三江平原沟渠网络结构对区域景观格局的影响

农业开发进程中产生的沟渠作为农业景观中廊道内部的动因主体,会对周围自然生态系统产生不同程度的影响;同时沟渠网络的形成,又使得这种影响作用更加深入和复杂.以根据三江平原建三江管局辖区2004年的Landsat-TM卫星影像解译的土地利用现状图以及沟渠分布水利图为基础资料,在地理信息系统(GIS)支持下,选择3个30×30km2的取样区为研究对象,分析了各样区的景观结构特征和沟渠网络结构.在此基础上,用典范相关分析(CCA)定量研究了沟渠网络结构对于区域景观格局的影响.结果表明:沟渠网络的结构对区域景观格局有显著影响,沟渠密度越大,网络结构越复杂,则区域景观中斑块数目越多,平均斑块面积越小;同时农业用地所占比例越大,自然湿地所占比例越小.通过各沟渠网络结构指标与CCA排序轴的相关性分析发现,对区域景观格局影响最大的指标是沟渠密度,其次是线点率和环度,而反映沟渠网络连通性的连通度指标影响相对较小.     

宁夏第三排水沟底泥细菌群落结构特征和空间分布

【背景】微生物对环境有指示作用,微生物群落组成是水环境的研究热点之一。【目的】探究宁夏第三排水沟底泥细菌群落结构及空间分布。【方法】在底泥理化性质分析的基础上,采用MiSeq PE300测序平台对沟道及主要支流共11个采样点的表层底泥细菌进行16S rRNA基因扩增子测序。【结果】三排底泥呈弱碱性,底泥有机碳、全氮、全磷、氨氮和硝态氮等理化指标存在空间差异。平罗县段底泥有机碳、全氮和全磷均低于贺兰县和惠农区;下游惠农区段底泥细菌的物种丰富度和多样性明显高于上游贺兰县段,十二分沟与干流差异较明显。三排底泥优势细菌菌门为变形菌门(Proteobacteria,24.41%–44.40%)、绿弯菌门(Chloroflexi,5.46%-17.55%)、放线菌门(Actinobacteria,9.12%–21.21%)、拟杆菌门(Bacteroidetes,6.96%–13.10%)、热脱硫杆菌门(Thermodesulfobacteria,3.40%-12.20%)、厚壁菌门(Firmicutes,3.31%–14.61%)和酸杆菌门(Acidobacteria, 2.00%-9.77%)。...     

Temporal and spatial variations of dissolved oxygen concentrations in some Dutch polder ditches

This study deals with the temporal and spatial variations of dissolved oxygen concentration, temperature and occasionally pH in three polder ditches in the Netherlands. A routine programme including different environmental parameters served to characterize the ditch environment. Conclusions concerning water quality criteria are presented briefly.     

An improved test for evaluating the pathogenicity of isolates of Fusarium solani f.sp. pisi on pea

An improved in vitro test is described for determining the pathogenicity of Fusarium solani f.sp. pisi isolates on pea. This technique involves the use of polypropylene fibre Milcap plugs to suspend peas in boiling tubes containing spore suspensions in 0.1% water agar. Results were available after 14 days of incubation at 25°C. Four levels of pathogenicity were detected on pea cultivars Little Marvel and Dark Skinned Perfection using a total of eight isolates and strains of F. solani f.sp. pisi.     

Seed morphology and anatomy in someAnnonaceae

Twelve species ofAnnonaceae, namelyAncana sp.,A. stenopetala, Annona cherimola, A. montana, A. muricata, A. squamosa, Bocagea sp.,Bocageopsis canescens, two species ofUnonopsis, Xylopia aromatica, andX. emarginata, were investigated with respect to the morphology and anatomy of the seed. They show the basic structural pattern characteristic of annonaceous seeds: perichalaza, fibrous mesotesta, and rumination developed by both integuments. However, several differential characters, some of them never previously described, were found: All taxa exhibit an additional endotestal mechanical layer which forms the micropylar plug except inAncana. InAncana the plug is built by the inner integument. Aril, sarcotesta and pits on the seed surface are present in some taxa and show different origin and structure. Special anatomical adaptations possibly functioning during germination are described. The results obtained from the investigated taxa are discussed and compared with published data on seed structure inAnnonaceae.     

The copulatory plug delays ejaculation by rival males and affects sperm competition outcome in house mice

Females of many species mate with multiple males (polyandry), resulting in male–male competition extending to post‐copulation (sperm competition). Males adapt to such post‐copulatory sexual selection by altering features of their ejaculate that increase its competitiveness and/or by decreasing the risk of sperm competition through female manipulation or interference with rival male behaviour. At ejaculation, males of many species deposit copulatory plugs, which are commonly interpreted as a male adaptation to post‐copulatory competition and are thought to reduce or delay female remating. Here, we used a vertebrate model species, the house mouse, to study the consequences of copulatory plugs for post‐copulatory competition. We experimentally manipulated plugs after a female's first mating and investigated the consequences for rival male behaviour and paternity outcome. We found that even intact copulatory plugs were ineffective at preventing female remating, but that plugs influenced the rival male copulatory behaviour. Rivals facing intact copulatory plugs performed more but shorter copulations and ejaculated later than when the plug had been fully or partially removed. This suggests that the copulatory plug represents a considerable physical barrier to rival males. The paternity share of first males increased with a longer delay between the first and second males' ejaculations, indicative of fitness consequences of copulatory plugs. However, when males provided little copulatory stimulation, the incidence of pregnancy failure increased, representing a potential benefit of intense and repeated copulation besides plug removal. We discuss the potential mechanisms of how plugs influence sperm competition outcome and consequences for male copulatory behaviour.     

STORAGE AND STRUCTURAL PRODUCTS FORMED DURING PHOTOSYNTHESIS IN THE SIPHONOUS ALGA CAULERPA SIMPLICIUSCULA(CHLOROPHYCEAE)1

The distribution of radioactivity into storage and intermediary metabolites during photosynthesis over periods of up to three hours was followed in the siphonous green alga Caulerpa simpliciuscula C. Ag. After the first hour, almost all the carbon assimilated was recovered as insoluble 1,4-α-glucan. There was rapid movement of carbon into insoluble 1,3-β-glucans during the first 20 min of photosynthesis, but little additional carbon moved into these compounds after that time. This contrasted with the movement of carbon into the soluble 1,3-β-glucan fraction, which continued for 2 h. Sucrose accumulated very little ¹⁴C during the entire period of photosynthesis. There was a very slow transfer of ¹⁴C into lipid throughout the period but the rate was linear. Protein labelling showed a lag of 2 h before it reached the same rate of ¹⁴C accumulation as shown by the lipid initially. It is suggested that the distribution of radioactivity can be explained in part by proposing that the tissue is in the latter stages of recovery from the wounding which look place at the time of dividing the thallus into sections.     

The conserved nature and taxonomic utility of pollen morphology in Cantua (Polemoniaceae)

Pollen exine morphology of nine of the ten species of Cantua (Polemoniaceae) is examined using light and scanning electron microscopy. A total of 28 specimens of C. bicolor, C. buxifolia, C. candelilla, C. cuzcoensis, C. flexuosa, C. pyrifolia, C. quercifolia, C. volcanica, and an as yet undescribed species (Cantua sp. nov.) are examined using either fresh or herbarium material. Pollen grains are found to be spheroidal, pantoporate, and quite large; mean diameter varies from 62 to 87?μm. Mean number of pores varies from 4.5 to 21.2 and mean pore size varies from 4.86 to 12.40?μm. Pollen grains of all species have insulate semitectate sexines. This feature distinguishes the pollen of Cantua species from the remainder of the Polemoniaceae. Insulae are evenly distributed over the surface of the pollen grain, with the exception of C. flexuosa and occasionally C. buxifolia, where insulae are more sparsely and haphazardly distributed. The majority of the species examined have irregularly shaped tectal insulae, with the exception of the large rounded insulae in C. quercifolia and the elongated narrow insulae in C. volcanica. Cantua quercifolia and C. volcanica have supratectal verrucae, a possible synapomorphy. In comparison to close relatives, the pollen grains of Cantua are evolutionarily conserved, and show little variation among species.