太阳辐射变化对千烟洲亚热带人工针叶林净CO_2交换量的影响

太阳辐射是植被进行光合作用的重要驱动因子,影响着森林生态系统的净CO2吸收。本研究基于千烟洲亚热带人工针叶林30 min的通量和常规气象数据,以晴空指数为指标,分析了2003—2010年太阳辐射变化对该森林生态系统净CO2交换(NEE)的影响。结果表明:在晴空指数为0.4~0.6的中等辐射条件下NEE达到最大;与晴朗天空的强太阳辐射相比,中等辐射条件下散射辐射增加、气温以及饱和水汽压差的下降是NEE增加的原因;晴空指数在0.4~0.5和0.5~0.6的NEE显著大于晴空指数在0.7~0.8的NEE;该地晴空指数在0.6~0.7和0~0.1出现的频率较大,表明该地经常出现的天空状况以及对应的太阳辐射强度不是提高该生态系统净CO2吸收的最适条件。     

辐射变化对中亚热带杉木人工林净CO2交换的影响

太阳总辐射是影响森林生态系统碳交换的重要因子.为认识辐射变化对杉木人工林碳交换的影响,本研究利用开路式涡度相关系统和气象梯度观测系统测得的CO2通量和气象因子长期定位监测数据,用晴空指数(kt)表示太阳辐射情况,分析了kt对中亚热带杉木人工林生长季(4-10月)净C02交换(NEE)的影响.结果 表明:晴天时的太阳总辐...     

散射辐射对亚热带人工针叶林光能利用率的影响

地表接受的太阳辐射中散射辐射的改变是影响森林生态系统光能利用率(Light Use Efficiency,LUE)的重要因素。以千烟洲亚热带人工针叶林为研究对象,利用30 min通量和常规气象观测数据,以晴空指数(kt)和地表接受的散射辐射(S_f)占太阳总辐射(S_0)的比值(S_f/S_0)为指标,分析了2003—2012年生长旺季(6—8月)散射辐射变化对千烟洲亚热带人工针叶林光能利用率的影响,并利用改进的光响应曲线模型分析了散射辐射变化对植被光合特性的影响。研究结果表明:2003—2012年生长旺季中,kt在0.6—0.7范围内的LUE比kt在0.4—0.5范围内的LUE平均减少了44.66%;S_f/S_0在70%—85%之间的LUE比S_f/S_0在55%—70%之间的LUE平均提高了22.24%。由此可以看出,与晴朗天空相比,多云及气溶胶增加导致的散射辐射增加可使该生态系统的LUE提高。并且,未受到高温干旱影响的2005、2006、2008、2009、2010及2012年散射辐射下该生态系统的初始量子效率αf比直接辐射下的αr平均增加了0.63 g CO2/mol;而10年间所有年份散射辐射下的光饱和时的潜在最大光合作用速率比直接辐射下平均提高了0.81 mg CO_2m~(-2)s~(-1),说明散射辐射可使该生态系统植被光合能力提高。     

太阳辐射对长白山阔叶红松林净生态系统碳交换的影响

太阳辐射是植物进行光合作用的前提条件, 因此成为影响植被吸收大气CO₂的重要环境因子。该研究基于30 min通量和常规气象数据, 以相对辐射和晴空指数为指标, 分析了2003~2006年生长旺季(6~8月)太阳辐射的改变对长白山阔叶红松(Pinus koraiensis)林净生态系统碳交换(Net ecosystem exchange, NEE)的影响。结果表明: 天空有一定云层的覆盖对阔叶红松林碳的净吸收有明显的促进作用。4年里6~8月间生态系统最大光合速率在天空有云覆盖时较晴空条件下分别提高了34%、25%、4%和11%。在晴空指数约为0.5的中等辐射条件下, 该生态系统的NEE达到最大。对生态系统碳的净吸收有促进作用的临界相对辐射约为37%, 而使该生态系统NEE达到最大的最适相对辐射约为75%。进一步分析表明, 天空云量的增多和云层厚度的增加会引起散射辐射比例的增加、大气温度和水汽亏缺程度的降低等环境效应, 由此可能会导致冠层光合作用的增加和地上部分呼吸的减弱, 从而共同决定了净生态系统碳吸收作用的增强。     

青藏高原高寒草甸净生态系统碳交换对散射辐射变化的响应

青藏高原是地球上接收太阳辐射能最多的地区之一,具有世界上最高的高寒草甸生态系统,对区域乃至全球碳循环起着重要作用.为了探究太阳辐射变化对高寒草甸生态系统碳动态的影响,本研究利用涡度相关技术和微气象观测系统对高寒草甸生态系统CO₂净交换(NEE)、太阳总辐射、散射辐射及其相关环境要素进行观测;根据晴空指数(CI,到达地面的太阳辐射与大气上界太阳辐射的比值)将天空状况划分为晴天(CI≥0.7)、多云(0.32·m^-2·s^-1)对应的光量子通量密度(PPFD)约为1400 μmol·m^-2·s^-1,出现在CI为0.6～0.7范围内的多云天空,高于CI≥0.7的最高值(-0.57 mg CO₂·m^-2·s^-1)(NEE负值为碳吸收,正值为排放,为方便起见在此均用绝对值描述);CI<0.6条件下,NEE随散射辐射的增加呈显著的对数增加;CI在0.6～0.7范围内,NEE达到最大值,CI≥0.7时,NEE随CI的上升呈降低趋势,说明生态系统的光合作用可能出现了光抑制现象,且散射辐射的增加有利于提高生态系统固碳能力;生态系统呼吸(R_e)随温度升高呈明显的指数上升趋势,高寒草甸NEE最高值对应的温度为15 ℃,当温度高于15 ℃时,NEE随温度的升高呈下降趋势.晴天状况下,温度升高增加了R_e,进而降低了NEE.当饱和水汽压差(VPD)<0.6 kPa时,NEE随VPD增加呈增加趋势;当VPD>0.6 kPa时,NEE随VPD的升高呈缓慢下降趋势,说明相对较高的VPD抑制了生态系统的光合作用.晴天的强辐射并不能促进青藏高原高寒草甸的碳吸收能力,而晴空指数在0.6～0.7范围的多云天气最有利于生态系统碳固定.     

三江并流核心区亚高山森林非生长季净生态系统CO2交换量及其影响因素

采用开路式涡度相关系统,针对三江并流核心区西藏红拉山滇金丝猴国家自然保护区,通过测量和分析非生长季亚高山常绿针叶林净生态系统碳交换量(NEE),探讨了亚高山森林非生长季CO₂通量特征及其主要影响因子。保护区常绿针叶林NEE值在非生长季具有明显“U”型变化曲线,白天表现为碳吸收,夜间表现为碳释放,日间CO₂吸收高峰介于12:00到15:00之间,平均每天碳汇时间在10 h左右。非生长季各月NEE大小依次为：4月> 3月>2月>11月>1月>12月。研究期内气温(T)、相对湿度(RH)、饱和水汽压差(VPD)和光合有效辐射(PAR)等气象因子对净生态系统CO₂交换量影响显著。此外,森林碳吸收对温度响应敏感,光合作用在整个非生长季较为明显。各影响因子中光合有效辐射对碳交换影响最大;夜间NEE与5 cm土壤温度呈极显著相关性(P<0.01)且NEE随着土壤温度升高而增大;整个非生长季NEE、生态系统呼吸量(Re)和总生态系统CO₂交换量(GEE)分别为-596.759 g...     

华北低丘山地人工林生态系统净碳交换与气象因子的关系

植树造林使我国森林碳储量显著增加,人工林潜在的碳汇功能不容忽视.基于涡度相关技术,对华北低丘山地30年生栓皮栎-刺槐-侧柏人工混交林生态系统进行了连续2a的碳通量观测,以探讨净碳交换(NEE)与气象因子的关系.结果表明:在主要生长季(4～9月份),夜间日平均NEE(生态系统呼吸)随气温升高呈指数增长(P<0.01).2006年和2007年生态系统呼吸的温度敏感系数(Q_(10))分别为1.92和1.86.气温在10℃以下时,NEE日总量较小.气温超过10℃后,人工林以净吸收大气CO_2为主,且日吸收量随温度升高迅速增加.白天净碳吸收量随光合有效辐射(PAR)增加而增大(P<0.01),可由直角双曲线方程描述;不过,当饱和差(VPD)小于1.0 kPa时,二者呈线性相关(P<0.01).2006年和2007年主要生长季(4～9月份)的平均表观初始光能利用率(α)分别为0.032和0.019,平均最大光合速率(P_(max))分别为0.96mg · m~(-2) · s~(-1)和1.10 mg · m~(-2) · s~(-1).α和P_(max)都存在季节变化.在月尺度,P_(max)与VPD和PAR呈明显的负相关关系(分别为P<0.01和P<0.05),但与气温相关性不显著;α与对应的PAR、气温和VPD均无明显相关关系.     

黄河小浪底人工混交林冠层CO2储存通量变化特征

基于黄河小浪底人工混交林2008年的CO2浓度和碳通量数据,分析了不同天气条件下CO2浓度在时间和空间上的变化特征,对比了CO2浓度廓线法和涡度相关法估算的CO2储存通量,研究了CO2储存通量的日、季变化特征。结果表明:人工混交林冠层上方月平均CO2浓度具有明显的季节变化规律。月平均CO2浓度最大值出现在3月(370μmol/mol),最低值出现在8月(347μmol/mol)。涡度相关法估算的CO2储存通量比廓线法所得结果偏低9%。生长季,冠层CO2储存通量和净生态系统碳交换量(NEE)日平均值分别为-0.0004和-0.091 mg CO2m-2s-1,冠层CO2储存通量在NEE中仅占0.4%。2008年CO2储存通量和NEE分别为-46.1、-1133 g CO2m-2a-1。在年尺度上,CO2储存通量占NEE的4.1%。因此,在日和年尺度上计算黄河小浪底人工混交林NEE时,CO2储存通量可以忽略。     

洪泽湖湿地杨树林生长季碳通量变化特征及其影响因子

洪泽湖调蓄灌溉与南水北调常态化调水影响下,湖区水位显著波动对湿地土壤水分及植被生长产生深刻影响。以洪泽湖湿地典型杨树林为对象,借助涡度相关系统,研究杨树生长季(4—9月)CO2通量的动态变化特征,解析气象因子的影响。结果表明:杨树生长季净生态系统CO2交换量(NEE)与环境因子均具有明显的日、月变化特征。NEE的月平均日变化总体表现为"U"型曲线,累计达-1758.10 g CO2·m-2,在生长季表现为明显的碳"汇"。光合有效辐射(PAR)与日间净生态系统CO2交换量(NEEd)的变化符合双曲线关系,PAR能解释34.3%~75.5%生长季的NEEd的变化。5 cm土壤温度(Ts)与夜间净生态系统CO2交换量(NEEn)之间符合极显著的指数函数关系,Ts能解释38.9%~55.2%生长季的NEEn的变化。不同时间尺度碳通量与环境因子的分析发现,NEE的日变化主要受土壤含水量(SWC)、净辐射(Rn)和水汽压亏缺(VPD)的影响,而月变化主要受降雨量(P)和土壤含水量(SWC)的影响。因此,洪泽湖水位变化对湿地土壤水分的影响可能显著改变湿地碳汇功能。     

环境和生物因子对黄河三角洲滨海湿地净生态系统CO2交换的影响

通过涡度相关和微气象观测技术,对黄河三角洲滨海湿地净生态系统CO₂交换(NEE)以及环境、生物因子进行了观测,探究湿地NEE变化规律及环境和生物因子对NEE的影响. 结果表明: 在日尺度上,生长季NEE呈明显“U”型曲线,非生长季变幅较小;在季节尺度上,NEE生长季波动较大,表现为碳汇,非生长季波动较小,表现为碳源;在年尺度上,滨海湿地生态系统表现为碳汇,总净固碳量为-247 g C·m^-2. 白天NEE主要受控于光合有效辐射(PAR),且生态系统表观量子产量(α)与白天生态系统呼吸(R_eco,d)均于8月达到最大值,最大光合速率(A_max)于7月达到最大值;夜间NEE随气温(T_a)呈指数增加趋势,生态系统的温度敏感系数(Q₁₀)为2.5,且土壤含水量(SWC)越高,Q₁₀值越大.非生长季NEE只与净辐射(R_n)呈显著的线性负相关,与其他环境因子无显著相关关系.生长季NEE与R_n、T_a、土壤10 cm温度(T_{s 10})等环境因子以及叶面积指数(LAI)呈显著的线性负相关,但与地上生物量(AGB)无显著相关关系.多元回归分析表明,R_n和LAI对生长季NEE的协同影响达到52%.     

Terahertz Radiation at ANKA, the New Synchrotron Light Source in Karlsruhe

ANKA is a new synchrotron light source atthe Karlsruhe Research Center in southwestGermany. The acronym stands for Ångstrøm Source Karlsruhe.The ANKA-IR beamline provides a highbrilliance infrared beam through the near,mid and far-infrared range. Thefar-infrared range is of particularinterest, since at frequencies lower thanaround 200 cm^-1 (6 THz) synchrotronlight begins to outperform conventionalthermal sources in terms of total intensityas well as brilliance. The extraction ofthe entire flux is a challenge in the THzrange, since the natural verticaldivergence of synchrotron radiationincreases with wavelength and the openingangle for collection is limited by designconstraints. At ANKA-IR, this problem issolved by the collection of radiationemitted from a bending magnet edge source,which has a much smaller verticaldivergence than conventional synchrotronradiation emitted from the constantmagnetic field region within the dipolemagnet. Edge radiation at ANKA permits theextraction of the entire infrared flux downto around 100 cm^-1 (3 THz) while withconventional synchrotron radiation thiswould only be the case for frequencies downto 2500 cm^-1. ANKA-IR provides usableintensity down to 4 cm^-1 (120 GHz).     

电离辐射诱导基因的研究进展

电离辐射诱导基因是一类受电离辐射调控表达的基因,其表达随辐射条件和所处生理环境的不同呈现复杂多变的特征。电离辐射诱导基因参与细胞内各种代谢途径,在细胞周期调控、细胞生长调节、细胞凋亡、DNA损伤修复中发挥着重要的作用。介绍了电离辐射诱导基因的种类、功能,及其引起的生物效应的分子机制及应用。     

A new paradigm in leaf-level photosynthesis: direct and diffuse lights are not equal

Global-change scenarios suggest a trend of increasing diffuse light due to expected increases in cloud cover. Canopy-level measurements of plant-community photosynthesis under diffuse light show increased productivity attributed to more uniform distribution of light within the forest canopy, yet the effect of the directional quality of light at the leaf level is unknown. Here we show that leaf-level photosynthesis in sun leaves of both C(3) and C(4) plants can be 10-15% higher under direct light compared to equivalent absorbed irradiances of diffuse light. High-light-grown leaves showed significant photosynthetic enhancement in direct light, while shade-adapted leaves showed no preference for direct or diffuse light at any irradiance. High-light-grown leaves with multiple palisade layers may be adapted to better utilize direct than diffuse light, while shade leaf structure does not appear to discriminate light based on its directionality. Based upon our measurements, it appears that leaf-level and canopy-level photosynthetic processes react differently to the directionality of light, and previously observed increases in canopy-level photosynthesis occur even though leaf-level photosynthesis decreases under diffuse light.     

Resistance to schistosome infection in Biomphalaria glabrata induced by gamma radiation

Two strains of Biomphalaria glabrata were studied with respect to the effects of ionizing radiation on their susceptibility to Schistosoma mansoni infection. Gamma radiation at levels of 3.5 and 5 krad did not induce susceptibility in the resistant S-3 strain, but was found to initiate resistance in the susceptible PR-1 strain. In an attempt to understand the induced resistance in irradiated snails, histopathologic examinations and analyses of snail hemolymph were performed. Results indicated that miracidia invading irradiated snails were quickly surrounded and encapsulated by amoebocytes. Similarly, alterations in the hemolymph of irradiated snails suggested that radiation induced aging. It is suggested that radiation-altered snails may be of value in studying the defense mechanisms of these organisms.     

Adaptive radiotherapy in patients receiving neoadjuvant radiation for soft tissue sarcoma

AimThe aim of this study is to evaluate tumor volume changes during preoperative radiotherapy and to assess the role of adaptive radiation.BackgroundContemporary neoadjuvant radiotherapy utilizes image guidance for precise treatment delivery. Moreover, it may depict changes in tumor size and shape.Materials and methodsBetween 2016 and 2018, 23 patients aged ≥18 years with soft tissue sarcoma were treated with neoadjuvant radiation followed by surgical resection. The tumor volumes (cc) were measured using the Pinnacle planning system prior to starting radiotherapy and during treatment, the changes in volume and absolute differences were estimated. Moreover, patient's position on the machine was evaluated to assess setup offsets. The triggers for plan adaptation were >1 cm expansion or unacceptable setup offsets.ResultsThe mean tumors volume at presentation was 810 cc (range, 55–4000). At last cone beam CT the tumor volume had changed in 14 patients (61%); it was stable in nine patients (39%). Disease regression was documented in eight patients (35%), with median shrinkage of −20.5% (range, −2 to −29%), while tumor progression was observed in six cases (26%), the median change was 12.5% (range, +10 to +25%).Adaptive radiation was required in four patients (17%). For the remaining 19 cases (83%), the dose distribution was adequate to cover target volumes.ConclusionsChange in soft tissue sarcoma volume during radiation is not uncommon. Image guidance should be used to reduce setup errors and to detect differences in tumor volume. Image guidance and adaptive radiation are paramount to ensure optimal radiation delivery.     

Effect of superoxide dismutase on early radiation injury of lungs in the rat

Early responses of lungs to a single radiation dose of 30 Gy were marked by an inflammatory reaction and the onset of pneumonitis within 4 weeks following hemithorax radiation in the rat. Superoxide dismutase reduced the severity of radiation lesions in lungs.     

No evidence for radiation-induced clastogenic factors after in vitro or in vivo exposure of human blood

Experiments were performed with human plasma irradiated in vitro or in vivo in order to evaluate the extent to which clastogenic factors might disturb the adaptive response to DNA-damaging factors currently studied in our laboratory. The studies were carried out with plasma isolated from whole blood given 4 Gy of X-rays in vitro and with plasma from people receiving local radiotherapy at a total dose of about 60 Gy gamma rays. Addition of irradiated plasma to culture medium did not result in a statistically significant increase in structural aberrations in chromosomes of non-irradiated normal blood.     

Effects of pubescence and waxes on the reflectance of leaves in the ultraviolet and photosynthetic wavebands: a comparison of a range of species

Total reflectance of ultraviolet and photosynthetically effective wavelengths was measured for a range of different leaf types. Two approaches were employed. Firstly, reflectance of monochromatic wavebands at 330 and 680 nm was measured for a total of 45 different species covering a wide range of genera. In the second, specific leaf types that displayed different degrees of reflectance were treated to remove hairs and waxes that contributed to their reflectance. Selected waxy and non‐waxy leaves were also studied in more detail over the spectral range 270–500 nm. It was found that both pubescence (presence of hairs) and glaucousness (presence of a thick epicuticular wax layer) had marked effects on total reflectance. Pubescent leaves tended to be more effective in reflecting longer wavelengths than ultraviolet radiation. The extent of this effect depended on hair type. Glaucous leaves demonstrated that surface waxes were very effective reflectors of both UV and longer wavelength radiation.     

Effect of solar ultraviolet radiation on growth in the marine macroalga Dictyota dichotoma (Phaeophyceae) at Helgoland and its ecological consequences

At Helgoland, in the North Sea, growth of the high sublittoral brown macroalga Dictyota dichotoma (Hudson) Lamoroux was examined in October (the time of tetraspore release) in an outdoor tank by exposing 2-day-old germlings to four solar radiation treatments achieved with different filter materials or an additional artificial light source: photosynthetically active radiation (PAR; 395–700 nm), PAR plus ultraviolet (UV)-A (320–700 nm), full solar spectrum, or solar spectrum plus artificial UV radiation (UVR). Based on length measurements over a period of 3 weeks, the growth rate in germlings strongly decreased in conditions with UVR compared to PAR: by 14% under PAR+UV-A, by 31% under the full solar spectrum and by 65% with additional UVR. Although growth rates of germlings under UVR were reduced mainly in the first week, the plants did not regain the size of the untreated plants even after 9 weeks. Regardless of the exposure, no defects in morphology or anatomy including the exposed apical meristem were detected, except for a reduction in cell division rates perhaps due to additional cost for photoprotective or repair mechanisms. Depending on the actual position of D. dichotoma plants in the natural habitat, individuals in high positions receive substantial amounts of the more harmful UV-B while those lower down might only receive UV-A during part of the day, thus the effect of UV-B on the growth of D. dichotoma will depend on its position in the field. The effects of tidal variation of the light climate and the implications of our results for the zonation of D. dichotoma are discussed. Received in revised form: 6 July 2000 Electronic Publication