Water use efficiency in response to interannual variations in flux-based photosynthetic onset in temperate deciduous broadleaf forests

Climate change has significantly influenced the productivity of terrestrial ecosystems through water cycles. Water use efficiency (WUE) is an important indicator for understanding how water couples with the carbon cycle. Abiotic factors such as climatic factors and CO₂ concentration have been investigated to understand the mechanisms involved in the coupled carbon-water cycle of terrestrial ecosystems in response to climate change. However, the effects of biotic factors on WUE are less clear. By analyzing 66 site-years of flux and meteorological data obtained from 8 temperate deciduous broadleaf forest sites across North America and Europe, we found that ecosystem-scale WUE (defined here as the ratio of gross primary production (GPP) to evapotranspiration (ET)) in the spring significantly increased with the advance of the flux-based photosynthetic onset (FPO), mainly because an earlier FPO could lead to a steeper increase in GPP than in ET. However, the advance of FPO probably reduced summer WUE as a result of the enhancement of water stress by ET in the spring in temperate deciduous broadleaf forest. Our results also implied that spring warming had an indirectly positive effect on WUE through advancing spring phenology, but such a positive effect will likely weaken once the sensitivity of spring phenology to warming decreases as reported. Here, we argue that phenology, which exerts critical biotic control over most ecological processes, plays a larger role than expected in the regulation of the seasonal WUE and cannot be ignored in earth system models.     

Carbon–water coupling and its relationship with environmental and biological factors in a planted Caragana liouana shrub community in desert steppe,northwest China

宁夏荒漠草原区中间锦鸡儿灌丛群落碳水循环特征及其与生物环境因子的关系 干旱半干旱区的人工植被重建可能会改变陆地生态系统的重要生物物理过程——碳水循环,然而在人类活动背景下,仍然缺乏对这些区域生态系统的碳水耦合机制的认识。本研究基于涡度相关系统测量了宁夏盐池荒漠草原区人工种植的中间锦鸡儿(Caragana  liouana)灌丛群落的CO2和H2O通量,通过分析总初级生产力(Gross Primary Productivity, GPP)、蒸散发(Evapotranspiration, ET)和水分利用效率(Water Use Efficiency, WUE)的变化,探讨了人工灌丛生态系统碳水通量及其耦合关系,并进一步分析驱动其变化的生物环境因子。研究结果表明,气候因子的季节变化导致了生物物理特征和碳水通量呈周期性变化。在生长季,GPP和ET波动较大,而WUE变化相对稳定。GPP、ET和WUE显著受辐射(Global Radiation, Rg)、温度(Ta和Ts)、水汽压亏缺、叶面积指数和植物水分胁迫指数(Plant Water Stress Index, PWSI)的驱动。其中Rg、温度和PWSI是影响WUE的最重要因素。Rg和温度会对WUE产生直接的促进作用,但同时也会间接地提高PWSI进而抑制WUE。PWSI会抑制光合作用和蒸腾作用,当植物水分胁迫超过一个阈值(PWSI > 0.54)时,WUE会下降,这是因为GPP对植物水分胁迫的响应比ET更敏感。这些研究结果表明,在荒漠草原区通过大规模种植灌木可实现固碳的作用,但也必须充分考虑区域的水资源消耗和水分利用效率的状况。     

Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China

Through 2–3-year (2003–2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter-ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types in China, the four ecosystems are an alpine swamp meadow ecosystem, an alpine shrub-meadow ecosystem, an alpine meadow-steppe ecosystem, and a temperate steppe ecosystem, which illustrate a water availability gradient and thus provide us an opportunity to quantify environmental and biological controls on ecosystem WUE at different spatiotemporal scales. Seasonally, WUE tracked closely with GPP at the four ecosystems, being low at the beginning and the end of the growing seasons and high during the active periods of plant growth. Such consistent correspondence between WUE and GPP suggested that photosynthetic processes were the dominant regulator of the seasonal variations in WUE. Further investigation indicated that the regulations were mainly due to the effect of leaf area index (LAI) on carbon assimilation and on the ratio of transpiration to ET ( T /ET). Besides, except for the swamp meadow, LAI also controlled the year-to-year and site-to-site variations in WUE in the same way, resulting in the years or sites with high productivity being accompanied by high WUE. The general good correlation between LAI and ecosystem WUE indicates that it may be possible to predict grassland ecosystem WUE simply with LAI. Our results also imply that climate change-induced shifts in vegetation structure, and consequently LAI may have a significant impact on the relationship between ecosystem carbon and water cycles in grasslands.     

基于FORCCHN模型的中国典型森林生态系统碳通量模拟

森林生态系统是陆地碳循环的重要组成部分,其固碳能力显著高于其他陆地生态系统,研究森林生态系统碳通量是认识和理解全球变化对碳循环影响的关键。碳循环模型是研究森林生态系统碳通量有效工具。以长白山温带落叶阔叶林、千烟洲亚热带常绿针叶林、鼎湖山亚热带常绿阔叶林和西双版纳热带雨林等4种中国典型森林生态系统为研究对象,利用涡度相关2003-2012年观测数据,评估FORCCHN模型对生态系统呼吸（ER）,总初级生产力（GPP）,净生态系统生产力（NEP）的模型效果。结果表明：（1） FORCCHN模型能够较好的模拟中国4种典型森林生态系统不同时间尺度的碳通量。落叶阔叶林和常绿针叶林ER和GPP的逐日变化模拟效果较好（ER的相关系数分别为0.94和0.92,GPP的相关系数分别为0.86和0.74）;（2）4种森林生态系统碳通量季节动态模拟值和观测值显著相关（P<0.01）,ER、GPP、NEP的观测值和模拟值的R²分别为0.77-0.93、0.54-0.88和0.15-0.38;模型可以很好地模拟森林生态系统不同季节碳汇（NEP>0）,碳源（NEP<0）的变化规律;（3）4种森林生态系统碳通量模拟值与观测值的年际变化有很好的吻合度,但在数值大小上存在差异,模型高估了常绿阔叶林的ER和GPP,略微低估了其他3种森林生态系统ER和GPP。     

亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值比较研究

植物干重热值(GCV)是衡量植物生命活动及组成成分的重要指标之一,反映了植物光合作用中固定太阳辐射的能力。利用氧弹量热仪测定了亚热带和暖温带两个典型森林生态系统常见的276种常见植物叶片的干重热值,探讨了亚热带和暖温带植物热值分布特征,以及不同生活型、乔木类型间植物热值的变化规律。实验结果发现:亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值的平均值分别为17.83 k J/g(n=191)和17.21k J/g(n=85),整体表现为亚热带植物暖温带植物。不同地带性植被的植物叶片热值在不同生活型间表现出相似的规律,其中亚热带常绿阔叶林表现为:乔木(19.09 k J/g)灌木(17.87 k J/g)草本(16.65 k J/g);暖温带落叶阔叶林表现为:乔木(18.41 k J/g)灌木(17.94 k J/g)草本(16.53 k J/g);不同乔木类型间均呈现常绿乔木落叶乔木、针叶乔木阔叶乔木的趋势。落叶阔叶乔木表现为亚热带暖温带,而常绿针叶乔木则呈现亚热带暖温带的趋势。此外,我们对于两个分布区域内的4种针叶树种叶片热值进行了比较,发现华北落叶松(19.32 k J/g,暖温带)杉木(19.40 k J/g,亚热带)马尾松(19.82 k J/g,亚热带)油松(20.95 k J/g,暖温带)。亚热带常绿阔叶林和暖温带落叶阔叶林植物热值的特征及其变化规律,为森林生态系统的能量流动提供了理论基础。     

科尔沁草甸生态系统水分利用效率及影响因素

生态系统水分利用效率(WUE)是衡量碳水循环耦合程度的重要指标。利用科尔沁温带草甸草地碳水通量观测数据,对该生态系统总初级生产力水分利用效率(WUEGPP)的日季变化规律及对环境和生理因子的响应进行分析。结果表明:(1)WUEGPP日变化呈下降-稳定-上升的变化趋势,最大值出现在日出后1—2 h,阴天条件下WUEGPP高于晴天,生长中期WUEGPP高于生长初期和末期;(2)总初级生产力、总蒸散和WUEGPP季节变化均呈夏季高、春秋低的形式,生长季平均值分别为0.57 mg m-2s-1、0.08 g m-2s-1和5.97 mg/g,最大值分别为1.49 mg m-2s-1、0.16 g m-2s1和13.62 mg/g;(3)总初级生产力与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系;总蒸散与气温呈二次曲线关系,与饱和差、叶面积指数和冠层导度相关性均不显著;(4)WUEGPP与饱和差、气温和叶面积指数均呈二次曲线关系,与冠层导度呈对数曲线关系,饱和差、冠层导度和叶面积指数分别为2.0 k Pa、0.0015 m/s和4.2是控制WUEGPP增加的阈值;(5)净生态系统生产力水分利用效率(WUENEP)和净初级生产力水分利用效率(WUENPP)季节变化规律与WUEGPP一致,均值分别为3.47和5.47 mg/g。     

宁夏陆地生态系统水分利用效率特征及其影响因子

生态系统水分利用效率(Water Use Efficiency, WUE)是表征生态系统碳水耦合程度的重要指标,能反映生态系统碳水循环规律及其相互作用关系。基于MODIS数据以及宁夏生态系统类型数据,分析2000—2017年宁夏不同生态系统WUE的变化特征,探讨了NPP和ET两种因子对WUE年际与年内变化的影响。结果表明:(1)全区陆地生态系统的年均WUE为1.03 g·C/kg·H_2O,值域在0.55—2.98 g·C/kg·H_2O之间,总体上呈现南北高、中部低的特征。(2)不同生态系统的WUE差异较大,由高到低为水体及湿地、森林、农田、草地、聚落、荒漠和其他生态系统,在同类生态系统中,植被生物量和盖度越高的亚类生态系统,其WUE也越高。(3)宁夏陆地生态系统WUE存在着每年0.0141 g·C/kg·H_2O的下降趋势,年内WUE呈典型的单峰形态,变化范围在0.02—2.16 g·C/kg·H_2O之间。(4)年际尺度上,宁夏陆地生态系统WUE与年蒸散(Evapotranspiration,ET)有极显著负相关性(P0.01),而与净初级生产力(Net Primary Production,NPP)没有相关性;年内尺度上,WUE变化与ET呈显著正相关(P0.05),与NPP呈极显著正相关(P0.01),这与植被的年内季节性生长过程有关。(5)根据ET强弱和WUE高低,可将宁夏陆地生态系统水分利用效率特征划分为4类,即低ET低WUE区、低ET高WUE区、高ET低WUE区和高ET高WUE区。宁夏的生态恢复工程在增强植被生产力的同时,也增强了区域水分消耗,致使陆地生态系统整体水分利用效率下降,这为宁夏未来水资源调控和生态重建提供了科学依据。     

Modelling Seasonal and Inter-annual Variations in Carbon and Water Fluxes in an Arid-Zone <Emphasis Type="Italic">Acacia</Emphasis> Savanna Woodland, 1981–2012

Changes in climatic characteristics such as seasonal and inter-annual variability may affect ecosystem structure and function, hence alter carbon and water budgets of ecosystems. Studies of modelling combined with field experiments can provide essential information to investigate interactions between carbon and water cycles and climate. Here we present a first attempt to investigate the long-term climate controls on seasonal patterns and inter-annual variations in water and carbon exchanges in an arid-zone savanna-woodland ecosystem using a detailed mechanistic soil–plant–atmosphere model (SPA), driven by leaf area index (LAI) simulated by an ecohydrological model (WAVES) and observed climate data during 1981–2012. The SPA was tested against almost 3 years of eddy covariance flux measurements in terms of gross primary productivity (GPP) and evapotranspiration (ET). The model was able to explain 80 and 71% of the variability of observed daily GPP and ET, respectively. Long-term simulations showed that carbon accumulation rates and ET ranged from 20.6 g C m^?2 mon^?1 in the late dry season to 45.8 g C m^?2 mon^?1 in the late wet season, respectively, primarily driven by seasonal variations in LAI and soil moisture. Large climate variations resulted in large seasonal variation in ecosystem water-use efficiency (eWUE). Simulated annual GPP varied between 146.4 and 604.7 g C m^?2 y^?1. Variations in annual ET coincided with that of GPP, ranging from 110.2 to 625.8 mm y^?1. Annual variations in GPP and ET were driven by the annual variations in precipitation and vapour pressure deficit (VPD) but not temperature. The linear coupling of simulated annual GPP and ET resulted in eWUE having relatively small year-to-year variation.     

三江平原植被水分利用效率时空变化及其对气象因子变化的响应

水分利用效率(water use efficiency,WUE)是陆地生态系统响应全球变化的重要参数,分析区域生态系统WUE的变化特征及其与气象因子之间的响应关系,对于区域生态系统碳水循环研究以及水资源的科学管理具有重要意义。本文以三江平原为研究区,基于MODIS GPP和ET遥感数据、气象数据以及2000年、2014年土地覆盖数据,分析2000-2014年间植被WUE的时空变化特征以及植被WUE与关键气象因子之间的响应关系,并分析了土地覆盖变化下各植被类型WUE的变化特征。结果表明:三江平原WUE年均值变化呈波动式减少趋势,多年平均植被WUE为1.44 g C·kg^-1H2O;WUE年内变化均近似呈"单峰型"曲线,1-3月及11、12月,WUE均处于最低值,在植被生长季(5-9月)期间,WUE均较高;季节WUE均值由高到低依次为夏季>秋季>春季>冬季;各植被类型WUE年内变化呈"双峰型"曲线,峰值主要分布在4-6月和9月;不同植被类型的年均WUE值从大到小依次为:混交林>针叶林>阔叶林>草地>耕地>永久湿地;三江平原植被WUE与降水、相对湿度、水气压呈正相关,与气温、日照时数呈负相关;随着耕地面积的减少,耕地WUE增加了11.1%,随着落叶阔叶林、草地面积的增加,其植被WUE分别增加了12.8%、15.9%。     

中国4种典型森林中常见乔木叶片的非结构性碳水化合物研究

植物叶片的非结构性碳水化合物(non-structural carbohydrates,NSC)不仅为植物的代谢过程提供重要能量,还能一定程度上反映植物对外界环境的适应策略。以温带针阔混交林(长白山)、温带阔叶林(东灵山)、亚热带常绿阔叶林(神农架)和热带雨林(尖峰岭)4种森林类型的树种为研究对象,利用蒽酮比色法测定了163种常见乔木叶片可溶性糖、淀粉和NSC(可溶性糖+淀粉)含量,探讨了不同森林类型植物叶片NSC的差异及其地带性变化规律。结果显示：（1）从森林类型上看,植物叶片NSC含量从北到南递减,即温带针阔混交林(170.79 mg/g)>温带阔叶林(100.27 mg/g)>亚热带常绿阔叶林(91.24 mg/g)>热带雨林(80.13 mg/g)。（2）从生活型上看,无论是落叶树还是阔叶树,其叶片可溶性糖、淀粉和NSC含量均表现为：温带针阔混交林>温带阔叶林>亚热带常绿阔叶林>热带雨林;北方森林叶片可溶性糖、淀粉和NSC含量均表现为落叶树种>常绿树种,或阔叶树种>针叶树种。（3）森林植物叶片NSC含量、可溶性糖与淀粉含量比值与年均温和年均降水量均呈显著负相关。研究表明,森林植物叶片可溶性糖、淀粉和NSC含量以及可溶性糖与淀粉含量比值均具有明显的从北到南递减的地带性规律;其NSC含量以及可溶性糖与淀粉含量比值与温度和水分均呈显著负相关的变化规律可能是植物对外界环境适应的重要机制之一。该研究结果不仅为阐明中国主要森林树种碳代谢和生长适应对策提供了数据基础,而且为理解区域尺度森林植被对未来气候变化的响应机理提供新的视角。     

海河流域生态水分利用效率时空变化及其与气候因子的相关性分析

生态水分利用效率(water use efficiency,WUE)是碳-水循环的重要参数之一,明晰其时空演变特征对水资源短缺地区生态系统的健康发展具有重要的意义。海河流域水资源短缺是区域农业发展的重要制约因素,基于遥感、气象数据,利用趋势分析、相关分析等方法分析了海河流域2000—2014年总初级生产力(gross primary productivity,GPP)、蒸散量(evapotranspiration,ET)及WUE的时空分布特征,并识别WUE对降水、气温及干旱的响应。研究结果表明:(1)时间上,GPP和ET的变化趋势不显著,WUE呈现显著的增加趋势,增速为0.0185 gC/kg H_2O a~(-1)(R~2=0.6299,P0.01);(2)空间上,WUE和GPP均呈现从东南向西北减小的趋势,高值区主要分布在华北平原农业生态区和京津唐城镇与城郊农业生态区。从变化趋势来看,黄土高原农业与草原生态区的GPP和WUE上升趋势最大;(3)植被类型中,农田的WUE值最高,草地的WUE最低,农田、有林草原和草地均呈现显著的增加趋势(P0.05);(4)影响因素上,降水对WUE的影响最大,WUE由降水、干旱和气温控制的区域分别占整个流域植被面积的44.44%、39.23%和16.01%。     

Enhanced evapotranspiration was observed during extreme drought from Miscanthus,opposite of other crops

The impact of extreme drought and heat stress that occurred in the Midwestern U.S. in 2012 on evapotranspiration (ET), net ecosystem productivity (NEP), and water‐use efficiency (WUE) of three perennial ecosystems (switchgrass, miscanthus, prairie) and a maize/soybean agroecosystem was studied as part of a long‐term experiment. Miscanthus had a slower initial response but an eventually drastic ET as drought intensified, which resulted in the largest water deficit among the crops. The substantially higher ET at peak drought was likely supplied by access to deep soil water, but suggests that stomatal conductance of miscanthus during the drought may respond differently than the other ecosystems, consistent with an anisohydric strategy. While there was a discrepancy in the water consumption of maize and switchgrass/prairie in the early time of drought, all these ecosystems followed a water‐saving strategy when drought intensified. The gross primary production (GPP) of miscanthus dropped, but was reversible, when temperature reached 40 °C and still provided the largest total GPP among the ecosystems. Increased ET for miscanthus during 2012 resulted a large decline in ecosystem WUE compared to what was observed in other years. The biophysical responses of miscanthus measured during an extreme, historic drought suggest that this species can maintain high productivity longer than other ecosystems during a drought at the expense of water use. While miscanthus maintained productivity during drought, recovery lagged associated with depleted soil moisture. The enhanced ET of miscanthus may intensify droughts through increase supply of deep soil moisture to the atmosphere.     

长白山阔叶红松林演替序列水分利用效率特征

水分利用效率是反映植物水分利用的客观指标,对其研究有助于了解陆地生态系统的碳水耦合机制.本研究利用稳定碳同位素技术分析了长白山阔叶红松林演替序列下3种林分(中龄杨桦林、成熟杨桦林、阔叶红松林)中优势树种的水分利用效率.结果 表明:3种林分的水分利用效率在不同演替阶段存在阔叶红松林＞中龄杨桦林＞成熟杨桦林的大小顺序,且同...     

黄河流域植被格局变化对水分利用效率的影响

黄河流域横跨3个气候带,是全球人类活动最为强烈的地区之一,特殊的地理位置和复杂的下垫面导致其碳-水循环过程较为复杂。研究黄河流域碳水循环不仅是区域水资源利用的基础,也是实现气候变化条件下双碳目标的关键。水分利用效率(WUE)作为表征碳水过程的重要指标,可用于反映生态系统碳水耦合规律及其相互作用关系。基于此,利用全球陆表特征参量数据(GLASS)的净初级生产力(NPP)和蒸散(ET)产品以及中国逐年土地利用与覆盖数据集(CLUD-A),分析了黄河流域植被格局变化背景下WUE在1990—2018年的时空变化特征及其驱动力。结果表明：(1)黄河流域全域WUE在29 a的均值处在0.18—1.53 g C/kg H₂O之间,存在明显的空间异质性,上游地区WUE明显高于中下游地区,分别在0.66—0.92 g C/kg H₂O和0.43—0.62 g C/kg H₂O之间波动,二者均存在波动上升态势。(2)黄河流域全域WUE在以2000年为中间点的10 a的增速达到近29 a的峰值,流域植被格局变化所带来的流域内NPP与ET变化速...     

石羊河流域水分利用效率及其对饱和水汽压差的响应

水分利用效率(WUE)是叶片通过光合作用调节水分生理过程的指标,是联系生态系统碳循环与水循环关系的关键,反映了植被生态系统对立地环境快速调整和资源的变化适应策略。基于卫星遥感和地面观测数据,利用光能利用率模型和蒸散发经验估算模型,模拟石羊河流域2000—2019年植被总初级生产力(GPP)和蒸散发(ET)数据,估算2000—2019年不同植被类型的WUE空间分布特征,研究GPP/ET/WUE与饱和水汽压差(VPD)的相关性,探讨干旱区不同类型植被对水分利用及胁迫的适应策略。结果表明：(1) 2000—2019年石羊河流域植被WUE、GPP和ET的平均值分别为0.80 gC m^-2 mm^-1、256.52 gC/m²和302.52 mm,其三者的空间分布特征表现为“南高北低”,即由流域源头至下游逐渐减少的空间分布。(2)近20年内,流域内WUE、GPP和ET的变化率的平均值分别为0.017 gC m^-2 mm^-1 a^-1,6.99 gC m^-2     

青藏高原植被水分利用效率时空变化及与气候因子的关系

水分利用效率(WUE)是研究陆地碳水循环耦合的有效指标,青藏高原是我国最重要的生态安全屏障,了解WUE的特征以及变化机制,对研究高原生态系统碳水循环和水资源合理利用有重要意义。本研究基于MODIS的总初级生产力(GPP)和蒸散发(ET)数据,分析青藏高原WUE的时空变化特征以及气候因子对WUE的影响。结果表明: 2001—2020年,在GPP和ET的共同作用下,青藏高原WUE呈上升趋势;WUE平均值较高的区域为高原东南部、东北部,低值区为高原中部。草地、沼泽、高山植被WUE呈增长趋势,灌丛、阔叶林、针叶林呈下降趋势。WUE与年均气温呈显著正相关,敏感性随着气温的升高而增加;WUE与年降水量呈非线性关系,降水量小于700 mm时,WUE对降水敏感性随着降水增加而减小,降水量大于700 mm,降水敏感性随着降水增加而增大。青藏高原超过75%的区域WUE与降水呈负相关,与气温相比,WUE受降水影响的面积更大,未来气候暖湿化将导致WUE降低。     

亚热带常绿阔叶林冠层附生植物叶片形态结构及生理功能特征的适应性研究

以南亚热带常绿阔叶林林冠层不同部位的4种附生植物:瓜子金(Dischidia chinensis Champ.ex Benth.)、蔓九节(Psychotria serpens L.)、白背瓜馥木(Fissistigma glaucescens (Hance) Merr.)和山萎(Piper hancei Maxim.)为研究对象,比较其叶片解剖结构和光合、蒸腾等生理特性,探讨附生植物叶片形态结构、生理生态功能对冠层不同部位水、热和光资源的适应以及叶片形态结构与生理生态功能的联系.结果表明:着生在冠层上部的两种附生植物瓜子金和蔓九节叶片小而厚(厚度分别为3558±63 μm和217.1±33.1 μm),气孔面积小(分别为185.7±3.7 μm2和225 4±5.2 μm2)且覆盖角质膜,有利于降低蒸腾速率(两者分别为0.17±0.02 mmol H2O和0.34±0.05 mmol H2O),提高水分利用效率WUE(分别为11.35±0.87 μmol CO2/mmolH2O和7.88±1.31 μmol COJmmol H2O),更适应冠层顶部高温、低湿、强光照的生境.这些结构特征却不利于气体交换,会致使瓜子金和蔓九节的光合作用降低(二者最大净光合速率Pmax分别为2.2±0.1 μmol CO2 ·m-2·s-1和3.2±0 4 μmol CO2·m-2·s-1).冠层中下部的白背瓜馥木和山蒌叶片相对较薄(厚度分别为90.8±9.9 μm和114 9±18.2 μm),气孔面积较大(分别为260.6±6.3 μm2和362.5±8.7 μm2),叶肉细胞分化明显,海绵组织排列松散,有利于提高对弱光的利用,增强光合能力(二者Pmax分别为9.5±1.3 μmol CO2·m-2·s-1和7.1±0.8 μmol CO2·m-2·s-1,是瓜子金和蔓九节Pmax的3～4倍),更适应冠层中下部低温、高湿、弱光照环境.这些结构同时会导致白背瓜馥木和山蒌蒸腾速率提高(两者分别为0.67±0.10 mmol H2O和0.74 +0.13 mmol H2O),WUE下降(分别为4.4±1.01μmol CO2/mmol H2O和3.4±0.9 μmol CO2/mmol H2O,仅为瓜子金和蔓九节WUE的30％ -48％).这表明着生在林冠层不同部位的附生植物叶片形态结构特征随着光合有效辐射、温度、湿度等微环境因子的变化表现出显著的差异,并致使各自的生理生态功能发生了相应的适应,是植物适应环境条件的重要表现.     

Changes in Stomatal Conductance,Transpiration and Water Use Efficiency of Ten Species Experienced in High CO2 Concentrations in Biosphere 2

The stomotal conductance, transpiration and water use efficiency (WUE) were measured using a LI-6400 portable photosynthesis system for 5 tropical rain forest species and 5 desert species in Biosphere 2, USA. All the species have experienced in very high CO2 ( > 2 200 μmol• mol- 1 ) for more than 4.5 years. The results showed that the stomatal conductance and transpiration of rain forest species decreased from ( 127.4 ± 65.6) and (2.04 ± 0.61 ) mmol• m- 2•s- 1 to (61.3 + 30.5) and ( 1.54 ± 0.65 ) mmol• m-2• s -1 respectively, while WUE increased from (2.90 ± 0.55) to (8.45 ± 2.71) μmol CO2 •mmo1-1 H2O, with CO2 increasing from 350 – 400 to 700 – 820 μmol• mol-l. For the desert species, stomatal conductance and transpiration decreased from respectively (142.8±94.6) and (2.09±0.71) mmol•m-2•s-1 to (57.7±35.8) and (1.36±0.52) mmolm-2•s-l, but WUE increased from (4.69 ± 1.39) to (9.68 ± 1.61) μmol CO2•mmo1-1 H2O, with the CO2 increase from 320 - 400 to 820 – 850 μtmol• mol- 1. The stomatal conductance, transpiration and WUE were less influenced by light intensity under high CO2 than low CO2 concentrations. Most rain forest species reached their light saturation points at light intensity of 500 μmol• m-2•s-1, while desert species at 1 000 μmol•m-2•s-1. Among different species, the desert C3 tree, Nicotiana glauca Grah., had the highest decrease in stomatal conductance and transpiration and the highest increase in WUE, by 78%, 69% and 310% respectively. The enhancement of increasing CO2 to the stomatal, transpiration and WUE of species with different photosynthesis pathway and life forms in Biosphere 2 could be concluded as: C3 species > C4 species, and desert C3 species > rain forest C3 species.     

气候变化下中国不同植被区总初级生产力对干旱的响应

干旱变化具有明显的空间分异,不同植被类型对干旱的响应亦有差别。开展气候变化下不同植被覆盖类型对干旱响应的差异分析,厘清温升干旱化进程对植被的影响,对了解植被发展动态及预测未来格局有着非常重要的意义。基于1982—2017年的总初级生产力(GPP)数据和同时期东安格利亚大学气候研究中心(CRU)时间序列(TS)气候数据,分析了中国8个植被区GPP和干旱的变化趋势,通过对比标准化降水指数(SPI)和标准化降水蒸散指数(SPEI)的趋势差异识别了典型的温升干旱化区域,在此基础上研究气温上升如何影响GPP对干旱的响应,进一步讨论了不同植被类型对干旱的敏感性差异。结果表明：(1) 36年来8个植被区除青藏高原高寒植被区呈湿润化,其他植被区均呈现变干趋势;(2)气温上升大面积加剧了温带荒漠区和温带草原区的变干趋势;(3)亚热带常绿阔叶林区和热带季风雨林、雨林区的GPP受温度和干旱影响相当,青藏高原高寒植被区和针叶、落叶林混交林区的GPP受温度主导,其他植被区GPP均受干旱主导。     

Drought-induced dynamics of carbon and water use efficiency of global grasslands from 2000 to 2011

Drought is frequently recorded as a result of climate warming and elevated concentration of greenhouse gases, which affect the carbon and water cycles in terrestrial ecosystems, particularly in arid and semi-arid regions. To identify the drought in grassland ecosystems and to determine how such drought affects grassland ecosystems in terms of carbon and water cycles across the globe, this study evaluated the drought conditions of global grassland ecosystems from 2000 to 2011 on the basis of the remotely sensed Drought Severity Index (DSI) data. The temporal dynamics of grassland carbon use efficiency (CUE) and water use efficiency (WUE), as well as their correlations with DSI, were also investigated at the global scale. Results showed that 57.04% of grassland ecosystems experienced a dry trend over this period. In general, most grassland ecosystems in the northern hemisphere (N.H.) were in near normal condition, whereas those in the southern hemisphere (S.H.) experienced a clear drying and wetting trend, with the year 2005 regarded as the turning point. Grassland CUE increased continually despite the varied drought conditions over this period. By contrast, WUE increased in the closed shrublands and woody savannas but decreased in all the other grassland types. The drought conditions affected the carbon and water use mainly by influencing the primary production and evapotranspiration of grass through photosynthesis and transpiration process. The CUE and WUE of savannas was most sensitive to droughts among all the grassland types. The areas of grassland DSI that showed significant correlations with CUE and WUE were 52.92% and 22.11% of the total grassland areas, respectively. Overall, droughts sufficiently explained the dynamics of grassland CUE, especially in the S.H. In comparison with grassland CUE, the grassland WUE was less sensitive to drought conditions at the global scale.