Atsunobu Kadono

In situ short-term dynamics of CO2 flux and microbial biomass after simulated rainfall in dry croplands in four tropical and continental ecosystems

Abstract The wet–dry cycles of soil primarily drive carbon (C) dynamics in dry croplands that mainly experience sporadic rainfall events. We evaluated the in situ short-term (hourly) dynamics of soil carbon dioxide (CO2) efflux and microbial biomass, to compare the significance of a single rainfall event with/without C substrate to reveal the effects of a single rainfall on the soil C dynamics in clayey dry croplands in four different climates and ecosystems. The experiments were conducted on four clayey dry croplands as follows: Thailand (TH) and Tanzania (TZ) in tropical climates, and Kazakhstan (KZ) and Hungary (HG) in continental climates. Hourly measurements of soil CO2 efflux, in situ microbial biomass (MB) and in situ microbial activity (qCO2) were conducted after the application of simulated rainfall (W plots) and rainfall/glucose (WG plots) treatments. We also evaluated the easily mineralizable carbon (EMC) by incubation. The rainfall treatment caused an increase in the qCO2 but not in MB, causing a clear but short C flush in all W plots (10–37 h), while the WG treatment caused an increase both of qCO2 and MB, resulting in substantially longer and larger C flush in the WG plots (ca. 100 h). The ratio of the cumulative soil CO2 flux caused by rainfall treatment to EMC was larger in TH-W and TZ-W plots (8.2 and 4.9%, respectively) than in the KZ-W and HG-W plots (2.9 and 1.1%, respectively). In addition, applied glucose was more heavily mineralized in the TH-WG and TZ-WG plots (15.0 and 9.7%, respectively) than in the KZ-WG and HG-WG plots (6.4 and 3.4%, respectively), because of the different MB increment patterns for the first 24 h, i.e., immediate and large MB increments in TH and TZ, but not in KZ and HG. These results reveal a possible mechanism that causes the rapid decomposition of soil organic carbon and applied organic matter in the dry tropical cropland.

Could Soil Acidity Enhance Sequestration of Organic Carbon in Soils

On the basis of field and laboratory measurements of the dynamics of soil organic matter (SOM) in Japan, Thailand, Indonesia, Kazakhstan, and Ukraine having different soil pH levels, we postulate that soil acidity plays an important role in the accumulation of SOM through two processes. Firstly, the amount of potentially mineralizable C (C 0) in the acid soils of Kalimantan or light-fraction C in the Japanese acid soils often increased drastically. Hence, it seems that high soil acidity can enhance the accumulation of organic materials in surface soils by decreasing the soil microbial activities for SOM decomposition. Secondly, field measurements of C flux in various soils under forest showed that the internal leaching of dissolved organic carbon (DOC) from litter layers or surface soils increased under low pH conditions, typically for Humods in Japan and Udults in Kalimantan. This indicates a downward movement of DOC in acid soils that increases the tendency of the subsoils to accumulate SOM as organo-mineral complexes. It is concluded that high soil acidity can enhance the storage level of soil organic materials in the form of readily mineralizable organic materials in the surface soils and by organo-mineral complexes formed in subsoils as a result of accelerated leaching of DOC from the O horizon.

Grassland degradation caused by tourism activities in Hulunbuir, Inner Mongolia, China

The recent increase in the number of tourists has raised serious concerns about grassland degradation by tourism activities in Inner Mongolia. Thus, we evaluated the effects of tourism activities on the vegetation and soil in Hulunbuir grassland. We identified all the plant species, measured the number and height of plant and plant coverage rate, and calculated species diversity, estimated above-ground biomass in use plot and non-use plot. We also measured soil hardness, and collected soil samples for physical and chemical analysis in both plots. The obtained results were as follows: a) the height of the dominant plants, plant coverage rate, species diversity, and above-ground biomass were significantly lower in use plot than in non-use plot, b) Carex duriuscula C.A.Mey., indicator plant for soil degradation, was dominant in use plot, c) soil hardness was significantly higher in use plot than in non-use plot, and spatial dependence of soil hardness was only found in the use plot, d) CEC, TC, TN and pH in the topsoil were significantly lower in use plot than non-use plot. On the basis of the results, we concluded that the tourism activities can be another major cause of the grassland degradation in Inner Mongolia.