湖北中泥盆世一植物新属的研究

植物自晚志留世登陆以来，经过对恶劣的陆生环境长期而艰难的适应，在泥盆纪，特别是中上泥盆世开始其大规模的演化发展。在此其间，石松类、楔叶类、前蕨类、真蕨类以及前裸子植物等相继出现，使得陆生植物进入其第一个空前繁盛时期。 但是，也正是在这个介于陆地植物起源及其大规模发展的阶段，植物分类以及各植物之间的亲缘关系很不清楚。特别是前蕨类，它起源于三枝蕨类，并且被认为是真蕨类和前裸子植物的祖先，但目前对它是如何从三枝蕨类进化到真蕨类和前裸子植物却几乎一无所知。就如同一个黑匣子，有一个入口和两个出口，我们的任务就是打开这个黑匣子，弄清楚前蕨类中各植物的自然分类位置以及他们之间的亲缘关系。那么，有关早期陆地植物进化的一些悬而未决的问题也便迎刃而解了。 本论文正是为此目的而作。并且，植物新属变枝蕨的发现将无疑为最终达到这个目的做出很大的贡献。

陆地植物对环境变化的响应

陆地植物起源以后，地球上的环境发生了巨大的变化。大气CO2浓度自泥盆纪早期的2000-4OOOμml•mol_1下降至石炭一二叠纪的300μml•mol_1左右，02浓度在泥盆纪至石炭一二叠纪时期，由20-30μml•mol_1上升到70-80μml•mol_1，随后又下降到目前的水平。陆地植物登陆后，形态结构也发生了显著的改变，气生部分表而分化出了通气结构--气孔器和保护结构--角质层。泥盆纪首选标志植物刺镰蕨（Drelpanophycus spinaefrmis）在整个泥盆纪，广布全世界。刺镰蕨的气孔器类型一直存在两种观点，一种认为刺镰蕨的气孔器是平列型，即气孔器山两个保卫细胞和两个副卫细胞组成：另一观点认为刺镰蕨的气孔器为不规则型，即气孔器仅有两个保卫细胞构成，不具副卫细胞。我们借助于扫描电镜、石蜡制片技术和叶表皮离析法，细致地研究了现代石松（Lycopodium japonicum）叶的横切而、表皮及气孔器的内外表面结构，并同刺镰蕨的表皮和气孔器进行了对比。认为刺镰蕨的气孔器和所有的化石石松类及现代石松类的气孔器一样，均属于不规则型。从而解决了关于刺镰蕨气孔器类型的长期争论的关键性科学问题。 胡桃科青钱柳属植物起源于晚白垩世的环北太平洋沿岸，化石植物最早发现于北美古新世和早始新世的Motana,，Wyoming，North Dakota，north Colorado地区，欧亚地区仅出现在渐新世至上新世的Kazakhstan、Germany、Romnania、Russia、Japan、中国云南远谋和四川米易地区。我们将采于吉林省珲春组始新世的叶化石鉴定为一青钱柳相似种，该化石成为东亚地区出现最早的青钱柳属植物，这一发现也支持晚白垩至早第三纪时期环北太平洋两岸曾经相连的观点，青钱柳属在晚白垩由北美起源，在始新世经东亚向欧亚大陆扩散，由于环境变迁，第四纪以后，青钱柳属仪剩一种植物分布于中国的亚热带地区。文中还利用共存分析方法估测出始新世吉林省珲春地区属于暖温带至亚热带气候。 统万城遗址位于我国黄土高原向毛乌素沙漠过渡地带的北缘，属于暖温带森林草原向温带干草原、温带荒漠草原过渡的地区，同时又是东部季风区向西北干旱区过渡的生态环境敏感带。今天统万城地区的自然景观属于沙漠，仅存稀疏的次生灌丛和草本群落。但是，通过对统万城城墙内的孢粉和木材进行的综合研究表明，在约1600年前，当地为温带草原，在塬面或山丘上分布有侧柏林，沟谷、河岸边生长喜温湿的乔木，河流、湖泊、沼泽中水生植物繁盛，在丘间低洼处或盐碱土上分布有灌木和草本植物。当时该地区的年均温为7.8 ℃-9.3℃，最热月平均温度23.0℃-24.9℃，最冷月平均温度-12℃-5.6℃，年较差28.5℃-3 8.2℃，年降雨量403.4-550．Omm，最大月降雨量83.8-123.9mm，最少月降雨量4.4-12.2mm，当时气候比现在温暖湿润，年均温比现在高出0.2-0.7℃，年降雨量也高出60--lOOmm。而如此的历史景观今天已经向南迁移，侧柏林或森林草原退缩至延安以南地区。在此近1600年的时间里，毛乌素沙漠分布范围不断扩大，其南部边缘推进了约200 km，推测沙漠扩展的速率达到平均125m/a。

中国二叠纪—三叠纪陆生植物多样性变化的研究

本文基于华南、华北地区二叠纪—三叠纪陆生植物大化石和孢粉的数据库， 对中国二叠纪—三叠纪陆生植物的多样性变化进行了统计分析研究，并重点探讨了在二叠纪—三叠纪界线（Permian-Triassic Boundary，PTB ）陆生植物是否与同期的海洋动物一样发生了同步的集群灭绝事件。 统计分析表明，华南、华北陆生植物大化石的分异度穿过PTB 均显示了较长时续（约37.8Ma）的下降和残存阶段，而孢粉化石在早三叠世的分异度则是上升的。总体上，陆生植物分异度穿过PTB 的变化较同期的海洋动物平稳缓慢。华南地区陆生植物大化石在晚二叠世末长兴期（Changhsingian）虽然伴随着最高的属灭绝率85.94% 和最低的属新生率28.12%，发生了最大的灭绝事件，但在晚二叠世早期和早三叠世的属的灭绝率也较高，分别为61.02% 和66.67% 。种的灭绝率在晚二叠世早期从早二叠世晚期的39%大幅度上升到80.36%，晚二叠世晚期达峰值97%，早三叠世稍降为93%，显然高于其它时段灭绝率范围（30—70%）。种和属的灭绝率呈现了同样的高峰阶段，从晚二叠世早期至早三叠世，时续为20.8 百万年（Ma）。基于更替率分析，华南地区陆生植物的高更替率事件分别发生在早二叠世晚期（93.75%）、早三叠世（90.92%）和晚三叠世（91.38%），但陆生植物在穿越早二叠世晚期—晚三叠世的整个过程中，更替率波动不大、比较平稳。华北地区陆生植物大化石穿越PTB 的灭绝率比华南地区低，属级高灭绝率事件集中在晚二叠世早期（67.31%）和晚二叠世晚期（63.89%）， 时续为14.8Ma，种级高灭绝率事件与华南地区类似，集中在晚二叠世早期（85.67%）、晚二叠世晚期（90.86%）和早三叠世（80.28% ）三个阶段，时续为20.8Ma 。显而易见，这比同期海洋动物集群灭绝的时续（3—11Ma ）要长。 本文基于这些分析结果，仔细考虑了集群灭绝的4 个特点（即量值、广度、幅度和时续），认为华南、华北陆生植物在PTB 并未发生集群灭绝事件，而是发生了演化替代，即陆生植物穿过PTB 经历了大的植物群重组和新种的演化。总体上，中国二叠纪—三叠纪陆生植物中选择性灭绝非常明显，古生代占优势的种子蕨、真蕨类、木本石松类和楔叶类逐渐被早中生代比较进化的裸子植物和真蕨类植物所替代，陆生植物穿过PTB 显示了危机（灭绝）—残存—复苏—辐射的宏演化式样。

A comparative study of thermolysis characteristics and kinetics of seaweeds and fir wood

Thermal analysis and thermolysis kinetics of three kinds of seaweeds and fir wood (M. glyptostriboides Huet Cheng), a kind of typical land plant, had been conducted. The results showed that thermal stability follows the order of Grateloupia filicina < Ulva lactuca < Dictyopteris divaricata < fir wood. A notable difference on heat flow between seaweeds and fir wood during thermolysis was that the former were mainly connected with exothermic processes at relatively lower temperature regimes. while the latter was connected with an apparent endotherm at a relatively higher temperature regime followed by a maximum exothermic peak. This suggested that the heat coupling might be realized if co-thermolysis of seaweeds and fir wood were carried out. The main devolatilization phase of each seaweed could be described by Avrami-Erofeev equation, which indicated that thermolysis of seaweeds follows the mechanism of random nucleation and nuclei growth, whereas that of fir wood by Z-L-T equation and its thermolysis mechanism was three-dimensional diffusion. The activation energies calculated for both seaweeds and fir wood increase as conversion increases. However, those for the former have wider distribution. (c) 2006 Elsevier Ltd. All rights reserved.

The effect of land management on carbon and nitrogen status in plants and soils of alpine meadows on the Tibetan plateau

Large-scale grassland rehabilitation has been carried out on the severely degraded lands of the Tibetan plateau. The grasslands created provide a useful model for evaluating the recovery of ecosystem properties. The purposes of this research were: (1) to examine the relative influence of various rehabilitation practices on carbon and nitrogen in plants and soils in early secondary succession; and (2) to evaluate the degree to which severely degraded grassland altered plant and soil properties relative to the non-disturbed native community. The results showed: (1) The aboveground tissue C and N content in the control were 105-97 g m(-2) and 3.356gm(-2), respectively. The aboveground tissue C content in the mixed seed treatment, the single seed treatment, the natural recovery treatment and the severely degraded treatment was 137 per cent, 98 per cent, 49 per cent and 38 per cent, respectively, of that in the control. The corresponding aboveground tissue N content was 109 per cent, 84 per cent, 60 per cent and 47 per cent, respectively, of that in the control. (2) Root C and N content in 0-20 cm depths of the control had an 2 2 average 1606 gm(-2) and 30-36 gm(-2) respectively. Root C and N content in the rehabilitation treatments were in the range of 26-36 per cent and 35-53 per cent, while those in the severely degraded treatment were only 17 per cent and 26 per cent of that in the control. (3) In the control the average soil C and N content at 0-20 cm was 11307 gm(-2) and 846 gm(-2), respectively. Soil C content in the uppermost 20 cm in the seeded treatments, the natural recovery treatment and the severely degraded treatment was 67 per cent, 73 per cent and 57 per cent, respectively, while soil N content in the uppermost 20cm was 72 per cent, 82 per cent and 79 per cent, respectively, of that in the control. The severely degraded land was a major C source. Restoring the severely degraded lands to perennial vegetation was an alternative approach to sequestering C in former degraded systems. N was a limiting factor in seeding grassland. It is necessary for sustainable utilization of seeding grassland to supply extra N fertilizer to the soil or to add legume species into the seed mix. Copyright (c) 2005 John Wiley & Sons, Ltd.