水位变化对三峡库区消落带落羽杉营养特征的影响

三峡大坝建成蓄水后,其独特的水位调度节律对水库消落带植物的生境造成巨大干扰。为了解落羽杉在消落带特殊生境下的生理生态过程,探究其水淹耐受机制,在三峡库区消落带植被修复忠县示范基地建立3 a后,对试验样地内种植于消落带海拔175—165 m范围的落羽杉进行叶片、根系样品采集,并调查其生长情况,测定分析落羽杉营养元素含量及其与植株生长和土壤养分间的关系。结果表明:(1)水位变化对适生树种落羽杉营养元素吸收造成了明显影响。随着淹水深度和淹水时间的延长,落羽杉根系能量代谢受阻,根系功能紊乱,营养元素吸收与运输受到抑制,落羽杉N、P、K、Ca、Zn吸收减少;水淹导致土壤中Fe~(2+)、Mn~(2+)含量升高,落羽杉Fe、Mn吸收增加。(2)相关性分析表明,落羽杉株高与N、K、Mg含量呈极显著正相关关系,与P含量呈显著正相关关系,而与Fe、Cu含量呈极显著负相关关系,与Mn含量呈显著负相关关系;落羽杉冠幅与植株N、P、K、Mg含量呈极显著正相关关系,而与Fe、Cu含量呈极显著负相关关系;落羽杉营养元素含量与土壤元素含量无显著相关性。(3)消落带不同海拔落羽杉营养元素的积累量均不低于植物正常生长水平,未见严重的缺素状况。研究结果表明,落羽杉对三峡库区消落带水位变化具有很好的适应能力,能够对水位变化做出积极的响应,平衡各元素的积累量,维持植株正常生长。

Effect of water-level change on nutritional characteristics of Taxodium distichum in the hydro-fluctuation belt of the Three Gorges Reservoir

The construction of the Three Gorges Dam reservoir spans the Yangtze River, China, forming a hydro-fluctuation belt with a water level drop of nearly 30 m and an area of 300 km². The unique anthropogenic hydrological regime of the Three Gorges Dam has had significant negative impacts on the reservoir''s riparian ecosystem. Some flooding-intolerant plants living within the belt gradually died off, which exacerbated vegetation habitat fragmentation and deleteriously affected the biological diversity, ecosystem structures, and functions of the water-fluctuation zone. Therefore, a pressing scientific challenge is to recover and restore the vegetation there and ensure proper ecological function. Previous studies have shown that Taxodium distichum is a flooding-tolerant plant and has been used for vegetation reconstruction. The nutritional characteristics of plants in a particular area can reflect the eco-physiological processes of plants, and can serve as crucial indicators of the structure and function of the local ecosystem. The nutritional characteristics play a key role in adaptation to anti-seasonal flooding, and might reveal clues about the adaptation mechanisms of plants in the hydro-fluctuation belt of the Three Gorges reservoir area. To contribute to this understanding, the nutritional characteristics of T. distichum growing in the reservoir riparian region of Zhongxian county, which had been planted in 2012, were studied. Element contents of three sample zones in low water elevation (165 m)-SD, high water elevation (170 m)-SL, and the control-CK(175 m) were determined in 2015. The macroelement, secondary element, and micronutrient contents in root and leaves of plants were measured. The results showed that:(1) Concentrations of N, P, K, Ca, and Zn in leaves and roots of T. distichum under flooding significantly decreased compared to CK, whereas Fe and Mn contents significantly increased. (2) Some nutrient concentrations of T. distichum under flooding decreased, but still maintained their normal performance. (3) Correlation analysis showed that plant heights were positively correlated with the concentrations of N, P, K, and Mg; plant heights were negatively correlated with the concentrations of Fe, Cu, and Mn; canopies of plants were positively correlated with the concentrations of N, P, K, and Mg, but negatively correlated with Fe and Mn. This investigation indicates that water level change had significantly influenced the nutritional characteristics of T. distichum in water-level-fluctuating zone of the Three Gorges Reservoir. T. distichum had good adaptability to the changed water habitat.