磷在土壤中，被植物利用時所遭遇最大問題，是大部分的磷易轉變為溶解度低的物質，且其移動性亦甚低，因而造成土壤溶液中磷的濃度偏低，使得磷的有效性降低。本研究在探討植物幼苗根圈在溶解難溶性的無機鈣磷時所產生的現象及分泌物質，以供溶磷菌應用對象之參考。選擇一些常見的作物包括豆科作物、禾本科作物、蔬菜作物等，首先將作物種植在半固體試管培養基中，以收集根圈分泌物，高速離心後分析其內容物之可溶性磷含量及利用HPLC分析分析有機酸成分。另將種子消毒後種在含銨態氮的難溶性鈣磷培養基上，觀察作物之根圈是否會產生透明圈，以此判定是否有溶磷現象的進行。並拍照且紀錄其根圈溶磷之特徵。
結果顯示，在不同氮肥的培養基中，植物根部產生的可溶性磷的量，以利用銨態氮為氮肥處理者的所測得的可溶性磷含量最高，但對於植物幼苗的生長，卻沒有多大的影響。植物根部所分泌的酸會隨著不同的氮肥處理而有所不同，植物的根部所分泌的酸有草酸、二酮基葡萄糖酸以及D—葡萄糖酸等。利用平面培養法所種植的十種作物均會產生溶磷現象，且溶磷的範圍會隨著時間愈久而擴大。其中以禾本科的作物的溶磷區域最大，十字花科最少。The major problem with the utilization of soil phosphate by plants is that the large portion of soil phosphate easily becomes insoluble. The insoluble soil phosphate has low mobility and thus causes low phosphate concentration in soil solution, or low phosphate availability. The soil available phosphate, which can be taken up by plants includes H2PO4-. Combined with Ca, Fe or Al, phosphate can form Ca-P, Fe-P and Al-P complexes, which are the major constituents of soil inorganic phosphate. Phosphate solubilization can convert these recalcitrant phosphates into the available forms, and thus plants can more effectively absorb phosphate.
This study investigated weather the exudes within the seedling rhizosphere could solubilize the recalcitrant inorganic calcium phosphate. The crops selected for this study include legumes, Graminae and vegetables. The seeds of the crops were sterilized, and then sown on cultural medium of Ca-P solubilization. Two weeks later, it was observed if the rhizosphere of crops produced clear zones, which were used to judge the existence of phosphate-solubilization. The changing area and characteristic of clear zone of phosphate-solubilization were recorded. The crops with phenomenon of phosphate -solubilization were selected and planted in tubes with semi-solid cultural medium. The rhizosphere exudes were collected, centrifuged and then analyzed for their soluble P and for composition of organic acids, using HPLC analysis.
The results show that seedlings had the highest concentration of soluble P when grown in the medium with NH4+ as Nitrogen source. However, the Nitrogen source in the growth medium had little effect on growth of seedlings. The exudates of roots varied with N sources in the growth medium. The variety of root exudates included oxalic acid, 2-keto-gluconic acid and D-gluconic acid. Ten agronomic species grown in the plate dishes for 15 days showing translucent zones around the roots indicate the phenomenon of phosphate solubilization. The clear zone of phosphate -solubilization expanded with time. Among all, the species of Gramineae had the largest clear zone of phosphate-solubilization, and those of Cruciferae had the smallest.中文摘要…………………………………………………………...Ⅰ
英文摘要…………………………………………………………...Ⅱ
目錄………………………………………………………………...Ⅲ
表次………………………………………………………………...Ⅳ
圖次………………………………………………………………...Ⅴ
前言…………………………………………………………………1
前人研究……………………………………………………………2
一、磷在土壤中的固定………………………………………..3
二、磷在土壤中的型態………………………………………..4
三、土壤磷對植物的供應……………………………………..5
四、植物根圈與磷吸收之關係………………………………..8
五、植物根分泌物……………………………………………..8
六、促進植物生長及磷吸收的根圈微生物…………………10
材料與方法………………………………………………………..18
一、分析作物幼苗根圈之分泌物及所含水溶性磷含量……..18
鉬藍法…………………………………………………….22
二、作物幼苗溶磷現象的觀察 ─ 培養皿平板測試………...23
(1) 培養基配置……………………………………………23
(2) 測試作物種類…………………………………………23
(3) 種子表面消毒過程……………………………………23
(4) 幼苗種植………………………………………………24
結果與討論………………………………………………………..28
一、作物幼苗在試管中之溶磷試驗………………………….28
1. 作物幼苗溶解磷酸三鈣的潛能分析………………….28
2. 不同氮源處理下對作物幼苗生長之影響…………….29
3. 植物幼苗在磷酸三鈣培養基中的有機酸分析……….32
二、作物幼苗溶磷現象的觀察 ─ 培養皿平板測試………...42
結論………………………………………………………………..54
參考文獻…………………………………………………………..55
附錄………………………………………………………………..6
