The impact of the unusually severe drought associated with the 1997–1998 El Niño on tropical forest dynamics in Sarawak, Malaysia was examined. Mortality during the non-drought period (1993–1997) in a core plot (1.38 ha) was 0.89 % y−1, while that during the drought period (1997–1998) in the same plot and a peripheral plot was 6.37 and 4.35 % y−1, respectively. The basal area lost in the drought interval was 3.4 times that of the annual incremental basal area in 1993–1997. Drought mortality was higher for the smaller trees, though it was less size dependent than the non-drought mortality. Dipterocarpaceae, which is the dominant family in the study plot, had a mortality 12–30 times higher in the drought than the non-drought period. There were no significant differences in mortality among the topographic types. From the results of a log-linear model (multi-factored contingency table), the death of trees was correlated with size class, indicating a change in the size-class structure of the forest. Thus, both the species composition and structure are totally affected by such an episodic drought even in a per-humid tropical forest.

Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the TeaComposition initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 °C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.

Community-level mass flowering, known as general flowering, which occurs in South-East Asia at supra-annual irregular intervals, is considered a particularly spectacular phenomenon in tropical ecology. Recent studies have proposed several proximate factors inducing general flowering, such as drought and falls in minimum temperature. However, limited empirical data on the developmental and physiological processes have been available to test the significance of such factors. To overcome this limitation and test the hypotheses that general flowering is triggered by the proposed factors, we conducted an ‘ecological transcriptome’ study of a mass flowering species, Shorea beccariana, comparing meteorological data with genome-wide expression patterns obtained using next-generation sequencing. Among the 98 flowering-related genes identified, the homologs of a floral pathway integrator, SbFT, and a floral repressor, SbSVP, showed dramatic transcriptional changes before flowering, and their flowering functions were confirmed using transgenic Arabidopsis thaliana. Expression in drought-responsive and sucrose-induced genes also changed before flowering. All these expression changes occurred when the flowering-inducing level of drought was reached, as estimated using data from the preceding 10 years. These genome-wide expression data support the hypothesis that drought is a trigger for general flowering.

Genome duplication is widespread in wild and crop plants. However, little is known about genome-wide selection in polyploids due to the complexity of duplicated genomes. In polyploids, the patterns of purifying selection and adaptive substitutions may be affected by masking owing to duplicated genes or homeologs as well as effective population size. Here, we resequence 25 accessions of the allotetraploid Arabidopsis kamchatica, which is derived from the diploid species A. halleri and A. lyrata. We observe a reduction in purifying selection compared with the parental species. Interestingly, proportions of adaptive non-synonymous substitutions are significantly positive in contrast to most plant species. A recurrent pattern observed in both frequency and divergence–diversity neutrality tests is that the genome-wide distributions of both subgenomes are similar, but the correlation between homeologous pairs is low. This may increase the opportunity of different evolutionary trajectories such as in the HMA4 gene involved in heavy metal hyperaccumulation.

A commercial colony of Bombus terrestris (L.) was introduced to Japan in 1992 for crop pollination in greenhouses. Since then wild colonies have developed and spread in some regions. In the present study, we measured the spatial distribution and temporal change in abundance of B. terrestris in the Chitose River Basin, Hokkaido, Japan to elucidate the relation of greenhouses to the bee's distribution and to evaluate its potential effects on native bumblebees. Bumblebees were collected with window traps in windbreak forests roughly 1, 2, 4, and 6 km NNW and SSE of a large greenhouse. The peak catch of B. terrestris queens occurred in early June, suggesting that they had successfully hibernated in the field. The distributions of B. terrestris and the native B. ardens were mutually exclusive, while the native B. hypocrita appeared at all sites. Catches of B. terrestris were restricted to within 4 km of the nearest greenhouse, suggesting that the invasion was still in the initial phase in this area. The reduction in abundance of the native bumblebees in the sites of high B. terrestris abundance suggests the presence of interspecies competition between B. terrestris and the native bumblebees during the early part of the colony activity, although such reduction in B. ardens can be explained by habitat suitability.