The use of aquatic plants for phytoremediation is an important method for restoring polluted ecosystems. We sought to analyze the capacity of different aquatic plant species to absorb heavy metals and to summarize available relevant scientific data on this topic. We present a meta-analysis of Cu, Zn, and Cd absorption capacities of aquatic plants to provide a scientific basis for the selection of aquatic plants suitable for remediation of heavy-metal pollution. Plants from the Gramineae, Pontederiaceae, Ceratophyllaceae, Typhaceae and Haloragaceae showed relatively strong abilities to absorb these metals. The ability of a particular plant species to absorb a given metal was strongly correlated with its ability to absorb the other metals. However, the absorption abilities varied with the plant organ, with the following trend: roots > stems > leaves. The pH of the water and the life habits of aquatic plants (submerged and emerged) also affect the plant’s ability to absorb elements. Acidic water aids the uptake of heavy metals by plants. The correlation observed between element concentrations in plants with different aquatic life habits suggested that the enrichment mechanism is related to the surface area of the plant exposed to water. We argue that this meta-analysis would aid the selection of aquatic plants suitable for heavy-metal absorption from polluted waters.

Mercury pollution in soil poses serious risks to human health through consumption of contaminated vegetables. We used a meta-analysis to examine the mercury enrichment ability of different vegetables and the main factors affecting mercury uptake. We drew the following conclusions. (1) Plants with a lower bioconcentration factor (BCF) include cowpea, long bean, and radish, whereas plants with a higher BCF include green pepper, spinach, cabbage, and Chinese cabbage. (2) Leaf and cucurbit have the highest and lowest capacity, respectively, for mercury enrichment. (3) When soil pH is <6.5, mercury level uptake by the plant increases, whereas it decreases when the pH is >7.5, meaning that increased soil pH reduces mercury uptake in soil. (4) When soil organic matter (SOM) is lower than 20 g/kg, tuber plants have the highest and eggplant has the lowest mercury adsorption capacity, respectively. When SOM is 20–30 g/kg, cucurbit has the lowest and leaf the highest adsorption capacity, respectively. When SOM is higher than 30 g/kg, however, eggplant has the highest mercury adsorption capacity, but there were no significant differences among the five types of vegetables. We argue that this meta-analysis aids in selecting vegetables suitable for absorption of heavy metals from polluted soil.

Herein, greenhouse experiments were designed to reveal the role of nitrogen-doped carbon dots (N-CDs) in enhancing maize drought tolerance. Two humidity conditions were created: adequate watering (soil moisture, 75%) and drought stress (soil moisture, 35%). Corn seedlings were harvested after spraying the N-CD solution (5 mg·L–1) on maize leaves for 5 days. The results indicated that foliar application of N-CDs increased the net photosynthesis rate (28.6%) of maize, and the fresh and dry weights of roots and shoots increased by 224.5, 360.0, 230.8, and 63.3% under drought stress, respectively. N-CDs showed high reactive oxygen species (ROS)-scavenging activity, resulting in enhanced superoxide dismutase activity (26.7%) and reduced malondialdehyde enzyme activity (18.9%). Besides, N-CDs could be used as light-harvesting materials to improve the light utilization efficiency, upregulate psbA gene expression (81.7-fold), and promote fast synthesis of the D1 protein, which could repair photosystem II under drought stress. Therefore, foliar-sprayed N-CDs could improve photosynthesis through multiple pathways under drought stress: light harvesting, photoprotection, and light repairing. Then, N-CD exposure reduced the corn yield loss under drought by nearly 30% compared with those of the control groups in a full life cycle study. Therefore, this study found for the first time that N-CD-enabled nanoagriculture could ensure crop growth and yield under drought stress, which would be important for global crop cultivation and a promising alternative to deal with the global climate change.

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