内蒙古温带荒漠草原生长季地表反射率特征及数值模拟

基于内蒙古苏尼特左旗温带荒漠草原生态系统野外观测站2008年生长季(5月1日-10月15日)的气象和生物要素观测资料,分析了地表反射率日、季动态,并构建了温带荒漠草原地表反射率模型.结果表明：研究区地表反射率日变化主要受太阳高度角影响,呈早晚高、中午低的U形曲线特征;生长季地表反射率在0.20～0.34,平均为0.25,以5月较高、6月下降、7-9月相对稳定、10月增大;研究区地表反射率的季节动态与冠层叶片的物候变化有关,同时受降水过程的影响;土壤含水量和叶面积指数是影响该区地表反射率的关键因子;反映土壤含水量和叶面积指数共同作用的地表反射率模型的模拟值与野外实测值具有较好的一致性.     

长白山阔叶红松林生长季热量平衡变化特征

根据长白山阔叶红松林2001年5月下旬至10月上旬微气象梯度观测资料和辐射、土壤热通量资料,用波文比-能量平衡方法(BREB方法)计算了森林的显热通量和感热通量,并计算了森林大气和植被体的储热量,分析了阔叶红松林热量平衡各项的日变化和季节变化,结果发现,热量平衡(净辐射)与太阳总辐射呈线性关系;热量平衡各项都与净辐射有相同的日变化特征,为昼正夜负的曲线．各项的绝对值一般表现为净辐射>潜热通量>感热通量>储热变化．受日照时间的影响,6～10月各分量正值的日持续时间逐渐缩短．月平均结果,白天净辐射6月份最大,10月上旬最小,变化于0～527W·m^-2,夜间的净辐射在0～-121W·m^-2．潜热通量白天和夜间分别在0～441、0～-81W·m^-2,感热通量昼夜分别在0～80、0～-26W·m^-2．储热变化则为0～44、0～-26W·m^-2．白天潜热通量占净辐射的比例8～10月逐渐下降,而感热通量和储热变化的比例9～10月明显上升,特别在严霜后2～3d,出现潜热通量比例突减、感热通量比例突增的现象．文中还对通量观测仪器、方法进行了简要分析．     

基于塔载辐射监测帽儿山落叶阔叶林冠层叶面积指数动态

基于通量塔常规辐射测量的宽带植被指数(BVI)具有高时间分辨率的优点,有利于获得更详细的森林冠层叶面积指数(LAI)动态信息.本文以帽儿山通量观测站的温带落叶阔叶林为例,研究宽带归一化差值植被指数(NDVI_B)、宽带增强型植被指数(EVIB)、近红外反射率与光合有效辐射反射率比值(SR_(NP))和太阳辐射反射率与光合有效辐射反射率比值(SR_(SP))4种BVI时间序列的控制因子及其滤波方法,并以凋落物收集法为参考,评估采用BVI估测冠层LAI的可行性.结果表明:Huemmrich、Wilson和Jenkins 3种方法计算的同一BVI值略有不同,但其季节变化趋势高度一致.BVI主要受太阳高度角和太阳高度角与坡度夹角的影响而呈现明显的日变化,太阳高度角与坡度夹角最大时刻(12:30)前后的BVI相对稳定.晴空指数可以作为BVI日值滤波的有效参数,不同时刻数据构成的日BVI时间序列的晴空指数阈值以及滤波后的有效数据率存在差异,应综合考虑平滑效果和有效数据率选择合适的时间点代表BVI日值.NDVI_B与凋落物收集法测定的LAI呈显著的线性关系,而EVIB、SR_(NP)和SRSP与LAI均呈显著的对数关系.因此,NDVI_B在表征冠层LAI季节动态和LAI外推中更为精确、方便.鉴于大部分森林碳水通量观测塔配备能量平衡观测系统,如果同时测定光合有效辐射反射率,即可实现冠层LAI长期连续联网监测.     

基于塔载辐射监测帽儿山落叶阔叶林

基于通量塔常规辐射测量的宽带植被指数(BVI)具有高时间分辨率的优点,有利于获得更详细的森林冠层叶面积指数(LAI)动态信息.本文以帽儿山通量观测站的温带落叶阔叶林为例,研究宽带归一化差值植被指数(NDVI_B)、宽带增强型植被指数(EVI_B)、近红外反射率与光合有效辐射反射率比值(SR_NP)和太阳辐射反射率与光合有效辐射反射率比值(SR_SP)4种BVI时间序列的控制因子及其滤波方法,并以凋落物收集法为参考,评估采用BVI估测冠层LAI的可行性.结果表明: Huemmrich、Wilson和Jenkins 3种方法计算的同一BVI值略有不同,但其季节变化趋势高度一致.BVI主要受太阳高度角和太阳高度角与坡度夹角的影响而呈现明显的日变化,太阳高度角与坡度夹角最大时刻(12:30)前后的BVI相对稳定.晴空指数可以作为BVI日值滤波的有效参数,不同时刻数据构成的日BVI时间序列的晴空指数阈值以及滤波后的有效数据率存在差异,应综合考虑平滑效果和有效数据率选择合适的时间点代表BVI日值.NDVI_B与凋落物收集法测定的LAI呈显著的线性关系,而EVI_B、SR_NP和SR_SP与LAI均呈显著的对数关系.因此,NDVI_B在表征冠层LAI季节动态和LAI外推中更为精确、方便.鉴于大部分森林碳水通量观测塔配备能量平衡观测系统,如果同时测定光合有效辐射反射率,即可实现冠层LAI长期连续联网监测.     

帽峰山常绿阔叶林辐射通量特征

常绿阔叶林作为南亚热带气候条件下森林的典型代表,在森林辐射研究中扮演着重要的角色.基于广州帽峰山常绿阔叶林1 a的辐射观测数据,分析了其时序变化和分配等规律.结果表明:太阳总辐射(K ↓)、反射辐射(K↑)和净辐射(Rn)通量日变化呈典型的单峰曲线,大气逆辐射(L↓)、森林长波辐射(L↑)呈余弦曲线,长波有效辐射(Ln)呈波浪形.各辐射总量均为雨季大于旱季,Ln除外;帽峰山常绿阔叶林K ↓年总量为4201.22 MJ/m2,Rn、K↑和Ln占其比例分别为63％、11％和26％.Rn通量分配率日变化呈倒“U”型曲线,Ln和K↑呈“U”型曲线.林冠上光合有效辐射(PARa)日平均值旱季小于雨季,林冠下(PARb)则相反;PARa变异系数旱雨季均小于PARb;PARa日变化呈典型的单峰曲线,PARb整体和PARa一致,仅在中午时刻出现微弱双峰.PAR透射率日峰值出现时间范围与K↓基本一致,尤其是在雨季,PAR透射率日平均值雨季大于旱季.帽峰山常绿阔叶林PAR/K↓比率为20％左右.     

内蒙古荒漠草原地表反照率变化特征

基于2008年全年内蒙古荒漠草原的气象观测数据对荒漠草原地表反照率的变化特征分析发现,内蒙古荒漠草原的地表反照率在晴天呈早晚高、正午前后低的U形变化特征,降水引起的土壤含水量变化将导致地表反照率减小,云对地表反照率的影响比较复杂。荒漠草原地表反照率的月平均日变化类似于晴天条件下的日变化,大多数月份呈现早晚高正午前后低的U形变化趋势,仅在1-2月份及11-12月份呈现V形。地表反照率的季节变化较为明显。在生长季,由于存在植被覆盖使得地表反照率较低;而在冬季,地表反照率较高,特别是1\,2月份,其月均值分别为0.56和0.48,甚至高于沙漠。9月份地表反照率月均值达到最小值0.230, 7、8\,9月份地表反照率接近,分别为0.236、0.232和0.230。而且在生长季,荒漠草原的地表反照率高于退化草地、农田及麦田,低于沙漠的地表反照率,但是荒漠草原的地表反照率除7-10月份明显低于沙漠地表反照率外(相差大于0.02),生长季的其它月份与沙漠相差不大。晴天地表反照率随太阳高度角的增大而减小,当太阳高度角大于40°时,地表反照率趋于稳定,其与太阳高度角呈指数关系。土壤含水量的增大会导致地表反照率的减小,地表反照率与土壤含水量呈指数或线性关系。根据地表反照率与这两个因子之间的单因子关系式,建立了内蒙古荒漠草原晴天地表反照率随太阳高度角与土壤含水量变化的双因子参数化公式,而且太阳高度角和土壤含水量两者共同解释了地表反照率变化的68%左右。该公式可以较好地模拟内蒙古荒漠草原晴天地表反照率的变化。该公式是否可以进一步耦合到天气或气候模式中,还需要借助更多代表性的观测资料的验证,但是本研究无疑对陆面模式中地表反照率更准确的参数化及模拟提供了参考依据。     

哀牢山亚热带常绿阔叶林与林外草地太阳辐射比较

太阳辐射是森林生态系统的主要能量来源,为探讨亚热带常绿阔叶林对太阳辐射的影响,本研究利用哀牢山亚热带森林生态系统研究站太阳辐射观测数据,对林外草地、林冠上的太阳辐射平衡各分量的年、季节变化特征进行了分析.结果表明:森林辐射的季节变化因随植被的变化而与林外草地辐射有所差异.森林有效辐射占总辐射的比率、反射率均低于林外草地,导致净辐射占总辐射比率高于后者.与我国各地的辐射分配率相比,哀牢山亚热带常绿阔叶林的净辐射占总辐射比率较高,反射率较低.总辐射与相近纬度同植被类型的鼎湖山、鹤山相比,分别高207.7和357.5MJ·m-2,这对生长在海拔2200m以上、温凉潮湿环境下的亚热带常绿阔叶林来说,显得异常重要.     

大豆和玉米冠层光合有效辐射各分量日变化

通过实测大豆和玉米冠层光合有效辐射各分量并计算其反射率、透射率,分析了各分量日变化规律及其影响因素。结果表明:光合有效辐射分量(FPAR)在一天中均接近于常数,特别是在8:00—11:00和14:00—16:00相对稳定;晴天大豆冠层入射光合有效辐射变化曲线较阴天平滑,反射率和透射率曲线没有阴天平滑;由于云层的吸收和散射作用,阴天中光合有效辐射(PAR)最大值的出现时间比晴天晚1h左右;植被冠层空间异质性对光合有效辐射各分量影响较大,不同作物类型的各分量之间有较大差异;大豆冠层空间异质性较玉米小,其光合有效辐射各个分量曲线较平滑;线性光量子传感器与太阳入射方向垂直投影线成30°时,冠层入射光合有效辐射平均偏离度值最小,为0.657%。     

利用多光谱扫描仪测定空心莲子草冠层光谱的影响因素

【背景】太阳光的入射辐射是影响多光谱扫描仪测定植物冠层光谱反射率的主要因素。本研究旨在探讨不同测定条件对空心莲子草冠层光谱特征值的影响,确定应用多光谱扫描仪测定空心莲子草冠层光谱特征的适宜环境条件。【方法】采用多光谱扫描仪,在不同天气条件、仪器探头高度、太阳高度角、叶片湿度等外界因素条件下,测定空心莲子草冠层光谱反射率的变化。【结果】天气条件、仪器探头高度、太阳高度角、叶片湿度4个因素对空心莲子草冠层在绿光区560nm、黄光区660nm和近红外光区810nm3个特征波段处的光谱反射率均有显著影响。【结论与意义】利用多光谱扫描仪测定空心莲子草冠层光谱数据,应选择晴朗无云的天气,仪器探头距离冠层1.3m,适宜的数据采集时间为10：00～14：00,以保障适度的太阳高度角和干燥的叶面,从而保持稳定的光谱测量结果。本研究可为完善多光谱扫描评价技术提供理论依据。     

中天山地区草地地表辐射收支演变规律

地表辐射对研究地表能量平衡及气候形成机制具有重要意义。利用中天山乌拉斯台地区陆气相互作用观测站2018年5月至2019年4月地表辐射数据,分析了中天山草地不同时间尺度和不同天气条件下的地表辐射与反照率变化特征。结果表明：(1)地表辐射月平均日变化除大气长波辐射较弱外,其余分量均呈单峰型,极值大小及时间存在差异,太阳总辐射与净辐射最大日峰值均出现在6月,为920.9与603.3 W/m~2,大气与地表长波辐射分别出现在7月和8月,为327.5 W/m~2与471.7 W/m~2,而反射短波辐射则出现在2月,为520.6 W/m~2。(2)太阳总辐射、反射短波辐射、大气与地表长波辐射年曝辐量分别为6860.62、2101.72、7171.25、10089.69 MJ/m~2;就季节变化而言,反射短波辐射曝辐量在冬季明显高于其它季节,其它分量则均表现为夏季>春季>秋季>冬季。(3)不同月份地表反照率日变化均呈“U”型曲线,年均值为0.393,最大与最小月均值分别出现在12月与8月,为0.760与0.217。这种变化体现在季节上则为冬季>秋季>春季>夏季。(...     

落叶阔叶林反照率的时间变化与影响因素

反照率原位测量对生态系统能量收支及其遥感应用至关重要,但目前坡面地形反照率的测量方式有局限且可见光与近红外波段反照率时间变化的差异尚不清楚。本研究以东北地区帽儿山森林生态站的落叶阔叶林为例,探究入射和反射太阳辐射(SR,300～2800 nm)、光合有效辐射(PAR,400～700 nm)、近红外辐射(NIR,700～2800 nm)的反照率时间变化特征及其影响因子,同时分析了两种辐射表安装方式反照率的差异。结果表明: 晴天SR和NIR反照率日变化呈上下午不对称的U型曲线,但PAR从早到晚递增;阴天反照率均先急剧下降后趋于稳定。平行于坡面测量增大了反照率的日均值,但缓和了SR、NIR反照率日不对称的现象。从整个生长季来看,SR、NIR与PAR反照率水平测量时最大值分别为0.16、0.27和0.11,最小值分别为0.07、0.11和0.03。SR和NIR反照率季节变化均为先增大后减小(7月为峰值),PAR则相反,SR反照率主要受NIR而不是PAR控制。各波段反照率季节变化的影响因子按照贡献率排序为宽带归一化植被指数(61.7%～78.5%,可表征叶面积指数)>太阳高度角(15.4%～36.9%)>晴空指数(0.4%～36.9%)。     

Diurnal Phototropism in Solar Tracking Leaves of Lavatera cretica

On a clear day, leaf laminas of Lavatera cretica tracked the solar position throughout the day. The laminar azimuth did not diverge from the solar azimuth by more than 12° from sunrise to sunset. Tracking of the solar elevation started 1 to 2 hours after sunrise and ceased 1 to 2 hours before sunset. On an overcast day, the laminas reoriented horizontally. After sunset, following a clear day, the laminas performed a nocturnal reorientation, with three well defined phases. During the initial phase the laminas relaxed their strained sunset-facing orientation to one perpendicular to their petioles. This equilibrium configuration was maintained throughout the following phase, which was apparently concerned with time-measuring. During the final phase, the laminas reoriented, before sunrise, to a position facing the direction of the anticipated sunrise. This directional information is phototropic and was retained for 3 to 4 diurnal cycles, probably in the pulvinus itself, which is the site of the response. Laminas of plants transferred from sunlight either to darkness, or to a simulated natural photoperiod under overhead illumination, were facing the originally anticipated direction of sunrise at the time of each of the three to four subsequent sunrises (after which they reverted to the dark orientation in darkness, or to the horizontal one with overhead illumination). Cotyledonary laminas required directional information for the nocturnal reorientation during 3 or 4 cycles of simulated sunrise to sunset transitions.     

Effects of solar radiation on the endemic Mediterranean red alga Rissoella verruculosa: photosynthetic performance, pigment content and the activities of enzymes related to nutrient uptake

The effects of full-spectrum solar radiation and of solar radiation deprived of total u.v. radiation (λ<395 nm) on the endemic Mediterranean red alga Rissoella verruculosa (Bertoloni) J. Agardh were studied in situ in early summer, from sunrise to sunset. Photosynthetic performance, pigment content and the activities of enzymes related to nutrient uptake, were monitored under both radiation conditions throughout a daylight period.
The doses of solar radiation, measured on the day during which the experiments were carried out (24 June 1997), were 9228·25, 1109·70 and 13·03 kJ m⁻² for PAR (λ=400–700 nm), u.v.-A (λ=315–400 nm) and u.v.-B (λ=280–315 nm), respectively. Under these conditions, a clear daily variation in photosynthetic performance was found. However, no significant differences were detected between the two radiation conditions. At noon, strong sunlight impaired O₂ evolution by 75%, but complete recovery occurred during the afternoon, reaching similar values to those measured in the early morning. By contrast, photoinhibition of optimal quantum yield ( F _v/ F _m), and the relative electron transport rate was followed by only a slight recovery during the afternoon. The rate of photosynthesis in air (simulating emersion conditions), estimated by CO₂ exchange, showed a negative balance at noon, which was accentuated in plants exposed to the full-solar spectrum.
Significant changes in the activities of nitrate reductase and carbonic anhydrase were found throughout the day under both radiation conditions. In thalli receiving solar radiation deprived of u.v., total CA activity decreased throughout the day. However, in thalli exposed to full-spectrum solar radiation, the activity of the enzyme tended to increase in the afternoon, correlating with an increase in NR activity.     

猫儿山不同海拔植物群落树木构型差异及其影响因子

通过对猫儿山海拔梯度上常绿阔叶林(低海拔,1100 m)、常绿落叶阔叶混交林(中海拔,1500 m)和常绿针阔叶混交林(高海拔,1900 m)3种典型植物群落中乔木层植物构型性状以及环境因子的测定,分析乔木层植物构型性状在3个群落间的变异规律及其影响因素.结果表明:随海拔升高,乔木层树冠面积、45 cm基径、胸径和叶片聚集度持续增加,树高、枝下高和树冠厚度先增加后减小;枝条伸展方向表现为在低海拔群落中水平枝条比例最大,高海拔群落次之,中海拔群落最小;中海拔群落中乔木层植物构型性状之间的相关性更强.冗余分析表明,土壤有机质和总辐射是乔木层植物构型性状变异的主要环境影响因素,它们分别解释了构型性状39.6%和23.9%的变异.土壤有机质对树冠面积和枝下高影响较大,总辐射对胸径和45 cm基径影响较大,且都呈正相关.猫儿山乔木层植物在不同海拔群落间存在构型分异,影响乔木层植物构型变化的主要环境驱动力是土壤有机质和总辐射.     

Sinusoidal swimming in fishes: the role of season,density of large zooplankton,fish length,time of the day,weather condition and solar radiation

The sinusoidal swimming of fish, previously interpreted as foraging behaviour, was studied with respect to season, density of large zooplankton, fish length, time of the day, weather condition and solar radiation in Římov Reservoir, Czech Republic, using a bottom-mounted, split-beam transducer (7°, nominal angle; frequency 120 kHz). The proportion of sinusoidally swimming fish increased from April to August while this behaviour was absent in October. The occurrence of sinusoidal swimming showed an apparent pattern throughout the day; it increased sharply around sunrise, was highest within 5–6 h around solar noon, and sharply decreased around sunset. Significantly less frequent occurrence of sinusoidal swimming was recorded during cloudy days compared to sunny days. The vast majority of records came from fish of standard length ranging from 100 to 400 mm, which represents the typical size range of common bream Abramis brama and roach Rutilus rutilus of age >1+, the main zooplanktivores in the reservoir. The presence of these larger fish in the open water of the reservoir, as well as the presence of sinusoidal swimming, apparently correlates with the presence of large zooplankton (Daphnia, Leptodora and Cyclops vicinus) in the epilimnion. The increase of sinusoidal swimming between April, June and finally August resulted in an increase of zooplankton component in fish guts. It appears that high values of solar radiation, and stable calm weather during high pressure periods, result in optimal optical conditions for sinusoidal swimming, making this foraging behaviour more efficient and widely used in fishes exploiting the zooplankton production in the reservoir.     

Daylight spectra (400–740 nm) beneath sunny,blue skies in Tasmania,and the effect of a forest canopy

Abstract The photosynthetically active radiation (PAR) incident on a horizontal surface at an open mountain site is positively correlated with solar altitude for sunny, blue sky conditions. The proportion of red light in PAR decreases with increasing solar altitude, while that of blue increases. These results are consistent with the wavelength dependency of Rayleigh and Mie scattering. The ratio of near infrared radiation to PAR decreases with increasing solar altitude towards solar noon and with decreasing solar altitude towards sunset. Thus surface reflection seems to be an important part of the light climate. The relative transmission of daylight through a forest canopy to a horizontal surface is not correlated with solar altitude for sunny, blue sky conditions at a mountain site. The amount of diffuse daylight is negatively correlated with per cent canopy interception, and the amount of direct sunlight is negatively correlated with per cent solar track interception. Daylength is negatively correlated with both canopy and solar track interceptions. The proportion of red light in PAR increases with increasing solar altitude, while that of blue decreases. These results are opposite those for the open site and are due to the spatial patterns of canopy obstruction of the sky vault, and of the spectral quality of daylight across the sky. The ratio of near infrared radiation to PAR in shadelight increases with increasing canopy interception due to the selective scattering properties of the canopy. The ratio for shadelight is positively correlated with the ratio for sunflecks.     

祁连山青海云杉树干液流密度的优势度差异

以祁连山排露沟小流域青海云杉林为研究对象,选取有代表性的优势木、亚优势木、中等木和被压木各3—5株,2015年6月16日至10月14日应用热扩散技术对不同优势度青海云杉树干液流密度进行测定,并同步测定相关的林外气象因子。结果表明:(1)青海云杉液流密度呈昼高夜低趋势,晴天液流密度变化幅度较大,而阴雨天变化幅度较小。(2)晴天树木优势度越大,其液流在日内的启动越早,结束越晚,峰值也越大;优势木的平均液流密度为(0.0758±0.0475)m L cm~(-2)min~(-1),是亚优势木的1.5倍,是中等木和被压木的1.68倍。(3)青海云杉平均液流密度基本呈现6月份最大,其次是8月份,9、10月份明显减小,且优势木亚优势木中等木被压木。(4)相关性分析和逐步回归表明,青海云杉日均液流密度与太阳辐射强度、饱和水气压差和空气温度呈正相关关系,与空气相对湿度和降雨量呈负相关关系。影响优势木、亚优势木和中等木液流密度的主要气象因子是太阳辐射强度,被压木液流密度主要受空气相对湿度的影响。     

Temporal activity patterns of crested porcupines Hystrix cristata

The activity of radiotagged adult crested porcupines Hystrix cristata L., 1758, was studied in a rural hilly area of Central Italy, from July 1990 to June 1991. Three males and one female were monitored every 15 minutes for 18–24 hours/individual/week, and their activity patterns were correlated to ambient temperature, precipitation and lunar phases. Three individuals, out of the four monitored, showed a fall of activity in the beginning of the cold season, but generally porcupines appeared adapted to a wide spectrum of temperatures. The mean duration of nocturnal and crepuscular activity was 9 h 22'±42', showing little variation throughout the year. In the cold months, i.e. when nights are relatively longer, porcupines usually left their burrows after sunset and came back some hours before sunrise. In the warm season they left their burrows at sunset, or shortly before, and returned at sunrise, or shortly after. Overall diurnal activity was scarce (2 h 11' ± 1 h 30'), but in spring it increased to over 40% of the diel activity (3 h 22' ± 3 h). Moonlight avoidance was slight. Precipitation did not seem to influence the activity of porcupines.