中国东北样带三种针茅草原群落初级生产力对降水季节分配的响应

分析3种针茅草原群落初级生产力的年季动态,并利用积分回归模型探讨其对降水量季节性分配的响应,揭示水分有效性对植物初级生产力的影响.结果表明,制约3类针茅群落初级生产力年度变化的是水分,即前一年11月到当年8月的月降水量的年度变异是直接导致群落初级生产力年度变化的主要原因.降水的季节分配对于3类针茅群落初级生产力的形成有着不同的作用.前一年11月至当年4月降水对于植物群落的初级生产力具有正效应,从5月开始降水对植物初级生产力的促进作用有了不同程度的降低.大针茅和克氏针茅群落的季节降水量格局较为相近,但是大针茅群落与克氏针茅群落相比对降水的利用效率较高;贝加尔针茅群落则表现出更高效的降水利用率.由此可见,降水量月季分配及其对针茅群落影响程度的不同是造成3种针茅草原地带性分布的原因.     

武夷山甜槠生态系统的养分平衡研究（英文）

本文通过比较大气降水的养分输入与由地表径流和地下渗流的养分输出,对武夷山甜槠林生态系统的养分平衡进行了研究。结果表明：在1993年4月至1994年4月期间,通过大气降水进入甜槠林的养分元素以N最高,为34.207kg·hm-2,其余依次为Ca(22.99kg·hm-2)、S(12.722kg·hm-2)、Na(6.679kg·hm-2)、K(3.558kg·hm-2)和Mg(2.057kg·hm-2),以P的输入最低,仅1.779kg·hm-2;由地表径流和地下渗流的养分输出总量N、P、K、Ca、Mg、S、Na分别为5.68、1.016、7.345、3.430、0.620、0.534、0.576kg·hm-2,以K的输出量最高,S的输出最少。其中,通过地下渗流的养分损失占输出总量的85.97％～96.38％,而地表径流的养分输出仅占总输出的3.62％～14.03％;在该系统中,N、Ca和S有大量的积累(分别为28.527、19.560和12.188kg·hm-2),Mg和Na有少量积累(分别为 1.437和6.103kg·hm-2),P基本上处于平衡状态(0.763kg·hm-2),而K则为净的输出损失(-3.787kg·hm-2)。岩石风化对于该生态系统K的补偿可能起重要作用,而其他养分元素仅通过降水输入即可得到补充。     

Morphological and physiological variation in western redcedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) populations under contrasting soil water conditions

Adaptation to precipitation conditions may induce genetic diversity that changes morphological and physiological traits. This hypothesis was investigated in the seedlings of seven western redcedar (Thuja plicata Donn ex D. Don) populations, which were collected along a precipitation transect from the Pacific coast to the southern interior of British Columbia, Canada. The experimental seedlings were either well-watered or soil-droughted and measured for growth, gas exchange rates, transpiration efficiency, and carbon isotope discrimination during or at the end of the third growing season. Significant variation was found in most of these morphological and physiological traits among the populations. Much of this variation occurred under well-watered, but not so much under droughted conditions. Mean height increments and transpiration efficiency showed a significant linear relationship, but biomass increments exhibited a quadratic relationship with precipitation on the origin site of these populations. Measurements of water use efficiency obtained from instantaneous gas exchange measurements, carbon isotope discrimination, and transpiration efficiency were intercorrelated in the seedlings. However, neither did any of these measurements consistently rank the populations, nor were they indicative of adaptation to climatic precipitation conditions in these western redcedar populations.     

Fine structure of in situ microbial iron deposits

The fine structure of iron deposits produced by Leptothrix spp. from two caverns and a surface spring were observed. In the case of Leptothrix pseudovacuolata, the iron occurred as an amorphous deposit within the cell sheath and the cells contained gas vesicles. In the case of the other Leptothrix spp., the iron was deposited within the cell sheath either as a hexagonal or fibrillar matrix. In the case of fibrillar iron deposits, fibrils resembling those of the sheath were found within the cytoplasm of the cells. This suggests that the deposition of iron could have occurred within the cells as well as at the cell surface. In some cases, the fine structure of microbial iron deposits could provide a means of distinguishing biological from abiological iron deposition.     

Production as a function of resource availability: Slopes and efficiencies are different

Abstract. A number of investigators have interpreted the slope of a linear production‐resource relationship as a measure of efficiency of resource utilization. However, this is rarely true and may lead to incorrect conclusions. Here, by means of simple mathematical equations and conceptual definitions, we point out the theoretical differences between slope and efficiency. While a slope represents the change in the dependent variable per unit change in the independent variable, efficiency expresses the amount of output produced by a unit amount of input. Practical implications of using slopes as indicators of resource‐use efficiency are less important as the resource amount increases. Slopes may be used as indicators of the sensitivity of production to changes in input, which is by itself an interesting property of biological systems. Finally, production function intercepts determine whether the efficiency will decrease, increase, or remain constant as resources increase.     

黄土高原春小麦地上鲜生物量高光谱遥感估算模型

通过田间小区试验,测定了4个春小麦品种(定西24号、陇春8139、高原602和定西38号)在不同生育期和不同种植密度下冠层光谱反射率及其对应的地上鲜生物量,分析了春小麦地上鲜生物量随生育期的变化以及地上鲜生物量与冠层反射光谱和一阶微分光谱之间的相关关系,采用相关系数较大的特征波段及其组合构建光谱特征参数以其作为变量,建立了春小麦地上生物量的高光谱估算模型,并对模型进行检验。结果表明：以参数F₇₈₀和D₇₁₉为变量的对数形式y=3.9498ln F₇₈₀+7.0596和乘幂形式y=512.99D₇₁₉^1.0174估算水平最高,前者均方根误差(RMSE)为0.2173,相对误差(RE)为10.45%,预测值与实测值相关系数为0.854;后者RMSE为0.2188,RE为9.96%,预测值与实测值相关系数为0.853。因此,上述两个模型可作为陇中黄土高原地区春小麦地上鲜生物量的最佳估算模型。     

Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub

Shrub encroachment is a widely observed problem in Southern African savannas. Although the effects of herbivory and grass height on woody species recruitment have been studied individually, little information exists about how these factors interact. In this study seeds and seedlings of the encroaching shrub Dichrostachys cinerea were planted in clipped and unclipped grass plots, with and without large herbivores present. Seed germination, seedling survival and seedling predation were monitored for 8 months. Germination started earlier in plots where herbivores were excluded. Overall, the earlier the seeds germinated, the longer the seedlings survived. Clipping positively affected the number of germinated seeds, seedling growth and survival but effects varied among herbivore exclusion treatments and sites. Invertebrates caused the majority of the seedling damage. We conclude the recruitment of D. cinerea is influenced by the interplay of grass height and herbivory. In this study, the presence of large herbivores early in the wet season, and the absence of simulated grazing later on, affected the regeneration of D. cinerea negatively. However, differences in effects among sites suggest that the mechanisms found here may work differently in other habitats.      

全球变暖对太行山植被生产力及土壤水分的影响

将相同的自然植被用Lysimeter从高海拔下移至低海拔,温度升高2℃,同时设置平均降水,增加10％降水,增加20％降水,减少10％降水和减少20％降水5个降水处理,模拟全球变暖带来的温度升高和降水变化对植被生产力和土壤水分的影响,两年的野外实验表明,温度升高造成生态适应性差的野古草（Arundinelia hirta)生产力显著下降,致使整个测试群落生产力降低,低海拔实验点生产力显著低于高海拔实验点,温度升高对铁杆（Artemisia sacrorum)和黄背草（Themeda japonica)的影响较小,太行山区的植被对降水的变化反映,降水增加使植被的生产力水平显著提高,其中降水增加20％的处理生产力比平均降水处理的生产力增加22％,增加降水处理的土壤含水量显著高于平均降水和降水减少的实验处理,由于植被的减少,温度升高的实验点从第二年开始土壤水分较高。     

Floristic composition across a climatic gradient in a neotropical lowland forest

Abstract. This study deals with the floristic composition of lowland tropical forest in the watershed of the Panama Canal. The floristic composition of large trees in 54 forest plots was analysed with respect to environmental factors, including precipitation, geologic parent material, stand age, topography, and soils. The plots contain 824 species of trees with a diameter at breast height ≥10 cm and represent a regional flora with exceptional β‐diversity. Plot data indicate that the Panamanian forest is strongly spatially structured at the landscape scale with floristic similarity decreasing rapidly as a function of inter‐plot geographic distance, especially for distances <5 km. The ordinations and patterns of endemism across the study area indicate broad floristic associations well correlated with Holdridge life zones. The results indicate the positive aspects of life zone classification at regional scales, while simultaneously highlighting its inadequacy for finer scales of analysis and resource management. Multivariate gradient analysis techniques (Non‐metric Multidimensional Distance Scaling and Detrended Correspondence Analysis) show clear patterns of floristic variability correlated with regional precipitation trends, surficial geology, and local soil attributes. Geologic and edaphic conditions, such as acidic soils or excessively drained limestone substrates, appear to override the effects of precipitation and modify forest composition. We conclude that the Panamanian forest shows clear patterns of spatial organization along environmental gradients, predominantly precipitation. The rapid decline in floristic similarity with distance between stands also suggests a role for dispersal limitation and stochastic events.