Plant fine roots affect the amount of soil inorganic nitrogen (N) via their N uptake and their effects on organic matter decomposition and N mineralization. However, the effects of the fine roots of canopy trees on N availability in forest soil remain largely unknown owing to the limitations of in-situ measurements. Therefore, to reveal the effects of the fine roots of canopy trees on forest soil N availability, we developed a novel in-situ method that combines a modified in-situ resin-core method, using live fine roots, with a tree N demand estimation, using the N-balance method. Furthermore, we measured soil extracellular enzyme activities in the rhizosphere and bulk soils to determine whether fine roots stimulate soil enzyme activities. The results showed that soil enzyme activities were stimulated by the fine roots of canopy trees, especially in the rhizosphere, and this indicates that fine roots stimulate organic matter decomposition and N mineralization. However, fine roots had no significant effect on either the pool size or leaching of inorganic N. The estimated amount of potential N uptake by fine roots was greater than the amount of inorganic N released via fine root-induced N mineralization. Overall, our results indicate that almost all of the fine root-induced increment of mineralized inorganic N is taken up by the fine roots; thus, the fine roots of canopy trees did not affect N availability in forest soil. This study was limited by the fact that the fine roots in the resin cores were less dense than natural roots, and the fact that the actual root N uptake can differ from the estimated N uptake; these limitations should be resolved in future studies. Nevertheless, the proposed method can be used to investigate the effects of fine roots on the N cycle in forest soil under field conditions considering N uptake and priming.

植物细根通过吸收氮及其对有机物分解和氮矿化的影响来影响土壤无机氮的含量。然而，由于实地测量的局限性，冠层树的细根对森林土壤中氮的有效性的影响仍然未知。因此，为了揭示冠层树的细根对森林土壤氮素有效性的影响，我们开发了一种新颖的原位方法，该方法结合了改良的原位树脂核方法，使用活的细根，使用N平衡方法，估计N棵树。此外，我们测量了根际和块状土壤中的土壤细胞外酶活性，以确定细根是否刺激了土壤酶的活性。结果表明，冠层的细根特别是根际刺激了土壤酶的活性，这表明细根刺激了有机质的分解和氮的矿化。但是，细根对矿池的大小或无机氮的浸出均无显着影响。细根潜在的氮吸收量估计大于细根诱导的氮矿化释放的无机氮量。总体，我们的结果表明，几乎所有细根诱导的矿化无机氮增量都被细根吸收。因此，冠层树的细根不会影响森林土壤中的氮素有效性。这项研究受到以下事实的限制：树脂核中的细根比自然根密度低，并且实际根部N吸收量可能与估计的N吸收量不同；这些局限性应在以后的研究中解决。尽管如此，在考虑到氮素吸收和引发的田间条件下，该方法仍可用于研究细根对森林土壤氮素循环的影响。实际根系氮素吸收量可能与估计的氮素吸收量不同；这些限制应在以后的研究中解决。尽管如此，在考虑到氮素吸收和引发的田间条件下，该方法仍可用于研究细根对森林土壤氮素循环的影响。实际根系氮素吸收量可能与估计的氮素吸收量不同；这些限制应在以后的研究中解决。尽管如此，在考虑到氮素吸收和引发的田间条件下，该方法仍可用于研究细根对森林土壤氮素循环的影响。