非生物逆境與生物刺激素對薄荷之生長與機能性成分之影響

Abstract

薄荷為唇形花科(Lamiaceae)薄荷屬(Mentha)之香草植物，廣泛分布於各大洲。薄荷具有香氣且富含機能性成分的特性使其能夠應用於許多領域。本研究選用日本薄荷(M. arvensis subsp. piperascens)及胡椒薄荷(M. ×piperita)作為試驗材料，探討兩種薄荷在非生物逆境及葉面施用生物刺激素後生長及其成分之變化，藉以釐清兩種薄荷在逆境下的耐受性及生物刺激素對薄荷的效果。 乾旱逆境試驗共四種處理，分別以田間容水量100%、70%、40%、及70%/40%為標準，低於設定田間容水量即澆灌。在FC70下，兩薄荷之生長指標較佳，FC40缺水下日本薄荷葉色較黃且主枝長度較短。日本薄荷在FC100下總酚含量最高，兩種薄荷之類黃酮含量各處理無顯著差異。兩薄荷主要揮發性成分為薄荷醇及薄荷酮，日本薄荷之兩成分於FC100與FC70/40較高，胡椒薄荷則在FC70與FC70/40較高。 鹽害逆境試驗共0、20、40、80、160 mM五種濃度處理。結果顯示兩薄荷之生長勢皆隨鹽害程度提升受到抑制，在鹽害處理下葉色較為濃綠。在鹽害程度較高處理，兩薄荷的總酚及類黃酮含量較低，顯示鹽害對植株造成氧化損傷嚴重。揮發性成分結果於兩薄荷呈現一致趨勢，20與40 mM處理測得薄荷醇濃度較高，20 mM處理下薄荷酮濃度較高。 葉施腐植酸試驗分為57.5、115、230、及460 mg·L-1，並以葉施清水作為對照。在57.5及115 mg·L-1處理下，兩薄荷植株較茂盛，生長指標高於其它處理，過高濃度腐植酸會抑制生長。兩種薄荷總酚含量與生長情形呈正相關，皆在57.5 mg·L-1處理最高，對照組或更高濃度之腐植酸處理較低；總類黃酮含量方面，日本薄荷在460 mg·L-1處理顯著較低，胡椒薄荷無顯著差異。日本薄荷之薄荷醇含量在57.5 mg·L-1處理達最高，薄荷酮含量在對照組較高，兩物質呈相反趨勢。胡椒薄荷之薄荷醇含量在57.5 mg·L-1處理最高，薄荷酮含量處理間無顯著差異。 葉施海藻萃取物試驗分為0.5、1.0、2.0、及4.0 mL·L-1，並以葉施清水作為對照組。施用海藻萃取物可以促進兩薄荷之生長，在2.0 mL·L-1處理之葉片鮮乾重較高，過高海藻萃取物濃度會抑制生長。日本薄荷的總酚與類黃酮含量隨施用濃度提升而增加，胡椒薄荷含量則在1.0及2.0 mL·L-1處理達到最高。日本薄荷的薄荷酮與薄荷醇含量於1.0及2.0 mL·L-1處理較高；胡椒薄荷之薄荷酮含量不受海藻萃取物施用濃度影響，而施用1.0-4.0 mL·L-1海藻萃取物相較對照組能有效提升薄荷醇含量。 結合上述四試驗，將逆境及葉施藥劑同時對薄荷進行處理。乾旱以FC40作為基準，鹽害以40 mM為施用濃度；腐植酸濃度選用57.5 mg·L-1，海藻萃取物為2 mL·L-1。在乾旱及鹽害處理下，兩薄荷之生長指標皆低於對照組，生長受到明顯抑制。施用腐植酸或海藻萃取物能促進生長，逆境下施用生物刺激素處理之葉片鮮乾重可提升至接近對照組或更高之重量。施用生物刺激素顯著提升總酚及類黃酮濃度，而施用生物刺激素之處理生長狀態較佳，其含量亦有上升趨勢。鹽害逆境及施用生物刺激素之處理皆對於揮發性成分合成具有正面效益，日本薄荷在鹽害下施用海藻萃取物，可得最高之薄荷酮、薄荷醇、及香芹酮含量；胡椒薄荷對逆境較敏感，無逆境下施用腐植酸較能提升薄荷酮及薄荷醇之含量。 無論是乾旱或鹽害逆境，皆會造成兩種薄荷生長受到抑制，而施用適量生物刺激素有促進生長及緩解逆境之影響，然施用過高濃度會產生抑制情形。各項數據顯示日本薄荷皆優於胡椒薄荷，且台灣之生長環境較適合栽培日本薄荷，相較胡椒薄荷更有經濟推廣價值。

Mint (Mentha), a genus of aromatic herbs in the family Lamiaceae, is widely distributed across continents. Its pleasant aroma and richness in functional compounds have enabled broad applications in various fields. In this study, Japanese mint (M. arvensis subsp. piperascens) and peppermint (M. ×piperita) were used as experimental materials to investigate their growth performance and phytochemical responses under abiotic stresses and foliar application of biostimulants. The objective was to clarify the stress tolerance of the two species and to determine the effects of biostimulants on mint cultivation. The drought experiment included four treatments based on 100%, 70%, 40%, and 70%/40% field capacity (FC), with irrigation applied when soil moisture fell below the designated threshold. Both species exhibited better growth at FC70, whereas Japanese mint grown under FC40 showed yellowish leaves and shorter main stem length due to water deficiency. Total phenolic content was highest in Japanese mint at FC100, while flavonoid concentrations showed no significant differences among treatments for either species. Menthol and menthone were identified as the major volatile compounds; in Japanese mint, both compounds were higher at FC100 and FC70/40, whereas in peppermint, the highest levels occurred at FC70 and FC70/40. The salinity experiment consisted of 0, 20, 40, 80, and 160 mM NaCl treatments. Increasing salinity inhibited the growth of both species, and leaves appeared darker green under salt stress. Higher salinity treatments resulted in reduced total phenolic and flavonoid contents, indicating severe oxidative damage to the plants. Volatile compound profiles showed similar trends in both species, with higher menthol concentrations detected at 20 and 40 mM NaCl, and menthone content elevated at 20 mM. The foliar humic acid experiment included 57.5, 115, 230, and 460 mg·L-1 treatments, with water spray as the control. The 57.5 and 115 mg·L-1 treatments promoted vigorous growth in both species, while excessive concentrations suppressed growth. Total phenolic content was positively correlated with growth performance, reaching the highest level at 57.5 mg·L-1 and decreasing at higher concentrations or in the control. For flavonoids, Japanese mint showed significantly lower levels at 460 mg·L-1, while peppermint exhibited no significant differences. Menthol content in Japanese mint peaked at 57.5 mg·L-1, whereas menthone was higher in the control, showing opposite patterns. In peppermint, menthol was highest at 57.5 mg·L-1 and menthone did not differ significantly among treatments. The foliar seaweed extract experiment tested 0.5, 1.0, 2.0, and 4.0 mL·L-1 applications, with water spray serving as the control. Seaweed extract enhanced the growth of both species, with the highest leaf fresh and dry weight observed at 2.0 mL·L-1; excessive concentration inhibited growth. In Japanese mint, both total phenolics and flavonoids increased with higher application concentrations, whereas peppermint showed the highest levels at 1.0 and 2.0 mL·L-1. For volatile compounds, Japanese mint exhibited higher menthol and menthone contents at 1.0 and 2.0 mL·L-1. In peppermint, menthone content was unaffected by seaweed extract, while seaweed extract at 1.0–4.0 mL·L-1 effectively increased menthol content compared with the control. To integrate the above findings, a combined treatment experiment was conducted using FC40 (drought), 40 mM NaCl (salinity), 57.5 mg·L-1 humic acid, and 2.0 mL·L-1 seaweed extract. Both mints showed reduced growth under drought or salinity, but the application of humic acid or seaweed extract alleviated stress effects, with leaf fresh and dry weights approaching or exceeding those of the control. Biostimulant treatments significantly increased total phenolic and flavonoid concentrations, and improved growth corresponded with elevated levels of these compounds. Both salinity stress and biostimulant application enhanced the biosynthesis of volatile compounds. In Japanese mint under salinity stress, seaweed extract produced the highest menthone, menthol, and carvone contents. Peppermint was more sensitive to stress, and humic acid application under non-stress conditions was more effective in increasing menthol and menthone contents. Overall, both drought and salinity stresses suppressed the growth of Japanese mint and peppermint, whereas appropriate doses of biostimulants promoted growth and mitigated stress effects; however, excessive application led to inhibition. Across all experiments, Japanese mint consistently outperformed peppermint, indicating that Taiwan’s cultivation environment is more favorable for Japanese mint and that it holds greater potential for economic production compared with peppermint.