植物天然更新过程中种子和幼苗死亡的影响因素

植物天然更新包括有种子搬运、种子库动态、种子萌发和幼苗定居等过程。从种子生产到幼苗定居的更新是植物生活史中最为敏感的阶段之一 ,多种因素的影响种子和幼苗的命运。其中包括 :( 1 )动物取食或病原体侵袭。种子在扩散和搬运过程中 ,易被小哺乳动物或无脊椎动物取食。蛀虫也可以使种子失去萌芽能力。病原体感染种子和幼苗 ,容易引起种子和幼苗的死亡。 ( 2 )异质生境的影响。在不同生境中 ,光照条件、土壤水分和化学成分等因子的组合严重影响种子和幼苗的命运。 ( 3 )干扰的影响。小尺度和大尺度的干扰都可以影响到植物更新时种子和幼苗的命运。林窗作为特殊的干扰体系 ,为不同种类植物提供了更新的机会。 ( 4 )繁殖体特征。种子大小、质量和保护色等特征影响种子和幼苗在更新过程中的生存。种子休眠期间 ,由于生理衰老和腐烂的原因使种子失去活力而不能萌发。 ( 5 )密度和距离制约。母株附近由于密度竞争的影响 ,种子和幼苗死亡率都较高。

Factors influencing mortality of seed and seedling in plant nature regeneration process

Associated with the species dispersal,plant nature regeneration processes include seed removal,seed bank dynamics,seed germination and seedling establishment. The stage from seed production to seedling colonization is the most sensitive stage in plant life history. After seed dispersal,numerous biotic and abiotic factors influence seed fates and seedling mortality. Factors including the following:(1)Seeds may be predated by small mammals other invertebrates. Insects and pathogen can make seed viability lost by attracting seed. Insects also can influence seedling survival by attracting the leaf and bud of seedling. (2)Heterogeneous environment. The combination of environment factors such as light, soil moisture and chemical composition, greatly affects seed fates. (3)Effect of disturbance. Disturbance can affect the fate of seeds and seedling in their regeneration process. As a special disturbance regime, canopy-gap provides opportunity of regeneration for many plant species. (4)The characteristics of progeny. Many species take the advantage in offspring regeneration with larger seed bank or larger seed size. Physiological senescence and seed decay in seed dormancy affect seeds mortality and survival of seedlings. (5)Effects of distance-dependent and density-dependent. Seedling and seed near around parent tree show higher mortality rate because of density competition.