首冠藤的生态生物学特征

通过样地调查,对首冠藤(Bauhinia corymbosa)的生态生物学特征进行研究.结果表明,首冠藤是阳生性藤本植物,主要分布于热带亚热带地区光照较好的山坡、疏林边缘或村旁;耐贫瘠,适宜生长的土壤为红壤和赤红壤.其平均光合速率为3.306 μmolm~(-2)s~(-1),气孔导度为0.25 molm~(-1)s~(-1),蒸腾速率为4.10 mmolm~(-2)s~(-1).首冠藤对营养元素的利用率较高,植株体内N、P、K、Ca、Na、Mg加权平均养分含量分别为1.11%、0.09%、0.56%、0.86%、0.21%、0.06%,其中叶片N含量最高,枝Na含量最高,根部P和Mg含量最高.首冠藤的生态生物学特征有利于其快速生长、攀附和适应环境.     

城市区域绿色屋顶普及对水量水质的影响

绿色屋顶是城市降雨径流管理的主要措施之一,为了解绿色屋顶普及对城市流域降雨径流量和径流水质的影响,本文以重庆大学虎溪流域为研究载体,评估了绿色屋顶规模化应用与流域降雨产流和径流水质的响应关系.结果表明： 在城市流域进行屋面绿化有助于消减降雨径流以及产污负荷,且屋顶绿化规模和空间分布情景影响降雨径流水质.在屋顶占城市区域总面积的比例为25%、降雨持续时间15 min、降雨强度14.8 mm·h^-1的条件下,当区域内屋顶全部绿化时,峰值降雨径流降低5.3%,降雨径流总量降低31%;总悬浮物（TSS）、总磷（TP）、总氮（TN）的污染负荷分别降低40.0%、31.6%、29.8%,峰值浓度分别降低21.0%、16.0%、-12.2%,平均浓度分别降低13.1%、0.9%、-1.7%;随屋顶绿化率的增加,TSS、TP浓度消减率有所提高,而TN浓度消减率则呈降低趋势,靠近流域总出水口进行屋面绿化,更有利于径流水质的改善.     

江苏公路绿地系统的树种结构与发展水平评价

对江苏省 13个市 70多条国省干线公路绿化树种的种类、数量和结构进行了调查统计 ,结果表明 :在树木数量结构中 ,杨树 (Populusspp .)最多 ,占总量的 45 %,其他依次为水杉 (MetasequoiaglyptostroboidesHuetCheng) 2 0 %、女真 (LigustumlucidumAifon) 9%、香樟〔Cinnamomumcamphora (L .)Presl〕7%、柳树 (Salixspp .) 3%、银杏 (GinkgobilobaL .) 3%、冬青 (Ilexspp .) 2 %、松树 (Pinusspp .) 2 %和广玉兰 (MagnoliagrandifloraL .) 2 %,乔木与灌木的比例为 2∶1。对树种及树种结构因子与环境 (气候 )和经济因素进行了相关分析 ,发现除树木种类和密度外 ,树种结构因子均与气候或经济因素呈极显著正相关或负相关 ,说明这 2个因素对绿化质量影响较大。采用简单灰色关联法对各市公路绿化系统树种结构综合因子进行了排序和评价 ,结果表明 :以无锡市的综合性状关联度最高 (r =0 .76 5 1) ,表明该市的绿化结构为最好 ,公路绿化发展水平最高 ,其次为镇江 (r=0 .6 0 42 )和苏州 (r=0 .5 92 2 )。     

Compound droughts slow down the greening of the Earth

Vegetation response to soil and atmospheric drought has raised extensively controversy, however, the relative contributions of soil drought, atmospheric drought, and their compound droughts on global vegetation growth remain unclear. Combining the changes in soil moisture (SM), vapor pressure deficit (VPD), and vegetation growth (normalized difference vegetation index [NDVI]) during 1982–2015, here we evaluated the trends of these three drought types and quantified their impacts on global NDVI. We found that global VPD has increased 0.22 ± 0.05 kPa·decade⁻¹ during 1982–2015, and this trend was doubled after 1996 (0.32 ± 0.16 kPa·decade⁻¹) than before 1996 (0.16 ± 0.15 kPa·decade⁻¹). Regions with large increase in VPD trend generally accompanied with decreasing trend in SM, leading to a widespread increasing trend in compound droughts across 37.62% land areas. We further found compound droughts dominated the vegetation browning since late 1990s, contributing to a declined NDVI of 64.56%. Earth system models agree with the dominant role of compound droughts on vegetation growth, but their negative magnitudes are considerably underestimated, with half of the observed results (34.48%). Our results provided the evidence of compound droughts-induced global vegetation browning, highlighting the importance of correctly simulating the ecosystem-scale response to the under-appreciated exposure to compound droughts as it will increase with climate change.     

Multicellular computer simulation of morphogenesis: blastocoel roof thinning and matrix assembly in Xenopus laevis

In the blastocoel roof (BCR) of the Xenopus laevis embryo, epibolic movements are driven by the radial intercalation of deep cell layers and the coordinate spreading of the overlying superficial cell layer. Thinning of the lateral margins of the BCR by radial intercalation requires fibronectin (FN), which is produced and assembled into fibrils by the inner deep cell layer of the BCR. A cellular automata (CA) computer model was developed to analyze the spatial and temporal movements of BCR cells during epiboly. Simulation parameters were defined based on published data and independent results detailing initial tissue geometry, cell numbers, cell intercalation rates, and migration rates. Hypotheses regarding differential cell adhesion and FN assembly were also considered in setting system parameters. A 2-dimensional model simulation was developed that predicts BCR thinning time of 4.8 h, which closely approximates the time required for the completion of gastrulation in vivo. Additionally, the model predicts a temporal increase in FN matrix assembly that parallels fibrillogenesis in the embryo. The model is capable of independent predictions of cell rearrangements during epiboly, and here was used to predict successfully the lateral dispersion of a patch of cells implanted in the BCR, and increased assembly of FN matrix following inhibition of radial intercalation by N-cadherin over-expression.     

Changes in the protein composition of cytoplasmic ribsomes during the greening of etiolated barley leaves

We examined changes in the protein composition of cytoplasmic ribosomes in etiolated barley leaves following illumination. Cytoplasmic ribosomes were isolated from greening barley leaves by sucrose density gradient centrifugation, and were analyzed by radical-free highly reducing polyacrylamide gel electrophoresis (RFHR-PAGE). Eighty-nine proteins were resolved from the ribosomal fraction; among them, 8 proteins changed their copy numbers depending on the stage of greening. We designated these as phase dependent ribosomal proteins (PD1–PD8). Two of the proteins (PD1 and 5) present in the ribosomes of etiolated leaves showed a decrease in level during greening. In contrast, the levels of 6 ribosomal proteins (PD2, 3, 4, 6, 7 and 8) increased as greening proceeded. N-terminal amino acid sequence of PD8 showed high homology to rat ribosomal protein L34. The ribosomal proteins that appeared after illumination were not found in any fraction of the etiolated leaves, suggesting that they were synthesized after the onset of illumination. Copy numbers of other ribosomal proteins did not change during greening.     

Characterization of early events leading to the formation of chlorophyll-proteins of PSII in Euglena gracilis

Development of chlorophyll-proteins in photosystem II was studied with Euglena gracilis Z. during dark-light transition. Upon illumination of the dark-grown cells, protochlorophyllide was photoconverted to chlorophyll(ide) a with a low efficiency (14%). After a lag time of 1-2 h, chlorophylls, apoproteins of antenna chlorophyll-protein complex CP 43/47 and of light-harvesting chlorophyll-protein complex (LHCII) accumulated in the thylakoid membrane in a coordinated fashion. There was, however, a significant difference in the stability between the newly formed LHCII and CP 43/47 judging from non-denaturing lithium dodecyl sulfate-polyacrylamide gel electrophoresis. The possibility that efficiencies of incorporation and stabilization of chlorophylls in the apoproteins differ among the chlorophyll-proteins in the early stage of greening of Euglena is discussed.     

The consequences of delayed greening during leaf development for light absorption and light use efficiency

Many species of rainforest plants have an unusual form of leaf development such that leaves delay greening until after full leaf expansion. Chlorophyll accumulation was measured during leaf development in five woody rainforest species, three with white young leaves, and two with ‘normal’ greening. In the three species with white leaves, the chlorophyll content of the expanding leaves was about 0.4mg dm^?2, whereas in the two species with green young leaves, chlorophyll content was about 2.1 mg dm^?2. Chlorophyll accumulation in greenhouse and field experiments was independent of light level. During leaf expansion, species with delayed chloroplast development only absorb 18–25% of the maximum possible light, compared with 80% for species with normal greening. Furthermore, species with delayed greening have low chlorophyll contents and reduced absorption for at least 30 d after full expansion. At a PPFD typical of the forest under story, the photosynthetic light use efficiency based upon incident radiation was 0.030–0.036 for species with delayed chloroplast development and 0.068–0.085 for the two species with normal greening. The lower light use efficiency of white species was primarily due to decreased light absorption. However, they also had a slightly lower light use efficiency based upon absorbed radiation, suggesting that development of other components of the photo-synthetic apparatus also may be delayed. Despite the fact that delayed greening decreases light absorption and light use efficiency during leaf development, it is extremely common in shade-tolerant species. We suggest that an advantage of delayed greening is that resources are not invested in the leaf until it is fully expanded and better defended from herbivores.     

Isolation and initial characterization of virescent mutants of Arabidopsis thaliana

In higher plants, development of the chloroplasts must be coordinated with development of the leaf. In order to study the signals that synchronize these two developmental processes, we have isolated virescent (delayed in greening) mutants of Arabidopsis thaliana. Two such mutants that have pale-green young leaves which gradually green more fully during leaf maturation have been partially characterized. The two, vir1 and vir2, are due to separate nuclear recessive mutations. The pale leaves of vir1 and vir2 both had reduced 77°K fluorescence emission at 730–734 nm relative to that at 686–687 nm, indicating a reduction in the relative amount of LHC I compared to WT. As leaves greened, the amount of LHC I increased to near wildtype levels. The shift in the fluorescence emission peak from 730 nm to 734 nm, characteristic of maturing LHC I, was seen for vir1, but not vir2, suggesting that vir1 is a regulatory mutant while vir2 may be defective in a specific aspect(s) of LHC I function.Abbreviations D dark - EMS ethyl methanesulfonate - er erecta - gl1 glabrous1 - L light - LHC I light harvesting complex of Photosystem I - LHC II light harvesting complex of Photosystem II - M2 second generation of mutagenized seed - M3 third generation of mutagenized seed - vir virescent - WT wildtype