Similar temperature responses suggest future climate warming will not alter partitioning between denitrification and anammox in temperate marine sediments

Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12‐week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima (T_opt) and apparent activation energy (E_a), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59 °C. With a few exceptions, T_opt and E_a of denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments, E_a was somewhat lower for anammox compared to denitrification across all treatments. However, T_opt did not differ between processes, and neither E_a nor T_opt changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature responses, and these responses were not influenced by warming. This led us to reject the hypothesis that anammox is more cold‐adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification.     

生物多样性与生态系统多功能性: 进展与展望

全球变化和人类活动引起的生物多样性丧失将会对生态系统功能产生诸多不利影响, 如生产力下降、养分循环失衡等。因此, 始于20世纪90年代的生物多样性与生态系统功能(biodiversity and ecosystem functioning, BEF)研究一直是生态学界关注的热点。然而, 随着研究的深入, 人们逐步认识到生态系统并非仅仅提供单个生态系统功能, 而是能同时提供多个功能, 这一特性被称之为“生态系统多功能性” (ecosystem multifunctionality, EMF)。尽管有此认识, 但直到2007年, 研究者才开始定量描述生物多样性与生态系统多功能性(biodiversity and ecosystem multifunctionality, BEMF)的关系。目前, BEMF研究已成为生态学研究的一个重要议题, 但仍存在很多问题和争议, 如缺少公认的多功能性测度标准、生态系统不同功能之间的权衡问题等。本文概述了BEMF研究的发展历程、常用的量化方法、EMF的维持机制和不同研究视角下BEMF的关系。针对现有研究中的不足, 本文还总结了需要进一步深入研究的地方, 特别强调了优化EMF测度方法和研究不同维度生物多样性与EMF间关系的重要性, 以期对未来的BEMF研究有所帮助。     

Modeling nitrous oxide emission from rivers: a global assessment

Estimates of global riverine nitrous oxide (N₂O) emissions contain great uncertainty. We conducted a meta‐analysis incorporating 169 observations from published literature to estimate global riverine N₂O emission rates and emission factors. Riverine N₂O flux was significantly correlated with NH₄, NO₃ and DIN (NH₄ + NO₃) concentrations, loads and yields. The emission factors EF(a) (i.e., the ratio of N₂O emission rate and DIN load) and EF(b) (i.e., the ratio of N₂O and DIN concentrations) values were comparable and showed negative correlations with nitrogen concentration, load and yield and water discharge, but positive correlations with the dissolved organic carbon : DIN ratio. After individually evaluating 82 potential regression models based on EF(a) or EF(b) for global, temperate zone and subtropical zone datasets, a power function of DIN yield multiplied by watershed area was determined to provide the best fit between modeled and observed riverine N₂O emission rates (EF(a): R² = 0.92 for both global and climatic zone models, n = 70; EF(b): R² = 0.91 for global model and R² = 0.90 for climatic zone models, n = 70). Using recent estimates of DIN loads for 6400 rivers, models estimated global riverine N₂O emission rates of 29.6–35.3 (mean = 32.2) Gg N₂O–N yr⁻¹ and emission factors of 0.16–0.19% (mean = 0.17%). Global riverine N₂O emission rates are forecasted to increase by 35%, 25%, 18% and 3% in 2050 compared to the 2000s under the Millennium Ecosystem Assessment's Global Orchestration, Order from Strength, Technogarden, and Adapting Mosaic scenarios, respectively. Previous studies may overestimate global riverine N₂O emission rates (300–2100 Gg N₂O–N yr⁻¹) because they ignore declining emission factor values with increasing nitrogen levels and channel size, as well as neglect differences in emission factors corresponding to different nitrogen forms. Riverine N₂O emission estimates will be further enhanced through refining emission factor estimates, extending measurements longitudinally along entire river networks and improving estimates of global riverine nitrogen loads.     

草原灌丛化对生态系统多功能性的影响

草原灌丛化现象在干旱半干旱区广泛发生,影响了生态系统的结构、过程和功能。生态系统具有同时提供多种功能的能力,即生态系统多功能性。灌丛化是否会引起草原生态系统多功能性的减少,其内在的作用机制又是什么？这些问题仍有待明晰。理解草原灌丛化对生态系统多功能性的影响,对于促进草原地区"草-畜-人"平衡和实现区域可持续发展至关重要。从响应规律、影响路径和控制因素三个方面总结评述了草原灌丛化对生态系统多功能性影响的研究进展,主要包括:(1)阐明了单一生态系统功能和多种生态系统功能对草原灌丛化的响应特征;(2)从生物路径、非生物路径以及气候变化和人类活动的影响方面探讨了灌丛化对生态系统多功能性的影响路径;(3)从灌丛化物种、灌丛化阶段和草原类型三个方面明晰了草原灌丛化对生态系统多功能性影响的控制因素。在此基础上,针对灌丛化对生态系统多功能性的影响机制,对生产-生态功能权衡的影响等方面对未来研究进行了展望,并面向可持续发展目标探讨了灌丛化生态系统的可持续管理路径。研究可为我国灌丛化草原的恢复和管理提供支撑。     

The potential to mitigate global warming with no-tillage management is only realized when practised in the long term

No‐tillage (NT) management has been promoted as a practice capable of offsetting greenhouse gas (GHG) emissions because of its ability to sequester carbon in soils. However, true mitigation is only possible if the overall impact of NT adoption reduces the net global warming potential (GWP) determined by fluxes of the three major biogenic GHGs (i.e. CO₂, N₂O, and CH₄). We compiled all available data of soil‐derived GHG emission comparisons between conventional tilled (CT) and NT systems for humid and dry temperate climates. Newly converted NT systems increase GWP relative to CT practices, in both humid and dry climate regimes, and longer‐term adoption (>10 years) only significantly reduces GWP in humid climates. Mean cumulative GWP over a 20‐year period is also reduced under continuous NT in dry areas, but with a high degree of uncertainty. Emissions of N₂O drive much of the trend in net GWP, suggesting improved nitrogen management is essential to realize the full benefit from carbon storage in the soil for purposes of global warming mitigation. Our results indicate a strong time dependency in the GHG mitigation potential of NT agriculture, demonstrating that GHG mitigation by adoption of NT is much more variable and complex than previously considered, and policy plans to reduce global warming through this land management practice need further scrutiny to ensure success.     

地膜覆盖和施氮量对旱作春玉米农田净温室效应的影响

以旱作雨养条件下的春玉米为试验对象,在长武黄土高原农业生态试验站进行田间试验,研究了地膜覆盖和施氮量对农田净温室效应和温室气体排放强度的影响.结果表明:采用地膜覆盖与增加施氮量都会影响净温室效应与温室气体排放强度,地膜覆盖条件下(FM),不同施氮量的春玉米产量为1643~16699 kg·hm-2,净温室效应(CO_2当量,下同)为595~4376 kg·hm^-2·a^-1,温室气体排放强度为213~358 kg·t^-1;无覆膜条件下(UM),不同施氮量的春玉米产量为956~8821 kg·hm-2,净温室效应为342~4004 kg·hm^-2·a^-1,温室气体排放强度为204~520 kg·t^-1.研究表明,对于旱作春玉米农田系统,地膜覆盖可以有效降低温室气体排放强度,增加作物产量,地膜覆盖下施氮250 kg·hm-2可以实现高产与降低环境代价的双赢.     

Floods increase carbon dioxide and methane fluxes in agricultural streams

1. Changes in climate are causing floods to occur more often and more intensely in many parts of the world, including agricultural landscapes of southern Wisconsin (U.S.A.). How flooding and greater flood frequency affect stream carbon dioxide (CO₂) and methane (CH₄) fluxes and concentrations is not obvious. Thus, we asked how diffusive fluxes of CO₂ and CH₄ varied over time, particularly in response to floods, in agricultural streams, and what were likely causes for observed flood responses.
2. We measured concentrations and diffusive fluxes of CO₂ and CH₄ at 10 stream sites in mixed agricultural and suburban catchments in southern Wisconsin (U.S.A.) during the growing season (March–November) in a year that experienced multiple floods. Habitat, hydrologic, and water chemistry attributes were also quantified to determine likely drivers of changes in gas concentrations and fluxes.
3. Habitat and water chemistry, as well as CO₂ and CH₄ concentrations and fluxes were temporally erratic and lacked any seasonality. Carbon dioxide and CH₄ concentrations and fluxes were higher during floods along with increased water velocity, turbidity, and dissolved organic carbon and decreases in dissolved oxygen, soft sediment depth, and macrophyte cover.
4. Increased gas concentrations and fluxes were probably due to flushing of gases from soils, respiration of organic matter in the channel, and increased gas exchange velocities during floods.
5. Flooding alleviated both supply and transfer limits on CO₂ and CH₄ emissions in these agricultural streams, and frequent and prolonged flooding during the growing season led to sustained high emissions from these streams. We hypothesise that such persistent increases in emissions during floods may be a common response to high precipitation periods for many agricultural streams.

     

Optimizing rice yields while minimizing yield‐scaled global warming potential

To meet growing global food demand with limited land and reduced environmental impact, agricultural greenhouse gas (GHG) emissions are increasingly evaluated with respect to crop productivity, i.e., on a yield‐scaled as opposed to area basis. Here, we compiled available field data on CH₄ and N₂O emissions from rice production systems to test the hypothesis that in response to fertilizer nitrogen (N) addition, yield‐scaled global warming potential (GWP) will be minimized at N rates that maximize yields. Within each study, yield N surplus was calculated to estimate deficit or excess N application rates with respect to the optimal N rate (defined as the N rate at which maximum yield was achieved). Relationships between yield N surplus and GHG emissions were assessed using linear and nonlinear mixed‐effects models. Results indicate that yields increased in response to increasing N surplus when moving from deficit to optimal N rates. At N rates contributing to a yield N surplus, N₂O and yield‐scaled N₂O emissions increased exponentially. In contrast, CH₄ emissions were not impacted by N inputs. Accordingly, yield‐scaled CH₄ emissions decreased with N addition. Overall, yield‐scaled GWP was minimized at optimal N rates, decreasing by 21% compared to treatments without N addition. These results are unique compared to aerobic cropping systems in which N₂O emissions are the primary contributor to GWP, meaning yield‐scaled GWP may not necessarily decrease for aerobic crops when yields are optimized by N fertilizer addition. Balancing gains in agricultural productivity with climate change concerns, this work supports the concept that high rice yields can be achieved with minimal yield‐scaled GWP through optimal N application rates. Moreover, additional improvements in N use efficiency may further reduce yield‐scaled GWP, thereby strengthening the economic and environmental sustainability of rice systems.     

Comparing global warming potential,energy use and land use of organic,conventional and integrated winter wheat production

To ensure a sustainable food supply for the growing population, the challenge is to find agricultural systems that can meet production requirements within environmental constraints and demands. This study compares the impacts of winter wheat production on energy use, land use and 100 years Global Warming Potential (GWP₁₀₀) under different arable farming systems and farming practices. Life cycle assessment was used to simulate the impacts of organic, conventional and integrated farming (IF) systems along the production chain from input production up to the farm gate. The IF system models were designed to combine the best practices from organic and conventional systems to reduce negative environmental impacts without significant yield reductions. An integrated system that used food waste digestate as a fertiliser, and utilised pesticides and no‐tillage had the lowest energy use and GWP per functional unit of 1000 kg wheat output. When the impacts of some specific practices for reducing energy use and GWP were compared, the highest energy use reductions were achieved by replacing synthetic nitrogen fertilisers with anaerobically treated food waste or nitrogen fixing crops, increasing yields through crop breeding and using no‐tillage instead of ploughing. The highest GWP reductions were achieved by using nitrification inhibitors, replacing synthetic nitrogen fertilisers and increasing yields. The major contributors to the uncertainty range of energy use were associated with machinery fuel use and the assumed crop yields. For GWP results, the main source of uncertainty related to the N₂O emissions. In conclusion, farming systems that combine the best practices from organic and conventional systems have potential to reduce negative environmental impacts while maintaining yield levels.     

施用生物炭与硝化抑制剂对菜地综合温室效应的影响

采用静态暗箱-气相色谱法,研究施用生物炭与添加硝化抑制剂对菜地周年综合温室效应的影响.结果表明: 与不施用生物炭相比,施用生物炭处理N₂O和CH₄的综合温室效应增加8.7%~12.4%,蔬菜产量增加16.1%~52.5%,温室气体强度降低5.4%~28.7%.添加硝化抑制剂显著减少N₂O排放,不影响CH₄排放,综合温室效应减少17.5%~20.6%,蔬菜产量增加21.2%~40.1%,温室气体强度显著降低.混合施用生物炭与硝化抑制剂一方面增加蔬菜产量,另一方面显著增加综合温室效应(增幅为10.6%～11.2%).因此,在菜地添加硝化抑制剂,既能保证蔬菜产量又能减少温室气体排放,是合适的减排措施.     

Greenhouse gas emissions from a Cu-contaminated soil remediated by in situ stabilization and phytomanaged by a mixed stand of poplar,willows, and false indigo-bush

Phytomanagement of trace element-contaminated soils can reduce soil toxicity and restore soil ecological functions, including the soil gas exchange with the atmosphere. We studied the emission rate of the greenhouse gases (GHGs) CO₂, CH₄, and N₂O; the potential CH₄ oxidation; denitrification enzyme activity (DEA), and glucose mineralization of a Cu-contaminated soil amended with dolomitic limestone and compost, alone or in combination, after a 2-year phytomanagement with a mixed stand of Populus nigra, Salix viminalis, S. caprea, and Amorpha fruticosa. Soil microbial biomass and microbial community composition after analysis of the phospholipid fatty acids (PLFA) profile were determined. Phytomanagement significantly reduced Cu availability and soil toxicity, increased soil microbial biomass and glucose mineralization capacity, changed the composition of soil microbial communities, and increased the CO₂ and N₂O emission rates and DEA. Despite such increases, microbial communities were evolving toward less GHG emission per unit of microbial biomass than in untreated soils. Overall, the aided phytostabilization option would allow methanotrophic populations to establish in the remediated soils due to decreased soil toxicity and increased nutrient availability.     

Long‐term no‐till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long‐term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emissions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N₂O) and methane (CH₄) fluxes and SOC changes (ΔSOC) at a long‐term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, United States. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha^?1 yr^?1, respectively) under no‐till (NT) or conventional disk tillage (CT) with full irrigation (n = 4). Soil N₂O and CH₄ fluxes were measured for five crop‐years (2011–2015), and ΔSOC was determined on an equivalent mass basis to ~30 cm soil depth. Both area‐ and yield‐scaled soil N₂O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprised <1% of total emissions, with NT being CH₄ neutral and CT a CH₄ source. Surface SOC decreased with stover removal and with CT after 14 years of management. When ΔSOC, soil GHG emissions, and agronomic energy usage were used to calculate system GWP, all management systems were net GHG sources. Conservation practices (NT, stover retention) each decreased system GWP compared to conventional practices (CT, stover removal), but pairing conservation practices conferred no additional mitigation benefit. Although cropping system, management equipment/timing/history, soil type, location, weather, and the depth to which ΔSOC is measured affect the GWP outcomes of irrigated systems at large, this long‐term irrigated study provides valuable empirical evidence of how management decisions can impact soil GHG emissions and surface SOC stocks.     

海草场生态系统及其修复研究进展

海草场能够提供重要的生态系统服务。自20世纪末以来,由于人类活动和自然灾害的影响,全球范围内的海草场出现了急剧衰退,由此也促进了海草场生态系统的研究以及海草场人工修复技术的发展。近年来,针对海草场生境流失的现状,中国也开始开展海草场修复工作。从以下方面进行论述:(1)海草的种类、分布,海草场生态系统功能及其生态系统服务:与陆地系统相比,全球海草物种多样性较低,了解海草的分布特征有助于通过了解海草如何适应当地环境压力,以揭示海草适应环境的能力;海草场提供重要而广泛的自然生态系统服务,特别是在维护近岸生态系统健康和满足人类需求过程中起到重要的作用;(2)海草场的衰退及其原因:认识并缓解人类压力对海草场的危害是促进海草场生态系统可持续发展的重要一环;(3)国内外海草场修复现状:以此阐明海草场修复原理,为海草场修复提供科学的方法;(4)总结与讨论:基于科学研究背景,为中国海草场生态系统保护和修复提出建议。海草场的修复和保护应当相辅相成,并与我国海岸长远规划相结合,以此推动我国海草场生态系统服务的可持续发展。     

Leguminous plants significantly increase soil nitrogen cycling across global climates and ecosystem types

Leguminous plants are an important component of terrestrial ecosystems and significantly increase soil nitrogen (N) cycling and availability, which affects productivity in most ecosystems. Clarifying whether the effects of legumes on N cycling vary with contrasting ecosystem types and climatic regions is crucial for understanding and predicting ecosystem processes, but these effects are currently unknown. By conducting a global meta-analysis, we revealed that legumes increased the soil net N mineralization rate (R_min) by 67%, which was greater than the recently reported increase associated with N deposition (25%). This effect was similar for tropical (53%) and temperate regions (81%) but was significantly greater in grasslands (151%) and forests (74%) than in croplands (−3%) and was greater in in situ incubation (101%) or short-term experiments (112%) than in laboratory incubation (55%) or long-term experiments (37%). Legumes significantly influenced the dependence of R_min on N fertilization and experimental factors. The R_min was significantly increased by N fertilization in the nonlegume soils, but not in the legume soils. In addition, the effects of mean annual temperature, soil nutrients and experimental duration on R_min were smaller in the legume soils than in the nonlegume soils. Collectively, our results highlighted the significant positive effects of legumes on soil N cycling, and indicated that the effects of legumes should be elucidated when addressing the response of soils to plants.     

Analyzing the ecosystem carbon and hydrologic characteristics of forested wetland using a biogeochemical process model

A comprehensive biogeochemical model, Wetland‐DNDC, was applied to analyze the carbon and hydrologic characteristics of forested wetland ecosystem at Minnesota (MN) and Florida (FL) sites. The model simulates the flows of carbon, energy, and water in forested wetlands. Modeled carbon dynamics depends on physiological plant factors, the size of plant pools, environmental factors, and the total amount and turnover rates of soil organic matter. The model realistically simulated water level fluctuation, forest production, carbon pools change, and CO₂ and CH₄ emission under natural variations in different environmental factors at two sites. Analyses were focused on parameters and inputs potentially cause the greatest uncertainty in calculated change in plant and soil C and water levels fluctuation and shows that it was important to obtain accurate input data for initial C content, climatic conditions, and allocation of net primary production to various forested wetland components. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on site‐specific conditions such as climate and soil. This paper explores the ability of using the biogeochemical process model Wetland‐DNDC to estimate the carbon and hydrologic dynamics of forested wetlands and shifts in these dynamics in response to changing environmental conditions.