We combine spectroscopic and geochemical approaches to interpret the fate of potassium (K) during forest soil development along a 4-million-year chronosequence sampled from relatively undisturbed rainforests in Hawai‘i. Potassium derived from weathering of lava is dominant in the youngest site (0.3 ky), but its contribution to the soil K budget declines as weathering progresses. Sites older than 0.3 ky are characterized by substantial K depletion (τ_K,Nb ∼ -1), with soil isotopic composition (⁴¹K/³⁹K, δ⁴¹K) varying from -1.91±0.08‰ to -0.09±0.08‰, relative to the homogeneous basaltic substrate (-0.48‰). Exchangeable and interlayered K show δ⁴¹K values ranging from -1.32±0.06‰ to 0.06±0.08‰, higher than their corresponding bulk δ⁴¹K values. The δ⁴¹K patterns of soils and exchangeable components are vertically similar, implying similar environmental controls. The variability in K phase and isotope composition reflects the accumulative effect of different processes. Chemical weathering and plant cycling retain isotopically light K in soils, in particular for 20-150 ky sites. In contrast, atmospheric inputs of marine aerosols (0.14‰) and mineral aerosols (-0.44‰) add heavier K (than native basalts) and crust-like K (similar to basaltic δ⁴¹K) in soils, respectively. In sites older than 150 ky, nearly complete depletion of basaltic K and reduced plant K imprints result in the dominance of atmospheric inputs in soils. In sum, this study emphasizes the sensitivity of δ⁴¹K to terrestrial biotic and abiotic K cycles.

我们结合光谱和地球化学方法来解释钾 (K) 在森林土壤发育过程中的命运，这些钾 (K) 沿着从夏威夷相对未受干扰的热带雨林采样的 400 万年时间序列进行。来自熔岩风化的钾在最年轻的场地（0.3 ky）中占主导地位，但随着风化的进行，其对土壤 K 预算的贡献下降。大于 0.3 ky 的场地以大量 K 消耗为特征（τ _K,Nb ∼ -1），土壤同位素组成（⁴¹ K/ ³⁹ K, δ ⁴¹ K）从 -1.91±0.08‰ 到 -0.09±0.08‰ 变化，相对于均质玄武岩基质（-0.48‰）。可交换和夹层 K 显示 δ ⁴¹K 值范围为 -1.32±0.06‰ 至 0.06±0.08‰，高于其相应的体积 δ ⁴¹ K 值。土壤和可交换成分的 δ ^{41 K 模式在垂直方向上相似，这意味着相似的环境控制。}K相和同位素组成的变化反映了不同过程的累积效应。化学风化和植物循环在土壤中保留同位素轻钾，特别是对于 20-150 ky 的场地。相比之下，海洋气溶胶 (0.14‰) 和矿物气溶胶 (-0.44‰) 的大气输入增加了较重的 K（比天然玄武岩）和壳状 K（类似于玄武岩 δ ⁴¹K) 分别在土壤中。在超过 150 ky 的地点，玄武质 K 几乎完全耗尽，植物 K 印记减少，导致土壤中大气输入占主导地位。总之，本研究强调了 δ ⁴¹ K 对陆地生物和非生物 K 循环的敏感性。