Copper stress alleviation in corn (Zea mays L.): Comparative efficiency of carbon nanotubes and carbon nanoparticles

Copper (Cu) stress is one of the predominant crop yield-reducing factors in agriculture. Application of carbon nanomaterials (CNMs) could have promotive effects on crop growth; however, their effects on alleviation of Cu stress for plants have rarely been documented. In this study, we investigated the comparative role of carbon nanotubes (CNTs) and carbon nanoparticles (CNPs) in corn (Zea mays) seed germination, seedling growth as well as Cu stress alleviation. The results showed that CNTs and CNPs stimulated corn seed germination by significantly increasing germination rate (GR), shortening the mean germination time (MGT), and increasing overall germination index (GI). They also significantly elongated seedling length and increased fresh biomass with optimal application rates ranging from 50 to 100 mg L^-1. Principle component analysis (PCA) confirmed that seed germination indexes and seedling growth were positively affected by CNTs or CNPs, but inversely influenced by high levels of Cu stress (> 20 mg L^-1). Furthermore, higher Cu accumulation and anti-oxidative enzyme activity (SOD, POD, CAT) were observed in plants co-exposed to Cu²⁺ and either CNTs or CNPs compared to plants exposed to Cu²⁺ alone. CNPs had stronger improvement on plant growth and Cu stress alleviation than CNTs, which suggest they may be cost-effective agriculture amendments to improve plant growth under heavy metal stress.