Knowledge Resource Center for Ecological Environment in Arid Area
| 毛乌素沙地一年生植物沙蓬生活史重要阶段对变化环境的响应机制 | |
| 其他题名 | Response mechanisms of important life history stages in an annual plant Agriophyllum squarrosum to environmental change in Mu Us Sandland |
| 高瑞如 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 黄振英 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 每一种植物都发展出复杂的生存机制，以确保其能够在特定的环境中生存和发展。对于分布在温带半干旱区的植物来说，温度和水分是限制它们生长的主要因子。本研究以生长在我国北方半干旱区毛乌素沙地的一年生植物沙蓬为研究案例，以植物生活史几个关键阶段对温度和水分响应特征为线索，通过野外观测、野外控制实验和实验室实验相结合的方法，探讨了(1)种子特性及其对土壤温度和湿度变化的萌发响应；(2)地上与土壤种子库的年际动态对环境温度和降水变化的适应特征，以及(3)植株生长、结实格局、子代种子萌发特征等对降水格局变化(5个降雨量 × 5个频度，降雨量：448、364、280、196和112 mm；降雨频度：120、12、6、4 和1 d/次)的响应机制，以探讨未来气候变化背景下，温带半干旱区植物对变化环境的可能适应能力及适应机制。具体研究结果如下： 1. 对沙蓬新成熟种子萌发特性与环境因子关系的研究结果表明：(1)新成熟沙蓬种子存在非深度生理休眠，划破种皮和干燥贮藏均可促进种子萌发，湿/干循环可打破休眠，而低温层积处理则不能有效打破休眠；(2)黑暗和变温条件有利于种子萌发，渗透势-0.1 MPa、沙埋深度0.5 cm和14.0%沙土水分含量分别为种子萌发的适宜条件；(3)种子休眠特性(或萌发特性)呈现季节性周期变化：条件休眠(冬季)-非休眠(春季)-次生休眠(夏季和秋季)，这种休眠变化可能受季节性降雨和土壤温度调节，并且这也可能是沙蓬应对不利环境变化的策略之一。 2. 沙蓬种子同时具有气生和土壤种子库，两种子库在沙蓬生活周期中扮演不同的生态角色。沙蓬气生和土壤种子库的形成过程和幼苗出现的动态过程表明：(1)沙蓬种子在秋天成熟后，仅有少量的种子脱落，形成土壤种子库，大部分种子保留在植株上，形成气生种子库；(2)气生种子库在第二年春季开始散布，种子散布与风速成正相关；(3)先期形成的土壤种子库中种子在早春低温(5-15 °C)和黑暗下萌发较气生种子库高，因而早期出现的幼苗主要来自土壤种子库，而后期出现的幼苗则主要来自气生种子库散布的种子；(4)研究期间，早期出现的幼苗由于早春霜冻而全部死亡，后期出现的幼苗则可能存活至成功繁殖，因而早期出现幼苗的适合度可能低于后出现幼苗。以上结果说明，沙蓬气生和土壤种子库在种子萌发和幼苗行为上的差异导致其对种群维持贡献的不同，并且两种种子库风险均摊，采用两头下注对策来适应严酷的沙丘生境。 3. 降水格局变化对沙蓬植株的生长特性具有显著影响。(1)在所测定的5个降水量和5个降水频度中，极端降水(112 mm降水量和120 d降水频度)处理下，植株全部死亡；其它处理条件下，植株存活随降水量下降而降低，随降雨频度升高而增加；(2)植物叶片的光合、蒸腾、气孔导度及水分利用效率均随降水格局的变化而呈脉冲式变化，并出现阈值-延迟响应和脉冲-储存效应；(3)植株的功能性状(高度、总生物量和根、叶及繁殖生物量)均随降水量减小而降低，随降水频度的升高而增加，并且在降水量上的可塑性高于降雨频度；(4)植株的根冠比和叶生物量分配随降水量减小而增加，而繁殖分配则减小；根冠比随降水频度升高而增加，叶生物量分配减小，而繁殖分配则保持不变。研究结果不仅阐明了降水量和频度对植物生存和生长的影响趋势，也揭示了沙蓬通过功能性状的可塑性及营养和繁殖生长之间、根和叶生长之间的权衡及保持较为稳定的繁殖分配策略来适应未来降水格局变化。 4. 降水格局变化对沙蓬繁殖物候、结实及其分配和子代种子萌发也具有显著的影响。(1)相同降水频度下，随降水量减少，第一朵花开时间延迟(9-17 d)，而种子成熟提前(1-11 d)；相同降水量下，两者均不受降水频度影响；(2)相同降水频度下，随降水量减少，种子有变小的趋势，而相同降水量下，随降水频度的升高，种子有增大的趋势；(3)相同降水频度下，单株种子数量随降水量减少而减小，结实分配呈下降趋势，而相同降水量下，单株种子数量在4-6 d降水频度时最大，植物结实分配因降水量不同而不同；(4)相同降水频度下，子代种子萌发随降水量减少而增大；相同降水量下，种子萌发在4-6 d的降水频度下萌发最高。研究结果表明降水格局变化改变了沙蓬的繁殖物候、结实性状和子代萌发行为等生活史性状，而沙蓬则通过繁殖可塑性来适应未来降水格局变化。 综上所述，沙蓬种子在长期进化过程中形成非深度生理休眠、土壤种子休眠的季节性周期变化以及形成气生和土壤种子库等多种方式，来应对温带半干旱区冬季低温、早春霜冻和季节性干旱等不利条件的影响；同时，沙蓬改变繁殖物候、调整生物量分配、权衡种子数量与萌发等一系列生活史性状的可塑性组合来应对降水格局变化。因而，在未来气候变化背景下，沙蓬通过生活史各阶段的多种适应方式来应对半干旱区沙丘生态系统的温度和水分变化，从而使其种群能够得以维持、更新和发展。 |
| 英文摘要 | Every plant has evolved diverse survival strategies to ensure its survival and regeneration in specific environments. For plants inhabiting in temperate semi-arid region, water and temperature are the major factors that constrain their growth and development. The dissertation presents a case study of the responses of several important stages of life history of Agriophyllum squarrosum (Amaranthaceae), a pioneer and dominant species in Mu Us sand land in northern China, to variations in rainfall and temperature. A combined method of field survey, controlled field trial and laboratory experiments was used to explore (1) seed characteristics and germination responses to seasonal soil temperature and moisture fluctuations; (2) adaptation of the seasonal dynamics of aerial and soil seed bank to environmental temperature and rainfall; (3) effects of the projected rainfall patterns (5 rainfall amounts × 5 frequencies; rainfall amounts: 448, 364, 280, 196, 112 mm; rainfall frequencies: once/120 d, once/12 d, once/6 d, once/4 d, once/1 d) on plant growth, fecundity and offspring germination of the annual plant. The adaptive strategies of plants in temperate semiarid zone to the changing climate are also discussed. The results showed as follows: Firstly, the study of the relationship between germination of fresh A. squarrosum seeds and environmental factors showed that: (1) freshly matured seeds was in non-deep physiological dormancy which was broken by scarifying testa, dry storage and wet-dry cycling, but not by cold stratification; (2) seed germination under full darkness and alternating temperatures was higher than under alternating of light and darkness and constant temperature, and the highest germination occurred at osmotic potential of -0.1 MPa, soil depth of 0.5 cm and soil water content of 14.0%; (3) seed dormancy and germination showed seasonal pattern: conditional dormancy in winter → non-dormancy in spring → secondary dormancy in summer and autumn. This pattern might be regulated by seasonal rainfall and soil temperature and could be an adaptation to the unpredictable environment. Secondly, A. squarrosum has aerial and soil seed banks which function differently in the life history of this species. The study of formation of the two seed banks and seedling emergence dynamics showed that: (1) after maturation, only small proportion of seeds dispersed to soil seed bank, and the size of the aerial seed bank was higher than that of soil seed bank throughout the growing season; (2) seed release of aerial seed bank began in the Spring of the second year and was positively related with wind velocity; (3) compared with soil seed bank, seed germination from aerial seed bank was lower in low temperature (5/15 °C). Therefore, early-emerged seedlings were mainly from soil seed bank, and late-emerged seedlings were mainly from aerial seed bank; (4) early-emerged seedlings died due to frost, but seedlings that emerged during the following months survived to successfully reproduce, indicating lower fitness of early-emerged seedlings than that of late-emerged seedlings. Therefore, the differences in seed germination and seedling emergence between aerial and soil seed banks determine their different contributions to population maintenance, which forms the risk-spreading (bet-hedging) strategy to adapt to the harsh sand dunes. Thirdly, variation in rainfall pattern had significant effects on plant survival and growth of A. squarrosum. (1) for the five rainfall amounts and five frequencies, all plants died in extremes events (at all rainfall intervals with 112 mm rainfall, and at 120 d rainfall intervals across all rainfall amounts), and plant survival decreased with the decrease of rainfall amount or frequency, respectively; (2) photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency were “pulsed” with variation in rainfall pattern and showed threshold-delay response and pulse-reserve effect; (3) plant functional traits (height, total biomass, root, leaf and reproductive biomass) decreased with the decrease of rainfall amount and increased with the increase of rainfall frequency, and these traits showed higher plasticity to rainfall amount than to frequency; (4) root/shoot ratio and allocation of biomass to leaf increased with the decrease of rainfall amount, but reproductive allocation decreased; with the increase of rainfall frequency, root/shoot ratio increased, allocation of biomass to leaf decreased, and productive allocation kept relatively constant. Our results not only explain the effects of rainfall amount and frequency on plant survival and growth, but also highlight the roles of high plasticity in functional traits and trade-offs between vegetative and reproductive growth (maintaining a stable productive allocation) and between root and leaf growth in this species to cope with variable rainfall patterns. Finally, variation in rainfall pattern also had significant effects on reproductive phenology, fecundity and offspring germination. (1) with the decrease of rainfall amount at given frequency, the first flowering days were delayed for 9-17 days, and the seed matured days was advanced for 1-11days; the rainfall frequency had no impact on reproductive phenology at the same of rainfall amount; (2) seed mass decreased with the decrease of rainfall amount at given rainfall frequency, and seed mass increased with the increase of rainfall frequency at given rainfall amount; (3) the number of number per plant and fecundity allocation decreased with the decrease of rainfall amount at given rainfall frequency, and the peaks of seed number per plant were showed at rainfall intervals of 4-6 days, but the fecundity allocation depended on the rainfall amount, at the same of rainfall frequency; (4) offspring germination increased with the decrease of rainfall amount at given frequency, and the peak of offspring germination occurred at rainfall intervals of 4-6 days at the same of rainfall amount. Therefore, variation in rainfall pattern changed reproductive phenology and fecundity of A. squarrosum, and further changed germination behavior of offspring seeds, suggesting that reproductive plasticity enables the species to cope with the climate change in semi-arid sand dune ecosystems. A. squarrosum has evolved diverse strategies, such as non-deep physiological dormancy, dormancy cycling of soil seed bank and formed both aerial and soil seed bank, to cope with the unfavorable conditions in the temperate semiarid zone (cold winter, spring frost and seasonal drought). In addition, the combined plasticity in life history traits of change in reproductive phenology, adjustment of biomass allocation, trade-off between seed number and germination were developed to cope with the variation in rainfall pattern. Therefore, under future climate change, A. squarrosum can use diverse adaptive strategies in different stages of life history to adapt to variations in temperature and rainfall, and to maintain population persistence and regeneration in semi-arid sand dune ecosystems. |
| 中文关键词 | 适应对策 ; 沙蓬 ; 气候变化 ; 休眠循环 ; 种子库 |
| 英文关键词 | adaptive strategy Agriophyllum squarrosum climate change dormancy cycling seed bank |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院植物研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287633 |
| 推荐引用方式 GB/T 7714 | 高瑞如. 毛乌素沙地一年生植物沙蓬生活史重要阶段对变化环境的响应机制[D]. 中国科学院大学,2015. |
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