Net primary productivity of China's terrestrial ecosystems from a process model driven by remote sensing

The terrestrial carbon cycle is one of the foci in global climate change research. Simulating net primary productivity (NPP) of terrestrial ecosystems is important for carbon cycle research. In this study, China's terrestrial NPP was simulated using the Boreal Ecosystem Productivity Simulator (BEPS), a carbon-water coupled process model based on remote sensing inputs. For these purposes, a national-wide database (including leaf area index, land cover, meteorology, vegetation and soil) at a 1 km resolution and a validation database were established. Using these databases and BEPS, daily maps of NPP for the entire China's landmass in 2001 were produced, and gross primary productivity (GPP) and autotrophic respiration (RA) were estimated. Using the simulated results, we explore temporal-spatial patterns of China's terrestrial NPP and the mechanisms of its responses to various environmental factors. The total NPP and mean NPP of China's landmass were 2.235 GtC and 235.2 gCm(-2)yr(-1), respectively; the total GPP and mean GPP were 4.418 GtC and 465 gCm(-2)yr(-1); and the total RA and mean RA were 2.227 GtC and 234 gCm(-2)yr(-1), respectively. On average, NPP was 50.6% of GPP. In addition, statistical analysis of NPP of different land cover types was conducted, and spatiotemporal patterns of NPP were investigated. The response of NPP to changes in some key factors such as LAI, precipitation, temperature, solar radiation, VPD and AWC are evaluated and discussed.     

川藏铁路沿线地区夏季气温日较差的影响因素研究

利用ERA5再分析资料,分析了1979—2018年川藏铁路沿线区域气候特征.研究了2014—2018年夏季气温日较差(DTR)的变化趋势,以及2014—2018年夏季DTR与地面太阳辐射(SSR)、总降水量(TP)、总云量(TCC)、海拔(DEM)和地表平均蒸发率(MER)的相关性.结果表明:研究区域气温呈上升趋势,2...     

工程铲车斗齿套的锻造成形工艺分析

此文对工程铲车斗齿套的锻造成形方案进行了定性分析,详细地讨论了锻造成形楔形孔薄壁件的方法,并确定了合理的成形工艺、设备选择和工艺流程。此文作者的研究和实践对解决楔形孔薄壁件的锻造成形问题具有普遍的指导意义。     

Ecological responses to variation in seasonal snow cover

Seasonal snow is among the most important factors governing the ecology of many terrestrial ecosystems, but rising global temperatures are changing snow regimes and driving widespread declines in the depth and duration of snow cover. Loss of the insulating snow layer will fundamentally change the environment. Understanding how individuals, populations, and communities respond to different snow conditions is thus essential for predicting and managing future ecosystem change. We synthesized 365 studies that examined ecological responses to variation in winter snow conditions. This research encompasses a broad range of methods (experimental manipulations, measurement of natural snow gradients, and long-term monitoring), locations (35 countries), study organisms (plants, mammals, arthropods, birds, fish, lichen, and fungi), and response measures. Earlier snowmelt was consistently associated with advanced spring phenology in plants, mammals, and arthropods. Reduced snow depth often increased mortality or physical injury in plants, although there were few clear effects on animals. Neither snow depth nor snowmelt timing had clear or consistent directional effects on body size of animals or biomass of plants. However, because 96% of studies were from the northern hemisphere, the generality of these trends across ecosystems and localities is also unclear. We identified substantial research gaps for several taxonomic groups and response types; research on wintertime responses was notably scarce. Future research should prioritize examination of the mechanisms underlying responses to changing snow conditions and the consequences of those responses for seasonally snow-covered ecosystems.     

喜马拉雅东段错那地区雪中主要离子年际变化及来源分析

雪中阴阳离子化学记录可以提供关于大气环流、气候和环境变化的信息,喜马拉雅山因其独特的位置和丰富的冰川资源成为研究雪化学的重要地区。本论文基于两个年度(2018年2～3月和2018年12月～2019年1月)在喜马拉雅东段错那地区采集的新雪样品,对雪中主要离子的组成和浓度特征的年际变化进行分析,并结合相关分析法、海盐示踪法和气团后向轨迹法对其来源进行研究。结果表明,错那地区两年度雪中主要阳离子均为Ca²⁺,主要阴离子均为SO^2-₄。受2019年强降雪清除作用的影响,2019年度各离子的浓度明显低于2018年度。错那地区雪中Ca²⁺的含量明显高于喜马拉雅山其他研究区域,可能是由于其海拔较低,受近源陆地粉尘影响较大。离子来源分析结果表明,错那地区雪中离子以局地陆源物质输入为主,部分来源于海洋源(Cl^-、Na⁺)、盐湖矿物风化(Cl^-、Na⁺、K⁺和SO^2-₄)以及人为源(NH⁺₄、NO^-₃、SO^2-₄)。本文可为错那地区生态建设管理及喜马拉雅地区的雪化学和大气环流特征研究提供参考。