Rice-related greenhouse gases in Japan, variations in scale and time and significance for the Kyoto Protocol

The contribution of rice production to the three major greenhouse gases CO₂, CH₄ and N₂O in 1990, the base year of the Kyoto protocol is investigated for Japan. For the CO₂ assessment, we use a top-down life cycle approach, CH₄ is assessed using the Japanese GHG emission inventory and N₂O is assessed according to the ratio of rice area divided by the total area of agricultural soils. In total, 1.6% of greenhouse gas (GHG) emissions in 1990 originated from rice production. Next, we assess regional variations in nine rice-producing regions, based on the CO₂ data of 1990. General trends in rice production from 1960 to 2000 and data from the Japanese GHG emission inventory since 1990 are used to assess variations in time. The rice-related GHG emissions decreased to 1.05% of the total GHG emissions in 2001 and will be less than half the 1990 level in 2012, mainly due to the decrease in rice production. Contrary to the trend in GHG emissions of rice, overall GHG emissions increased as rice production fulfils important roles, in mitigating global warming and in adapting to changing climates. The protection of rice production is required to counter the increase of GHG emissions in transportation, waste and domestic sectors and to minimize problems related to landscape, water and natural hazard management.     

Effect of agricultural management practices on arbuscular mycorrhizal fungal abundance in low-input cropping systems of southern Africa: a case study from Zimbabwe

Previous research, mostly in temperate agricultural systems, has shown that management practices such as fallow period, tillage, crop rotation, and phosphorus (P) fertilizer applications can influence the abundance of arbuscular mycorrhizal fungi (AMF), but relatively little is known about their effect in smallholder farmers’ fields in sub-Saharan Africa. In this study, we evaluated the effect of four subsistence crops that form associations with AMF, moderate P fertilization, tillage, and fallow period on the subsequent AMF abundance on three contrasting low fertility soils in south-western Zimbabwe. Arbuscular mycorrhizal fungal abundance was estimated based on early mycorrhizal colonization of maize (Zea mays L.) or lablab (Lablab purpureus L.) following the various treatments. The previously grown crop significantly affected AMF abundance (p < 0.001). It was highest after lablab followed by pigeonpea (Cajanus cajan L.), maize, and groundnut (Arachis hypogaea L.), and there were significant positive correlations between AMF abundance and aboveground biomass of pigeonpea, lablab, and maize. Contrary to much previous research, P fertilization, fallowing, and tillage did not significantly decrease AMF abundance. In smallholder farmers’ fields in the semi-arid tropics of sub-Saharan Africa, therefore, growing vigorous mycorrhizal plants prior to the dry season could be more important than minimizing P fertilizer applications, fallow periods, and tillage to maintain or increase AMF abundance.     

Dependence of fish on subtropical riverine mangroves as habitat in the Ryukyu Islands,Japan

To examine whether fish were dependent on mangrove habitat in the Ryukyu Islands (southern Japan), fish assemblage structures were compared on the downstream side between mangrove-rich and mangrove-free rivers on Ishigaki and Okinawa Islands in 2014 and 2015. The mean species richness and abundance of fish were significantly higher in mangrove-rich rivers than in mangrove-free rivers. Mangrove-related food feeders (e.g., benthic invertebrate and detritus) were more abundant in mangrove-rich than mangrove-free rivers while mangrove-unrelated food feeders (e.g., zooplankton feeders) showed no difference between river types. Cluster and ordination analyses demonstrated that fish assemblage structures were clearly different between mangrove-rich and mangrove-free rivers. Of all of the fish species collected (88 species), half of the species (45 species, 51%) occurred exclusively in the mangrove-rich rivers, 9 species (10%) in the mangrove-free rivers and 34 species (39%) were common in both types of rivers. Commercially important fish (e.g., Lutjanus fulvus and L. argentimaculatus) showed greater abundance of juveniles in mangrove-rich rivers than in the mangrove-free rivers, indicating that mangrove-rich rivers can provide important habitat for a variety of fish, including those commercially important to fisheries.