Growth and Physiological Responses of Blackberry Seedlings to Different NH₄⁺:NO₃⁻ Ratios

In order to reveal the regulator mechanism of different NH₄⁺:NO₃⁻ ratios on the growth and development of blackberry seedlings for the first time. We explored the effect of different NH₄⁺:NO₃⁻ ratios on growth parameters, biomass accumulation, chlorophyll, photosynthesis, sugars, and antioxidant capacity in blackberry plants. This study exhibited that the blackberry plants treated with NH₄⁺:NO₃⁻ (75:25) not only grew better with the maximum leaf N content, total biomass and photosynthesis, but also maintained the higher contents of chlorophylls and sugars and the higher activities of superoxide dismutase (SOD) and catalase (CAT) during the treatment period. However, excessive NO₃⁻ caused ion toxicity and stress to the blackberry plants, which was detrimental to the growth and development of plants. Compared with NO₃⁻, NH₄⁺ could better promote the photosynthesis, antioxidant capacity, biomass accumulation and N metabolism of blackberry plants. Moreover, CAT may be critical to the antioxidant system of blackberry plants. Correlation and principal component analysis displayed that the excessive accumulation of superoxide anion radical (O₂.⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) destroyed the normal physiological and metabolic activities of blackberry plants. A 75:25 ratio of NH₄⁺:NO₃⁻ was most beneficial for blackberry plants growth and development, and it was not recommended to apply too much NO₃⁻ to blackberry plants. These results provided technical guidance and a reference value for the application of N fertilizer to blackberry plants in actual plantings.