以功能特徵預測小苗存活與生長的種間差異

Abstract

植物功能特徵通常定義為影響植物存活、生長、繁殖與適存度的形態和生理特徵。辨識影響植物存活與生長的功能特徵，有助於瞭解植物對於環境資源的利用方式，推估植物群聚的建構規則。本研究使用功能導向的研究方式，比較七種中度耐陰至耐陰樹種小苗的存活與生長差異，推測樹種間的棲地分化與共存機制。我探討以 下三個問題：（1）耐陰樹種小苗的存活與生長主要受到那些環境因子影響？光線與土壤是否造成小苗存活與生長之種間差異？（2）何種功能特徵最能用於預測耐陰樹種小苗的存活時間與生長速率？（3）耐陰樹種小苗的存活時間與生長速率間是否具有權衡？本研究於墾丁高位珊瑚礁森林動態樣區進行，自2007 年7 月至2013 年1月間，每三個月於144 個小苗樣區內，進行木本植物小苗普查。本研究使用混合比例風險迴歸模型，分析種子、葉與光合作用特徵對小苗存活的影響，並使用廣義線性混合模型分析小苗相對生長速率與功能特徵間的關係。結果顯示各樹種小苗約可存活185~469 天，小苗存活時間顯著受土壤深度與乾季光量影響，且樹種與土壤深度及乾季光量具有顯著的交互作用。影響小苗存活時間的主要功能特 徵為種子重量、比葉面積和葉厚度，而小苗相對生長速率主要與比葉面積和光合潛力相關。本研究顯示墾丁高位珊瑚礁森林七個中度耐陰至耐陰樹種之共存，主要與乾季光量和土壤深度息息相關。高位珊瑚礁森林的地質特徵，使土壤保水不易，土壤水分可能成為高位珊瑚礁森林中，最重要的限制因子。

Plant functional traits are usually defined as morphological and physiological traits of plants that may influence their survival, growth, reproduction and fitness. Identifying key functional traits to predict the survival and growth of plants in a given habitat and provides an effective approach to understand the strategies of resource exploitation. Such understand may serve as a basis to construct community assembly rules. In this study, I applied a trait-based approach to compare the survival and growth of seven shade-tolerant species during their seedling stage in the Kenting karst forest. Niche differentiation among seven intermediate and shade-tolerant species and mechanisms of species coexistence were studied. In this study, three questions were addressed. (1) Which environment factors may cause interspecific differences in seedling survival and growth? Do seedling survival and growth vary with light availability and soil depth? (2) Which functional traits are the best predictors to model seedling survival and growth? (3)Are there trade-offs between seedling survival and growth? This study was carried out in the Kenting Karst Forest Dynamics Plot. Seedling censuses were executed every three months during July, 2007 - January, 2013. The survival status and height of seedlings were measured in 144 seedling plots. Proportional hazard mixed models were used to explore the relationships between seedling survival and various functional traits, such as seed mass and specific leaf area. Seedling growth was analyzed by generalized linear mixed models. Our results indicated that seedlings could survived for 185~469 days on average. The survival intervals were significantly influenced by soil depth and light availability during the dry season. In the survival model, the interactions between species and two environmental factors, light availability and soil depth, were significant. Seedling survival was significantly correlated with seed mass, specific leaf area (SLA) and leaf thickness. Meanwhile, relative growth rates of seedling were significantly correlated with SLA and photosynthetic capacity. This study indicated that interspecific variability in seedling survival was critical for these seven species in Kenting karst forest, which may be highly influenced by light availability during the dry season and soil depth. Such results suggested that soil water availability may be the most critical limiting factor in the karst forest.