Effects of Fulvic Acid on Growth and Nitrogen Utilization Efficiency in M9T337 Seedlings

Abstract

Both fulvic acid (FA) and nitrogen (N) play important roles in agricultural production in China. Plants typically show a higher nitrogen utilization efficiency (NUE) under FA application. However, the role of FA application in apple growth and NUE remains unclear. A hydroponic culture experiment was performed, and M9T337 seedlings (a dwarf apple rootstock) were used as the experimental subjects. The biomass, photosynthesis, accumulation, and distribution of photosynthates, N absorption and assimilation, and relative gene expression in the seedlings were examined after treatment with five different concentrations of FA (0, 60, 120, 180, and 240 mg·L−1, represented by CK, FA1, FA2, FA3, FA4, respectively). The results showed that the seedling dry weight and 15NUE were enhanced by FA, and both were highest under the FA2 (the concentration of fulvic acid is 120 mg·L−1) treatment. Further analysis revealed that under the FA2 treatment, the root morphology was optimized, and the root activity was relatively high. Compared with CK (control, the concentration of fulvic acid is 0 mg·L−1), the FA2 treatment strengthened photosynthesis, elevated the key enzyme activities related to C metabolism, upregulated the gene expression of sugar transport proteins, and increased the root sorbitol and sucrose contents, which suggested that the FA2 treatment optimally affected the root growth and N absorption because it enhanced photosynthate synthesis and the leaf-to-root translocation of photoassimilates. The seedlings in the FA2 treatment group also showed a significantly higher NO3− influx rate and NRT (nitrate transporter) gene expression in the roots. Moreover, relatively high N metabolism-related enzyme activities in the leaves and roots were also observed under the FA2 treatment. The isotope labeling results showed that the optimal FA2 supply not only promoted seedling 15N absorption but also optimized the distribution of C and N in the seedlings. These results suggested that an optimal FA supply (120 mg·L−1) enhanced seedling NUE by strengthening photoassimilate synthesis and transport from leaves to roots, regulating N absorption, assimilation, and distribution.

Fulvic acid alleviates cadmium-induced root growth inhibition by regulating antioxidant enzyme activity and carbon–nitrogen metabolism in apple seedlings

“…Total RNA was extracted from 0.1 g of the roots using the RNAiso Plus extraction kit (Takara, Otsu, Shiga, Japan). Subsequently, RNA extraction, reverse transcription, and qRT-PCR procedures followed a previously reported procedure ( Yu et al., 2023a ). The relative gene expression levels were normalized according to the 2 –ΔΔCT method, and the MdActin gene was used as the internal reference gene.…”

“…Therefore, it is very important to maintain C and N assimilation homeostasis to mitigate the inhibitory effects of external stress conditions on plant growth ( Ren et al, 2021 ). Although numerous studies have shown that FA application could promote plant growth through the regulation of C and N metabolism ( Gao et al., 2022 ; Yu et al., 2023a ), details regarding the effects of Cd stress on C and N metabolism in apple plants and whether FA is sufficient to mitigate the inhibitory effects of Cd stress on apple plants growth, from the perspective of the regulation of C and N metabolism, both remain unclear.…”