Stimulatory Effect of Fe3O4 Nanoparticles on the Growth and Yield of Pseudostellaria heterophylla via Improved Photosynthetic Performance

Nanomaterials have recently been used as growth stimulants to promote the production of crops in saline-alkali through root application. However, if applied through leaves, little is known about the effect of Fe 3 O 4 nanoparticles (NPs) on the root growth and yield, especially for medicinal crops. To fill this gap, a single factor experiment was conducted to explore the effects of Fe 3 O 4 NPs on growth, yield, the dry matter distribution, chlorophyll content, photosynthetic characteristics, chlorophyll fluorescence parameters, and polysaccharide content of Pseudostellaria heterophylla by foliar spraying under field conditions. Fe 3 O 4 NPs (20–50 mg·L –1 ) significantly promoted growth, the dry matter distribution of root and root tuber yield per unit area. Fe 3 O 4 NPs enhanced net photosynthetic rate ( P n ) by increasing chlorophyll content. And Fe 3 O 4 NPs increased the daily mean and peak value of P n , and alleviated the phenomenon of “midday depression” by improving nonstomatal limitation. Chlorophyll fluorescence parameters indicating that Fe 3 O 4 NPs promoted the photochemical activity of PSII and alleviated photoinhibition by enhancing the photochemical use of excess excitation energy. Gray correlation analysis showed that Fe 3 O 4 NPs enhanced the adaptability of P . heterophylla photosynthesis to high temperatures and strong light. Of note, Fe 3 O 4 NPs enhanced the polysaccharide content of the root tuber. Phytotoxic effect was recorded at high NPs (100 mg·L –1 ) doses. Collectively, Fe 3 O 4 NPs could promote performance of P . heterophylla by improving photosynthetic performance, enhancing its adaptability to the environment, and increasing the distribution ratio of photosynthates to the underground part.