泥沙掩埋和干旱对三峡库区消落带狗牙根生长恢复的影响

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。蓄水期后引种三峡库区消落带狗牙根,掩埋于不同粒径和埋深的沉降泥沙,探讨泥沙掩埋、干旱对反季节淹水后狗牙根出苗和生长恢复的影响。结果表明:在埋深≥8cm和粒径1.25 mm条件下消落带狗牙根萌发苗不能穿透覆盖层出苗。泥沙掩埋导致狗牙根出苗率显著降低,随着埋深增加狗牙根出苗率迅速下降;并且在埋深相同的条件下随着粒径减小狗牙根出苗速率呈增大趋势。随着埋深增加和粒径减小处理组株高、叶长的增长显著被抑制,处理组的株高、叶片数、叶长显著低于对照组。随着干旱、泥沙掩埋复合胁迫时间延长狗牙根分株株高、叶片数、叶长、叶宽的生长发育显著被抑制,且随着泥沙粒径减小和埋深增加其光合电子传递速率呈显著降低趋势,热耗散量显著增大。同时,干旱、泥沙掩埋复合胁迫导致处理组分株光合电子传递速率和热耗散能力显著低于对照组,光合作用能力显著降低,易受到夏季高光伤害。因此,三峡库区周年淹水导致狗牙根对泥沙掩埋以及干旱复合胁迫的耐受能力显著降低,在泥沙掩埋以及干旱复合胁迫下消落带狗牙根的生长恢复能力随粒径减小和埋深增加呈显著降低趋势,会导致库区消落带狗牙根种群衰退演替加快。

Influence of sand burial and drought on growth recovery of Cynodon dactylon in a water-level-fluctuating zone of the Three Gorges Reservoir

In a water-level-fluctuating zone (WLFZ) of the Three Gorges Reservoir, vegetation restoration is challenged not only by submersion for long periods, but also by sand deposition, drought, and other factors. To study the influence of sand burial and drought on the germination and growth recovery of Cynodon dactylon in a WLFZ of the Three Gorges Reservoir, C. dactylon was transplanted and buried in sand of several particle sizes at various depths after anti-seasonal flooding. Germinating seedlings of C. dactylon in the WLFZ could not penetrate sand layers deeper than 8 cm with a particle size of less than 1.25 mm. Sand burial significantly decreased the emergence rate of C. dactylon. As burial depth increased, the emergence rate dropped sharply; at the same burial depth, the emergence rate significantly increased as particle size decreased. Plant height and leaf length were significantly inhibited as the burial depth increased and the particle size decreased The plant height, leaf number, and leaf length of buried plants were significantly smaller than those of controls. As stress time increased, drought and sand burial significantly decreased plant height, leaf number, leaf length, and leaf width. The photosynthetic electron transport rate decreased significantly and the heat dissipation rate increased significantly as burial depth increased and particle size decreased. Combined stress of sand burial and drought significantly decreased the photosynthetic electron transport rate and heat dissipation ability in the treatment groups compared to control groups; combined stress also significantly decreased the photosynthetic ability of treated plants, and resulted in them being easily damaged by high light intensity in the summer. Thus, annual flooding significantly decreased the endurance of C. dactylon for sand burial and drought in the Three Gorges Reservoir. The ability of C. dactylon for growth recovery was significantly reduced as particle size decreased and the burial depth increased under conditions of sand burial and drought. These conditions would lead to more rapid population decline of C. dactylon in WLFZs of the Three Gorges Reservoir.