佛山城市典型森林群落土壤重金属分布、流通及枯落物富集特征

富集重金属的枯落物分解可能提高重金属暴露率,增加人体接触健康风险。为了解南方城市土壤重金属在森林生态系统中的分布及流转情况,通过调查研究了佛山市8个典型森林群落土壤及枯落物重金属含量,分析了各森林群落枯落物对不同重金属的富集效应及重金属随枯落物回归土壤流通量。结果表明:1)城市森林各土壤重金属含量在不同典型群落间差异显著(P<0.05),差异最大为Pb、Cr、Zn,As、Cu、Ni次之,Hg、Cd最小;土层深度(0—20,20—40,40—60 cm)对重金属含量影响显著(P<0.05),差异最大为Cd、Hg,其次为As、Cu,最小为Zn、Ni、Pb、Cr。整体上,Cd、Hg、As、Pb、Zn在0—20 cm最高,表层富集特征明显,Cr和Ni在40—60 cm最高。2)8个森林群落中阴香—白楸—醉香含笑群落(CMMC)枯落物对8种重金属的综合富集系数(TBCF,66.76)最高,其中以Cd的富集效果最突出,富集系数为44.45,且对Pb、Cu、Zn也相对富集;最低的为黧蒴锥—香椿—樟树群落(CTCC),综合富集系数(TBCF)为8.09,仅对Cd、Cr、Cu相对富集,对其余...     

水资源约束下西北干旱区城市经济发展与城市化阈值

城市化水平阈值是指在水资源硬约束下,在确保经济发展达到一定速度与规模、生态环境建设得到基本保障、并具备足以支撑城市接纳一定数量农民进城转为非农人口的经济能力时,能达到的“农转非”人口占总人口的最大比例。以干旱区河西走廊为例,分析了在水资源约束下城市经济发展总量及其对应的城市化阈值。采用阈值模型计算表明,未来30a在不跨区调水的前提下,河西走廊总需水量的上限阈值为7.81×109m3,其中生态需水、生产需水和生活需水比例调整为13.2:83.5:3.3,总需水量对应的国内生产总值为1.81×1011元,历年平均增长速度最快可达到6.91%,第一、二、三产业结构调整为18.99:47.20:33.81。在总需水量阈值、经济总量、需水结构与产业结构调整优化和经济增长速度不低于7%、农业需水按0.61%的速度退水9.12×108m3、生态需水比例不低于13%等多重条件约束下,求得河西走廊未来30a能够达到的总人口为5.82×106人,城镇非农业人口可达到2.05×106人,城市化水平可达到35.14%,这一水平仅相当于中国2001年的平均城市化水平。在跨区调水1.31×109m3的条件下,城市化水平可望达到47.17%。进而采用总人口人均拥有的GDP、非农业人口人均拥有的第二、三产业增加值、农业人口人均拥有的第一产业增加值3项经济指标对水资源约束下经济发展总量对城市化水平的保障程度进行了验证分析。由于各城市的缺水状况、取水条件、发展性质、发展阶段与经济发展实力与前景等各不相同,致使不同城市之间对应的总需水量、经济总量、经济增长速度和城市化水平等均表现出较大的差异性。     

Evidence for slow turnover in a fraction of Photosystem II complexes in thylakoid membranes

We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to Q_A in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of Q_A at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q₄₀₀, the Fe²⁺ near Q_A, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e⁻ / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e⁻ / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to Q_A rapidly, but the reoxidation of Q⁻_A is slow (t1/2 = 2 s). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS II_β reaction centers. One corollary of this conclusion is that electron transfer from P-680 to Q_A in PS II_β reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift.     

人为干扰对武汉市城市绿地鸟类群落结构的影响

城市绿地生态系统是城市景观的重要组成部分,具有重要的生态与文化价值。鸟类是城市绿地生态系统的指示类群,研究人类活动对鸟类资源的影响能够为城市生态景观的建设与维护提供重要理论依据。本研究于2021年10月至2022年5月,采用样线法对武汉市不同干扰强度的城市绿地内林鸟群落进行调查。共记录到鸟类11目34科100种,其中国家二级重点保护鸟类9种,在物种组成上以雀形目为主(76种,占调查到总鸟种数的76%),在居留型上以留鸟为主(42种,42%),在区系上主要属于东洋界(45种,45%)。繁殖季鸟类物种数高于非繁殖季,主要是由于夏候鸟和旅鸟的增加导致。在不同干扰强度中,重度干扰斑块的平均鸟类个体数最多,轻度干扰斑块的鸟类物种丰富度、多样性指数和均匀度指数最高,而中度干扰斑块的鸟类个体数、物种丰富度、多样性指数和均匀度指数均为最低,且繁殖季和非繁殖季鸟类群落结构在不同人为干扰强度中的格局未发生变化。综上所述,武汉市城市绿地的鸟类多样性较为丰富,随着干扰强度增加,鸟类多样性出现非线性差异,揭示了人为干扰与自然干扰对生态影响的差异;在面积狭小、破碎化严重的斑块中,人为干扰可能有利于城市绿地鸟类多样性的维持。     

武汉东湖星形柄裸藻种群与宿主的关系以及生态因子对它的影响

星形柄裸藻与附生宿主之间的相互作用为:它是偏利者,而对宿主无很大影响;当其在宿主体表大量附着时,才对宿主有偏害作用。它的种群密度(N,个/L)与宿主密度(Na,个/L)有密切的正相关关系:N=0.0858e0.0528Na(r=0921,pT,天)对星形柄裸藻的平均附着量(m,个/每个甲壳动物)和附着量(B,个/L)的影响是:在一定的蜕皮间隔时间范围内呈正相关性:m=aebT和B=aebT(a和b为方程常数,下同);超过这个范围呈负相关性:m=aT-b和B=aT-b。而宿主蜕皮间隔时间(T,天)对星形柄裸藻附着率(R,%)的影响则仅为正相关性:R=a+blnT。星形柄裸藻对宿主的附生有一定的选择性。水温(t,℃)与星形柄裸藻种群密度(N,个/L)的关系为:在5-12℃时呈正相关性,N=0.309e0.624t(r=0.914,pN=0.0000617e190.2/t(r=0.941,pR,%)的影响则仅呈负相关关系:R=bln(30-t)-a。水的透明度(d,cm)与星形柄裸藻种群密度(N,个/L)的相关方程为:N=0.020e0.037d(r=0.838,pS,mg/L)与种群密度(N,个/L)有一定的正相关性:N=0.00254e0.178S(r=0.816,pN,个/L)与4个主要因子:宿主密度(N,个/L),透明度(d,cm),水温(t,℃),含钙量(S,mg/L)的多元回归方程为:N=1.208Na+0.698d+5.584t+2.942S-357.957(R=0.853,df=11,k=4,p<0.01)。       

基于GIS的城市绿地景观引力场研究——以宁波市为例

城市绿地是城市用地的重要组成部分 ,也是城市生态系统的一个子系统。城市绿地景观的评价是城市生态系统研究的重要课题之一。在 GIS技术支持下 ,对城市绿地景观进行了研究。在研究过程中 ,将物理学中“场”的相关理论引入城市绿地景观的研究 ,提出绿地景观引力场的概念及评价方法。绿地景观引力场是城市绿地系统为城市居民提供服务能力的大小或潜力 ,其主要影响因素有绿地景观本身的质量、城市人口分布状况、城市土地利用现状、城市主要交通设施等。在研究中需要建立以下相关模型 :城市阻力的空间分布模型、城市人口的空间分布模型、城市公共绿地的空间分布模型、城市绿地景观引力场的空间分布评价模型。研究结果得出以下结论 :(1)景观引力场用于城市绿地系统的评价 ,能够更好地反映城市绿地的空间分布格局 ;(2 )丰富了城市绿地系统评价的指标内容和评价方法 ;(3)该方法从景观设计上提供了一个可供决策参考的依据 ;(4 )景观引力场还可用于城市其它服务设施的合理性与有效性的评价与研究。     

山东植物区系中的特有现象

对山东植物区系中的特有现象进行了初步研究。全省共有５３个特有种,可分为４种分布式样即全省布型、鲁中南－山东半岛间断分布型、鲁中南山地分布和山东半岛分布型;提出了山东植物区的两个特有现象中心,即崂山昆嵛山中心和泰山蒙山中心,并初步探讨了其形成原因。     

京津冀城市群土地利用变化对地表径流的影响

城市化的显著特征之一是地表景观格局被人为改变,大量硬化地表覆盖、取代了原本自然或半自然的土地覆盖类型,极大地干扰了区域水文循环过程。其中,最直接的体现是对地表径流过程的影响。城市群作为当前我国城市化的重要模式,其聚集连片的扩张模式,对区域地表径流过程的干扰尤为严重。以京津冀特大城市群为研究区域,应用长期水文影响评价模型(L-THIA),以1980、1990、2000、2010、2015年5期土地利用数据、土壤数据以及1950—2015年逐日降雨数据为输入,模拟计算了不同土地利用/覆被格局对多年平均地表径流量的影响。结果表明,(1)经过率定的L-THIA模型能够较为准确地模拟京津冀城市群地区的地表径流分布特征,模型模拟误差在±10%内;(2)1980—2015年,京津冀城市群地区不透水地表面积急剧增加,其净增长值为12690.14 km~2。北京与天津等超大城市不透水地表面积增加最明显;(3)随着土地利用格局的变化,京津冀地区地表径流量呈逐年增长趋势。1980—2015年,京津冀城市群地区地表径流量的绝对增长值为17.84亿m~3,增幅11.83%。其中,1990—2000年及2010—2015年期间地表径流年均增长率较大,分别为0.36%与0.46%。对地表径流贡献较大的土地利用类型为耕地和不透水地表,其5期土地利用情景下的平均产流占比分别为35.38%、22.71%;(4)城市尺度上,不同城市的标准化年均径流深(NAARD)存在较大差异。天津、石家庄的产流能力较强,承德、衡水等城市的产流能力较弱,北京市的标准化年均径流深处于中等水平。另一方面,不同城市标准化年均径流深增长规律也存在较大差异。1980—2015年,天津市的NAARD增长最多,承德市增长最少,北京市的NAARD增长处于中等水平。本文对于京津冀城市群水文过程的时空演变研究以及国土空间优化指导具有参考意义。     

Photosystem I photochemistry at low temperature. Heterogeneity in pathways for electron transfer to the secondary acceptors and for recombination processes

Electron transport has been studied by flash absorption and EPR spectroscopies at 10–30 K in Photosystem I particles prepared with digitonin under different redox conditions. In the presence of ascorbate, an irreversible charge separation is progressively induced at 10 K between P-700 and iron-sulfur center A by successive laser flashes, up to a maximum which corresponds to about two-thirds of the reaction centers. In these centers, heterogeneity of the rate for center A reduction is also shown. In the other third of reaction centers, the charge separation is reversible and relaxes with a t_1/2 ≈ 120 μs. When the iron-sulfur centers A and B are prereduced, the 120 μs relaxation becomes the dominant process (70–80% of the reaction centers), while a slow component (t_1/2 = 50–400 ms) reflecting the recombination between P-700⁺ and center X⁻ occurs in a minority of reaction centers (10–15%). Flash absorption and EPR experiments show that the partner of P-700⁺ in the 120 μs recombination is neither X nor a chlorophyll but more probably the acceptor A⁻₁ as defined by Bonnerjea and Evans (Bonnerjea, J. and Evans, M.C.W. (1982) FEBS Lett. 148, 313–316). The role of center X in low-temperature electron flow is also discussed.     

Urban development and sustainability challenges chronicled by a century of construction material flows and stocks in Tiexi,China

Construction materials are considerable forces of global environmental impacts, but their dynamics vis‐à‐vis urban development are poorly documented, in part because their long lifespans require elusive and sometimes nonexistent decade‐long high‐resolution data. This study analyzes the construction material flow and stock trends that shaped and were shaped by the development, decline, and renewal of the Tiexi district of Shenyang, a microcosm of China's urban transformations since the early 20th century. Chronicling building‐by‐building the material flows and stock accumulations involved in the buildup of this area, we shed light on the physical resource context of its socioeconomic history. We find that 42 million tonnes of construction materials were needed to develop the Tiexi district from 1910 to 2018, and 18 million tonnes of material outflows were generated by end‐of‐life building demolition. However, over 55% of inflows and 93% of outflows occurred since 2002 during a complete redevelopment of the district. Only small portions of end‐of‐life materials could have been reused or recycled because of temporal and typological mismatches of supply and demand and technical limitations. Our analysis reveals a dramatic decrease in median building lifetimes to as low as 6 years in the early 21st century. These findings contribute to the discussion of long‐term environmental efficiency and sustainability of societal development through construction and reflect on the challenges of urban renewal processes not only in China but also in other developing and developed countries that lost (or may lose) their traditional economic base and restructure their urban forms. This article met the requirements for a Silver/Silver JIE data openness badge described at http://jie.click/badges .