Crustacean plankton in Høylandet

Crustacean plankton was studied in 12 lakes in theHøylandet area in 1986–87. Basic lake characteristicsare elevation 134–415 m, surface area 9–530 ha, pH 5.9–7.1,conductivity (25 °C) 12–40 µS cm^-1 andSecchi depth 4–9 m. Number ofspecies present varied between 3 and 11. Populationnumbers between 4000 and 400 000 per m² andbiomasses were within the range 30 to1800 mg m^-2 dry weight. Cladocera dominated overCopepoda in lakes with allopatric brown trout (Salmo trutta L.), on the contrary to lakes also populatedby Arctic charr (Salvelinus alpinus (L.)). Thesevariations are caused by differences in elevation,lake morphometry, water quality, fish predation andthe general distribution of the species. The largestlakes at lowest elevation were richest in species. Theacid sensitive genus Daphnia was represented by 3species. The lakes Storgrønningen (530 ha) andRøyrtjønna (27 ha) were sampled monthly in theice-free seasons of 1986–89, and Storgrønningen moreintensively from June to November in 1987 and 1988. The same6 species of Cladocera and 5 of Copepoda were presentin both lakes. Their life cycles were traditional orknown from several other Scandinavian lakes. Meanseasonal biomasses were of the range600–750 mg m^-2. At the species level, there wereconsiderable variations between years inStorgrønningen and particularly in Røyrtjønna. Noeffects of human impacts on the crustacean planktonwere found. The Høylandet lakes are representative forScandinavian oligotrophic to almost ultra-oligotrophiclakes. Storgrønningen is well qualified as a referencesystem. The between year variations in Røyrtjønna areso extreme, that any human impact could only be traced at alevel causing the extinction of species.     

Inhibition of parathormone-stimulated bone resorption by type I interferon

The effect of Type I interferon on bone resorption was studied by measuring its effect on parathormone-stimulated calcium release from neonatal murine calvaria in vitro. A pure human recombinant leukocyte interferon hybrid of the A and D subtypes was used, which has high antiviral activity on mouse cells. Calcium release was inhibited in a dose dependent fashion with 50% inhibition at about 10(-10) M or 600 U/ml, and the inhibition was reversible. The presence of interferon was required before or during the activation phase of the resorptive response, when the formation of osteoclasts from precursor cells would occur. When added to actively resorbing bone it had no effect. The data suggest that Type I interferon can inhibit the parathormone-regulated development of active osteoclasts, possibly by inhibiting osteoclast precursor differentiation.     

Predicting the distribution of plant communities using annual rainfall and elevation: an example from southern Africa

Abstract. Using the results of a total floristic survey of two veld types (Arid Sweet Bushveld and Mixed Bushveld) in the northeastern Transvaal, South Africa, we linked median annual rainfall from a surface response model to each of 139 samples. The samples had been classified floristically into 15 plant communities. These communities represent two broad divisions, corresponding with the concepts embodied in the two veld types. Using contingency tables, we defined the conditions of median annual rainfall and elevation for each of the veld types. Using a geographic analysis system we predicted the distribution of the veld types in an area of 120 000 km² outside the study area. The predicted distribution was validated by comparison with a digitized version of the Acocks map. We conclude that the defined conditions of median annual rainfall and elevation provide confident criteria for the definition of these veld types.     

Estimating thermal properties of simulated aquatic soils from their composition

Heat penetration and thermal lag in the submersed soil surrounding the roots of aquatic plants depends on two fundamental thermal properties of the substrate, volumetric heat capacity (C_V) and thermal conductivity (k). The relationship of these parameters to the fractions of organic and mineral matter, gas and water in natural and simulated aquatic soils was investigated. The gas fraction was found to be insignificant and it was possible to make good estimates of C_V and k from a knowledge of substrate water content alone.     

环境因素对油松林木材生产影响的定量评价

本文使用多元统计分析方法, 定量评价了环境因素对陕西省油松人工林木材生产的影响程度。在地理-地形-土壤环境因素组中, 土壤类型对油松林的生长影响最大, 占38.75%。在气候因素组中, 7月平均气温对陕南及秦岭一带油松林的生长影响最大, 占34.46%。在陕北地区, 对油松林生长影响最大的因素是年降雨量, 占27.8%。不同气候因素作用于不同地区森林的程度有较大差异。根据综合环境因素对油松林木材生产的影响及林分生长表现, 在陕西省划分了3个油松生长区:(1)陕南及秦岭油松生长区;(2)关中及陕北南部生长区;(3)陕北北部生长区。并对各区的特点进行了总结。     

Refining the cheatgrass–fire cycle in the Great Basin: Precipitation timing and fine fuel composition predict wildfire trends

Larger, more frequent wildfires in arid and semi‐arid ecosystems have been associated with invasion by non‐native annual grasses, yet a complete understanding of fine fuel development and subsequent wildfire trends is lacking. We investigated the complex relationships among weather, fine fuels, and fire in the Great Basin, USA. We first modeled the annual and time‐lagged effects of precipitation and temperature on herbaceous vegetation cover and litter accumulation over a 26‐year period in the northern Great Basin. We then modeled how these fine fuels and weather patterns influence subsequent wildfires. We found that cheatgrass cover increased in years with higher precipitation and especially when one of the previous 3 years also was particularly wet. Cover of non‐native forbs and native herbs also increased in wet years, but only after several dry years. The area burned by wildfire in a given year was mostly associated with native herb and non‐native forb cover, whereas cheatgrass mainly influenced area burned in the form of litter derived from previous years’ growth. Consequently, multiyear weather patterns, including precipitation in the previous 1–3 years, was a strong predictor of wildfire in a given year because of the time needed to develop these fine fuel loads. The strong relationship between precipitation and wildfire allowed us to expand our inference to 10,162 wildfires across the entire Great Basin over a 35‐year period from 1980 to 2014. Our results suggest that the region's precipitation pattern of consecutive wet years followed by consecutive dry years results in a cycle of fuel accumulation followed by weather conditions that increase the probability of wildfire events in the year when the cycle transitions from wet to dry. These patterns varied regionally but were strong enough to allow us to model annual wildfire risk across the Great Basin based on precipitation alone.     

模拟氮沉降和干旱对准噶尔盆地两种一年生荒漠植物生长和光合生理的影响

氮素和水分是荒漠生态系统的两个主要限制因子, 研究两者对荒漠植物的效应有助于深入了解荒漠生态系统对全球变化的响应。该文选择准噶尔盆地荒漠地区两种常见的一年生植物涩荠(Malcolmia africana)和钩刺雾冰藜(Bassia hyssopifolia), 设置0、0.18和0.72 g N·m ^-2·week ^-13个施氮浓度和湿润与干旱两个土壤水分处理, 研究模拟氮沉降增加和干旱对其生长和光合生理的影响。结果表明: (1)两种植物的根长、根重、叶片数、叶面积、总生物量和冠根比均随着施氮浓度的增加而增加, 干旱能够抑制氮对植物生长的促进作用, 但是, 氮的增加同时也能部分缓解干旱对植物生长的影响。与钩刺雾冰藜相比, 涩荠的根长、生物量和冠根比更易受氮增加和干旱的影响。(2)两种植物的最大净光合速率、叶绿素含量、可溶性蛋白含量随着氮浓度增加而增加, 但涩荠和钩刺雾冰藜对氮增加和干旱的生理响应也有所不同, 涩荠的响应更加敏感。两种植物对氮沉降和干旱胁迫响应的差异可能是其生活型等生物学特性差异所引起。通过对两种一年生植物的生长和光合生理分析表明, 在古尔班通古特沙漠, 春季丰富的降水和氮素增加将有利于涩荠和钩刺雾冰藜的生长和生产力的增加, 相对地下生长, 地上部分增加更显著。当干旱季节来临时, 氮的增加又能够在一定程度上降低干旱对这两种植物的负效应, 说明其对干旱具有一定的生态补偿作用。     

Biomass carbon density and carbon sequestration capacity in seven typical forest types of the Xiaoxing’an Mountains,China

森林生物碳储量作为森林生态系统碳库的重要组成部分,在全球碳循环中发挥着重要作用。以小兴安岭7种典型林型为研究对象,通过外业样地调查与室内实验分析相结合的方法,从林分尺度对林分生物量与碳密度进行计量,分析了林分生物碳储量的空间分配格局,并对林分年固碳能力与碳汇潜力进行了探讨。结果表明:小兴安岭不同林型从幼龄林到成熟林的乔木层碳密度增长速率为:蒙古栎(Quercus mongolica)林>兴安落叶松(Larix gmelinii)林>云冷杉(Picea-Abies)林>樟子松(Pinus sylvestris var.mongolica)林>山杨(Populus davidiana)林>红松(Pinus koraiensis)林>白桦(Betula platyphylla)林。7种典型林型不同龄组(幼龄林、中龄林、近熟林和成熟林)林分生物量碳密度分别为:红松林31.4、74.7、118.4和130.2 t·hm–2;兴安落叶松林28.9、44.3、74.2和113.3 t·hm–2;樟子松林22.8、52.0、71.1和92.6 t·hm–2;云冷杉林23.1、44.1、77.6和130.3 t·hm–2;白桦林18.8、35.3、66.6和88.5 t·hm–2;蒙古栎林25.0、20.0、47.5和68.9 t·hm–2;山杨林19.8、28.7、43.7和76.6 t·hm–2。红松林、兴安落叶松林、樟子松林和蒙古栎林在幼龄林时林分年固碳量较高,其他林型在成熟林时林分年固碳量较高。7种典型林型不同龄组的林分生物量碳密度均随林龄增长而增加,但不同林型的碳汇功能存在差异,同一林型不同林龄的生物量碳密度增幅差异也较大。林分年固碳量在0.4–2.8 t·hm–2之间,碳汇能力较强、碳汇潜力较大。尤其是小兴安岭目前林分质量较差,幼龄林和中龄林所占的比重较大,具有较大的碳汇潜力。研究结果可为森林经营管理及碳汇功能评价提供参考。     

科尔沁沙地3种草本植物根系生长动态

利用微管对狗尾草(Setaria viridis)、黄蒿(Artemisia scoparia)和沙米(Agriophyllum squarrosum)根系生长动态进行了观测。结果表明:1)在观察期内,狗尾草和黄蒿的根系生长表现出先增后减的“抛物线”型,而沙米的根系成指数生长。在7月末至8月初狗尾草、黄蒿和沙米根系具有最高的生产量,其根量密度分别为4 690.91、2 975.76和2 354.55条·m^-2;在8月末,狗尾草和黄蒿根系都表现出不同程度的衰减,沙米根数保持增加。2)狗尾草优先生长表层根系,根系主要生长在0~30 cm的土层内,根长密度最大时为2.23 cm·cm^-2;黄蒿生长前期表层根长密度大,生长后期下层根长密度开始增加;沙米优先发展下层根系,快速生长期后,地下30~50 cm处的根长密度增加高于上层。3)生长前期和快速生长期,0~50 cm狗尾草根长密度最大,黄蒿次之,沙米最小,生长末期,沙米根长密度大于狗尾草。     

西江下游浮游植物群落周年变化模式

西江肇庆段是珠江干流汇入珠三角河网水域的咽喉通道,对2009年该江段的浮游植物群落组成及变化进行系统阐析.调查期间共发现浮游植物7门,245种(包括变种、变型),其中硅藻和绿藻是浮游植物群落组成的最主要类群,分别占总种数的42.44％和34.69％,其次是裸藻和蓝藻.PCA分析结果显示,浮游植物各类群的种类丰富度和生物量的周年变化趋势主要受水温和径流量的影响.浮游植物种类丰富度的周年变化呈现明显的高温季节高,低温季节低的特征,除因大多数藻类物种直接喜好高温之外,径流量的增大有助于真浮游绿藻种类的外源注入及半浮游和偶然性浮游硅藻种类的增加.浮游植物生物量的周年变化呈现明显的双峰型,峰值分别出现在8月和11月.然而8月份第1个高峰出现之前,生物量波动不大,尽管水温的升高有助于生物量的增加,但是径流量增大所带来的稀释作用掩盖了水温上升对浮游植物生长的促进作用.真浮游植物生物量的变化趋势和数值与总浮游植物极其接近,主要得益于真浮游硅藻物种颗粒直链藻在总种群中的绝对优势地位.综上,水温升高对浮游植物种类丰富度和生物量的增长均有促进,径流量的增大虽然有助于种类丰富度的增加,但不利于生物量的增加.