Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2003
Publication Date: 12/10/2003
Citation: Bi, G., Scagel, C.F., Cheng, L., and Fuchigami, L. Soil and Foliar Nitrogen Supply Affects the Composition of Nitrogen and Carbohydrates of Young Almond Trees. J. Hort. Sci. Biotech. 2004. 79(2) p.175-181.
Interpretive Summary: Deciduous fruit trees store nitrogen (N) and carbohydrates in the previous year and use these stored compounds for new growth in the following growing season. The levels of amino acids in dormant trees is considered an indicator of the N status of the tree. However, it is not known how the pool of amino acids and carbohydrates in storage responds to different fertilization practices used in nursery production of almond trees. Understanding the role of carbohydrates and amino acid reserves in response to different methods of fertilizer application and the implications to new growth has direct practical implications. Optimal levels of N fertigation to promote new growth should increase N reserves in plants without negatively influencing carbohydrate reserves. June-budded 'Nonpareil/Nemaguard' almond trees were fertigated with different N concentrations from July to September and half the trees were sprayed twice with 3% urea in October. Trees were destructively sampled during winter storage and the amount of amino acids, protein, and non-structural carbohydrates (TNC) were determined. Increasing N fertigation concentration or application of foliar urea increased concentrations of amino acids, but decreased C/N ratios in trees. As N supply increased, the proportion of N stored as free amino acids increased, however, protein was the main form of N reserves. There was a negative relationship between amino acid and TNC concentrations, suggesting TNC was used for N assimilation as N supply increased. Urea decreased the concentrations of glucose, fructose, and sucrose but had little influence on sorbitol and starch. The synthesis of amino acids and proteins resulting from increased N availability occurs at the expense of non-structural carbohydrates.
Technical Abstract: June-budded 'Nonpareil/Nemaguard' almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with differnt nitrogen (N) concentrations (0, 5, 10, 15, and 20 mM) from July to September. In October, trees were sprayed twice with water or 3% urea, harvested after natural leaf fall, and stored at 20C. Trees were destructively sampled during winter storage to determine amino acids, protein, and non-structural carbohydrates (TNC). Increasing N fertigation concentration during the growing season or foliar urea applications in the fall increased the concentrations of both free and total amino acids, but decreased their C/N ratios. As N supply increased, the proportion of N stored as free amino acids increased. However, protein was still the main form of N used for storage. Arginine was the predominant amino acid in both free amino acid and total amino acid pools. Arginine N accounted for an increasing proportion of the total N in free amino acids and total amino acids as N supply increased. However, the proportion of arginine N in free amino acids is higher than that in total amino acids. There was a negative relationship between total amino acid and non-structural carbohydrate concentrations, suggesting the increased use of TNC for N assimilation as N supply increased. Urea application decreased the concentrations of glucose, fructose, and sucrose but had little influence on concentrations of sorbitol and starch in trees. We conclude that protein is the primary form of storage N even though the proportion of N stored as free amino acids increased as N supply increased. Arginine is the predominant amino acid in free amino acid and proteins. The synthesis of amino acids and proteins is at the expense of non-structural carbohydrates.