We simultaneously quantified the fate of soil absorbed mineral nitrogen in different tree compartments along with nitrogen immobilization by microorganisms during spring in 20-year-old oak trees. A soil-applied 15N solution was traced in situ into the fine roots, medium roots, xylem, phloem, branches, leaves, extractable soil, and microbial biomass before and after budburst, until LAI maximum was reached. During the three weeks following the labeling, around half of the 15N applied was incorporated into the microbial biomass while the leafless trees absorbed less than 10% of the 15N. Before and after budburst, the microbial compartment was the main pool of 15N, and yet the soil-absorbed 15N still significantly contributed to the leaf nitrogen pool at budburst. This contribution in leaves sharply increased in the days following budburst. The potential competition for mineral nitrogen between trees and the soil microbial biomass is strong during spring. The dependence of the leaf nitrogen pool to internal or external stocks of nitrogen at budburst could be conditioned by environmental conditions.

中文翻译：

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20 年生 Quercus petraea (Matt.) Liebl 萌芽前后树木-土壤-微生物系统中矿物质 N 的原位归宿。

我们同时量化了 20 岁橡树春季期间不同树间室中土壤吸收矿质氮的命运以及微生物对氮的固定。土壤施用的 15N 溶液原位追踪到细根、中根、木质部、韧皮部、树枝、叶子、可提取土壤和萌芽前后的微生物生物量，直到达到 LAI 最大值。在贴上标签后的三周内，大约一半的 15N 应用被纳入微生物生物量，而无叶树吸收了不到 10% 的 15N。芽前和芽后，微生物区室是15N的主要库，但土壤吸收的15N仍然对芽时叶片氮库有显着贡献。在萌芽后的几天里，这种对叶子的贡献急剧增加。春季，树木和土壤微生物生物量之间对矿物氮的潜在竞争很强。叶片氮库对萌芽时内部或外部氮储备的依赖性可能受环境条件的影响。