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洪水漫溢下胡杨(Populus euphratica)种子萌发及幼苗生长机制研究
于波
学位类型博士
导师赵成义
2015
学位授予单位中国科学院大学
学位授予地点北京
学位专业自然地理学
关键词洪水漫溢 种子散布 种子萌发 幼苗生长 幼苗更新
摘要塔里木河流域是我国胡杨林(Populus euphratica)保存最完整,分布最集中的区域,在中亚荒漠区占有极其重要的生态学地位。受气候变化和人类活动影响,胡杨的繁育特性、生态格局与过程发生了根本变化。很多文献报道了胡杨林沿河岸分布及幼苗的发生与河漫滩有关,但洪水漫溢在胡杨林繁殖更新、群落演替中的作用机制研究较少。本文以洪水漫溢为主控因子,通过野外观测、控制试验,研究了洪水漫溢对胡杨种子散布、着床、萌发、生长和存活的影响,建立了洪水漫溢下胡杨幼苗安全更新的概念模型,初步阐明了胡杨幼苗的自然更新机制。主要结论如下: (1)胡杨从7月中旬起开始散种,至9月底散种结束,散种高峰为8月下旬到9月中旬。胡杨种子散布以林缘为中心20m范围内种子密度较大,随着与林缘距离的加大种子密度逐渐减小。胡杨种子的散布期与洪水期在时间上一致。 (2)胡杨种子属短寿命种子,全光照条件下生活力只保持7d,遮阴条件下为40d。胡杨种子萌发时间短,遇水即能迅速萌发,初始萌发率达90%以上。胡杨种子萌发温度范围较宽,种子在5℃-40℃均能萌发;光照对种子初始萌发率无影响,种子属光不敏感型,但光照对胡杨胚芽形态建成有影响。水、盐对胡杨种子萌发有显著影响。胡杨种子的萌发率随水分的增加而增加,随盐分的增加而减小。当溶液水势为-2.04Mpa,或盐浓度为2.3%时,胡杨种子基本不萌发。 (3)胡杨幼苗在1-2cm/day的地下水位下降速率下长势最好,随着地下水位下降,能量优先分配给根生长,根的生长速率可达2.5mm/day。 (4)洪水淹没可减缓胡杨幼苗的生长,改变其生物量的分配模式,即减少根的分配比例,而增加茎、叶的分配比例。洪水完全淹没可抑制胡杨幼苗生长,排水后可恢复正常生长。长时间的洪水淹没,胡杨幼苗的存活率为100%,没有出现死亡现象,水淹茎杆部位出现大量的肥大皮孔,皮孔肥大是植物耐水淹的重要标志之一,表明胡杨幼苗具有耐水淹特性。 (5)洪水淹没可降低胡杨幼苗净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(E),同时叶绿素荧光参数Fv/Fm、Fv′/Fm′、ΦPSⅡ、ETR也随淹水时间呈下降趋势。洪水淹没引起的净光合速率的下降是由气孔因子和非气孔因子共同主导:气孔因子是由气孔导度减小而引起的气孔关闭;非气孔因子是由叶绿素含量和光合系统电子传递活力降低引起。胡杨幼苗在洪水淹没条件下,增加了可溶性糖和丙二醛(MDA)的含量,这是胡杨幼苗在逆境胁迫下的一种自我保护。 (6)洪水漫溢改变了河漫滩表层土壤的颗粒组成,增加了土壤容重,增强了土壤的持水能力。洪水漫溢增加了土壤的含水量和养分,减小了土壤的盐分含量,为胡杨幼苗的成功定居提供了理想的发生区。种子散布是在重力、风力、水冲击力共同作用下,构建了胡杨在河漫滩萌发早期的分布格局。 (7)洪水漫溢为胡杨繁殖更新提供理想生境的同时,当年洪水的多次反复和来年洪水的淹没、侵蚀和沉积导致大量幼苗死亡。 (8)初步构建了胡杨幼苗安全更新概念模型。胡杨幼苗安全更新的主要生态驱动力包括:区域的水文过程、种子的散布时机、幼苗抵御干旱和洪水的能力。区域水文过程决定了潜在种床和生长季地下水位变化的条件和有效性;胡杨种子寿命短,种子的散布时间决定了河岸区种子萌发的时空分布;胡杨幼苗更新出现在洪水消退期,抵御干旱和后来洪水的能力是胡杨幼苗长期存活的关键。只有三者关系形成耦合,胡杨幼苗成功更新才会出现。因此,胡杨幼苗的更新需要一定的时间间隔。
其他摘要Tarim River basin, the most complete preservation and concentrated distribution area of Populus euphratica in China, occupies an extremely important position in ecology of Central Asia desert area. The characteristics of breeding, ecological pattern and process of P.euphratica has been fundamentally changed by the impact of climate change and human activities. P.euphratica forest along the riverbank and seedlings distribution relate to the floodplain were mentioned in a lot of literature, but the details are vague. The effect of flood disturbance on occurrence and development of P. euphratica is poorly understood. There are few scholars pay attention to the effect of flooding on regeneration and community succession of P. euphratica forest. In older to investigate the effect of flooding on seed dispersal, implantation, germination, growth and survival of P.euphratica, control experiments were carried out. Through long-term field observations, the concept model of P. euphratica seedlings was established. This study can preliminarily clarify recruitment mechanism of P. euphratic, and also can provide a theoretical basis for recovery of P. euphratica forest recession in downstream of Tarim River. (1) The dispersal of the P. euphratica seed began in middle July, and ended in late September. Most of the populous seed distributed between end of August and mid-Sepetember. In spatial, the density of the seed is decreased with the distance increased. The highest seed density of populous is located around 20 m away from P. euphratic. The seed dispersal time of P. euphratic is consistence with the time of flooding. (2) The seed of P. euphratica is a type of short lifetime seed. The viability of seeds under full light and shading conditions was 7d and 40d respectively. The seeds of P.euphratica germinated rapidly. The temperature range for germination was from 5℃ to 40℃. The seed wasn’t sensitive to light. It could germinate under all light conditions. However, the light showed significant influence on the radicle growth. When the solution water potential was -2.04Mpa, or a salt concentration of 2.3%, P.euphratica seeds could hardly germinate. (3) The decreased of groundwater table is the main reason for the death of the P. euphratica seeding. The experiment showed that the best groundwater decreased speed for P. euphratica seeding growth is 1-2cm/day. The energy was distributed to growth of root priority, and the growth rate was 2.5mm/d with water table decline. (4) The inundation inhibited the development of the populous seedling, and changed the biomass allocation pattern. More accumulated biomass was distributed to stem and leaf, and less biomass was distributed to root after inundation. P. euphratica would not grow under long period of inundation, but after water was drainage, the populous would recovery to growth again. The survival rate of P. euphratica seedlings is 100% under long time period inundation. For adaption to the inundation condition, the lenticel hypertrophy occurred at stem, which indicate that the plant is a water resistant species. P. euphratica appears to be a flood-tolerant tree species. (5) Flooded seedlings showed a tendency for reduction of net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E) and intercellular CO2 concentration (Ci). This pattern also occurred in the Fv/Fm, Fv'/Fm', ΦPSII and qP parameters. A decline in net photosynthetic rate subjected to flooding not only depends on stomatal factors but also on non-stomatal ones. Stomatal closure is induced by the decline of stomatal conductance, and also by decline in the content of chlorophyll and phyotosynthetic electron transport activity. Flood resulted in an increase in the soluble sugar and MDA content. Under adversity stresses, plants start their own defense systems, which reduce the level of stress injury and maintain normal plant growth. (6) The inundation would change the particle size composition of soil on the floodplain, increase the soil density and the soil water capacity. At the same time, the inundation would increase the soil water content and nutrient; reduce the salt content in the soil. So the flood could provide suitable condition for P. euphratica seeding. The distribution of P. euphratica seeding is powered by force of gravity, wind and water. (7) P. euphratica seedlings become established on bare, moist and newly deposited sediment floodplain after flood recession. Flood inundation, scouring and deposition are the reasons for the mass mortality of P. euphratica seedlings. (8) The conceptual model has been developed to describe P. euphratica seedling safe recruitment. The key ecological drivers of P. euphratica seedling recruitment include three components: site hydrology, seed release timing, and seedling tolerance to arid and flood. Because these species have short lifetime seeds, dispersal timing controls when and where on the riverbanks seeds terminate. Recuitment typically occurs as floodwaters recede. The ability to resist drought and flooding is critical for long term survival. If only coupling the relationship between the three forms, seedling recruitment can occur. So it will take time for the successful recruitment of P. euphratica needs times.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14626
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
推荐引用方式
GB/T 7714
于波. 洪水漫溢下胡杨(Populus euphratica)种子萌发及幼苗生长机制研究[D]. 北京. 中国科学院大学,2015.
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