南仁山森林樹苗一日碳收支及利用斑光之研究

Carbon Budgets and Sunfleck Utilization by Tree Seedlings in Nanjenshan Forests

彭世賢(Shih-Hsien Peng)

指導教授 ： 郭耀綸

國立屏東科技大學/農學院/森林系所/碩士(2009年)

https://doi.org/10.6346/NPUST.2009.00207

摘要

本研究於墾丁國家公園南仁山生態保護區迎風坡森林，測定林下樹苗的淨光合作用率日變化，供計算一日碳收支，並探討斑光對林下樹苗一日光合作用量的貢獻。選取的樹種有小葉樟、大頭茶、台灣八角、台灣蕘花、恆春石斑木及長尾尖葉櫧等6種耐陰樹種，以及白桕、白匏仔及野牡丹等3種陽性樹種的天然更新苗各4株。測定期間為2007年5月至2008年4月，每月測定一日光合作用日變化。
測定結果發現供試9種樹苗在11個測定日中，白天碳收入減去夜間碳支出所得的單位葉面積一日碳收穫量，以恆春石斑木最高，達2.92 g CO2 m-2 d-1，最低者為白匏仔，僅有1.28 g CO2 m-2 d-1。供試樹種一日碳收穫量皆與白天累積光量有顯著正相關。將各植株的一日碳收穫量分別乘以單株總葉面積，得單株一日碳收支，結果以長尾尖葉櫧最高，達88.7 mg CO2 d-1，其次為野牡丹及大頭茶，分別為84.1及42.3 mg CO2 d-1。單株葉面積較高的植株可有較高的一日碳收支。測定期間有7種樹種各測定日的單株一日碳收支皆為正值，然而白桕及白匏仔分別有2株及3株樹苗，因自然擾動使植株受損，致單株一日碳收支在某期間呈現負值，短期之後即死亡。本研究發現，各樹種的光合作用潛力、接受到較高光資源的機會、能否長出較多的葉面積，以及是否遭遇自然擾動，都會影響植株一日碳收支量，進而影響在林下低光環境的生存機會。
在斑光對林下樹苗光合作用的貢獻方面，6種供試樹苗於白天8小時期間，平均只有18%的時間能照射到斑光，但有斑光照射時累積的光量及光合作用量分別可達白天總量的45%及35%，顯示斑光對這些樹苗的碳收穫有很大的貢獻。供試6種耐陰樹種中，台灣蕘花及恆春石斑木對斑光的利用效率最高。

關鍵字

碳收穫 ； 一日碳收支 ； 光合作用日變化 ； 葉面積 ； 光資源 ； 斑光

並列摘要

This study investigated the diurnal course of photosynthesis, daily carbon budget, and photosynthetic utilization of sunflecks in seedlings of nine hardwood species growing in the windward sites in Nanjenshan Ecological Reserve, Kenting National Park. These species included 6 shade-tolerant species, Cinnamomum brevipedunculatum, Gordonia axillaries, Illicium arborescens, Wikstroemia taiwanensis, Rhaphiolepis indica, and Castanopsis cuspidate, as well as 3 shade-intolerant species, Sapium discolor, Mallotus paniculatus, and Melastoma candidum. Four seedlings of each species were monitored for their daily photosynthetic variation once every month from May 2007 to April 2008.
Results showed that seedlings of Rhaphiolepis indica had the highest daily carbon gain of 2.92 g CO2 m-2 d-1, while seedlings of Mallotus paniculatus had the lowest (1.28 g CO2 m-2 d-1). In general, daily carbon gain showed positive relationship with light availability. By multiplying daily carbon gain with total leaf area of a seedling, we had daily carbon budget. Castanopsis cupidata had the highest daily carbon budget of 88.7 mg CO2 d-1, followed by Melastoma candidum (84.1 mg CO2 d-1) and Gordonia axillaris (42.3 mg CO2 d-1). Seedlings with larger per stem leaf area generally possessed higher daily carbon budget. Besides Sapium discolor and Mallotus paniculatus, seedlings of the other 7 species all had positive daily carbon budget. Some seedlings of Sapium discolor and Mallotus paniculatus were damaged by natural disturbance, so that their daily carbon budget became negative in some periods, and died shortly after. We found that photosynthetic potential, opportunities of receiving higher light resources, per stem leaf area, and natural disturbance would all affect daily carbon budget of a seedling, and further affect its survival under low light environment of understroy.
As to the contribution of sunflecks to photosynthesis of seedlings in the understory, seedlings of the 6 shade-tolerant species could receive sunflecks only in 18% of day time. However, the cumulative light of the sunflecks and photosynthesis reached 45% and 35% of total amount, respectively. This result indicated that sunflecks did contribute greatly to carbon gain in these seedlings. Among the 6 species, Wikstroemia taiwanensis and Rhaphiolepis indica were the most efficient in utilizing sunflecks.

並列關鍵字

carbon gain ； daily carbon budget ； diurnal photosynthetic rate ； leaf area ； light resources ； sunflecks

參考文獻

郭耀綸、尤國霖、楊月玲、王相華 (2007) 颱風擾動對台灣南部墾丁森林林下光量及六種樹苗生長的影響。台灣林業科學22(4): 351-364。

郭耀綸、范開翔 (2003) 南仁山森林倒木孔隙三年間的更新動態。台灣林業科學18(2): 143-151。

郭耀綸 (2000) 南仁山熱帶低地雨林白榕冠層及林下植物的光合作用。台灣林業科學15(3): 351-363。

郭耀綸、楊月玲、吳祥鳴 (1999) 墾丁熱帶森林六種樹苗生長性狀及光合作用對光量的可塑性。台灣林業科學14(3): 255-273。

鄭鈞謄 (2002) 南仁山低地雨林二氧化碳濃度的動態變化及其對林床幼苗光合作用的影響。國立屏東科技大學森林系研究所碩士論文，83頁。