In a recent study, Chinese researchers found that citrus seedlings clearly prefer nitrate over ammonium as a nitrogen source. The researchers — Hao Xu, Wenlang Hu, Kaiyuan Du, Yan Dong, Qingru Fan, Zengrong Huang, Lin-Tong Yang, Li-Song Chen and Jiuxin Guo — are with the Fujan Agriculture and Forestry University.
In their study, the researchers compared two citrus cultivars (C. reticulata and C. sinensis) under two nitrogen forms (ammonium vs. nitrate) to draw insights for nitrogen management in citrus production. Nitrate and ammonium are the two predominant nitrogen forms utilized by plants. However, the physiological mechanisms underlying citrus response to different nitrogen forms are still poorly understood.
The results of the study revealed significant differences in morphological and physiological features. Results demonstrated how nitrogen forms affect plant growth by regulating nitrogen assimilation, photosynthetic performance and the antioxidant system.
Nitrate supply enhanced growth by boosting nitrogen-assimilation enzyme activity and coordinating carbon–nitrogen metabolism. This, in turn, preserved chloroplast structure and photosynthetic efficiency while minimizing oxidative stress.
The findings provide a scientific basis for optimizing fertilizer nitrogen forms in citrus cultivation to improve plant performance and sustainability.
Compared with ammonium treatment, nitrate treatment significantly promoted plant growth by regulating the physiological and morphological characteristics of roots and leaves. Under ammonium conditions, there was an excessive accumulation of free amino acids and soluble proteins in both leaves and roots. This suppressed the activity of nitrogen assimilation enzymes and consequently reduced plant nitrogen uptake.
Furthermore, ammonium treatment inhibited photosynthetic performance by decreasing chlorophyll content, damaging chloroplast structure, and disrupting photosynthetic electron transport chain. Consequently, this led to the accumulation of non-structural carbohydrates in both leaves and roots, ultimately affecting the morphogenesis of citrus plants.
Additionally, ammonium treatment induced an oxidative stress response, increasing malondialdehyde levels and eliciting an antioxidant response in citrus seedlings.
Read the full study here.
Source: BMC Plant Biology
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