Changes In Carbon Content Research Articles

人工油松林表层土壤团聚体活性有机碳含量对短期氮添加的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 人工油松林表层土壤团聚体活性有机碳含量对短期氮添加的响应 DOI: 10.5846/stxb201608021590 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41371508）；中国科学院重点部署项目（KFZD-SW-306-2） Response of labile organic carbon content in surface soil aggregates to short-term nitrogen addition in artificial Pinus tabulaeformis forests Author: Affiliation: 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:大气氮沉降正在显著影响着森林生态系统的土壤碳循环过程。目前关于大气氮沉降如何影响土壤不同粒级团聚体内活性有机碳含量还不是十分清楚，制约人们对森林土壤碳循环的认识和有关碳循环模型的发展。通过近2年的林地梯度氮添加（0、3、6、9 g N m-2 a-1）实验，研究了短期氮添加对人工油松林表层土壤团聚体中不同活性有机碳含量的影响。结果表明：短期氮添加对表层土壤（0-10 cm）水稳性团聚体分布无显著影响；随着氮添加水平增加，大、微团聚体有机碳含量，大、微团聚体中活性和高活性有机碳含量呈先升高后降低的变化规律，并在N6处理（6 g N m-2 a-1）下上述各指标达到最大；同一处理下土壤大、微团聚体活性有机碳含量都表现为高活性有机碳 > 中活性有机碳 > 低活性有机碳；相比CK处理，N6处理大团聚体低、中、高活性有机碳含量分别增加115.06%、178.73%和79.61%，微团聚体低、中、高活性有机碳含量增加32.84%、 166.79%和62.05%。大、微团聚体中活性有机碳含量增幅最大，表明团聚体中活性有机碳对氮添加响应最为明显。研究发现，短期氮添加主要通过影响表层大、微团聚体中的中活性有机碳进而影响土壤表层有机碳含量。主成分分析表明，N添加改变了土壤理化性质，进而导致根系生物量增加并促进凋落物分解，是表层土壤团聚体活性有机碳变化的主要原因。 Abstract:Increasing nitrogen (N) deposition is significantly affecting the carbon cycle in forest ecosystems. However, it is not clear how N deposition affects the content of labile organic carbon in soil aggregates, which restricts our understanding of the soil carbon cycle and the development of the carbon cycle model. This study was conducted in an artificial Pinus tabulaeformis forest and simulated N deposition for nearly 2 years. Three N treatments, namely, N3 (3 g N m-2 a-1), N6 (6 g N m-2 a-1), and N9 (9 g N m-2 a-1), and a control treatment with no N added were applied, and each was replicated six times. Three labile organic carbon in soil aggregates were measured. There was no significant effect of short-term N addition on surface soil aggregates, while soil organic carbon was dramatically affected by N addition. Soil organic carbon content in the 0-10 cm soil layer was higher in the three N addition treatments and was highest in the N6 treatment. Additionally, the change in organic carbon content in macro-and micro-aggregates generally followed the pattern of soil organic carbon, and moderately, highly labile organic carbon also followed. In soil aggregates, the amount of highly labile carbon was greatest, then moderately labile carbon, and the content of minimally labile carbon was lowest. Compared to three labile organic carbon of CK treatment, the amount of minimally, moderately, and highly labile organic carbon in the N6 treatment increased by 115.06%, 178.73%, and 79.61% in macro-aggregate, respectively. And the amount of three labile organic carbons in the micro-aggregate increased by 32.84%, 166.79%, and 62.05%, respectively. Among the three labile organic carbon categories, the change of moderately active organic carbon in the macro-and micro-aggregates was highest, which indicated that the moderately active organic carbon in soil aggregates was the most sensitive to short-term N addition. The results showed that short-term N addition affected surface soil organic carbon content by changing the amount of moderately labile organic carbon in the surface soil macro-and micro-aggregates. The results of a principal components analysis showed that soil total N and pH were affected by short-term N addition and it also caused a change in soil texture and total P. The changes of soil physical and chemical properties may result in an increase in root biomass and litter decomposition which brought a significantly change on active organic carbon content in surface soil aggregates. 参考文献 相似文献 引证文献

Identification and Timing of Dormant and Ontogenetic Phase for Sweet Cherries in Northeast Germany for Modelling Purposes

Some important stages of plant development, such as dormancy release and beginning of ontogenetic development, cannot be easily observed so that semi-mechanistic phenological models of spring phases mostly does not accurately reflect the control of these physiological stages. For this reason, over 6 years we studied weekly changes of Fresh Weight (FW), Dry Weight (DW), Water (WC), Nitrogen (NC) and Carbon Content (CC) in sweet cherry buds (Prunus avium L., cultivar ‘Summit’), from October to mid of April (stage ‘open cluster’, BBCH 56). Together with an experimental study to determine the date of endodormancy release, we were able to define the annual variability and average duration in the timing of para- endo-, and ecodormancy phase for sweet cherries, cultivar ‘Summit’. The secession of growth in autumn starts when all leafs has fallen down (BBCH 97) and marks the transition from para-to endodormancy. During endodormancy all investigated parameters reached a constant level which also did not change during ecodormancy. Our results showed that ecodormancy can be a relatively long phase in temperate climates, which must be adequately handled in phenological models. Beginning of ontogenetic development was clearly related to steadily rising water contents in cherry buds, which stayed stable during endo- and ecodormancy. Thus, this study highlights the importance of bud’s water content to define dormancy phases as well as beginning of ontogenetic development. The latter one was induced by continuously rising air temperatures above the freezing point. Physiologically, beginning of ontogenetic development is a flexible date which occurred on average 26 days before bud swelling was observed.

Global warming potential and greenhouse gas emission under different soil nutrient management practices in soybean-wheat system of central India.

Soil nutrient management is a key component contributing to the greenhouse gas (GHG) flux and mitigation potential of agricultural production systems. However, the effect of soil nutrient management practices on GHG flux and global warming potential (GWP) is less understood in agricultural soils of India. The present study was conducted to compare three nutrient management systems practiced for nine consecutive years in a soybean-wheat cropping system in the Vertisols of India, in terms of GHG flux and GWP. The treatments were composed of 100% organic (ONM), 100% inorganic (NPK), and integrated nutrient management (INM) with 50% organic+50% inorganic inputs. The gas samples for GHGs (CO2, CH4, and N2O) were collected by static chamber method at about 15-day interval during 2012-13 growing season. The change in soil organic carbon (SOC) content was estimated in terms of the changes in SOC stock in the 0-15cm soil over the 9-year period covering 2004 to 2013. There was a net uptake of CH4 in all the treatments in both soybean and wheat crop seasons. The cumulative N2O and CO2 emissions were in the order of INM>ONM>NPK with significant difference between treatments (p<0.05) in both the crop seasons. The annual GWP, expressed in terms of CH4 and N2O emission, also followed the same trend and was estimated to be 1126, 1002, and 896kg CO2 eqha-1year-1 under INM, ONM, and NPK treatments, respectively. However, the change in SOC stock was significantly higher under ONM (1250kgha-1year-1) followed by INM (417kgha-1year-1) and least under NPK (198kgha-1year-1) treatment. The wheat equivalent yield was similar under ONM and INM treatments and was significantly lower under NPK treatment. Thus, the GWP per unit grain yield was lower under ONM followed by NPK and INM treatments and varied from 250, 261, and 307kg CO2 eqMg-1 grain yield under ONM, NPK, and INM treatments, respectively.

Endure and call for help: strategies of black mustard plants to deal with a specialized caterpillar

SummaryPlants have evolved inducible resistance and tolerance mechanisms against insect herbivores. Resistance mechanisms that affect herbivorous insects directly can be effective against generalist herbivores, but will not deter specialist herbivores from attacking the plant. Tolerance mechanisms and indirect plant resistance are more likely effective strategies used by plants when dealing with specialist herbivores. However, inducible indirect resistance and tolerance mechanisms have rarely been investigated within the same study system.We studied multiple tolerance mechanisms and the role of natural enemies in reducing fitness loss ofBrassica nigraplants incurred by feeding by the specialist herbivorePieris brassicae. For this, we measured the changes in carbon and nitrogen triggered by herbivore attack and quantified plant biomass and seed production under field conditions, in the presence or absence of natural enemies of the herbivores. We also assessed whetherB. nigraincreased selfing rates when exposed to herbivore infestation, and investigated whether infestation byP. brassicaerenderedB. nigraplants more attractive to night‐active pollinators than control plants.We found thatB. nigraflowers are rarely visited by insects during the night, and exposure to herbivores did not influence selfing rates.Brassica nigraplants compensated for herbivory in terms of vegetative biomass. Seed set was negatively affected by herbivory in the absence of natural enemies, but not in the presence of natural enemies. Plants responded to herbivory with drastic changes in nitrogen contents of leaves and flowers, whereas no changes in carbon concentrations were detected.The investment in reproduction or re‐growth of vegetative tissues is not sufficient to sustain plant fitness. Reproductive output of flowering mustard plants is only sustained when interactions with the natural enemies of the herbivores are preserved. We conclude that natural enemies of herbivorous insects play an important role as component of the plant's defence strategy. This study reveals that both tolerance and indirect resistance are strategies of this plant species to sustain fitness.

Soil organic carbon status and sustainability of slash-and-burn cultivation in India

ABSTRACTThe study was carried out (a) to identify the changes in the soil organic carbon (SOC) content during the different phases of slash-and-burn cultivation—i.e., before slash-and-burn (Phase 1), after slash-and-burn (Phase 2), and after harvest (Phase 3); and (b) to determine the status of soil organic carbon content in the primary undisturbed forest (Site 1) and in the secondary forests, where slash-and-burn cultivation was taken up ~25 yr (Site 2), 15 yr (Site 3), and 5 yr back (Site 4). The undisturbed forest holds the largest amount of SOC % (5.25) followed by 25 yr (3.07), 5 yr (2.86), and 15 yr (2.27) fallow. The mean percentages of SOC in the 0- to 15-cm layer fell from 3.07 in Phase 1 to 2.53 and 2.37, respectively, in Phases 2 and 3; in the subsurface 15- to 30-cm layer, they fell from 1.95 to 1.62 and 1.63, respectively. Although, the SOC in Phase 3 still seems sufficient to support another round of cultivation, further studies are needed to examine crop yields in successive cultivation cycles, suitability of other rice varieties, and weed and pest types and rates of invasion. Tribal population dynamics is another major concern, which needs assessment for monitoring future land requirements.

Heat treatment response of TiC-reinforced steel matrix composite

A particulate TiC-reinforced SKD11 steel matrix composite is fabricated by using a pressure infiltration casting, achieving a homogeneous distribution of the particles with 60 vol%. The retained austenite fraction in the composite matrix is approximately 19% after quenching from the austenitization temperature of 1010 °C, which is larger than 13% in as-quenched condition of unreinforced SKD11. A combined analysis on the austenite lattice parameter using XRD profiles and first-principle calculation suggests the increase of carbon content in the steel matrix possibly by partial dissolution of TiC during casting. The change of carbon content and prior austenite grain size reasonably accounts for the increase of retained austenite fraction in the composite matrix. In the austenitizing temperatures ranging from 950 °C to 1040 °C, the retained austenite fraction in the composite matrix in as-quenched condition increases more rapidly than that of unreinforced SKD11 with the increase of austenitization temperature, while the hardness of the composite is less sensitive to the austenitization temperature. This suggests that it is advantageous to conduct the austenitization at a temperature below 1010 °C, which is typical practice of austenitization of the unreinforced SKD11, because the retention of austenite is effectively suppressed while minimizing the loss of hardness.

ABOUT THE ISSUE OF CARBIDES FE3C AND FE7C3 FORMATION IN HIGH-CHROMIUM CAST IRONS

Purpose. This article analyzes the formation conditions, transformation and systematization of carbide phases formed in the system Fe – C – Cr.Methodology. Conversion of the elements’ content from mass % into atomic % and vice versa was carried out using standard methods. In order to identify the structural components and etching of carbides the Marble etchant was applied. Cast iron 300Х28Н2 in cast state without heat treatment and after isothermal holding at 1050 °С during 4.5 hours with further normalization was studied. Findings. Isothermal state diagrams of the Fe–C–Cr system don’t take into account the existence of Fe7C3 carbide alloyed with chromium. But there is evidence of the existence of chromic carbides containing 24…37.6 % of chromium, which exceeds its maximum solubility in cementite, but is not enough to form Cr7C3.Analysis of chromium and carbon content in carbide phases which are formed in high-chromium cast irons allowed to substantiate the formation of Fe7С3 carbide, stabilized with chromium. Assessment of the carbide phase by chemical composition in mass percent doesn’t allow determining the main carbide-forming element with sufficient accuracy. It is shown that with the increase of chromium concentration in carbides, mass content of carbon increases. Areas of existence of carbides of different types depending on carbon and chromium content in them were determined. Maximum content of chromium in the carbide (Fe, Cr)7C3 is 44.0 %. Allocation of alloyed cementite occurs on the present carbides Ме7C3 or grain boundaries, and with the increase of cooling rate – in the grain volume. This process is thermodynamically inevitable due to the decrease of carbon solubility in ferrite or austenite at temperatures when chromium diffusion is impeded, and only carbon diffusion is possible. At high chromium concentrations carbide Fe7C3 is formed, which transforms into Cr7C3 carbide as chromium diffusion takes place. Originality. The model of laminated structure of carbides, formed out of the liquid phase in the system Fe–C–Cr was built. The identification of the carbide phase based on the elements’ concentration in atomic percent was suggested. The model of the change of carbon content in carbides of different types depending on chromium concentration was built. Practical value. The suggested system of carbide classification and their structural model allows optimizing the cast irons’ composition and heat treatment modes for different exploitation conditions.

Effect of carbon equivalent on thermal and mechanical properties of compacted graphite cast iron

Abstract

Long (MIS 5e – 3) environmental history of a paleolake in central Poland recorded in the succession from Kubłowo

One of the longest (above 7 m thick) uninterrupted Eemian-Vistulian (Weichselian) pollen successions in Poland is known from Kubłowo (central Poland). The huge importance of this succession is manifested in the possibility of study the evolution of the lake environment under the influence of changing, from interglacial to glacial climatic conditions.The reconstruction of the environmental changes at Kubłowo and its surroundings show the short climate fluctuations and a detailed picture of the natural conditions prevailing in central Poland (central Europe) during the period from approximately 126,000 to 55,000 years BP. Based on the results of multi-proxy analysis, four lacustrine stages linked with a higher water level and three boggy stages (low water level) of evolution of the Kubłowo paleolake were observed.The pollen diagram from Kubłowo reveals a succession of eighteen local pollen assemblage zones (K1-K18 L PAZ). The K1 to K7 LPAZ zones record the interglacial succession correlated with the Eemian. The next pollen zones, K8 to K18, are linked with the Vistulian. The pollen sequence shows, between the Eemian Interglacial (MIS 5e) and the last glaciation (second stadial of the Plenivistulian (MIS 4-3), four cold intervals that are interpreted as stadial phases: Herning, Rederstall, Schalkholtz and Ebersdorf separated by three temperate intervals (interstadials): Brörup, Odderade and Oerel.In the studied sediments, 25 species of subfossil Cladocera were identified, and ten zones of fauna development were distinguished. The unique feature of this profile is the good preservation of above 100,000-year-old Cladocera remains and a high diversity of species, which are primarily littoral. The Middle and Late Eemian were periods convenient to Cladocera development due to high temperatures, high water levels, high trophy and occurrence macrophytes. A deterioration of fauna living conditions started in the Late Eemian and next took place in the Vistulian cold events.The results of isotopic and geochemical analyses of organic matter from Kubłowo have enabled the reconstruction of varying environmental conditions and the origin of organic matter. The organic carbon content (TOC) changes from 1% to 40% and is closely related to climatic conditions. During the Eemian, the amount of TOC systematically increased. The lowest values are recorded in the coldest periods during the Herning, Rederstall and Schalkholz Stadials. The C/N atomic ratio fluctuates from 13 to 34 and the highest values occur in the Brörup Interstadial. The values of δ13C change from −27.9 to −12.9‰, and δ15N values oscillate between −1.6 and +5.3‰.

How do changes in bulk soil organic carbon content affect carbon concentrations in individual soil particle fractions?

We test the common assumption that organic carbon (OC) storage occurs on sand-sized soil particles only after the OC storage capacity on silt- and clay-sized particles is saturated. Soil samples from a Brookston clay loam in Southwestern Ontario were analysed for the OC concentrations in bulk soil, and on the clay (<2 μm), silt (2–53 μm) and sand (53–2000 μm) particle size fractions. The OC concentrations in bulk soil ranged from 4.7 to 70.8 g C kg−1 soil. The OC concentrations on all three particle size fractions were significantly related to the OC concentration of bulk soil. However, OC concentration increased slowly toward an apparent maximum on silt and clay, but this maximum was far greater than the maximum predicted by established C sequestration models. In addition, significant increases in OC associated with sand occurred when the bulk soil OC concentration exceeded 30 g C kg−1, but this increase occurred when the OC concentration on silt + clay was still far below the predicted storage capacity for silt and clay fractions. Since the OC concentrations in all fractions of Brookston clay loam soil continued to increase with increasing C (bulk soil OC content) input, we concluded that the concept of OC storage capacity requires further investigation.

Irrigation regime affected SOC content rather than plow layer thickness of rice paddies: A county level survey from a river basin in lower Yangtze valley, China

While the impacts of farm management practices such as fertilization, tillage and straw return on soil organic carbon dynamics in croplands have been widely studied, the effects of irrigation management in irrigated rice paddies have not yet been widely assessed. Changes in plow layer thickness and soil organic carbon content of rice paddies were analyzed using data obtained in a county-level survey of soil fertility conducted in 2005 and 2006 in Guichi County, Anhui Province, China. Both soil thickness and organic carbon content of plow layer showed skewed normal distributions, with their averages of 14.58±3.92cm, and 16.45±6.02g/kg, respectively. The irrigation method was found to have significant influences on both plow layer thickness and soil organic carbon content, as the plow layer thickness and soil organic carbon content had an inverse response to the irrigation intensity derived from different irrigation methods. The land-level performance of irrigation/drainage infrastructure and the irrigation water sources were detected to have significant effect on plow layer thickness, but little influence on soil organic carbon content. While the capacity of irrigation/drainage infrastructure had a remarkable effect on soil organic carbon content but little impact on plow layer thickness. However, the irrigation condition for surveyed fields was detected to have little effect on both plow layer thickness and soil organic carbon content. These results indicated that irrigation management should keep the balance between surface erosion on plow layer thickness and soil organic carbon accumulation. Hence, developing new technique for good irrigation infrastructure and water management in future will help soil organic carbon accumulation as well as improve the soil for enhanced crop growth in rice agriculture.

Experimental investigation and numerical simulation on interfacial carbon diffusion of diamond tool and ferrous metals

We numerically simulated and experimentally studied the interfacial carbon diffusion between diamond tool and workpiece materials. A diffusion model with respect to carbon atoms of diamond tool penetrating into chips and machined surface was established. The numerical simulation results of the diffusion process reveal that the distribution laws of carbon atoms concentration have a close relationship with the diffusion distance, the diffusion time, and the original carbon concentration of the work material. In addition, diamond face cutting tests of die steels with different carbon content are conducted at different depth of cuts and feed rates to verify the previous simulation results. The micro-morphology of the chips is detected by scanning electron microscopy. Energy dispersive X-ray analysis was proposed to investigate the change in carbon content of the chips surface. The experimental results of this work are of benefit to a better understanding on the diffusion wear mechanism in single crystal diamond cutting of ferrous metals. Moreover, the experimental results show that the diffusion wear of diamond could be reduced markedly by applying ultrasonic vibration to the cutting tool compared with conventional turning.

Changes in The Content of Biodegradable Organic Matter in Tap Water in The City of Częstochowa / Zmiany Zawartości Biodegradowalnej Materii Organicznej w Wodzie Wodociagowej Dla Miasta Częstochowy

Abstract This paper presents research aimed at the assessment of biodegradable organic carbon content changes (BDOC) during water disinfection process. The water samples examined in the research came from intakes, pumping stations at treatment plants situated in the Silesia district and water consumers. The examined water was underground water. One water sample was disinfected by sodium sub chloride while the other one by ozone. BDOC was determined using the Joret method, which involves observation of dissolved organic carbon (DOC) decrease in the examined water. The research has shown that BDOC content fluctuates at every stage of the treatment process and distribution of the examined water. Another analyzed parameter was biological stability of water.

Small to intermediate strain properties of fly ashes with various carbon and biomass contents

High-carbon-content fly ashes with biomass particles are typically landfilled in accordance with the ASTM C618 regulation. To quantify their geotechnical properties relating to storage and disposal, this study evaluates the small to intermediate strain properties of fly ashes with various carbon and biomass contents. Tested fly ashes had carbon contents ranging from 1.1% to 9.6%, resulting from co-combusting coal with biomass (biomass contents ranging from 0% to 8.2% by weight). The small-strain stiffness and intermediate-strain constrained modulus were evaluated using consolidation tests performed in a modified oedometer cell equipped with bender elements. It was found that initial void ratio governed the compressibility (or constrained modulus) of fly ashes, and with an increase in carbon and biomass contents, the small-strain stiffness of fly ashes decreased due to the decrease in number of direct contacts between microspheres. In addition, the interfine void ratio, ef, was employed instead of global void ratio to capture the alteration of interparticle contact or interparticle coordination between microspheres, due to the change in carbon and biomass contents. Finally, the stiffness in an overconsolidated state and the stiffness anisotropy of fly ashes were evaluated.

Modeling aerobic decomposition of rice straw during the off-rice season in an Andisol paddy soil in a cold temperate region of Japan: Effects of soil temperature and moisture

ABSTRACTSubmerged rice paddies are a major source of methane (CH4) which is the second most important greenhouse gas after carbon dioxide (CO2). Accelerating rice straw decomposition during the off-rice season could help to reduce CH4 emission from rice paddies during the single rice-growth season in cold temperate regions. For understanding how both temperature and moisture can affect the rate of rice straw decomposition during the off-rice season in the cold temperate region of Tohoku district, Japan, a modeling incubation experiment was carried out in the laboratory. Bulk soil and soil mixed with 2% of δ13C-labeled rice straw with a full factorial combination of four temperature levels (−5 to 5, 5, 15, 25°C) and two moisture levels (60% and 100% WFPS) were incubated for 24 weeks. The daily change from −5 to 5°C was used to model the freezing–thawing cycles occurring during the winter season. The rates of rice straw decomposition were calculated by (i) CO2 production; (ii) change in the soil organic carbon (SOC) content; and (iii) change in the δ13C value of SOC. The results indicated that both temperature and moisture affected the rate of rice straw decomposition during the 24-week aerobic incubation period. Rates of rice straw decomposition increased not only with high temperature, but also with high moisture conditions. The rates of rice straw decomposition were more accurately calculated by CO2 production compared to those calculated by the change in the SOC content, or in its δ13C value. Under high moisture at 100% WFPS condition, the rates of rice straw decomposition were 14.0, 22.2, 33.5 and 46.2% at −5 to 5, 5, 15 and 25°C temperature treatments, respectively. While under low moisture at 60% WFPS condition, these rates were 12.7, 18.3, 31.2 and 38.4%, respectively. The Q10 of rice straw decomposition was higher between −5 to 5 and 5°C than that between 5 and 15°C and that between 15 and 25°C. Daily freezing–thawing cycles (from −5 to 5°C) did not stimulate rice straw decomposition compared with low temperature at 5°C. This study implies that to reduce CH4 emission from rice paddies during the single rice-growth season in the cold temperate regions, enhancing rice straw decomposition during the high temperature period is very important.

Calcium Nodules as a Proxy for Quaternary Paleoclimate Change on China's Loess Plateau.

Different proxies have been used to investigate Quaternary paleoclimate change. Here, we used weathering of calcium nodules in paleosols on China’s Loess Plateau as a proxy for Quaternary paleoclimate changes to provide an alternative indicator of these changes. Paleosol and carbonate nodules were collected from Luochuan and Lantian counties in Shaanxi Province, China. We found that this approach allowed quantitative reconstruction of temperature, rainfall, soil mineral composition, and the effects of weathering and leaching. The changes in carbonate content in the loess and paleosol sequences were controlled by alternating dry and wet climatic conditions. Nodule formation conditions were directly affected by the leaching and migration of elements. The loess and paleosol sequences developed calcium nodules, and their formation was closely related to the rainfall and leaching characteristics of the paleoclimate. The paleoclimate and soil minerals affected the vegetation types and directly influenced changes in the soil. During formation of the calcium nodules, the surface vegetation evolved slowly, and the number of species and quantity of vegetation both decreased.

Changes in Ocean Heat, Carbon Content, and Ventilation: A Review of the First Decade of GO-SHIP Global Repeat Hydrography.

Global ship-based programs, with highly accurate, full water column physical and biogeochemical observations repeated decadally since the 1970s, provide a crucial resource for documenting ocean change. The ocean, a central component of Earth's climate system, is taking up most of Earth's excess anthropogenic heat, with about 19% of this excess in the abyssal ocean beneath 2,000 m, dominated by Southern Ocean warming. The ocean also has taken up about 27% of anthropogenic carbon, resulting in acidification of the upper ocean. Increased stratification has resulted in a decline in oxygen and increase in nutrients in the Northern Hemisphere thermocline and an expansion of tropical oxygen minimum zones. Southern Hemisphere thermocline oxygen increased in the 2000s owing to stronger wind forcing and ventilation. The most recent decade of global hydrography has mapped dissolved organic carbon, a large, bioactive reservoir, for the first time and quantified its contribution to export production (∼20%) and deep-ocean oxygen utilization. Ship-based measurements also show that vertical diffusivity increases from a minimum in the thermocline to a maximum within the bottom 1,500 m, shifting our physical paradigm of the ocean's overturning circulation.

Assessing the potential of amino acid &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C patterns as a carbon source tracer in marine sediments: effects of algal growth conditions and sedimentary diagenesis

Abstract. Burial of organic carbon in marine sediments has a profound influence in marine biogeochemical cycles and provides a sink for greenhouse gases such as CO2 and CH4. However, tracing organic carbon from primary production sources as well as its transformations in the sediment record remains challenging. Here we examine a novel but growing tool for tracing the biosynthetic origin of amino acid carbon skeletons, based on naturally occurring stable carbon isotope patterns in individual amino acids (δ13CAA). We focus on two important aspects for δ13CAA utility in sedimentary paleoarchives: first, the fidelity of source diagnostic of algal δ13CAA patterns across different oceanographic growth conditions, and second, the ability of δ13CAA patterns to record the degree of subsequent microbial amino acid synthesis after sedimentary burial. Using the marine diatom Thalassiosira weissflogii, we tested under controlled conditions how δ13CAA patterns respond to changing environmental conditions, including light, salinity, temperature, and pH. Our findings show that while differing oceanic growth conditions can change macromolecular cellular composition, δ13CAA isotopic patterns remain largely invariant. These results emphasize that δ13CAA patterns should accurately record biosynthetic sources across widely disparate oceanographic conditions. We also explored how δ13CAA patterns change as a function of age, total nitrogen and organic carbon content after burial, in a marine sediment core from a coastal upwelling area off Peru. Based on the four most informative amino acids for distinguishing between diatom and bacterial sources (i.e., isoleucine, lysine, leucine and tyrosine), bacterially derived amino acids ranged from 10 to 15 % in the sediment layers from the last 5000 years, and up to 35 % during the last glacial period. The greater bacterial contributions in older sediments indicate that bacterial activity and amino acid resynthesis progressed, approximately as a function of sediment age, to a substantially larger degree than suggested by changes in total organic nitrogen and carbon content. It is uncertain whether archaea may have contributed to sedimentary δ13CAA patterns we observe, and controlled culturing studies will be needed to investigate whether δ13CAA patterns can differentiate bacterial from archeal sources. Further research efforts are also needed to understand how closely δ13CAA patterns derived from hydrolyzable amino acids represent total sedimentary proteineincous material, and more broadly sedimentary organic nitrogen. Overall, however, both our culturing and sediment studies suggest that δ13CAA patterns in sediments will represent a novel proxy for understanding both primary production sources, and the direct bacterial role in the ultimate preservation of sedimentary organic matter.

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

Nitrate (NO3 −) and ammonium (NH4 +) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 −:NH4 + ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 − or NH4 +. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 − and +NH4 +) in five streams. Biomass-specific uptake rates (U spec ) of NO3 − and NH4 + were then measured using in situ additions of 15N-labeled NO3 − and NH4 +. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U spec -NO3 − of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U spec -NO3 − was one order of magnitude greater and more variable than U spec -NH4 +, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 − and +NH4 +) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U spec -NO3 − and for the +NH4 + than for the +NO3 − treatments. In particular, enrichment with NH4 + reduced biofilm U spec -NO3 − uptake, which has important implications for N cycling in high NH4 + streams.

Influence of wildfire severity on soil physical degradation in two pine forest stands of NW Spain

This study examined the effect of wildfire on the physical degradation of two forest soils in NW Spain and compared this against changes produced by controlled laboratory heating experiments in which unburned soils from neighbouring sites were exposed to five different heating regimes. The physical soil degradation was considered with respect to organic carbon content, dry aggregate size distribution, water aggregate stability, water repellency, and hydraulic conductivity. The results of this analysis show that the changes in the physical properties of the wildfire-affected soils were similar to the changes observed in the heating experiments. However, the wildfire had contrasting effects in terms of soil physical degradation at the two study sites, which can be attributed to differences in soil heating regimes and fire severity. At one study site, the wildfire did not produce marked changes in organic carbon content or in aggregation, except for a slight fragmentation of macro-aggregates into micro-aggregates. Also, soil water repellency remained very strong after the wildfire, resulting in low hydraulic conductivity. Based on the laboratory experiments, the soil at this site was not exposed to temperatures above 220°C. The wildfire at the other study site resulted in more pronounced degradation of the soil, as shown in the reduction of organic carbon content by almost 50%, resulting in reduced stability of the aggregates. The wildfire also reduced soil water repellency considerably, but hydraulic conductivity did not increase noticeably. In this case the soil could be exposed to temperatures between 220 and 380°C.