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INTERACTIONS BETWEEN SOIL TEMPERATURE AND PLANT GROWTH STAGE ON NITROGEN UPTAKE AND AMINO ACID CONTENT OF APPLE NURSERY STOCK DURING EARLY SPRING GROWTH
Dong, S., C. F. Scagel, L. Cheng, L. H. Fuchigami, AND P T. Rygiewicz. INTERACTIONS BETWEEN SOIL TEMPERATURE AND PLANT GROWTH STAGE ON NITROGEN UPTAKE AND AMINO ACID CONTENT OF APPLE NURSERY STOCK DURING EARLY SPRING GROWTH. TREE PHYSIOLOGY. Heron Publishing, Victoria, B.C, Canada, 21:541-547, (2001).
In the spring, nitrogen (N) uptake by apple roots is known to be delayed about three weeks after bud break. We used one-year-old 'Fuji' (Malus domestica Borkh) on M26 bare-root apple trees to determine whether timing of N uptake in the spring is dependant solely on the growth stage of the plant or is a function of soil temperature. At five different times during early season growth, N uptake and total amino acid content was measured on trees growing at above ground temperatures of 23/15 C day/night and below ground temperatures of 8, 12, 16, or 20 C. Using 15NH415NO3 we found total N uptake and rate of uptake was significantly influenced by both soil temperature and plant growth stage. Uptake of 15N increased with increasing soil temperature and changed with plant growth stage. Before bud break, 15N was not detected in trees growing in the 8 C soil treatment, while 15N uptake increased with increasing soil temperatures between 12 and 20 C. Ten days after bud break, 15N was still not detected in trees growing in the 8 C soil treatment, while total 15N uptake and uptake rate continued to increase with increasing soil temperatures between 12 and 20 C. Twenty-one days after bud break trees at all temperatures were able to acquire 15N from the soil, although the amount of uptake increased with increasing soil temperatures. Distribution of 15N in trees changed as plants grew. Most of the 15N absorbed by trees before bud break (~5% of 15N given a tree) remained in the roots. Forty-six days after bud break, approximately one-third of the 15N absorbed by the trees in the 12-20 C treatments remained in the roots, while the shank, stem, and new growth contained about two-thirds. Total amino acid content and distribution of amino acids in trees changed with plant growth stage but only the amino acid content in new growth was affected by soil temperature. Prior to bud break the root, shank, and stem portions of trees contained approximately the same levels of amino acids. After bud break amino acid content in roots and shanks increased slightly then remained level during the next 46 days, while the amino acid content in stems increased during the first 21 days after bud break then declined. Ten days after bud break the amino acid content in new growth increased with increasing soil temperature. Although total amino acid content in new growth decreased between 21 to 46 days after bud break, the difference in amino acid content between different temperature treatments remained similar. Our results indicate that a combination of low soil temperature and plant developmental stage influences the ability of apple trees to efficiently take up and use N from the soil in the spring. This suggests that early fertilizer application in the spring when soil temperatures are low or when the above ground portion of the tree is not growing rapidly, may not be effective in terms of nutrient use efficiency.