四種殼斗科幼苗在不同光度下生長優勢與形態之表現

Abstract

中文摘要 本研究之目的在探討四種殼斗科樹種幼苗，毽子櫟、赤皮、錐果櫟及鬼櫟對光環境之適應性。藉觀察三種相對光度下，種子發芽後至九個月生長期間之相對生長率，評估試驗樹種之生長優勢是否會有轉變，並由生物量分配策略及形態表現來瞭解植物如何適應不同光環境。 以相對生長率判定四種樹種之生長優勢轉變，其發生時間約為生長五個月後且保持其優勢度。在高光下（相對光度80%）下，錐果櫟及赤皮相對生長率較高，在高光下較具有優勢；在中低光下（相對光度10% 及5% ）下，則以毽子櫟及鬼櫟有較高相對生長率，此二種樹種在低光下較具有優勢。 光度與相對生長率之迴歸分析顯示，四樹種之相對生長率因光度增加而增加，錐果櫟與赤皮之相對生長率對於光度增加，呈線性反應，而毽子櫟與鬼櫟之相對生長率，則隨光度的增加而趨於平緩。 錐果櫟與赤皮之生物量，在高光下之累積遠大於中低光；對毽子櫟而言，中高光下生物量分配差異小，鬼櫟生物量在不同相對光度下仍有一定之累積量。 錐果櫟及赤皮苗高在相對光度80% 下較高，毽子櫟及鬼櫟苗高則在相對光度10% 下較高，表示毽子櫟及鬼櫟在低光下會以增加苗高而獲取更多光源。 錐果櫟、赤皮及鬼櫟在不同相對光度下，均以葉部生物量分配最多。毽子櫟生物量分配隨時間增加，以全方面發展並趨於一致，根莖葉分配比相近。 四種樹種之葉面積比與比葉面積皆隨著光度減少而增加，表示在低光下適應方式，以葉片變大變薄來增加獲取光源面積。各形態參數相關性分析顯示，相對生長率和葉面積比與比葉面積成負相關。葉部比和莖部比及根部比成負相關但和葉面積比成正相關。根部比和葉面積比和比葉面積成負相關。葉面積比和比葉面積成正相關。相對生長率為植物適應環境綜合表現的結果，此試驗中，並無法藉由形態上表現的參數作為很好的預測，此部分需待進一步研究。 由生長優勢轉變、相對生長率和光度的關係與苗高的反應，均可將四種樹種分為二群:（一）錐果櫟與赤皮在高光下較適合其生長，（二）毽子櫟與鬼櫟在中低光下生長較佳。驗證不同樹種對於光的適應性確實會不同，各樹種在不同光資源下會有生態棲位分化的現象。 關鍵詞: 相對生長率、相對光度、生長優勢

Abstract To investigate whether crossover in seedling growth ranks among four potentially co-occurring Fagaceae species, namely, Cyclobalanopsis acuta var. paucidentata, Cyclobalanopsis longinux var. longinux, Cyclobalanopsis gilva, and Lithocarpus lepidocarpus would occur between low and high irradiance, the relative growth rates (RGR) of seedlings grown under three relative light intensities (5%, 10%, and 80% of full light) were determined over a period of 9 months. In addition, to understand the likely seedling adaptation strategies of the four species under different relative light intensities, seedling biomass allocation patterns and morphological attributes were also investigated. Results showed that the growth rank patterns were inconsistent among the four species during the first four months. However, from the fifth month and onward, Cyclobalanopsis longinux var. longinux and Cyclobalanopsis gilva had higher relative growth rates under 80% relative light intensity, whereas Cyclobalanopsis acuta var. paucidentata and Lithocarpus lepidocarpus had higher relative growth rates under both 10% and 5% relative light intensities. Thus, crossover in seedling growth ranks did occur among the four species. For Cyclobalanopsis acuta var. paucidentata and Lithocarpus lepidocarpus, their RGR’s showed a curvilinear response to the three relative light intensities, whereas for both Cyclobalanopsis longinux var. longinux and Cyclobalanopsis gilva, the responses were linear. For all the species, their seedlings biomass increased with increasing relative light intensity. Cyclobalanopsis longinux var. longinux and Cyclobalanopsis gilva had higher seedling height under 10% relative light intensity. In contrast, Cyclobalanopsis acuta var. paucidentata and Lithocarpus lepidocarpus had higher seedling height under lower relative light intensities. Regardless of relative light intensity, Cyclobalanopsis longinux var. longinux, Cyclobalanopsis gilva allocated more biomass toward the foliar component. In contrast, for Lithocarpus lepidocarpus, Cyclobalanopsis acuta var. paucidentata the biomass were equally partitioned among the foliar, stem, and root components. For the four species, leaf area ratio (LAR) and species leaf ratio (SLA) increased with decreasing relative light intensity. For all four species, RGR was negatively correlated with SLA and LAR. Based the responses to the three relative light intensities, the four species could be separated into two groups: Cyclobalanopsis longinux var. longinux and Cyclobalanopsis gilva could be considered as shade-intolerant species since they grew much better under high light environment than under low light environment; whereas Cyclobalanopsis acuta var. paucidentata and Lithocarpus lepidocarpus could be considered as shade-tolerant species since they still had good growth performance under relatively low light environment. This study suggested that one of the reasons that the four species could co-occur was in their abilities to differentiate along the light gradient. Keywords: Relative growth rate, relative light intensity, growth rank