Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO₂ exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO₂ exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO₂ exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to ?48 μmol CO₂ m^?2 s^?1 and 20 μmol CO₂ m^?2 s^?1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO₂ uptake was high, the annual budget of ?229 ± 7 ± 49 g C m^?2 y^?1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.     

典型断陷盆地流域生态系统服务价值时空差异研究

以典型断陷盆地——小江流域为研究对象,以1982年的TM影像、2003年的Landsat ETM+影像和2016年的Landsat OLI影像为数据源,结合云南省测绘局所提供的150 000的土地利用状况图,采用 Costanza 公式对生态系统服务价值进行评估,精细刻画出云南小江流域“盆—山”共存的地质分异结构下生态系统服务价值的时空变化特征。结果表明:（1）小江流域以农田生态系统为主,研究期内生态系统格局总体稳定,耕地、建设用地、林地和园地都有不同程度的增加,而未利用地面积减少,水域面积基本不变;（2）1982-2016年,研究区生态系统服务总价值呈上升趋势,1982、2003和2016年生态系统服务总价值分别为90.11×108元、105.65×108元和136.81×108元,耕地、林地、园地和水域的生态系统服务价值整体上升,而未利用地的生态系统服务价值减少;（3）整体上,小江流域南部和东部生态系统服务价值增加明显,而中部和西部地区生态系统服务价值呈阶段性变化或持续下降趋势,小江岩溶河谷区的生态系统服务价值最高,而沉积平坝区的生态系统服务价值密度最低,且为唯一一个衰退型生态系统服务功能区;（4）研究期内小江流域各项生态系统服务价值均呈上升趋势,调节服务居主导地位,且以气候调节服务价值最高。小江流域生态系统服务价值缺乏弹性,水域生态系统面积变化对研究区生态系统价值的变化具有放大作用。实施封山育林、退耕还林、小流域治理工程等石漠化综合治理工程可增加生态系统服务价值。      

Cross-site analysis of perceived ecosystem service benefits in multifunctional landscapes

Rural development policies in many Organization for Economic Co-operation and Development (OECD) member countries promote sustainable landscape management with the intention of providing multiple ecosystem services (ES). Yet, it remains unclear which ES benefits are perceived in different landscapes and by different people. We present an assessment of ES benefits perceived and mapped by residents (n = 2,301) across 13 multifunctional (deep rural to peri-urban) landscapes in Europe. We identify the most intensively perceived ES benefits, their spatial patterns, and the respondent and landscape characteristics that determine ES benefit perception. We find outdoor recreation, aesthetic values and social interactions are the key ES benefits at local scales. Settlement areas are ES benefit hotspots but many benefits are also related to forests, waters and mosaic landscapes. We find some ES benefits (e.g. culture and heritage values) are spatially clustered, while many others (e.g. aesthetic values) are dispersed. ES benefit perception is linked to people’s relationship with and accessibility to a landscape. Our study discusses how a local perspective can contribute to the development of contextualized and socially acceptable policies for sustainable ES management. We also address conceptual confusion in ES framework and present argumentation regarding the links from services to benefits, and from benefits to different types of values.     

Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m⁻²) is similar to phytoplankton production (6–10 g C m⁻²). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m⁻² yr⁻¹. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m⁻² yr⁻¹ is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m⁻² yr⁻¹ of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m⁻² yr⁻¹ was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.     

生态系统模型中物候的参数化方法研究进展

物候和叶面积指数的季节动态在落叶林中是决定生态系统净生产力的关键因素。尽管物 候对能量和CO2 通量的影响可以简单地通过描述发芽和落叶的时间以及叶面积指数的季节动态 来表示, 但是由于对驱动物候的物理过程缺乏全面正确的理解, 在陆地生态系统模型中物候就成 为最难以参数化的一个过程。目前, 在陆地生态系统模型中描述物候主要有两种不同的方法: 一 种是基于气候变量( 主要是温度或积温) 的经验方法, 即是通过建立物候不同阶段与气候变量的 经验关系来预测关键物候事件发生的时间。另一种方法是基于碳吸收的物候参数化方案, 物候的 任何阶段都和当前的碳平衡相联系。在生态系统模型中, 基于碳吸收的物候参数化方法可以大大 降低物候模拟的经验性, 提高模型的适用性和模拟精度, 比基于气候变量的经验模型更适于模拟 未来气候变化影响。未来随着生理和分子水平上, 对控制物候和LAI 动态过程机理的揭示, 建立 基于过程的物候参数化方案和LAI 动态模拟模型就成为生态系统模型或气候模型的发展方向。     

岩溶生态系统脆弱性研究

生态系统的脆弱性评价对于生态系统管理具有重要作用。在分析岩溶生态系统脆弱性特 征和影响因素的基础上,构建了针对岩溶自然系统的脆弱性评价指标体系, 涵盖了岩溶生态系统 的结构脆弱性、生态过程脆弱性、生态功能脆弱性和人为胁迫脆弱性4 个方面,评价指标分别是 结构稳定性、多样性生境、能量利用和积累、直接使用价值、石漠化程度和速率等。以不同类型的 原生岩溶生态系统的生态基准值作为比较基础, 评价系统将现有的退化岩溶生态系统的脆弱性 划分为轻微脆弱、中度脆弱、重度脆弱以及系统崩溃4 级。     

陆地生态系统氮状态对碳循环的限制作用研究进展

陆地生态系统碳循环和氮循环密切相关, 碳贮量与碳通量在很大程度上受氮循环的影响 和限制。由于氮循环的复杂性, 在以往的大多数碳循环研究中, 更多考虑水分、温度和大气CO2 浓 度等因子的影响, 考虑碳氮相互作用的研究较少。氮素可限制植物光合、有机质分解、同化产物的 分配以及生态系统对大气CO2 浓度升高的响应。根据目前有关碳氮模型的发展状况可将碳氮耦 合循环模型分为三大类: 一是静态模型, 它的土壤养分水平或者叶氮含量不变, 是常数, 这类模型 适合于在站点或氮素浓度变化不大的区域应用; 二是土壤氮限制模型, 能够保持稳定的生态系统 氮收支, 在NPP(Net Primary Productivity, 净初级生产力)的模拟中考虑土壤氮有效性的动态变化 的影响, 使模拟结果更为合理; 三是叶氮限制模型, 在NPP 的模拟中考虑叶片氮浓度的动态变化 的影响。这三类模型虽然都考虑了氮对碳循环的限制作用, 但在氮碳循环机理方面尚有不少欠 缺, 所以在研究中可能会带来很大的不确定性。在以后的研究中, 应通过加强碳氮相互作用的实 验研究, 增进对碳氮过程的深入了解, 进而建立综合动态的碳氮耦合模型, 以减少目前碳循环研 究中的不确定性。     

Some phenomena of the interaction between vegetation and a atmosphere on multiple scales

This article studies the response of the distribution pattern and the physiological characteristics of the ecosystem to the spontaneous precipitation and the interaction between vegetation and the atmosphere on multiple scales in arid and semi-arid zones, based on measured data of the ecological physiological parameters in the Ordas Plateau of northern China. The results show that the vegetation biomass and the energy use efficiency of photosynthesis are especially sensitive to the annual precipitation; strong and complex interactions exist between the vegetation and the atmosphere on multiple scales leading to supernormal thermal heterogeneity of the underlying surface, the strong vortex movement and turbulence. This study can facilitate understanding of the land surface processes and the influences of global climate change as well as human activities on the human environment in the arid and semi-arid zones. It also aids in improving the parameterization schemes of turbulent fluxes of a heterogeneous underlying surface for land surface processes in climate models.     

陆表自然和人文要素相互作用——“全球变化及应对”重点专项研究进展

在国家重点研发计划支持下,项目提出了陆表不均一性检测和订正的新方法,解决了渐变型不均一性检测和订正的难题,构建了中国地表太阳辐射、气温、地温、风速和降水等参数均一化站点和格点数据集,修订了关于中国地表风速变化趋势、增温格局及其形成机制的结论。融合多源数据,构建并验证了千米级、流域级或县域级的电厂、人口、生物质能、取水量、氮排放、二氧化碳排放等影响自然系统的关键人文要素历史和未来预估数据集。构建了未来关键人文要素情景,研制了碳中和目标下甲烷和氧化亚氮排放情景和用于驱动全球模式的未来情景,预估了中国碳中和战略的实施对全球变暖的减缓作用,发现中国碳中和对远期和中期全球变暖的减缓作用显著。给出了中国各省份水体氮排放安全阈值及超越时间,阐明了中国粮食产量与氮施肥的关系,提出了在保障粮食安全的前提下减少水体氮排放的有效途径,指出重构城乡养分循环体系是同时保障粮食安全和恢复水质的必要途径。发现全球饱和水汽压差的年际变化与大气二氧化碳浓度上升速率的年际变化显著相关,阐明了饱和水汽压差变化在调控生态系统生产力中的重要角色以及多因素耦合作用在生态系统生产力变化中的复杂影响。建议更全面细致地评估中国各种碳中...