地中海沿岸沙丘微生境对幼苗出现时空格局的影响

The impact of microhabitats on the temporal and spatial patterns of seedling emergence in Mediterranean coastal sand dunes

实验样地设在地中海沿岸沙丘 ,选择了 3个不同的微生境代表 :(1 )稳定沙丘上的开阔地片段 ,(2 )稳定沙丘上的灌丛下区域 ,(3)不稳定沙丘的路径区域 ;从 2 0 0 1年 1 1月至 2 0 0 2年 4月的整个生长季节 ,每一个微生境出现的幼苗在 4个日期被监测 ,并在每一个取样日把每一株幼苗鉴定、计数后 ,用剪刀把地上部分移去 ;研究调查了 3种微生境幼苗出现的时空分布格局 ,并分析了雨量与幼苗出现数量的关系。结果发现 :在地中海沿岸沙丘生态系统 ,幼苗出现在时间上具有明显的分布特征 ,大多数幼苗出现在第一观测期 ,整个生长季幼苗都不断出现 ,但幼苗出现的数目却逐渐下降 ;各功能群的幼苗占幼苗总数的比例分别为 :1年生阔叶草 4 7.4 % ,多年生阔叶草 2 .5 % ,豆科植物 1 7.0 % ,菊科植物 1 4 .5 % ,1年生禾草为 1 1 .7% ,多年生禾草为1 .9% ,十字花科植物 3.7% ,伞形科植物 1 .4 %。在空间上 ,总幼苗密度、物种丰富度和物种多样性等显示出重要的微生境差异 ,开阔地区域具有最大的幼苗密度、物种丰富度和物种多样性 ;3个微生境的幼苗出现不是同步的 ,微生境影响种子萌发的时间分布格局 ,灌丛下种子萌发具有滞后现象 ;大多数功能群的幼苗密度分布基本上具有显著的微生境差异 。

Differences in temporal and spatial patterns of seedling emergence were investigated in Poleg Stream Nature Reserve, Israel. Three microhabitats representative of Mediterranean coastal sand dunes were selected: (1) open patches in a stabilized sand dune, (2) shrub understory in a stabilized sand dune, and (3) trail in an unstabilized sand dune. Seedling emergence was monitored in each microhabitat during the growing season between November 2000 and April 2001. The seedling densities of main species and functional groups at each observation time and over the whole growing season were compared between microhabitats by analysis of variance (ANOVA). Species diversity indices were calculated using Shannon-Weiner index, and H′-diversities of the microhabitats were compared by analysis of variance (ANOVA). Most of seedlings emerged during the first census. Although germination occurred over the entire growing season, the total number of seedlings decreased gradually with time. All seedlings in three microhabitats belong to 54 genera and 59 species. Overall average seedling density was 1685±279 m^(-2). Among three microhabitats, seedling density in the open area was highest, at 2635±612 m^(-2), while that of the shrub understory was lowest, 1068±110 m^(-2). Representation of functional groups among seedlings was as follows: annual forbs 47.4%, perennial forbs 2.5%, legumes 17.0%, compositaes 14.5%, annual grasses 11.7%, perennial grasses 1.9%, umbeliferaes 1.4% and crucifers 3.7%. Microhabitats differ significantly in total seedling densities, seedling species diversity (P<0.0001) and species richness (P<0.0001). The open area generally possessed the greatest species diversity and species richness. Seedling distribution patterns for the main species and most functional groups differed significantly among the three microhabitats. However, no clear differences were observed in the distribution patterns of annual grasses or umbeliferaes between the microhabitats. Different plant species had different distribution patterns. Seedling densities under the shrubs were lower than those in the open area or the trail area for some species. The seedling densities in the open area were greater than those in the trail and under shrubs for certain species, such as Trifolium palaestinum, Plantago psyllium, Arenaria leptocladus, Ifloga spicata, and Rumex bucephalophorus. Seedlings of Polycarpon succulentum and Cutandia philistaea occurred at highest frequencies in the trail microhabitat. In addition, the seedlings of Anagalis arvensis were seldom found in the trail and the seedlings of Vanlantia hispida and Fumaria jewdica were often seen under the shrubs. Seedling germination differed temporally among the three microhabitats, with shrub understory seedlings lagging behind the others. The seedling number observed at the first census accounted for 72.11% of the whole growing season in the trail microhabitat, 53.02% in the open area and 44.52% under shrubs. No clear relationship was found between seedling number and rainfall.