Carbon cycling and budget in a forested basin of southwestern Hokkaido, northern Japan

Quantification of annual carbon sequestration is very important in order to assess the function of forest ecosystems in combatting global climate change and the ecosystem responses to those changes. Annual cycling and budget of carbon in a forested basin was investigated to quantify the carbon sequestration of a cool-temperate deciduous forest ecosystem in the Horonai stream basin, Tomakomai Experimental Forest, northern Japan. Net ecosystem exchange, soil respiration, biomass increment, litterfall, soil-solution chemistry, and stream export were observed in the basin from 1999–2001 as a part of IGBP-TEMA project. We found that 258 g C m–2 year–1 was sequestered annually as net ecosystem exchange (NEE) in the forested basin. Discharge of carbon to the stream was 4 g C m–2 year–1 (about 2% of NEE) and consisted mainly of dissolved inorganic carbon (DIC). About 43% of net ecosystem productivity (NEP) was retained in the vegetation, while about 57% of NEP was sequestered in soil, suggesting that the movement of sequestered carbon from aboveground to belowground vegetation was an important process for net carbon accumulation in soil. The derived organic carbon from aboveground vegetation that moved to the soil mainly accumulated in the solid phase of the soil, with the result that the export of dissolved organic carbon to the stream was smaller than that of dissolved inorganic carbon. Our results indicated that the aboveground and belowground interaction of carbon fluxes was an important process for determining the rate and retention time of the carbon sequestration in a cool-temperate deciduous forest ecosystem in the southwestern part of Hokkaido, northern Japan

Response of Background Herbivory in Mature Birch Trees to Global Warming

Given the time scale based on the duration of exposure to global warming, natural climate-gradient studies and experimental manipulations have detected long-term (decades to centuries) and short-term (years to decades) ecological responses to global warming. Combination of these two complementary approaches within a single study may enable prediction of the likely responses of ecological processes to global warming. To understand how global warming affects plant-herbivore interactions within a canopy of Erman's birch, we combined an elevational gradient study and a warming experiment involving mature birch trees in which the soil and tree branches were warmed separately. In the elevational gradient study, herbivory by chewing insects and plant growth increased as elevation decreased, and the concentrations of condensed tannins and total phenolics in the leaves decreased. In the warming experiment, soil warming alone increased herbivory, and the addition of branch warming amplified the effect on herbivory. Soil warming alone decreased the tannin concentration, and the addition of branch warming led to a further reduction. The variation in herbivory was best explained by the tannin content of leaves. Our experimental results demonstrate that the decreased tannin content of leaves due to a combination of soil and branch warming was an important driver of increased herbivory in the canopy of the mature birch trees. The similar tendencies in the short- and long-term responses imply that global warming is likely to increase background herbivory in mature birch trees by decreasing the tannin content of leaves in the canopy.</p

Genome-Scale Assessment of Age-Related DNA Methylation Changes in Mouse Spermatozoa

<div><p>DNA methylation plays important roles in the production and functioning of spermatozoa. Recent studies have suggested that DNA methylation patterns in spermatozoa can change with age, but the regions susceptible to age-related methylation changes remain to be fully elucidated. In this study, we conducted genome-scale DNA methylation profiling of spermatozoa obtained from C57BL/6N mice at 8 weeks (8w), 18 weeks (18w) and 17 months of age (17m). There was no substantial difference in the global DNA methylation patterns between 18w and 17m samples except for a slight increase of methylation levels in long interspersed nuclear elements in the 17m samples. We found that maternally methylated imprinting control regions (mICRs) and spermatogenesis-related gene promoters had 5–10% higher methylation levels in 8w samples than in 18w or 17m samples. Analysis of individual sequence reads suggested that these regions were fully methylated (80–100%) in a subset of 8w spermatozoa. These regions are also known to be highly methylated in a subset of postnatal spermatogonia, which might be the source of the increased DNA methylation in 8w spermatozoa. Another possible source was contamination by somatic cells. Although we carefully purified the spermatozoa, it was difficult to completely exclude the possibility of somatic cell contamination. Further studies are needed to clarify the source of the small increase in DNA methylation in the 8w samples. Overall, our findings suggest that DNA methylation patterns in mouse spermatozoa are relatively stable throughout reproductive life.</p></div

Stability of DNA methylation levels of various genomic features.

<p>Mean methylation levels (%) of CpG cytosines in promoter, exon, intron, intergenic regions LINE, LTR, SINE and L1 elements. The evolutionary ages of the L1 elements [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167127#pone.0167127.ref035" target="_blank">35</a>] are indicated. Data are shown as mean ± standard error (SE). Different letters indicate statistically significantly methylation differences (P < 0.05).</p

Identification of differentially methylated promoters.

<p>(A) Hierarchical clustering of differentially methylated promoters. Z-scored methylation levels are color-coded as shown. CGI and non-CGI promoters are also indicated. (B) Chromosome distribution of the differentially methylated promoters. (C) GO analysis of the promoters in Cluster I. Statistically significant (<i>P</i> < 0.05) GO terms are indicated with BH-corrected <i>P</i>-values. (D) Methylation levels of the promoters in Cluster I. Data are shown as mean ± SE. Different letters indicate statistically significantly methylation differences (<i>P</i> < 0.05). (E) Methylation pattern of the <i>Mael</i> promoter. The vertical axis indicates the methylation levels (%).</p

Heterogeneity of methylation levels of spermatogenesis-related promoters in 8w spermatozoa.

<p>(A) Heterogeneity of DNA methylation levels in spermatozoa. Methylation patterns of individual sequence reads are useful to verify whether subsets of spermatozoa have full methylation levels (pattern I) or not (pattern II). Note that the mean methylation levels are the same for both patterns. (B) Heterogeneity of the <i>Mael</i> promoter. <i>Mael</i> methylation patterns of 8w, 18w and 17m samples are shown. The region contains 6 CpG cytosines. The number of reads is indicated on the right side. Each line represents one read. Blue, unmethylated CpG cytosine; red, methylated CpG cytosine. (C) Analysis of individual sequence reads mapped to spermatogenesis-related gene promoters. Sequence reads were classified into five groups according to their methylation levels. The distribution of the methylation levels is shown as stacked bar charts.</p