Soil carbon dioxide partial pressure and dissolved inorganic carbonate chemistry under elevated carbon dioxide and ozone

Global emissions of atmospheric CO₂ and tropospheric O₃ are rising and expected to impact large areas of the Earths forests. While CO₂ stimulates net primary production, O₃ reduces photosynthesis, altering plant C allocation and reducing ecosystem C storage. The effects of multiple air pollutants can alter belowground C allocation, leading to changes in the partial pressure of CO₂ (pCO₂) in the soil , chemistry of dissolved inorganic carbonate (DIC) and the rate of mineral weathering. As this system represents a linkage between the long- and short-term C cycles and sequestration of atmospheric CO₂, changes in atmospheric chemistry that affect net primary production may alter the fate of C in these ecosystems. To date, little is known about the combined effects of elevated CO₂ and O₃ on the inorganic C cycle in forest systems. Free air CO₂ and O₃ enrichment (FACE) technology was used at the Aspen FACE project in Rhinelander, Wisconsin to understand how elevated atmospheric CO₂ and O₃ interact to alter pCO₂ and DIC concentrations in the soil. Ambient and elevated CO₂ levels were 360±16 and 542±81 l l^–1, respectively; ambient and elevated O₃ levels were 33±14 and 49±24 nl l^–1, respectively. Measured concentrations of soil CO₂ and calculated concentrations of DIC increased over the growing season by 14 and 22%, respectively, under elevated atmospheric CO₂ and were unaffected by elevated tropospheric O₃. The increased concentration of DIC altered inorganic carbonate chemistry by increasing system total alkalinity by 210%, likely due to enhanced chemical weathering. The study also demonstrated the close coupling between the seasonal ¹³C of soil pCO₂ and DIC, as a mixing model showed that new atmospheric CO₂ accounted for approximately 90% of the C leaving the system as DIC. This study illustrates the potential of using stable isotopic techniques and FACE technology to examine long- and short-term ecosystem C sequestration.     

基于森林清查资料的江西和浙江森林植被固碳潜力

以我国江西、浙江两省的森林植被为研究对象,基于1999-2003年间第六次全国森林清查数据及收集的1030个亚热带森林样地文献资料,依据林分生长的经验方程,估算了两个地区森林2004-2013年的固碳潜力,并基于455个样点的调查数据研究了不同森林管理措施(纯林间种、间伐、施肥)对森林未来固碳潜力的影响.结果表明:第六次森林清查以来的10年(2004-2013)间,江西森林植被年均自然固碳潜力约11.37 Tg C·a-1(1Tg=1012g),而浙江省森林植被年均自然固碳潜力约4.34 Tg C·a-1.纯林间种对江西、浙江两省森林植被固碳潜力影响最大,其次为间伐抚育,施肥的影响最小,纯林间种、间伐和施肥3种森林管理措施使江西省森林植被固碳潜力分别提高(6.54±3.9)、(3.81±2.02)和(2.35±0.6) Tg C·a-1,浙江省森林植被固碳潜力分别提高(2.64±1.28)、(1.42±0.69)和(1.15±0.29) Tg C·a-1.     

Elevated atmospheric carbon dioxide increases soil carbon

The general lack of significant changes in mineral soil C stocks during CO₂‐enrichment experiments has cast doubt on predictions that increased soil C can partially offset rising atmospheric CO₂ concentrations. Here, we show, through meta‐analysis techniques, that these experiments collectively exhibited a 5.6% increase in soil C over 2–9 years, at a median rate of 19 g C m^?2 yr^?1. We also measured C accrual in deciduous forest and grassland soils, at rates exceeding 40 g C m^?2 yr^?1 for 5–8 years, because both systems responded to CO₂ enrichment with large increases in root production. Even though native C stocks were relatively large, over half of the accrued C at both sites was incorporated into microaggregates, which protect C and increase its longevity. Our data, in combination with the meta‐analysis, demonstrate the potential for mineral soils in diverse temperate ecosystems to store additional C in response to CO₂ enrichment.     

An oxygen-mediated positive feedback between elevated carbon dioxide and soil organic matter decomposition in a simulated anaerobic wetland

We examined the effects of elevated atmospheric CO₂ on soil carbon decomposition in an experimental anaerobic wetland system. Pots containing either bare C₄‐derived soil or the C₃ sedge Scirpus olneyi planted in C₄‐derived soil were incubated in greenhouse chambers at either ambient or twice‐ambient atmospheric CO₂. We measured CO₂ flux from each pot, quantified soil organic matter (SOM) mineralization using δ¹³C, and determined root and shoot biomass. SOM mineralization increased in response to elevated CO₂ by 83–218% (P<0.0001). In addition, soil redox potential was significantly and positively correlated with root biomass (P= 0.003). Our results (1) show that there is a positive feedback between elevated atmospheric CO₂ concentrations and wetland SOM decomposition and (2) suggest that this process is mediated by the release of oxygen from the roots of wetland plants. Because this feedback may occur in any wetland system, including peatlands, these results suggest a limitation on the size of the carbon sink presented by anaerobic wetland soils in a future elevated‐CO₂ atmosphere.     

Temporal and spatial development of soil solution chemistry and element budgets in different mine soils of the Lusatian lignite mining area

Lignite and pyrite contents in the dump materials of the Lusatian opencast mining district in East Germany result in high acidification and salinization potentials. These extreme conditions require considerable amounts of alkaline materials like ash or lime to enable recultivation and revegetation. Investigations at chronosequence sites on different mining substrates show characteristic developments of the soil solution chemistry. Processes like weathering of primary and formation of secondary mineral phases, acid production and buffering, and their impacts on both the solid and the liquid soil phase result in high temporal and spatial dynamics especially in the initial phase of soil and ecosystem development. To study these processes we continuously collected soil solutions from different soil depths at seven sites with two representative soil substrates. All sites were afforested with pine and cover stand ages from 1 to 60 yr. The results show that actual pyrite oxidation occurs at the youngest sites on lignite and pyrite containing substrates leading to extremely low pH values and high Feⁿ⁺ and SO₄ ²- concentrations. The considerable acid production causes weathering of aluminium silicates resulting in high Alⁿ⁺ concentrations. Ca²⁺ concentrations are unexpectedly high even at low pH showing no correlation to amelioration amounts or depths. Therefore it seems most probable that these mining substrates contain geogenic Ca sources. The transport of dissolved weathering products is limited due to low leaching rates enabling formation of secondary phases which control the actual composition of the soil solution. Depth gradients of the soil solution composition at the chronosequence sites point to a gradual transport and leaching of these secondary phases from the soil profiles. Soil solution composition and dynamics at lignite and pyrite free sites show completely different patterns and have a higher potential for successful sustainable recultivation. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon Sequestration in Two Alpine Soils on the Tibetan Plateau

Soil carbon sequestration was estimated in a conifer forest and an alpine meadow on the Tibetan Plateau using a carbon- 14 radioactive label provided by thermonuclear weapon tests （known as bomb-^14C）. Soil organic matter was physically separated into light and heavy fractions. The concentration spike of bomb-^14C occurred at a soil depth of 4 cm in both the forest soil and the alpine meadow soil. Based on the depth of the bomb-^14C spike, the carbon sequestration rate was determined to be 38.5 g C/m^2 per year for the forest soil and 27.1 g C/m^2 per year for the alpine meadow soil. Considering that more than 60% of soil organic carbon （SOC） is stored in the heavy fraction and the large area of alpine forests and meadows on the Tibetan Plateau, these alpine ecosystems might partially contribute to ＂the missing carbon sink＂.     

Trees,Mycorrhiza and Minerals –Field Relevance of in vitro Experiments

Ectomycorrhizal fungi are mutualistic symbionts of boreal forest trees and may mediate mineral weathering through their direct access to photosyntentically derived carbon. In soil, fungal mycelia (i) provide a large surface for nutrient uptake; (ii) induce intense colonization of nutrient rich substrates; (iii) cause local acidification and (iv) produce organic acids. Mechanisms of ectomyorrhizal fungi induced weathering in response to nutrient limiting growth conditions remains largely unresolved. This review summarizes how current knowledge on fungal weathering is affected by experimental setup and conditions, i.e., pure or symbiotic growth, nitrogen source, the mean of detecting weathering activity and species examined.     

Year-round observations of the net ecosystem exchange of carbon dioxide in a native tallgrass prairie

An Ameriflux site was established in mid 1996 to study the exchange of CO₂ in a native tallgrass prairie of north‐central Oklahoma, USA. Approximately the first 20 months of measurements (using eddy covariance) are described here. This prairie, dominated by warm season C4 grasses, is typical of the central Kansas/northern Oklahoma region. During the first three weeks of the measurement period (mid‐July–early August 1996), moisture‐stress conditions prevailed. For the remainder of the period (until March 1998), however, soil moisture was nonlimiting. Mid‐day net ecosystem CO₂ exchange (NEE), under well‐watered conditions, reached a maximum magnitude of 1.4 mg CO₂ m^?2 s^?1 (flux toward the surface is positive) during peak growth (mid‐July 1997), with green leaf area index of 2.8. In contrast, under moisture‐stress conditions in the same growth stage in 1996, mid‐day NEE was reduced to near‐zero. Average night NEE ranged from near‐zero, during winter dormancy, to ? 0.50 mg CO₂ m^?2 s^?1, during peak growth. Most of the variance in average night NEE was explained by changes in soil temperature (0.1 m depth) and green leaf area. The daytime NEE measurements were examined in terms of a rectangular hyperbolic relationship with incident photosynthetically active radiation. The analysis showed that the quantum yield during peak growth was similar to those measured in other prairies and the y‐intercept, so obtained, can be potentially used as an estimate of night‐time CO₂ emissions when eddy covariance data are unavailable. Daily integrated NEE reached its peak magnitude of 30.8 g CO₂ m^?2 d^?1 (8.4 g C m^?2 d^?1) in mid‐July when the green LAI was the largest (about 2.8). In general, the seasonal trend of daily NEE (on relatively clear days) followed that of green LAI. Annually integrated carbon exchange, between prescribed burns in 1997 and 1998, was 268 g C m^?2 y^?1. After incorporating carbon loss during the prescribed burn , the net annual carbon exchange in this prairie was near‐zero in 1998.     

土壤有机碳和外源添加碳对水稻土土体呼吸的影响

土体呼吸输出碳来源于土壤固有有机碳和外源添加碳,而以往关于不同施肥措施对水稻土碳排放的研究少有区分碳的来源。本试验利用一个长达30年的水稻土定位试验,在保证原有定位试验继续正常开展的前提下变更部分施肥处理,得到继续施用高量有机肥(HOM)、施用常量有机肥30年后改施高量有机肥(N-H)、继续施用常量有机肥(NOM)、施用化肥30年后改施常量有机肥(C-N)、施用高量有机肥30年后改施化肥(H-C)、施用常量有机肥30年后改施化肥(N-C)、继续施用化肥(CF)等7种施肥处理。通过观测早稻生长期间原有施肥和改施肥处理土体CO2排放通量(FCO2),研究不同后续施肥对水稻土FCO2的影响,以期探讨土壤原始有机碳和外源添加碳对土壤FCO2的影响。结果表明:7种不同施肥处理土体CO2平均排放通量(F珔CO2)分别为85.34、69.10、51.27、49.15、14.89、12.92和11.59 mg C.m-2.h-1;对施用无机肥料和常量有机肥料的土体而言,土壤本身有机碳含量对F珔CO2无显著影响,但对施用高量有机肥的土体而言,土壤本身的高有机碳含量会增强F珔CO2;CO2排放通量(Y)与添加外源碳量(x)之间符合指数方程:Y=13.33e1.719 x(R2=0.967,n=21),施入的外源有机碳对土体FCO2产生极显著影响;当季外源添加碳以CO2-C矿化分解释放的碳占其总碳量的14%左右,且该分解率受土壤有机碳含量和有机物料添加量的影响较小。     

The Effect of Plants on Mineral Weathering

This paper is centered on the specific effects of plants on the soil weathering environment; we attempt to address how to quantify this component of the ecosystem and assess feedbacks between plants and weathering processes that influence the degree and rates of mineral weathering. The basic processes whereby plants directly influence the soil chemical environment is through the generation of weathering agents, biocycling of cations, and the production of biogenic minerals. Plants may indirectly influence soil processes through the alteration of regional hydrology and local soil hydrologic regime which determines the residence time of water available for weathering. We provide a brief review of the current state of knowledge regarding the effects of plants on mineral weathering and critical knowledge gaps are highlighted. We summarize approaches that may be used to help quantify the effects of plants on soil weathering such as state factor analyses, mass balance approaches, laboratory batch experiments and isotopic techniques. We assess the changes in the soil chemical environment along a tropical bioclimatic gradient and identify the possible effects of plant production on the soil mineralogical composition. We demonstrate that plants are important in the transfer of atmospheric carbon dioxide into the mineral weathering cycle and speculate how this may be related to ecosystem properties such as NPP. In the soils of Hawaiian rainforests subjected to deforestation, pasture grasses appear to change the proportion of non crystalline to crystalline minerals by altering the soil hydrologic regime or partitioning silica into more stable biogenic forms. A better understanding of the relationship between soil weathering processes and ecosystem productivity will assist in the construction predictive models capable of evaluating the sensitivity of biogeochemical cycles to perturbations.     

Carbon and nitrogen in a temperate agroforestry system: Using stable isotopes as a tool to understand soil dynamics

Natural exchanges of carbon (C) between the atmosphere, the oceans, and terrestrial ecosystems are currently being modified through human activities as a result of fossil fuel burning and the conversion of tropical forests to agricultural land. These activities have led to a steady increase of atmospheric carbon dioxide (CO₂) over the last two Centuries. The goal of this study was to determine the potential of temperate agroforestry systems to sequester C in soil. Therefore, changes in the soil organic C (SOC) and nitrogen (N) pools were quantified and the δ¹³C and δ¹⁵N stable isotope technique was applied to assess soil C and N dynamics in a 13-year old hybrid poplar alley cropping system in Southern Canada. Results from this study showed that after 13 years of alley cropping the SOC and N pools did not differ significantly (p = 0.01) with distance from the tree row, although a trend of a larger SOC and N pool near the tree row could be observed. Soil organic C after 13 years of alley cropping, was 19 mg C g⁻¹ compared to 11 mg C g⁻¹ upon initiation of agroforestry. Soil organic C and N were not evenly distributed throughout the plow layer. The largest C and N pool occurred in the top 20 cm, which is due to the accumulation of organic material in the upper horizons as a result of no-till cultivation. The entire soil, to a 40 cm depth, showed a δ¹³C shift to that of C₃ residue. This shift reflects the greater input of residues from C₃ plants such as that derived from beans, wheat, and hybrid poplar leaf litterfall. The proportion of C derived from a C₃ source ranged from 64 to 69% to a 40 cm depth. The soil δ¹⁵N signature of this study is similar to that of mineral soil, and reflect values characteristic of N mineralization processes. However, the entire soil shows a positive shift in δ¹⁵N as a result of historical additions of manure and current use of mineral fertilizers, and ongoing processes of denitrification and nitrate leaching, which leads to an enrichment of the soil.     

土壤溶解性有机碳在陆地生态系统碳循环中的作用

土壤溶解性有机碳(DOC)是有机碳库的活跃组分,在陆地生态系统碳循环中发挥重要作用.本文从碳循环重要性着手,综述了土壤DOC在土壤碳固持与温室气体排放中的作用;结合我国的现实情况(如土壤酸化、气候变暖等),探讨了土壤DOC的相关影响因素如土壤性质、环境因素、人为活动对土壤DOC的影响及作用机制,对进一步理解土壤DOC在陆地生态系统碳循环与温室气体减排中的作用具有重要意义.     

Mineral Influence on Microbial Survival During Carbon Sequestration

Geologic carbon sequestration involves the injection of supercritical carbon dioxide into deep saline aquifers. Some of the CO₂ dissolves into the brines, perturbing water chemistry and water-rock interactions, and impacting microbial habitat and survival. In this study 3 model organisms were tested for their ability to survive high pressures of CO₂ exposure in batch cultures: the gram-negative Shewanella oneidensis (SO) strain MR-1, the gram-positive Geobacillus stearothermophilus (GS), and the methanogenic archaeon Methanothermobacter thermoautitrophicus (MT). Results indicate that GS can survive the highest pressures of CO₂ for the longest periods of time while SO is the most sensitive to CO₂ toxicity. Survival was then evaluated for SO with various minerals and rocks representative of deep saline aquifers to determine if minerals enhanced survival. Cultures were exposed to 25 bar of CO₂ for 2 to 8 h and were plated for viable cell counts. Results show that biofilm formation on the mineral surface is important in protecting SO from the harmful effects of CO₂ with quartz sandstones providing the best protection. The release of toxic metals like Al or As from minerals such as clays and feldspars, in contrast, may enhance microbial death under CO₂ stress.     

Controls on Soil Carbon Sequestration and Dynamics: Lessons from Land-use Change

Soil carbon (C) dynamics and sequestration are controlled by interactions of chemical, physical and biological factors. These factors include biomass quantity and quality, physical environment and the biota. Management can alter these factors in ways that alter C dynamics. We have focused on a range of managed sites with documented land use change from agriculture or grassland to forest. Our results suggest that interactions of soil type, plant and environment impact soil C sequestration. Above and below ground C storage varied widely across sites. Results were related to plant type and calcium on sandy soils in our Northern sites. Predictors of sequestration were more difficult to detect over the temperature range of 12.4°C in the present study. Accrual of litter under pines in the moist Mississippi site limited C storage in a similar manner to our dry Nebraska site. Pre-planting heterogeneity of agricultural fields such as found in Illinois influences C contents. Manipulation of controls on C sequestration such as species planted or amelioration of soil quality before planting within managed sites could increase soil C to provide gains in terrestrial C storage. Cost effective management would also improve soil C pools positively affecting soil fertility and site productivity.     

Carbon cycling in cultivated land and its global significance

Long-term data from Sanborn Field, one of the oldest experimental fields in the USA, were used to determine the direction of soil organic carbon (SOC) dynamics in cultivated land. Changes in agriculture in the last 50 years including introduction of more productive varieties, wide scale use of mineral fertilizers and reduced tillage caused increases in total net annual production (TNAP), yields and SOC content. TNAP of winter wheat more than doubled during the last century, rising from 2.0–2.5 to 5–6 Mg ha^–1 of carbon, TNAP of corn rose from 3–4 to 9.5–11.0 Mg ha^–1 of carbon. Amounts of carbon returned annually with crop residues increased even more drastically, from less than 1 Mg ha^–1 in the beginning of the century to 3–3.5 Mg ha^–1 for wheat and 5–6 Mg ha^–1 for corn in the 90s. These amounts increased in a higher proportion because in the early 50s removal of postharvest residues from the field was discontinued. SOC during the first half of the century, when carbon input was low, was mineralized at a high rate: 89 and 114 g m^–2 y^–1 under untreated wheat and corn, respectively. Application of manure decreased losses by half, but still the SOC balance remained negative. Since 1950, the direction of the carbon dynamics has reversed: soil under wheat monocrop (with mineral fertilizer) accumulated carbon at a rate about 50 g m^–2 y^–1, three year rotation (corn/wheat/clover) with manure and nitrogen applications sequestered 150 g m² y^–1 of carbon. Applying conservative estimates of carbon sequestration documented on Sanborn Field to the wheat and corn production area in the USA, suggests that carbon losses to the atmosphere from these soils were decreased by at least 32 Tg annually during the last 40–50 years. Our computations prove that cultivated soils under proper management exercise a positive influence in the current imbalance in the global carbon budget.     

Nitrogen Management Affects Carbon Sequestration in North American Cropland Soils

Agricultural soils in North America can be a sink for rising atmospheric CO₂ concentrations through the formation of soil organic matter (SOM) or humus. Humification is limited by the availability of nutrients such as nitrogen (N). Recommended management practices (RMPs) that optimize N availability foster humus formation. This review examines the management practices that contribute to maximizing N availability for optimizing sequestration of atmospheric CO₂ into soil humus. Farming practices that enhance nutrient use, reduce or eliminate tillage, and increase crop intensity, together, affect N availability and, therefore, C sequestration. N additions, from especially, livestock manure and leguminous cover crops are necessary for increasing grain and biomass yields and returning crop residues to the soil thereby increasing soil organic carbon (SOC) concentration. Conservation tillage practices enhance also the availability of N and increase SOC concentration. Increase in cropping intensity and/or crop rotations produce higher quantity and quality of residues, increase availability of N, and therefore foster increase in C sequestration. The benefit of C sequestration from N additions may be negated by CO₂ and N₂O emissions associated with production and application of N fertilizers. More studies need to be conducted to ascertain the benefits of adding N via manuring versus N fertilizer additions. Furthermore, site specific adaptive research is needed to identify RMPs that optimize soil N use efficiency while improving crop yield and C sequestration thereby curbing greenhouse gas (GHG) emissions. Due to the wide range of climate in North America, there is a large range of C sequestration potential in agricultural soils through N management. Humid croplands may have the potential to sequester 8–298 Tg C yr^?1 while dry croplands may sequester 1–35 Tg C yr^?1. These estimates, however, are highly uncertain and wide-ranging. Clearly, more research is needed to quantify, more precisely, the C sequestration potential across different N management scenarios especially in Mexico and Canada.