惠蓀林場三種原生樹種木質部水勢及養分分析研究

Abstract

本研究以惠蓀林場原生樹種園為試驗地，自2004年6月至2005年4月，調查木荷、臺灣烏心石及牛樟三種臺灣原生樹種，探討其木質部水勢及木質部汁液養分濃度的變化。結果顯示，木質部水勢的日變化都有一規則性，在黎明前，三種樹種皆以黎明前木質部水勢為一日變化之最高，中午時木質部水勢為最低，顯然受到環境因子所影響，特別是相對濕度因子。植物水分散失與吸收動態關係，取決於植物的水分狀態，在三種樹種之中，以木荷中午時木質部水勢為最低（-1.65MPa），表示木荷較臺灣烏心石及牛樟吸水能力強，且較能忍受乾旱的環境生長。 木質部汁液養分濃度變化受到木質部水勢、季節、樹種、植物的物候及土壤養分所影響，分析木質部汁液陰陽離子濃度發現，下午木質部汁液養分濃度比上午木質部汁液濃度高；乾季時木質部養分濃度低，濕季時木質部養分濃度高；植物在展新葉、開花時，木質部汁液養分濃度也會升高，尤以臺灣烏心石最為明顯。植物生長季節時，木質部汁液養分分析比土壤及葉片養分分析，更能代表林木的養分狀態。因此，木質部汁液養分分析不僅提供林木與土壤養分之平衡訊息，也可提供林木水分逆壓程度及能量儲存狀況。

The purposes of this study were to investigate the variation of both xylem water potential and xylem sap of Schima superba var. superba, Michelia compressa var. formosana and Cinnamomum kanehirai at the native tree species area in Hui-Sun experiment forest from June 2004 to April 2005. The result showed that the xylem water potential fluctuation had its regularity in the diurnal change. The predawn xylem water potential of the three tree species was all the highest before dawn, and all the lowest at noon. The variations in xylem water potential during a day were apparently related to environment factors, particularly to the relative humidity factor. The dynamic relationship between the rates of water loss and uptake depended on plant water status. In the three tree species, the minimum of xylem water potential was -1.65MPa, of Schima superba var. superba at noon. It indicated that Schima superba var. superba had better ability on water uptake and drought resistant than Michelia compressa var. formosana and Cinnamomum kanehirai had. The xylem water potential, season, species phenology of plant and soil chemistry influencing on the ion concentrations in xylem sap were discussed. From the analysis of the anion and cation concentrations in xylem sap, we found that the xylem sap nutrient concentration at noon were higher than those in the morning. Xylem sap nutrient concentrations in drought season were lower than in wet season. When leaf emergence or bloom, xylem sap nutrient concentrations also increased, especially to Michelia compressa var. formosana. In the plant growth period, xylem sap provided more information on tree nutrient status than either soil extracts or foliar analyses. Therefore, xylem sap analysis not only provided plant and soil nutrient balance, but also to indicate the degree of tree water stress and stored energy.