池杉在三峡水库消落带生态修复中的适应性

冬季淹没和夏季干旱的交替作用会导致三峡水库消落带生态系统质量下降. 为了探索有效的生态系统修复方式,选用池杉树种开展了消落带林泽工程试验,并采用统计分析和RDA(冗余分析)排序对水淹胁迫下池杉的生长响应进行了研究. 结果表明:种植在海拔169 m以上的池杉经历两轮冬季淹水后成活率约为84.52%；树高、冠幅和枝叶密度平均变化量较小,分别为0.10 m、0.04 m和-0.11%,而胸径和枝下高变化明显,平均改变量分别为0.78 cm和-0.64 m；树高、胸径、冠幅和枝叶密度等指标变化率在没顶和部分淹水情况下存在显著差异. 部分淹水时,池杉对水淹胁迫的适应能力较强,随着淹水深度的增加,各生长指标变化量均呈下降趋势,部分植株有枯梢,没顶和部分淹水情况下枯梢率分别为43.56%和11.76%. RDA结果表明,水力条件和初始生长特征共同对淹水后池杉生长变化产生影响,二者对池杉生长指标变化的总体解释率为31.20%,独立解释率分别为11.90%、14.40%,共同解释率为4.90%. 池杉作为适应三峡水库消落带水位变动的本土耐淹树种,其经历水淹后的生长变化不仅与水位变动有关,同时也与其淹水前的生长状态有关. 研究结果有助于三峡水库消落带类似生态修复工程的进一步深入开展. 

Suitability of Taxodium ascendens in Ecological Restoration of the Littoral Zone of the Three Gorges Reservoir

Abstract: The littoral zone ecosystem of the Three Gorges Reservoir has been altered and degraded by prolonged winter flooding and summer drought. Taxodium ascendens was selected as an afforestation species for use in littoral woodland engineering. Sapling growth characteristics (e.g., height, diameter at breast height, crown width, foliage density and under crown height) were measured every year from 2009 to 2011. Statistical analysis of variations in these characteristics was conducted with SPSS 17.0 software, and redundancy analysis (RDA) was used to evaluate the growth responses of the saplings to influencing factors including growth characteristics and hydraulic factors (e.g., altitude, water-logging duration, submersion depth and duration of complete submergence). The results showed that the survival rate of T. ascendens saplings planted over 169 m above sea level was 84.52% after two rounds of winter flooding. Mean variations of height, crown width and foliage density were moderate, with values of 0.10 m, 0.04 m and -0.11% respectively. Mean variations of breast height and under-crown height were more obvious, with values of 0.78 cm and-0.64 m respectively. Rates of change of height, breast height, crown width and foliage density of T. ascendens under different submersion conditions were significantly different. Partially submerged saplings adapted well to the water level fluctuation, but all measured growth indices decreased as the flood depth increased. Up to 43.56% of the completely-submerged group and 11.76% of the partly-submerged group died back from the stem tip. Six influencing factors (altitude, water-logging duration, diameter at breast height, under crown height, foliage density and crown width) were identified by a manual forward selection method based on the Monte Carlo permutation test (499 permutations, P<0.05). RDA results indicated that 31.20% of sapling growth variations could be explained by the selected influencing factors, and the first two canonical axes accumulatively explained 82.90% of the species-environment relationships. Partial RDA results showed that 11.90% of sapling growth variation could be explained solely by the hydrological effects, and 14.40% by the initial growth characteristics effects; the combined explanation rate was 4.90%. It was concluded that littoral woodland engineering is a promising model for ecosystem restoration in the Three Gorges Reservoir given the potential ecosystem functions of providing habitat, acting as a carbon sink and intercepting pollution. It is proposed that future research may include:continuous monitoring, studies of understory vegetation and complex littoral woodland ecosystem construction and modeling. The results provide experiences and reference points for similar restoration projects in the littoral zone of the Three Gorges Reservoir.