福山三種地形主要樹種葉部養分濃度之季節變化

Abstract

植物葉部養分對植物的活力與生產力具有重要的影響，季節的變化與地形的差異造就了植物葉部養分在時間上與空間上的變異，因此是植物生理生態學上重要且值得探討的主題。本研究以福山試驗林第一集水區的11種植物為調查對象，研究植物葉部養分濃度受季節變化與地形的影響，並採集三個地形的土壤以了解土壤特性與植物養分間的關係。自2005年4月至2005年11月，共採集植物樣本4次及土壤樣本1次以進行葉部養分及土壤性質分析。結果顯示，受到地形的影響，福山土壤養分肥力狀況與植物葉部養分地位皆可分為「溪谷型」與「中坡─稜線型」兩大類。溪谷型土壤的pH、土壤有效性磷、可交換性陽離子鈣、鎂與土壤鹽基飽和度顯著高於中坡─稜線型土壤(P ≦ 0.0087)。溪谷植物葉部巨量元素(氮、磷、鉀、鈣、鎂)養分濃度顯著高於中坡─稜線植物(P < 0.0001)，可能是反應溪谷土壤肥力較高的結果。在季節變化方(依據植物不同生理年齡，4月新葉〜11月老葉)面，植物葉部氮、磷、鉀的濃度會隨著季節變化而減少，鈣、錳的濃度則會隨著季節變化而增加，鎂的濃度季節變化則較不一致，隨植物種類不同而異。在養分再吸收效率的表現上，磷(58.3%)、鉀(48.1%)的再吸收效率顯著高於氮(23.7%)的再吸收效率(P = 0.0001)；中坡─稜線植物磷(64.1%)、鉀(55.4%)的再吸收效率顯著高於溪谷植物磷(41.1%)、鉀(26.1%)的再吸收效率(P ≦ 0.0047)，而氮的再吸收效率在兩地形則無顯著差異。中坡─稜線植物葉部具有較高的養分再吸收效率(例如：PRE)，可能是為了適應土壤肥力較低環境所形成的因應策略。在11月時兩類地形之植物葉部氮濃度皆很高，顯示氮尚未再吸收完全；在11月時溪谷的磷濃度也很高，顯示磷也尚未再吸收完全，相對地，中坡─稜線植物磷濃度則接近再吸收作用的臨界值，顯示在土壤肥力較低的環境磷再吸收作用較完全。

Foliar nutrition can influence vigor and productivity of plants. The seasonal changes and topographical difference cause the temporal and spatial variations in foliar nutrient composition. Both are important topics and worth further discussion in plant ecophysiology. In this study, I collected leaf samples from 11 plant species and soil samples to investigate the effects of seasonal change and topographical difference on foliage nutrient compositions in Watershed #1, Fushan Experimental Forest. I collected leaf samples four times and soil samples once from April to November, 2005. The results showed that soil fertility and nutrient concentrations in foliage could be classified into “bottom type” and “middle-top type”. Bottom type soil had significantly higher pH, available phosphorous, exchangeable calcium, exchangeable magnesium, and base saturation than middle-top type soil (P ≦ 0.0087). The foliar concentrations of nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), were significantly higher in bottom type plants than in middle-top type plants (P < 0.0001). The differences in the foliar nutrient compositions could be a response to the differences in soil fertility between bottom type and middle-top type. In eight out of eleven species, the foliar concentrations of N, P and K increased with sampling sequence, but those of Ca and manganese (Mn) decreased. Seasonal patterns of foliar Mg concentrations were inconsistent and dependent on plant species. In nutrient resorption efficiency (RE), P (58.3%) and K (48.1%) resorption efficiency (PRE, KRE) were significantly higher than N (23.7%) resorption efficiency (NRE) (P = 0.0001). Middle-top type plants had significantly higher PRE (64.1%) and KRE (55.4%) than bottom type plants (P ≦ 0.0047), whereas there was no significant difference in NRE between bottom type and middle-top type plants. The high resorption efficiency might be a strategy of plants to adapt to low soil fertility. In November the foliar N concentrations were still rather high in plants of both types, suggesting the incomplete resorption. In November, similarly, the high concentrations of foliar P in bottom type plants also suggested the incomplete resorption. By contrast, the foliar P concentrations in middle-top type plants had approached the threshold of resorption proficiency in November, indicating the more complete P resoprtion in the soil with low fertility.