Diversity profiling of soil bacterial and fungal communities in the Ogasawara (Bonin) Islands, Japan.

Island biogeography research provides insight into microbial diversity patterns; however, little is known about the diversity and distribution of soil microbial communities on remote and poorly accessible islands. Here, we present amplicon sequencing data from bacterial and fungal communities in the surface soils of the Ogasawara (Bonin) Islands, Japan.

Climate amelioration, abrupt vegetation recovery, and the dispersal of Homo sapiens in Baikal Siberia.

The dispersal of Homo sapiens in Siberia and Mongolia occurred by 45 to 40 thousand years (ka) ago; however, the climatic and environmental context of this event remains poorly understood. We reconstruct a detailed vegetation history for the Last Glacial period based on pollen spectra from Lake Baikal. While herb and shrub taxa including Artemisia and Alnus dominated throughout most of this period, coniferous forests rapidly expanded during Dansgaard-Oeschger (D-O) events 14 (55 ka ago) and 12 to 10 (48 to 41 ka ago), with the latter presenting the strongest signal for coniferous forest expansion and Picea trees, indicating remarkably humid conditions. These abrupt forestation events are consistent with obliquity maxima, so that we interpret last glacial vegetation changes in southern Siberia as being driven by obliquity change. Likewise, we posit that major climate amelioration and pronounced forestation precipitated H. sapiens dispersal into Baikal Siberia 45 ka ago, as chronicled by the appearance of the Initial Upper Paleolithic.

Discharge of suspended solids and radiocesium into stream water in a forested watershed before and after line thinning with spur road construction.

In an experimental watershed located around 120 km southwest of the Fukushima Daiichi Nuclear Power Plant with a drainage area of 59.9 ha, suspended solids (SS) and radioactive cesium discharge from a forested headwater catchment were monitored before and after line thinning. The lower slopes in the experimental watershed were covered with plantation conifer trees (Japanese cedar), while the upper slopes were covered with deciduous trees. In 2012, line thinning was carried out at a thinning rate of 35% across 17% of the northeastern part of the watershed and across the remaining part in 2013. Spur roads were constructed along all tributaries without water, and logged trees were dragged and grappled using forestry machinery and transported along these roads to timber yards using forwarder-type forestry vehicles. A V-notch weir and a water level gauge were installed at the watershed outlet and stream water was sampled twice a month during base flow, whereas during flood flow, stream water samples of 1 L were collected every hour using an automatic water sampler. These samples were filtered through 0.5 µm glass fiber filters to measure the SS concentration. SS concentration data was collected for 21 floods before thinning and for 37 floods after thinning. A time-integrated SS sampler was installed in the stream close to the weir and SS samples were collected every two or three months to measure their Cs-137 concentrations. SS concentrations before (from July 2010 to August 2012) and after thinning (from October 2013 to December 2018) were compared, where the maximum SS concentrations before and after thinning were 211 and 790 mg L-1, respectively. It was discovered that some SS concentrations during flood flow were higher after carrying out thinning than before. Some ΣLss values (specific cumulative load of SS in a flood event) also showed the same results as the SS concentrations. Thus, it was clear that SS discharge immediately increases after thinning, but as it increases Cs-137 export is limited. This is related to a change in SS source brought about by the process of thinning, a decrease with time in the Cs-137 concentration in organic solid expected from that in litter, and a regrowth of vegetation on spur roads, protecting them against soil erosion. Therefore, it was concluded that thinning does not drastically increase Cs-137 export from a forested watershed.

Global 137Cs fallout inventories of forest soil across Japan and their consequences half a century later.

Japanese forests were exposed to multiple sources of radioactive contamination. To acquire scientific guidance on forest management planning, it is crucial to understand the long-term radiocesium (137Cs) distribution (and redistribution) over time. To obtain robust evidence of the residual global fallout of 137Cs (137Cs-GFO) after a few decades, we determined 137Cs-GFO inventory in forest soil at 1171 soil pits of 316 plots evenly spaced across Japan from 2006 to 2011, shortly before the Fukushima Dai-ichi Nuclear Power Plant accident. The activity concentration measurements were performed using a NaI well-type scintillation counter. The average (±SD) 137Cs-GFO in forest soil (0-30 cm from the surface) of the National Forest Soil Carbon Inventory (NFSCI) sampling plots uniformly extracted from the entire country was estimated to be 2.27 ± 1.73 kBq m-2 (n = 316) as of Oct. 1, 2008. A high nationwide spatial variation was found in 137Cs-GFO, where relatively high 137Cs-GFO was found along the Sea of Japan compared with the total annual precipitation. We also obtained a reconstructed decay-corrected cumulative 137Cs-GFO dataset from the fallout observatories as the initial 137Cs-GFO. The cumulative 137Cs-GFO of fallout observatories averaged 2.47 ± 0.95 kBq m-2 (n = 39) as of Oct. 1, 2008 and displayed spatial variation similar to that in forest soil. To identify whether 137Cs-GFO remains in forest soil across Japan, we examined a general linear mixed-effect model comparing 137Cs-GFO between forest soil and the observatory under normalized annual precipitation and region. The model did not indicate a significant difference, but relatively lesser 137Cs-GFO was found in forest soil, where the least-squares mean of 137Cs-GFO in forest soils was 79.1% of that of the observatory. The variation in 137Cs-GFO in forest soils within NFSCI sampling plots was 1.4 times greater than that among plots. The high spatial variation in 137Cs-GFO within a 0.1-ha plot strongly suggested the redistribution of 137Cs-GFO within the forest catchment. The vertical distribution pattern of 137Cs-GFO across three depth layers indicated that the 137Cs-GFO redistributions were likely attributed to the movements of sediments and mass. Moreover, when extracting soil pits assumed to have the least soil disturbance from the vertical distribution pattern, no significant difference in 137Cs-GFO was observed between forest soil and observatory data. These findings provide important insights into the stability of 137Cs-GFO in the forest ecosystem. Considering the potential hotspot where 137Cs-GFO can accumulate deeper in the soil (>30 cm in depth), most 137Cs-GFO has remained in the forest for decades. Our study offers microscale heterogeneous 137Cs-GFO distribution in forests for ensuring long-term forest management planning necessary for both the long-term migration and local accumulation of 137Cs in forests.

The use of soil pollen to determine the sex of overhead individuals of a temperate dioecious shrub.

PREMISE OF THE STUDY: In dioecious species, determining the sex of individual plants from one-time phenological observations is rarely feasible when some individuals capable of reproducing are not flowering or fruiting at the time of observation. Currently, sexing those individuals requires long-term phenological data on individuals and populations, but such data are rarely available or feasible to collect. We tested the hypothesis that differences in soil pollen concentrations beneath the crowns of female and male plants would exist and be sufficient to reliably determine the sex of the individual plant overhead in a dioecious species. We predicted that soil pollen concentrations beneath male plants would be significantly higher than beneath female plants because only males produce pollen and pollen should accumulate in the soil underneath the male plants over repeated flowering events. METHODS: We collected samples from surface soil under both sexes of the insect-pollinated dioecious shrub, Aucuba japonica (Garryaceae). KEY RESULTS: Pollen grains were present in surface soil in both Oe and A horizons, and mean pollen concentration under males was significantly higher than under females. Pollen concentrations beneath males were positively correlated with male plant height, potentially reflecting greater pollen production by larger individuals. CONCLUSIONS: Considering the small plant size and relatively low pollen production of A. japonica, this method may hold promise for sexing other dioecious species in the absence of direct phenological data. Our phenology-free and relatively low-cost method for sexing dioecious plants may be especially useful in tropical forests where many species are dioecious.

The total amounts of radioactively contaminated materials in forests in Fukushima, Japan.

There has been leakage of radioactive materials from the Fukushima Daiichi Nuclear Power Plant. A heavily contaminated area (≥ ¹³4,¹³7Cs 1000 kBq m⁻²) has been identified in the area northwest of the plant. The majority of the land in the contaminated area is forest. Here we report the amounts of biomass, litter (small organic matter on the surface of the soil), coarse woody litter, and soil in the contaminated forest area. The estimated overall volume and weight were 33 Mm³ (branches, leaves, litter, and coarse woody litter are not included) and 21 Tg (dry matter), respectively. Our results suggest that removing litter is an efficient method of decontamination. However, litter is being continuously decomposed, and contaminated leaves will continue to fall on the soil surface for several years; hence, the litter should be removed promptly but continuously before more radioactive elements are transferred into the soil.