Climatic factors associated with phytoplankton community succession during and after the 1977 drought for the San Francisco Bay-Delta Estuary [abstract]

Principal coordinates analysis and multiple regression analysis were used to determine the environmental factors associated with the decline in phytoplankton production during and after the 1977 drought for the San Francisco Bay-Delta Estuary. Physical, chemical and biological data were collected semimonthly or monthly during the spring-summer between 1973 and 1982 from 15 sampling sites located throughout the Bay-Delta. A decline in phytoplankton community diversity and density during the 1977 drought and subsequent years (1978 through 1981) was described using principal coordinates analysis. The best multiple regression which described the changes in phytoplankton community succession contained the variables water temperature, wind velocity and ortho-phosphate concentration. Together these variables accounted for 61 percent of the variation in the phytoplankton community among years described by principal coordinates analysis. An increase in water temperature, wind velocity and ortho-phosphate concentration within the Bay-Delta, beginning in June 1976 and continuing through 1981, was demonstrated using weighted moving averages. From the strong association between phytoplankton community succession and climatic variables it was hypothesized that the decline in phytoplankton production during and after the 1977 drought was associated with climatic changes within the northeast Pacific.

Drought frequency analysis for California from observed, synthetic, and proxy data

Drought frequency analysis can be performed with statistical techniques developed for determining recurrence intervals for extreme precipitation and flood events (Linsley et al 1992). The drought analysis method discussed in this paper uses the log-Pearson Type III distribution, which has been widely used in flood frequency research. Some of the difficulties encountered when using this distribution for drought analysis are investigated.

小麦-多枝赖草抗性纯合易位系统的培育及其遗传标记

本研究以小麦与多枝赖草属间杂种后代BC_2F_3-F_6为基本材料，首先对其进行抗性鉴定和细胞学分析，从中选出一些抗性较好且体细胞染色体数2n = 42、PMC减数分裂期染色体配对比较正常的株系，进而以此为试材进行花药培养。研究过程中，解决了小麦远缘杂种后代花药培养愈伤组织诱导出愈率、绿苗分化率、最终绿苗得率、移栽成活率以及自然加倍率低等一个个障碍着小麦远缘杂种后代花药培养的关键性技术难题，获得了小麦与多枝赖草杂种后代花药培养的成功，共得到了150多个后代纯系的种子。 对这些后代纯系进行遗传标记技术鉴定。形态标记结果表明，后代材料中带有多枝赖草的标记性状，如耐盐、抗旱、抗黄矮、白粉病等;细胞学分析发现加倍单倍体（H_1）植株减数分裂染色体配对出现环形四价体、测交检测发现棒状二价体增加，初步鉴定选择出小麦与多枝赖草的纯合易位系。进一步利用现代分子生物学技术，进行分子标记、染色体原位杂交，结果表明材料中有外源（多枝赖草）染色体片段的存在。RFLP分析结果不仅证实外源基因的存在，而且初步实现了外源染色体片段的定位。RAPD分析结果，筛选出22个在多枝赖草与普通小麦间有多态性的引物，可以用来对多枝赖草的杂交后代进行分析。所鉴定的三个后代材料中，均扩增出了多枝赖草的同源特性征带，其中“82”2条、“87”2条、“116”6条。进一步说明这些材料中含有多枝赖草的染色体片段。从分子水平上分析证实已将多枝赖草的染色体片段或基因导入普通小麦，获得了纯合易位系。结合综合农艺性状调查、小区产量比较试验以及田间筛选试验等方面的工作，从中筛选鉴定出了一批既有外源基因（如抗黄矮病、抗旱、耐盐等）导人，且农艺性状好的小麦易位系新种质。同时，结合以往的研究工作，建立起一套小麦属间杂种通过花药培养快速获得纯合易位系的技术体系和相应的操作程序。