百原 新

A series of deposits recording the early Holocene drastic changes in coastal environment was investigated in terms of sedimentology and paleontology at the Okinoshima archeological site on the southwest coast of Boso Peninsula, central Japan. The deposits, ca. 3 m thick exposed in trenches, consist of structureless mud and overlying stratified sand, divided into three units, I, II, and III in ascending order. Unit I is poorly sorted sandy mud with abundant opal phytoliths. Unit II, gradually overlying unit I, is poorly sorted sandy mud containing more organic material and pieces of wood, and archeological remains. Unit III overlies unit II with a sharp erosional contact and is composed of well-sorted medium-grained sand intercalated by mud layers with abundant plant fossils. Unit I suggests a dry surface on a coastal plain near uplands. Unit II was transported from the upland onto the coastal plain by a debris flow. Unit III deposits resulted from high-energy river and storm surge flows onto the coastal plain. The succession records that the sedimentary environments of the study site changed successively from a slope near the uplands, to a fluvial plain, to a coastal plain in response to a sea-level rise in the early Holocene. AMS ages of the units are approximately 10,000 cal BP, and deposition occurred within 1000 years. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.

The relict dawn redwood Metasequoia glyptostroboides Hu et Cheng is endemic to the region bordering Hubei and Hunan provinces and Chongqing municipality in south-central China. It is critically endangered. We investigated its population size and age structure, and provided a comparison to the study of Chu and Cooper (1950), documenting the changes of the past 60 years. Our study included all the known wild individuals of the species as well as analyses of the floristic diversity of their habitats. In the last 41 years, habitat changes have effectively ended recruitment of M. glyptostroboides and have reduced species richness in direct response to human disturbance, as shown on several indices. The remaining specimens ranged from roughly 41 to some 265 years for an average near 95 years, with heights of 12-51 m averaging 27 m. The detrimental activities of human residents include cultivation of profitable plants in the understory, selective cutting, harvesting of wood for fuel, and thoroughgoing collection of seeds for sale on the active market. Under present environmental conditions and land use, the dawn redwood will not maintain its natural range in south-central China. Our work detailing the plant populations in the habitats of this living fossil will be useful in establishing priorities for its recovery and conservation. (C) 2010 Elsevier Ltd. All rights reserved.

新第三紀から第四紀への植物相と植生の変遷に基づいた，中部ヨーロッパと中部日本の新第三紀・第四紀境界の研究史をレビューし，酸素同位体比曲線が示す新第三紀から第四紀への気候変化との関連で，植生・植物相の変化の様相が変わる時期を検討した．中部ヨーロッパ，日本とも氷期・間氷期サイクルの様式が変わり，氷期がより寒冷になる時期に，植生や植物相の変化がおきている．中部ヨーロッパでは，第四紀の氷期の特徴となる植生変化が第四紀初頭のPraetiglianに起きている．近畿地方では，約3.3～2.6 Ma, 約1.2～0.9 Ma, 0.5 Ma～20 kaに第三紀に繁栄した植物群の絶滅が集中し，1.7 Maには第四紀の氷期を特徴づける大型植物化石群が出現した．中部日本周辺の鮮新・更新世の植物群の絶滅は，気候の寒冷・乾燥化だけではなく，海水準変動や地形の変化も関連していると考えられた．

アマミヒイラギモチ（Ilex dimorphophylla Koidz.）は奄美大島の湯湾岳山頂付近に発達した風衝林内に生育するモチノキ科の樹木である。本種における樹木サイズと葉の二型性について自生地で調査した。84 シュートの生育を確認し，そのうちの32 シュートが全縁の成熟葉を，残りの52 シュートが鋭い鋸歯のある幼葉のみをもっていた。葉の二型性は樹木高で約130―210 cm，根元直径で15―27mm を境にして分かれていることが明らかになった。

A late Pliocene (1.8-1.9 Ma) wetland fossil forest community that was dominated by Metasequoia and Glyptostrobus was reconstructed based on the species composition of the stumps and other plant macrofossil assemblages. The plant fossils were recovered from a fossil forest preserved in deposits of the Kobiwako Group that are exposed in the Echi River, Shiga Prefecture, central Japan. Fossil wood of Metasequoia and Glyptostrobus was distinguished based on anatomical characteristics. Apportionment of the wood from different horizons in the fossil forest indicates Metasequoia grew over a long period of time in a stable environment, while Glyptostrobus and Alnus grew in unstable environments characterized by short-interval floods. The fossil forest as a whole represents a fluvial back-marsh environment. The upland forest was composed of mixed evergreen conifers and deciduous broad-leaved trees including Chamaecyparis pisifera, Tsuga, Magnolia, and Acer. Aquatic and wetland herbs such as Cyperus, Carex, Scirpus, Polygonum, and Menyanthes grew in and around the wetland forest. The assemblage of fossil plants recovered from the fossil forest consists of plants that are currently distributed in the cool temperate climate zone, such as Picea, Thuja, Betula maximowicziana, Pterocarya rhoifolia, and Menyanthes trifoliata. Glyptostrobus is distributed only in subtropical areas at present, but it also grew under a cool temperate climate zone in Japan during the latest Pliocene.

湖沼や河川の水辺に生育する水生植物は、近年、開発や水質汚染によって生息地が減少し、多くの種が絶滅に瀕するようになった。絶滅が危惧されている水生植物のうち、ヒルムシロ科ヒルムシロ属の沈水植物ツツイトモは、レッドデータブックでは最も絶滅の危険度の高い絶滅危惧IA類に分類されている。この植物は、淡水域から汽水域にかけての流水・止水域に生育する小型の多年草で、繊細な線形の葉をもつ。ツツイトモは主に種子と殖芽とよばれる栄養繁殖体により増殖・越冬を行うが、その生態や生活史はよくわかっていない。そこで本論文では、発生地でのツツイトモの埋土種子分布状況を報告する。次に、複数の種類の水生植物をアメリカザリガニに与えて嗜好性を調べた実験結果から、ツツイトモが他の水生植物に比べて動物の被食による被害を受けやすいことを明らかにする。これらの影響を抑えるためには、冬の休眠時に生育地の水域を水干しして乾燥させることが有効だと考えられるが、その際にツツイトモ個体群の越冬・繁殖にとって重要な殖芽が、どれだけ冬季の乾燥に耐えられるかを調べた。

第三紀鮮新世後半の約300万年前を境に,北半球に大陸氷河が発達し始め,氷期-間氷期の気候変化が激しくなった.ほぼ同時期に,日本がアジア大陸と切り離された島になったが,この時代以降の環境変化に伴って,日本列島固有のフロラや植生の形成が促進されたと考えられる.日本に分布する約5,600種の維管束植物のうち,約35%にあたる1,950種が日本の固有植物で,日本は地球上で固有値物の多い地域の一つになっている(Mittermeier et al.2004).日本の植生で優占する植物もシラビソ,オオシラビソ,コメツガ,モミ,スギ,ブナ,イヌブナなど,日本の固有種が多い.第三紀以降の環境変遷史を北半球の他の温帯地域と比較すると,日本列島は植物の種多様性の維持に適した地理的位置にあり,しかも第四紀の環境変化も種の分化を促進させる要因になったことがわかる.たとえば,第四紀の氷期には大陸氷河の影響を受けず,海に取り囲まれて比較的湿潤温暖な気候下にあったために,氷期-間氷期の気候変化も極端ではなく,気候変化に伴う植物の移動が大きくなかったことが北半球中緯度の他地域と異なる.また,第三紀末から第四紀に山地や盆地,海峡といった地形の形成が活発に起こり,それらが気候の地域差をもたらし,植物の移動の障壁にもなったことも重要である.日本列島は,新第三紀以降に地殻変動が極めて活発に起こったために地層の堆積速度が極めて速く,地層の対比編年に有効な火山噴出物が豊富に含まれている.しかも,日本各地には第三紀末から第四紀にかけて連続的に堆積した地層が広く分布し,そこには,保存状態のよい種実類や葉,花粉などの植物化石が豊富に含まれている.したがって,層序学的位置が明らかな植物化石資料を集積していくことで,フロラや植生の時間的・空間的分布変化を明らかにすることができる.植物化石を含む日本の鮮新・更新世の地層は,地層の編年・対比が極めて詳細に明らかになっている.地層の堆積速度の速さと,時間的・空間的連続性を考えると,地球上の他地域の地層よりもはるかに高い精度で,植生変遷や地理的な分布の変化を解明できるフィールドである.ここでは,これまでの地質学的・古生物学的資料から,第三紀末から第四紀にかけての中部日本を中心とした日本列島の古地理変化を概説したうえで,植物化石記録から明らかになっているフロラの変遷について述べる.

Archaeobotanical remains of Setaria grains and chaff were found at the Chengtoushan site in south-central China (ca. 5800 cal B.P.). Grain shape was determined, using length to breadth ratios, and morphological variation in the upper lemma of modern domesticated and wild Setaria species were examined using scanning electron microscopy as a basis for identifying archaeobotanical remains. Grains of S. viridis, S. yunnanensis, and S.xpycnocoma are slender, whereas S. italica, S. italica var. germinica, S. lutescenes, S. faberi, S. glauca, S. pallidefusca and S. intermedia are round in shape. The papillae distributed on the upper lemma of S. italica are small (8-15 mu m) with a non-ridged base, while other Setaria species have large papillae (15-20 mu m) with a widely ridged base. The remains of the Setaria from the Neolithic layers at Chengtoushan included S. italica, based on these identification characters. These new finds of foxtail millet are the earliest discoveries from the Yangtze River basin of southern China and are also the earliest evidence for co-cultivation of foxtail millet with rice. The implications of these findings for understanding foxtail millet domestication centres are discussed.

Intraspecific polyploidy and cytogeography were clarified in the samples of Houttuynia cordata (Saururaceae) studied in the Sino-Japanese region of eastern Asia, ranging from Nepal, China, northern Thailand, Taiwan to Japan. Five chromosome numbers of 2n=72, 80, 96, 112 and 128 were detected, four of which were firstly recorded here. These chromosome numbers suggested that the basic chromosome number of Houttuynia could be x=8. The observed cytotypes were evaluated as 2n=72, 80, 96, 112 and 128, and represented 9x, 10x, 12x, 14x, and 16x, respectively. The continental part of east Asia harbored intraspecific polyploidy ranging from 9x to 16x, and only one cytotype of 12x or 2n=96 was found from the eastern edge of the Asian continent between Taiwan and Japan. The evolution of basic chromosome number was discussed based on a phylogenetic tree of the Saururaceae, suggesting that x=11 was an archaic basic chromosome number in this family. Houttuynia may have experienced a disploid reduction from x=11 to x=8, as an autoapomorphy and subsequent intraspecific polyploidization in continental eastern Asia.

The genetic diversity of the species, Potamogeton lucens subsp. sinicus var. teganumensis, which is critically endangered in Japan, was investigated. This species now occurs in only two known localities in Japan. One is a native population (Oitoike population), but the other (Teganuma-Okahotto population) is found in a small artificial pond that was dug in 1998. It is considered that the Teganuma-Okahotto population grew from a soil seed bank. Based on RAPD variation, we compared the genetic diversity of the two populations of P lucens var. teganumensis in Japan and one population of P. lucens subsp. sinicus var. sinicus in China. The Teganuma-Okahotto population showed RAPD variation, suggesting that it may be derived from more than one seed buried in old sediments. This population also had the highest value of Shannon's Information Index among the three study populations. This finding suggests that seeds buried in sediments can contain genetic variability, and may be used to conserve the genetic diversity of rare and endangered plants. (c) 2006 Elsevier B.V. All rights reserved.

We investigated the phylogenetic relationships within the genus Cardiandra based on plastid DNA sequences. The phylogenetic tree showed that Cardiandra populations from the Ryukyu Islands (Japan) and Taiwan were monophyletic (Ryukyu-Taiwan clade), whereas taxa from China and mainland Japan were sisters to this clade. The divergence time between the Ryukyu-Taiwan clade and the other species was estimated to be 0.082 MYA, i.e., the late Pleistocene. The infrageneric and/or infraspecific differentiation of Cardiandra is estimated to have depended largely on allopatric differentiation caused by the presence or division of the past landbridge of the Ryukyu Islands, which connected mainland Japan to the Asian Continent during the Quaternary.

千葉県袖ケ浦市吉野田の更新統下総層群清川層 (MIS7.3) から, ナウマンゾウやシカ, カメ類化石とともに11分類群の大型植物化石が取り上げられた. 大型植物化石群は, サルスベリ属, ハリモミ近似種, ブナ, フジを含み, いずれも印象化石だった. このうち, サルスベリ属はヤクシマサルスベリ近似の化石種に同定された. 吉野田の当時の気候は, シマサルスベリの北限の温量指数102℃月前後の気温条件と推定された.

千葉県吉野田の下総層群清川層は, 約20万年前の古動植物群を産する化石密集層で知られるが, この動物群の一部が現在の中国揚子江河口域以南の亜熱帯種に類似するのに対し, 植物群は関東地方北部の冷温帯を示唆するなど, 互いに共存しえないほどの古気温推定上のずれを与える問題が生じていた. この問題点を説明するために, 本稿では清川層の花粉群組成を調べるとともに, 同時代の記録として過去43万年間の琵琶湖花粉層序を参照した. また, 房総半島と揚子江河口域の現在の気温状態を比較した. さらに, 地球軌道要素の変動に基づく日射量変動の電算結果を検討した. 結果として, MIS7に対し気温年較差の増大を仮定し, 吉野田動物群の一部が夏の気温に, 植物群がおもに冬の気温に規制されていたとするならば, 両者のずれが整合的に説明されうることを述べた. 年間総熱量の反映としての年平均気温は, 年較差増大を仮定するならば, 現在よりやや低温が要求される.

The buried peat deposit was foud in the sand beach on the Desaki coast (Tamano City, Okayama Prefecture), the northeastern coast of Seto Inland Sea. In this study, we performed sulfur and diatom analyses of the deposit. The results were used along with 14C dates and the eruption age (7300 cal BP) of Kikai-Akahoya tephra (K-Ab) to derive sedimentary environments of the deposit. K-Ah was detected just below the peat deposit. At the culmination of the Jomon transgression, the peat deposit had been formed in brackish environments of salt marsh for about 300 years. In order to reconstruct local paleovegetation, we analyzed pollen, wood and plant fossils in the deposit. The results show vegetational transition from a deciduous broadleaved forest mainly of Ouercus subgen. Lepidobalanus to Pinus forest. In spite of the Holocene thermal optimum, the vegetation dominated by Ouercus subgen. Cyclobanopsis was not recognized at the Desaki site, as has been shown in many other regions of regions of western Japan. Ouercus sect. Prinus was replaced by Ouercus sect. Aegilops as the dominant section of Ouercus subgen. Lepidobalanus, suggesting early establishment of traditional rural vegetation of 'Satoyama' in Japan. However, no evidence for human agency has been obtained from the mid-Holocene archaeological sites around the Desaki site. Thus it is more likely that this vegetational transition resulted from the succession caused by natural forces such as ecological disturbance and climatic and/or endemic situations rather than by cultural deforestation.

岐阜県多治見市大洞地区の中新統土岐口陶土層の堆積相を調査し, そこに含まれる植物化石の組成, 堆積構造, 堆積物の粒度組成を調べた. ここでは, 10堆積相が認定でき, 湖沼・湿地に近接した網状河川システムが復元された. このことから, 砂・泥の卓越する河川～湖沼・湿地の堆積環境が, 東海層群下部の陶土層の堆積盆地に共通していることが明らかになった. さらに, 大型植物化石の産状から, 植物片の運搬・堆積過程について考察した. 1) 洪水流堆積物中の大型植物化石には, ベッドロードとして堆積するものと, 浮遊沈降して堆積するものが存在すること, 2) 両者の違いは, 植物片の大きさ, 細毛表面といった形態の違いに左右されること, 3) 植物化石は, 水理学的淘汰を受けて堆積したこと, 4) 洪水流堆積物は3タイプに区別でき, 植物化石をもとに, それぞれの洪水流の水理環境を推定できること, が明らかになった.

Two peat profiles from the Manchurian Plain in northeastern China, with chronology based on 20 AMS measurements, provide new evidence for natural and anthropogenic environmental changes that occurred in the region during late Holocene. The onset of continuous organic accumulation interpreted as climatically induced shift in hydrological regime was dated at the Muchang site to 4200 (uncal.) BP, and at the Dahuofang site to at least 3560 BP. The start of peat growth, documented in the Muchang profile, was preceded by temporal intensification of fluvial processes around 4400/4300 BP. The evidence of hydrological changes in the Manchurian Plain correlates with the spread of Korean pine in the nearby Changbai mts. area in 4300-4000 BP, and can be associated with the initial stages of a trend towards present-day climatic conditions in the region. Late Holocene pollen sequences from Muchang and Dahuofang revealed the presence of oak and pine forests with the other minor deciduous constituents as Ulmus, Tilia, Carpinus, Acer and Fraxinus. Local distribution of oak was confirmed by plant macrofossil remains (leaf fragments) ascribed to Quercus x hopeiensis. The vegetation cover formed sparse woodland or mosaic of forests and steppe communities with Artemisia, Gramineae and Chenopodiaceae. Fossil pollen data clearly indicates that the spread of grasslands in the western part of Manchurian Plain occurred as a result of human impact. Extensive deforestation accompanied by agricultural practices (buckwheat cultivation) has been dated to 900-1100 cal yr AD and were correlated with development of the state of Liao dynasty (907-1125 AD). Evidence of earlier human involvement in forest destruction has been dated to around 900 cal yr BC. With each progressing anthropogenic deforestations phase, there was increased circulation of eolian dust resulting from landscape opening and soil erosion. © 2004 Elsevier Ltd and INQUA. All rights reserved.

青森県の黒石市井戸沢,青森市大矢沢,十和田市赤伏における十和田八戸テフラによって埋積された晩氷期(約13,000yrsBP)の埋没林において,大型植物化石群から当時の古植生を復元した.当時の植生はトウヒ属バラモミ節,トドマツ,グイマツが混生する針葉樹林にカバノキ属を伴い,林床は森林性蘚類が優占するコケ型林床であった.針葉樹3種のうち,トウヒ属バラモミ節がすべての地域で最も多く,トドマツとグイマツは比較的少なかった.3地域の古植生を比較すると,当時低湿地だった大矢沢・十和田地域ではイワダレゴケ,オオフサゴケといった湿った場所を好む蘚類が多く,岩礫地だった黒石地域ではグイマツを欠き,蘚類の種類が豊富だった.復元された古植生とその立地から,トウヒ属バラモミ節,トドマツ,グイマツの分布立地を検討した.その結果,3地域で優占していたトウヒ属バラモミ節は当時から低湿地,岩礫地といった未発達土壌で分布が優勢であり,逆に量的には少なかったトドマツは未発達土壌では優占できなかった.グイマツは低湿地を中心に分布していたと考えられるが,岩礫地であった黒石地域には多雪の影響で分布できなかったと考えられた.

現在すでに消滅してしまった千葉県手賀沼の水生植物相を,自然環境が良好だった40年前以前に湖底に堆積した埋土種子から再生させることを目的に,手賀沼干拓前の地層を調査し,埋土種子の地層中での分布状態や堆積環境,保存状態,種子群の種構成の調査,地層の花粉分析,休眠種子の発芽試験を行った。その結果,埋土種子は堆積物中に均一に分布するわけではなく,堆積環境の違いで種子の分布や保存状態,種構成が変化することが明らかになった。流水環境で比較的急速に堆積した種子群では,種皮が完全な状態で保存されていれば胚乳が保存されていることが多く,センニンモの発芽も確認された。

Species composition of plant macrofossil assemblages from the Tokiguchi Porcelain Clay Formation in Tajimi City，central Japan are compared on a stratigraphic basis．The formation was deposited in a fluvial environment in a sedimentary basin at about 10 Ma（early Late Miocene）．The fossil assemblages always contained subtropical elements indicating warm climate．Cool temperate elements increased in the upper hodzon，along with herbaceous taxa including annuals．This change is thought to reflect topographic changes in and around the sedimentary basin．During deposition of the lower horizon，plant macrofossils were derived from wetland vegetation and forests between the distal end of the fan and uplands along the sedimentary basin．The forest there was composed mainly of deciduous broad-leaved trees mixed with conifers and evergreen broad-leaved trees，and the herb layer was less developed．During deposition of the upper horizon，the drainage basin of the river expanded to include higher mountains，from which the cool temperate elements were derived．Active tectonism at this time increased disturbance，creating the habitat which enabled herbaceous plants（including annuals）to grow on the deposits of a large gravelly rivers．

Two emergence events in the past 3 800 years have been recognized from the welldated marshy deposits of Lake Sagata. Each emergence event was associated with changes in fossil diatom assemblages. In the mud layers, planktonic Aulacoseira granulata, A. ambigua, and Fragilariaceae dominated, while two peat layers were characterized by aerial and/or aeroterrestrial taxa such as Eunotia praerupta var. bidens and Hantzschia amphioxys. Radiocarbon ages suggest the events had occurred 2100-1700 yr. B. P. and 1700-1300 yr. B. P. Past changes in the balance between precipitation and evaporation might have induced these emergence events.

Cathaya (Pinaceae) pollen was discovered from the Pliocene Koka Formation of the Kobiwako Group, Shiga Prefecture, Japan. The pollen morphology was examined with the light and scanning electron microscopes. The characteristics indicate that the bisaccate pollen is Cathaya. This discovery suggests that further study on the pollen flora of the Plio-Pleistocene Kobiwako Group will clarifythe disappearance process and horizon of Cathaya in the area with relation to the climate change.

ヤツガタケトウヒとヒメバラモミの生育立地の特性を,それらと混生する樹種の立地と比較することにより明らかにした。赤石山脈北西部巫女淵山中(標高1,300~1,800m)の64地点で,四分法調査,斜面傾斜と露岩被度の計測,実生調査を行った。64地点全体における胸高断面積合計比ではコメツガが25%で最も優占し,ウラジロモミが続いた。ヤツガタケトウヒとヒメバラモミは,いずれも14%程度を占めるにすぎず,分布が斜面傾斜36°以上,露岩被度31%以上の岩塊急斜面にほぼ限られた。これに対し,コメツガの分布は斜面傾斜,露岩被度に関係なく一様であった。ウラジロモミは露岩被度20%以下の腐植土が被覆する立地に集中した。一方,実生についてみると,ヤツガタケトウヒとヒメバラモミは母樹周辺の露岩面上に集中した。コメツガは腐朽倒木•根株上に,ウラジロモミは腐植土面上にそれぞれ多かった。以上より,ヤツガタケトウヒとヒメバラモミは,種子散布が母樹周辺に限られることと実生の定着が露岩面上にほぼ限られることによって,岩塊急斜面以外の地形では個体群の維持が困難であると考えられた。

An all-core boring reaching 625 m in depth was conducted at Negoro in the Wakayama Plain which is a tectonic basin formed under the influence of the Median Tectonic Line active fault system. At the depth of 137m, sedimentary rocks belonging to the Upper Cretaceous Izumi Group and their sheared materials (lithologic unit : NG-1) are in contact with unconsolidated sediments by a reverse fault dipping about 30° northward. Unconsolidated sediments are composed of a sequence of alternating beds of pebble, sand and silt intercalating peaty layers and a volcanic ash layer (V290). They are divided lithologically into 4 units (NG-2 to NG-5). Some plant macrofossils were collected and paleomagnetic measurements were carried out. The sequence is divided into Zone 1, Zone 2 and Zone 3 in descending order on the basis of paleomagnetic polarities, and Zones 1, 2 and 3 are correlative to the Matuyama, Gauss and Gilbert chrons respectively, as the result of the correlation of widespread tephras and biostratigraphic constraints of plant fossils. These unconsolidated sediments correspond to the beds of the Shobudani Formation distributed in the hills, east of the Wakayama Plain. It is presumed that the formation has gently tilted northward in the basin and has contacted with the basement rocks by a fault at the northernmost part of the plain.