Composition and partition of biomass in a smith fir (Abies georgei var.smithii) timberline forest on the Sergyemla Mountain,southeastern Tibetan Plateau

The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent. Quantification of vegetation biomass in the forests at the timberline is essential for understanding carbon balance, forest structure and functional changes in the forests at timberlines. We describe biomass and its constituent components of a smith fir tim- berline forest occurring at an elevation of 4320 m on the Sergyemla Mountain in the southeastern Tibetan Plateau. The results show that, in the tree layer, the average diameter at breast height （DBH） was 35.6 cm, the density 251 trees per hectare with a total biomass of 309.9 t.ha 1. Of the total biomass, the tnmks accounted for 70.49%, branches for 9.09%, leaves for 5.57% and roots for 14.85%. The total biomass in the shrub layer was 77.9 t＇ha-~ of which the biomass of trunks, branches, leaves and roots accounted for 42.8, 14.9, 4.6 and 15.6 t.ha-1, respectively. The total biomass in the herb layer was 3.0 t.ha-1. The total vegetation biomass in the smith fir timberline forest was 390.9 t-ha-l, to which the tree layer contributed the most （79.3%）, followed by shrubs （19.9%） and herbs （0.8%）. We estimate that the smith fir forest stand at the timberline had a higher total biomass than other fir or spruce forest stands in the surrounding area.

Estimation of CO_2 Emissions of Locomotives in China(1975-2005)

基于中国铁路统计中心收集的年度统计数据，机车的 CO2 排出物在 1975-2005 期间被计算，当柴油机机车的与时间增加了时，排放紧张和它的动态特征是蒸气机车的 CO2 排出物减少了的 analyzed.The 结果表演，由于到柴油机和电的 locomotives.The 总数的从蒸气的连续移动，在中国的蒸气和柴油机机车的 CO2 排出物从 42.23

Oxidative DNA damages by chemical exposures at work

Oxidative DNA damage is an inevitable consequence of cellular metabolism, with a propensity for increased levels following toxic insult. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. There are many chemicals in workplaces that could cause oxidative DNA damages such as carcinogens. This review concentrated on studies published between the years 2000 and 2012 that used to detect 8-oxodG in humans (workers), laboratory animals and in cell lines. Given the recent toxicological results from oxidative stress, it is important to review these studies to improve the current understanding of the oxidative DNA damages by chemical exposures at work. It also suggests that biomarkers may be responsible for understanding the role of oxidative DNA damage in disease, highlighting the need for further studies.

Natural^(15)N abundance in soils and plants in relation to N cycling in a rangeland in Inner Mongolia

Aims Natural 15N abundance provides integrated information about nitrogen(N)input,transformation and output,indirectly reflecting N cycling traits within terrestrial ecosystems.However,relationships between natural 15N abundance and N cycling processes are poorly understood in China.Here,our primary objectives were to(i)examine the effects of grazing at varying levels of intensity on d15N of soils and plants in a semi-arid grassland;(ii)detect the relationships between d15N of soils and four major N cycling processes(i.e.mineralization,nitrification,denitrification and ammonia volatilization);and(iii)determine whether d15N of soils can be used as an indicator of N cycling in this semi-arid grassland.Methods The field experiment was conducted within the long-term(17-year)grazing enclosures in a semi-arid grassland in Inner Mongolia.Five grazing intensities(0.00,1.33,2.67,4.00 and 5.33 sheep ha
1)were designed.d15N values of topsoils(0–10 cm),surface soils(0–2 cm)and plants were measured in 2006.Differences in d15N of soils and plants between the five grazing intensities were examined.Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons.The d15N values of topsoils were linked to the four N cycling processes to investigate their relationships.Important Findings The d15N values of topsoils(5.20–5.96&)were substantially higher than the d15N values of plants(2.51–2.93&)and surface soils(1.44–2.92&)regardless of grazing intensities.The 15N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher d15N values in topsoils than in surface soils.In addition,the d15N values of topsoils were positively correlated with the d15N values of both plants and surface soils.Grazing,especially the high-intensity grazing(5.33 sheep ha
1),resulted in a significant decrease in d15N of surface soils.However,no statistically significant variations in d15N of topsoils and plants were found in response to grazing.The d15N values of topsoils exhibited significant dependence on the cumulative rates of NH3 volatilization,net nitrification and denitrification in 2005 but not in 2006.