三峡库区172m蓄水期间泥、沙沉降对低位狗牙根种群的影响

三峡库区消落带植物恢复不仅面临长期淹水逆境,还面临泥沙、干旱等环境因素的胁迫。2009年实验、调查研究了三峡库区长寿段低位消落带的狗牙根(Cynodon dactylon L.)种群,探讨了泥、沙沉降对狗牙根种群的影响。结果表明,泥沉降和沙沉降均显著促进了狗牙根芽的萌发,而抑制了狗牙根的芽形成和萌发苗的生长,且前者的抑制作用显著大于后者。泥沉降导致总芽数、萌发苗的茎长和茎宽分别比对照低65.4%(P<0.05)、97.0%(P <0.05)、31.2%(P <0.05),而沙沉降导致前述参数分别比对照低17.1%(P<0.05)、21.2%(P<0.05)、1.0%(P>0.05)。分别将被沉降泥掩埋的狗牙根移植、掩埋于12cm厚的泥和沙中,40d后对照和S'_d组(覆盖沙)狗牙根芽萌发后均能在地面上形成正常的分株,而S'_l组(覆盖泥)的萌发芽无法穿透覆盖层,形成分株。S'_l组狗牙根芽的萌发率显著高于对照和S'_d组,但其萌发苗的茎长和茎节数均显著低于对照,分别为对照的30.3%(P<0.05)、80.4%(P<0.05);而S'_d组分株的茎长、茎节数、叶片数、叶长和叶宽均显著高于对照组,分别比后者高87.9%(P<0.05)、53.0%(P<0.05)、24.2%(P<0.05)、23.4%(P<0.05)和24.1%(P<0.05)。S'_l组萌发苗的鲜质量、干质量和干鲜质量比分别比对照组低83.3%(P<0.05)、86.2%(P<0.05)、15.8%(P<0.05);而S'_d组萌发苗的鲜质量、干质量和干鲜质量比分别比对照组高76.8%(P<0.05)、110.1%(P<0.05)、20.0%(P<0.05)。表明,低位消落带的狗牙根对沙沉降具有较强的适应能力,而对泥沉降的适应能力较低,泥沉降是库区低位消落带狗牙根种群恢复的主要影响因素之一。

Influence of Silt Deposition and Sand Deposition on Cynodon dactylon Population in Low-Water-Level Zone of tThree Gorges Reservoir During 172m Water Accumulation

Ecosystems in the water-level-fluctuating zone are seriously damaged with the Three Gorges Reservoir storing water. Now, more attention should be payed to the restoration and reconstruction of the damaged ecosystems, with the key technical system in the reservoir. Especially, the technology of vegetations restoration is the most crucial part of the technical system. In the Three Gorges Reservoir, Vegetations restoration would not only face the prolem of being submerged for a long time, but also be threatened by silt deposition, sand deposition, drought, and so on. Cynodon dactylon is mainly distributed in the water-level-fluctuating zone from 145m to 156 m, which is one of the main dominant species.To investigate influence of silt deposition and sand deposition on Cynodon dactylon population in low-water-level-fluctuating zone of the Three Gorges reservoir, C. dactylon populations in Changshou area were studied in 2009. Results showed that both silt deposition and sand deposition significantly promoted germination of C. dactylon buds, but inhibited buds formation and growth of seedlings. Additionally, the inhibition of silt deposition was significantly greater than that of sand deposition. Compared to the control, silt deposition resulted in decreasing of total buds number, stem length and stem width of germination seedling with 65.4% (P<0.05), 97.0% (P<0.05), 31.2% (P<0.05) respectively. Sand deposition lead to a decline of 17.1% (P<0.05), 21.2% (P<0.05), 1.0% (P>0.05) respectively. Then, C. dactylon, buried by silt was transplanted and covered by 12cm thick silt or sand respectively. After 40 days, germinating buds of the control group and S'_d Group (covered by sand) had developed ramets on the ground, while germinating buds of S'_l group (covered by silt) failed to penetrate the covering layer and develop ramets. Germination rate of S'₁ group was significantly higher than that of the control and S'_d group, but stem length and node number of its germinating seedlings were significantly lower than that of the control, only being 30.3% (P <0.01) and 80.4% (P <0.05) of the control respectively. Stem length, node number, leaf number, leaf length and leaf width of S'_d Group's ramets were significantly higher than those of the control, with an increasing of 87.9% (P <0.05), 53.0% (P <0.05), 24.2 % (P <0.05), 23.4% (P <0.05) and 24.1% (P <0.05) respectively. Fresh mass, dry mass and ratio of dry-and-fresh mass of S'₁ Group's seedlings were 83.3% (P <0.01), 86.2% (P <0.01), 15.8% (P <0.05) lower than the control, respectively. And those of S'_d Group's seedlings exhibited 76.8% (P <0.01), 110.1% (P <0.01), 20.0% (P <0.05) higher than those of the control, respectively. These results indicated that C. dactylon, in low-water-level-fluctuating zone has a strong adaptability to sand deposition, instead of silt deposition. In conclusion, silt deposition is one of the main influencing factors of C. dactylon populations restoration in low-wate-level-fluctuating zone of the Three Gorges Reservoir.