Chih-Hsin Cheng

Ageing of black carbon along a temperature gradient.

Black carbon (BC) is regarded as a chemically and biologically stable form of carbon and the changes of BC properties in nature are generally assumed to be minute. However, more and more observations have argued the inertness of BC. The objectives of this study were to characterize the changes of BC properties through ageing processes and to identify if these changes are associated with temperature. Our results showed that ageing of BC occurs over a temperature range from -22 degrees C to 70 degrees C within a short period of 12 months. The main changes of BC properties through ageing were found in elemental composition, surface chemistry, and adsorption properties, where the aged BCs were shown to have higher oxygen concentrations, surface acidity, and negative surface charge but lower C concentrations, pH, surface basicity, point of zero net charge, and also a lower adsorption capacity of hydroquinone, an allelopathic compound, than fresh BC. These ageing processes of BC were affected by temperature and changed over time, with higher temperature and longer incubation time enhancing BC ageing. Our results from a wide temperature range suggest that ageing of BC is likely to occur in any terrestrial regime and that the changes of BC properties through ageing should not be overlooked.

Biomass carbon accumulation in aging Japanese cedar plantations in Xitou, central Taiwan

BackgroundJapanese cedar (Chrytomeria japonica D. Don) is an important plantation species in Taiwan and represents 10% of total plantation area. It was first introduced in 1910 and widely planted in the northern and central mountainous areas of Taiwan. However, a change in forest management from exotic species to native species in 1980 had resulted in few new Japanese cedar plantations being established. Most Japanese cedar plantations are now between 30 and 50 years old and reaching their rotation period. It is of interest to know whether these plantations could be viable for future carbon sequestration through the accumulations of stand carbon stocks. Twelve even-aged Japanese cedar stands along a stand age gradient from 37 to 93 years were selected in Xitou of central Taiwan. The study aims were to investigate the basic stand characteristics and biomass carbon stock in current Japanese cedar stands, and determine the relationships among stand characteristics, tree biomass carbon, and stand age.ResultsOur results indicate that existing Japanese cedar plantations are still developing and their live tree biomass carbon continues to accumulate. At stands with a stand age of 90 years, tree density, canopy height, mean diameter at breast height, basal area, and live tree biomass carbon stocks reach to nearly 430 tree ha-1, 27 m, 48 cm, 82 m2 ha-1 and 300 Mg C ha-1, respectively.ConclusionsTherefore, with no harvesting, current Japanese cedar plantations provide a carbon sink by storing carbon in tree biomass.

Isotopic composition of carbon (δ13C) and nitrogen (δ15N) in foliage and soil as a function of tree species

209 Isotopic composition of carbon (δ 13 C) and nitroo gen (δ 15 N) is widely used for characterizing the state and changes in ecosystems [1]. Despite of general understanding of ecological factors determining the isotopic composition of carbon and nitrogen in plants and soils, the species effects of plants growing in simii lar environments on isotopes in plants and soils remain poorly understood [2, 3]. The aim of the work was to distinguish the effect of different tree species common for Siberia and growing under common garr den conditions on isotopic composition of carbon and nitrogen in foliage and soil, as well as on the differr ences in isotopic composition between foliage and soil. It was demonstrated that (1) tree species differ in the isotopic composition of carbon in needles and leaves and less in δ 15 N; (2) deciduous species (birch and aspen) had smaller δ 13 C values, indicating their smaller water use efficiency compared to coniferous species; (3) δ 15 N in plants correlated with soil microo bial activities of the nitrogen cycle. The samples of leaves, needles, and soil were coll lected from the Siberian afforestation experiment. The experiment was established in 1971 on the gray forest soil, which was initially homogeneous in physical and chemical and microbiological properties. Six domii nant in Siberia tree species were planted, including the spruce (Picea abies), Scots pine (Pinus sylvestris), Arolla pine (Pinus cembra), larch (Larix sibirica), birch (Betula pendula), aspen (Populus tremula) [4]. The square of each plot with one tree species was 2400 m 2. Thus, the development of forest stands proo ceeded under similar geomorphological and climatic conditions. Each plot with a tree species was divided into three subplots (A, B, and C), which were used as a replicates for statistical analysis. Altogether, 18 mixed soil samples and 18 mixed needles/leaves samples (six tree species, three subplots) were coll lected. The content of C, N and δ 13 C, δ 15 N values were determined in the samples using the mass specc trometer connected to elemental analyzer (EAA IRMS). Several soil microbiological characteristics related to C and N cycle were previously described for this afforestation experiment [5, 6] and were used for the correlation analysis in the present work. Tree species strongly differed in δ 13 C in foliage (p < 0.001); the lowest values were found in deciduous spee cies (birch and aspen); larch …

Positive response of carbon mineralization to nitrogen addition in forest soils of Siberia

173 Human activities and production of nitrogen fertill izers have altered the global nitrogen cycle to a greater extent than the carbon cycle [1, 2]. At the same time, nitrogen inputs into various ecosystems, in the form of either fertilizers or atmospheric depositions, lead to substantial changes not only in nitrogen, but also in carbon cycles [2, 3]. Nitrogen input into an ecosystem usually enhances its biological productivity and often results in increased carbon accumulation in plants. As estimated for temperate and boreal forests, addition of 1 kg of nitrogen leads to accumulation of extra 25 kg of carbon in plant biomass [4]. The fate of the main biosphere carbon reservoir, the soil carbon, is less understood. Addition of nitrogen may lead to either accumulation [5] or loss of soil car bon [6]. The published data suggest that in most cases, with increasing nitrogen input, carbon accumulation in soil predominates because of the inhibition of the activity of soil heterotrophic microorganisms [7]. However, most published reports are based on the experiments conducted in Central Europe, United States [8], and, recently, in China [9], i.e., in highly industrialized countries with a high level of atmoo spheric N depositions. At low and average inputs of nitrogen into an ecosystem, the response of carbon transformation processes is assumed to be fundamenn tally different [8]. In Siberia, where the atmospheric nitrogen depositions are among the lowest in the world (0.25–1 (kg ha –1 year –1)) [10], there is no data on the influence of elevated nitrogen depositions on minerall ization of soil carbon. The goal of this study was to assess the influence of nitrogen additions on carbon mineralization activity in soils beneath different tree species and adjacent grassland. We have demonstrated that the addition of nitrogen stimulates activity of heterotrophic microorr ganisms that mineralize soil organic matter. Our data suggest that Siberian ecosystems are not exposed to nitrogen pollution even in the vicinity of industrial centers, such as Krasnoyarsk, and, therefore, the effect of nitrogen added to soil is fundamentally differr ent as compared to the effect of high atmospheric nitrogen depositions on soils of the industrialized countries. Soils were sampled on the experimental plots of the Institute of Forest, Siberian Branch, Russian Acadd emy of Science, where six different tree species were planted in 1971 [11, 12]. The samples of the upper mineral horizon A1 (0–10 cm) and of the litter were …