Effects of soil water status on late season shoot and root growth of low chill Asian pears in lowland subtropical Taiwan

本研究於國立臺灣大學生物資源暨農學院附設農業試驗場園藝分場戶外進行，處理始於2007年10月8日，結束於2008年1月3日，水分試驗期間調查測量植株地上部葉片與根系之生長，探討秋季土壤水分變化對臺灣亞熱帶低海拔地區低需冷性梨樹地上部與根系生長之影響。本試驗以2年生，嫁接於鳥梨 (Pyrus lindleyi Rehder) 實生苗之蜜雪梨 (Pyrus pyrifolia Nakai cv. ‘Tainung No.2’) 裸根苗為試驗材料，分別進行5種灌溉處理，處理一為控制組 (CK)，該處理之土壤體積含水量 (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。試驗結果如下，比較水分試驗期間各受試植株地上部葉片之生長可知，乾旱 (D) 與土壤水分劇烈變化 (D + 3F, D + 5F) 促進植株成熟葉提早脫落。而由水分試驗期間梨樹根系之生長可知，水分試驗前期各受試植株具2至3次之生長高峰，於冬季水分試驗後期根系生長量降低，1月後新生根大量死亡，各受試植株僅保留少數白色與黃色根越冬。比較水分試驗前期梨樹根系生長模式可知，劇烈土壤水分變化降低新生根存活率；CK、D、D + 3F、LD + 3F與D + 5F處理於水分試驗前期之新生根總存活率分別為89.26±1.21%、82.95±2.43%、74.14±6.14%、92.28±2.10%與68.08±4.30%，各處理間比較達顯著差異水準。比較水分試驗前期與後期各受試植株標定新生根維持白色比率與新生根存活力下降至50%所需之日數可知，CK、D與LD + 3F處理之標定新生根存活力高於D + 3F與D + 5F處理。分析水分試驗前期植株宿存葉下降比例與標定新生根存活力兩者間之相關性可知，植株宿存葉下降比例與與新生根存活力呈顯著負相關；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、新生根存活率與植株宿存葉下降比例之決定係數分別為0.5562與0.7371。This research was carried out in Horticulture Research and Experimental Farm, College of Bio-Resources and Agriculture of National Taiwan University from October 8, 2007 to January 3, 2008. We measured shoot and root growth of low chill Asian pears in lowland subtropical Taiwan to document the effect of soil water status on late season shoot and root growth of potted two-year-old ‘Tainung No.2’/Lindley’s pear trees. Trees were irrigated with five irrigation treatments: Control treatment (CK), plants were maintained at 30-45% soil water content; Drought treatment (D), plants were not watered until soil water content below 20% and then irrigated back to 45%; Drought and 3 three-day Flooding (D+3F), plants were not watered until soil water content below 20% and then flooded for 3 days; Moderate Drought and 3 three-day Flooding (LD+3F), plants were not watered until soil water content to 20-30% and then flooded for 3 days; Drought and five-day Flooding (D+5F), plants were not watered until soil water content below 20% and then flooded for 5 days. Mature leaves after D, D+3F and D+5F treatments defoliated sooner than those subjected to CK and LD+3F. During the early period of the experiment, there were two to three peaks of root growth. In January, the vast majority of the new roots turned dark brown or was invisible, leaving on a small portion of survival white and yellow roots. By comparing the five irrigation treatments during the early period of the experiment, soil moisture fluctuation significantly decreased new root survival. New root survival (%) for the five irrigation treatments during the early period were: 89.26±1.21% (CK), 82.95±2.43% (D), 74.14±6.14% (D+3F), 92.28±2.10% (LD+3F), and 68.08±4.30% (D+5F). Overall by analyzing the longevity at when 50% of the new white roots turned yellow and at when 50% of the new roots turned dark brown, black or invisible, we found that plants subjected to CK, D and LD+3F had a higher new root survivorship compared to those subjected to D+3F and D+5F. By analyzing the correlation of canopy mature leaf retention (% of DAT0) versus cohort new roots remaining white (%) in DAFR40, we found that there was a high correlation between these two events. The coefficient of determination, r2, between new roots remaining white and canopy mature leaf retention (% of DAT0), and between new root survival and canopy mature leaf retention (% of DAT0) were 0.5562 and 0.7371, respectively