本試驗探討土壤水分變化對秋季梨樹地上部與根部生長之影響，以2 年生嫁接於鳥梨 (Pyrus lindleyi Rehder)實生苗之蜜雪梨(P. pyrifolia Nakai ‘Tainung No.2’)盆植植株為試驗材料， 2007 年10 月8 日至2008 年1 月3 日於國立臺灣大學園藝試驗分場，進行5 種灌溉處理，控制組 (CK)之土壤體積含水量(θv)維持於30%-45%；處理二(D)之植株於灌溉後停止供水至θv<20%再給 水至θv=45%；處理三(D+3F)之植株於灌溉後停止供水至θv<20%時行淹水處理3 日；處理四(LD+3F) 之植株於灌溉後停止供水至θv=25%-30%時行淹水處理3 日；處理五(D+5F)之植株於灌溉後停止 供水至θv<20%時行淹水處理5 日。定時調查測量植株地上部葉片與根系之生長。試驗期間各處 理植株宿存葉比例變化可概分出2 個群組：CK、LD+3F 與D、D+3F、D+5F。前者於試驗期間落 葉率較緩和，後者落葉率較高。D+3F 與D+5F 處理之新葉生長量較高，CK、D 與LD+3F 處理之 新葉生長量較低。然而不論何種處理，試驗前期全樹葉面積之組成多以宿存葉為主，試驗後期除 D 與LD+3F 處理之全樹葉面積組成以宿存葉為主外，CK、D+3F 與D+5F 處理之全樹葉面積組成 皆以試驗期間所長出之新葉為主。水分試驗前期各處理之有效根系分佈相對生長速率變化較大， 水分試驗後期除LD+3F 處理之有效根系分佈量持續增加外，D+3F 與D+5F 處理之有效根系分佈 相對生長速率則隨試驗時間增加而遞減，而CK 與D 處理之有效根系分佈相對生長速率則於處理 85 天之後下降。試驗前期各處理之新生根總生產量與總死亡量未達顯著差異水準，新生根總存活 率以LD+3F 處理者最高。試驗後期亦以LD+3F 處理之新生根總生產量高於其他處理。試驗前期 各處理標定新生根維持白色比率與新生根存活力下降至50%所需之日數以CK 與LD+3F 處理較 高。試驗後期CK、D 與LD+3F 處理之新生根存活力高於D+3F 與D+5F 處理。試驗前期新生根 存活力隨宿存葉比例下降而減少，水分試驗前期新生根維持白色比率與新生根存活率之決定係數 分別為0.61 與0.74。試驗後期之植株宿存葉下降比例與新生根存活力之相關性則較低；水分試驗 後期之新生根維持白色比率與新生根存活率之決定係數分別為0.31 與0.38。結果顯示在亞熱帶氣 候的秋冬季，低需冷性的梨樹進入休眠之前，頻繁且劇烈的土壤乾濕交替變化，易導致大量新葉 萌發及提高新生根死亡率，兩者皆不利溫帶果樹生理與發育。

To document the effects of soil moisture fluctuation in autumn on canopy and root growth, 2-year-old ‘Tainung No. 2’ pears (Pyrus pyrifolia Nakai ‘Tainung No.2’) on (P. lindleyi Rehder) seedling rootstocks grown in containers were treated from 8 October 2007 to 3 January 2008. The irrigation schedules were as follows, control (CK): plants were watered to maintain volumetric soil water content (θv) between 30% and 45%; (D): plants were not watered until θv < 20% and then re-watered to restore θv to 45%; (D+3F): plants were not watered until θv < 20% and then flooded for 3 days; (LD+3F): plants were not watered until θv between 25% and 30%, and then flooded for 3 days；(D+5F): plants were not watered until θv < 20% and then flooded for 5 days. Canopy and root growth after treatments were measured periodically. Two distinctive patterns of leaf retention were identified among treatments. Plants in CK and LD+3F had slow defoliation than those in D, D+3F, and D+5F. Plants subjected to D+3F and D + 5F had more new leaf growth than those subjected to CK, D and LD + 3F。In the early stage of the experiment, canopy leaf area was mainly contributed by mature leaves regardless of treatments. In the late stage of the experiment, canopy leaf area of plants in CK, D+3F, and D+5F was contributed largely by new leaves. A higher fluctuation in relative growth of effective roots was observed in the early stage than in the late stage of the experiment. In the early stage, two growth peaks was observed in CK, D and D+5F, while 3 peaks were observed in D+3F and LD+3F. In the late stage, the effective root distribution of plants in LD+3F continuously increased while that in the other treatments gradually decreased. There was no significant difference in new root growth or mortality among treatments in the early stage, except a slightly more new root growth in LD+3F. Plants in CK and LD+3F had higher percentages of new roots remaining white and new root survivalship in the early stage. In the late stage, plants in CK, D and LD+3F had more root survival than the other groups. In the early stage, percent reduction in mature leaves was negatively related to new root remaining white and survival, with R2 = 0.608, 0.737, respectively. In the late stage, percent reduction in mature leaves was less related to new root remaining white and survival, with R2 = 0.306, 0.381, respectively. Our results indicated that in the subtropical autumn, frequent and severe soil moisture fluctuations resulted in off-season leafing and high new root mortality rate, both are detrimental for the physiology and development of temperate fruit trees.