生物演化过程中的突变性及其植物学证据

物种的形成过程并非遵循达尔文倡导的渐变论，而是当环境恶化时由祖先种通过自身的调节突然产生的。植物也可以因种间、属间或更高级分类单元间的杂交产生能繁育后代的新种，其过程无疑也是通过突变实现，对此本文暂不做深入讨论。在突变发生以后，生物的性状极少变化，为稳定期。古植物学中大叶系植物由无叶类演化到具大型羽状复叶的过程，有节类茎的纵脊在节上由直通到相错、叶由分叉到连合的过程；以及现代植物中的观音座莲从二次羽状复叶变为一次羽状复叶和车前草在南方种身上长出北方种的事实都证明了这一点。

Late Holocene Environmental History of Lake Victoria Basin： Evidence from Geochemical Proxies

Sedimentary TOC （total organic carbon）, TN （total nitrogen） and C/N （carbon/nitrogen） at selected sites of Lake Victoria basin have provided evidence of phytoplankton productivity, input of nitrates and allochthonous （land） plant materials/catchment destruction in the basin during the late Holocene period （last 4,000 years to present）. TOC and TN in the sediment cores were determined using EuroEA3000 Series Elemental Analyser and radiocarbon dating done using AMS （accelerator mass spectrometry） standard method. Results showed that TOC （13.45%-20.78%） and TN （1.07%-1.92%） values were higher at Napoleon Gulf from about 4,186 years before present （ca. 4,186 yr. BP） to present than at inlet of river Kagera （TOC： 3.27%-6.32% and TN： 0.30%-0.59%） from about 190 years before present （ca. 190 yr. BP） to present. Generally TOC and TN had a negative correlation （r = -0.37, p = 0.04, n = 32） at Napoleon Gulf in the last 4,186 years to present signifying that C/N ratios were governed mostly by phytoplankton productivity which markedly increased during some periods in the last 370 years to present possibly as a result of increased input of nitrates. However, the periods from about 4,186 years to 1,684 years before present （ca. 4,186 yr. BP to 1,684 yr. BP） and some periods between the last 370 years to present indicated increased input of allochthonous plant materials/catchment destruction. On overall, there was a positive correlation between C/N and TOC at inlet of river Kagera （r = 0.57, p = 0.01, n = 20） in the last 190 years to present possibly signifying that C/N ratios were governed mainly by input of allochthonous plant materials hence increased catchment destruction. Input of land plant materials （catchment destruction） along Kagera basin declined during some period after 1950 AD. However the most recent years have shown increased input of land plant materials （catchment destruction） in Kagera basin.

Scientists Use Palaeobotanical Evidence to Estimate Early Miocene Elevation in Northern Tibet

The area and elevation of the Tibetan Plateau over time has directly affected Asia’s topography,the characteristics of the Asian monsoon,and modified global climate—but in ways that are poorly understood.Charting the uplift history is crucial for understanding the mechanisms that link elevation and climate irrespective of time and place.While some palaeoelevation data are available for southern and central Tibet,clues to the uplift history of northern Tibet remain sparse and largely circumstantial.Lately,

First record of extinct fruit genus Chaneya in low-latitude tropic of South China

Fossil reproductive structure from the Eocene of the Changchang Basin (Hainan Island,South China) is recognized as Chaneya hainanensis sp.nov.This new species is characterized by persistent corolla of five obovate petals with three subparallel primary venation linked by arching secondary veins,circular central disk bearing two orbicular ovaries or fruit bodies.This discovery confirms the presence of the extinct fruit genus Chaneya in low-latitude tropical area,providing significant fossil evidence for investigating the origin,migration,and phytogeography of this genus and discussing the Tertiary floristic exchanges among North America,eastern Asia,and Europe.Considering the distribution of this genus and its extant relatives and the climate changes during the Cenozoic,we hypothesize that Chaneya was a widespread tropical or subtropical taxon,but,with climate cooling,became extinct in northern latitudes and evolved into Picrasma (Simaroubaceae) and Rutaceae mainly in modern tropics and subtropics.