Li Feng-Rui, Zhao Li-Ya, Zhao Xue-Yong, Zhang Tong-Hui, Li Guangdi
Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 260 Donggang West Road, Lanzhou 730000, China.
Ann Bot. 2005 Dec;96(7):1215-23. doi: 10.1093/aob/mci271. Epub 2005 Sep 30.
The relative importance of pre- and post-germination determinants for recruitment of natural plant communities is rarely explored. An annual plant community on moving sandy land was chosen for a case study. Answers to the following questions were sought: (a) Does recruitment of new individuals within the community of annual plants differ in time and space? (b) Is there spatial concordance between seed deposition, seedling emergence, survival and recruitment? (c) What are the direct and indirect effects of pre- and post-germination determinants on plant recruitment.
An integrative approach combining investigation of natural recruitment processes with regression, correlation and path analyses was adopted. Data on seed deposition and seedling recruitment were collected by monitoring the number of seeds deposited in the top 5 cm of the soil and the numbers of seedlings emerged and recruited from all annual plants at sites to a range of distances from the existing shrub Artemisia halodendron (Asteraceae) in eight compass directions for two consecutive growing seasons.
Community-level recruitment was strongly affected by inter-annual rainfall variation and was highly site- and density-dependent. Low recruitment rate in this system was due to low emergence rate and low post-emergence survival rate. Of the pre- and post-germination determinants studied, it was the number of seedlings which emerged and the post-emergence survival rate that had the greatest direct effects on recruitment, with a combination of both variables explaining the majority of the variance (97 %) in recruitment.
This study suggests that post-germination determinants (emergence and survival) rather than pre-germination determinants (seed deposition) substantially determined the final pattern of recruitment. Although the density of seeds deposited did not have a significant direct effect on recruitment, it contributed to observed variation in recruitment indirectly through density-dependent emergence of seedlings.
很少有人探讨萌发前和萌发后决定因素对天然植物群落补充更新的相对重要性。本研究选取移动沙地的一年生植物群落作为案例进行研究。试图回答以下问题：（a）一年生植物群落中新个体的补充更新在时间和空间上是否存在差异？（b）种子沉降、幼苗出土、存活和补充更新之间是否存在空间一致性？（c）萌发前和萌发后决定因素对植物补充更新的直接和间接影响是什么？
采用一种综合方法，将对自然补充更新过程的调查与回归分析、相关性分析和通径分析相结合。通过监测在连续两个生长季节中，八个罗盘方向上距离现存灌木盐生蒿（菊科）一定距离的各个地点土壤表层5厘米内沉降的种子数量，以及所有一年生植物出土和补充更新的幼苗数量，来收集种子沉降和幼苗补充更新的数据。
群落水平的补充更新受到年际降雨变化的强烈影响，并且高度依赖于地点和密度。该系统中较低的补充更新率是由于较低的出土率和出土后的低存活率。在所研究的萌发前和萌发后决定因素中，出土的幼苗数量和出土后的存活率对补充更新具有最大的直接影响，这两个变量的组合解释了补充更新中大部分的变异（97%）。
本研究表明，萌发后决定因素（出土和存活）而非萌发前决定因素（种子沉降）在很大程度上决定了最终的补充更新模式。虽然沉降种子的密度对补充更新没有显著的直接影响，但它通过依赖密度的幼苗出土间接导致了观察到的补充更新差异。
