南仁山森林內的二氧化碳濃度梯度及其對林下小苗光合作用的影響

Forest CO2 Gradient and Its Effects on Photosynthetic Characteristics of Understory Seedlings in the Nanjenshan Forest

鄭鈞謄(Chun-Teng Cheng) ； 郭耀綸(Yau-Lun Kuo)

《台灣林業科學》 19卷2期 (2004/06) Pp. 143-152

https://doi.org/10.7075/TJFS.200406.0143

摘要

本研究測定南仁山低地雨林冠層垂直剖面的CO2濃度，並比較30種天然更新小苗在二種CO2濃度下淨光合作用率的反應。測定結果發現，森林冠層內CO2濃度隨冠層高度的降低而升高，具分層現象，在近地表處最高。於2000年測得離地表2及20 cm處白天的CO2濃度分別為423±38及381±9μlL^(-1)，而樹冠頂只有361±54μlL^(-1)。在季節變化方面，近林床至20 cm高範圍內的CO2濃度在夏季(7-9 mo)較高，而冠層上方的CO2濃度在同時期最低。天然更新的24種耐蔭小苗與6種非耐蔭小苗，當CO2濃度由360提高至400μlL^(-1)時，光合作用光補償點分別降低25及13%，暗呼吸率分別降低25及5%。在15μmol m^(-2)s^(-1)低光條件下，當CO2濃度升高40μlL^(-1)時，耐蔭種小苗的光合作用CO2利用效率為非耐蔭種的3倍。本研究也發現各種小苗的需光指標值與其CO2利用效率有顯著負相關，越耐蔭的小苗對CO2利用效率越高。耐蔭小苗可利用林床自然增加的CO2資源，在林下低光環境可使光合作用生產力提高。

關鍵字

樹冠層 ； 二氧化碳利用效率 ； 暗呼吸率 ； 光補償點 ； 二氧化碳分層現象

並列摘要

We monitored the CO2 profile within the canopy in the lowland rainforest of Nanjenshan. We also measured the responses of net photosynthesis in 30 species (24 shade-tolerant and 6 shade-intolerant species) of naturally regenerated seedlings under 2 different CO2 concentrations. Results showed that stratification of CO2 concentrations did exist, such that as the height above the ground decreased, CO2 concentrations increased. As a result the highest CO2 concentration was measured near the forest floor In 2000, the avenge daytime CO2 concentrations measured at 2 and 20 cm above the ground were 432±38 and 381±9μ1L^(-1), respectively, while it was only 361±5.4μ1L^(-1) at the top of forest canopy. CO2 concentrations were the highest at heights below 20 cm, and the lowest at the canopy top during summer months (July~September). As CO2 concentrations rose from 360 to 400μ1L^(-1), photosynthetic light compensation points in seedlings of shade-tolerant and shade-intolerant species decreased 25 and 13%, and their dark respiration rates decreased 25 and 5%, respectively. Under low light (15μmol m^(-2)s^(-1)) and high CO2 (400μ1L^(-1)) conditions, photosynthetic CO2-use efficiency of the shade-tolerant seedlings was triple that of the shade- intolerant seedlings. A negative relationship between CO2-use efficiency and the light-demand index of all species tested was also found. These results indicated that shade-tolerant young seedlings growing under the canopy may benefit from the naturally enriched CO2 resource near the forest floor Thus, higher CO2 concentrations experienced under the canopy compensate the light limitation of photosynthesis of low-light grown shade-tolerant species.

並列關鍵字

canopy ； CO2-use efficiency ； dark respiration ； light compensation point ； stratification of CO2 concentration