Effects of elevated CO_2 concentration and nitrogen supply on biomass and active carbon of freshwater marsh after two growing seasons in Sanjiang Plain, Northeast China

An experiments were carried out with treatments differing in nitrogen supply （0, 5 and 15 g N/m^2） and CO2 levels （350 and 700 μmol/mol） using OTC （open top chamber） equipment to investigate the biomass of Calamagrostis angustifolia and soil active carbon contents after two years. The results showed that elevated CO2 concentration increased the biomass of C. angustifolia and the magnitude of response varied with each growth period. Elevated CO2 concentration has increased aboveground biomass by 16.7% and 17.6% during the jointing and heading periods and only 3.5% and 9.4% during dough and maturity periods. The increases in belowground biomass due to CO2 elevation was 26.5%, 34.0% and 28.7% during the heading, dough and maturity periods, respectively. The responses of biomass to enhanced CO2 concentrations are differed in N levels. Both the increase of aboveground biomass and belowground biomass were greater under high level of N supply （15 g N/m^2）. Elevated CO2 concentration also increased the allocation of biomass and carbon in root. Under elevated CO2 concentration, the average values of active carbon tended to increase. The increases of soil active soil contents followed the sequence of microbial biomass carbon （10.6%） 〉 dissolved organic carbon （7.5%） 〉 labile oxidable carbon （6.6%） 〉 carbohydrate carbon （4.1%）. Stepwise regressions indicated there were significant correlations between the soil active carbon contents and plant biomass. Particularly, microbial biomass carbon, labile oxidable carbon and carbohydrate carbon were found to be correlated with belowground biomass, while dissolved organic carbon has correlation with aboveground biomass. Therefore, increased biomass was regarded as the main driving force for the increase in soil active organic carbon under elevated CO2 concentration.

Soil and Root Respiration Under Elevated CO_2 Concentrations During Seedling Growth of Pinus sylvestris var.sylvestriformis

The objectives of this study were to investigate the effect of higher CO2 concentrations （500 and 700 μmol mol^-1） in atmosphere on total soil respiration and the contribution of root respiration to total soil respiration during seedling growth of Pinus sylvestris vat. sylvestriformis. During the four growing seasons （May-October） from 1999 to 2003, the seedlings were exposed to elevated concentrations of CO2 in open-top chambers. The total soil respiration and contribution of root respiration were measured using an LI-6400-09 soil CO2 flux chamber on June 15 and October 8, 2003. To separate root respiration from total soil respiration, three PVC cylinders were inserted approximately 30 cm deep into the soil in each chamber. There were marked diurnal changes in air and soil temperatures on June 15. Both the total soil respiration and the soil respiration without roots showed a strong diurnal pattern, increasing from before sunrise to about 14：00 in the afternoon and then decreasing before the next sunrise. No increase in the mean total soil respiration and mean soil respiration with roots severed was observed under the elevated CO2 treatments on June 15, 2003, as compared to the open field and control chamber with ambient CO2. However, on October 8, 2003, the total soil respiration and soil respiration with roots severed in the open field were lower than those in the control and elevated CO2 chambers. The mean contribution of root respiration measured on June 15, 2003, ranged from 8.3% to 30.5% and on October 8, 2003, from 20.6% to 48.6%.

Distribution of CO_(2)in Soil Air Affected by Vegetation in the Shilin National Park

This paper studies the CO2 distribution of soil atmosphere in the Shilin National Park. The measurement sites were chosen according to different topographic features and different vegetations. Seven measurement sites on 3 cross sections were chosen to pass through 3 karstic depressions or on the slopes of depressions. All measurement results show soils with pH values lower than 7.0 (from 5.4 to 6.6). There are 2 cases for the pH values of soil in different topographic features: the pH values of 2 profiles on the ridges or upper slopes of depressions are lower than those in the depressions; and the pH values of 2 soil profiles on the slopes of depressions are higher than those in the depressions. Most samples show relatively low humidity and CO2 contents on the ridges or slopes of depressions compared with soil profiles in the depressions. High CO2 contents occur at depths from ?40 to ?80 cm and high and dense grassland shows high CO2 contents in the soil atmosphere. Grass roots may grow and are distributed mainly at depths from ?20 to ?40 cm; while tree roots predominantly as deep as ?60 cm even ?80 cm. The influences of pine, cypress and eucalyptus on soil CO2 have been studied. Soil CO2 influenced by pine and cypress are generally concentrated in an area surrounding the tree with a diameter of 1 m and the strongly influenced distance is 50 cm. Eucalyptus will strongly affect the CO2 contents in an area with a diameter of 2 m, especially 1 m distant from the tree. The highest concentration of soil CO2 at a depth of ?30 and 100 cm from the tree reaches 92000 ppm.

Impact of elevated CO_2 concentration under three soil water levels on growth of Cinnamomum camphora

Forest plays very important roles in global system with about 35% land area producing about 70% of total land net production. It is important to consider both elevated CO2 concentrations and different soil moisture when the possible effects of elevated CO2 concentration on trees are assessed. In this study, we grew Cinnamomum camphora seedlings under two CO2 concentrations （350 μmol/mol and 500μmnol/mol） and three soil moisture levels [80%, 60% and 40% FWC （field water capacity）] to focus on the effects of exposure of trees to elevated CO2 on underground and aboveground plant growth, and its dependence on soil moisture. The results indicated that high CO2 concentration has no significant effects on shoot height but significantly impacts shoot weight and ratio of shoot weight to height under three soil moisture levels. The response of root growth to CO2 enrichment is just reversed, there are obvious effects on root length growth, but no effects on root weight growth and ratio of root weight to length. The CO2 enrichment decreased 20.42%, 32.78%, 20.59% of weight ratio of root to shoot under 40%, 60% and 80% FWC soil water conditions, respectively. And elevated CO2 concentration significantly increased the water content in aboveground and underground parts. Then we concluded that high CO2 concentration favours more tree aboveground biomass growth than underground biomass growth under favorable soil water conditions. And CO2 enrichment enhanced lateral growth of shoot and vertical growth of root. The responses of plants to elevated CO2 depend on soil water availability, and plants may benefit more from CO2 enrichment with sufficient water supply.

Soil-vegetation-atmosphere interaction over a hilly forest in the southern Huaihe River Basin:Long-term field experiment and preliminary analysis of basic observations

To improve the understanding of the CO_(2) exchange and the cycling of energy and water between the land surface and atmosphere over a typical hilly forest in southeastern China,a long-term field experimental observatory was established in Huainan,Anhui Province.Here,the authors briefly describe the three parts of ongoing research activities:the environmental monitoring at the site,the meteorological observations on a high tower,and particularly the intensive measurement of soil-vegetation-atmosphere interaction on a lower tower.Specifically,the diurnal variation of basic meteorological variables on a typical clear day(13 July 2018),and their temporal variation in the first three months of the low tower’s operation(4 June to 31 August 2018),and in combination with simultaneous data from the high tower,are analyzed.Results show that the data demonstrate reasonable variabilities,and the variables exhibit significant diurnal variation,characteristics of summer values,and considerable differences in summer months.The daily and monthly average albedos above the forest canopy were both 0.13.The daily average soil CO_(2) concentration was 1726 and 4481 ppm at 2 and 10 cm,respectively.The soil CO_(2) concentration changed with soil volumetric moisture contents,but showed a weak correlation with soil temperature in summer 2018.As the observatory continues to run and data continue to be collated,further investigation of the long-term variation of monsoon characteristics should be performed in the future.The experiment is useful in ecosystem and atmosphere interaction research,as well as for the development and evaluation of climate models,in the transitional climate zone of the Huaihe River basin.

Effects of the Adjustment of Energy Structure on 24-h Average of NO_2 Concentration in Different Regions of Urumqi City in Winter

[ Objective] The study aimed to discuss the effects of the adjustment of energy structure on daily average concentration of NO2 in different regions of Urumqi city in winter. [ Method] The changes of daily average concentration of NO2 in different areas of Urumqi City from January to February （ NO2 pollution was most serious） before and after the implementation of the project ＂changing coal to gas＂ were analyzed. [ Result] After the implementation of the project, daily average concentration of NO2 in different areas of Urumqi City was increased due to the rapid increase of ve- hicle quantity, but there were certain differences in the increase among various regions. From south to north, daily average concentration of NO2 in winter was decreased gradually, that is, daily average concentration of NO2 was the highest in the south area, while in the north area, it didn＇t change significantly before and after the implementation of the project, but it was still high. Therefore, the local government should pay more attention to pollution NO2 during environmental management process. [ Conclusion] The research could provide scientific references for the control of atmospheric pollution in future.

Spatio-temporal variation of soil CO_(2) concentration in Loess Area of northwestern Shanxi Province,China

CO_(2) released by soil serves as an important link between terrestrial ecosystems and atmospheric CO_(2), whose small chang‐es may significantly affect the global carbon cycle. In order to reveal the spatio-temporal variations of CO_(2) concentrations in deep loess, this paper takes Qingliangsi Gully watershed in northwestern Shanxi Province, China as an example to sys‐tematically study soil CO_(2)concentration and its spatio-temporal variations and carbon sink significance under different watershed locations and different land use types. Results show that: (1) The release potential of the loess soil is larger in the depth range of 2 m, which is much more likely to be the CO_(2) release area. (2) Grassland and forest are more advanta‐geous in terms of soil microbial activity and soil carbon reserve compared with farmland. In addition, the change of land use type from farmland to grassland can increase soil organic carbon reserve, which is of far-reaching significance to the global carbon cycle. This is especially true in an area like the Loess Plateau with densely covered hills, gullies, and serious soil erosion in an area of 64×104 km2. (3) In the study area, the diurnal concentration of soil CO_(2) at different depths shows a weak "high-low-high-low" trend from 08:00 to 07:00 next day;and in deep soil it has a lag time compared with the daily change of temperature, generally about 4−12 h, which may be caused largely by the more compact loess structure. It is worth pointing out that the Loess Plateau in China, with a thickness of the loess of tens to hundreds of meters, has the most abundant soil resources in the world, and also stores a large amount of terrestrial soil carbon, which carries the hope of promoting the research of global carbon cycle.

Responses of soil enzymes to long-term CO_2 enrichment in forest ecosystems of Changbai Mountains

A study was conducted to determine the responses of soil enzymes （invertase, polyphenol oxidase, catalase, and dehydrogenase） to long-term CO2 enrichment at the Research Station of Changbai Mountain Forest Ecosystems, Chinese Academy of Sciences （42°24＇N, 128°28＇E; 738 m in elevation） in the northeast China during 1999-2006. Three treatments of the CO2 enrichment, designed as 500 μmol·mol-1 CO2 open-top chamber （OTC）, ambient control chamber and unchambered field （approx. 370 μmol·mol^-1CO2）, were conducted with Pinus koraiensis and Pinus sylvestriformis tree species. Soil sampling was made and analyzed separately in spring, summer and autumn in 2006 after the soil enzymes were exposed to elevated CO2 concentration （500 μmol·mol^-1） for eight growing seasons. Results showed that, at elevated CO2 concentration （500 μmol·mol^-1）, the activities of invertase （except for the summer samples of P. koraiensis） presented a remarkable decline in all growing seasons, while the activities of dehydrogenase had an increase but only part of the results was remarkable; the activities of polyphenol oxidase in P. sylvestriformis rhizosphere showed a remarkable decrease; the catalase activities increased in spring, while in turn were decline in other seasons. This study also revealed that the soil enzyme activities are significantly correlated with the tree species under the CO2 enhancement.

Effects of elevated atmospheric CO2 and nitrogen fertilization on nitrogen cycling in experimental riparian wetlands

Studies on the relationship between plant nitrogen content and soil nitrogen reduction under elevated CO2 conditions and with different nitrogen additions in wetland ecosystems are lacking. This study was meant to assess the effects of elevated CO2 concentrations and inorganic nitrogen additions on soil and plant nitrogen cycling. A cultured riparian wetland, alligator weeds, and two duplicated open top chambers （OTCs） with ambient （380μmol/mol） and elevated （700 μmol/mol） CO2 concentrations at low （4 mg/L） and high （6 mg/L） nitrogen fertilization levels were used. The total plant biomass increased by 30.77% and 31.37% at low and high nitrogen fertilization levels, respectively, under elevated CO2 conditions. Plant nitrogen content decreased by 6.54% and 8.86% at low and high nitrogen fertilization levels, respectively. The coefficient of determination （R2） of soil nitrogen contents ranged from 0.81 to 0.96. Under elevated CO2 conditions, plants utilized the assimilated inorganic nitrogen （from the soil） for growth and other internal physiological transformations, which might explain the reduction in plant nitrogen content. A reduction in soil dissolved inorganic nitrogen （DIN） under elevated CO2 conditions might have also caused the reduction in plant nitrogen content. Reduced plant and soil nitrogen contents are to be expected due to the potential exhaustive use of inorganic nitrogen by soil microorganisms even before it can be made available to the soil and plants. The results from this study provide important information to help policy makers make informed decisions on sustainable management of wetlands. Larger-scale field work is recommended in future research.

THE IMPACTS OF GLOBAL CHANGE ON DESERTIFICATION IN CHINA

Global change and desertification are the serious environmental problems in the world today and exert great impacts on human existence and social development. Therefore, the United Nations has set up quite a number of relevant organizations to encourage millions upon millions of people to combat this harmful problem. At the same time, since the 1992 UN Conference on Environment and Development (UNCED) in Rio de Janeiro, the UN Convention to Combat Desertification has been signed and this signment of the Convention will powerfully promote the concrete action programs to combat desertification of each affected country and enlarge the exchange and cooperation among the affected countries. According to recent information of UN Organizations, more than 100 countries and their one-fifth world of population are facing the problem of desertification processes and desertification impacts, and are suffering from expansion of desertification. The total areas of arid, semi-arid and dry sub-humid zones cover approximately about 6.5 billion ha, occupying 41 percent of the total land area of the earth. There are 3.6 billion ha of arable land and grazing land under the impact of desertification in the world. From 1984 to 1991, the annual increase of land desertification is 3.4 percent. The harmful results of desertification on human existence in terms of environment, societies and economy are serious and called for great attention from the UN Systems. It is concluded that desertification is the most serious environmental problem in the world and its resulting impact is socially and economically surprising.

THE CLIMATE CHANGE AND FORESTRY OF HEILONGJIANG PROVINCE IN 1990'S

The background of global climate change was briefly simarized. The comprehensive effects of various factors, including seawater temperature, sunspots' activities, volcanic explosion, CO2 concentration change, O3 concentration change and characteristics of atmospheric circulation index, onthe climate change of Heilongiiang Province were analyzed. The tendency of climate change of Heilongjiang in the next 10 years was predicted according to the data of historical climate collectedtorm passed 100 years and the above analysis. The climate of Heilongjiang Province in the next 10yedrs will be mainly warin and dry. There will be still annual tluctuation. Although the general tendency of climate change accords with global climate change, the regional characteristic is also distinctive. The probable influence of climate change on forestry was put forward and forestry response strategy was elementary discussed.

Soil Respiration in Drying of an Organic Soil

Drying of soil was linearly related to time, soil volume decreased and ratio of air within the soils increased. Respiration was related with decreasing humidity, storage of CO2 in soil water results in RQ < 0.5 in the larger soil items at least for a while. Rate of drying decreased in the second part of the process. RQ increased as the CO2 stored was aerated when its solvent-water evaporated and access of air into the soil increased;eventually RQ = 1.0 in the last days of the experiment. Respiration of the experimental soil stopped when GWC reached 0.15. ΣRQ for the whole process is about 0.7, a bit higher in experiments with less soil suggesting less anoxia.

Laboratory-scale model of carbon dioxide deposition for soilstabilisation

Olivine sand is a natural mineral,which,when added to soil,can improve the soil’s mechanical properties while also sequester carbon dioxide(CO2)from the surrounding environment.The originality of this paper stems from the novel two-stage approach.In the first stage,natural carbonation of olivine and carbonation of olivine treated soil under different CO2pressures and times were investigated.In this stage,the unconfined compression test was used as a tool to evaluate the strength performance.In the second stage,details of the installation and performance of carbonated olivine columns using a laboratory-scale model were investigated.In this respect,olivine was mixed with the natural soil using the auger and the columns were then carbonated with gaseous CO2.The unconfined compressive strengths of soil in the first stage increased by up to 120% compared to those of the natural untreated soil.The strength development was found to be proportional to the CO2pressure and carbonation period.Microstructural analyses indicated the presence of magnesite on the surface of carbonated olivinetreated soil,demonstrating that modified physical properties provided a stronger and stiffer matrix.The performance of the carbonated olivine-soil columns,in terms of ultimate bearing capacity,showed that the carbonation procedure occurred rapidly and yielded a bearing capacity value of 120 k Pa.Results of this study are of significance to the construction industry as the feasibility of carbonated olivine for strengthening and stabilizing soil is validated.Its applicability lies in a range of different geotechnical applications whilst also mitigates the global warming through the sequestration of CO2.

Effect of elevated [CO_2] and nutrient management on wet and dry season rice production in subtropical India

The present experiment was conducted to evaluate the effect of elevated [CO_2] with varying nutrient management on rice–rice production system. The experiment was conducted in the open field and inside open-top chambers(OTCs) of ambient [CO_2](≈ 390 μmol L-1) and elevated [CO_2] environment(25% above ambient) during wet and dry seasons in 2011–2013at Kharagpur, India. The nutrient management included recommended doses of N, P, and K as chemical fertilizer(CF), integration of chemical and organic sources, and application of increased(25% higher) doses of CF. The higher [CO_2] level in the OTC increased aboveground biomass but marginally decreased filled grains per panicle and grain yield of rice, compared to the ambient environment. However, crop root biomass was increased significantly under elevated [CO_2]. With respect to nutrient management, increasing the dose of CF increased grain yield significantly in both seasons. At the recommended dose of nutrients, integrated nutrient management was comparable to CF in the wet season, but significantly inferior in the dry season, in its effect on growth and yield of rice. The [CO_2] elevation in OTC led to a marginal increase in organic C and available P content of soil, but a decrease in available N content. It was concluded that increased doses of nutrients via integration of chemical and organic sources in the wet season and chemical sources alone in the dry season will minimize the adverse effect of future climate on rice production in subtropical India.

Effect on greenhouse gas balance of converting rice paddies to vegetable production

Rice paddies are increasingly being converted to vegetable production due to economic benefits related,in part,to changes in demand during recent decades.Here,we implemented a parallel field experiment to simultaneously measure annual emissions of CH_4and N_2O,and soil organic carbon(SOC)stock changes,in rice paddies(RP),rice paddy–converted conventional vegetable fields(CV),and rice paddy–converted greenhouse vegetable fields(GV).Changing from rice to vegetable production reduced CH_4emissions by nearly 100%,and also triggered substantial N_2O emissions.Furthermore,annual N_2O emissions from GV significantly exceeded those from CV due to lower soil p H and higher soil temperature.Marginal SOC losses occurred after one year of cultivation of RP,CV,and GV,contributing an important share(3.4%,32.2%,and 10.3%,respectively)of the overall global warming potential(GWP)balance.The decline in CH_4emissions outweighed the increased N_2O emissions and SOC losses in CV and GV,leading to a 13%–30%reduction in annual GWP as compared to RP.These results suggest that large-scale expansion of vegetable production at the expense of rice paddies is beneficial for mitigating climate change in terms of the overall GWP.

The Soil Moisture and Net Primary Production Affected by CO_2 and Climate Change Using a Coupled Model

In this paper, a coupled model was used to estimate the responses of soil moisture and net primary production of vegetation(NPP) to increasing atmospheric CO2 concentration and climate change. The analysis uses three experiments simulated by the second-generation Earth System Model(CanESM2) of the Canadian Centre for Climate Modelling and Analysis(CCCma), which are part of the phase 5 of the Coupled Model Intercomparison Project(CMIP5). The authors focus on the magnitude and evolution of responses in soil moisture and NPP using simulations modeled by CanESM, in which the individual effects of increasing CO2 concentration and climate change and their combined effect are separately accounted for. When considering only the single effect of climate change, the soil moisture and NPP have a linear trend of 0.03 kg m–2 yr–1 and –0.14 gC m–2 yr–2, respectively. However, such a reduction in the global NPP results from the decrease of NPP at lower latitudes and in the Southern Hemisphere, although increased NPP has been shown in high northern latitudes. The largest negative trend is located in the Amazon basin at –1.79 gC m–2 yr–2. For the individual effect of increasing CO2 concentration, both soil moisture and NPP show increases, with an elevated linear trend of 0.02 kg m–2 yr–1 and 0.84 gC m–2 yr–2, respectively. Most regions show an increasing NPP, except Alaska. For the combined effect of increasing atmospheric CO2 and climate change, the increased soil moisture and NPP exhibit a linear trend of 0.04 kg m–2 yr–1 and 0.83 gC m–2 yr–2 at a global scale. In the Amazon basin, the higher reduction in soil moisture is illustrated by the model, with a linear trend of –0.39 kg m–2 yr–1, for the combined effect. Such a change in soil moisture is caused by a weakened Walker circulation simulated by this coupled model, compared with the single effect of increasing CO2 concentration(experiment M2), and a consequence of the reduction in NPP is also shown in this area, with a linear trend of-0.16 gC m-2 yr-2.

Bowen Ratio Energy Balance Measurement of Carbon Dioxide (CO₂) Fluxes of No-Till and Conventional Tillage Agriculture in Lesotho

Global food demand requires that soils be used intensively for agriculture, but how these soils are managed greatly impacts soil fluxes of carbon dioxide (CO2). Soil management practices can cause carbon to be either sequestered or emitted, with corresponding uncertain influence on atmospheric CO2 concentrations. The situation is further complicated by the lack of CO2 flux measurements for African subsistence farms. For widespread application in remote areas, a simple experimental methodology is desired. As a first step, the present study investigated the use of Bowen Ratio Energy Balance (BREB) instrumentation to measure the energy balance and CO2 fluxes of two contrasting crop management systems, till and no-till, in the lowlands within the mountains of Lesotho. Two BREB micrometeorological systems were established on 100-m by 100-m sites, both planted with maize (Zea mays) but under either conventional (plow, disk-disk) or no-till soil mangement systems. The results demonstrate that with careful maintenance of the instruments by appropriately trained local personnel, the BREB approach offers substantial benefits in measuring real time changes in agroecosystem CO2 flux. The periods where the two treatments could be compared indicated greater CO2 sequestration over the no-till treatments during both the growing and non-growing seasons.

Soil CO2 Efflux Dynamics and Its Relationship with the Environmental Variables in a Sub-Tropical Mixed Forest

Soil CO2 efflux is an ongoing process of respiration from soil;plant parts/ microbes below the ground to the atmosphere which is known for faster cycling of carbon sources. A large portion of carbon sequestered and fixed by forests is returned to the atmosphere through soil CO2 efflux and multiple controlling parameters mainly temperature, precipitation, and growth factors interact with the soil CO2 efflux variation. This study assessed the soil CO2 efflux every month for consecutive 2-years (August 2015 to July 2017) by using the closed chamber method to determine the role of ecological parameters that govern the soil CO2 efflux and its temporal modification in a sub-tropical mixed forest of central region in Nepal. The results of this study manifested that soil CO2 efflux accounted 63.2% (y = 31.96e0.128x), 71.3% (y = 44.77e0.123x) and 64.5% (y = 44.11e0.117x) variations in soil temperature with significantly (p < 0.05) exponential positive relation in the year 2015/2016, 2016/2017 and the two years when merged. And the temperature sensitivity value (Q10) of the soil CO2 efflux was 3.6, 3.4, and 3.2, respectively. Soil water content also expressed significantly (p < 0.05) positive exponential effect on soil CO2 efflux and accounted 62.0% (y = 138.3e0.057x), 46.1% (y = 88.42e0.052x) and 40.5% (y = 133.1e0.0447x) in its variability in different years and the merged years. Evident variations of soil CO2 efflux, soil temperature, soil water content, and litter were observed in the forest seasonally and inter-annually. Two years mean total annual soil CO2 efflux of the forest was estimated at 904.76 g C·m-2·y-1. The study revealed that sub-tropical forests could be more influenced by precipitation regimes in progressing warm climates i.e. vulnerable to climate change, illustrating the comprehensive dynamics of the representative forest carbon cycle in the tropical region.

Effects of elevated atmospheric CO_2 concentration and temperature on the soil profile methane distribution and diffusion in rice–wheat rotation system

The aim of this experiment was to determine the impacts of climate change on soil profile concentrations and diffusion effluxes of methane in a rice-wheat annual rotation ecosystem in Southeastern China. We initiated a field experiment with four treatments：ambient conditions（CKs）, CO2 concentration elevated to - 500 μmol/mol（FACE）,temperature elevated by ca. 2°C（T） and combined elevation of CO2 concentration and temperature（FACE ＋ T）. A multilevel sampling probe was designed to collect the soil gas at four different depths, namely, 7 cm, 15 cm, 30 cm and 50 cm. Methane concentrations were higher during the rice season and decreased with depth, while lower during the wheat season and increased with depth. Compared to CK, mean methane concentration was increased by 42%, 57% and 71% under the FACE, FACE ＋ T and T treatments, respectively, at the 7 cm depth during the rice season（p 〈 0.05）. Mean methane diffusion effluxes to the 7 cm depth were positive in the rice season and negative in the wheat season, resulting in the paddy field being a source and weak sink, respectively. Moreover, mean methane diffusion effluxes in the rice season were 0.94, 1.19 and 1.42 mg C/（m^2·hr） in the FACE,FACE ＋ T and T treatments, respectively, being clearly higher than that in the CK. The results indicated that elevated atmospheric CO2 concentration and temperature could significantly increase soil profile methane concentrations and their effluxes from a rice-wheat field annual rotation ecosystem（p 〈 0.05）.

The seasonal and daily CO_2 concentration variance in karst meadow soil profile with depth in Central Guizhou, China

THE seasonal variance of soil CO2 concentration with depth in soil profile was widely studied. Few similarresearches on this topic have been done in karst area which comprises 15% global terrestrial area. In thisnote, the research results about the seasonal and daily soil CO2 concentration variance in karst area arereported. The soil gases were collected respectively by the sampling device at 200, 5,0, -5, -10,-15, -25, -35 and -45 cm from the land surface in meadow soil profile described by Zheng andlocated in the Hongfeng lake area in the central Guizhou Plateau which lies in the central East-Asia karstarea. Sampling time is in the morning, midday and at night in April, August and November, 1998 aswell as in January, 1999, respectively. Concentrations （volume percent） of CO2 in soil gas samples