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.

How photosynthetic-related leaf traits of non-nitrogen (N)-fixing pioneer species respond to extreme habitat conditions of primary succession is still not well-elucidated, especially in volcanically N-deplete habitats. The effect of N-deplete soil on photosynthetic-related leaf traits can provide a basis for predicting how plants adjust their strategies to adapt to such habitats. To examine the responses of leaf traits to extreme conditions, we investigated Miscanthus condensatus (a non-N-fixing C₄ pioneer grass) which grows on a volcanically devastated area on Miyake-jima Island, Japan, in which the volcanic ash has been deposited for 17–18 years since the 2000-year eruption. Leaf N content (N_area), light-saturated photosynthetic rate (A_max), and photosynthetic N use efficiency (PNUE) in three contrasting study sites: bare land (BL), shrub land gap (SLG), and shrub land under canopy (SLUC) were determined. Results indicated that compared to previous studies and internal comparison of Miyake Island, M. condensatus in BL was able to maintain a relatively high A_max, N_area and PNUE. The higher A_max was in part a result of the higher PNUE. This is a characteristic necessary for its successful growth in N-deplete soils. These results suggest that M. condensatus has photosynthetic-related advantages for adaptation to volcanically N-deplete habitats.