黄土高原草地净初级生产力时空趋势及其驱动因素

草地净初级生产力是生态系统碳循环的关键环节和重要组成部分.本研究使用分段线性回归分析和Pearson相关分析,分析了黄土高原2000-2015年间土地利用类型未改变的草地净初级生产力(NPP)的变化趋势及气候核心因子(年降水量、年强降水量、年有效降水日数、年平均温度、年最高温度、年最低温度)对NPP变化的影响,并借助增...     

黑龙江省大兴安岭地区塔河县森林火险天气指标动态

基于大兴安岭地区塔河县1974-2008年森林火灾数据和同期气象数据,结合加拿大火险天气系统(CFFWIS),定量和定性分析了该区森林火险天气指标动态.结果表明:1974-2008年,研究区森林火灾年均发生次数呈增加趋势,2000-2008年森林火灾年均发生次数比1974-1999年增加了72.2%;可燃物湿度码、火行为指标和火灾控制难易度指标总体呈增加趋势,且这种增加趋势随着时间的推进更加明显.未来该区森林火灾发生概率将显著递增,可燃物将更加干燥,林火强度增强,控制火灾将更加困难,火险天气状况更加严峻.该区应重点加大森林火灾的防控,尤其是夏季火灾的防控;并应加大计划可燃物的烧除,减少可燃物载量,从可燃物这一源头上减少火灾发生概率和降低火灾强度.     

Forest insects and climate change: long‐term trends in herbivore damage

Long‐term data sets, covering several decades, could help to reveal the effects of observed climate change on herbivore damage to plants. However, sufficiently long time series in ecology are scarce. The research presented here analyzes a long‐term data set collected by the Hungarian Forest Research Institute over the period 1961–2009. The number of hectares with visible defoliation was estimated and documented for several forest insect pest species. This resulted in a unique time series that provides us with the opportunity to compare insect damage trends with trends in weather patterns. Data were analyzed for six lepidopteran species: Thaumetopoea processionea, Tortrix viridana, Rhyacionia buoliana, Malacosoma neustria, Euproctis chrysorrhoea, and Lymantria dispar. All these species exhibit outbreak dynamics in Hungary. Five of these species prefer deciduous tree species as their host plants, whereas R. buoliana is a specialist on Pinus spp. The data were analyzed using general linear models and generalized least squares regression in relation to mean monthly temperature and precipitation. Temperature increased considerably, especially over the last 25 years (+1.6°C), whereas precipitation exhibited no trend over the period. No change in weather variability over time was observed. There was increased damage caused by two species on deciduous trees. The area of damage attributed to R. buoliana decreased over the study period. There was no evidence of increased variability in damage. We conclude that species exhibiting a trend toward outbreak‐level damage over a greater geographical area may be positively affected by changes in weather conditions coinciding with important life stages. Strong associations between the geographical extent of severe damage and monthly temperature and precipitation are difficult to confirm, studying the life‐history traits of species could help to increase understanding of responses to climate change.     

The influence of shade and clouds on soil water potential: The buffered behavior of hydraulic lift

In the sagebrush/bunchgrass steppe of the North American Great Basin soil water potential has been shown to exhibit diel fluctuations with water potential increasing during the night as a result of water loss from roots in relatively dry soil layers. We hypothesized that environmental conditions promoting low transpiration rates (shading, cloudiness) would cause a net increase in soil water potential as a result of reduced soil water depletion during the day and continuing water efflux from roots during the night. We examined the response of soil water potential to artificial shading in sagebrush/bunchgrass plantings and used a simple model to predict how soil water potential should respond to reduced transpiration. Field measurements of soil water potential indicated that shading reduced daytime soil water depletion, but that the magnitude of the soil water potential increase during the night was related to the magnitude of the soil water potential decline during the preceding day. As a result, shading had little net effect on soil water potential. This behavior was consistent with model results and appears to result from the fact that soil water depletion during the day is largely responsible for creating the water potential gradients that drive nocturnal recharge of the shallow soil layers. The overall effect of such behavior is to buffer the seasonal course of soil water depletion in the rooting zone against day-to-day fluctuations in evapotranspiration. Despite the buffered behavior of soil water potential change, reduced evapotranspiration during light summer rains, and resulting soil water redistribution in the rooting zone, may enhance plant water status to a greater extent that would be expected on the basis of the rainfall received.     

近10年北京极端高温天气条件下的地表温度变化及其对城市化的响应

以北京市为研究区,利用2000年和2010年极端高温发生时MODIS卫星的地表温度（LST）产品数据,结合DMSP/OLS夜间灯光数据,应用差值、等温线、剖面分析等方法,分析了北京市近十年来极端高温发生时地表温度的时空变化特征及其对城市化的响应。研究结果表明：（1）近十年来,极端高温时的地表温度升高,高温区范围增加,城市功能拓展区与发展新区的高温区增加面积大于首都功能核心区与生态涵养区;（2）北京市城市化发展迅速,城市扩张对极端高温条件下的地表温度时空分布与变化趋势起着主导作用。     

中国喀斯特洞穴维管植物多样性

洞穴是喀斯特景观中普遍存在的地质地貌结构, 拥有丰富的植物资源。仅2001-2020年间, 就发表了中国喀斯特洞穴维管植物新属1个; 新种(含种下等级) 170个, 隶属于16科31属, 占近20年发表的中国维管植物新种的3.9%, 说明洞穴植物具有较高的物种多样性潜力。据统计, 中国喀斯特洞穴维管植物有110科339属871种, 主要分布于广西、广东、贵州、云南、重庆等地。物种数排名前5的科包括苦苣苔科、荨麻科、鳞毛蕨科、秋海棠科和茜草科, 其所含物种数共占整个洞穴植物种类的39.4%; 排名前5的属包括报春苣苔属(Primulina)、楼梯草属(Elatostema)、耳蕨属(Polystichum)、秋海棠属(Begonia)和凤尾蕨属(Pteris), 其所含物种数共占整个洞穴植物种类的25.1%。本名录的所有洞穴植物中, 草本习性的种类占一半以上。从洞内分布来看, 仅有10.7%的种类分布于弱光带, 其中石松类和蕨类植物占比远高于被子植物, 说明前者更能适应弱光带的极端环境。不仅如此, 洞穴维管植物也具有较高的特有性成分, 其中省级特有种占比25.8%, 分别包括非洞穴特有种(11.0%)、多洞穴特有种(3.3%)和单洞穴特有种(11.5%)。依据文献显示受威胁种类有115种(占13.0%)。受威胁种类占比较高的类群均是近年来发表新种较多的科, 包括鳞毛蕨科、苦苣苔科、荨麻科、秋海棠科、茜草科等。针对这些类群, 有待更详细地调查来完善对它们的评估。此外, 本名录中至少有36%的种类没有任何分子数据, 亟待补充。     

极端干旱对温带荒漠土壤真菌群落和生态网络的影响

评估极端干旱对温带荒漠土壤真菌群落的影响有助于进一步认识干旱导致的区域荒漠化特征。本研究利用在古尔班通古特沙漠建立的干旱三年和干旱十年样地, 分析了长期极端干旱对温带荒漠土壤真菌群落和生态网络的影响。结果显示, 干旱三年与干旱十年处理对总真菌和丰富真菌的Chao1和Shannon多样性指数均无显著性影响, 而对稀有真菌的Shannon多样性指数有显著促进作用; 干旱三年和干旱十年处理显著影响总真菌、丰富和稀有真菌的群落组成, 且极端干旱对稀有真菌群落变异的影响(ANOSIM, R = 0.378-0.595, P < 0.01)大于对丰富真菌的影响(ANOSIM, R = 0.282-0.555, P < 0.01), 表明丰富真菌具有更强的干旱抵抗力; 另外, 极端干旱显著降低了总真菌、丰富和稀有真菌的β多样性, 表明极端干旱具有生态过滤作用。分子生态网络结果显示, 干旱三年与干旱十年处理降低了荒漠土壤真菌群落网络复杂性, 表明极端干旱减弱了真菌物种间的相互作用; 相比稀有真菌, 丰富真菌具有更高的节点拓扑参数(P < 0.05), 表明丰富真菌对维持极端干旱下的真菌物种间相互作用的重要性。综上所述, 极端干旱显著改变了荒漠表层土壤真菌群落组成, 减弱了真菌物种间的相互作用; 稀有真菌敏感响应极端干旱, 有利于减缓荒漠土壤真菌群落响应的滞后性; 丰富真菌作为网络的核心菌群, 对维持极端干旱下的真菌群落稳定性以及物种间的相互作用很关键。     

Anoxygenic phototrophic bacteria from extreme environments

A diverse group of anoxygenic phototrophic bacteria thrive in habitats characterized by extremes of temperature, pH, or salinity. These `extremophilic' anoxygenic phototrophs are optimally adapted to the conditions of their habitats and are ideal model systems for defining the physiochemical limits of photosynthesis. Extremophilic phototrophs have provided new insight into the evolution of photosynthesis and play ecological roles as primary producers in their unusual habitats. This revised version was published online in August 2006 with corrections to the Cover Date.     

土壤增温与氮添加对杉木幼苗细根径级根长分布的影响

通过在福建省三明市陈大林业国有林场内开展土壤增温(增温5 ℃、不增温)和氮添加(不添加、4、8 g N·m^-2·a^-1)的交互试验(共6个处理),研究土壤增温、氮添加及二者交互作用对杉木细根径级根长分布的影响,用扩展模型可很好地拟合6个处理的径级根长分布(R²=0.97).结果表明: 增温使杉木细根总根长变小,但对细根直径影响不显著;氮添加使杉木细根总根长和直径均变小;增温和氮添加的交互作用对细根总根长有显著影响,但对细根直径无显著影响.6个处理细根径级根长分布均能用极值函数模型较好地拟合(R²>0.98).相关分析显示,直径<1 mm细根的比根长与极值模型拟合参数c值呈显著负相关,实际总根长与极值模型拟合参数b呈显著正相关.增温和氮添加及其交互作用可以影响杉木细根形态特征;极值模型拟合各处理径级根长分布所得参数在一定程度上可以反映细根形态特征对环境条件变化的响应.     

The response of soil respiration to precipitation change is asymmetric and differs between grasslands and forests

Intensification of the Earth's hydrological cycle amplifies the interannual variability of precipitation, which will significantly impact the terrestrial carbon (C) cycle. However, it is still unknown whether previously observed relationship between soil respiration (R_s) and precipitation remains applicable under extreme precipitation change. By analyzing the observations from a much larger dataset of field experiments (248 published papers including 151 grassland studies and 97 forest studies) across a wider range of precipitation manipulation than previous studies, we found that the relationship of R_s response with precipitation change was highly nonlinear or asymmetric, and differed significantly between grasslands and forests, between moderate and extreme precipitation changes. Response of R_s to precipitation change was negatively asymmetric (concave‐down) in grasslands, and double‐asymmetric in forests with a positive asymmetry (concave‐up) under moderate precipitation changes and a negative asymmetry (concave‐down) under extreme precipitation changes. In grasslands, the negative asymmetry in R_s response was attributed to the higher sensitivities of soil moisture, microbial and root activities to decreased precipitation (DPPT) than to increased precipitation (IPPT). In forests, the positive asymmetry was predominantly driven by the significant increase in microbial respiration under moderate IPPT, while the negative asymmetry was caused by the reductions in root biomass and respiration under extreme DPPT. The different asymmetric responses of R_s between grasslands and forests will greatly improve our ability to forecast the C cycle consequences of increased precipitation variability. Specifically, the negative asymmetry of R_s response under extreme precipitation change suggests that the soil C efflux will decrease across grasslands and forests under future precipitation regime with more wet and dry extremes.