地下水是影响西北地区植被分布、生长和群落演替的重要因子,通过人工装置模拟30 cm(D30)、40 cm(D40)、50 cm(D50)、60 cm(D60)、70 cm(D70)5个潜水梯度,从生长发育、根系形态、拓扑结构与分形维数以及表型可塑性四个方面来分析不同潜水埋深对单叶蔷薇幼苗的影响,力求揭示单叶蔷薇幼苗对不同水分环境的适应性策略,这将对今后开展单叶蔷薇植被恢复和保育工作具有重要价值。研究结果表明:(1)单叶蔷薇幼苗可通过增加扎根深度、总根长、根表面积、根体积、根尖数量、分支数量、地上干物质和根系干物质来应对不同潜水埋深带来的干旱胁迫,D50、D60、D70和CK处理下的幼苗还可以通过提高根冠比来适应更长久的干旱环境。(2)不同潜水埋深处理下,单叶蔷薇幼苗根系的拓扑指数基本保持在0.8-0.9之间,说明该根系属于典型的人字形分支模式,受环境影响较小。其中,短而细的密集细根(0-2 mm)构成了单叶蔷薇幼苗根系的主体。从资源分配的角度来看,该种拓扑结构相对简单、内部竞争较小、碳消耗少,有利于根系扩大土壤资源获取效率,从而保障植株生长发育的物质供需平衡,这是单叶蔷薇对环境胁迫的适应性策略。(3)适度的干旱,如50-70 cm的潜水埋深,可以促进单叶蔷薇幼苗扎根深度;而在较浅的潜水埋深(30-40 cm)环境中,单叶蔷薇幼苗能快速解除干旱,转向地上器官的生长发育,同时它通过降低垂直根系长度、增加分支和根尖数量来获取更多氧气和适应水分充足的新环境,到第75天时生长旺盛,在株高、总根长、根表面积、根体积、根尖数量、分支数量、地上干物质、根系干物质、根组织密度和分形维数10个指标上与CK组具有显著差异,说明单叶蔷薇幼苗对水分充足和严重干旱的极端环境均有较好的适应能力,表型可塑性强。
Groundwater is an important factor affecting vegetation distribution, growth and community succession in northwest China. By simulating 5 groundwater levels of 30 cm (D30), 40 cm (D40), 50 cm (D50), 60 cm (D60) and 70 cm (D70), this study analyzed the influence of groundwater levels on Rosa persica seedlings from the growth and development, root morphology, topology index and the fractal dimension and phenotypic plasticity, tried to reveal the adaptive strategies of R. persica seedings to different water environment, which would be of great value for carrying out its vegetation restoration and conservation work in the future. The results showed that: (1) R. persica seedlings could deal with drought stress from different groundwater levels by increasing the root depth, the total root length, root surface area, root volume, root tip number, branch number, above-ground biomass and root biomass. The seedlings under D50, D60, D70 and CK treatments could also improve the root-shoot ratio to adapt to more long-term drought environment. (2) The topological index of root of R. persica seedlings basically kept between 0.8 and 0.9 under different treatments of groundwater levels, indicating that its root belonged to a typical herringbone branching pattern and was less affected by the environment. Especially, short and dense fine roots (0-2 mm) constituted the main root system of R. persica seedlings. From the perspective of resource allocation, this kind of topology index was relatively simple, less internal competition and less carbon consumption, which was conducive to the root system to improve the efficiency of soil resource acquisition, so as to ensure the plant growth and development of resource supply and demand balance. It was an adaptive strategy of R. persica to environmental stress. (3) Moderate drought, such as 50-70 cm, could promote the root depth of R. persica seedlings, while in the shallow environment (30-40 cm), it could quickly relieve drought, and turn to the growth and development of above-ground organs. Meanwhile, it got more oxygen and adapted to new watery environment by reducing vertical root length, increasing the branch and root tip number. It thrived on the 75th day, and had significant difference in 10 indicators with CK group, including plant height, total root length, root surface area, root volume, root tip number, branch number, above-ground biomass, root biomass, root tissue density and fractal dimension, which demonstrated that R. persica seedlings had good adaptability and phenotypic plasticity to extreme environment, whether enough moisture or severe drought.