Evolutionary trend of plant community and adaptive strategies of dominant plants in the water-level-fluctuation zone of the Three Gorges Reservoir

Abstract

三峡水库周期性蓄水显著改变了消落区植物群落组成及多样性,植物群落的演变过程能反映和影响整个消落区生态系统的变化,但目前还缺乏长期连续的观测数据记录,因而本研究基于2009-2021年6月的固定样方长时间序列监测数据和优势植物叶片功能性状数据,分析了消落区3个高程(145~155、155~165和165~175 m)区域植物群落多样性和优势植物重要值的变化趋势,通过冗余分析和蒙特卡罗检验揭示了水库运行特征参数和气象因子对消落区植物特征的影响。研究发现:1)消落区3个高程区域,优势植物差异明显,145~155和155~165 m区域以狗牙根、香附子和苍耳等为主,165~175 m区域以狗牙根、野胡萝卜和鬼针草等为主。145~155 m区域植物群落Shannon-Wiener多样性指数(1.47±0.47)和Pielou 均匀度指数(0.67±0.07)显著低于165~175 m区域。2)2009-2021年期间,高程145~155和155~165 m区域Shannon-Wiener多样性指数和Pielou 均匀度指数呈波动下降趋势,优势植物狗牙根和香附子的重要值呈增加趋势。3)RDA分析表明,与水库运行特征密切相关的淹没时间、周期性淹没次数和高程均能显著影响消落区优势植物重要值的大小。狗牙根、喜旱莲子草和苍耳等物种重要值与周期性淹没次数呈正相关,狗尾草和水蓼的重要值与淹没次数呈负相关。野胡萝卜、鬼针草和黄花蒿等物种重要值与高程呈正相关,狗牙根、香附子和水蓼的重要值与高程呈负相关。4)不同植物的适应策略各有不同,消落区植物狗牙根的比叶面积最大,为(32.8±7.2)mm²/mg,鬼针草和苍耳次之,分别为(30.6±3.9)和(30.0±3.0)mm²/mg,均小于未淹没对照区植物的比叶面积。5)狗牙根耐水淹能力强,以S策略投资为主(53.4%),苍耳的比叶面积大,以C投资策略主(61.3%)。小白酒草(64.6%)和鬼针草(50.9%)以R策略为主,种子小数量多,喜旱莲子草也以R策略为主(71.3%),具有发达的根茎。本研究结果可加深对大型水库消落区植物群落演变趋势及优势植物的生态适应策略的科学认知。;The periodic impoundment of the Three Gorges Reservoir has significantly changed the composition and diversity of plant communities in the water-level-fluctuation zone (WLFZ), and its succession process can reflect and influence the changes of the whole reservoir bank ecosystem. At present, there is still a lack of long-term continuous observational records. Based on the monitoring data of fixed sample sites from June 2009 to June 2021 and leaf functional traits of dominant plants, this study analyzed the change trend of plant community diversity and the important value of dominant plants at the altitudes of 145-155 m, 155-165 m and 165-175 m in the WLFZ, and revealed the influence of reservoir operation characteristic parameters and meteorological factors on plant characteristics in the WLFZ through redundancy analysis. The results showed that: 1) dominant plants varied obviously in different elevation areas. The dominant species exhibiting higher important value (IV) at the altitude of 145-155 m and 155-165 m were Cynodon dactylon, Cyperus rotundus and Xanthium sibiricum with the higher water-tolerant capacity, while C. dactylon, Daucus carota and Bidens pilosa were dominant at the altitude of 165-175 m. The Shannon-Wiener diversity index of plant communities (1.47±0.47) and the Pielou index (0.67±0.07) at the altitude of 145-155 m were significantly lower than those at the altitude of 165-175 m. 2) From 2009 to 2021, the Shannon-Wiener diversity index and Pielou index at the elevation of 145-155 m and 155-165 m decreased, while the importance value of C. dactylon and C. rotundus increased. 3) RDA analysis showed that the flooding time, number of periodic flooding and elevation can significantly affect the IV of dominant plants. The IV of species such as C. dactylon, A. philoxeroides and X. sibiricum were positively correlated with number of periodic flooding. The IV of Setaria viridis and Polygonum hydropiper were negatively correlated with number of periodic flooding. With increasing elevation, the IV of D. carota, B. pilosa and Artemisia annua increased, however, the IV of C. dactylon, C. rotundus and P. hydropiper declined. 4) The adaptation strategies of different plants varied. Specific leaf area (SLA) of C. dactylon (32.8±7.2) mm²/mg was the largest, followed by B. pilosa (30.6±3.9) mm²/mg and X. sibiricum (30.0±3.0) mm²/mg. The SLA of these plans in the WLFZ were lower than those of plants in the unflooded area. 5) The investment proportion of S strategy of C. dactylon was 53.4% with high flooding-resistant ability. The investment proportion of C strategy of X. sibiricum was 61.3% with the largest leaf area. The proportions of R strategy of Comnyza canadensis and B. pilosa were 64.6% and 50.9% that have a lot of small seeds. The proportions of R strategy of A. philoxeroides was 71.3% with developed roots. The results of this study may deepen the scientific understanding of the change trend of plant communities and the ecological adaptation strategies of dominant plants in the WLFZ of large reservoirs.