Soil-surface carbon dioxide efflux and microbial biomass in relation to tree density 13 years after a stand replacing fire in a lodgepole pine ecosystem

The effects of fire on soil‐surface carbon dioxide (CO₂) efflux, F_S, and microbial biomass carbon, C_mic, were studied in a wildland setting by examining 13‐year‐old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha^?1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (～110‐year‐old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season F_S increased with tree density in young stands (1.0 µmol CO₂ m^?2 s^?1 in low‐density stands, 1.8 µmol CO₂ m^?2 s^?1 in moderate‐density stands and 2.1 µmol CO₂ m^?2 s^?1 in high‐density stands) and with stand age (2.7 µmol CO₂ m^?2 s^?1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g^?1 dry soil over the growing season; C_mic was significantly greater in mature stands (0.5–0.8 mg C g^?1 dry soil). Soil‐surface CO₂ efflux in young stands was correlated with biotic variables (above‐ground, below‐ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below‐ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but C_mic pools and overall F_S rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of F_S and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.     

人红细胞膜上阴离子交换蛋白和葡萄糖运输蛋白的相互影响

用细胞松弛素Ｂ抑制红细胞膜上葡萄糖运输蛋白（ＧｌｕＴ－１）对葡萄糖的运输,观察到对阴离子运输有促进作用。当ＧｌｕＴ－１结合其底物分子－葡萄糖后同样加快了阴离子运输速率．另一方面,实验办给出了葡萄糖跨膜运输特性和Ｃｌ－离子浓度的关系,表明随着Ｃｌ－离子浓度的加大能使葡萄糖运输过程中Ｋｍ减小、Ｖ（ｍａｘ）增大。这些结果表明了在完整红细胞膜上阴离子交换蛋白Ｂａｎｄ３和ＧｌｕＴ－１之间存在着双向联系,即一种膜蛋白的构象改变能影响另一种膜蛋白的功能。     

红原鸡与家鸡的亲缘关系研究

对中国红原鸡滇地亚种和海南亚种与我国茶花鸡,泰和鸡和寿光鸡等地方鸡种以及芦花鸡,洛岛红等外国鸡种进行了血型（３个位点,１３个等位基因）,蛋白质（酶）多态（５个位点,１１个等位基因）和ＤＮＡ指纹分析,结果表明,红原鸡与茶花鸡（原始型品种）的亲缘关系较近;与泰和鸡,寿光鸡,芦花鸡,洛岛红（进化型品种）的亲缘关系较远,呈红原鸡－茶花鸡－泰和鸡,寿光鸡或芦花鸡,洛岛红这样一个进化阶梯,以上结果与国外资料（     

Managing the pattern of forest harvest: lessons from wildfire

Managing forests for sustainable use requires that both the biological diversity of the forests and a viable forest industry be maintained. A current approach towards maintaining biological diversity is to pattern forest management practices after those of natural disturbance events. This paradigm hypothesizes that ecological processes will be maintained best where active management approximates natural disturbance events. The forest management model now used in most sub-boreal and boreal forests calls for regularly dispersed clearcuts no greater than 60–100 ha in size. However, the spatial characteristics of the landscape produced by this model are distinctly different from the historic pattern generated by wildfire, which was heretofore the dominant stand-replacing process in these forests. Wildfire creates a more complex landscape spatial pattern with greater range in patch size and more irregular disturbance boundaries. Individual wildfires are often over 500 ha but leave patches of unburned forest within them. The combination of these attributes is not present in recent clearcuts. Allowing a proportion of larger (i.e.>500ha) harvest units may provide distinct economic advantages that could outweight the opportunity costs of leaving some patches of forest behind. For the forest type examined, further evaluation of modelling forest harvest patterns more closely after the patterns created by wildfire is required as it may achieve a good balance and strike a suitable compromise between certain ecological and economic objectives of sustainable development.     

红细胞的前向光散射

本文从红细胞前向光散射的观点出发对红细胞的尺寸、红细胞的变形性研究以及红细胞容积、血红蛋白浓度等参数的测定作了系统的思考。提出在红细胞与周围悬浮介质折射车相差不大时,反常衍射比夫朗和费衍射更适合用于红细胞前向光散射的研究。利用两组不同角间隔的前向散射光来同时测量红细胞容积和血红蛋白浓度。同时其它一些标识红细胞的参数如平均红细胞容量（ＭＣＶ）、平均血红蛋白量（ＭＣＨ）等均可直接或间接由这两项参数导出。最后还将红细胞的光散射与Ｍｉｅ理论作了对比．     

The effects of grazing and burning on soil and plant nutrient concentrations in Colombian páramo grasslands

The impact of extensive livestock farming on the physical and chemical characteristics of the volcanic soils and on the nutrient status of green plant tissues of neotropical alpine grasslands (páramo) is studied. Soil and plant samples were taken over a one-year period at five sites with different agricultural (grazing and burning) management. In the undisturbed páramo ecosystem, soil moisture (50–250%) and organic matter content are high (7–27%) and decomposition (11–35% yr^-1) and element concentrations are low. Low temperatures (max < 10°C) and phosphorus fixation by the soil (5 mg P g^-1 soil) determine the low mineralization and turn-over rates.Multivariate analysis of laboratory results indicates that the season of sampling and the agricultural practice are the most important explanatory factors for variation of soil characteristics. After long-term heavy grazing, soils have a higher bulk density and a lower moisture content. The outcome of a litterbag experiment confirms the hypothesis of higher decomposition rates at grazed sites. In the intermediate (wet-dry) season, conditions were somewhat better for plant growth but the system remained nutrient limited.Surprisingly, no relation between soil density, moisture or carbon content and concentrations of available nutrients in the soil is found. This is supported by the rather uniform nutrient concentrations in green plant tissue among the sites. It is concluded therefore that the effect of burning and grazing on páramo soils is principally restricted to physical characteristics, and that differences in chemical characteristics of the soil do not cause differences in vegetation structure between grazed, burned and undisturbed sites.The Netherlands Centre for Geo-ecological Research, ICG.     

Estimation of sperm numbers in insects by fluorometry

Summary To facilitate the study of mating biology in the desert leaf-cutter antAcromyrmex versicolor, methods were developed that allowed storage and easy quantification of sperm samples collected from both male and female reproductive tracts. Sperm samples stored frozen were sonicated, stained with a fluorescent DNA stain, and the fluorescence emitted by the stained sperm heads was measured. The intensity of fluorescence was shown to be a linear function of the number of sperm in the sample as determined by counting.     

Ca2+-activated K+ channels of human and rabbit erythrocytes display distinctive patterns of inhibition by venom peptide toxins

Despite recent progress in the molecular characterization of high-conductance Ca²⁺-activated K⁺ (maxi-K) channels, the molecular identities of intermediate conductance Ca²⁺-activated K⁺ channels, including that of mature erythrocytes, remains unknown. We have used various peptide toxins to characterize the intermediate conductance Ca²⁺-activated K⁺ channels (Gardos pathway) of human and rabbit red cells. With studies on K⁺ transport and on binding of ¹²⁵I-charybdotoxin (ChTX) and ¹²⁵I-kaliotoxin (KTX) binding in red cells, we provide evidence for the distinct nature of the red cell Gardos channel among described Ca²⁺-activated K⁺ channels based on (i) the characteristic inhibition and binding patterns produced by ChTX analogues, iberiotoxin (IbTX) and IbTX-like ChTX mutants, and KTX (1–37 and 1–38 variants); (ii) the presence of some properties heretofore attributed only to voltage-gated channels, including inhibition of K transport by margatoxin (MgTX) and by stichodactyla toxin (StK); (iii) and the ability of scyllatoxin (ScyTX) and apamin to displace bound ¹²⁵I-charybdotoxin, a novel property for K⁺ channels. These unusual pharmacological characteristics suggest a unique structure for the red cell Gardos channel.We thank Dr. Chris Miller of Brandeis University for generously providing recombinant ChTX mutants, Dr. Maria Garcia of Merck Research Laboratories for MgTX and Dr. Regine Romi of Laboratoire d'Ingenierie des Proteines (Marseille, France) for synthetic KTX,1–37 and KTX,1–38. This research was supported by grant HL-15157 from the National Institutes of Health.     

Characterization of the growth and lipid content of the diatom Chaetoceros muelleri

Chaetoceros muelleri (Schütt) was cultured on a thermal gradient plate, subjected to two media types with a range of specific conductances, and evaluated for growth and neutral lipid accumulation. Growth was measured directly by daily changes in cell numbers and indirectly by changes in optical density at 750 nm. C. muelleri exhibited a growth rate of at least two doublings day-1 over broad temperature (20 to 35 °C) and conductance ranges (10 to over 60 mS cm-1) and the optimum growth rate approached 4.0 doublings day-1 at 30 °C and a conductance of 25 mS cm-1. Intracellular neutral lipid storage was evaluated with fluorometry and epifluorescent microscopy using the fluorochrome Nile Red. Gravimetric analysis revealed a total lipid content in nitrogen-depleted cultures of C. muelleri of over 400 mg L-1, five to seven times that observed in nitrogen-replete cultures. Based on its high growth rate, tolerance to a broad range of temperatures and specific conductances, and large quantity of intracellular lipid, C. muelleri may have potential for exploitation as a renewable precursor to liquid fuels or as a lipid source. This revised version was published online in August 2006 with corrections to the Cover Date.     

Arthropod biodiversity loss and the transformation of a tropical agro-ecosystem

The coffee (Coffea arabica) agro-ecosystem in the Central Valley of Costa Rica was formerly characterized by a high vegetational diversity. This complex system has been undergoing a major transformation to capital-intensive monocultural plantations where all shade trees are eliminated. In this study we examined the pattern of arthropod biodiversity loss associated with this transformation. Canopy arthropods were sampled in three coffee farms: a traditional plantation with many species of shade trees, a moderately shaded plantation with only Erythrina poeppigeana and coffee, and a coffee monoculture. An insecticidal fogging technique was used to sample both canopy and coffee arthropods. Data are presented on three major taxonomic groups: Coleoptera, non-formicid Hymenoptera, and Formicidae. Data demonstrate that the transformation of the coffee agro-ecosystem results in a significant loss of biological diversity of both canopy arthropods as well as arthropods living in coffee bushes. Percentage of species overlap was very small for all comparisons. Furthermore, species' richness on a per tree basis was found to be within the same order of magnitude as that reported for trees in tropical forests. If results presented here are generalizable, this means that conservation efforts to preserve biological diversity should also include traditional agro-ecosystems as conservation units.