埋藏和环境因子对辽东栎(Quercus liaotungensis Koidz)种子更新的影响

摘要

The Liaodong oak (Q. liaotungensis is sparsely distributed in the mountain areas of Beijing, China. Although with good acorn production the natural regeneration of the oak by direct seeding is extraordinary low. Previous studies indicated that rodents are very important in affecting seedling recruitment of the oak. The purpose of this study aims to investigate (1) impact of burial on the seedling recruitment; (2) impact of environmental factors (e.g. slope, ground vegetation cover) on seedling recruitment. On September 24, 1996, 37 plots of 5 sites were selected for acorn placement test. Six parallel 20 cm transects were located on each plot at 10 cm interval. Ten acorns were placed on the soil surface at 2 cm interval along the first transect of each plot. Acorns were then buried at 2 cm interval along the 2nd transect of each plot, and acorns were planted similarly at increasing depths (4 cm, 6 cm, 8 cm, 10 cm) along the other transects within each plot. The numbers of seedlings was checked on June 15, 1997 and October 4, 1997 respectively. The seedling recruitment rate (seedlings/acorns, %) is positively correlated to the burial depth in both summer and autumn. The burial improved the seedling recruitment by both increasing the micro-climate (+18%) and reducing predation by rodents (-2%). However the predation rate by rodents on acorns buried in soil was still very high (87%). Seedlings grew equally well in both sunny or shade slopes by autumn, but acorns planted in sunny slope germinated earlier. The seedling recruitment rate was significantly and negatively correlated with the ground vegetation cover only in summer. Dense ground vegetation cover reduced seedling recruitment probably by increasing competition for water or nutrition with the acorns. The seedling height was not significantly correlated with either grass cover or grass height. There was an increase of seedling numbers from June to October, and most of this increase came from the increase of seedlings planted deeper or in shade sites.%辽东栎萌生丛零散地分布在北京山区，虽然其种子量很大，但自然状况下的实生苗非常稀少。鼠类搬运并吃掉大量散落在地表的辽东栎种子，但鼠类是否影响辽东栎的自然更新尚不清楚。本研究主要在于了解：（1）将种子埋入土层内后对辽东栎种子出苗率的影响；（2）环境因子（如坡向、地表植被等）对辽东栎种子出苗率的影响。1996年9月24日，选取5块样地（Site），在每块样地各设置1条样线(Transect) ，每条样线上设置若干样点(Plot)，样点间隔10 m，用于种子埋藏实验。在每个样点设置6条平行线 (Parallel transect)，间隔10 cm，各埋入10粒种子，种子间隔2cm；第1、2、3、4、5、6条线的埋藏深度分别为0、2、4、6、8、10cm。分别于1997年6月15日和10月4日调查出苗情况。研究结果表明，夏季和秋季辽东栎种子出苗率均与埋藏深度呈正相关。埋藏通过改善湿度和减少鼠类等动物的取食而增加了出苗率，其贡献分别占18%和12%。但鼠类对埋入土层内种子的取食率依然很高（87%）。辽东栎种子在阴坡和阳坡的最终出苗率都很高，但阳坡出苗要早于阴坡。夏季辽东栎种子出苗率均与地表植被覆盖度呈负相关。地表植被可能是通过与辽东栎种子竞争水分和养分而降低辽东栎种子出苗率的。辽东栎幼苗的高度与地表植被盖度和高度相关不显著。从夏季到秋季，辽东栎种子出苗率有所增加，主要是由于埋藏在深处或阴坡处的种子出苗较晚的缘故。