Changes in the fungal and bacterial biomass and community structure in litter after the volcanic eruptions of Mount Usu, northern Japan were investigated using a chronosequence approach, which is widely used for analyzing vegetation succession. The vegetation changed from bare ground (10 years after the eruptions) with little plant cover and poor soil to monotonic grassland dominated by Polygonum sachalinense with undeveloped soil (33 years) and then to deciduous broad-leaved forest dominated by Populus maximowiczii with diverse species composition and well-developed soil (100 years). At three chronosequential sites, we evaluated the compositions of phospholipid fatty acids (PLFAs), carbon (C) and nitrogen (N) contents and the isotope ratios of C (delta C-13) and N (delta N-15) in the litter of two dominant species, Polygonum sachalinense and Populus maximowiczii. The C/N ratio, d13C and d15N in the litter of these two species were higher in the forest than that in the bare ground and grassland. The PLFAs gradually increased from the bare ground to the forest, showing that microbial biomass increased with the development of the soil and/or vegetation. The fungi-to-bacteria ratio of PLFA was constant at 5.3 +/- 1.4 in all three sites, suggesting that fungi were predominant. A canonical correspondence analysis suggested that the PLFA composition was related to the successional ages and the developing soil properties (P < 0.05, ANOSIM). The chrono-sequential analysis effectively detected the successional changes in both microbial and plant communities
We measured differences in %C, %N, 13C and 15N of plant functional types 17 (PFTs) between burned and unburned ground surfaces soon after a wildfire on a north-18 facing slope in interior Alaska. The C and N were measured for 16 species and 19 Sphagnum litter. 13C differed among the PFTs and was low for trees and shrubs, 20 suggesting that woody stems slowed C dynamics or showed low water use efficiency. 21 15N concentrations suggested that the herbaceous plants depended less on the 22 mycorrhizal associations that became weak on the burned surfaces. The shrub leaves 23 showed the lowest 15N of PFTs and showed higher 15N on the burned surface, showing 24 that N transfer from the soils to the leaves in the shrubs was slowed by the wildfire. 25 Mosses showed the highest C/N ratio. Sphagnum litter decomposed faster on the burned 26 surface, and %N and 15N in the litter increased from the second to third year on both 27 burned and unburned surfaces, while %C changed little. In conclusion, the responses to 28 the wildfire differed among the PFTs as characterized by their C and N dynamics. 29
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Key words: Burned and unburned ground surface, carbon (C) and nitrogen (N), Alaskan 31 taiga, plant functional type, stable isotope
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