Nano-zinc oxide seed treatment affects seed germination and seedling establishment under straw-induced stress in...

Straw return is an important agricultural practice, however, the accumulation of allelopathic substances from straw return inhibits rice see germination and seedling establishment, posing a critical bottleneck for its sustainable application. The application of nanomaterials in agriculture has garnered considerable attention. In particular, the use of nanoparticles for seed priming and coating represents a novel and efficient strategy to protect seedlings during their most vulnerable stage by mitigating the impacts of biotic and abiotic stresses. To investigate the effects of nano-zinc oxide (nano-ZnO) treatment and rice straw extract on rice seed germination and seedling growth, a pot experiment was conducted using two rice cultivars: Xiangyaxiangzhan and Yuxiangyouzhan. Five seed treatments (CK: No treatment, C0: 0 mg L^-1 nano- ZnO coating, C1: 50 mg L^-1 nano-ZnO coating, S0: 0 mg L^-1 nano- ZnO seed soaking, S1: 50 mg L^-1 nano-ZnO seed soaking) were designed. We evaluated seed germination, seedling growth, antioxidant responses, and photosynthetic pigment characteristics. The study revealed that nano-zinc oxide seed treatments interact with rice straw extract to differentially regulate seed germination and seedling growth in a genotype-specific manner. The germination rate of Yuxiangyouzhan was higher than that of Xiangyaxiangzhan during the germination period, but it was more inhibited by the straw extract at 7 days after sowing. Seed soaking with 50 mg·L⁻¹ nano-ZnO (S1) increased the germination rate of Xiangyaxiangzhan by up to 156.7% at 1 day after sowing. At the seedling stage, the straw extract inhibited shoot growth, while nano-ZnO coating (C1) significantly increased the root dry weight and total dry weight of Xiangyaxiangzhan. By 12 days after sowing, all seed treatments increased the root-to-shoot ratio of Xiangyaxiangzhan by 4.19% to 31.05%. Antioxidant enzyme activities (peroxidase and catalase) were variably affected by the treatments. Specifically, the S1 treatment increased superoxide dismutase activity at 5-7 days after sowing and enhanced the contents of photosynthetic pigments (chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll) in both cultivars, even under high concentrations of straw extract. Correlation analysis confirmed strong positive links between early germination and subsequent biomass, and between root development and total dry weight. Based on these findings, we propose the following recommendations for practical application: In paddy fields practicing straw return, differentiated nano-ZnO seed treatment strategies should be adopted, considering the specific rice variety and residual straw concentration in the field. For fields with high straw residue or when cultivating varieties sensitive to allelopathic stress, such as 'Xiangyaxiangzhan', seed soaking with 50 mg L⁻¹ nano-ZnO is recommended to effectively ensure germination uniformity and early establishment. For varieties like 'Yuxiangyouzhan' or in fields with moderate straw levels, seed coating with 50 mg L⁻¹ nano-ZnO could be employed to promote root development and optimize the physiological status of seedlings. In practice, it is advisable to validate and optimize the nano-treatment concentration and method on a small scale, taking into account local straw return amounts, soil conditions, and the target variety. This approach would facilitate the translation of nano-priming technology into an effective agronomic measure for stabilizing seedling quality and enhancing the sustainability of straw return systems. This study indicates that the 50 mg L⁻¹ nano-ZnO seed treatment strategies based on variety and straw return conditions can effectively enhance seedling establishment, providing technical support for the sustainability of rice production under straw return systems.