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Chapter 2 - Importance and roles of soil respiration

The advanced process‐based model, National Integrated Catchment‐based Eco‐hydrology (NICE)‐BGC, which incorporates the whole process of carbon cycling in land, was modified to include the feedback between soil organic content and overland carbon fluxes. It is a crucial and difficult task to evaluate the balance of the terrestrial carbon budget including the effect of inland water robustly. To accomplish this purpose, NICE‐BGC was applied to quantify the global biogeochemical carbon cycle closely associated with the complex hydrological cycle during the 36 years between 1980 and 2015. The model demonstrated that the inter‐annual variations of carbon cycle have been greatly affected by the extreme weather patterns. In particular, spatial distribution of temporal trends in riverine carbon fluxes and their relation to soil organic carbon (SOC) were analysed between different biomes and major river basins. Although there was a positive relationship between SOC and riverine flux of dissolved organic carbon and particulate organic carbon in the northern boreal region, it is difficult to see this relation in other regions. Further, the evaluation of potential controlling factors of temporal trends in SOC and fluvial carbon exports was also helpful to quantify the inter‐annual variation or temporal trend caused by the various effects. SOC was more influenced by temperature variations, whereas riverine carbon exports were mainly determined by precipitation variations. Finally, net land flux including inland water (−1.49 ± 0.50 PgC/year) showed a slight decrease in the carbon sink in comparison with previous values (−2.33 ± 0.50 PgC/year). These results help to distinguish the carbon cycle in different river basins and to re‐evaluate carbon cycle change explicitly including the effect of inland water because this effect has been so far implicitly included within the range of uncertainty in the Earth's global carbon cycle comprising land, oceans, and atmosphere.

Organic Matter Budgets for Streams: A Synthesis

Responses of soil respiration to phosphorus addition in global grasslands: A meta-analysis

Quantifying organic carbon (OC) removal in streams is needed to integrate the functional role of inland waters into landscape carbon budgets. To illustrate how in‐stream OC removal measurements can be used to characterize ecosystem and landscape carbon fluxes, we compared two common methods: (a) Bioassays measuring water column dissolved organic carbon (DOC) uptake and (b) daily rates of whole‐stream metabolism and OC spiraling calculated from fluorescent dissolved organic matter, oxygen, and discharge measurements. We then assessed how OC removal rates from these two methods, measured in two low‐productivity heterotrophic streams, affected estimates of terrestrial OC loading and export using a mass balance model. OC mineralization velocities calculated from whole‐stream metabolism (0.06 ± 0.03 m d−1 (mean ± SD)) were greater than water column bioassay DOC uptake velocities (0.01 ± 0.01 m d−1), which resulted in higher in‐stream OC removal estimates (0.5%–15.2% and 0.02%–4.2% removal for whole‐stream metabolism and bioassays, respectively). Furthermore, the terrestrial OC inputs needed to sustain in‐stream OC concentrations differ among methods, with simulated inputs ranging from 79 to 1,300 or 3–350 g OC d−1 for whole‐stream metabolism or bioassays, respectively. We show how in‐stream OC removal can be used to quantify terrestrial‐aquatic linkages by estimating OC inputs needed to fuel whole‐stream metabolism in low‐productivity streams, and offer future directions to better link OC removal with whole‐ecosystem OC budgets. Without appropriate conversions to whole‐stream processes, bioassays systematically underestimate whole‐stream carbon cycling. By integrating whole‐stream metabolism with OC transport, we can better elucidate the role of running waters in landscape carbon budgets and the global carbon cycle.

Our small planet is now vulnerable to the cumulative effects of our normal activities. There are two specific grand challenges associated with sustainability that are worth our attention—the global carbon cycle and the global nitrogen cycle. Human beings are disrupting the carbon cycle by releasing carbon, dug out of coalmines and oil fields, into the atmosphere. Mainly due to human beings’ activities, the concentration of carbon dioxide in the atmosphere has increased by more than 30% over the last 250 years, with an annual increase of about 0.5%. Two-thirds of the rise has occurred during the past 50 years. Fossil fuel accounts for 85% of the world’s energy system, and has been the principle agent of interference with the natural cycle for carbon. Such a disrupted carbon cycle, with a high carbon dioxide concentration, is posing tremendous challenges, including wide-spread global warming, rising sea level, significant threats to human health, more frequent extreme weather, and harmful disrupted ecological systems, and so on. Unless there is a change, the world will see much higher concentration of carbon dioxide, and it is thus a must for the world to redesign its energy system to become much less dependent on fossil fuels and less harmful to the carbon cycle. Besides the carbon cycle, the nitrogen cycle is another fundamental feature of life on the planet. The nitrogen cycle is also being disrupted by human beings. Organisms on this planet require nitrogen to survive, but the nitrogen in the atmosphere must be modified to be useful. The nitrogen needed by life is produced by “nitrogen-fixing bacteria” that break the triple bond of atmospheric nitrogen (N2, or N≡N) and produce “available” nitrogen. Only a few bacteria can act as “nitrogen-fixing bacteria.” Additional nitrogen fixation is accomplished by lightning. However, for the past hundred years, human beings have been able to produce available nitrogen from atmospheric nitrogen industrially, using the Haber-Bosch process. The most important product, globally, is nitrogen fertilizer, which has enabled a great expansion of the world’s food supply. The world is now more and more dependent on fertilizers to fix nitrogen. And now, more nitrogen is fixed in fertilizer factories than by the bacteria of the world. Another new source of available nitrogen comes from combustion of fossil fuels, which produces nitrogen oxides (“NOx,” which subsumes NO, NO2, N2O5, and other oxides of nitrogen). Significant increases in NOx emissions could occur over the next several decades due to both population growth and per capita increases in fossil-fuel use, although there are many technologies that can reduce NOx emissions. The extra nitrogen fixation today will seriously affect many environment systems—changing the balance of species, producing unwanted biological growth (eutrophication) in aqueous systems, and increasing the emissions of nitrous oxide (N2O, a greenhouse gas) to the atmosphere. International attention to the nitrogen cycle has gradually increased and focuses on the complexity of human alteration of the nitrogen cycle. Coordinated management of the nitrogen and carbon cycles is desirable. Engineering can provide remedies to disrupted ecosystems and has managed to achieve partial successes. There are many reasons to be optimistic that much can be accomplished, the world still has a terribly inefficient system for using carbon and nitrogen, and there is so much room to improve our energy system, food system, and agricultural system. The word “smart” is a key word to describe what engineers can contribute—smart buildings, appliances, infrastructure, vehicles, and food systems, with a core aim to achieve better efficiency. In order to achieve that, we can use a carbon price and a nitrogen price to promote efficient use. Also, we have an enormous amount of global infrastructure still to build, especially in the developing world (Table 1). Crucially, young scientists and engineers now find the challenges of carbon and nitrogen management exciting. As a main engineering method to protect the carbon cycle, carbon dioxide can be captured at a coal plant, then compressed and sent into porous rocks deep below ground. Someday all coal plants may separate the burning of coal from the emission of carbon dioxide. The already existing network of carbon dioxide pipelines in the USA shows that such a route for a low-carbon future

Mangroves are usually characterized by their high potential for long-term sequestration of organic carbon. Sediment accretion by these valuable habitats increased their capability of organic carbon sequestration. In this study, we aimed to examine the organic carbon sequestration of mangrove expansion (Avicennia germinans) in southern Iran. Different variables have been investigated in the sampled sediments, including δ13C, δ 15N, TOC, TN, and C/N ratio. Our findings indicated the significant variation of measured variables in several top intervals, reflecting the existence of autochthonous and allochthonous organic substances. Our data showed that the minority of δ13C values are lower than -23% in the S3 site, suggesting that mangrove litter is a critical input OC (δ13C, -28 to -30%). On the other hand, the significantly higher value of δ13C (-14 to -23%) indicates that phytoplankton and possibly local microphytobenthos are the primary sources of organic materials inputs. Moreover, site S4 presents the highest mean value of C/N, TN, and δ15N, which can be justified because of its proximity to the estuary and supply of organic matters imported from algal sources. The substantial role of mangrove forests depositing organic carbon should be investigated in the global carbon cycle.

Tillage and residue management affect growing-season soil respiration in paddy fields

Organic carbon cycling in the sediments of Prydz Bay, Eastern Antarctica: Implications for a high carbon sequestration potential

Rivers around the world have been heavily engineered, and these man‐made changes are affecting important biogeochemical cycles. Rivers play a key role in the global carbon cycle, by mobilizing organic carbon from land and delivering it to the oceans. River engineering techniques, like levees that prevent flooding, change the way carbon is cycled through rivers, but it is difficult to identify and quantify these changes. Shen et al. (2021) were able to quantify changes in river organic carbon fluxes induced by bank stabilization in the Mississippi River. The authors compared the age distribution of organic carbon in modern river sediment and old river sediment deposited before the construction of extensive levee systems. They found that bank stabilization significantly reduces the amount of time organic carbon spends in the river system before being exported to the Gulf of Mexico. As a result, less organic carbon is oxidized to CO2 and more organic carbon is exported to the ocean, ultimately reducing atmospheric CO2. This study highlights an important effect of anthropogenic activity on river carbon fluxes that should be considered in global carbon cycle models.

Quantification of the components of ecosystem respiration is essential to understanding carbon (C) cycling of natural and disturbed landscapes. Soil respiration, which includes autotrophic and heterotrophic respiration from throughout the soil profile, is the second largest flux in the global carbon cycle. We measured soil respiration (soil CO2 emission) at an undisturbed mature jack pine (Pinus banksiana Lamb.) stand in Saskatchewan (old jack pine, OJP), and at a formerly continuous portion of the stand that was clear-cut during the previous winter (clear-cut, CC). Tree harvesting reduced soil CO2 emission from ~22.5 to ~9.1 mol CO2 cdot m-2 for the 1994 growing season. OJP was a small net sink of atmospheric CO2, while CC was a net source of CO2. Winter emissions were similar at both sites. Reduction of soil respiration was attributed to disruption of the soil surface and to the death of tree roots. Flux simulations for CC and OJP identify 40% of CO2 emission at the undisturbed OJP site as near-surface respiration, 25% as deep-soil respiration, and 35% as tree-root respiration. The near-surface component was larger than the estimated annual C input to soil, suggesting fast C turnover and no net C accumulation in these boreal uplands in 1994.

Biological productivity and carbon cycling in the Arctic Ocean

Inland waters play a crucial role in the global carbon cycle, with lakes integrating carbon from various sources within their catchment in addition to that fixed by local primary productivity. Isotopic measurements of carbon pools can differentiate contributions from these sources, with natural abundance radiocarbon (14C) a particularly powerful tool due to the large range in 14C characteristics among carbon sources. Here, we present 14C measurements of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from monthly water column samplings over the course of a year in Lake Geneva, a large oligotrophic hard water perialpine lake in Western Europe. We find that DIC in the lake is significantly 14C‐depleted relative to the atmosphere primarily due to the dissolution of carbonate rocks in the lake's catchment. Variability in DI14C is largely tied to the Rhône River inflow, where DI14C values were also found to vary seasonally. DOC has a 14C signature similar to that of DIC, reflecting the fact that much of the lake DOC pool is autochthonous. However, more 14C‐depleted DOC was observed in July and tied to increased river discharge from snow and glacier melt within the upper Rhône River basin. These observations shed light on carbon sources and dynamics within Lake Geneva and its alpine catchment and highlight the importance of preaged dissolved carbon inputs to the largest natural lake in Western Europe.

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区三种典型退耕还林地土壤固碳效应差异 DOI: 10.5846/stxb201201020003 作者: 作者单位: 西北农林科技大学资源与环境学院,西北农林科技大学农学院,西北农林科技大学资源与环境学院,西北农林科技大学资源与环境学院,西北农林科技大学资源与环境学院,西北农林科技大学资源与环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 陕西省自然科学基础研究计划资助项目(2010JQ5001); 教育部高等学校博士点基金(20090204120038); 国家自然基金(30971695); 西北农林科技大学基本科研业务费专项(QN2011153); 西北农林科技大学博士启动金(2010BSJJ032) Variance analysis of soil carbon sequestration under three typical forest lands converted from farmland in a Loess Hilly Area Author: Affiliation: Northwest Agricultural & Forestry University,Northwest Agricultural & Forestry University,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:探讨了黄土丘陵区退耕种植10-40a的柠条、沙棘及刺槐林地土壤总有机碳库及其活性组分密度随退耕时间、土层分布及相对比例的变化差异。结果表明:100 cm深土壤碳库在退耕10a时仅柠条林地碳库未比坡耕地显著增加,但退耕20-40a 3种林地比退耕10a时都已有显著增加,且增幅均为刺槐＞沙棘＞柠条,其中总有机碳的最大增幅分别达到90.92、27.87、14.89 Mg/hm2,活性有机碳的分别达到30.28、10.51、9.67 Mg/hm2。各还林地碳库增加在退耕10a时主要来自0-40 cm浅层土,而40-100 cm深层土碳库到退耕20a起才开始显著增加。对比退耕10a时,到退耕40a时柠条、沙棘及刺槐林地0-20 cm表层土分别平均累积了35.4%、27.9%、27.1%的总有机碳,20.2%、45.1%、23.1%的活性有机碳,而20-100 cm各土层间对碳库累积比例大小变化无一致规律,平均每20 cm厚土层累积了17.4%的总有机碳和17.6%活性有机碳。并且相比坡耕地,各林地均使100 cm深土壤活性有机碳占总有机碳的比例提高,改良了碳库质量。综上分析,长期退耕下3种林地固碳效应有明显差异,以刺槐林地碳累积效应较强。 Abstract:Quantifying soil carbon sequestration may be an important consideration under large scale afforestation because it has been counted in global carbon budgets according to the Kyoto Protocol. The conversion of cropland to forest as part of a huge ecological afforestation engineering scheme has played a very important role in reversing ecological destruction in the Loess Plateau and strongly affects the carbon cycle. This research was conducted to determine the changes in total soil organic carbon and its labile fraction in soil to 100 cm under three typical forested lands. These typical forest lands are Caragana, Buckthorn, and Robinia, which have been converted from farmland between 10 and 40 years ago in a Loess Hilly Area. The results showed that, compared with sloped farmland, the concentration of total organic carbon and labile organic carbon in soil at 100 cm was not higher in Caragana forest land 10 years after conversion from farmland. The carbon pool was significantly increased in Buckthorn and Robinia after the same period. Compared with 10 years since farmland conversion, the total organic carbon and labile carbon was further increased in all forest lands after 20 to 40 years of conversion from farmland. This increase followed the order Robinia > Buckthorn > Caragana, and the highest increase in total organic carbon reached 90.92, 27.87, and 14.89 Mg/hm2, and for labile organic carbon was 30.28, 10.51, and 9.67 Mg/hm2 respectively. The changes in soil organic carbon in different soil layers were also significantly different with time since farmland conversion. The soil organic carbon and its labile fraction was increased mainly in the 0-40 cm soil layer 10 years after farmland conversion in all forest lands. The soil organic carbon pools in the 40-100 cm layer were increased significantly 20 years after farmland conversion. As a result, all soil layers showed a contribution to soil organic carbon increase with long term conversion of cropland to forest. Forty years after farmland conversion 35.4%, 27.9%, and 27.1% of the increased total organic carbon and 20.2%, 45.1%, and 23.1% of the increased labile organic carbon in the soil to 100 cm was sequestrated in the 0-20 cm layer under Caragana, Buckthorn, Robinia forest land respectively. By contrast, the proportion of soil organic carbon sequestration showed inconsistent changes among the forest lands in the 20-100 cm soil layer, with an average of 17.4% of the increased total organic carbon and 17.6% of the increased labile organic carbon sequestrated in each 20 cm layer. Additionally, in comparison with sloped farmland, the ratio of labile organic carbon to total organic carbon was significantly different in each soil layer of all forest lands 40 years after farmland conversion. This was especially so in the 60-100 cm soil layer where the ratio was increased by 146.7%, 76.9%, and 126.1% in Caragana, Buckthorn, and Robinia forest lands, respectively. The ratio in the 100 cm soil layer also increased by 63.7%, 34.0%, and 47.0% in Caragana, Buckthorn, and Robinia, respectively, which indicated the activation of soil carbon pools had been enhanced, and the quality of soil was improved indirectly. Consequently, conversion of cropland to forest could sequestrate carbon in soil and Robinia is the better forest land to improve the soil organic carbon pool. Soil carbon sequestration following the afforestation of former arable land would be a powerful carbon sink for anthropogenic CO2 production in the Loess Plateau in the future. 参考文献 相似文献 引证文献

Subglacial environments are a previously neglected component of the Earth's global carbon cycle, a reflection of the view held until recently that they are dominated by abiotic and oxic conditions. Here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over North America and Europe during glaciations were host to significant populations of anaerobic microorganisms, including methanogens, able to metabolize organic carbon sequestered during interglacials and overridden during Quaternary glacials. In doing so, we review the current evidence for subglacial methane release during deglaciation, estimate the size of the subglacial reservoir of organic carbon (SOC), and assess the amount of SOC available to subglacial microbes and the likely pathways and rates of carbon turnover. We then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations. We calculate that the SOC equates to 418–610 Pg C and includes carbon from terrestrial soils/vegetation, peatlands, lake, and marine sediments. The SOC that is potentially available for microbial conversion to methane is smaller than this estimate due to (1) glacial erosion, (2) accumulation of recalcitrant organic carbon compounds over time, (3) conversion to carbon dioxide by aerobic/anaerobic respiration, and (4) incomplete conversion of labile organic matter to methane. We estimate that the total SOC available for conversion to methane is 63 Pg C. Our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates. We believe, however, that there is a strong likelihood that subglacial microbes could convert 63 Pg of SOC to methane during a glacial cycle. If this were the case, release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations. Our findings suggest that it may well be important to consider subglacial environments as active components of the Earth's carbon cycle. Conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation, however, awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions.