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延迟开放(Serotiny)是木本植物在火灾环境下的一种常见特征和生活史策略,它表现为种子在冠层封闭的球果中保留了1个以上的繁殖周期[1]。研究发现,目前有1 000余种植物存在种子延迟开放现象,其中,普遍认为松属(Pinus Linn.)植物是延迟开放的代表[1],大量关于延迟开放的研究是基于松属植物开展的[2-5]。
具有延迟开放性状的树种林冠中储存了大量成熟和健康的多年宿存的种子,只有在火灾后才会迅速打开,以提高森林的火灾恢复能力,使森林在火灾后能够迅速恢复[6]。虽然大量研究表明,高温可以促进延迟开放的球果打开[7-10],但是球果延迟开放背后的机制尚不明确。
松树成熟的球果鳞片是由死细胞组成,不具有自主运动的能力[11]。在电子显微镜观察下,发现鳞片由2层组织组成,鳞片的内表面由纤维组织构成,成束排列,鳞片的外表面由厚壁细胞组成[12-13]。二者的拉伸刚度和吸湿膨胀系数都存在显著差异,水分的变化引起纤维运动,从而导致鳞片张开或闭合[11, 14]。延迟开放的球果是由于鳞片中有松脂,松脂作为一种粘合材料起到密封球果不让内部水分丢失,使球果成熟后保持长期闭合。有研究表明,松脂粘合力消失的温度大概在45~50℃[15-17],高温可能使松脂粘合力消失,从而导致球果打破延迟开放,但是松脂含量与延迟开放之间的关系尚不清楚。
云南松(P. yunnanensis Franch.)、高山松(P. densata Mast.)、思茅松(P.kesiya var. langbianensis Gaussen.)以及马尾松(P.massoniana Lamb.)是中国西南地区4种常见松属植物,也是常见的采脂树种[18],其中,云南松是我国西南地区的特有种,以云南高原为起源和分布中心,在四川、贵州、广西、西藏均有分布,在云南西北横断山区与高山松毗连,在云南西南部则与思茅松邻接[19]。云南松种群具有丰富的多态性、突出的生态地理变异以及明显的种群间多型性,其变种有生态小种地盘松(P. yunnanensis var. pygmaea Hsueh.)和地理小种细叶云南松(P. yunnanensis var. tenuifolia Cheng et Law.)[20]。已有研究表明,云南松是延迟开放树种[5],其球果在枝头宿存多年后内部种子仍有较高的萌发率,且高温烘烤会打破云南松球果的延迟开放[10]。
中国西南几种松树球果鳞片松脂含量对球果延迟开放的影响
Effect of Resin Content in Cone Scales on Cone Serotiny in Pines in Southwest China
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摘要:
目的 探究松树球果延迟开放的机制,讨论松树球果鳞片松脂含量对延迟开放的影响。 方法 以云南松、地盘松、细叶云南松、高山松、马尾松和思茅松为研究对象,调查球果宿存年、延迟开放度。采集当年生球果并测定球果鳞片中松脂含量,分析松树球果鳞片松脂含量与延迟开放度的相关性。 结果 球果宿存是延迟开放的基础,当球果鳞片松脂含量低于6%时的物种,其球果没有延迟开放现象。在具有延迟开放的云南松种内的3个变种,其球果鳞片松脂的含量与其延迟开放度呈正相关(R2=0.997,P=0.036),但在种间水平,球果鳞片松脂含量与其延迟开放度并无线性关系(R2=0.01,P=0.902),推测是由于环境和基因的差异较大所致。 结论 球果鳞片松脂含量对球果延迟开放起重要作用,含量过低则没有延迟开放;在具有延迟开放的云南松变种内,球果鳞片松脂含量显著影响其延迟开放程度。 Abstract:Objective To investigate the effect of resin content of pine cone scales on serotiny. Method Cone persistent ages, the degree of serotiny and the resin content of current-year cone scales in six pine species (Pinus yunnanensis Franch., P. yunnanensis var. pygmaea Hsueh., P. yunnanensis var. tenuifolia Cheng et Law., P. densata Mast., P. massoniana Lamb., and P. kesiya var. langbianensis Gaussen.) were investigated, and the correlation between resin content of cone scales and the degree of serotiny were analyzed. Result For the species whose resin content of cone scales less than 6%, the persistence of cones, which is the indication of serotiny, was not observed. In P. yunnanensis varieties characterized by serotiny, the resin content of cone scales was positively related to the degree of serotiny (R2=0.997, P=0.036). However, the relationship between the cone scale resin content and the degree of serotiny was not significant (R2=0.01, P=0.902) across these taxa, which may be due to the large genetic and environmental differences. Conclusion The results indicate that the resin content of cone scales plays an important role in pine serotiny and there will be no serotiny when it is too low. In P. yunnanensis varieties with serotiny, the serotiny degree is effected by the resin content of cone scales. -
Key words:
- pine; persistent
- / serotiny
- / cone scales
- / resin content
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