长期不同施氮水平对草原植物群落结构的影响

为探讨施氮对贝加尔针茅草原植物群落结构的影响,该研究于内蒙古贝加尔针茅草原设置不同施氮水平0(N0)、15(N15)、30(N30)、50(N50)、100(N100)、150(N150)、200(N200)和300(N300)kg·hm-2·a-1,研究连续施氮9年后贝加尔针茅草原群落物种组成、重要值、多样性及生物量等指标对不同施氮水平的响应。结果表明:(1)长期施氮导致植物群落物种组成发生了明显的变化,在高浓度氮素添加量下群落物种数最低,但可显著提高优势种在群落中的重要值(P<0.05)。(2)长期施氮使贝加尔针茅草原植物多样性指数不同程度地降低,使优势度指数增加,其中N300添加水平效果最为明显(P<0.05)。(3)长期施氮使草原植被生产力(地上、地下生物量)整体呈先上升后下降的趋势,地上生物量在N100水平时出现峰值,地下生物量在N50水平时出现最大值(P<0.05),且根系分布具有明显的表聚特征(0~10 cm)。(4)RDA分析表明,寸草苔和狭叶柴胡地上生物量与土壤pH呈显著正相关关系(P<0.05);展枝唐松草和二裂委陵菜地上生物量与土壤有机质含量呈显著正相关关系(P<0.05)。研究认为,长期不同施氮水平均可改变贝加尔针茅草原群落物种组成,降低物种多样性,对植物群落结构有着明显的影响。     

FORMULATING A NEW PASSION FRUIT JUICE BEVERAGE WITH DIFFERENT SWEETENER SYSTEMS

The aim of this work was to optimize the acceptability of a natural passion fruit beverage using different levels of passion fruit pulp and sucrose, and to determine the equi-sweet concentrations of aspartame, sucralose, and a blend of 80% aspartame  +  20% acesulfame-K for the optimized formula. A 2² central composite design was used to optimize the acceptability of the sucrose-sweetened beverage, which was accessed using a 9-point structured hedonic scale. Acceptability data were fitted to a second-order model equation provided in the design. The selected pulp content and sucrose concentration were, respectively, 2.5 ° Brix and 10%. Measurements of sweetness equivalence were accomplished using two types of sensory methods: magnitude estimation and difference-from-control tests. The concentrations of aspartame, sucralose and a blend of 80% aspartame  +  20% acesulfame-K found as equi-sweet to 10% sucrose in the studied passion fruit beverage were, respectively, 0.043, 0.016 and 0.026%.

PRACTICAL APPLICATIONS

This article deals with formulating a new passion fruit juice beverage with different sweetener systems. The research makes a very important contribution to the literature on sensory science used on product development by demonstrating the necessity to study the substitution of sucrose by high-intensity sweeteners every time a formulation is changed or a new product is developed.     

Hypocotyl features of Myrtus communis (Myrtaceae): a many-sided strategy for possible enhancement of seedling establishment in the Mediterranean environment

Seed germination and seedling development were studied in Myrtus communis L. (Myrtaceae), an evergreen shrub widespread in Mediterranean woodlands, maquis and garrigues, to investigate the presence of morphological and anatomical adaptations that enhance successful seedling establishment under biotic and abiotic stresses. Seeds were germinated under controlled conditions and were observed daily to identify different post-germination stages of development. The anatomy of developing hypocotyls and emerging radicles was studied through light and epi-fluorescence microscopy using both cross and longitudinal sections. Tegument rupture was caused by hypocotyl elongation, which, when water availability in the substrate was limited, was accompanied by a dense ring of hairs in the lower region. Absorption tests showed that the hypocotyl hairs were functional in water uptake. They might also enhance the anchorage of the seedling to the substrate. Further investigations showed the early formation of a suberized layer of cells (exodermis) in the radicle and the occurrence of phenolics in the hypocotyl cells of cortical parenchyma. In conclusion, our results show that seedlings of M. communis have developed a strategy of establishment that: (a) regulates water uptake through hypocotyl hairs and the exodermis; (b) might allow mechanical support through hypocotyl hairs; and (c) accumulates phenolics that might defend the plant against animal predation.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 195–202.     

The fermentation of cell wall substances in grass silage and in potato pulp

Summary The amount of acid formed in grass silage was greater than could have been formed from the soluble sugars present, even when only a lactic fermentation took place. This seemed to point to fermentation of cell wall substances by lactic acid bacteria. Lactic acid fermentation in potato pulp always takes place with cell wall substances as substrates, as sugars are absent. It was found that galactose, probably occurring as galactan, and also some pectic acid were fermented in potato pulp. Some lactobacilli were isolated from potato pulp; streptobacteria which could ferment galactan but no pectic or galacturonic acid, and betabacteria which could ferment galacturonic acid but no galactan or pectic acid. A number of homofermentative lactobacilli were all found to belong to the speciesStreptobacterium casei. It was shown that a strain of this species could ferment galactan in potato pulp sterilised previously with ethylene oxide. Part of this work was carried out at the Netherlands Institute for Dairy Research, Ede, Netherlands.     

Phylogenetic analyses of mtDNA sequences reveal three cryptic lineages in the widespread neotropical frog Leptodactylus fuscus (Schneider, 1799) (Anura, Leptodactylidae)

Leptodactylus fuscus is a neotropical frog ranging from Panamá to Argentina, to the east of the Andes mountains, and also inhabiting Margarita, Trinidad, and the Tobago islands. We performed phylogenetic analyses of 12S rRNA, 16S rRNA, tRNA-Leu, and ND1 mitochondrial (mt) DNA sequences from specimens collected across the geographic distribution of L. fuscus to examine two alternative hypotheses: (i) L. fuscus is a single, widely distributed species, or (ii) L. fuscus is a species complex. We tested statistically for geographic association and partitioning of genetic variation among mtDNA clades. The mtDNA data supported the hypothesis of several cryptic species within L. fuscus. Unlinked mtDNA and nuclear markers supported independently the distinctness of a 'northern' phylogenetic unit. In addition, the mtDNA data divided the southern populations into two clades that showed no sister relationship to each other, consistent with high differentiation and lack of gene flow among southern populations as suggested by allozyme data. Concordance between mtDNA and allozyme patterns suggests that cryptic speciation has occurred in L. fuscus without morphological or call differentiation. This study illustrates a case in which lineage splitting during the speciation process took place without divergence in reproductive isolation mechanisms (e.g. advertisement call in frogs), contrary to expectations predicted using a biological species framework.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 325–341. No claim to original US government works.     

Biodiversity from a historical geology perspective: a case study from Marajó Island, lower Amazon

Assessing patterns of abundance and distribution of Amazonian species is still an overwhelming task that requires integration of multiple disciplines. This work is based on background information gathered from previous reconstructions of the geological history of the lower Amazon drainage basin, in order to analyse biodiversity patterns within the context of landscape transformation. A highly dynamic geological scenario is depicted for this area during the Plio‐Pleistocene and Holocene, which consisted of a large palaeovalley formed as a response of tectonic reactivation. This palaeovalley was filled with sediments transported by a north/northwest orientated palaeo‐Tocantins River. The palaeodrainage became abandoned as the main river course was deviated to the northeast, initiating the separation of Marajó Island from mainland. Geology had a direct impact on the modern physiognomy, with open vegetation dominating in areas with Holocene sedimentation, while closed forests prevailing in older Quaternary and, probably also, Pliocene terrains. Data from fossil and modern mammalian groups indicate the connection of Marajó Island to the mainland during the Last Glacial Maximum, when open vegetation seems to have dominated. Tectonic subsidence was responsible for the maintenance of this vegetation pattern on the eastern side of the Marajó Island, keeping it as a habitat favourable for savanna adapted faunal elements. Based on this kind of information, this work attempts to highlight the importance of integrating studies combining geological and biological events as the key to understand biodiversity patterns in Amazonia. It is expected to open new lines of research dealing with the comprehension of ecology, species and genetic diversity, biogeography, evolutionary scenarios, and speciation mechanisms.     

The auxin response factor,OsARF19, controls rice leaf angles through positively regulating OsGH3‐5 and OsBRI1

Auxin and brassinosteroid (BR) are important phytohormones for controlling lamina inclination implicated in plant architecture and grain yield. But the molecular mechanism of auxin and BR crosstalk for regulating lamina inclination remains unknown. Auxin response factors (ARFs) control various aspects of plant growth and development. We here report that OsARF19‐overexpression rice lines show an enlarged lamina inclination due to increase of its adaxial cell division. OsARF19 is expressed in various organs including lamina joint and strongly induced by auxin and BR. Chromatin immunoprecipitation (ChIP) and yeast one‐hybrid assays demonstrate that OsARF19 binds to the promoter of OsGH3‐5 and brassinosteroid insensitive 1 (OsBRI1) directing their expression. OsGH3‐5‐overexpression lines show a similar phenotype as OsARF19‐O1. Free auxin contents in the lamina joint of OsGH3‐5‐O1 or OsARF19‐O1 are reduced. OsGH3‐5 is localized at the endoplasmic retieulum (ER) matching reduction of the free auxin contents in OsGH3‐5‐O1. osarf19‐TDNA and osgh3‐5‐Tos17 mutants without erected leaves show a function redundancy with other members of their gene family. OsARF19‐overexpression lines are sensitive to exogenous BR treatment and alter the expressions of genes related to BR signalling. These findings provide novel insights into auxin and BR signalling, and might have significant implications for improving plant architecture of monocot crops.