●第四段：
段意：
本段指出特殊矿物质的过量存在同样对植物生长有害。
难句分析：
1. Saline soils, which have high concentrations of sodium chloride and other salts, limit plant growth, and research continues to focus on developing salt-tolerant varieties of agricultural crops.
短语：high concentrations of：高浓度的
salt-tolerant：耐盐的;
释义：含盐土壤通常具有很高的氯化钠等盐类物质浓度，这会阻碍植物生长，因此科学研究持续关注着如何培育耐盐的作物品种。
2. Research has focused on the toxic effects of heavy metals such as lead, cadmium, mercury, and aluminum; however, even copper and zinc, which are essential elements, can become toxic in high concentrations.
主干：reseach has focused on the toxic effects of heavy metals;however,even copper and zinc can become toxic…;
释义：研究目前正在关注重金属物质，如铅，镉，水银，铝等对植物的毒害作用;然而，即使是铜和锌这类植物必须的营养元素也可能在高浓度时产生毒效。
●第五段：
段意：
本段指出科学家发现一些超聚植物，它们能够将某种矿物质高浓度地聚集在自身周围。
难句分析：
1. Hyperaccumulators run the entire range of the plant world.
短语：run the entire range of：存在于包括(从…到…)之间的各类事物
释义：超聚植物在植物世界的各个品种中都存在。
2. Many are found in tropical and subtropical areas of the metals may afford some protection against plant-eating insects and microbial pathogens.
短语：afford protection：提供保护
分句：Many are found in tropical and subtropical areas of the metals实际上是“Many of
the metals are found in tropical and subtropical areas”，倒装是为了使“metals”顺接后面的“may afford some protection”
释义：许多在热带和亚热带发现的金属很可能为植物提供某种保护，使其免受害虫和微生病原体的侵害。
●第六段：
段意：
本段指出科学家通过利用超聚植物来低成本清理污染地区。
难句分析：
1. Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals – an environmentally friendly approach known as phytoremediation.
释义：本句介绍了利用超聚植物清洁过量重金属的办法----植物修复术(phytoremediation)。
直到现在研究者们开始考虑利用超聚植物来清洁那些被过量重金属污染的土壤和地区，这是一种环保手段，被称为植物修复术。
2. A harvest of the shoots would remove the toxic compounds off site to be burned or composted to recover the metal for industrial uses.
词汇：recover：文中指将金属还原
主干：a harvest of the shoots would remove the toxic compounds to be burned or composted…
释义：通过收割超聚植物的秧苗可以将土壤中的有害物质移除，将其掩埋或进行堆肥，为工业生产还原金属原料。
3. After several years of cultivation and harvest, the site would be restored at a cost much lower than the price of excavation and reburial, the standard practice for remediation of contaminated soils.
分句：“the standard practice for remediation of contaminated soils”作定语，指前句中的“excavation and reburial”，指采掘和填埋这类传统去污手段
释义：经过几年的种植和收割，人们能够以远远低于采掘和填埋这类传统去污手段成本的价格来恢复污染地区。