Yowhan Son

The effect of multi-walled carbon nanotubes on soil microbial activity

Nanomaterials such as multi-walled carbon nanotubes (MWCNTs) are applied to various industrial products and thus may be released to soils, but their potential environmental impacts remain largely undetermined. We investigated the short-term effect of MWCNTs on the activity and biomass of microorganisms inhabiting two different soil types in an incubation study. Up to 5000 μg MWCNT g(-1) soil was applied and the activities of 1,4-β-glucosidase, cellobiohydrolase, xylosidase, 1,4-β-N-acetylglucosaminidase, and phosphatase and microbial biomass were measured. In both soil types, most enzyme activities showed a tendency to be repressed under 500 μg MWCNT g(-1) soil, and all enzymatic activities as well as microbial biomass C and N were significantly lowered under 5000 μg MWCNT g(-1) soil. Our results suggest that high concentrations of MWCNTs could lower the microbial activity and biomass in soils, and they may serve as an important guideline in regulating the release of MWCNTs to the soil environment.

Forest biomass carbon sinks in East Asia, with special reference to the relative contributions of forest expansion and forest growth

Forests play an important role in regional and global carbon (C) cycles. With extensive afforestation and reforestation efforts over the last several decades, forests in East Asia have largely expanded, but the dynamics of their C stocks have not been fully assessed. We estimated biomass C stocks of the forests in all five East Asian countries (China, Japan, North Korea, South Korea, and Mongolia) between the 1970s and the 2000s, using the biomass expansion factor method and forest inventory data. Forest area and biomass C density in the whole region increased from 179.78 × 10(6) ha and 38.6 Mg C ha(-1) in the 1970s to 196.65 × 10(6) ha and 45.5 Mg C ha(-1) in the 2000s, respectively. The C stock increased from 6.9 Pg C to 8.9 Pg C, with an averaged sequestration rate of 66.9 Tg C yr(-1). Among the five countries, China and Japan were two major contributors to the total regions forest C sink, with respective contributions of 71.1% and 32.9%. In China, the areal expansion of forest land was a larger contributor to C sinks than increased biomass density for all forests (60.0% vs. 40.0%) and for planted forests (58.1% vs. 41.9%), while the latter contributed more than the former for natural forests (87.0% vs. 13.0%). In Japan, increased biomass density dominated the C sink for all (101.5%), planted (91.1%), and natural (123.8%) forests. Forests in South Korea also acted as a C sink, contributing 9.4% of the total regions sink because of increased forest growth (98.6%). Compared to these countries, the reduction in forest land in both North Korea and Mongolia caused a C loss at an average rate of 9.0 Tg C yr(-1), equal to 13.4% of the total regions C sink. Over the last four decades, the biomass C sequestration by East Asias forests offset 5.8% of its contemporary fossil-fuel CO2 emissions.

Experimental warming studies on tree species and forest ecosystems: a literature review

Temperature affects a cascade of ecological processes and functions of forests. With future higher global temperatures being inevitable it is critical to understand and predict how forest ecosystems and tree species will respond. This paper reviews experimental warming studies in boreal and temperate forests or tree species beyond the direct effects of higher temperature on plant ecophysiology by scaling up to forest level responses and considering the indirect effects of higher temperature. In direct response to higher temperature (1) leaves emerged earlier and senesced later, resulting in a longer growing season (2) the abundance of herbivorous insects increased and their performance was enhanced and (3) soil nitrogen mineralization and leaf litter decomposition were accelerated. Besides these generalizations across species, plant ecophysiological traits were highly species-specific. Moreover, we showed that the effect of temperature on photosynthesis is strongly dependent on the position of the leaf or plant within the forest (canopy or understory) and the time of the year. Indirect effects of higher temperature included among others higher carbon storage in trees due to increased soil nitrogen availability and changes in insect performance due to alterations in plant ecophysiological traits. Unfortunately only a few studies extrapolated results to forest ecosystem level and considered the indirect effects of higher temperature. Thus more intensive, long-term studies are needed to further confirm the emerging trends shown in this review. Experimental warming studies provide us with a useful tool to examine the cascade of ecological processes in forest ecosystems that will change with future higher temperature.

HydroKorea and CarboKorea: cross-scale studies of ecohydrology and biogeochemistry in a heterogeneous and complex forest catchment of Korea

The KoFlux program is dedicated to understanding the fluxes of energy and matter, water resource management, and net ecosystem production in key ecosystems of Monsoon Asia. Under the framework of AsiaFlux, it is a joint effort with determined, comprehensive international strategies to bring Asia’s key ecosystems under observation. Built upon the augmented KoFlux infrastructure (i.e., Gwangneung supersite), the ‘HydroKorea’ and ‘CarboKorea’ projects pursue new methodologies to assess water and carbon cycles at various temporal, spatial, and process scales. Particularly, the multiscaling approaches are used to link process-level studies, flux footprint, ecohydrological and biogeochemical schemes, and high-resolution satellite images. We hope that the work presented here encourages more ground-breaking studies aimed at bridging the gaps in the cross-scale studies of ecohydrological and biogeochemical cycles in heterogeneous and complex landscapes.

High concentrations of single-walled carbon nanotubes lower soil enzyme activity and microbial biomass

Nanomaterials such as single-walled carbon nanotubes (SWCNTs) may enter the soil environment with unknown consequences resulting from the development of nanotechnology for a variety of applications. We determined the effects of SWCNTs on soil enzyme activity and microbial biomass through a 3-week incubation of urban soils treated with different concentrations of SWCNTs ranging from 0 to 1000 μg g(-1) soil. The activities of cellobiohydrolase, β-1,4-glucosidase, β-1,4-xylosidase, β-1,4-N-acetylglucosaminidase, L-leucine aminopeptidase, and acid phosphatase and microbial biomass were measured in soils treated with powder and suspended forms of SWCNTs. SWCNTs of concentrations at 300-1000 μg g(-1) soil significantly lowered activities of most enzymes and microbial biomass. It is noteworthy that the SWCNTs showed similar effects to that of multi-walled carbon nanotubes (MWCNTs), but at a concentration approximately 5 times lower; we suggest that this is mainly due to the higher surface area of SWCNTs than that of MWCNTs. Indeed, our results show that surface area of CNTs has significant negative relationship with relative enzyme activity and biomass, which suggests that greater microorganism-CNT interactions could increase the negative effect of CNTs on microorganisms. Current work may contribute to the preparation of a regulatory guideline for the release of CNTs to the soil environment.

Allometry and biomass of Korean pine (Pinus koraiensis) in central Korea.

Aboveground tree biomass of Korean pine (Pinus koraiensis Sieb. et Zucc.) was determined for a natural forest of Korean pine and mixed deciduous trees and seven age classes of plantation forests in central Korea. Regression analyses of the dry weights of stem wood, stem bark, branches, and needles versus diameter at breast height were used to calculate regression equations of the form of log Y = a + b log X. Biomass of Korean pine in the mixed forest was 118 Mg ha(-1), and biomass in the plantations was linearly related to stand age, ranging from 52.3 Mg ha(-1) in 11 to 20-year-old stands to 317.9 Mg ha(-1) in 71 to 80-year-old stands. The proportions of stem wood and stem bark in the total aboveground biomass decreased with stand age while those of branch and needle increased. Specific leaf area of Korean pine ranging from 35.2 to 52.1 cm2 g(-1) was significantly different among crown positions and needle ages; in general, lower crown position and current needles had the greatest surface area per unit dry weight.

Non-symbiotic nitrogen fixation in forest ecosystems

Since the first attempts to increase forest growth using nitrogen (N) fixation, biological N fixation has been intensively studied. Numerous studies that focused on symbiotic N fixation and rates were well quantified. However, the rates and importance of non-symbiotic N fixation in forest ecosystems remains incomplete. In this review, reports of non-symbiotic N fixation from various studies throughout the world were examined and the ecological significance of non-symbiotic N fixation in temperate forest ecosystems was investigated. The reported rates of non-symbiotic N fixation varied greatly, and ranged from < 0.01–5 kg N ha-1 year-1. However, an average input of 2–3 kg N ha-1 year-1 could be expected when all ecosystem components were included. In several studies, non-symbiotic N fixation seemed to decrease with stand age. Some methodological considerations such as incubation time and conversion factor in the acetylene reduction method were presented. Also, it should be noted that more detailed studies on non-symbiotic N fixation in boreal and tropical forests are needed to understand the importance of N fixation in these forest ecosystems.

Soil carbon dioxide evolution, litter decomposition, and nitrogen availability four years after thinning in a Japanese larch plantation

Abstract Soil carbon dioxide (CO2) evolution, litter decomposition, and nitrogen availability was measured four years after thinning in a 19-year-old Japanese larch (Larix leptolepis Gord.) plantation of central Korea. Four different thinning intensities [control (C), 10% (T10), 20% (T20), and 40% (T40)] were applied. There were significant differences in seasonal mean soil temperature, moisture, and CO2 evolution among the thinning intensities. Annual soil CO2 evolution (Mg CO2 ha−1) was 29.8 for C, 27.0 for T10, 24.2 for T20, and 23.8 for T40, respectively, and decreased with the thinning intensity. High soil CO2 evolution in the control and light thinning plots might be related to root respiration from high stand densities. After decomposing for four years, 30 and 23%, 30 and 27%, 21 and 10%, and 28 and 30% of the original needle litter dry mass and nitrogen mass remained for control, T10, T20, and T40, respectively. However, there were no significant trends with the thinning intensity. Needle litter acted as a net source for nitrogen during its 4th year of decomposition in this site. Thinning did not increase or decrease , , or total inorganic nitrogen concentrations, measured using the ion exchange resin bag method. Growing season sum resin inorganic nitrogen concentration (mg N bag−1) was 8.7 for C, 9.6 for T10, 8.6 for T20, and 9.2 for T40, respectively.

Biomass, production and nutrient distribution of a natural oak forest in central Korea

Biomass, production, and nutrient distribution of a pure Quercus variabilis Bl. stand (stand 1) and two mixed Q. variabilis–Q. mongolica Fisch. stands (stand 2 and 3) were investigated in central Korea. Stand 1 naturally occurred on a site with a southern aspect while stand 2 and stand 3 occurred on sites with a northern aspect. Total (overstory + understory vegetation) biomass (t ha-1) and annual production (t ha–1 year–1) were 137.8 and 11.1 for stand 1, 216.2 and 16.6 for stand 2, and 253.3 and 19.7 for stand 3. Nutrient contents (kg ha–1) in the vegetation were distributed as follows: K, 478–860; N, 471–839; Ca, 428–791; Mg, 72–125; Na, 77–141; and P, 37–71, and were greatest in stand 3 followed by stand 2, and stand 1. Stand density influenced the differences in biomass, annual production and nutrient contents in the vegetation. Forest floor dry mass and N content (kg ha–1) were 13 400 and 169 for stand 1, 10 400 and 133 for stand 2, and 11 200 and 127 for stand 3. Total amounts of N, P and Na in the ecosystem were greatest in the upper 40 cm of mineral soil followed by the vegetation and forest floor. However, the vegetation contained a greater amount of K than the mineral soil. It appeared that microenvironments, such as, aspect influenced the distribution of natural oak species within a relatively small area and resulted in differences in biomass, production and nutrient distribution among the stands.

Fine root biomass, production and turnover in a fertilized Larix leptolepis plantation in central Korea

The effects of fertilization [control (C), 200 kg N ha−1 + 25 kg P ha−1 (LNP) and 400 kg N ha−1 + 50 kg P ha−1 (HNP)] on fine root dynamics were examined in a 40-year-old Larix leptolepis plantation in central Korea. The average fine root biomass during the growing season for C, LNP and HNP was 957, 934 and 814 kg ha−1, respectively, whereas the fine root production for C, LNP and HNP was 2103, 2131 and 2066 kg ha−1, respectively. Nitrogen and P inputs into the soil via fine root turnover for C, LNP and HNP were 23.0 and 1.2, 23.3 and 1.2 and 22.6 and 1.2 kg ha−1, respectively. There were no significant differences in fine root biomass, production and N and P inputs through fine root turnover between the fertilization treatments during the first growing season after fertilization.