Kansai Research Center, Forestry and Forest Products Research Institute, Nagai-kyutaro, Momoyama, Fushimi, Kyoto 612-0855, Japan.
Forestry and Forest Products Research Institute, Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
Sci Total Environ. 2018 Dec 15;645:179-191. doi: 10.1016/j.scitotenv.2018.07.038. Epub 2018 Jul 17.
Some tree species increase fine root production under soil acidification, thus changing the balance of litter input from leaves and roots. Litter leaches a significant amount of acidic materials during its decomposition, which might facilitate soil acidification. In this context, we focused on dissolved organic matter (DOM) as the major component of acidic materials. We hypothesized that both the quality and quantity of DOM, which control its function (i.e., proton supply), differ between leaf and root litter. To test this hypothesis, we conducted a 2.5-year laboratory incubation experiment using fresh fine roots and fresh green leaves as litter of two coniferous species (Cryptomeria japonica and Chamaecyparis obtusa) and investigated the leachate pH and DOM composition based on the optical properties. After the early stage of decomposition when flash leaching of DOM converged, the amount of dissolved organic carbon (DOC) leached from roots increased again and leachate pH declined. In contrast, DOC concentrations continued to decrease in leaf leachates during the incubation period, and the pH decrease was not as striking as that of root leachates. Optical properties (ultraviolet visible absorption and fluorescence) of DOM revealed that humic-like substances in DOM played a central role in the acidic pH of root leachates. The total amount of protons released from roots of C. japonica and C. obtusa is about 13 and 18 times higher, respectively, than that from leaves. These results imply that the increase of fine root biomass may induce a positive plant-soil feedback in acidic soils, affecting soil biogeochemical functions of terrestrial ecosystems.
一些树种在土壤酸化条件下会增加细根的产生，从而改变叶和根的凋落物输入的平衡。凋落物在分解过程中会淋滤出大量的酸性物质，这可能会促进土壤酸化。在这种情况下，我们专注于溶解有机物质（DOM）作为酸性物质的主要成分。我们假设，控制其功能（即质子供应）的 DOM 的质量和数量在叶凋落物和根凋落物之间存在差异。为了验证这一假设，我们进行了一项为期 2.5 年的实验室培养实验，使用新鲜的细根和新鲜的绿叶作为两种针叶树（日本柳杉和扁柏）的凋落物，并根据光学特性研究了淋滤液 pH 值和 DOM 组成。在 DOM 快速淋溶收敛的分解早期之后，从根中淋滤出的溶解有机碳（DOC）量再次增加，淋滤液 pH 值下降。相比之下，在培养期间，叶凋落物中的 DOC 浓度继续下降，pH 值下降不如根凋落物那么明显。DOM 的光学特性（紫外可见吸收和荧光）表明，DOM 中的类腐殖质物质在根凋落物的酸性 pH 值中起核心作用。来自日本柳杉和扁柏的根释放的质子总量分别比叶高出约 13 倍和 18 倍。这些结果表明，细根生物量的增加可能会在酸性土壤中引起正的植物-土壤反馈，影响陆地生态系统的土壤生物地球化学功能。
