虾池清塘排出物沉积厚度对老鼠簕幼苗的影响

模拟直接排入红树林的虾池清塘排出物在林地的不同沉积厚度（0、2、4、8 cm），研究其对培养424 d的红树植物老鼠簕（Acanthus ilicifolius）幼苗生长和生理的影响。清塘排出物的加入对老鼠簕幼苗茎高、基径、叶片数、叶面积、生物量和相对生长率等生长指标都有显著促进作用。总体长势表现为沉积厚度8 cm>4 cm> 2 cm>0 cm。生长指标显示只需少量清塘排出物的沉积（沉积厚度2 cm、4 cm）就能对幼苗的生长产生明显的促进作用，但大量排出物沉积的积累并不会带来更明显的促进作用。清塘排出物沉积的加入能显著提高叶片光合能力，尤其利于叶绿素a的合成。沉积厚度2 cm和4 cm时，幼苗叶片游离脯氨酸的积累并不显著，但丙二醛、可溶性糖、可溶性蛋白含量显著高于正常水平；沉积厚度8 cm则使叶片中游离脯氨酸、丙二醛和水溶性化合物均有大量积累；而叶片中抗氧化酶活性只有在大量沉积物加入（沉积厚度8 cm）时才显著低于对照组水平。总之，老鼠簕幼苗对清塘排出物沉积厚度4 cm以下具有较强的抗逆性和适应力，沉积厚度8 cm会使老鼠簕幼苗受到一定程度的逆境伤害，但本实验期间还未影响其生长。

Effects of sedimentation thickness of shrimp pond cleaning discharges on Acanthus ilicifolius seedlings

In landward coastal zones of most mangrove swamps in China, there are many shrimp ponds with surface sediments rich in nutrients such as N and P. During pond cleaning periods, some of these surface sediments are usually directly discharged into mangrove swamps after being flushed by using high-pressure hydraulic giants. Gradually, these sediments from shrimp ponds will accumulate on the floor of mangrove swamps, resulting in the increase in sedimentation thickness. However, the effects of sedimentation of shrimp pond cleaning discharges on mangrove ecosystems are still unknown. Therefore, to study their responses and endurances in growth and physiological characteristics, four thickness treatments (0, 2, 4, 8 cm) were applied to simulate the sedimentation condition of shrimp pond discharges into the mangrove swamp, and Acanthus ilicifolius seedlings were cultivated under these treatments for 424 days. In terms of growth indexes, including stem diameter, stem height, leaf number, leaf area, total biomass and relative growth rate, growths of A. ilicifolius seedlings were promoted due to the sedimentation of shrimp pond cleaning discharges. The growth condition of A. ilicifolius seedlings under four treatments followed the order of 8 cm > 4 cm > 2 cm > 0 cm. Results also indicated that a small quantity of cleaning discharges (sedimentation thickness of only 2 cm) could obviously enhance the growth of A. ilicifolius seedlings, and this enhancement would not be stronger comparing with the increasing of the sedimentation thickness. The sedimentation of shrimp pond cleaning discharges enhanced the leaf photosynthetic capacity, especially synthesized more chlorophyll a. With 2 and 4 cm sedimentation thicknesses, contents of MDA, soluble protein and soluble sugar in leaves were significantly higher than normal levels, but there was no significant accumulation of free proline in leaves; 8 cm sedimentation thickness resulted in abundant accumulation of MDA, soluble protein, soluble sugar and free proline in the leaves; only in the 8 cm sedimentation thickness group, activities of antioxidant enzymes in leaves were significantly lower than the control group. In a conclusion, A. ilicifolius seedlings had strong endurance and adaptability to shrimp pond cleaning discharges with the sedimentation thickness less than 4 cm; a sedimentation thickness of over 8 cm resulted in stress damages to seedling physiology, but the damage to seedling growth was not obvious during this experiment period. Impacts of sedimentation of shrimp pond cleaning discharges on mangrove ecosystems will be long and profound. Related government departments should attach great importance to it, enhance the management and monitor of mangroves nearby aquaculture areas, and balance the relationship between the development of aquaculture and the ecological restoration of mangroves. In addition, shrimp pond cleaning discharges may contain a variety of residual drugs such as disinfectants and antibiotics used for pond disinfection and disease prevention, which may be toxic to the environment. However, the toxic mechanisms and processes of these substances to mangrove ecosystems are still unclear. Therefore, further studies should be focused on the long-term effects of sedimentation and chemical pollution of shrimp pond discharges on mangrove ecosystems.