EFFECTS OF FIRE IN TALLGRASS PRAIRIE ON GROWTH AND REPRODUCTION OF PRAIRIE CONEFLOWER (RATIBIDA COLUMNIFERA: ASTERACEAE)

Effects of fire on growth and reproduction of the perennial forb Ratibida columnifera were studied on the Konza Prairie Research Natural Area in northeastern Kansas, USA. Populations were sampled in seven different tallgrass prairie watersheds that varied in fire frequency and in the number of years elapsed since the last fire. Plants from sites not burned for many years were 2.6 times larger and produced 50% more stems than plants from recently burned sites. Number of seeds per plant was also higher in long-unburned sites due to greater numbers of flower heads per plant and greater numbers of achenes produced per head. Reproductive effort (ratio of inflorescence biomass to total vegetative biomass) was 33% lower in annually burned prairie than in any of the other sites. Significant differences in the relationships of inflorescence biomass to vegetative plant biomass in burned vs. unburned sites indicated that burning causes direct changes in plant reproductive effort independent from its effects on plant size. There was no clear relationship between patterns of seed production among sites and patterns of R. columnifera abundance. Ratibida columnifera responses to fire are most likely a result of changes in the relative competitive abilities of forbs and the dominant perennial grasses due to post-fire changes in abiotic conditions rather than a result of direct effects of fire on the fate of buds and subsequent vegetative and floral development.     

DEVELOPMENT OF A BIMODAL HEART RATE PATTERN IN UNDISTURBED FETAL HARBOR SEALS

Fetal and maternal heart rates were studied in unrestrained, pregnant harbor seals during the last third of gestation. Heart rates were recorded while the mothers were resting on land or performing trained simulated dives of up to 2.25 min. Data from resting mothers showed the development of a bimodal or two-speed fetal heart rate pattern during late gestation. The mean faster and slower fetal heart rates at term were 125 ± 3.7 and 79 ± 3.1 (mean + SEM) respectively. The amount of fetal bradycardia observed increased steadily towards term, and fetal heart rate changes were not correlated with changes in maternal heart rate or maternal respiration. The bimodal fetal heart rate was also seen during the simulated dives, and no decrease in either the faster or slower heart rate was found. Heart rates from resting, unrestrained harbor seal pups were also studied. The pups displayed a bimodal heart rate similar to the fetuses' with the slower rate occurring during breath-holds. The bradycardia in the pups was equivalent to the slower fetal heart rate. These findings suggest that the regulatory mechanism that determines the apneic bradycardia in young harbor seals during non-stressful conditions develops in the last quarter of gestation.     

密闭式鸡舍内环境参数对罗曼蛋鸡生产性能的作用研究

本文应用多元分析对密闭式鸡舍内的热因素与罗曼蛋鸡产蛋性能间的关系进行了研究,结果表明,热因素与产蛋性能间的关系非常密切,其中舒适度指数（THI）在产蛋高峰期和产蛋后期对产蛋性能的影响较为明显,在高温高湿环境下,舍内的干球温度（Tdb）和湿球温度（TWb）两个参数对产蛋性能影响较大．当舒适度指数超过60～72范围时,产蛋性能明显下降．     

PREDICTION OF NET PRIMARY PRODUCTIVITY OF FORESTS IN CHINA IN RESPONSE TO CLIMATE CHANGE

根据中国不同地理区森林生产力和气候环境变量的数据构建了中国森林气候生产力模型,以此为基础研究了气候变化对中国森林生产力的影响。结果表明在所构建的模型中,除海拔高度与净生产力的相关模型外,其它模型均有较高的实用价值,模型的拟合曲线变化,基本反映了中国森林现实生产力的地理分布格局;中国森林生产力的分布格局主要取决于气候环境中的水热条件,水分条件是决定中国大部分地区森林生产力水平和地理分布格局的主导因素;根据7个GCM