Revising the distributive networks models of West, Brown and Enquist (1997) and Banavar, Maritan and Rinaldo (1999): metabolic inequity of living tissues provides clues for the observed allometric scaling rules

Basic assumptions of two distributive network models designed to explain the 3/4 power scaling between metabolic rate and body mass are re-analysed. It is shown that these models could have consistently accounted for the observed scaling patterns if and only if body mass M had scaled as L4, where L is body length, in the model of Banavar et al. (1999, Nature 399, 130-132), or if spatial volume VF occupied by the distributive network had scaled as M3/4 in the model of West et al. (1997, Science 276, 122-126). Lack of agreement between these predictions and observational evidence invalidates both models rendering them mathematically controversial. It is further shown that consideration of distributive networks can nevertheless yield realistic values of scaling exponents under the major assumption that living organisms are designed so as to keep the mass-specific metabolic rate of important functional tissues in the vicinity of a size-independent optimum value. Mass-specific metabolic rate of subsidiary mechanical tissues can be small and vary with body mass. Different patterns of spatial distribution of metabolically active biomass within the organism result in different patterns of allometric scaling. From the available evidence the presumable optimum value of mass-specific metabolic rate of living matter is estimated to be in the vicinity of 1-10 W kg-1.     

中国楤木属药用植物花粉和叶片的形态学研究

本文对12种国产楤忽木属药用植物的花粉和叶片进行了描扫电镜和组织解剖学研究,结果表明楤木属植物花粉表面纹饰除已发现的网纹型外,尚具脑纹型和中间过渡类型,花粉特征和某些形态相近种有分类价值;种间叶表特征差异较大,叶下表面特征可分为两类:楤木型和长刺楤木型,综合运用这些特征对于该植物种的鉴定是有价值的。     

瑞香狼毒茎叶化学成分研究

新鲜瑞香狼毒（Ｓｔｅｌｅｒａｃｈａｍａｅｊａｓｍｅ）茎叶经正己烷提取,脱腊后进行ＧＣＭＳＤＳ联用分析,鉴定出２０个化合物。主要成分为正十八烷;正十九烷;２,６,１０,１４四甲基十六烷;十六烷酸;十六烷酸甲酯;十六烷酸乙酯;９,１２,１５十八碳三烯酸甲酯;９,１２十八碳二烯酸;９,１２,１５十八碳三烯酸和十八烷酸。     

采后菠菜叶片失水萎蔫对膜透性及膜脂过氧化作用的影响

本文分析了菠菜叶片失水萎蔫时叶绿素、相对含水量、膜透性及膜脂过氧化产物丙二醛的变化,结果表明:叶片萎蔫衰老时随着相对含水量的降低,叶绿素含量减少,膜透性和丙二醛含量增大;并且随萎蔫程度加深,膜透性与丙二醛含量也明显增加.这说明菠菜叶片失水萎蔫与膜结构完整性的破坏有密切的关系。     

高CO_2浓度对大豆不同叶位叶片叶绿体淀粉粒积累的效应

对高CO_2浓度下生长的大豆(Glycine max(L.)Merr.)不同叶位的叶片进行了电镜观察,揭示出大豆不同叶位叶片的叶绿体对倍增的CO_2浓度反应不一。其显著的超微结构差异特征是:1.叶位居中的叶片叶绿体积累的淀粉粒不仅很大,而且最多,有的叶绿体中的淀粉粒可达20个,几乎充满着叶绿体的基质空间。2.下位叶叶绿体的淀粉粒积累较多,通常为2～5个;3.上位叶叶绿体所含淀粉粒既小又少,虽然有的叶绿体中也积累有3～4个淀粉粒,但大多数叶绿体中所含淀粉粒仅有1～2个。以上结果联系到大豆中位叶的光合作用速率较高及对籽粒产量起作用最大来讨论是很有意义的。     

西双版纳傣族贝叶文化与植物多样性保护

生物多样性保护的一个重要的策略是必须提高公众意识,支持社区、青年及妇女积极参与保护行动。所以,近年来,传统知识与生物多样性管理已成为国际社会关注的一个热点。本文以西双版纳的傣族为例,探讨了贝叶文化与植物多样性保护以及持续利用的关系,包括佛主与植物、佛经的文字载体植物、佛寺的用材树种、赕佛活动的植物和佛寺庭园的植物等。     

Whole-stream nitrate addition affects litter decomposition and associated fungi but not invertebrates

We assessed the effect of whole-stream nitrate enrichment on decomposition of three substrates differing in nutrient quality (alder and oak leaves and balsa veneers) and associated fungi and invertebrates. During the 3-month nitrate enrichment of a headwater stream in central Portugal, litter was incubated in the reference site (mean NO₃-N 82 μg l⁻¹) and four enriched sites along the nitrate gradient (214–983 μg NO₃-N l⁻¹). A similar decomposition experiment was also carried out in the same sites at ambient nutrient conditions the following year (33–104 μg NO₃-N l⁻¹). Decomposition rates and sporulation of aquatic hyphomycetes associated with litter were determined in both experiments, whereas N and P content of litter, associated fungal biomass and invertebrates were followed only during the nitrate addition experiment. Nitrate enrichment stimulated decomposition of oak leaves and balsa veneers, fungal biomass accrual on alder leaves and balsa veneers and sporulation of aquatic hyphomycetes on all substrates. Nitrate concentration in stream water showed a strong asymptotic relationship (Michaelis–Menten-type saturation model) with temperature-adjusted decomposition rates and percentage initial litter mass converted into aquatic hyphomycete conidia for all substrates. Fungal communities did not differ significantly among sites but some species showed substrate preferences. Nevertheless, certain species were sensitive to nitrogen concentration in water by increasing or decreasing their sporulation rate accordingly. N and P content of litter and abundances or richness of litter-associated invertebrates were not affected by nitrate addition. It appears that microbial nitrogen demands can be met at relatively low levels of dissolved nitrate, suggesting that even minor increases in nitrogen in streams due to, e.g., anthropogenic eutrophication may lead to significant shifts in microbial dynamics and ecosystem functioning. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Chalcones and other constituents of Dorstenia prorepens and Dorstenia zenkeri

The twigs of Dorstenia prorepens furnished the digeranylated chalcone, 5,3'-(3,7-dimethyl-2,6-octadienyl)-3,4, 2',4'-tetrahydroxychalcone while Dorstenia zenkeri yielded the 3',4'-(3-hydroxy-2,2-dimethyldihydropyrano)-4,2'-dihydroxychalcone and a bichalcone. 4-Hydroxylonchocarpin was found in both plants. D. prorepens also yielded the known compounds: psoralen, bergapten, beta-sitosterol and its D-glucopyranosyl derivative. D. zenkeri yielded p-hydroxybenzaldehyde, dorsmanin A, 4,2',4'-trihydroxychalcone and 4,2',4'-trihydroxy-3'-prenylchalcone. Structures of the new compounds were established by UV, IR, MS and 2-D NMR analysis.     

Frost hardiness in the juvenile and adult life phase of ivy (Hedera helix L.)

The common ivy (Hedera helix L.) remains juvenileat its northern, eastern and altitudinal distribution limits although juvenileparts are largely killed by severe frost spells. In order to explain thisdiscrepancy we investigated the seasonal course of frost resistance in variousorgans of juvenile and adult parts of the same H. helixplants. Maximum frost resistance of leaves (LT₅₀–25°C) and axis (xylem parenchyma:LT₅₀ –29°C; cambium: LT₅₀–35°C) was quite the same in juvenile and adultparts. Thus, H. helix is able to acquire full frostresistance in its juvenile phase. However, hardening of leaves was slower anddehardening of axis was faster in juvenile parts. Leaves of juvenile partsremain 2 to 4 K less resistant than those of adult parts untilattaining the maximum resistance. This explains why mainly leaves of thejuvenile parts were damaged following severe frost episodes with temperaturesbelow –20°C. The occurrence of H.helix in its juvenile phase at the frost-caused distribution limitsmay be explained as follows: Leaves of juvenile plants may occasionally bekilled by severe frosts, but regeneration from dormant eyes enables survival.Loss of leaves may impede the change to the adult phase, but even if the plantsbecame adult frost killing of rest buds (2 to 3 K less resistantthan leaves) would induce rejuvenation.