中国环境规制对旅游业碳排放强度影响的空间异质性

环境规制作为实现旅游低碳发展的重要动力之一,也是实现旅游业“碳达峰、碳中和”目标的有效路径。基于综合指数法和“自下而上”法,测度2005—2019年中国大陆30个省份(中国港澳台及西藏统计数据尚缺)的环境规制水平和旅游业碳排放强度,并借助面板回归模型和面板门槛模型探讨了环境规制对旅游业碳排放强度的影响及其区域异质性。结果表明：(1)研究期内,中国整体旅游业碳排放强度呈下降趋势;其中,中部地区下降趋势最为明显,其次分别为西部、东部和东北地区。(2)中国环境规制水平呈增长态势,其规制效应对胡焕庸线右侧的地区更为显著,并呈现出自东向西递减的梯度分布特征。(3)中国环境规制对旅游业碳排放强度存在明显的“倒逼减排”效应,但东北地区却存在一定的“绿色悖论”现象;环境规制对旅游业碳排放强度的影响存在单一阈值,当旅游能源强度小于阈值时,存在显著的“倒逼减排”效应,当旅游能源强度超过阈值时则存在“绿色悖论”效应。(4)东部地区环境规制未通过门槛效应检验;中部地区存在单个门槛值,环境规制有效促进旅游业碳排放强度的下降,不存在“绿色悖论”现象;西部和东北地区分别存在单、双门槛效应,环境规制对旅游业碳排放强度...     

长三角地区植被覆盖演变城乡差异及其原因

城市生态环境和城市化之间的关系是城市可持续发展的关键。研究不同城市化水平下植被覆盖的长时间演变趋势,对理解城市化过程对植被生长动态的影响,城市更新以及推进城市绿化的科学管理具有重要意义。然而,目前对城市内部沿城乡梯度植被生长趋势差异的认识还比较有限。以我国城市化发展最为强烈的长三角地区为研究对象,基于2000-2020年长三角归一化植被指数数据,采用趋势分析和地理探测器方法,探究了长三角地区城市内部植被覆盖演变城乡差异,并从土地利用/覆被变化和城市化发展的角度解析其成因。研究结果表明：（1）2000-2020年长三角地区植被总体呈绿化趋势,植被明显绿化占最大比例（52.06%）,轻微绿化与稳定不变地区占31.68%,零星分布的褐化区占6.82%。（2）城市老城区植被覆盖变化总体呈现返绿趋势（0.016/10 a）,新城区褐化明显（-0.019/10 a）,农郊区绿化突出（0.023/10 a）。在上海、南京和杭州等人口城市化水平较高的城市中,老城区土地利用变化强度最高,其绿化趋势也最高,体现了城市更新过程对绿地空间的促进作用;而在人口城市化水平相对较低的宣城、蚌埠和阜阳等城市,土地利用变化强度相对较低的农郊区也呈现明显的绿化趋势,更多的是受到区域生态保护的影响。（3）土地城市化是长三角地区老城区和新城区植被覆盖变化的主导因子,而城市化因子对农郊区解释程度总体不显著。从长三角总体区域看,城镇人口比重、不透水面积/总面积以及地区生产总值三者对植被覆盖演变存在显著影响,其中城镇人口比重影响最大。     

Effect of light intensity and ammonium-N on carotenogenesis ofTrentepohlia odorata andDunaliella bardawil

AxenicTrentepohlia odorata was cultured at three different NH₄Cl levels (3.5 × 10^–2, 3.5 × 10^–3, 3.5 × 10^–4 M) and three different light intensities (48, 76, 122 µmol m^–2 s^–1). Chloride had no effect on growth over this range of concentration. High light intensity and high NH₄Cl concentration enhanced the specific growth rate. The carotenoid content increased under a combination of high light intensity and low N concentration. WhenD. bardawil was exposed to the same combination of growth conditions, there was an increase in its carotenoid content. The light saturation and the light inhibition constants (K _s andK _i, respectively) for growth, and the saturation constant (K _m) for NH₄Cl were determined. TheK _s andK _i values were higher inT. odorata (66.7 and> 122 mol m^–2 s^–1, respectively) than inD. bardawil (5.1 and 14.7 µmol m^–2 s^–1, respectively). TheK _m value determined at 122 µmol m^–2 s^–1, however, was lower inT. odorata (0.048 µM) than inD. bardawil (0.062 µM).Author for correspondence     

Influence of light and temperature on photoinhibition of photosynthesis inSpirulina platensis

Photoinhibition of photosynthesis and its recovery in the cyanobacteriumSpirulina platensis was studied to find how photosynthetic rates were influenced by light and temperature. By exposing cell samples from a turbidostat culture to combinations of light and temperature, a connection between light, temperature and photoinhibition was found. The experiments showed that a 10 degree increase from 20 °C to 30 °C considerably reduced the photoinhibition. At 25 °C a photon flux density of 1720 µmol m^–2 s^–1 reduced the photosynthetic rate by 50 % in 1 h, but a similarly high photon flux density had nearly no negative effect at 35 °C. Reactivation in low light from 50% photoinhibition was fast and complete in 60 min at 30 °C, while at 20 °C only about 1/6 of the full capacity was regained in the same time. Addition of the protein synthesis inhibitor streptomycin to cultures undergoing photoinhibition and regeneration indicated the presence also in this organism of a repair mechanism based on protein synthesis.Author for correspondence     

A mechanistic spatio-temporal modeling of COVID-19 data

Understanding the evolution of an epidemic is essential to implement timely and efficient preventive measures. The availability of epidemiological data at a fine spatio-temporal scale is both novel and highly useful in this regard. Indeed, having geocoded data at the case level opens the door to analyze the spread of the disease on an individual basis, allowing the detection of specific outbreaks or, in general, of some interactions between cases that are not observable if aggregated data are used. Point processes are the natural tool to perform such analyses. We analyze a spatio-temporal point pattern of Coronavirus disease 2019 (COVID-19) cases detected in Valencia (Spain) during the first 11 months (February 2020 to January 2021) of the pandemic. In particular, we propose a mechanistic spatio-temporal model for the first-order intensity function of the point process. This model includes separate estimates of the overall temporal and spatial intensities of the model and a spatio-temporal interaction term. For the latter, while similar studies have considered different forms of this term solely based on the physical distances between the events, we have also incorporated mobility data to better capture the characteristics of human populations. The results suggest that there has only been a mild level of spatio-temporal interaction between cases in the study area, which to a large extent corresponds to people living in the same residential location. Extending our proposed model to larger areas could help us gain knowledge on the propagation of COVID-19 across cities with high mobility levels.     

闽南渔场主要游泳动物时空生态位特征及其影响因素

根据2019—2021年在闽南渔场进行的秋季、冬季、春季和夏季四个航次定点底拖网调查资料,利用相对重要性指数、种群聚集强度、生态位宽度、生态位重叠及冗余分析对主要游泳动物时空生态位特征及其影响因素进行研究。结果表明,(1)调查海域共鉴定出游泳动物214种,主要优势种有18种,优势种存在明显的季节更替现象;夏季优势种的丛生指数和平均拥挤度较高,春季较低;(2)在时间维度上,须赤虾(Metapenaeposis barbata De Haan)生态位宽度最大(0.99), 7组种对时间生态位重叠值等于1.00;在空间维度上,带鱼(Trachurus japonicus Temminck&Schlegel)生态位宽度最大(2.57),空间生态位重叠值超过0.6的种类占71.3%;在时空维度上,带鱼生态位宽度最大(2.45),鹿斑仰口鲾(Leiognathus ruconius Hamilton)与赤鼻棱鳀(Thrissa kammalensis Bleeker)时空生态位重叠值最大(0.94);(3)冗余分析表明,底层温度和底层盐度是影响闽南渔场主要游泳动物时空生态位特征的重要环境因...     

干旱胁迫下红砂幼苗非结构性碳水化合物动态变化特征

该试验以荒漠区主要建群种红砂幼苗为研究对象,设置适宜水分(CK)、轻度干旱(MD)、中度干旱(SD)和重度干旱(VSD)4个胁迫处理(即田间持水量的80%、60%、40%和20%),采用盆栽控水试验,分别测定干旱胁迫15、30、45和60 d时红砂幼苗的叶、茎、粗根和细根中非结构碳水化合物(NSC)及其组分的含量,分析不同胁迫强度下不同干旱持续时间红砂幼苗NSC的动态变化及各组分差异,以揭示红砂NSC对干旱胁迫的响应机制。结果表明:(1)干旱胁迫强度和胁迫持续时间对红砂幼苗不同器官NSC及其组分均有显著影响,其中胁迫持续时间对NSC动态变化的影响尤为显著。(2)干旱胁迫初期,红砂叶中的NSC含量呈下降趋势,而茎中的NSC含量呈上升趋势,粗根和细根中NSC含量在各胁迫处理下基本保持稳定。(3)干旱胁迫后期,红砂叶和茎中的可溶性糖、淀粉和NSC含量逐渐增加,而粗根和细根中的淀粉和NSC含量呈下降趋势(中度干旱除外),且这一时期重度干旱处理下各器官可溶性糖和NSC的含量明显高于CK。研究发现,重度干旱胁迫能显著诱导提高红砂幼苗不同器官中的NSC含量,并通过分解根中淀粉和增加叶片中可溶性糖含量的方式来调节细胞渗透势平衡,以维持细胞活力,进而保持红砂在干旱胁迫后期的存活。     

短花针茅叶片水分利用效率对放牧强度的响应及其影响因素

为明确植物的用水策略及适应性机制,以内蒙古四子王旗短花针茅荒漠草原为研究对象,设置对照(CK)、轻度放牧(LG)、中度放牧(MG)和重度放牧(HG)4个放牧梯度,其载畜率分别为每1 hm^(2)每年0、0.93、1.82和2.71个羊单位的放牧强度,调查建群种短花针茅的高度、盖度、密度、地上生物量以及土壤的理化性状,并且采用稳定碳同位素法和红外光合仪法对短花针茅水分利用效率进行了测定,旨在阐明短花针茅水分利用效率在不同放牧强度下的响应规律及其影响因素。结果显示:(1)放牧对短花针茅盖度、密度以及地上生物量的影响显著;随着载畜率的增大,有利于短花针茅的扩散使其分布面积增加,且在中度放牧条件下尤为明显。(2)随着放牧强度的增加,土壤水分含量较对照显著提高,土壤全氮含量呈先增加后减少的变化趋势,土壤速效钾呈现降低的变化趋势,而对土壤全碳含量和pH无显著影响,说明适度放牧能够提高土壤水分含量、促进土壤氮含量的积累,但放牧会导致土壤速效钾减少。(3)随着放牧强度的增大,短花针茅长期水分利用效率(WUE l)呈现“V”形变化趋势,而瞬时水分利用效率(WUE t)与内在水分利用效率(WUE i)总体呈降低的变化趋势。(4)相关分析显示,放牧强度与短花针茅密度、地上生物量呈显著正相关关系,土壤全氮含量与有机碳、pH、WUE i呈显著正相关关系,WUE t与WUE i呈显著正相关关系;短花针茅内在水分利用效率与土壤有机碳含量密切相关。研究表明,重度放牧导致短花针茅株丛破碎化,增加了种群的扩散面积,是短花针茅长期水分利用效率提高的直接原因;短花针茅瞬时水分利用效率随放牧强度的增加而降低可能是由其内在水分利用效率降低引起的。     

CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN,A CYANOBACTERIAL SHEATH PIGMENT1

Scytonemin, the yellow-brown pigment of cyanobacterial (blue-green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near-ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near-ultraviolet-blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m^?2· S^?1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV-A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short-wavelength solar irradiance.     

Mechanisms responsible for the positive diversity–productivity relationship in Minnesota grasslands

Species’ extinctions have spurred debate on whether interactions among few or among many species cause a positive diversity–productivity relationship in experimentally assembled grasslands. We addressed this question by quantifying the productivity of 14 species across an experimental diversity gradient in Minnesota. We found that interspecific interactions leading to coexistence and competitive displacement both determine which species overyield; i.e. are more productive at high diversity. Overyielding species were either superior N competitors (C4 grasses) or N fixers (legumes). Surprisingly, these species were not most productive in monoculture, thus, the ‘selection’ of productive species in diverse plots did not cause the positive diversity–productivity relationship. Both positive (with legumes) and negative interspecific interactions (with C4 grasses) determined whether individual species overyielded. Foliar pathogens did not cause overyielding, although other natural enemies may be responsible. Overyielding species are not displacing underyielding species over time, implying that other diversity‐promoting interactions also operate in this experiment.