Seedling size and nutrient availability in the fall determine nitrogen resorption and storage compound allocation in Quercus variabilis

Abstract

Soil fertility and resorption of leaf compounds in the fall can influence resource buildup in plants. However, whether intraspecific differences in seedling size can affect nutrient reserve buildup is unknown. This study examined the effects of seedling size and fall fertilization on the uptake and resorption of nitrogen (N), as well as the allocation of non-structural carbohydrates (NSC) and N in cultivated Quercus variabilis Blume. After the formation of terminal buds (T1), seedlings were stratified into small (shoot height < 30 cm) and large seedlings. During the hardening period, seedlings were treated with three different rates of 15 N-enriched fertilizer (0, 12, or 24 mg N seedling−1) and monitored until leaf fall (T2). Small seedlings had lower N resorption efficiency and resorbed proportionally less N than large seedlings. Fall fertilization notably improved N and NSC reserves, without reducing N resorption efficiency. Large seedlings allocated proportionally less N to leaves than small seedlings although both sizes seedlings absorbed similar amounts of N from fall fertilization. The priority perennial organ for NSC allocation was roots, while N allocation was dependent on the phenological growth stage of the seedling. Roots were prioritized during the rapid growth phase, while stems were prioritized during the hardening period. Under same fertilizer regime during the growth phase, large seedlings tends to have lower N concentration and have higher resorption efficiency compare to small seedlings, fall fertilization can increase N storage in large seedlings and NSC levels in both seedling sizes, without affecting growth.