鉻、鎘與銅對番木瓜生長及營養元素吸收之影響

Abstract

隨著全球工業快速地發展，土壤重金屬污染已變成全球普遍的問題，土壤中過多的鉻、鎘與銅對植物的生長及養分吸收造成影響，且易進入食物鏈並逐漸累積在人體中。番木瓜為多年生半草本植物，生長快速且在莖和葉的部份富含白色乳汁，乳汁具有抗逆境的功能，是否亦具有耐重金屬之功能，是值得探討的課題。因此，本試驗之目的為探討在不同鉻、鎘與銅濃度對番木瓜生長及營養元素與重金屬吸收之影響。本試驗在本校農場簡易溫室利用水耕栽培台農 2 號番木瓜。以 Johnson 溶液為基本培養液，重金屬處理包括：0.5 μM 銅 (與 Johnson 溶液相同之銅濃度，故作為對照組)、10 μM 銅、50 μM 銅、0.5 μM 鎘、10 μM 鎘、50 μM 鎘、0.5 μM 鉻、10 μM 鉻、50 μM 鉻以及混合處理 (0.5 μM 之銅、鎘與鉻混合處理)。採逢機完全區集設計，每處理四重複。分別在重金屬處理後 7 天、21 天及 30 天採收，植體分為地上部及根部，於 70℃下烘乾至恆重後，秤其乾重，經植體粉碎機磨碎後進行化學分析，測定項目為氮、磷、鉀、鈣、鎂、鐵、錳、鋅等營養元素及銅、鉻、鎘等重金屬。結果顯示，隨著重金屬濃度越高，番木瓜植體中的重金屬濃度隨之增加，生質量顯著下降。營養元素的吸收也受到重金屬的影響：植體中的氮濃度隨鎘濃度增加而降低，銅和鉻處理抑制番木瓜磷的吸收，三種重金屬都會造成全株鉀、鈣及鋅濃度下降。鉻與鎘同時存在時，兩者互相競爭的結果使植體鉻及鎘濃度顯著降低，反而有類似解毒的效果。番木瓜對鉻、鎘與銅耐性較低，且大部分累積於根部。

Owing to the rapid development of industrialization, heavy metal contamination of soil has become a widespread global problem. The plant growth and uptake of nutrients were affected by copper (Cu), cadmium (Cd) and chromium (Cr) in the growth medium. The heavy metal can enter food chain. Papaya (Carica papaya L.) is a large tree-like and rapid growing plant, both the stem and leaves contain copious white milky latex. The latex is considered to relate to stress resistance. Therefore, whether this latex also relates to the heavy metal tolerance is intreasting. The purpose of this study was to investigate the effect of different concentrations of Cr, Cd, and Cu on the growth, and the nutrient, and heavy metal uptake of C. papaya. The experiment was conducted in the green house, National Taiwan University. The Tainung 2 cultivar was used in this study. The Cu, Cd, and Cr with the concentrations of 0.5, 10, and 50 μM respectively, were added to the Johnson’s solution; and there was also a treatment containing 0.5 μM Cu, Cd, and Cr simultaneously. All treatments were arranged in a randomized complete block design with four replications. The plants were harvested after treating for 7, 21, and 30 days. The harvested plants were separated into shoot and root then dried at 70℃ to constant weight. The concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn), Cu, Cd, and Cr in the plants were analyzed. The results show that the dry weight of plants decreased significantly with the increase of Cu, Cd, and Cr concentrations of the nutrient solution. The uptake of nutrients were affected by the treated heavy metals: the N concentrations of the plant decreased significantly with the increase of treated Cd concentrations. Phosphorus concentration of root decreased significantly with the increase of Cu and Cr concentrations of solution; K, Ca, and Zn concentrations of plants decreased significantly with the increase of treated Cu, Cd, and Cr concentrations. When Cd and Cr were present in the solution simultaneously, the competition between them resulted in the decreasing Cd and Cr concentrations in the plant. In summary, C. papaya can not accumulate Cr, Cd, and Cu to high concertrations, and showed no tolerance to these metals.