模拟喀斯特不同土壤生境下黑麦草对水分胁迫的生长和光合生理响应

以多年生草本黑麦草为对象,模拟喀斯特生境土壤特征设置浅而宽(Shallow and wide, SW:30×30×5 cm~3)和深而窄(Deep and narrow, DN:10×10×45 cm~3)两种土壤容器,以正常降水量为对照供水(W100%),设减水50%(W50%)和减水70%(W30%)共3种水分处理进行盆栽实验,探究了两种不同土壤生境中土壤水分变化对黑麦草生长及光合生理的影响,以进一步理解喀斯特地区植物的适应对策。结果显示:(1)SW生境对水分变化敏感,随供水减少土壤含水量显著下降。轻度减水下植物叶面积增大,光合速率提高,地上部分生长得到促进,但水分严重减少对其生长和光合生理有抑制作用,但地上质量分数和水分利用效率却显著升高;(2)DN生境保水能力较好,随供水减少土壤水分含量下降较为平缓。叶片相对含水量、气孔导度和比叶面积在各水分处理之间差异不显著,但严重减水条件下总生物量、地上质量分数和水分利用效率均有回升。研究表明:浅而宽生境中植物倾向于通过提高地上部分的生长,保持较高的光合速率,并向地上部分分配较多生物量来应对水分胁迫;而深而窄生境中植物会充分利用土壤空间条件,促进根系的生长来提高对水分的吸收,从而维持植物的生长。

Growth and photosynthetic physiological responses of Lolium perenne L. to water stress in the simulated karst soil habitats

In karst area, the soil thickness is uneven and the soil habitats are highly heterogeneous. Shallow soil habitats with shallow wide soil are formed on hilly slopes and deep soil habitats with deep narrow soil are formed in the rock trenches. Availabilities of underground space and soil moisture are different in different habitats. The previous studies have focused on the ecological effects of soil thickness changes. However, the underground space is also very important for plant growth, even exceeding soil resources. Therefore, studying the effects of soil thickness on plants must consider the important roles of soil moisture and soil space. In this experiment, we used the perennial grass Lolium perenne L. as plant material. Simulating the soil characteristics in karst habitats, we set two kinds of soil containers including shallow and wide (SW:30×30×5 cm³) and deep and narrow (DN:10×10×45 cm³). Taking average daily precipitation in Chongqing for the past 30 years as the control water, three water treatments were control group (normal water conditions, W100%), mild water reduction (50% reduction, W50%), and heavy water reduction (70% reduction, W30%), respectively. The effects of soil moisture changes on the aboveground growth and photosynthetic physiology of L. perenne in two different soil habitats were explored to further understand the adaptation strategies of plants in karst area. The main results were as follows:(1) The SW habitats were sensitive to soil water changes, and soil water content in which decreased significantly with decreasing water application. Under mild water reduction, the growth of aboveground parts was promoted, mainly in the increase of leaf area and photosynthetic rate. However, the growth and photosynthetic physiology were inhibited under heavy water reduction, while the aboveground mass fraction and water use efficiency increased significantly. (2) The DN habitats had better water retention capacity, in which the soil water content decreased slowly with the water supply reduction. The relative leaf water content, stomatal conductance, and specific leaf area were not significantly different among three water treatments. However, the total biomass, the aboveground mass fraction, and plant water use efficiency all rebounded under heavy water reduction. Overall, the results suggested that plants in shallow and wide habitats tended to maintain higher photosynthetic rate by increasing the growth of aboveground parts, and distributing more biomass in the aboveground parts to cope with water stress; while plants in deep and narrow habitats sufficiently used soil space to promote root growth to increase water uptake for maintaining plants growth.