The bare lands formed after volcanic eruptions provide an excellent opportunity to study the interactions between vegetation succession and soil formation. To explore the changes in soil physicochemical properties in the vegetation succession processes and the relationship between them, soil physicochemical properties of different volcanic ash accumulation on Miyake-jima Island were studied at different vegetation succession stages. The results showed that soil bulk density gradually decreased and that soil porosity, soil water content (SWC), pH, cation exchange capacity (CEC), soil total organic carbon (TOC), and total nitrogen (TN) increased significantly with vegetation succession. The physicochemical properties changes in the soil surface horizon were most obvious, and the deep soil accumulated a large amount of relatively stable soil carbon and nitrogen. The forest land formed a thicker organic matter horizon, accumulating more carbon and nitrogen than grassland, and the soil quality index (SQI) was higher than that of grassland and shrubland. In conclusion, our research indicates the significant change in soil physicochemical properties and the improvement in soil quality in the vegetation succession processes, emphasizing a significant relationship between vegetation succession and soil development in bare land.

The active Mt. Oyama volcano on Miyake-jima Island in the Izu Islands, Japan, erupted in 2000 followed by large amounts of volcanic gas containing high concentrations of SO₂has been emitted. The island ecosystem has been heavily damaged by the volcanic ash and gas. We detail the destruction and recovery of vegetation found in a 7-year study of 11 permanent plots from 2001 to 2007. Damage to vegetation by ash was worst near the crater in 2001. Trees began dying in 2001, apparently due to direct and/or indirect effects of volcanic gas emission. In contrast to the tree decline, two grass species,Miscanthus condensatusandCarex oshimensis, increased notably following the eruption, suggesting their high SO₂and acidic soil tolerance.Miscanthus condensatusandC. oshimensiswere not dominant species in early stage of primary succession before the 2000-year eruption. In the vegetation recovery after the eruption, the tolerances to SO₂and acidic soils are necessary for plant species to colonize on devastated sites.

The perennial gramineous grass Miscanthus condensatus functions as a major pioneer plant in colonizing acidic volcanic deposits on Miyake-jima, Japan, despite a lack of nitrogen nutrients. The nitrogen cycle in the rhizosphere is important for the vigorous growth of M. condensatus in this unfavorable environment. In the present study, we identified the nitrogen-cycling bacterial community in the M. condensatus rhizosphere on these volcanic deposits using a combination of metagenomics and culture-based analyses. Our results showed a large number of functional genes related to denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in the rhizosphere, indicating that nitrate-transforming bacteria dominated the rhizosphere biome. Furthermore, nitrite reductase genes (i.e., nirK and nirS) related to the denitrification and those genes related to DNRA (i.e., nirB and nrfA) were mainly annotated to the classes Alpha-proteobacteria, Beta-proteobacteria, and Gamma-proteobacteria. A total of 304 nitrate-succinate-stimulated isolates were obtained from the M. condensatus rhizosphere and were classified into 34 operational taxonomic units according to amplified 16S rRNA gene restriction fragment pattern analysis. Additionally, two strains belonging to the genus Cupriavidus in the class Beta-proteobacteria showed a high in vitro denitrifying activity; however, metagenomic results indicated that the DNRA-related rhizobacteria appeared to take a major role in the nitrogen cycle of the M. condensatus rhizosphere in recent Miyake-jima volcanic deposits. This study elucidates the association between the Miscanthus rhizosphere and the nitrate-reducing bacterial community on newly placed volcanic deposits, which furthers our understanding of the transformation of nitrogen nutrition involved in the early development of vegetation.

Pioneer species differing in their inherent ecological characteristics (e.g., N-fixing ability, photosynthetic pathway) can have a large impact on local ecosystems in the early stages of volcanic succession. However, it remains unclear as to how these pioneer species adapt to the extreme environment of volcanically devastated sites in terms of ecophysiological leaf traits. In this study, we compared the leaf traits (including morphological, physiological) of three co-occurring pioneer species, including a C₄ non-N-fixing grass, a C₃ N-fixing tree, and a C₃ non-N-fixing herb from a newly created (18 years after eruption) volcanically devastated site in Miyake-jima, Japan. Our results showed that three pioneer species have different sets of leaf traits that are associated with their ecophysiological growth advantages, respectively. Miscanthus condensatus shows the highest light-saturated photosynthetic rate (A_max). The higher A_max were partially the result of higher water use efficiency (WUE) and photosynthetic N-use efficiency (PNUE). The PNUE in M. condensatus appears to be high, even for a C₄ grass. Alnus sieboldiana rely on its N-fixing ability, has a higher leaf N content (N_area) that compensates for its photosynthetic machinery (Rubisco), and further ensures its photosynthetic capacity. Fallopia japonica var. hachidyoensis has a higher leaf mass per area (LMA), chlorophyll content (Chl), and maximum quantum yield of PSII (Fv/Fm), demonstrating its higher light capturing ability. These results make it possible to predict certain ecological processes that take place in the early stages of volcanic succession resulting from ecological characteristics and from some key leaf traits of pioneer species. It also provides a theoretical basis for species selection and species combination for volcanic ecological restoration.