水淹胁迫下饲料桑苗的生长及光合响应

Growth and photosynthesis characteristics of mulberry under flooding stress

三峡库区消落带耐淹植物的筛选一直是该区生态系统修复的关键问题。该文利用室内水淹模拟试验研究了不同程度水淹胁迫下饲料桑苗的生长及光合响应特性。试验以1 a生饲料桑为材料,水淹胁迫分为对照、根淹、深淹等不同水平处理。结果表明:1水淹胁迫下根淹处理和深淹处理桑苗都生出不定根,根淹处理桑苗出现的涝害症状较轻,而深淹处理则从水淹5 d开始出现叶斑、黄化等症状,水淹结束严重落叶;2水淹明显影响桑苗的生长,影响程度为根淹小于深淹,且根淹处理桑苗能维持较高的株高、地径生长率;3水淹降低了桑苗的净光合速率、气孔导度和蒸腾速率。根淹处理桑苗的光合响应指标在水淹40 d明显低于对照处理,但仍能维持较高水平,之后随水淹时间增加没有明显变化,而深淹处理桑苗的光合响应指标在水淹55 d已很微弱。4深淹胁迫对桑苗水下叶片光合能力的影响大于对水上叶片的光合能力的影响。水淹55 d深淹处理水上叶片的净光合速率甚至和根淹处理很接近。因此1 a生饲料桑苗无法抵抗长期深淹,却可很好地适应根淹,适合在消落带海拔较高、水淹深度较浅的区域生长。研究为库区消落带的生物治理提供了理论支持。

Due to the seasonal variation of water level in the Three Gorges Reservoir, its surrounding region has turned into a large area of frequent water-fluctuation. The seasonal submergence causes an environment that can lead to difficulty in keeping living for most plants, and thus the serious degradation of vegetation in this area. It is important to screen the flooding-tolerant species for the ecosystem restoration of the water-fluctuation areas in the Three Gorges Reservoir. In this study, we conducted an indoor simulated flooding experiment to study the influences of different flooding stress on the growth and photosynthetic characteristics of mulberry seedlings. One-year seeding of Mulberry was chosen, and three flooding treatments were designed including control with regular irrigation but without submergence, root submergence and deep submergence. The water level in the root submergence treatment was 1 cm higher than soil surface. The depth of water in root and deep submergence was 24 and 60 cm. External morphology of Mulberry were observed during the experiment, the plant height were measured by a measuring tape, the ground diameters were measured by a vernier caliper,and the photosynthetic parameters were measured by Li-cor 6400. The results showed that: 1) The mulberries in the root submergence and deep submergence grew adventitious root, the damage symptoms of mulberries in root submergence group were mild, but the leaves in the deep submergence begun to turn yellow and rot on the 5th day of submergence and barely had leaves in the end; 2) The inhibitory influence of flooding stress on the growth of height and ground diameter of deep-submerged group was far more obvious than the root-all-submerged group; For example, on the 90 th day of submergence, the plant height increment of mulberry in the control group, root submergence and deep submergence were 19.5, 14.13 and 2.92 cm, respectively, which was significantly different(P<0.05); 3) The photosynthetic rate, transpiration rate and stomata conductance of mulberries were reduced by the flooding stress; Comparatively, the photosynthetic characteristic values in the root-all-submerged group could remain a higher level, for example, the maximum net photosynthetic rate was up to 65.4% of that in control group; The photosynthesis of mulberry in the deep-submerged group was very weak on the 55 th day, when the maximum net photosynthetic rate was only 23.7% of that in the control group, which was significantly different(P<0.05); 4) The photosynthesis characteristic values of the above-water leaves in the deep-submerged group were higher than those of the under-water leaves on the 55 th day, suggesting that flooding stress had the large influence on the under-water part of plant than on above-water part; On the 55 th day of submergence, the maximum net photosynthetic rate of under-water leaves and above-water leaves in the deep-submerged treatment are 2.53 and 1.14 μmol/(m2·s), respectively, which was significantly different(P<0.05). In conclusion, the one-year mulberry seedlings could not survive for a long time under the deep flooding stress, but they could live well in the root submergence condition. They are more suitable to be planted in high altitudes of water-fluctuation areas of the Three Gorges Reservoir area with low water level during the water storage season. The study could provide data support for selection of plant species in ecological reservation in the Three Gorges Reservoir.