三種殼斗科樹種苗木在缺水逆境下之生長、光合作用及葉綠素螢光表現

Abstract

本試驗於台大農場溫室進行，以森氏櫟 (Cyclobalanopsis morii)、三斗石櫟 (Pasania hancei)及狹葉櫟 (Cyclobalanopsis stenophylloides) 作為試驗樹種。目的在探討這 3 種樹種在所擬訂的缺水逆境歷經不同持續時間之後其生長形態、氣孔導度、光合作用速率、葉綠素螢光參數等之變化。生長介質水勢分為3種變級：充分澆水 (1–2 日澆水一次，C)、中度水逆境 (-90~-50 kPa，M)及重度水逆境 (-190~-130 kPa，S)，並依這3種變級及持續時間1或2個月組合成5種處理 (CC、CS、MM、MS及SS)，隨後又恢復正常澆水1個月，試驗期間從 2008 年 5 月持續到 2008 年 8 月。 結果顯示：各級缺水逆境處理的苗高、苗徑相對生長量皆幾停滯而與對照處理間有顯著差異，受害最深者為森氏櫟，重度缺水2個月後苗木全部死亡。葉部長/寬比例也有顯著變化，而變得較為狹長。葉綠素濃度在各逆境處理下的變化因樹種而異，森氏櫟及三斗石櫟不論中度或重缺水處理皆下降，狹葉櫟則只在重度缺水下才顯著下降。 受缺水處理苗木之淨光合作用(Pn)率及氣孔導度(gs)皆下降，水分利用效率(WUE)雖有隨缺水處理而發生變化，三斗石櫟及狹葉櫟則只有重度缺水處理持續2個月後始有顯著差異，森氏櫟則在重度缺水1個月後即有顯著下降。螢光參數中之Fv/Fm、 F′v/F′m、ΦPSII及qP等依缺水程度及處理時間而呈現出PS II活性下降，此同時，NPQ則上升以消散多餘的能量並保護PS II並使其減少受損。暗反應參數中，Rd的上升顯示出碳水化合物的耗竭。光合作用速率亦隨著gs、Vcmax及Jmax的下降而受到抑制，即是在中度或是重度缺水的處理中，Pn同時受到氣孔與非氣孔限制因素之限制。 恢復供水後，Pn、gs以及WUE除了森氏櫟之SS處理因苗木已死亡之外，其它樹種及處理均有不同程度之恢復。Fv/Fm、F′v/F′m、qP、ΦPSII及NPQ等螢光參數亦隨各處理之受損程度不同而有不同程度的復原。暗反應參數中，Rd的復原同時受到處理水勢及逆境持續期間的影響。Vcmax及Jmax的表現則在各缺水處理仍與對照組有顯著差異。

This study investigated stomatal conductance, photosynthetic rate and chlorophyll fluorescence parameters of Morii oak (Cyclobalanopsis morii), Nanban tanoak (Pasania hancei) and Arishan oak (Cyclobalanopsis stenophylloides) in response to simulated water deficits in the greenhouse of NTU, Taipei, Taiwan. This experiment classified the medium water potentials into three levels: non-stress (C), middle stress (-90~-50 kPa, M) and severe stress (-190~-130 kPa, S). Three levels were performed for 1 or 2 months and combined into five treatments of watering regimes (CC, CS, MM, MS, SS), and one month rewatering followed. This experiment was conducted from May 2008 to October 2008. Result showed that the relative growth rates of both height and diameter were differed significantly between control and water stress treaments. The most appalling injury was appeared in Morii oak, the seedlings died after 2 months of severe stress. The leaf length/width ratios in three species were significantly increased. The concentrations of chlorophyll under stress varied according to species, which of Morii oak and Nanban tanoak were decreased significantly whether in middle or severe stresses but of Arishan oak were decreased only in severe stresses. The net photosynthetic rates (Pn) and stomatal conductances (gs) were decreased in the stressed seedlings of all three species. Significant differences of water use efficiency (WUE) appeared after two months of severe stress in Nanban tanoak and Arishan oak instead of one month in Morii oak. The fluorescence parameters, Fv/Fm, F′v/F′m, ΦPSII, and qP, were significantly fell depending on the levels of water deficits or the lengths of treated periods, revealed the decreased activity of PS II; meanwhile, the rising of NPQ quenched excess energy to protect PS II from damage. The dark reaction parameter of photosystem, Rd, showed that more carbonhydrate was exhausted. The photosynthetic rates of stressed treatments were decreaded due to decrease of gs, Vcmax and Jmax, which indicated both of stomatal and non-stomatal limitations were occurred under middle and severe stress. After rewatering, Pn, gs, and WUE were partially or mostly recovered in stress treatments except that the seedlings of SS treatment of Morii oak died. The fluorescence parameters, Fv/Fm, F′v/F′m, qP, ΦPSII, and NPQ were recovered according to the damage caused by treatments. The recovery of Rd was affected by both soil water potentials and the persistent period of stress. The performances of Vcmax and Jmax were still significantly different between stress and control set.