玉米各器官积累Pb能力的品种间差异

 为了研究不同玉米（Zea mays）品种及不同器官对Pb积累能力的差异，在土壤Pb含量为595.55 mg?kg－1 的高Pb胁迫和含量为195.55 mg?kg－1的低Pb胁迫（对照）条件下，采用盆栽试验结合火焰原子吸收等方法，测定了25个玉米品种各器官Pb的含量。结果表明：Pb 胁迫下供试玉米品种各器官含Pb量表现为根>茎≌叶>籽实；与对照相比，根、茎、叶Pb含量均大幅度提高，籽实含量的提高幅度相对较小；Pb胁迫条件下，有近半数的供试玉米品种的籽实Pb含量超过了国家规定的卫生标准，显示了在受重金属污染农田生产的玉米产品存在着较高的受Pb污染的风险。有22个品种平均籽实生物量在较强Pb胁迫下有所下降，降幅为0.9% ～ 38.7%，但平均降幅仅为12.6%，显示玉米在Pb胁迫下的减产不易察觉，从而增加了在受污染农田中玉米产品受Pb污染的风险。但研究也表明，在较高Pb胁迫下尚有52%的品种籽实Pb含 量未超过国家卫生标准最高限量值，因此可以利用这些品种在受Pb污染农田中进行玉米生产 ，以降低Pb经玉米产品进入人类食物链的风险。研究结果还发现供试玉米品种各营养器官间 Pb含量均呈极显著正相关，但营养器官与籽实Pb含量间无显著相关。其中在较强的胁迫条件下营养器官Pb含量特别高的品种No.1的籽实中Pb含量（0.19 mg?kg－1）比较低，未超过国家卫生标准；品种No.2、No.3和品种No.6也有类似的特点。除上述品种以及品种No.4外，其余品 种籽实Pb含量遵循与营养器官Pb含量成正比的一般规律。根中Pb含量特别高的品种No.1，籽 实产量在Pb胁迫下略有下降，但下降幅度最小。胁迫条件下，品种No.1的营养器官Pb总量最高（51.69 mg?plant－1），是对照的近12倍；籽实Pb含量符合国家标准的品种No.2 ，No. 3和No.6的营养器官Pb总量也较高，在36～42 mg?plant－1之间。由此可见，存在着在受Pb污染农田利用这些品种进行玉米生产同时修复受污染土壤的可能。

DIFFERENCES OF Pb ACCUMULATION AMONG PLANT TISSUES OF 25 ZEA MAYS VARIETIES

Pollutions of agricultural land by heavy metals impose a more and more serious risk to environmental and human health in recent years. Heavy metal pollutants may enter the human food chain through agricultural products and groundwater from the polluted soils. Progress has been made on phytoremediation, a safe and inexpensive approach to remove contaminants from soil and water using plants, in the past decade. However, in most cases, agricultural land in China can not afford to grow phytoremediator plants instead of growing crops to be economically sustainable. Therefore, new and effective methods to decrease the risk of heavy metal pollution in crops and to clean the contaminated soils are urgently needed. If we can find crop germplasms (including species and varieties) which sequester heavy metals in their edible parts, such as fruits of vegetables or grain of cereals, at low enough level for safe consumption, then we can grow these selected species or varieties in the lands contaminated or potentially contaminated by heavy metals. If we can find crop germplasms sequester low concentrations of heavy metals in their edible parts and high content of the metals in their ine dible parts, then we can use these selected species or varieties for soil remediation. In this study, the feasibility of the method is assessed by analyzing Pb contents in edible and inedible parts of 25 varieties of Zea mays grown under Pb contaminated soils. The soil concentrations of Pb were 595.55 mg?kg-1 in the high Pb_stress group and 195.55 mg?kg-1 in the control group.  The results showed that the Pb concentrations in different tissues were in the order of root>shoot≌leaf >grain. Compared with the control, the Pb concentration s in root, shoot and leaf were greatly increased under the highly Pb_ stressed c ondition, while the increments of Pb concentration in grain were relatively lower. Under the high Pb_stress, the grain Pb concentrations of 12 varieties exceede d the National Sanitation Standard of China (NSSC) and were inedible. This indic ates that there is a high Pb pollution risk for Zea mays grown on Pb polluted sites. Although 22 of the 25 tested varieties had harvest loss under the highly stressed condition, ranging from 0.86%-38.7% of the grain biomass acquired at the control, the average harvest loss of all tested varieties was only 12.6%, which is usually imperceptible in normal farming practices. Therefore the risk of Pb pollution in Zea mays products can not be promptly notified and prevented based on the outcome of the harvest. However, we did find 13 varieties of 25 tested varieties had grain Pb concentration lower than the NSSC. It is, therefore, possible to reduce the pollution risk if these favorable varieties are used for Zea mays production in Pb polluted or potentially polluted agricultural lands.  Pb concentrations in vegetative tissues (root, stem and leaf) were significantly correlated with each other, while Pb concentrations of each vegetative tissues were not significantly correlated with that of grain. Among the 25 tested varieties, some varieties had Pb concentrations in grain lower than (No.1-3 and No.6) or slightly above (No.4) the NSSC level, while their Pb concentrations in the vegetative tissues were among the highest. When excluding these varieties, correla tions between the Pb concentrations of grain and those of vegetative tissues of the rest of the tested varieties became highly significant. In addition, variety No.1 had the lowest harvest loss under high Pb_stress, and the highest Pb seque stration in vegetative tissues (51.69 mg?plant-1, 12 times as much as in the control). The similar features were also observed in varieties No.2, No.3 and No.6 , which sequestered 36-42 mg?Pb plant-1 under high Pb_stress. We recommen d these varieties of Zea mays to be used for bioremediation of Pb contaminated soil and crop production at the same time.