【作者】 赵兴征；

【导师】 王根轩；

【作者基本信息】 浙江大学 ， 生态学， 2006， 博士

【摘要】 快速城市化过程导致城乡区域环境差异,进而影响植物的生长和发育。叶片气孔是植物与外界环境进行物质、信号交流的门户,调控着光合和蒸腾等生理过程,进而影响植物生物量积累。目前,城市环境对植物生长影响方面的研究结果还存在很大分歧,具体调控基础和机制还不清楚。本研究以快速城市化的中等城市杭州为研究区域,亚热带常绿阔叶乔木樟树为研究对象,利用年轮宽度指数分析法研究了时间尺度上不同城市化阶段对植物生长量的影响,同时对叶片气孔分布格局、发育途径及其生态功能等进行了初步探讨。得到如下主要结论: 1.城市化在时间尺度上对香樟生物量积累的生态效应表现为由抑制转变为促进。在研究时段内,以农村区域作对照,计算时间序列上城市化对樟树的生态效应值,结果显示1994年以前,城市化对树木生长的影响主要是负效应,生态效应值为-0.10左右,1998年以后,城市化对樟树的生长表现出明显的促进效应,生态效应值在0.13左右。另外,物候期的观测结果表明城区樟树物候期提高20天和总生长季增加约2个月。 2.樟树叶片邻体气孔在叶片较早成熟部位分布较多,主要有聚群分布的气孔前体直接发育形成、新产生气孔与已有气孔相邻及气孔间表皮细胞分裂并被保卫细胞推开而间接形成三种发育途径。其中前两种途径已有相关报道,而第三种途径是我们所提出的假说,用来解释樟树叶片邻体气孔数量与总叶片气孔数量变化趋势不同步现象。 3.樟树叶片邻体气孔具有局部“增湿保水”的生态功能,有利于提高植物叶片的水分利用效率。与单独分散分布的气孔相比,邻体气孔表观直径增加,叶片外部水分扩散壳的总表面积减小,在叶片表皮气孔外围局部小范围内形成较高空气湿度,降低通过气孔的水分扩散速率。同时由于气孔导度的变化对水分蒸发的影响远大于对CO₂吸收的影响,所以邻体气孔结构在大幅度降低水分蒸发散失的同时,对吸收CO₂的抑制作用并不明显,从而可以提高植物叶片水平的水分利用效率。这被称为叶片邻体气孔的局部“增湿保水”假说。试验结果也表明邻体气孔密度的增加可以显著提高叶片水分利用效率。另外,邻体气更多还原

【Abstract】 Obvious environmental gradients between urban and rural areas brought by rapid urbanization progress all around the world strongly impact the growth and development of plant. Stomata are the "gateways" of substances and signals intercommunion between the interior of the leaf of plant and the atmosphere, with the functions of regulating plant physiological processes such as photosynthesis, respiration and transpiration so much as the biomass producing. Nowadays, there are great arguments on the effects of urbanization on plant growth, and it is even little known about the controlling foundations and mechanisms.Hangzhou, a middle city with rapid urbanization progress in China, was taken as the investigation area and Cinnamomum camphor a L. Presl, a broadleaved evergreen at subtropical zone was taken as the study object in this research. The plant biomass growth at different urbanization levels along time series were investigated with the utilization of tree ring width analytical method, and at meanwhile, the stomata distribution patterns were quantified, the development pathways were traced and the ecological functions of stomata cluster on leaf surface were primary discussed. The main results and conclusions are as follows:1. Effects of urbanization on plant growth shifted from negative to positive.By surveying the tree ring width index of C. camphor a, the data between 1986 and 2004 were analyzed, and the results indicated that the impacts of urbanization on tree growth was found shifting from negative to positive during the urbanization progress. And the effects on plant growth of urbanization shifted from -0.10 to 0.13. What’s more, the plant phenophases in urban sites were about 20 days ahead of the time at rural areas.2. The stomatal clusters distribute along the leaf veins and increase gradually from the newly generated parts to older parts, and they were developed by the clustered arranged meristemoids directly, or by means of the divisions of neighbor cells to form new stomata contacted presented stomata or little stomata pushing the epidermal cells between them aside on leaves of C. camphora.Stomata are usually scattered in the leaf epidermis and separated from one another by a stomata-free region preventing direct contact between the stomata in most wild-type plant species. However, stomata on leaf epidermis in C. camphora havenot been found distributed completely scattered, rather a few of them are arranged adjacently to form stomatal clusters. The study results of observing the stomata distribution pattern over the abaxial surface of the whole leaves showed that stomatal clustering occurs along the veins and stomatal cluster increased gradually from the apex to the base and the middle part to the margin part. The first two pathways have been documented by many researchers based on the observations of Arabidopsis thaliana L. Heynh. And the third one which had a strongly impact on the development as well as the pattern of stomatal clusters.is brought forward by us to explain the phenomenon that the stomatal cluster index (SCI) gradually increased while the stomata index (SI) decreased along with leaf development series.3. The stomatal clusters on leaf lower surface of C. camphora have the ecological function of "increasing local air humidity and conserving plant water" , and favor to improve plant water use efficiency (WUE).It is well known that when molecules pass though a pore, molecules which reach the edge will "spill over" and in effect have a shorter diffusion distance to get away from the pore, then water evaporates most rapidly around the outer edge, the perimeter of a pore. Water evaporates more rapidly from many small pores than from a few large ones, because the size of the perimeters added together is much greater. Compared with the one stomatal spacing pattern on leaf surface, the efficientperimeter and the diffusion shell surface area is much lower at stomatal clusters with stomata contacted each other directly, and then the water lose through stomata was reduced. And the effects of stomata on diffusion of CO2 are much weaker than that on water. Then we hypothesized that the WUE may be increased on leaves with more stomatal clusters.The evidences indicated that the leaves with the highest stomatal cluster density(SCD) and SCI have the highest WUE, while the stomatal density (SD) changedlittle, additionally, the SCD had negative correlation with soil moisture. Then weconcluded that the structure of stomatal cluster is favor for plant water conservation.These results may validate our hypothesis to a certain degree.The results of urbanization at different urbanization levels have different effects on plant growth may account for the arguments on the effects of urban environments on plant growth. Hypothesises of development pathway of stomatal cluster and their ecological function of "increasing local air humidity and conserving plant water" are based on our experimental phenomenon, it need more exactitude tracing observations to testify. If they are attested to be true, the hypothesises will not only indicate the physiological mechanism of stomatal cluster distribution pattern in nature, but also provide a new idea for biological water conservation, namely discovering and cloning plant high water use efficiency genes by modern biological techniques, and using the correlation genes to cultivate new high water use efficiency crop species, and then the problem of low agriculture water use efficiency will be settled.更多还原