以生長分析和模式化評估結球萵苣的生長變異與氣候條件之關聯

結球型萵苣（Lactuca sativa L.）是目前台灣秋冬至隔年晚春出口的指標蔬菜，尤其結球（heading）的表徵特性易受高溫限制，因此主要產期在當年10月至隔年4月間，若可經由分析不同期作氣候條件造成萵苣生長變異的關聯性，並導入模式化參數的管理指標，將可積極發展出萵苣田間生產的智慧管理系統。以結球萵苣的生產標的而言，有市場價值的部位在地上部葉球（leafy head）（未展開內葉），而已展開之外葉（outer leaf）則於採收與儲運過程具保護功能；但從植株成長過程的生理調節而言，外葉是光合產物的主要供源（source），而葉球是光合產物的標的積儲（sink），故外葉生長表現可謂主導葉球產量的首要栽培管理指標。本研究以2017-2018年於雲林縣二崙鄉兩處結球萵苣試驗田區（427號和382號）各3期作的植株生育調查與生長紀錄資料，分期作套配指數型的馬爾薩斯生長模式（Malthusian growth model），以推估結球萵苣生長的關鍵生理參數：相對生長率（relative growth rate; RGR）和相對葉生長率（relative leaf-growth rate; RLR），藉此探討不同期作結球萵苣的生長變異與氣候條件間之關聯性。結果顯示，不同期作生長模式的參數推估值確實與季節性氣候差異造成植株生長變異有關，生長期間的平均溫度較高或日照數較長有促進結球萵苣生物量累積和葉面積伸展之趨勢，而且平均溫度漸升或日照數漸增也較有利於植株生長。本研究再分別依總葉片和外葉為假設供源，以RGR和RLR推估值導入生長模式，計算淨同化率（net assimilation rate; NAR），由設定不同供源計算的NAR模擬曲線差異可推論得知，外葉為供源的光合產物大部分會轉移至地上部，以促進葉球內葉面積伸展及乾重累積，而葉球內葉並非主要供源。再者，依據不同供源計算的NAR曲線於生長初期之交會點，可用於回溯球心發育（hearting）的起始日期，並依平均生長積溫日數（growing degree days; GDD = 735）可推算最適採收日期。

關鍵字

指數函數；相對生長率（RGR）；葉面積比（LAR）；淨同化率（NAR）；結球

並列摘要

Crisphead lettuce (Lactuca sativa L.), which is often grown in cool-season region in Taiwan is the flagship vegetable for export. Because high temperature will cause bolting without head formation (i.e., heading), head lettuce is often cultivated from early autumn until the following spring. The relationship between lettuce growth variations and seasonal climate conditions was investigated by modeling parameters in plant physiology to positively develop a smart management system for lettuce production in the field. Only leafy head (i.e., curly inner leaves) of crisphead lettuce has a market value; outer leaves are mainly used for protection during harvest, storage and transportation. However, outer leaves play an important role in plant physiology by providing photosynthate (i.e., source) to support leafy head, which is the primary utilizer of photosynthate (i.e., sink) for growing inner leaves. Growth of outer leaves could be used as an index for the yield of leafy head during harvest and planting management. This study was conducted in two experimental sites no. 427 and 382 located at Erlun Township, Yunlin County during the period 2017-2018. Growth of lettuce plants was measured in three cropping seasons (I/2017, II/2017 and I/2018). In order to investigate the relationship between growth variations and climate conditions, the Malthusian growth model was used to estimate physiological parameters: relative growth rate (RGR) and relative leaf-growth rate (RLR). The results revealed that both RGR and RLR were related to the growth variations of lettuce in three cropping seasons, which would be due to the seasonal climate changes. Higher monthly average temperature and longer monthly daylight hours enhanced the biomass accumulation and leaf area expanding. Within cropping season, the gradual increases of average temperature and daylight hours were also beneficial for plant growth. In addition, the growth models for estimation of RGR and RLR were used to simulate net assimilation rates (NARs) in shoot, given that all leaves or outer leaves were the primary source of photosynthate. Based on the simulated curves of NAR, outer leaves provided most of photosynthates, which were transferred into shoots to promote area expanding and dry mass accumulation of curly inner leaves in leafy head. The intersection of both simulated curves of NAR derived from the outer leaves and all leaves indicated the date of hearting. Eventually, an average of growing degree days (GDD = 735) was suggested to be as an index of harvest date.

並列關鍵字

Exponential function ； Relative growth rate (RGR) ； Leaf area ratio (LAR) ； Net assimilation rate (NAR) ； Heading

國際替代計量

以生長分析和模式化評估結球萵苣的生長變異與氣候條件之關聯

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