Effects of ZnO nanoparticles on growth and photosynthetic performance of peanut seedlings

【Objective】To investigate effects of ZnO nanoparticles（ZnO NPs）of different concentrations on growth and photosynthetic performance of peanut seedlings，so as to provide a theoretical and practical basis for research and application of ZnO NPs in peanut production.【Method】 Seedlings of peanut cultivar Yuhua 37 were treated with ZnO NPs at different concentrations（0，0.01，0.05，0.10，0.50 mmol/L）for different times（5 and 10 d）by hydroponic method.Morphological indexes，gas exchange parameters，chlorophyll fluorescence parameters，chlorophyll relative content and nitrogen balance index of peanut seedlings were measured，and statistical analysis were conducted on above parameters.【Result】With the increase of ZnO NPs concentration and the extension of time，fresh weight，dry weight，total root length，total root surface area，net photosynthetic rate，stomatal conductance，photochemical property index，nitrogen balance index and chlorophyll relative content of peanut seedlings all showed a gradual or fluctuating decreasing trend.Transpiration rate first increased and then decreased，and the relative content of flavonoid gradually increased.After 10 d of treatment，fresh weight，root dry weight，net photosynthetic rate and photochemical performance index of seedlings treated with 0.10 and 0.50 mmol/L ZnO NPs were significantly decreased by 26.3%-41.7%，16.7%-41.7%，50.9%-80.7% and 46.7%-59.2%，respectively（P<0.05，the same below）.The nitrogen balance index of seedlings was significantly decreased by 19.1%-73.9% under ZnO NPs treatment of different concentrations and time.Correlation analysis showed that fresh weight and dry weight of the peanut seedlings were significantly or extremely significantly（P<0.01，the same below）positively correlated with total root length，net photosynthetic rate，transpiration rate and relative chlorophyll content.Fresh weight of seedlings was also extremely significantly positively correlated with photochemical performance index and nitrogen balance index.【Conclusion】 ZnO NPs inhibits the absorption of water and nitrogen by the roots of peanut seedlings，and at the same time it inhibits synthesis of chlorophyll in leaves，damages the structure of photosystem Ⅱ，reduces the net photosynthetic rate of seedlings and makes supply of water and nutrients insufficient，thus inhibiting the growth of peanut seedlings.