小白菜‘鳳京’苗期缺水 生理指標研究

Abstract

為了能夠提出植物生理證據佐證葉綠素螢光作為遙測工具的適切性，是故設計了本試驗計畫，探討小白菜‘鳳京’苗期缺水的葉片生理反應。當‘鳳京’小白菜苗第三片葉萌生後，即移植至改良過之Snow & Tingey系統上，進行四種不同程度的缺水處理：對照組（CK；液面差4 cm）、輕度缺水組（A；液面差22 cm）、中度缺水組（B；液面差30 cm）及重度缺水組（C；液面差47 cm）。主要調查項目有葉片數、葉面積、光合作用率（AN）、氣孔導度（gs）、蒸散速率（E）、葉片內部CO2濃度（Ci）及一些螢光介量（Fv/Fm、qP、qN、NPQ及ΦPSII）。結果顯示，輕微缺水組植株與對照組無明顯生長差異。中度及重度缺水植株之非光化學淬熄係數（qN或NPQ）約在開始調查後第4天明顯高於對照組，而PSII光量子產能（ΦPSII）則於第6天時顯著低於對照組。此二種葉綠素螢光介量均較AN、gs與E等光合特性對缺水敏感，且彼此間相關性亦甚高，顯見其似為指示植株光合特性缺水反應的良好生理指標。雖然中及重度缺水小白菜之葉面積在取樣開始6天後方顯著低於對照組，但缺水減少葉片數目之時間點顯然早於qN、NPQ與ΦPSII，所以此二螢光參數可能不適於反應葉片數與葉面積遭受缺水傷害的時間點。故此二參數應用在葉片生長量上勢必有所限制，至少於本試驗中僅適宜表達小白菜‘鳳京’光合特性的缺水損傷。

The leaf responses of Chinese mustard (Brassica rapa L. var. chinensis (Rupr.) Olsson) seedlings to water stress were investigated. When the third leaf emerged, seedlings were transplanted to modified Snow and Tingey system for four levels of water availability: control (CK, 4 cm below root screen), mild water stress (A, 22 cm below root screen), medium water stress (B, 30 cm below root screen), and severe water stresss (C, 47 cm below root screen). The measured parameters consists of the following: leaf numbers, the leaf area, the net photosynthetic rate (AN), the stomatal conductance (gs), the transpiration rate (E), the intercellular CO2 concentration (Ci) and some chlorophyll fluorescence parameters (Fv/Fm, qP, qN, NPQ and ΦPSII). It appears that the leaf responses of seedlings of mild water stress were identical with those of control. In this study the non-photochemical quenching (qN or NPQ) of plants which suffered medium and severe water stress performed significantly higher than those of control plants in about 4th sampled day, while the quantum yield of PSII electron transport (ΦPSII) was much lower in 6th day. These two chlorophyll fluorescence patterns are more sensitive to water stress than AN, gs and E. And fluorescence patterns are closely related to photosynthetic patterns. This leads to the possibility that qN, NPQ and ΦPSII are all well indicators to reflect the drought damage of photosynthetic patterns. Despite the fact that the leaf area of plants of medium and severe drought was significantly decline in 6th sampled day. If it is impossible to test the theory in any meaningful way, such claims have little credibility. There are flaws in attributing such importance to the cell enlargement alone. It must be noted that the decline of leaf numbers is more early than changes of qN, NPQ and ΦPSII. Stated another way, water deficit may effect the cell division very early. Thus these fluorescence patterns are less likely to indicate the damage of the leaf area. To conclude, results of this study showed that in Chinese cabbage qN, NPQ and ΦPSII are more likely to indicate the stress effect of photosynthetic patterns, but are less likely to work in leaf numbers and leaf area.