Forestry and Forest Products Research Institute, Tsukuba 305-8687, Japan,
J Biosci. 2013 Nov;38(4):761-76. doi: 10.1007/s12038-013-9369-9.
To estimate the N2 fixation ability of the alder (Alnus hirsuta (Turcz.) var. sibirica), we examined the seasonal variation in nitrogenase activity of nodules using the acetylene reduction method in an 18-year-old stand naturally regenerated after disturbance by road construction in Japan. To evaluate the contribution of N2 fixation to the nitrogen (N) economy in this alder stand, we also measured the phenology of the alder, the litterfall, the decomposition rate of the leaf litter, and N accumulation in the soil. The acetylene reduction activity per unit nodule mass (ARA) under field conditions appeared after bud break, peaked the maximum in midsummer after full expansion of the leaves, and disappeared after all leaves had fallen. There was no consistent correlation between ARA and tree size (dbh). The amount of N2 fixed in this alder stand was estimated at 56.4 kg ha-1 year-1 when a theoretical molar ratio of 3 was used to convert the amount of reduced acetylene to the amount of fixed N2. This amount of N2 fixation corresponded to the 66.4 percent of N in the leaf litter produced in a year. These results suggested that N2 fixation still contributed to the large portion of N economy in this alder stand.
为了估计桤木（Alnus hirsuta (Turcz.) var. sibirica）的固氮能力，我们采用乙炔还原法，检测了日本一条自然再生的 18 年生林分中，桤木根瘤的固氮酶活性的季节性变化。为了评估固氮作用对该桤木林分氮（N）收支的贡献，我们还测定了桤木的物候、凋落物量、叶凋落物分解率以及土壤中氮的积累。在野外条件下，单位瘤质量的乙炔还原活性（ARA）在芽开始膨胀后出现，在叶片完全展开后的仲夏达到最大值，在所有叶片脱落之后消失。ARA 与树木大小（胸径）之间没有一致的相关性。当使用 3 的理论摩尔比将还原乙炔的量转化为固定 N2 的量时，该桤木林分的固氮量估计为 56.4kg ha-1 year-1。这一固氮量相当于一年中产生的叶凋落物中氮的 66.4%。这些结果表明，固氮作用仍对该桤木林分的大部分氮收支产生影响。
