Effects of soil temperature and soil water content on soil respiration in three forest types in Changbai Mountain

Soil incubation experiments were conducted in lab to delineate the effect of soil temperature and soil water content on soil respirations in broad-leaved/Korean pine forest (mountain dark brown forest soil), dark coniferous forest (mountain brown coniferous forest soil) and erman's birch forest (mountain soddy forest soil) in Changbai Mountain in September 2001. The soil water content was adjusted to five different levels (9%, 21%, 30%, and 43%) by adding certain amount of water into the soil cylinders, and the soil sample was incubated at 0, 5, 15, 25 and 35°C for 24 h. The results indicated that in broad-leaved/Korean pine forest the soil respiration rate was positively correlated to soil temperature from 0 to 35°C. Soil respiration rate increased with increase of soil water content within the limits of 21% to 37%, while it decreased with soil water content when water content was over the range. The result suggested the interactive effects of temperature and water content on soil respiration. There were significant differences in soil respiration among the various forest types. The soil respiration rate was highest in broad-leaved/Korean pine forest, middle in erman's birch forest and the lowest in dark coniferous forest. The optimal soil temperature and soil water content for soil respiration was 35°C and 37% in broad-leaved/Korean pine forest, 25°C and 21% in dark coniferous forest, and 35°C and 37% in erman's birch forest. Because the forests of broad-leaved/Korean pine, dark coniferous and erman's birch are distributed at different altitudes, the soil temperature had 4–5°C variation in different forest types during the same period. Thus, the soil respiration rates measured in brown pine mountain soil were lower than those in dark brown forest and those measured in mountain grass forest soil were higher than those in brown pine mountain soil. Key words Soil temperature - Soil water content - Soil respiration - The typical forest ecosystem in Changbai Mountain CLC number S7118.51 Document code A Foundation item: This study was supported by grant from the National Natural Science Foundation of China (No. 30271068), the grant of the Knowledge Innovation Program of Chinese Academy of Sciences (KZ-CX-SW-01-01B-12) and the grant from Advanced Programs of Institute of Applied Ecology Chinese Academy of Sciences.Biography: WANG Miao (1964-), male, associate professor in Institute of Applied Ecology, Chinese Academy of Science, Shenyang 110016, P. R. China.Responsible editor: Song Funan

Effects of Enhanced UV-B Radiation on Soil Respiration of Barley Field

[Objective] The aim was to investigate the changing characteristics of soil respiration in clear day with enhanced UV-B radiation and in cloudy day without external UV-B radiation forcing.[Methods] Based on measuring soil respiration rate of barley field at jointing stage in typical clear day and cloudy day by means of Li-8100,the effects of enhanced UV-B radiation by 20% on soil respiration rate were studied. [Results] The results showed that enhanced UV-B radiation inhibited soil respiration of barley field obviously. In clear day,the average soil respiration rate of normal barley field(B) was 1.02 μmol/(m2·s) higher than that of barley field with the enhanced UV-B radiation by 20%(BU) . For cloudy day,the average soil respiration rate of B treatment was 0.71 μmol/(m2·s) lower than BU treatment without external UV-B radiation forcing. In clear day,UV-B radiation rise resulted into the decrease of Q10 value of soil respiration in barley field,but there was an increase in cloudy day without external UV-B radiation forcing,leading to various changes of soil respiration rate. [Conclusions] Supplemental UV-B radiation could inhibit soil respiration rate of barley filed significantly,thus affected the increase of crop yield.

THE EFFECTS OF ACUTE PROGRESSIVEHYPOXIA ON THE RESPIRATIONRATE OF THE CHINESE CRABEriocheir sinensis

The effects of acute progressive hypoxia on the respiration rate of the Chinese freshwater crab, Eriocheir sinensis, acclimated at three temperatures were investigated with a closed respiromet er. E. sinensis can maintain its respiration rate down to the critical point (Pc) and from this point its respiration rate declines rapidly, reaching zero at a lower ambient oxygen concentration called the zero respiration oxygen concentration. Because of this, a new hyperbolic equation is introduced to express the relationship between respiration rate and ambient oxygen concentration. A new method for calculating the PC value is also developed. The PC values for E. sinensis at 20-35℃ range from 1.92-3.47 mg/1.

Short-term effects of nitrogen deposition on soil respiration components in two alpine coniferous forests, southeastern Tibetan Plateau

Nitrogen (N) deposition to alpine forest ecosystems is increasing gradually, yet previous studies have seldom reported the effects of N inputs on soil CO2 flux in these ecosystems. Evaluating the effects of soil respiration on N addition is of great significance for understanding soil carbon (C) budgets along N gradients in forest ecosystems. In this study, four levels of N (0, 50, 100, 150 kg N ha^-1 a^-1) were added to soil in a Picea baifouriana and an Abies georgei natural forest on the Tibetan Plateau to investigate the effect of the N inputs on soil respiration. N addition stimulated total soil respiration (Rt) and its components including heterotrophic respiration (Rh) and autotrophic respiration (Ra);however, the promoted effects declined with an increase in N application in two coniferous forests. Soil respiration rate was a little greater in the spruce forest (1.05 μmol CO2 m^-2 s^-1) than that in the fir forest (0.97 μmol CO2 m^-2 s^-1). A repeated measures ANOVA indicated that N fertilization had significant effects on Rt and its components in the spruce forest and Rt in the fir forest, but had no obvious effect on Rh or Ra in the fir forest. Rt and its components had significant exponential relationships with soil temperature in both forests. N addition also increased temperature sensitivity (Q10) of Rt and its components in the two coniferous forests, but the promotion declined as N in put increased. Important, soil moisture had great effects on Rt and its components in the spruce forest (P<0.05), but no obvious impacts were observed in the fir forest (P>0.05). Following N fertilization, Ra was significantly and positively related to fine root biomass, while Rh was related to soil enzymatic activities in both forests. The mechanisms underlying the effect of simulated N deposition on soil respiration and its components in this study may help in forecasting C cycling in alpine forests under future levels of reactive N deposition.

The effects of aerated irrigation on soil respiration, oxygen, and porosity

To ameliorate soil oxygen deficiencies around subsurface drip irrigation(SDI) drippers, aerated irrigation(AI) was introduced to supply aerated water to the soil through venturi installed in the SDI pipeline. The objectives of this study were to assess the effects of AI on soil respiration(SR), air-filled porosity(AFP), soil temperature(ST), and oxygen concentrations(OCC). Total soil respiration(TSR), biological activity temperature index(BAT), and soil oxygen consumption(OCS) based on SR, ST, and OCC, respectively, were subsequently calculated to explore the relationships between TSR, BAT, OCS, OCC, and AFP. Greenhouse-based experiments included two treatments: AI and unaerated SDI(CK), during the tomato growing season in the fall of 2015. The results showed that compared with CK, AI treatment significantly increased OCC and AFP(by 16 and 7.4%, respectively), as well as TSR and OCS(by 24.21 and 22.91%, respectively)(P<0.05). Mean fruit yield with AI treatment was also 23% higher(P<0.05) than that with CK. When BAT was controlled, partial correlations between TSR, OCS, OCC, and AFP were all significant in the AI treatment but not in the CK treatment. TSR was more sensitive to the interaction effects of OCC, OCS, AFP, and BAT under the AI treatment. Thus, the significantly increased TSR with AI appeared to be due to the favorable soil aeration conditi ons(higher OCC and AFP). Furthermore, the improvements in soil aeration conditions and respiration with AI appeared to facilitate the improvement in fruit yields, which also suggests the economic benefits of AI.

The effect of fire disturbance on short-term soil respiration in typical forest of Greater Xing'an Range, China

We investigated the effect of fire disturbance on short-term soil respiration in birch （Betula platyphylla Suk.） and larch （Larix gmelinii Rupr.） forests in Greater Xing’an range, northeastern China for further understanding of its effect on the carbon cycle in ecosystems. Our study show that post-fire soil respiration rates in B. platyphylla and L. gmelinii forests were reduced by 14%and 10%, respectively. In contrast, the soil heterotrophic respiration rates in the two types of forest were similar in post-fire and control plots. After fire, the contribution of root respiration to total soil respiration was dramatically reduced. Variation in soil respiration rates was explained by soil moisture （W） and soil tem-perature （T） at a depth of 5 cm. Exponential regression fitted T and W models explained Rs rates in B. platyphylla control and post-fire plots （83.1% and 86.2%） and L. gmelinii control and post-fire plots （83.7%and 88.7%）. In addition, the short-term temperature coefficients in B.

Effect of heat-disturbance on microbial biomass carbon and microbial respiration in Chinese fir(Cunninghamia lanceolata) forest soils

Prescribed fire has now become the usual management practice in the Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） plantation in southern China. Heat generated during fire may affect carbon （C） dynam- ics in soils. We investigated the microbial biomass C （MBC） and microbial respiration in two Chinese fir forest soils （one is not exposed to fire for the past 88 years, and the other is recently exposed to prescribed fire） after soil heating （100 and 200 ℃） under three moisture regimes [25, 50 and 75 % of water holding capacity （WHC）]. For both soils, significant reduction in MBC with increasing heating temperature was found. Soils without exposing to fire previously had significantly greater MBC concentra- tion than the fire-exposed soils when heated at 100 or 200 ℃. Lower soil water content resulted in higher MBC concentrations in both soils. In contrast, both soils had the highest soil microbial respiration rate at 50 % WHC. Soils without exposing to fire previously had the greatest microbial respiration rates at 200 ℃, while the fire-ex- posed soils when heated at 100 ℃ had greatest microbialrespiration rates. During 14-days post-heat incubation, soil MBC in both soils was greatest after heating at 200 ℃ and 25 % WHC. However, soil previously exposed to fire had the lowest CO2 evolution when incubated at 25 % WHC.

Effects of Soil Fertility and Atmospheric CO_2 Enrichment on Leaf, Stem and Root Dark Respiration of Populus tremuloides

An open-top chamber experiment was conducted at the University of Michigan Biological Station near Pellston, Michigan, USA, to study the effects of soil fertility and CO2 on leaf, stem and root dark respiration (Rd) of Populus tremuloides. Overall, area-based day-time leaf Rd (Rda) was significantly greater at elevated than at ambient CO2 in high-fertility soil, but not in low-fertility soil. Mass-based leaf Rd (Rdm) was overall greater for high- than for low-fertility soil grown trees at elected, but not at ambient CO2. Nighttime leaf Rd. and Rdm were unthected by soil fertility or CO2, nor was stem Rda, which ranged from 1.0 to 1.4 μmol m-2 s-1 in the spring and 3.5 to 4.5 μmol m-2 s-1 in the summer. Root Rda. was significantly higher in high- than in low-fertility soil, but was unaffected by CO2. Since biomass production of P. tremuloides will be significantly greater at elevated CO2 while specific Rd will either increase or remain unchanged, we predict that carbon loss to the atmosphere through respiration from this ecologically important species would increase at higher CO2. Soil fertility would also interact with elevated CO2 in affecting the carbon flow in the plant-soil-air system.

Effect of experimental warming on soil respiration under conventional tillage and no-tillage farmland in the North China Plain

Understanding the response of soil respiration to global warming in agro-ecosystem is crucial for simulating terrestrial carbon （C） cycle. We conducted an infrared warming experiment under conventional tillage （CT） and no-tillage （NT） farmland for winter wheat and summer maize rotation system in North China Plain （NCP）. Treatments include CT with and without warming （CTW and CTN）, NT with and without warming （NTW and NTN）. The results indicated that warming had no sig- nificant effect on soil moisture in irrigated farmland of NCP （P〉0.05）. The elevated average soil temperature of 1.1-116℃ in crop growing periods could increase annual soil CO2 emission by 10.3% in CT filed （P〉0.05）, but significantly increase it by 12.7% in NT field （P〈0.05）, respectively. The disturbances such as plowing, irrigation and precipitation resulted in the obvious soil CO2 emission peaks, which contributed 36.6-40.8% of annual soil cumulative CO2 emission. Warming would enhance these soil CO2 emission peaks; it might be associated with the warming-induced increase of autotrophic respiration and heterotrophic respiration. Compared with un-warming treatments, dissolved organic carbon （DOC） and soil microbial biomass carbon （MBC） in warming treatments were significantly increased by 11.6-23.4 and 12.9-23.6%, respectively, indicating that the positive responses of DOC and MBC to warming in both of two tillage systems. Our study highlights that climate warming may have positive effects on soil C release in NCP in association with response of labile C substrate to warming.

The effects of DDT on the feeding, respiration, survival, and reproduction of Sinocalanus tenellus(Copepoda:Calanoida)

DDT （dichloro-diphenyl-trichloroethane） as a type of organochlorine pesticides, is an important compo nent of pesticides pollution whose impact on the marine ecosystem is urgently to be evaluated. To investi gate the biological effects of DDT on the marine ecosystem, copepods being the main contributor of sec ondary productivity in the marine ecosystem, were selected as target animals. The influence of DDT on the feeding, respiration, survival, and reproduction of Sinocalanus tenellus （S. tenellus） was analyzed and the antioxidant enzymes activities in the individuals were measured under different exposure concentrations of DDT. The 48 h median lethal concentration （LC50） and 96 h LC50 of DDT to S. tenellus were 5.44 and 2.50 pg/dma, respectively. The filtration rates, grazing rates, and respiration of S. tenellus decreased apparently with increased DDT concentrations. Under lower concentration （〈625 ng/dm3） of DDT, the activities of the antioxidant enzymes, including superoxide dismutase and catalase in the animals increased significantly compared with those in the animals without any exposure to DDT, which suggested that the antioxidant enzymes can protect the animals from oxidative damage. However, the activity of the antioxidant enzyme decreased when the animals were exposed to higher concentration （1250-2 500 ng/dma） of DDT. The sur-vival rate of both females and males was reduced when they were exposed to DDT less than 250 ng/dm3, but females showed higher survival rate than males when they are under the same concentration. The hatching ratio and the egg diameters of S. tenellus decreased significantly when they were exposed to DDT with a concentration of 25 and 250 ng/dm3, however, the cumulative egg production did not show any significant variation when the animals were exposed to the above DDT concentration. These data in the preset study suggested that exposure to DDT can cause the variation of the species composition of copepods, and further affect the marine ecosystem.

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.

Effect of temperature on soil respiration in a Chinese fir forest

Soil samples collected from the surface soil （0-10 cm） in an 88-year-old Chinese fir （Cunninghamia lanceolata） forest in Nanping Fujian, China were incubated for 90 days at the temperatures of 15℃, 25℃ and 35℃ in laboratory. The soil CO2 evolution rates were measured at the incubation time of 2, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 and 90 days. The results showed that CO2 evolution rates of soil samples varied significantly with incubation time and temperature during the incubation period. Mean CO2 evolution rate and cumulative amount of CO2 evolution from soil were highest at 35℃, followed by those at 25℃, and 15℃. Substantial differences in CO2 evolution rate were found in Q10 values calculated for the 2nd and 90th day of incubation. The Q10 value for the average CO2 evolution rate was 2.0 at the temperature range of 15-25℃, but it decreased to 1.2 at 25 35℃. Soil CO2 evolution rates decreased with the incubation time. The cumulative mineralized C at the end of incubation period （on the 90th day） was less than 10% of the initial C amounts prior to incubation.

Long-term thinning decreases the contribution of heterotrophic respiration to soil respiration in subalpine plantations

Interest in the dynamics of soil respiration(R_(S))in subalpine forest ecosystems is increasing due to their high soil carbon density and potential sensitivity to environmental changes.However,as a principal silvicultural practice,the long-term impacts of thinning on R_(S) and its heterotrophic and autotrophic respiration components(R_(h) and Ra,respectively)in subalpine plantations are poorly understood,espe-cially in winter.A 3-year field observation was carried out with consideration of winter CO_(2) efflux in middle-aged sub-alpine spruce plantations in northwestern China.A trench-ing method was used to explore the long-term impacts of thinning on Rs,Rn and R_(a).Seventeen years after thinning,mean annual Rs,Rn and R_(a) increased,while the contribu-tion of R_(h) to R_(s) decreased with thinning intensity.Thinning significantly decreased winter R,because of the reduction in R_(n) but had no significant effect on Ra.The temperature sensitivity(Q_(10))of R_(h) and R_(a) also increased with thinning intensity,with lower Q_(10) values for R_(h)(2.1-2.6)than for Ra(2.4-2.8).The results revealed the explanatory variables and pathways related to R_(n) and R_(a) dynamics.Thinning increased soil moisture and nitrate nitrogen(NO_(3)^(-)-N),and the enhanced nitrogen and water availability promoted R_(h) and R_(a) by improving fine root biomass and microbial activity.Our results highlight the positive roles of NO_(3)^(-)-N in stimulating R_(s) components following long-term thinning.Therefore,applications of nitrogen fertilizer are not recommended while thinning subalpine spruce plantations from the perspective of reducing soil CO_(2) emissions.The increased Q_(10) values of R_(s) components indicate that a large increase in soil CO_(2) emissions would be expected following thinning because of more pronounced climate warming in alpineregions.

Effects of Photoperiod on Alternative Respiration Pathway in Nectarine Flower Buds During Dormancy Induction

Characteristics of dormancy induction and alternative respiration pathway （also known as cyanide-resistant respiration） of nectarine flower buds in different photoperiods were studied to determine the function of photoperiod and alternative respiration pathway in dormancy induction. Oxygen-electrode system and respiratory inhibitors were used to measure total respiratory rates and rates of alternative respiration pathway. The results showed that total respiration rate （Vt） in flower buds showed to be double hump-shaped curves. Short day raised, brought the first-hump of Vt forward and delayed the second-hump, while long day delayed the whole curve. The capacity （Vast） and activity （pValt） of SD and LD changed synchronously and both showed to be double hump-shaped curves. Short day made the first climax of Vast and pValt existed much earlier, while long day increased their rates significantly. The length of day had little effects on the later period climax. Long day also increased the contributions of altemative respiration pathway in total respiration rate （pValt/Vt）. The changes in alternative respiration pathway were correlated with the induction of dormancy and adjusted by photoperiod. Short day promoted dormancy induction of nectarine trees, while long day delayed it.

Spatio-Temporal Effect on Soil Respiration in Fine-Scale Patches in a Desert Ecosystem

Soil organisms in terrestrial systems are unevenly distributed in time and space, and often aggregated. Spatiotemporal patchiness in the soil environment is thought to be crucial for the maintenance of soil biodiversity, providing diverse microhabitats tightly interweaving with resource partitioning. Determination of a ＂scale unit＂ to help understand ecological processes has become one of the important and most debatable problems in recent years. A fieldwork was carried out in the northern Negev Desert highland, Israel to determine the influence of fine-scale landscape patch moisture heterogeneity on biogeochemical variables and microbial activity linkage in a desert ecosystem. The results showed that the spatio-temporal patchiness of soil moisture to which we attribute influential properties, was found to become more heterogenic with the decrease in soil moisture availability （from 8.2 to 0.4 g kg^-1） toward the hot, dry seasons, with coefficient of variation （CV） change amounting to 66.9%. Spatio-temporal distribution of organic matter （OM） and total soluble nitrogen （TSN） was found to be relatively uniformly distributed throughout the wet seasons （winter and spring）, with increase of relatively high heterogeneity toward the dry seasons （from 0.25% to 2.17% for OM, and from 0 to 10.2 mg kg^-1 for TSN） with CV of 47.4% and 99.7% for OM and TSN, respectively. Different spatio-temporal landscape patterns were obtained for Ca （CV = 44.6%）, K （CV = 34.4%）, and Na （CV = 92%） ions throughout the study period. CO2 evolution （CV = 48.6%） was found to be of lower heterogeneity （varying between 2 and 39 g CO2-C g^-1 dry soil h^-1） in the moist seasons, e.g., winter and spring, with lower values of respiration coupled with high heterogeneity of Na^＋ and low levels of TSN and organic matter content, and with more homogeneity in the dry seasons （varying between 1 and 50 g CO2-C g^-1 dry soil h^-1）. Our results elucidate the heterogeneity and complexity of desert system habitats affecting soil biota activity.

Side－effects of organic and inorganic pollutants on soil nitrification and respiration

Side-effects of heavy metals(Cd and Zn)and organic pollutants(phenanthrene and paclobutrazol)on nitrification and respiration in a loam soil were investigated with its air-dried and fresh conditions. Critical levels for these test pollutants were derived from this investigation.Bioavailable concentrations of Cd and Zn were also determined. It was concluded that such critical levels as NOEL and LOEL of heavy metals should be expressed using bioavailable concentrations rather than total ones since different soil has different properties,especially different absorption ability to heavy metals.

Effects of converting natural grasslands into planted grasslands on ecosystem respiration： a case study in Inner Mongolia, China

With increasingly intensifying degradation of natural grasslands and rapidly increasing demand of high quality forages, natural grasslands in China have been converted into planted grasslands at an unprecedented rate and the magnitude of the conversion in Inner Mongolia is among the national highest where the areal extent of planted grasslands ranks the second in China. Such land-use changes（i.e., converting natural grasslands into planted grasslands） can significantly affect carbon stocks and carbon emissions in grassland ecosystems. In this study, we analyzed the effects of converting natural grasslands into planted grasslands（including Medicago sativa, Elymus cylindricus, and M. sativa＋E. cylindricus） on ecosystem respiration（F（eco）） in Inner Mongolia of China. Diurnal F（eco） and its components（i.e., total soil respiration（F（ts））, soil heterotrophic respiration（F（sh）） and vegetation autotrophic respiration（F（va））） were measured in 2012（27 July to 5 August） and 2013（18 July to 25 July） in the natural and planted grasslands. Meteorological data, aboveground vegetation data and soil data were simultaneously collected to analyze the relationships between respiration fluxes and environmental factors in those grasslands. In 2012, the daily mean F（eco） in the M. sativa grassland was higher than that in the natural grassland, and the daily mean F（va） was higher in all planted grasslands（i.e., M. sativa, E. cylindricus, and M. sativa＋E. cylindricus） than in the natural grassland. In contrast, the daily mean F（ts） and F（sh） were lower in all planted grasslands than in the natural grassland. In 2013, the daily mean F（eco）, F（ts） and F（va） in all planted grasslands were higher than those in the natural grassland, and the daily mean F（sh） in the M. sativa＋E. cylindricus grassland was higher than that in the natural grassland. The two-year experimental results suggested that the conversion of natural grasslands into planted grasslands can generally increase the F（eco） and the increase in F（eco） is more pronounced when the plantation becomes more mature. The results also indicated that F（sh） contributed more to F（eco） in the natural grassland whereas F（va） contributed more to F（eco） in the planted grasslands. The regression analyses show that climate factors（air temperature and relative humidity） and soil properties（soil organic matter, soil temperature, and soil moisture） strongly affected respiration fluxes in all grasslands. However, our observation period was admittedly too short. To fully understand the effects of such land-use changes（i.e., converting natural grasslands into planted grasslands） on respiration fluxes, longer-term observations are badly needed.

The weak effects of fencing on ecosystem respiration,CH4,and N2O fluxes in a Tibetan alpine meadow during the growing season

Fencing is the most common land-management practice to protect grassland degradation from livestock overgrazing on the Tibetan Plateau. However, it is unclear whether fencing reduces CO_2, CH_4, and N_2O emission. Here, we selected four vegetation types of alpine meadow(graminoid, shrub, forb, and sparse vegetation) to determine fencing effects on ecosystem respiration(Re), CH_4, and N_2O fluxes during the growing season. Despite increased average monthly ecosystem respiration(Re) for fenced graminoid vegetation at the end of the growing season, there was no significant difference between grazing and fencing across all vegetation types. Fencing significantly reduced average CH_4 uptake by about 50% in 2008 only for forb vegetation and increased average N_2O release for graminoid vegetation by 38% and 48% in 2008 and 2009,respectively. Temperature, moisture, total organic carbon, C/N, nitrate, ammonia, and/or bulk density of soil, as well as above-and belowground biomass, explained 19%~71% and 6%~33% of variation in daily and average Re and CH_4 fluxes across all vegetation types, while soil-bulk density explained 27% of variation in average N_2O fluxes. Stepwise regression showed that soil temperature and soil moisture controlled average Re, while soil moisture and bulk density controlled average CH_4 fluxes. These results indicate that abiotic factors control Re, CH_4, and N_2O fluxes; and grazing exclusion has little effect on reducing their emission—implying that climatic change rather than grazing may have a more important influence on the budgets of Re and CH_4 for the Tibetan alpine meadow during the growing season.

Effects of Intercropping and Shading Systems on Tea Photosynthesis and Respiration

[Objective] The aim was to provide references for constructing compound ecological tea gardens. [Method] In an ecological adult-tea garden, teas shaded by Prunus cerasoides, Prunus L., and Litsea pungens were selected and the teas without shades were taken as a control in order to explore effects of tree shading on photosynthesis, respiration and net photosynthetic intensities. [Result] In a growth cycle of one year, for teas shaded by Prunus cerasoides, Prunus L., and Litsea pungens, respiration intensity was significantly higher than that of the control; net photosynthetic intensity was extremely significant higher; photosynthesis intensity showed none rules. Both of net photosynthetic rate and intensity kept higher in winter of shaded teas. [Conclusion] It is of significance for high-yielding and high-quality teas to reduce respiration consumption and coordinate between photosynthesis and respiration given that tea grows well.

Effect of rain enrichment on soil respiration of Nitraria sphaerocarpa community in a hyperarid area

In order to analyze the effect of rain enrichment on soil respiration rate of a Nitraria sphaerocarpa community, we measured soil respiration rate in bare and vegetated areas in a hyperarid area （Dunhuang） during the growing season. Results show that rain enrichment can increase bare and vegetated soil respiration rates. The more rainfall enrichment, the greater the increment and the longer duration time effect for soil respiration rate. 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase bare soil respiration rates by 90% and 106% （P〈0.01）, respectively. By contrast, areas with 100% （8 mm）, 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase shrub area respiration rates by 68%, 157% and 205% （P〈0.01）, respectively. The response time of bare and vegetated soil respiration to rainfall enrichment is asynchronous. Response variable of soil respiration in vegetated soil is higher （118%） than in bare soil. There was significant positive correlation between soil respiration rate and soil water content during the growing season （P〈0.01）. For every 1 mm increment of precipitation, soil respiration rate increased by 0.01 and 0.04 pmol/（m2.s）, respectively in vegetated and bare soils.