【作者】 张强；

【导师】 曹坤芳；

【作者基本信息】 中国科学院研究生院（西双版纳热带植物园） ， 生态学， 2008， 博士

【摘要】 附着在树干、岩石表面、不从宿主上获取养分且不扎根于地面土壤的蕨类植物被称为附生蕨类植物,是热带雨林森林生态系统的重要组成部分。与地生蕨类植物相比,由于附生蕨类植物无法直接从土壤中吸收水分,忍受干旱胁迫是附生植物经常要经历的事情,因此保持体内必要的水分是其生存的关键因素。很多附生蕨类植物生长在林内光线很弱的环境下,因此它们对光斑的利用能力将影响它们的生长和发育。本研究通过对比附生和地生两种生活型的蕨类植物对干旱的响应来评价它们对干旱胁迫适应能力的差别;与半附生和地生两种生活型的榕属植物进行对比,研究蕨类植物对光斑的利用策略。此外,本研究还报道了西双版纳山地雨林蕨类植物的多样性。在控水实验中,对生长在4%光强下盆栽的2种附生蕨类(鸟巢蕨和星蕨)和2种地生蕨类植物(网脉铁角蕨和拟薄唇蕨)进行停水处理直到气孔完全关闭或接近关闭。研究结果发现:2种附生蕨类植物的叶片相对含水量(RWC)下降幅度明显低于2种地生蕨类植物,并且附生蕨在较高的叶片RWC下就关闭气孔。光合速率(An)、气孔导度(gs)和蒸腾速率(Tr)随着叶片RWC的下降而降低。35天干旱处理后,2种地生蕨类植物的An、gs和Tr均降到非常低的水平;49天干旱处理后,2种附生蕨类植物的An、gs和Tr均降到非常低的水平。地生蕨类植物复水9天,附生蕨类植物复水3天后其光合能力均已恢复。2种附生蕨类植物凌晨和正午Fv / Fm的值在水分胁迫期间并没有显著降低,附生鸟巢蕨的Chl NDI的值在整个水分胁迫期间也并没有显著下降,附生星蕨的Chl NDI的值虽然在水分胁迫期间有显著性下降,但复水后能快速地恢复到对照水平。2种地生蕨类植物凌晨和正午Fv / Fm的值在干旱处理的第28 d开始显著性的下降,但其值仍然在0.75以上,表明只发生了轻微的光抑制,而且复水9 d后光抑制解除。地生网脉铁角蕨的Chl NDI的值在干旱处理的第14 d开始显著下降,地生拟薄唇蕨的Chl NDI的值在第21 d后开始显著下降,但2种地生蕨的Chl NDI的值在复水9天后均能恢复对照水平。Fv / Fm和Chl NDI的结果表明在整个水分胁迫期间4种蕨类植物的光系统II的反应中心并没有受到不可逆的破坏,光合速率的下降主要是气孔关闭的结果。复水之后,4种蕨类植物的CO2同化能力能够快速恢复也证明了这一点。森林中4种蕨类在其自然生长方式下(即,地生或附生)的叶片相对含水量和叶绿素含量在干季和雨季并没有显著的差异,类胡萝卜素含量在旱季有显著提高。此外,它们的干季最大净光合速率和最大气孔导度显著低于雨季。由于附生蕨类植物在水分胁迫中能够保持光合系统的完整性、保持叶绿素含量的稳定性以及复水之后能够快速恢复,这是附生植物能够适应频繁水分胁迫的附生生境的重要原因。在光合诱导实验中,对12种植物对光斑的响应和光合诱导维持能力进行了测定。这12种植物包括6种蕨类植物和6种榕属植物。蕨类植物和榕属植物分别包括附生和地生2种生活型。研究结果发现:6种地生植物除了拟薄唇蕨和三叉蕨的诱导速率较慢外,其它4种地生植物种类达到最大净光合速率的90%所需要的时间(T90)为5.24 ~ 7.79 min,地生榕属植物的光合诱导响应时间T90明显比同属的3种半附生榕属植物要短,这有利于3种地生榕属植物在光斑下进行较快速的光合诱导,获得较高碳产量和维持较大的量子产额。而半附生榕属对光合诱导迟缓的反应可能是其幼苗阶段为了适应附生环境以保护水分为先的特性。诱导过程的快慢与初始气孔导度有关,初始气孔导度高的植物达到最大光合速率50%和90%所需的时间也相应较短。但初始气孔导度对T50和T90的影响均有一个阈值(50 mmol H2O m-2 s-1)。在光斑消失后,12种研究材料的光合诱导状态并没有立即消失,20分钟时仍然维持较高的诱导状态。从叶片结构来看,与地生植物相比,附生(包括半附生)植物有厚而密的叶片。从气孔特征来看,蕨类植物的气孔大而稀疏,但榕属植物的气孔小而密。蕨类植物的光合能力明显比榕属植物的低。此外,本文还对西双版纳热带山地常绿阔叶林蕨类组成特点及其数量特征等的进行了调查,根据4个50×50 m样地(400个5x5m小样方,共计1ha取样面积)的详细调查及对各样地外沿50m范围内蕨类的采集调查统计发现:滇南热带山地常绿阔叶林里记录有蕨类植物64种,以地面芽和地下芽生活型为主。在叶片特征上,以革质和纸质叶居多。蕨类植物有明显的季相变化;狗脊(Woodwardia japonica)、疏叶蹄盖蕨(Athyrium dissifolium)、苏铁蕨(Brainea insignis)、光叶鳞盖蕨(Microlepia calvescens)、清秀复叶耳蕨(Arachniodes spectabilis)和假稀羽鳞毛蕨(Dryopteris pseudosparsa)的重要值之和占蕨类植物重要值总和的84%,其中,狗脊的重要值占重要值总和的1/3以上,这6种蕨类植物是该森林群落中占优势的蕨类种类,为该森林群落的适宜种。勐腊凤尾蕨(Pteris menglaensis)为该森林群落的确限种。更多还原

【Abstract】 Epiphytic ferns grow above the ground surface, using other plants or objects such as rocks for support and do not obtain nutrients from their hosts. They are an important component of tropical rainforest ecosystems. Epiphytic ferns do not directly absorb water from the soil in the ground and frequently experience drought stress. Therefore, the ability of maintaining necessary water content is a key factor for the survival and growth of epiphytic ferns. The habitats of epiphytic ferns are associated with the dim light environment under the forest canopy or in the forest understorey; therefore, the ability of light-fleck utilization affects their growth and development. In the present study, the differences in adaptation to water stress were assessed by comparing the responses of epiphytic and terrestrial fern species to drought stress. The strategies of light fleck utilization of these two life-form ferns were also studied, with a comparison to those in hemiepiphytic and terrestrial figs. Moreover, the diversity of ferns in tropical montane rain forests in Xishuangbanna of Southwest China was also reported in the study.Using potted plants of two epiphytic fern species (Neottopteris nidus (L.) J. Sm and Microsorium punctatum (L.) Cop.) and two terrestrial fern species (Asplenium finlaysonianum Wall. ex Hook. and Paraleptochilus decurrens (Blume) Copel.) grown under 4% daylight, an experiment of simulated drought stress and subsequent rehydration was done. Leaf relative water content (RWC) in two terrestrial fern species declined more rapidly and to greater extent than that in two epiphytic fern species in the simulated-drought experiment and two epiphytic fern species closed their stomata at relatively high RWC level. Net photosynthetic rate (An), stomatal conductance (gs) and transpiration rate (Tr) decreased with decreasing leaf RWC. The An, gs and Tr of the two terrestrial and two epiphytic fern species studied declined to the much lower values (35 days and 49 days, respectively) and returned to the values of the control quickly after several days rewatering (3 days and 9 days or more, respectively). The values of Fv/Fm at predawn and midday in the two epiphytic fern species did not decline significantly during the whole period of the water-withholding experiment; moreover, the values of Chl NDI values, a spectral index of chlorophyll content, did not significantly decline during the water-withholding experiment in N. nidus. The Chl NDI values declined significantly during the water-withholding experiment in M. punctatum, however, it could return to the level of the control quickly after re-watering. The values of Fv/Fm at predawn and midday began to decline significantly from 28th day in the terrestrial fern species, while the values were still higher than 0.75, which indicated that slight photoinhibition occurred. The slight photoinhibition was relieved after re-watering for 9 d. The Chl NDI values began to decline significantly in A. finlaysonianum and P. decurrens from 14th and 21th day, respectively, and returned to the level of the control after re-watering for 9 d. These results indicated that no irreversible damage occurred in reaction center of photosystem II of all the four fern species studied and the decline of An may be due to stomata closure. The quick recovery in CO2 assimilation rates after rehydration also supported this. In their respective native habitats of the 4 fern species in a rainforest, no significant differences in leaf RWC and chlorophyll content were found between the rainy and dry seasons for all of the four fern species. However, their maximum net photosynthetic rates and maximum stomatal conductance in the rainy season were significantly higher than that in the dry season. The ability of maintaining integrity of photosystems and stable chlorophyll content during the water-stressed periods and rapid recovery of photosynthetic capacities after rewatering in water-stressed epiphytic ferns were probably the reasons for the survival of epiphytic ferns in the drought-prone epiphytic habitat.The photosynthetic induction and induction maintenance were examined on the potted plants of six fern species (three epiphytic and three terrestrial species) and six fig species (three hemi-epiphytic and three terrestrial species) grown under 4% daylight. The time required to reach 90% full induction state (T90) in six terrestrial species except for Pseudodrynaria coronans and Tectaria subtriphylla (15.92 and 16.25 min, respectively) was 5.24 ~ 7.79 min. T90 of three terrestrial fig species was significantly shorter than that in three terrestrial fig species, which was beneficial for light-fleck utilization of the terrestrial figs. The induction time required 50% and 90% maximum photosynthetic rate was nonlinearly and negatively correlated with initial stomatal conductance (gs-initial). Species with higher gs-initial tended to had shorter time required to reach 50% and 90% full induction state, with a threshold value of gs-initial at 50 mmol H2O m-2 s-1.According to the data from 4 sampling plots of 50 x 50 m (divided into 400 small plots of 5 x 5m), floristic composition and ecological characteristics of fern communities in a tropical montane rainforest in Xishuangbanna were studied. Totally, 64 fern species were recorded from the forest. These ferns were dominated by chamaephytes and geophytes with leathery and papery leaves. These ferns showed obvious seasonal change in physiognomy. Six fern species, including Woodwardia japonica, Athyrium dissifolium, Brainea insignis, Microlepia calvescens, Arachniodes spectabilis and Dryopteris pseudosparsa, had 84% of the important value (IV) summed from the total fern species. The IV of Woodwardia japonica was above 1/3 of total. This indicates these six fern species dominate the montane rainforests and are preferential species. The fern species Pteris menglaensis is the exclusive species of the montane rainforests.? ?更多还原