中国科学院西双版纳热带植物园机构知识库

作为多年生、木质化单子叶植物，竹类植物具有无次生生长、高生长速率、承担水分运输和储存功能的茎干竹壁较薄、茎干内维管束呈散点状不均匀排列以及具有庞大的地下茎系统等特点。竹类植物的水力结构比较特殊，因此它们的水分运输及利用方式可能有别于其它植物类群。然而，目前对竹类植物水力结构、水分利用及其生态适应性还没有进行过系统研究。本研究主要从以下四个方面来探讨竹类植物的水力结构、水分关系及其叶片对异质光环境的可塑性与适应性：（1）以自然分布在亚热带中山原始森林中的箭竹（Sinarundinaria nitida）为实验材料，通过测定其叶片和茎干的水分状态、导水率、气体交换以及根压的日变化，研究竹类植物的茎干和叶片在水力结构和日间水分利用方面的协同作用；（2）通过测定两个不同地区的同质园内54个竹种的根压和竹茎干的最大生长高度，研究来自热带和亚热带地区不同竹种的最大生长高度与其根压的关系，探讨限制竹类植物最大生长高度的机制；（3）通过比较生长和分布在异质光环境下（林缘和林下）箭竹（S. nitida）叶片在形态、结构和生理功能方面的可塑性，解释竹类植物能够在异质光环境中存活、生长和自然分布的机理；（4）为探究竹类植物的水分运输及利用方式，以一种高大的木质化丛生竹（黄金间碧竹，Bambusa vulgaris）为实验材料，我们利用热消散探针（TDP）测定竹茎干液流的日变化及季节变化。实验结果表明：（1）箭竹的叶片导水率和气孔导度的日间下调有助于减缓箭竹茎干中水分散失，从而避免竹茎干水分运输系统中导管发生气穴化，同时依靠夜间根压修复栓塞化的导管，将中午降低的叶片导水率恢复到其正常最大值，从而保持正常的水分运输功能。竹类植物的茎干和叶片中水分运输系统可以通过它们之间的协同作用和水力结构调整来保证整个植株水分运输系统的日间效率和安全性，使其能够适应短期日间水分亏缺。（2）无论是热带丛生竹种，还是亚热带散生竹种，竹类植物茎干的实际最大高度值与由夜间最大根压所推测的高度值相符。此外，竹类植物的水分传导运输系统主要依靠根压来修复植株水力结构功能障碍，进而维持叶片正常的日间水分运输，从而保证气体交换正常进行。因此，我们推测根压在修复竹类植物木质部气穴化导管中发挥着重要作用，根压可能是限制竹类植物的最大生长高度的重要因子。（3）与自然分布在林缘的箭竹叶片相比，林下的箭竹具有较大的叶片面积、较高的比叶面积、单位叶片干重的氮含量和单位叶片面积的叶绿素含量，较低的叶片厚度、叶脉密度、气孔密度、单位叶片干重的碳含量和总可溶性糖含量。另外，林缘的箭竹具有较高的最大光合速率、暗呼吸速率、非光化学淬灭及电子传递速率。叶片形态、解剖结构和生理特性等方面较强的可塑性可使得竹类植物能够在异质光环境下存活、生长和分布。（4）黄金间碧竹的茎干液流密度对不同环境气象因子的响应具有明显的季节差异。在雨季，黄金间碧竹茎干液流密度随着大气温度（Ta）的升高而线性增加，而在旱季，它的茎干液流密度随Ta的变化呈现出S型增长趋势；无论是在旱季还是雨季，白天茎干液流密度与饱和蒸汽压差均为指数曲线关系。与树木不同，黄金间碧竹的茎干储存水有可能被用于下午时段的蒸腾。根压驱动夜间茎干液流，除了修复发生气穴化的木质化导管外，还可以补充茎干储存水，从而维持整株植物的日间水分平衡。本论文通过对竹类植物水力结构、水分关系及其生态适应性的研究和讨论，有助于我们深入理解竹类植物的茎干和叶片中水分运输系统的协同作用、根压的重要作用、竹叶的结构和功能特征对不同光环境的可塑性以及竹类植物水分运输的季节性规律等。本研究结果对理解和预测单子叶植物（如竹类植物）对全球气候变化的响应具有一定的借鉴意义。

As woody monocotyledonous perennial grasses, bamboo species not only lack the capacity for secondary growth and exhibit rapid growth, but also have a thinner culm wall used for water transport and storage, random scatted vascular bundles in the culms, and large numbers of rhizomes. Bamboos may have unique hydraulic architecture that distinguish their water transport and water use characteristics from other plant groups. However, there is little knowledge about hydraulic architectures and water relations of bamboo species and their ecological adaptation. In the present study, bamboo hydraulic architecture, water relations of bamboo species and bamboo leaf plasticity to contrasting light environments were studied focusing on the following aspects:(1) By using a bamboo species (Sinarundinaria nitida (Mitford) Nakai) grown in subtropical evergreen broadleaf forest, we measured daily changes in water status of culm and leaf, hydraulic conductivity, gas exchange and root pressure. We tried to understand the coordination between bamboo culm and leaf in hydraulic architecture; (2) After measuring root pressure and the maximum culm growth height of 54 bamboo species grown in two common gardens, we investigated the relationship between the maximum height and root pressure in bamboo species from the tropical and subtropical areas. We tried to provide a new basis for understanding of the limits for plant growth height; (3) After comparing the leaf morphological, anatomical and physiological responses of a subtropical woody bamboo (S. nitida) to contrasting light environments (forest edge and understory), we attempted to understand the mechanism underlying the survival, growth and natural distribution of this bamboo species in heterogeneous light habitats;(4) In order to investigate water use patterns of woody bamboo species, we used thermal dissipation probes to monitor the seasonal and diurnal variations in sap flow of a woody, sympodial bamboo species (Bambusa vulgaris Schrader ex Wendland).Our results and conclusion were as follow:(1) Diurnal loss of leaf hydraulic conductance (Kleaf ), as well as midday depression in stomatal conductance, may help to prevent water loss and bamboo culm xylem embolism. Recovery of Kleaf did not occur during the day under negative pressure, therefore embolism refilling of this bamboo species may fully depend on positive root pressure occurring at night. Uncoupling of stem hydraulics from leaf hydraulics prevents culm xylem dysfunction and helps maintain adequate water balance of this bamboo species under both high and low light environments. The coordination between water transport systems in bamboo leaves and culms could be helpful for the growth and persistence of this woody monocot species.(2) The maximum heights of culms of bamboo species, both coming from the tropical and subtropical areas, were closely predicted by their maximum root pressure at night. We demonstrated that the water transport system of bamboo species is dependent on root pressure to repair hydraulic dysfunction sustained during normal diurnal gas exchange. We confirmed that the critical importance of root pressure in bamboo species and root pressure dependent refilling xylem embolism limit the maximum height of bamboo species.(3) Compared with leaves of S. nitida in open areas, its leaves in shaded areas had higher values in leaf size, specific leaf area, leaf nitrogen and chlorophyll concentrations per unit area but lower values in leaf thickness, vein density, stomatal density, leaf carbon concentration and total soluble sugar concentration. Leaves in the open habitat exhibited a higher light-saturated net photosynthetic rate, dark respiration rate, non-photochemical quenching and electron transport rate than those in the shaded habitat. This bamboo species exhibited a high plasticity in leaf structural and functional traits in response to different irradiance. The combination of high plasticity in leaf morphological, anatomical and physiological traits allows this bamboo species to grow in heterogeneous habitats.(4) There were evident seasonal patterns in the relationships between sap flux density (Fd) of a woody, sympodial bamboo (Bambusa vulgaris) and meteorological factors, including photosynthetically active radiation, air temperature (Ta) and vapor pressure deficit (VPD). In the rainy season, Fd increased linearly with the increase of Ta, whereas in the dry season, it increased sigmoidally. In both the rainy and dry seasons, daytime Fd responded to VPD exponentially. Sap flow of this bamboo species was also found to occur at night, suggesting that positive root pressure may be the primary force driving their water transport and culm water recharge during the night. Such water use strategies of B. vulgaris contribute to its diurnal water balance.Investigation of hydraulic architecture, water relations and ecological adaptation of bamboo species enable us to deeply understand the coordination between culm and leaf water transport systems of bamboos, the important function of root pressure, the plasticity in bamboo leaf structural and functional traits to different light environments, and seasonal water transportation characteristic of bamboo species. These results are crucial in predicting how monocotyledonous perennial grasses such as bamboo species respond to global climate change.