Yasuo Iimura

The effect of dense understory dwarf bamboo (Sasa senanensis) on soil respiration before and after clearcutting of cool temperate deciduous broad-leaved forest

To evaluate the effect of understory dwarf bamboo (Sasa senanensis) on soil respiration in forest ecosystems, we compared soil respiration rates between four deciduous broad-leaved forest sites representing two levels of understory Sasa (with and without) and two levels of forest stand age (50-year-old stand and 1-year-old stand after clearcut). The understory Sasa enhances the soil respiration rate both before and after the clearcutting of deciduous broad-leaved forest. The Sasa sites had larger total belowground biomass compared with the non-Sasa sites, which could be attributed to Sasa presence. Our results also suggest that clearcutting decreases temperature-normalized soil respiration rates (R15) and temperature sensitivity (Q10) in both Sasa and non-Sasa ecosystems. Clearcutting significantly reduced the fine root biomass of trees and Sasa. The fine roots of trees and Sasa had high specific respiration rates compared with larger roots and rhizomes at Sasa and non-Sasa sites, respectively. Therefore, we hypothesize that the loss of fine roots after clearcutting is responsible for the reduction in soil respiration rate. A comparison with other studies revealed a positive linear relationship between total (tree and Sasa) fine root biomass and R15, suggesting that fine root biomass controls soil respiration at the landscape scale. The Q10 value is also likely to be related to fine root biomass, although the relationship was not significant. We conclude that understory Sasa increases belowground biomass, especially fine roots, and the spatial variation in soil respiration at the landscape scale.

Characterization of DAX‐8 adsorbed soil fulvic acid fractions by various types of analyses

We investigated the optical absorption properties (A 400/C and A 600/C values), elemental composition, weight-averaged molecular weight (Mw), and liquid-state carbon-13 (13C) nuclear magnetic resonance (NMR) spectroscopy of DAX-8 adsorbed fulvic acid fractions (DAX-8 FAs) in various soils (n = 36) to establish the general trends in their chemical characteristics. We also compared our results with those of humic acids (HAs) obtained from the same soils used in this study and other published data to discuss the differences between them. Our results clearly indicate that DAX-8 FAs with high carboxyl C content have small Mw and low hydrogen to carbon (H/C) ratio. In addition, DAX-8 FAs with high carbonyl C and alkyl C content have high A 400/C values and H/C ratios, respectively. These results strongly suggest that DAX-8 FAs with high aliphatic chemical properties have low carboxyl C content, large Mw and high H/C ratio. There are significant differences in chemical characteristics among the various soil types in almost all data; e.g., DAX-8 FAs from Podzols showed significantly higher A 400/C values, larger Mw, higher carbonyl C and O-aryl C content than those obtained from Andosols. However, these two C functional groups are relatively low values in the total C content among all soil types, suggesting that DAX-8 FAs may exhibit only small differences in chemical properties among the various soil types. The comparison with published data regarding soil HAs shows that DAX-8 FAs are characterized by smaller Mw; lower C, H, and nitrogen (N); higher oxygen (O) content; higher O/C; lower O/H ratios; higher carboxyl C content; and lower aryl C content in total C.