Factors influencing decline in soil pH in Hawaiian Eucalyptus and Albizia plantations

Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest.     

市场经济条件下如何加强林业的基础地位

市场经济条件下如何加强林业的基础地位是关系到国民经济可持续发展的关键所在。当前我国林业基础环境、林业政策环境和投资环境存在一些问题 ,林业走向市场也存在困难 (分类经营问题、林业产业的弱质性问题等 )。通过系统实施林业分类经营、制定林业保护政策、建立和完善森林生态效益补偿制度、实施森林资源强制保险、加强宏观调控建立活立木市场等 6项对策来加强林业基础地位。     

Studies on mutlispecific resistance of gastrointestinal nematodes to benzimidazoles on dairy-goat farms

Multispecific resistance to benzimidazoles was studied in three selected farms. These farms had bred dairy goats for more than 15 years. The helminths were introduced with the goats at the establishment of the farms which afterwards remained isolated. Nematode resistance could then be related to their own management practices. Faecal egg count tests and egg hatch assays were performed to assess intensity of resistance. The generic (infective larvae in faecal cultures) and specific richness (adult worms) were assessed. The resistant species were Trichostrongylus colubriformis, Teladorsagia circumcincta, Haemonchus contortus and Oesophagostomum venulosum. Faecal egg count reduction tests and egg-hatch assays did not match exactly. Faecal larval counts after treatments gave a distorted picture of multispecific resistance: Haemonchus and Oesophagostomum were very largely over represented. The number of species found in the three farms was relatively low compared with other reports in goat farms of the area. This reduction of diversity might also be due in part to characteristics of breeding management and history (use of permanent pasture and introduction of goats at the establishment of farm).     

狗舌草提取物诱导淋巴细胞性白血病L1210细胞分化的研究

以单猪屎豆碱（MO）、槲皮素（QU）和环磷酰胺（CY）为参照，观察了狗舌草600mL／L乙醇提取物（EX）对淋巴细胞性白血病L1210细胞体外试验的形态变化；利用流式细胞术，从DNA分子水平上检查了EX对L1210细胞各周期相的影响，探讨EX对L1210细胞的分化机理。结果发现，EX能够使L1210细胞向淋巴细胞方向发展；经EX作用24h后，L1210细胞G0＋G1期的百分比较对照组明显升高。提示EX对L1210细胞增殖的抑制作用可能是由于G1期的阻滞所致。     

Quantitation of adenine nucleotides in equine colonic mucosal tissue using high performance liquid chromatography.

The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period.     

离心式压缩机喘振问题分析

当压缩机内气体的流量较低时,气体容易出现旋转脱离现象,导致压缩机不能正常工作,采取增加压缩机内部液体的流量,在出口处设置单向阀防止气体倒流等措施,可有效地防止喘振的发生,保证输气管道的正常运行.     

我国农村经济组织体系分析

通过分析我国现阶段农村经济组织的组织模式、功能及组织连接机制,指出我国农村经济组织已形成以农户家庭经营为基础层次,以社区合作经济组织、专业合作经济组织及以“公司 农户”为典型的契约型组织分别为第二、三、四层次,效能逐级递增,各层次之间具有互动作用的组织体系。     

沙棘嫩枝扦插的水分管理

介绍了沙棘嫩枝扦插苗木生根过程中的水分管理，可供生产实践参考。     

压力实时监测法在管道泄漏检测中的应用

检测输油管道漏油的方法很多，介绍了通过压力实时监测确定输油管道漏油点方法，以及实际应用情况。实践证明，通过压力实时监视确定输油管道漏油点的方法在实际输油运行中是切实可行的。