Soil respiration (Rs) consists of autotrophic (Ra) and heterotrophic (Rh) respiration, and the metabolic responses of Ra and Rh are supposedly affected by environmental factors. Our hypothesis was that the contribution of Ra and Rh would be affected by seasons. To characterize seasonal patterns of Rs, sap flow (as an indicator of photosynthetic activity), and environmental factors, we continuously measured temporal variation in Rs using an automated opening and closing chamber system in a cool temperate forest. Rs had counterclockwise hysteresis (Rs: spring < autumn) with soil temperature at a depth of 5 cm. Daily maximum Rs had a significant positive relationship with daily maximum sap flow over three seasons, and daily maximum sap flow was lower in autumn than in spring (Ra: spring > autumn). The amount of leaf litterfall increased significantly from August to October; the high Rs in autumn would be due to an increase in Rh (Rh: spring < autumn). These results suggest that Ra contributes more in spring than in autumn, and the contribution of Rh is high from summer through autumn.

Soil respiration is one of the largest carbon fluxes from terrestrial ecosystems. Estimating global soil respiration is difficult because of its high spatiotemporal variability and sensitivity to land-use change. Satellite monitoring provides useful data for estimating the global carbon budget, but few studies have estimated global soil respiration using satellite data. We provide preliminary insights into the estimation of global soil respiration in 2001 and 2009 using empirically derived soil temperature equations for 17 ecosystems obtained by field studies, as well as. MODIS climate data and land-use maps at a 4-km resolution. The daytime surface temperature from winter to early summer based on the MODIS data tended to be higher than the field-observed soil temperatures in subarctic and temperate ecosystems. The estimated global soil respiration was 94.8 and 93.8 Pg C yr(-1) in 2001 and 2009, respectively. However, the MODIS land-use maps had insufficient spatial resolution to evaluate the effect of land-use change on soil respiration. The spatial variation of soil respiration (Q(10)) values was higher but its spatial variation was lower in high-latitude areas than in other areas. However, Q(10) in tropical areas was more variable and was not accurately estimated (the values were >7.5 or <1.0) because of the low seasonal variation in soil respiration in tropical ecosystems. To solve these problems, it will be necessary to validate our results using a combination of remote sensing data at higher spatial resolution and field observations for many different ecosystems, and it will be necessary to account for the effects of more soil factors in the predictive equations. (C) 2017 Elsevier Ltd. All rights reserved.

Many terrestrial plants are C3 plants that evolved in the Mesozoic Era when atmospheric CO2 concentrations ([CO2]) were high. Given current conditions, C3 plants can no longer benefit from high ambient [CO2]. Kaempferia marginata Carey is a unique understory ginger plant in the tropical dry forests of Thailand. The plant has two large flat leaves that spread on the soil surface. We found a large difference in [CO2] between the partly closed space between the soil surface and the leaves (638 µmol mol−1) and the atmosphere at 20 cm above ground level (412 µmol mol−1). This finding indicates that the plants capture CO2 efflux from the soil. Almost all of the stomata are located on the abaxial leaf surface. When ambient air [CO2] was experimentally increased from 400 to 600 μmol mol−1, net photosynthetic rates increased by 45 to 48% under near light-saturated conditions. No significant increase was observed under low light conditions. These data demonstrate that the unique leaf structure enhances carbon gain by trapping soil CO2 efflux at stomatal sites under relatively high light conditions, suggesting that ambient air [CO2] can serve as an important selective agent for terrestrial C3 plants.

The authors have been conducting long-term continuous observation of fluxes, i.e. exchange of CO2, light, heat, water and so on, between the forest ecosystems and the atmosphere, and other relevant meteorological parameters at the towers in the mixed deciduous forest (MDF) in Mae Klong watershed research station and the dry evergreen forest (DEF) in Sakaerat Environmental Research Station. The towers are known as “MKL and SKR flux tower sites" among international flux monitoring communities such as AsiaFlux Network, and are also known as ones of the oldest CO2 flux monitoring towers in Thailand, located in a typical Southeast Asian tropical seasonal forests. Flux and meteorology monitoring at the MKL and SKR towers At each of the two towers, more than 50 meteorological and relevant items are measured and recorded every 10-30 minutes. The overview of the long-term continuous monitoring, such as monitored items, instrumentation, and some results obtained in the previous period of the monitoring, is introduced. We are currently attempting automation of data acquisition, processing and compilation in a database by making the tower and instruments online and accessible from the server computer located in AIST Tsukuba, to improve the continuousness of the measurement and the maintenance efficiency, for further long-term monitoring. Phenology monitoring using daily fixed-view photographs of forest canopies As one of the topics of the monitoring at the towers, the phenology monitoring by taking daily fixed-view photographs looking down the forest canopies and automatic discrimination of phenological events by numerical analysis of seasonal patterns of daily “RGB normalized intensities”, monochromatic intensities of respective channels of RGB, normalized by the panchromatic intensity over the field of interest in the image, is introduced (Maeda, Gamo and AIST, 2004, patented in Japan). The method was developed in the Takayama TKY flux tower where AIST group has been operating the flux monitoring since 1993. We have applied the method also to the MKL and SKR towers. The photos have been taken by the originally-developed automated fixed-view camera system, installed on the MKL and SKR towers since 2006. Some results of the image analyses that indicate the characteristics of the two forest types are presented.

To enable prediction of future rice production in a changing climate, we need to understand the interactive effects of temperature and elevated [CO2] (E[CO2]). We therefore examined if the effect of E[CO2] on the light-saturated leaf photosynthetic rate (Asat) was affected by soil and water temperature (NT, normal; ET, elevated) under open-field conditions at the rice free-air CO2 enrichment (FACE) facility in Shizukuishi, Japan, in 2007 and 2008. Season-long E[CO2] (+200 µmol mol−1) increased Asat by 26%, when averaged over two years, temperature regimes and growth stages. The effect of ET (+2°C) on Asat was not significant at active tillering and heading, but became negative and significant at mid-grain filling; Asat in E[CO2]–ET was higher than in ambient [CO2] (A[CO2])–NT by only 4%. Photosynthetic down-regulation at E[CO2] also became apparent at mid-grain filling; Asat compared at the same [CO2] in the leaf cuvette was significantly lower in plants grown in E[CO2] than in those grown in A[CO2]. The additive effects of E[CO2] and ET decreased Asat by 23% compared with that of A[CO2]–NT plants. Although total crop nitrogen (N) uptake was increased by ET, N allocation to the leaves and to Rubisco was reduced under ET and E[CO2] at mid-grain filling, which resulted in a significant decrease (32%) in the maximum rate of ribulose-1,5-bisphosphate carboxylation on a leaf area basis. Because the change in N allocation was associated with the accelerated phenology in E[CO2]–ET plants, we conclude that soil and water warming accelerates photosynthetic down-regulation at E[CO2].

Understory plants in tropical forests often experience a low-light environment combined with high CO2 concentration. We hypothesized that the high CO2 concentration may compensate for leaf carbon loss caused by the low light, through increasing light-use efficiency of both steady-state and dynamic photosynthetic properties. To test the hypothesis, we examined CO2 gas exchange in response to an artificial lightfleck in Dipterocarpus sublamellatus Foxw. seedlings under contrasting CO2 conditions: 350 and 700 μmol CO2 mol(-1) air in a tropical rain forest, Pasoh, Malaysia. Total photosynthetic carbon gain from the lightfleck was about double when subjected to the high CO2 when compared with the low CO2 concentration. The increase of light-use efficiency in dynamic photosynthesis contributed 7% of the increased carbon gain, most of which was due to reduction of photosynthetic induction to light increase under the high CO2. The light compensation point of photosynthesis decreased by 58% and the apparent quantum yield increased by 26% at the high CO2 compared with those at the low CO2. The study suggests that high CO2 increases photosynthetic light-use efficiency under both steady-state and fluctuating light conditions, which should be considered in assessing the leaf carbon gain of understory plants in low-light environments.

In tropical dry forests, uppermost-canopy leaves of evergreen trees possess the ability to use water more conservatively compared with drought-deciduous trees, which may result from significant differences in the photoprotective mechanisms between functional types. We examined the seasonal variations in leaf gas exchange, chlorophyll fluorescence and the amounts of photosynthetic pigments within lamina of the uppermost-canopy leaves of three drought-deciduous trees (Vitex peduncularis Wall., Xylia xylocarpa (Roxb.) W. Theob., Shorea siamensis Miq.), a semi-deciduous tree (Irvingia malayana Miq.) and two evergreen trees (Hopea ferrea Lanessan and Syzygium cumini (L.) Skeels) in Thailand. Area-based maximum carbon assimilation rates (Amax) decreased during the dry season, except in S. siamensis. The electron transport rate (ETR) remained unchanged in deciduous trees, but decreased during the dry season in evergreen and semi-deciduous trees. In the principal component analysis, the first axis (Axis 1) accounted for 44.3% of the total variation and distinguished deciduous from evergreen trees. Along Axis 1, evergreen trees were characterized by a high Stern-Volmer non-photochemical quenching coefficient (NPQ), high xanthophyll cycle pigments/chlorophyll and a high de-epoxidation state of the xanthophyll cycle, whereas the deciduous trees were characterized by a high ETR, a high quantum yield of PSII (ΦPSII = (Fm(') -F)/Fm(')) and a high mass-based Amax under high-light conditions. These findings indicate that drought-deciduous trees showing less conservative water use tend to dissipate a large proportion of electron flow through photosynthesis or alternative pathways. In contrast, the evergreens showed more conservative water use, reduced Amax and ETR and enhanced NPQ and xanthophyll cycle pigments/chlorophyll during the dry season, indicating that down-regulated photosynthesis with enhanced thermal dissipation of excess light energy played an important role in photoprotection. Trees with different water uses and leaf lifespans appear to employ different photoprotective mechanisms to overcome the unfavorable dry-season drought. Our data may suggest that future changes in precipitation will strongly impinge on forest structure and functions.

Soil respiration rate in two types of grassland dominated with Zoysia japonica and Miscanthus sinensis, respectively, and under two management practices (undisturbed and intentionally burned) for the M. sinensis grassland was investigated for understanding the effects of grassland vegetation type and management practices on the relationship between soil temperature and soil respiration in northern Japan. Soil temperatures at depth of 1 cm in the Z. japonica (ZJ) and burned M. sinensis (MSb) plots had a larger temporal variation than that in the control M. sinensis (MSc) plot prior to early July. However, the coefficient of temperature sensitivity () values, based on soil respiration rates and soil temperatures at 5 cm depth in the ZJ and MSb plots, were 1.3 and 2.9. These rates were lower than that in the MSc plot (4.3), meaning that soil respiration showed lower activity to an increase in soil temperature in the ZJ and MSb plots. In addition, monthly carbon fluxes from soil in these plots were smaller than that in the MSc plot. These results suggested that artificial disturbance would decrease soil microbial or/and plant root respiration, and it would contribute to the plant productivity. Future studies should examine the effects of the intensity and period of management on the soil respiration rate.

We attempted to determine the contribution of entrapped gas bubbles to the soil methane (CH4) pool and their role in CH4 emissions in rice paddies open to the atmosphere.

The simulation results may be valuable information for those, who examine the impact of land-use changes particularly in Malaysia, where forests have rapidly changed into oil palm plantations since 1990’s. The reviewer, however, thinks that the interpretation is still inadequate throughout, and that they should understand the impact of both input data and the procedures of calculation on model output thoroughly. Then their comments will be more appropriate in Results and Discussion. Also, please explain the model outline with a new figure and show the design of numerical simulations accurately in Materials and Methods. Therefore, the manuscript needs much-revise.

Quantification of rhizodeposition (root exudates and root turnover) represents a major challenge for understanding the links between above-ground assimilation and below-ground anoxic decomposition of organic carbon in rice paddy ecosystems. Free-air CO2 enrichment (FACE) fumigating depleted (CO2)-C-13 in rice paddy resulted in a smaller C-13/C-12 ratio in plant-assimilated carbon, providing a unique measure by which we partitioned the sources of decomposed gases (CO2 and CH4) into current-season photosynthates (new C) and soil organic matter (old C). In addition, we imposed a soil-warming treatment nested within the CO2 treatments to assess whether the carbon source was sensitive to warming. Compared with the ambient CO2 treatment, the FACE treatment decreased the C-13/C-12 ratio not only in the rice-plant carbon but also in the soil CO2 and CH4. The estimated new C contribution to dissolved CO2 was minor (ca. 20%) at the tillering stage, increased with rice growth and was about 50% from the panicle-formation stage onwards. For CH4, the contribution of new C was greater than for heterotrophic CO2 production; ca. 40-60% of season-total CH4 production originated from new C with a tendency toward even larger new C contribution with soil warming, presumably because enhanced root decay provided substrates for greater CH4 production. The results suggest a fast and close coupling between photosynthesis and anoxic decomposition in soil, and further indicate a positive feedback of global warming by enhanced CH4 emission through greater rhizodeposition.

Abstract:Spatial and seasonal variation in soil respiration rates were investigated in a tropical dry forest in Thailand. The spatial variation was examined at 50 points within a 2-ha plot in the forest floor during the dry and wet seasons. The seasonal and diurnal variations in soil respiration were measured at 16 and 5 points, respectively. The mean soil respiration rate during the wet season was 1041 ± 542 mg CO2 m−2 h−1 (mean ± SD), which is about twice that during the dry season. Soil respiration rate was negatively correlated with soil water content during the wet season. A polynomial equation using seasonal data describes soil respiration and water content: soil respiration rate increased with soil water content, but started to drop when soil water content exceeded 21%. The diurnal variation in soil respiration rate during the wet season was positively correlated with soil temperature, whereas during the wet season it was not correlated with soil temperature. The diurnal variation in soil respiration rate during the dry season showed a midday depression. The estimation of soil carbon flux with polynomial equations should incorporate different functions for the wet and dry seasons in tropical dry forests.

The functional surface of porcelain crowns are ground with diamond burs during occlusal adjustment in dental field. This procedure results in the introduction of surface and subsurface flaws(brittle-mode grinding), and can be accompanied by reduction in strength and fatigue lifetime. Recently, it was demonstrated that brittle ceramics can be ground without subsurface flaws(ductile-mode grinding). The aim of this study was to predict the ductile-brittle transition conditions in grinding of a dental porcelain material. By modeling the grinding process of an abrasive particle as an indentation of a spherical indenter, the elastic-plastic stress field under the indentation was calculated using Hill’s spherical cavity expansion solution. The ductile-brittle transition conditions were predicted by comparing the fracture toughness of the material to the stress intensity factors of penny-shaped pre-existing cracks under the stress field, and represented by a critical radius of the spherical indenter. The calculations showed that the critical radius in grinding of the porcelain material is deduced to be 2.0 microns. By modeling the grinding process by an abrasive particle as a Vickers indentation, a critical depth of cut is deduced to be 1.3 microns. It was concluded that the dental porcelain can be ground 歯科用陶材の研削における延性/脆性遷移条件 若 松 宣 一 ・ 大 元 秀 一 ・ 土 井 豊 朝日大学・歯学部・数学 朝日大学・歯学部・口腔機能修復学講座・歯科理工学分野 Ductile/Brittle Transition Conditions in Grinding of Dental Porcelain Nobukazu WAKAMATSU 1,2 , Shuuichi OOMOTO 2 and Yutaka DOI 2 Mathematics, Asahi University School of Dentistry 1 Department of Dental Materials Science, Division of Oral Functional Science and Rehabilitation, Asahi University School of Dentistry 2 朝日大学一般教育紀要 37, 67-74,2011 67 without subsurface cracks(ductile-mode grinding)by controlling either the radius of abrasive particles or the depth of cut.

Quantification of rhizodeposition (root exudates and root turnover) represents a major challenge for understanding the links between above-ground assimilation and below-ground anoxic decomposition of organic carbon in rice paddy ecosystems. Free-air CO enrichment (FACE) fumigating depleted CO in rice paddy resulted in a smaller C/ C ratio in plant-assimilated carbon, providing a unique measure by which we partitioned the sources of decomposed gases (CO and CH ) into current-season photosynthates (new C) and soil organic matter (old C). In addition, we imposed a soil-warming treatment nested within the CO treatments to assess whether the carbon source was sensitive to warming. Compared with the ambient CO treatment, the FACE treatment decreased the C/ C ratio not only in the rice-plant carbon but also in the soil CO and CH . The estimated new C contribution to dissolved CO was minor (ca. 20%) at the tillering stage, increased with rice growth and was about 50% from the panicle-formation stage onwards. For CH , the contribution of new C was greater than for heterotrophic CO production; ca. 40–60% of season-total CH production originated from new C with a tendency toward even larger new C contribution with soil warming, presumably because enhanced root decay provided substrates for greater CH production. The results suggest a fast and close coupling between photosynthesis and anoxic decomposition in soil, and further indicate a positive feedback of global warming by enhanced CH emission through greater rhizodeposition.