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Soil microorganisms play an important role in regulating nutrient cycling in terrestrial ecosystems. Most of the studies conducted thus far have been confined to a single forest biome or have focused on one or two controlling factors, and few have dealt with the integrated effects of climate, vegetation, and soil substrate availability on soil microbial communities and functions among different forests. In this study, we used phospholipid-derived fatty acid (PLFA) analysis to investigate soil microbial community structure, and extracellular enzymatic activities to evaluate the functional potential of soil microbes of different types of forests in three different climatic zones along the North-South transect in eastern China (NSTEC). In general, soil enzyme activities and microbial PLFAs were higher in primary forests than in secondary forests in temperate and warm temperate regions. In the subtropical region, soil enzyme activities were lower in the primary forests than in the secondary forests and microbial PLFAs did not differ significantly between primary and secondary forests. The microbial PLFAs and enzyme activities differed considerably between broadleaved and coniferous forests. Different species of coniferous trees may cause variations in soil microbial PLFAs and enzyme activities. Both climate and forest type had significant effects on soil enzyme activities and microbial communities with a considerable interactive effect. Litter nutrients made an important contribution to variations in the soil microbial communities and enzyme activities in temperate zones, while soil micro-climate and nutrients were the main controls on the soil microbial community structure and enzymatic activities in warm temperate and subtropical zones. Our results indicate that the main controls on soil microbes and functions vary across forest ecosystems in different climatic zones, and that the effects of soil moisture content, soil temperature, and the soil N/P ratio were considerable. This information will add value to modeling of microbial processes and will contribute to carbon cycling in large-scale carbon models. [ABSTRACT FROM AUTHOR]

Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m-2 yr-1 (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe- Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr-1, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor. [ABSTRACT FROM AUTHOR]

The regional determining factors underlying inter- and intra-site variation of 15N natural abundance in foliage, O horizon and mineral soil were investigated in eastern China.15N natural abundance values for these forest ecosystems were in the middle of the range of values previously found for global forest ecosystems. In contrast to commonly reported global patterns, temperate forest ecosystems were significantly more15N-enriched than tropical forest ecosystems, and foliage δ15N was negatively correlated with increasing mean annual temperature and net soil Nmineralisation in eastern China. TightNcycling in forest ecosystems and the use of atmospheric N deposition by trees might underlie the δ15N distribution patterns in eastern China. The existence of mycorrhizal fungi and root distribution profiles in the soil may also influence the15N natural abundance patterns in forest ecosystems of eastern China. [ABSTRACT FROM AUTHOR]

Emissions of nitrous oxide (N2O) from the soil following simulated nitrogen (N) deposition in a disturbed (pine), a rehabilitated (pine and broadleaf mixed) and a mature (monsoon evergreen broadleaf) tropical forest in southern China were studied. The following hypotheses were tested: (1) addition of N will increase soil N2O emission in tropical forests; and (2) any observed increase will be more pronounced in the mature forest than in the disturbed or rehabilitated forest due to the relatively high initial soil N concentration in the mature forest. The experiment was designed with four N treatment levels (three replicates; 0, 50, 100, 150 kg N ha−1 year−1 for C (Control), LN (Low-N), MN (Medium-N), and HN (High-N) treatment, respectively) in the mature forest, but only three levels in the disturbed and rehabilitated forests (C, LN and MN). Between October 2005 to September 2006, soil N2O flux was measured using static chamber and gas chromatography methodology. Nitrogen had been applied previously to the plots since July 2003 and continued during soil N2O flux measurement period. The annual mean rates of soil N2O emission in the C plots were 24.1 ± 1.5, 26.2 ± 1.4, and 29.3 ± 1.6 μg N2O–N m−2 h−1 in the disturbed, rehabilitated and mature forest, respectively. There was a significant increase in soil N2O emission following N additions in the mature forest (38%, 41%, and 58% when compared to the C plots for the LN, MN, and HN plots, respectively). In the disturbed forest a significant increase (35%) was observed in the MN plots, but not in the LN plots. The rehabilitated forest showed no significant response to N additions. Increases in soil N2O emission occurred primarily in the cool-dry season (November, December and January). Our results suggest that the response of soil N2O emission to N deposition in tropical forests in southern China may vary depending on the soil N status and land-use history of the forest. [ABSTRACT FROM AUTHOR]

The article discusses research which measured components of the energy budget continuously above a 300 year old temperate mixed forest in Northeastern China from January 1 to December 31 in 2003. Researchers found that the albedo showed pronounced seasonal trends and its values ranged from 0.07 to 0.20, that latent heat was the largest component of the energy budget on a yearly time scale, and was about 30% greater than sensible heat as indicated by the annual Bowen ratio beta values, and that despite the energy budget gap, the eddy covariance method should be a sound tool for measurement of turbulent fluxes, even under extremely cold conditions.