固碳速率是林地的2.2倍,从土壤固碳及水土流失防治的角度考虑,建议矿区排土场边坡植被重建优先选择草地,其次灌木。  相似文献   

Soil carbon and nitrogen accumulation with long-term no-till versus moldboard plowing overestimated with tilled-zone sampling depths     

Anita Gl  Tony J. Vyn  Erika Michli  Eileen J. Kladivko  William W. McFee 《Soil & Tillage Research》2007,96(1-2):42-51

Numerous investigators of tillage system impacts on soil organic carbon (OC) or total nitrogen (N) have limited their soil sampling to depths either at or just below the deepest tillage treatment in their experiments. This has resulted in an over-emphasis on OC and N changes in the near-surface zones and limited knowledge of crop and tillage system impacts below the maximum depth of soil disturbance by tillage implements. The objective of this study was to assess impacts of long-term (28 years) tillage and crop rotation on OC and N content and depth distribution together with bulk density and pH on a dark-colored Chalmers silty clay loam in Indiana. Soil samples were taken to 1 m depth in six depth increments from moldboard plow and no-till treatments in continuous corn and soybean–corn rotation. Rotation systems had little impact on the measured soil properties; OC content under continuous corn was not superior to the soybean–corn rotation in either no-till or moldboard plow systems. The increase in OC (on a mass per unit area basis) with no-till relative to moldboard plow averaged 23 t ha⁻¹ to a constant 30 cm sampling depth, but only 10 t ha⁻¹ to a constant 1.0 m sampling depth. Similarly, the increase in N with no-till was 1.9 t ha⁻¹ to a constant 30 cm sampling depth, but only 1.4 t ha⁻¹ to a constant 1.0 m sampling depth. Tillage treatments also had significant effects on soil bulk density and pH. Distribution of OC and N with soil depth differed dramatically under the different tillage systems. While no-till clearly resulted in more OC and N accumulation in the surface 15 cm than moldboard plow, the relative no-till advantage declined sharply with depth. Indeed, moldboard plowing resulted in substantially more OC and N, relative to no-till, in the 30–50 cm depth interval despite moldboard plowing consistently to less than a 25 cm depth. Our results suggest that conclusions about OC or N gains under long-term no-till are highly dependent on sampling depth and, therefore, tillage comparisons should be based on samples taken well beyond the deepest tillage depth.  相似文献   

Effects of the herbicide Topogard on soil respiration, nitrification, and denitrification in potato-cultivated soils differing in pH     

E. E. Kara  M. Arli  V. Uygur 《Biology and Fertility of Soils》2004,39(6):474-478

We investigated the effects of Topogard 50 WP (3 kg ha^–1) on soil respiration, mineral N content, and number of denitrifying and total bacteria in four coarse-textured volcanic soils for 91 days. Topogard application decreased CO₂ evolution in acid soils (Tepedibi and Karaçakl) whereas soil respiration was initially increased in neutral and alkaline soils (Kaba and Balar). The herbicide application significantly stimulated ammonification in Kaba and Balar soils, while Tepedibi and Karaçakl soils showed significantly lower NH₄⁺-N contents than the control. The treatment inhibited the activity of nitrifying microorganisms and, thus it decreased the NO₃^–-N content in Tepedibi, Karaçakl, and Kaba soils, whereas the NO₃^–-N content was increased in Balar soil. The NO₂^–-N content of soils was not affected by the treatment. The activity of denitrifying bacteria was stimulated by the addition of herbicide in all soils, whereas the total number of bacteria was not influenced. It may be concluded that the effects of Topogard on the microbiological characteristics of coarse-textured soils are likely to be dependent on soil pH.  相似文献   

Depth distribution of soil organic C and N after long-term soybean cropping in Texas   总被引：3，自引：0，他引：3  

Fugen Dou  Alan L. Wright  Frank M. Hons 《Soil & Tillage Research》2007,94(2):530-536

Crop management practices have potential to enhance subsoil C and N sequestration in the southern U.S., but effects may vary with tillage regime and cropping sequence. The objective of this study was to determine the impacts of tillage and soybean cropping sequence on the depth distribution of soil organic C (SOC), dissolved organic C (DOC), and total N after 20 years of treatment imposition for a silty clay loam soil in central Texas. A continuous soybean monoculture, a wheat–soybean doublecrop, and a sorghum–wheat–soybean rotation were established under both conventional (CT) and no tillage (NT). Soil was sampled after soybean harvest and sectioned into 0–5, 5–15, 15–30, 30–55, 55–80, and 80–105 cm depth intervals. Both tillage and cropping intensity influenced C and N dynamics in surface and subsurface soils. No tillage increased SOC, DOC, and total N compared to CT to a 30 cm depth for continuous soybean, but to 55 cm depths for the more intensive sorghum–wheat–soybean rotation and wheat–soybean doublecrop. Averaged from 0 to 105 cm, NT increased SOC, DOC, and total N by 32, 22, and 34%, respectively, compared to CT. Intensive cropping increased SOC and total N at depths to 55 cm compared to continuous soybean, regardless of tillage regime. Continuous soybean had significantly lower SOC (5.3 g kg⁻¹) than sorghum–wheat–soybean (6.4 g kg⁻¹) and wheat–soybean (6.1 g kg⁻¹), and 19% lower total N than other cropping sequences. Dissolved organic C was also significantly higher for sorghum–wheat–soybean (139 mg C kg⁻¹) than wheat–soybean (92 mg C kg⁻¹) and continuous soybean (100 mg C kg⁻¹). The depth distribution of SOC, DOC, and total N indicated treatment effects below the maximum tillage depth (25 cm), suggesting that roots, or translocation of dissolved organic matter from surface soils, contributed to higher soil organic matter levels under NT than CT in subsurface soils. High-intensity cropping sequences, coupled with NT, resulted in the highest soil organic matter levels, demonstrating potential for C and N sequestration for subsurface soils in the southern U.S.  相似文献   

Grassland plants affect dissolved organic carbon and nitrogen dynamics in soil     

M. Khalid  N. Soleman  D.L. Jones 《Soil biology & biochemistry》2007,39(1):378-381

Dissolved organic carbon (DOC) and nitrogen (DON) are central in many nutrient cycles within soil and they play an important role in many pedogenic processes. Plants provide a primary input of DOC and DON into soil via root turnover and exudation. Under controlled conditions we investigated the influence of 11 grass species alongside an unplanted control on the amount and nature of DOC and DON in soil. Our results showed that while the presence of plants significantly increases the size of a number of dissolved nutrient pools in comparison to the unplanted soil (e.g. DOC, total phenolics in solution) it has little affect on other pools (e.g. free amino acids). Grass species, however, had little effect on the composition of the DOC, DON or inorganic N pools. While the concentration of free amino acids was the same in the planted and unplanted soil, the flux through this pool was significantly faster in the presence of plants. The presence of plants also affected the biodegradability of the DOC pool. We conclude that while the presence of plants significantly affects the quantity and cycling of DOC and DON in soil, comparatively, individual grass species exerts less influence.  相似文献   

Microbial degradation of hydrolysable and condensed tannin polyphenol-protein complexes in soils from different land-use histories     

R. Mutabaruka  G. Cadisch 《Soil biology & biochemistry》2007,39(7):1479-1492

Polyphenols are capable of binding to proteins and form polyphenol-protein complexes thus reducing the release of N from decomposing plant materials. The objective of this work was to test if under polyphenol-rich vegetations adapted microbial communities had developed capable of breaking down recalcitrant polyphenol-protein complexes. Soils used for this investigation were from different 10-year-old tropical agricultural systems (maize, sugarcane plots and Gliricidia sepium or Peltophorum dasyrrachis woodlots) and natural systems (secondary forest and Imperata cylindrica grassland). TA (tannic acid, hydrolysable tannin), QUE (quebracho, condensed tannin), BSA (bovine serum albumin, protein) or TA/BSA and QUE/BSA polyphenol-protein complexes were incubated at 28 °C in these soils. CO₂-C and ¹³C evolution were periodically monitored and mineral N release, microbial biomass N and phospholipid fatty acid (PLFA) profiles measured at the end.QUE was able to bind about 25% more protein than TA. In all systems the individual uncomplexed substrates were more easily degraded than the complexes. On average, net cumulative CO₂-C evolution from TA/BSA complexes was more than 5 times higher than from QUE/BSA complexes, indicating higher C availability and/or lower protection capability of TA compared to QUE. However, net N release was higher from QUE/BSA than from TA/BSA probably due to their higher protein-binding capacity and associated larger degradation of partly unprotected protein as suggested by ¹³C-CO₂ signatures. Microbial respiration patterns indicated that polyphenol complexes were initially degraded more quickly in the maize cropping system than in soils from under polyphenol-rich communities (Peltophorum and natural forest) but this pattern reversed with time. Long-term incubation of QUE/BSA complexes even caused a negative effect on microbial respiration in agricultural soils with low polyphenol contents (e.g. maize and sugarcane).Incubation of polyphenol complexes in soil depressed microbial biomass N in maize, sugarcane, Imperata and forest systems and led to reduced soil pH. However, microbial biomass was increased under the polyphenol-rich vegetation of Peltophorum. The PLFA group 18:2w6,9 was highly enhanced by condensed tannin-protein complexes additions as compared to control and hydrolysable polyphenol-protein complexes in soils with high polyphenol contents. Polyphenol complexes increased the fungi:bacteria ratio in systems with a high polyphenol content, particularly with condensed tannin complexes. The results indicated that systems with a high polyphenol content favoured development of fungal communities that are highly adaptable to phenol-rich soil conditions and high acidity, particularly with regards to the more recalcitrant condensed tannin-protein complexes.  相似文献   

Soil carbon turnover and sequestration in native subtropical tree plantations     

Anna E. Richards  Ram C. Dalal  Susanne Schmidt 《Soil biology & biochemistry》2007,39(8):2078-2090

Approximately 30% of global soil organic carbon (SOC) is stored in subtropical and tropical ecosystems but it is being rapidly lost due to continuous deforestation. Tree plantations are advocated as a C sink, however, little is known about rates of C turnover and sequestration into soil organic matter under subtropical and tropical tree plantations. We studied changes in SOC in a chronosequence of hoop pine (Araucaria cunninghamii) plantations established on former rainforest sites in seasonally dry subtropical Australia. SOC, δ¹³C, and light fraction organic C (LF C<1.6 g cm⁻³) were determined in plantations, secondary rainforest and pasture. We calculated loss of rainforest SOC after clearing for pasture using an isotope mixing model, and used the decay rate of rainforest-derived C to predict input of hoop pine-derived C into the soil. Total SOC stocks to 100 cm depth were significantly (P<0.01) higher under rainforest (241 t ha⁻¹) and pasture (254 t ha⁻¹) compared to hoop pine (176-211 t ha⁻¹). We calculated that SOC derived from hoop pine inputs ranged from 32% (25 year plantation) to 61% (63 year plantation) of total SOC in the 0-30 cm soil layer, but below 30 cm all C originated from rainforest. These results were compared to simulations made by the Century soil organic matter model. The Century model simulations showed that lower C stocks under hoop pine plantations were due to reduced C inputs to the slow turnover C pool, such that this pool only recovers to within 45% of the original rainforest C pool after 63 years. This may indicate differences in soil C stabilization mechanisms under hoop pine plantations compared with rainforest and pasture. These results demonstrate that subtropical hoop pine plantations do not rapidly sequester SOC into long-term storage pools, and that alternative plantation systems may need to be investigated to achieve greater soil C sequestration.  相似文献   

Storage and dynamics of carbon and nitrogen in soil physical fractions following woody plant invasion of grassland   总被引：1，自引：0，他引：1  

J.D. Liao  J.D. Jastrow 《Soil biology & biochemistry》2006,38(11):3184-3196

Woody plant invasion of grasslands is prevalent worldwide. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by C₃ trees/shrubs have been replacing C₄ grasslands over the past 150 yr, resulting in increased soil organic carbon (SOC) storage and concomitant increases in soil total nitrogen (STN). To elucidate mechanisms of change in SOC and STN, we separated soil organic matter into specific size/density fractions and determined the concentration of C and N in these fractions. Soils were collected from remnant grasslands (Time 0) and woody plant stands (ages 10-130 yr). Rates of whole-soil C and N accrual in the upper 15 cm of the soil profile averaged 10-30 g C m⁻² yr⁻¹ and 1-3 g N m⁻² yr⁻¹, respectively, over the past 130 yr of woodland development. These rates of accumulation have increased soil C and N stocks in older wooded areas by 100-500% relative to remnant grasslands. Probable causes of these increased pool sizes include higher rates of organic matter production in wooded areas, greater inherent biochemical resistance of woody litter to decomposition, and protection of organic matter by stabilization within soil macro- and microaggregates. The mass proportions of the free light fraction (<1.0 g cm⁻³) and macroaggregate fraction (>250 μm) increased linearly with time following woody plant invasion of grassland. Conversely, the mass proportions of free microaggregate (53-250 μm) and free silt+clay (<53 μm) fractions decreased linearly with time after woody invasion, likely reflecting stabilization of these fractions within macroaggregate structures. Carbon and N concentrations increased in all soil fractions with time following woody invasion. Approximately half of the C and N accumulated in free particulate organic matter (POM) fractions, while the remainder accrued in stable macro- and microaggregate structures. Soil C/N ratios indicated that the organic C associated with POM and macroaggregates was of more recent origin (less decomposed) than C associated with the microaggregate and silt+clay fractions. Because grassland-to-woodland conversion has been geographically extensive in grassland ecosystems worldwide during the past century, changes in soil C and N storage and dynamics documented here could have significance for global cycles of those elements.  相似文献