三種殼斗科樹苗在水逆境處理及恢復供水對生長、光合作用及葉綠素螢光表現之影響

Abstract

本試驗於臺大農場溫室進行，以短尾葉石櫟(Pasania harlandi)、烏來柯(Castanopsis uraiana)和赤皮(Cyclobalanopsis gilva)作為試驗的樹種，目的在探討這3種樹種在所擬定的水分控制下，不同持續時間之光合作用速率、葉綠素螢光各參數之變化，本研究將生長介質水勢分為四級：充分澆水(1~2天澆水一次)、輕度水逆境(-60 kPa至-90 kPa)、中度水逆境(-120 kPa至-160 kPa)及重度水逆境(-190 kPa至-250 kPa)，試驗期間從2006年9月持續到2007年1月。 結果顯示在不同水逆境處理下，短尾葉石櫟的苗高淨生長量在處理間未有顯著差異，苗徑淨生長量在處理W1表現最好，而葉面積淨生長量及SPAD讀值隨水勢的降低而減少，恢復充分供水後，葉面積淨生長量及SPAD讀值在處理間已無顯著差異。烏來柯在苗高、苗徑、葉面積淨生長量及SPAD讀值在處理間無顯著差異，恢復充分供水後，處理W3有一部分幼葉會脫落，使葉面積呈現負成長，全株乾重未有顯著差異。赤皮的苗高、葉面積淨生長量及SPAD讀值會隨水勢的降低而減少，苗徑淨生長量在處理間未有顯著差異，恢復充分供水後，處理間的大小序列亦是如此。 苗木的淨光合作用率、氣孔導度及蒸散速率具有類似的趨勢，皆隨水勢的降低而下降，惟短尾葉石櫟的處理W1例外，與對照組無明顯差異。在螢光參數的表現，暗適應下的Fv/Fm，短尾葉石櫟的處理W3明顯低於其他處理；烏來柯則隨水勢的降低而下降；赤皮在處理間皆無顯著差異。光適應下各螢光參數，短尾葉石櫟的處理W1與對照組無明顯差異，處理W2與W3的ΦPSII及qP皆顯著下降，處理W3之F'v/F'm顯著低於其他處理，NPQ在各處理皆無顯著差異。烏來柯之ΦPSII及qP在處理W3最低，F'v/F'm 及NPQ在各處理皆無顯著差異。赤皮之ΦPSII隨水勢的降低而下降，對照組之F'v/F'm明顯高於其他處理，qP在處理W3最低，NPQ在處理W2表現最高，處理W1、W3居中且二者間無顯著差異，對照組最低。 恢復供水後，短尾葉石櫟的處理W3受嚴重傷害無法恢復而死亡，處理W1及W2的淨光合作用率、氣孔導度及蒸散速率皆比對照組高，螢光參數之Fo、Fm、Fv/Fm、ΦPSII、qP、F'v/F'm 及NPQ均在各處理間無顯著差異，顯示短尾葉石櫟於適當乾旱環境下可強化其耐旱能力。烏來柯的淨光合作用率、氣孔導度及蒸散速率及螢光參數均有恢復的情形，且處理W1已回復至正常水準，但處理W3仍然顯著較低，得知當土壤水分供應減少，烏來柯會利用微量的光合作用而生存下來，但是長久而言，可能較為不利。赤皮的淨光合作用率、氣孔導度及蒸散速率及螢光參數均有恢復的情形，且處理W1已回復至正常水準，其他處理皆在回復中，顯示苗木雖可生存在廣闊的水分梯度環境，但仍以在土壤水分充足的生育地者生理活性較強，生長較佳。

This study investigated photosynthetic rate and chlorophyll fluorescence parameters of Short-tail-leaved tanoak (Pasania harlandii), Urai tanoak (Castanopsis uraiana) and Red bark oak (Cyclobalanopsis gilva) in response to simulated water treatments in the greenhouse of NTU farm. This experiment classifies the medium water potentials into four levels: non-stress (W0), mild stress (-60kPa ~ -90kPa, W1), moderate stress (-120kPa ~ -160kPa, W2) and severe stress (-190kPa ~ -250kPa, W3). The experiment was conducted from September 2006 to January 2007. Results showed seedlings height growth of Short-tail-leaved tanoak did not differ significantly among water treatments, with the largest diameter growth occurring in W1. Leaf area growth and SPAD readings decreased with decreasing water potential. Rewatering, leaf area growth and SPAD readings did not differ significantly among water treatments. Height growth, diameter growth, leaf area growth and SPAD readings of Urai tanoak did not differ significantly among water treatments. Rewatering, some young leaves of Urai tanoak fell off in W3, resulting in negative growth of leaf area. The dry weight of whole seedling of Urai tanoak did not differ significantly among treatments. Height growth, leaf area growth and SPAD readings of Red bark oak decreased with decreasing water potential but not diameter growth. Rewatering, growth parameters of Red bark oak still decreased with decreasing water potential. The net photosynthetic rate, stomata conductance and transpiration rate generally decreased with decreasing water potential, with one exception in that Short-tail-leaved tanoak did not differ significantly with W0 and W1. Fv/Fm of Short-tail-leaved tanoak was significantly lower in W3 than in the other treatments, that of Urai tanoak decreased with decreasing water potential, and that of Red bark did not differ significantly among treatments. Compared to W0, W1 had no significant effect on all chlorophyll fluorescence parameters of Shortly tail-leaved tanoak with light-adaptation, W2 and W3 significantly decreased ΦPSII and qP, and W3 significantly decreased F'v/F'm. In Urai tanoak, ΦPSII and qP is lowest in W3; and F'v/F'm and NPQ did not differ significantly among treatments. In Red bark oak, ΦPSII decreased with decreasing water potential; F'v/F'm was significantly higher in W0 than in the others; qP is lowest in W3; NPQ is highest in W2, intermediate in W1 and W3, and lowest in W0. Rewatering, Short-tail-leaved tanoak could not recover from the serious damage caused by W3 and eventually died, and the net photosynthetic rate, stomata conductance and transpiration rate were higher in W1 andW2 than in W0. Chlorophyll fluorescence parameters of Short-tail-leaved tanoak, Fo, Fm, Fv/Fm, ΦPSII, qP, F'v/F'm and NPQ, did not differ significantly among treatments, indicating that this species had enhanced the drought tolerance with the appropriate drought treatment. Rewatering, the net photosynthetic rate, stomata conductance, transpiration rate and chlorophyll fluorescence parameters of Urai tanoak all had recovered to different extents, reaching the normal level in W1 and still significantly lower than the normal level in W3, suggesting that Urai tanoak could survive with very low photosynthesis rate, but might not be favored in the long term. In all water treatments, the net photosynthetic rate, stomata conductance, transpiration rate and chlorophyll fluorescence parameters of Red bark oak had been recovering rewatering, reaching the normal level in W1, suggesting that this species could survive the broad water gradient, but still favored the environment with sufficient water supply.