溫度、礦物營養與介質體積含水量對沙漠玫瑰生長之影響

Abstract

沙漠玫瑰[Adenium obesum (Forssk.) Roem. Schult. ]具特別的株形和豐富的花型花色，深受歡迎。然而亟待建立沙漠玫瑰穴盤育苗期間之養分管理標準，以加速整齊生產。本研究探討溫度、養液氮(N)濃度、N型態、磷(P)濃度、鉀(K)濃度及介質體積含水量對沙漠玫瑰‘Harry Potter’生長之影響，以供栽培參考。 種子以日均溫19.1、21.1、24.3、29.2及32.4℃處理，結果顯示，17天後各處理之最大發芽率皆達85%-89%，並於32.4℃時，有較快的發芽速率，於均溫19.1℃時則會延遲發芽，依迴歸計算發芽的基礎溫度為13.5℃，發芽最低積溫為33.1℃d。 於子葉展開後，置於均溫20.6、22.8、25.2、28.9、33.5℃，搭配每週施用自來水、50%、100%及200%強生氏養液1次。結果顯示，不論溫度為何，未施用養液均不利於植株生長，尤其以20.6℃搭配自來水處理者，生長顯著受到抑制。以50%-200%養液濃度處理加上28.9及33.5℃，顯著加速第2及3對葉展開。以100%養液搭配28.9℃處理者，具有較高的葉面積、葉片數及乾重。 於子葉展開後，每週施予含0-24 mM N之強生氏養液1次。結果顯示，缺氮(0 mM N)及低氮(4-8 mM N)顯著延緩葉片展開時間，缺氮處理者全株葉片黃化並且老葉特別黃，完全展開葉數少、葉面積小，根冠比高。葉面積及株高隨養液N濃度由0-24 mM上升而增加，莖徑、完全展開葉數及葉綠素計讀值亦隨養液濃度增加，約在16-24 mM N達飽和。沙漠玫瑰‘Harry Potter’植體N、P及鈣(Ca)及鎂(Mg)濃度隨著養液N濃度由0 mM提升至24 mM而增加。 於子葉展開後，每週施予含0-4 mM P之強生氏養液1次。結果顯示，缺P(0 mM P)處理者其葉片較小，並且老葉呈現些微的紫紅色，並且顯著延緩第3對葉展開。株高隨養液P濃度於0-4 mM上升而增加，在1-4 mM時達飽和。0.25-4 mM P之總展開葉數、葉面積、葉綠素計讀值、莖徑及總乾重無顯著差異。植體P濃度隨養液P濃度由0提升至4 mM增加而上升；植體K濃度於養液P濃度0至1 mM之間無差異，養液P濃度提高至2-4 mM時植體K濃度下降。 於子葉展開後，每週施予含0-10 mM K之強生氏養液1次。結果顯示，缺K(0 mM K)顯著延緩葉片展開時間，第3對葉在2-10 mM K處理間無顯著差異。缺K處理者老葉出現黃化、葉緣焦枯及落葉等徵狀。株高、葉面積及總展開葉數隨養液K濃度由0-8 mM 上升而增加，並於4-8 mM K達飽和；莖徑及葉綠素計讀值於2-10 mM K間無顯著差異。植株乾重以6 mM K處理為最重，根冠比則以缺K處理最高。植體K濃度隨養液K濃度由0 mM增加至10 mM而上升；植體N濃度隨養液K濃度提高而下降；P、Ca及Mg濃度於各養液K濃度處理間無差異。 子葉展開後，分別於夏季及冬季，每週施含20 mM N 銨硝比(NH4＋:NO3－)為0:100、25:75、50:50、75:25 和100:0 之強生氏養液1 次。夏季生長期間以100% NO3-N處理使株高、莖徑及乾重顯著低於養液含有NH4-N處理者，且根冠比最小。施用養液NH4＋:NO3－為50:50、75:25及100:0使莖徑、葉面積及葉片數較大。養液NH4-N的比例由0%增加至50%使沙漠玫瑰的淨光合作用速率會隨之提高，並於NH4-N比例50%-100%時無顯著差異。植體N濃度於100% NO3-N養液處理者最低。植體K濃度於各處理間無顯著差異。冬季生長期間以100% NH4-N養液處理會使其株高、葉面積及葉片數顯著低於養液含有NO3-N處理者。隨著養液NH4-N 的比例由0%增加至100%，莖乾重及全株乾重隨之下降。光合作用速率於各N型態及比例處理中無顯著差異。植體N、P及K濃度於各處理間無顯著差異。 將穴盤苗移植後，以20%、40%、70%及20/70%介質體積含水量處理124天，結果顯示，莖徑、株高、乾重及根冠比於各處理間無差異。在70%VWC處理之光合作用顯著低於其他處理，是由於氣孔因素所限制；以40% VWC及20/70%VWC處理，氣孔導度、蒸散速率及細胞間隙CO2濃度皆最高；以20% VWC處理者雖氣孔導度降低，但仍能有效利用細胞間隙 CO2以維持光合作用速率。顯示沙漠玫瑰‘Harry Potter’耐旱但不耐濕，澆水時以乾溼交替使生長較佳。

Desert rose [Adenium obesum (Forssk.), Roem. Schult.] is a popular flowering potted plant due to its attractive sculptural caudex with a wide range of flower colors. However, nutrition management during slow and long plug production has not yet been well established. This study aimed to determine the effects of temperature, nitrogen (N), phosphorus (P), and potassium (K) concentration, nitrogen form, and volumetric water content on growth of A. obesum ‘Harry Potter’. Seeds were sown at mean temperature of 19.1, 21.1, 24.3, 29.2, and 32.4℃. Results showed that the maximum germination rate of each treatment was 85%-89%. Seeds germination was fast at 32.4°C and slow at 19.1°C. The base temperature of ‘Harry Potter’ was estimated as 13.5 ℃, and minimum thermal time for germination was 33.1℃d. After cotyledon fully expanded, the seedlings were placed at a mean temperature of 20.6, 22.8, 25.2, 28.9, and 33.5°C combined with tap water, 50%, 100%, and 200% Johnson's solution once a week. Results showed that tap water treatment reduced seedling growth, especially for those grown at 20.6°C. The time required for the second and third leaf-pair expansion was shortened with 50% to 200% Johnson's solution at 28.9 and 33.5°C. Leaf area, leaf number and plant dry weights were highest with 100% Johnson's solution at 28.9°C Seedlings were applied with Johnson’s solution containing 0-24 mM N weekly started after the cotyledon had fully expanded. Results showed that N deficiency and 4-8 mM N treatments took longer time for third leaf pairs to expand. N deficiency resulted in small and chlorotic leaves especially in old leaves. Leaf area and plant height increased with increasing N concentration from 0 to 24 mM. Stem caliper, leaf number, and SPAD-502 value increased with increasing N concentration up to 16 mM and did not increase significantly with further increased N. Tissue N, P, Ca, and Mg concentrations increased with increasing solution N concentration from 0 to 24 mM. Seedlings were applied with Johnson’s solution containing 0-4 mM P weekly from the fully expanded cotyledon. Results showed that P-deficient plant had smaller leaves, with purplish red old leaves, and took longer time for third leaf pairs to expand. Plant height increased with increasing P concentration up to 1 mM and did not increase significantly with further increased P. Leaf number, leaf area, SPAD-502 value, stem caliper, and plant dry weight did not differ at 0.25-4 mM P treatments. Tissue P concentration increased with increasing solution P concentration from 0-4 mM. Tissue K concentration did not differ between 0-1 mM P, and decreased with increased P at 2-4 mM. Seedlings were applied with Johnson’s solution containing 0-10 mM K weekly from the fully expanded cotyledon. Results showed that K-deficient plants took longer time for leaf pairs to expand, had the highest root to shoot ratio, and grow poorly, with necrotic or yellow leaves. Plant height, leaf area, and leaf number were not different among 4 to 8 mM K treatments. Stem caliper and SPAD-502 value were not different among 2 to 10 mM K treatments. Maximum plant dry weight was recorded at 6 mM K. Tissue K concentration increased and N decreased with increasing solution K concentration from 0 to 10 mM. Tissue P, Ca, and Mg concentrations did not differ among 0 to 10 mM K treatments. Seedlings were applied with Johnson’s solution containing 20 mM N in 0:100, 25:75, 50:50, 75:25, and 100:0 of NH4+:NO3－ ratio from cotyledon fully expanded during summer and winter, respectively. During summer growth period (30.2/24.9°C, 1418.1µmol·m-2·s-1), plants had higher stem caliper, leaf area and leaf number when supplied with 50:50, 75:25, and 100:0 of NH4＋:NO3－ than those with 100% NO3-N. Net photosynthetic rate increased with increasing NH4-N ratio from 0% to 50%. Tissue N concentration was lowest when supplied with 100% NO3-N. Tissue K concentration was not different with all treatments. During winter growth period (24.1/17.6°C, 953.8 µmol·m-2·s-1), plants had the lowest plant height, leaf area, and leaf number when supplied with 100% NH4-N. Stem dry weight and plant dry weight decreased with increasing NH4-N ratio from 0% to 100%. Net photosynthetic rate and tissue N, P, and K concentractions were not different among all treatments. After the plug seedlings transplanted, they were treated with 20%, 40%, 70%, and 20/70% volumetric water contents for 124 d. Results showed that stem caliper, plant height, dry weight, and root to shoot ratio did not differ among the treatments. The net photosynthesis rate and intercellular CO2 concentration in plants at 70% VWC treatment was significantly lowest through stomatal limitation. Net photosynthesis rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration were higher in plants at 40% and 20/70% VWC treatments. Stomatal conductance was also reduced in plants at 20% VWC treatment, while the intercellular CO2 concentraction can still be effectively used to maintain the net photosynthesis rate. Thus, Adenium obesum was categorized as drought-tolerant and moisture-intolerant species, alternate dry and wet for better growth when watering.