不同氮水平下橡胶树氮素贮藏及翌年分配利用特性

以2年生幼龄橡胶树为试材,采用落叶期换土移栽法,利用 ¹⁵N同位素示踪技术,研究了少量施氮（N₂₈）、适量施氮（N₅₆）和过量施氮（N₈₄）3个氮素水平下幼树的生长差异及氮吸收、利用和分配特性。结果表明：适量施氮肥利于树体生长。以N₂₈处理为对照,N₅₆和N₈₄处理均通过促进根系生长进而促进地上部生长,且N₅₆处理对地上部生长的促进作用较N₈₄更为显著。N₂₈、N₅₆和N₈₄处理橡胶树当年氮肥利用率分别为47.55%、46.83%、39.09%,在第2年春季第一蓬叶稳定期后,各处理氮肥利用率分别为44.49%、43.79%、38.17%。橡胶树氮素的主要贮藏部位为主干和根系,其 ¹⁵N分配率为59.58%左右,主干木质部的 ¹⁵N分配率最高,N₂₈、N₅₆和N₈₄处理分别为24.65%、28.69%和25.50%;3个处理地上部枝干中的 ¹⁵N分配率为76.85%（N₂₈）、78.24%（N₅₆）和75.51%（N₈₄）。经过春季的重新再利用,第1年吸收贮藏的氮素由枝干和根系向新生器官（新梢木质部、新梢皮部、叶片及叶柄）大量运转,满足其生长发育的需要;N₂₈、N₅₆和N₈₄处理新生器官中的Ndff%较高,分别为9.60%~11.31%、18.39%~21.43%和31.67%~34.04%,而主干木质部中的Ndff%较低,分别为3.86%、7.90%和13.77%。贮藏氮在橡胶树春季器官的生长发育中起到重要作用,3个处理新生器官中的 ¹⁵N分配率为50.60%（N₂₈）、53.98%（N₅₆）和53.28%（N₈₄）。适量施氮水平下 ¹⁵N在地上部枝干中的贮藏比例较高,翌年新生器官中的分配率也高,有利于橡胶树氮素的季节性循环利用及生长发育的需要。

Effects of Different N Rates on Storage and Remobilization of Urea- 15N by Rubber Tree

Two-year old young rubber trees were used as the materials. The soil transfer in leaf fall periods method and ¹⁵N isotope tracer technique were used to study the growth difference, nitrogen absorption, utilization and distribution characteristics of young rubber trees using three levels of N: less nitrogen (N₂₈), proper nitrogen (N₅₆) and over-dose nitrogen (N₈₄). Results showed that the rational application rate of nitrogen fertilizer could promote the growth of young rubber trees in the current and following year. The N₅₆ and N₈₄ treatments promoted root growth and then above ground growth, and the N₅₆ treatment had a better promotion effect than the N₈₄ treatment on the shoot growth. The nitrogen use efficiency of rubber trees treatments with N₂₈, N₅₆ and N₈₄ was 47.55%, 46.83% and 39.09%, respectively. After the first leaf stabilization period in the spring of the second year, the nitrogen use efficiency of each treatment was 44.49%, 43.79% and 38.17%, correspondingly. The main storage sites of nitrogen in young rubber trees were trunks and roots, with the ¹⁵N distribution rate of about 59.58%, and the ¹⁵N distribution rate in the xylem of trunks was the highest. That for the N₂₈, N₅₆ and N₈₄ treatment was 24.65%, 28.69% and 25.50%, respectively. The ¹⁵N distribution rate of the ground shoots of the three treatments was N₂₈ 76.85%, N₅₆ 78.24% and N₈₄ 75.51%. After reuse in spring, the nitrogen absorbed and stored in the first year was transported to new organs (xylem of new shoots, bark of new shoots, leaves and petioles) in large quantities through branches and roots, meeting the needs of growth and development of seedlings. Among them, Ndff% of new growth organs of treatments with N₂₈, N₅₆ and N₈₄ was the highest, 9.60%-11.31%, 18.39%-21.43% and 31.67%-34.04% respectively. However, Ndff% in the xylem of trunks was the lowest, 3.86%, 7.90% and 13.77% respectively. Nitrogen storage played an important role in the growth and development of the organs of young rubber trees in spring. The ¹⁵N distribution rates in the new growth organs of the three treatments was N₂₈ 50.60%, N₅₆ 53.98% and N₈₄ 53.28%. Under the appropriate nitrogen application level, the storage ratio of ¹⁵N in trunks and roots were higher, and the distribution ratio in new growth organs in the following year was also higher. This had a very important role in the seasonal recycling of nitrogen in young rubber trees and their growth and development.