气候变化对中国森林生产力的影响 Ⅰ.中国森林现实生产力的特征及地理分布格局

本文从生产力与环境关系角度,比较分析了森林第一性生产力的地理分布特征,阐述了层的生产力与环境间的关系以及种生产力与群落结构间的关系。结果表明:森林净生产力,地上部年凋落量随纬度和海拔高度的增加而减少,而凋落物现存量呈相反的变化趋势,森林生产力的地理分布与环境水热条件密切相关;森林生物量无明显的地理规律性变化,但多物种复杂结构的成熟天然林生物量较高;层的生产力随环境条件产生相互排斥或补充各异变化;种的生产力反映了种在群落中的地位和作用,决定群落的结构特征。     

Genotypic Difference in the Responses of Seedling Growth and Cd Toxicity in Rice （Oryza sativa L.）

The experiment was carried out to study the genotypic difference in the responses of seed germination, growth and physiological characters of rice seedlings to Cd toxicity. The result showed that the germination was slightly stimulated under low Cd concentration （0.01-1.5 mM Cd）, while severely depressed under higher Cd concentration （2.0 mM）. Rice seedlings exposed to 0.01 mM Cd showed slight increases in plant height, root volume, biomass and chlorophyll concentration. These parameters were significantly reduced when Cd level in the medium was increased to 0.5 mM, and meanwhile corresponding increase in superoxide dismutase （SOD） and peroxidase （POD） activities, and MDA （malondialdehyde） content was observed. However, SOD and POD activities declined when plants were exposed to 1 mM Cd when compared with those under 0.5 mM Cd. Cadmium addition lowered Fe, Cu and Mn concentrations in roots and shoots. There was significant genotypic difference in the response of these parameters to Cd stress. Under Cd stress, Xiushui 110 had the least inhibition of growth and increase in MDA content, higher shoot Cd concentration, and greatest increase in POD and SOD activities, indicating its higher tolerance to Cd toxicity, while Bing 9914 had the greatest reduction of growth, and Zn, Cu, Fe, and Mn contents, but greatest increase in MDA content, and least increase in activities of antioxidative enzymes, indicating its sensitivity to Cd toxicity.     

Abortions and twin pregnancies in thoroughbreds: Rate of occurrence, treatments and prevention

Twin pregnancies recorded in German Thoroughbred mares were responsible for premature termination of 2.5% of 27 465 pregnancies between 1967 and 1992, and constituted 38.5% of all 1788 abortions (6.5% of all pregnancies) recorded over the same time. Over time, the rate of twin pregnancies dropped from 2.7% before 1984 to 1.7% thereafter (P<0.001). During the last 20 years several methods of treatment of early detected twin pregnancies were evaluated. Crushing of one embryo in 69 cases gave best results when conducted between Days 21 to 26 of pregnancy, resulting in 80% single gestations continuing. Curtailing food intake during early twin pregnancies to enforce regression of the weaker conceptus is difficult to manage. However, reducing feed intake for one cycle prior to breeding in three mares with histories of frequent twin pregnancies resulted in five single pregnancies in five attempts.     

BSAVA Congress Overseas speakers

NEXT year's BSAVA Congress has succeeded in luring some of the world's top speakers to these shores. To whet your appetite, three overseas speakers are featured this month, with the remaining speakers appearing in future issues of Bsava News.