Osmotic Regulation of Betaine Content in Leymus chinensis Under Saline-alkali Stress and Cloning and Expression of Betaine Aldehyde Dehydrogenase(BADH) Gene

The potted Leymus chinensis seedlings were treated with saline-alkali solution of six different（from Ⅰ to Ⅵ） concentrations. The results demonstrate that the betaine content and Betaine-aldehyde dehydrogenase（BADH： EC 1.2.1.8） activities have a direct relation with increased stressing time in the same treatment; both exhibit a single peak with increasing the concentration of saline-alkali solution, and number V shows the highest value. The BADH gene of Leyrnus chinensis was cloned by RT-PCR and RACE technology and was designated as LcBADH. The cDNA sequence of LcBADH was 1774bp including the open reading frame（ORF） of 1521bp（coding 506 amino acids）. The vector of prokaryotic expression was constructed by inserting the LcBADH gene fragmcnt into pET30a（＋） and transformed into E. coli BL21（DE3）. The result of SDS-PAGE shows that the idio-protein with a molecular mass of 56.78 kDa was effectively expressed in the recombinant bacteria induced by isopropyl fl-D-thiogalactoside（IPTG）.

Linking nutrient strategies with plant size along a grazing gradient： Evidence from Leymus chinensis in a natural pasture

St udying the changes in nutrient use strategies induced by grazing can provide insight into the process of grassland degradation and is important for improving grassland quality and enhancing ecosystem function. Dominant species in meadow steppe can optimize their use of limiting resources; however, the regulation of nutrient use strategies across grazing gradients is not fully understood. Therefore, in this study, we report an in situ study in which the impact of grazing rates on nutrient use strategies of Leymus chinensis, the dominant plant species in eastern Eurasian temperate steppes, was investigated. We conducted a large randomized controlled experiment（conducted continuously for five years in grassland plots in a natural pasture in Ha ilar, eastern Mongolia Plateau, China） to assess the effects of grazing rate treatments（0.00, 0.23, 0.34, 0.46, 0.69, and 0.92 adult cattle unit（AU） ha-1） on L. chinensis along a grazing gradient and employed a random sampling approach to compare the accumulation, allocation, and stoichiometry of C, N, and P in leaves and stems. Ou r findings demonstrated the follows：（i） The height of L. chinensis decreased with an increase in the grazing gradient, and the concentrations of C, N, and P significantly increased;（ii） the accumulation of C, N, and P per individual was negatively correlated with the concentration of aboveground tissues, suggesting that there was a tradeoff in L. chinensis between nutrient accumulation and concentration at the individual scale;（iii） the leaf-to-stem ratio of C, N, and P accumulation increased with grazing intensity, indicating a tradeoff in nutrient allocation and plant size at the individual plant level; and（iv） grazing rates were negatively correlated with the ratios of C：N and C：P in the stem; however, these ratios in leaves significantly increased with grazing intensity. Our findings suggest that L. chinensis in meadow steppe adapts to grazing disturbance through tradeoffs between plant size and nutrient use strategies. Moreover, our results imply that grazing produces a compensatory effect on nutrient use efficiency between the stems and leaves of L. chinensis.

Long-term effects of mowing on plasticity and allometry of Leymus chinensis in a temperate semi-arid grassland,China

Mowing is an important land management practice for natural semi-arid regions. A growing body of empirical evidence shows that different mowing regimes affect the functioning of grassland ecosystems. However, the responses of plant functional traits to long-term mowing and their allometric scaling under long-term mowing are poorly understood. For a better understanding of the effects of mowing on grassland ecosystems, we analyzed the allometric traits of leaves and stems of Leymus chinensis （Trin.） Tzvel., a dominant grass species in eastern Eurasian temperate grassland, at different mowing intensities （no clipping, clipping once every two years, once a year and twice a year）. Experiments were conducted on plots established over a decade ago in a typical steppe of Xilinhot, Inner Mongolia, China. Results showed that most of the functional traits of L. chinensis decreased with the increased mowing intensity. The responses of leaves and stems to long-term mowing were asymmetric, in which leaf traits were more stable than stem traits. Also significant allometric relationships were found among most of the plant functional traits under the four mowing treatments. Sensitive traits of L. chinensis （e.g. leaf length and stem length） were primary indicators associated with aboveground biomass decline under high mowing intensity. In conclusion, the allometric growth of different functional traits of L. chinensis varies with different long-term mowing practices, which is likely to be a strategy used by the plant to adapt to the mowing disturbances.

Synopsis of Leymus Hochst.(Triticeae:Poaceae)

Leymus is a genus in the Triticeae tribe, Poaceae. The taxa of this genus are allopolyploid species which possess the Ns and Xm genomes. According to cytological, cytogenetic and molecular genetic analyses, some species of Hystrix and Elymus ought to be transferred to this genus. A world revision of the genus Leymus is needed. In this paper we summarize experimental results, provide a key to sections, species and varieties, and list all the taxa we recognize in Leymus with their synonyms. This synopsis is a new taxonomic system to be used for the revision of Leymus.

Variation and heritability of morphological and physiological traits among Leymus chinensis genotypes under different environmental conditions

Intraspecific trait variation and heritability in different environmental conditions not only suggest a potential for an evolutionary response but also have important ecological consequences at the population, community, and ecosystem levels. However, the contribution of quantitative trait variation within a grassland species to evolutionary responses or ecological consequences is seldom documented. Leymus chinensis is an important dominant species in semi-arid grasslands of China, which has seriously suffered from drought and high temperature stresses in recent decades. In the present study, we measured variation and heritability of 10 quantitative traits, namely the number of tillers, maximum shoot height, number of rhizomes, maximum rhizome length, rhizome mass, aboveground mass, root mass, maximum net photosynthetic rate(Pmax), specific leaf area(SLA), and leaf length to leaf width ratio(LL/LW), for 10 genotypes of L. chinensis under one non-stress(Ck) condition and three environmental stress conditions(i.e., drought(Dr), high temperature(Ht), and both drought and high temperature(DrHt)). Result indicated that(1) the interaction of genotype and environmental condition(G×E) was significant for 6 traits but not significant for the other 4 traits as shown by two-way analysis of variance(ANOVA), suggesting that different selection forces were placed for different traits on the factors dominating phenotypic responses to different environmental conditions. Moreover, these significant G×E effects on traits indicated significantly different phenotypic adaptive responses among L. chinensis genotypes to different environmental conditions. Additionally, individuals could be grouped according to environmental condition rather than genotype as shown by canonical discriminant analysis, indicating that environmental condition played a more important role in affecting phenotypic variation than genotype;(2) by one-way ANOVA, significant differences among L. chinensis genotypes were found in all 10 traits under Ck and Dr conditions, in 8 traits under Dr Ht condition and only in 4 traits under Ht condition; and(3) all 10 traits showed relatively low or non-measurable broad-sense heritability(H_2) under stress conditions. However, the lowest H_2 value for most traits did not occur under DrHt condition, which supported the hypothesis of 'unfavorable conditions have unpredictable effects' rather than 'unfavorable conditions decrease heritability'. Results from our experiment might aid to improve predictions on the potential impacts of climate changes on L. chinensis and eventually species conservation and ecosystem restoration.

Responses of chlorophyll fluorescence and nitrogen level of Leymus chinensis seedling to changes of soil moisture and temperature

Controlled experiment of Leymus chinensis seedlings grown in the environmental growth chambers at 3 soil moisture levels and 3 temperature levels was conducted in order to improve the understanding how leaf photosynthetic parameters will respond to climatic change. The results indicated that soil drought and high temperature decreased the photochemical efficiency of photosystem(F v/F m), the overall photochemical quantum yield of PSII(yield), the coefficient of photochemical fluorescence quenching(q\-P), but increased the coefficient of non-photochemical fluorescence quenching(q\-N). Severe soil drought would decrease F v/F m and yield by 3.12% and 37.04% under 26℃ condition, respectively, and 6.60% and 73.33% under 32℃ condition, respectively, suggesting that higher temperature may enhance the negative effects of soil drought. All the soil drought treatments resulted in the decline in leaf nitrogen content. There was no significant effect of temperature on leaf nitrogen level, but higher temperature significantly reduced the root nitrogen content and the ratio of root nitrogen to leaf nitrogen, indicating the different strategies of adaptation to soil drought and temperature. It was also implied that higher temperature would enhance the effect of soil drought on leaf photosynthetic capacity, decrease the adaptability of Leymus chinensis to drought.

Effects of Vitamin E on the Activities of Protective Enzymes and Membrane Lipid Peroxidation in Leymus Chinensis under Drought Stress

Leymus chinensis seedlings were treated with 0.05--10 mmol/L vitamin E under osmotic stress in the presence of polyethylene glycol（PEG） as the stress reagent. The effects of the different concentrations of exogenous vitamin E on the activities of SOD, POD and free proline, and the MDA contents under drought stress were examined so as to ascertain the mechanism of Leymus chinensis resistance to drought stress and explore the possible preventive measures. The results indicate that the activities of SOD and POD decreased but the free proline and MDA contents increased as drought stress was accentuated, showing an enhancement of oxidative stress that may cause a decline in membrane stabilization. However, the activities of SOD and POD and the free proline content increased, whereas the MDA content reduced in Leymus chinensis pretreated with vitamin E in comparison with that of the control. This indicates that exogenous vitamin E enhanced the antioxidation of Leymus chinensis seedlings. It suggests that cytomembrane can be protected from damage by increasing the free proline content and the activities of SOD and POD that result in enhancing the drought resistance of Leymus chinensis seedlings.

Dynamics of Zn between soil and plant in Northeast Leymus chinensis grassland

A study was conducted to determine the dynamic of Zn content between soil and plant in the natural protection zone of Leymus chinensis grassland in Changling County （44°30′-44°45′N; 123°31 ′-124°10′E）, Jilin Province, China. Results showed that the total Zn content was lower, available Zn content had a moderate level in the soil, and the plants was not lack of Zn. During the growing season, content of total Zn and available Zn in soil showed a down-trend distribution along the soil profile. Content of total Zn had a significantly positive correlation with that of the organic matter, but it was negatively correlated to soil pH. Monthly dynamic of the average content of total Zn showed a ＂V＂ type curve in the growing season from May to August, and July was the nadir. The trend of the average content of available Zn was similar to the content of total Zn, but was down after August; Zn content variation in the organs and litter of L. chinensis was great, with the order of root〉rhizome 〉leaf〉stem〉litter. The ratio of available Zn content in A layer versus B layer was more than 2 times that of the total Zn, which indicated that the soil of A layer had higher enrichment capacity of available Zn. The enrichment of Zn in the root of L chinensis was 44.17 times as that in the soil. The absorbing intensity of root had a significantly negative correlation with the activity of Zn in the soil （r=-0.8800, p〈0.01）.

Comparative Analysis of Polysaccharides from Two Ecological Types of Leymus chinensis

Leymus chinensis（Trin.） Tzvel.,widely distributed at eastern Eurasian steppe and divided into gray-green type and yellow-green type,has different stress resistance to environment.In the present study,the water-soluble polysaccharides from two ecotypes of L.chinensis were analyzed in detail,and the differences between polysaccharides from the two ecotypes of L.chinensis in the yield,monosaccharide composition,molecular weight and structure were clarified.The polysaccharides of L.chinensis were composed of both neutral and acidic polysaccharides.The neutral polysaccharides contained mannose,glucose,galactose,xylose and arabinose,and mainly consisted of β-1,4-Glcp,α-1,3-Galp and α-1,2-Xylp residues.The acidic polysaccharides contained mannose,rhamnose,glucuronic acid,galacturonic acid,glucose,galactose,xylose and arabinose.However,the yields,monosaccharides contents and the molecular weights of the polysaccharides from the two ecotypes of L.chinensis were different.Moreover,the resistance type（gray-green type） of L.chinensis contained a number of α-1,3-Manp and reducing end of β-Glcp residues,and much more O-methyl groups than normal type（yellow-green type） of L.chinensis.The differences of the polysaccharides of the two ecotypes of L.chinensis might be due to the long-term environmental adaptability of plant,and the differences of the polysaccharides might influence the stress resistance of L.chinensis.

Effect of Autumn Cutting Date on Regrowth, Turning Green, Yield and Quality of <i>Leymus chinensis</i>Grassland in Songnen Plain, Northeast China

A field study was carried out to quantify the effects of different cutting time on Leymus chinensis population and community characteristic in Songnen grassland of northeast China from August, 2006 to August, 2007. The treatment interval was ten days with the remaining stubble height of 5 cm from 15th August to 4th October in 2006. Results showed that the L. chinensis made up about 90% of the dry matter of aboveground biomass, and there were about ten species in the L. chinensis community in the 1 m × 1 m plot. The L. chinensis and Kalimeris integrifolia regrew rapidly after autumn cutting in 2016. In the second year, the coefficients of the community similarity were high between the different cutting time treatments. The density, height, aboveground biomass, stem/leaf ratio, and crude protein of L. chinensis were not significant at the turning green stage and harvesting stage, the companion species of L. chinensis community contained higher crude protein, but the crude protein of the plant community were not significant. Thus, considering the weather factor for haymaking, the harvest dates should be concentrated from the middle ten days of August to the first ten days in September.

Intra-specific variations of two Leymus chinensis divergence populations in Songnen Plain, Northeast China

Population demography, seed production, biomass allocation, net photosynthesis and transpiration of two Leymus chinensis divergent populations and between two years in Songnen plain, northeast China were compared. Strong differences between the dry 1997 and moist 1998 occurred in vegetative shoot and sexual shoot densities, sexual differentiation and tiller densities, as well as in the lengths of inflorescence, seed numbers per inflorescence, seed weights and biomass allocation in each population respectively ( P < 0.01). While strong differences between the two populations occurred in vegetative shoot densities, sexual shoot densities, sexual differentiation and seed weights in each year ( P < 0.01). The differences between the two populations in tiller densities and in biomass allocation to sexual shoots were significant ( P <0.05). But there were no significant differences between the two populations in the lengths of inflorescence, seed numbers per inflorescence and biomass allocation to rhizomes and vegetative shoots ( P >0.05). Excepting the transpiration rate in the early June, the differences between the two populations in net photosynthesis and transpiration rate of vegetative shoots and sexual shoots were strongly significant in the early June and July respectively ( P <0.01). Relative stable variations in population demography and physiological traits between the two populations indicated that they are divergently in the Songnen Plain.

Effect of Different Proportions of Leymus chinensis in Diet on Plasma Enzymes Activities of Wulong Geese

Eight-month-old Wulong geese were fed with the diet with different proportions of Leymus chiesensis at the same energy and protein level. The activities of plasma Alkaline Phosphatase （AKP）, Acid Phosphatase （ACP）, Choline Esterace （CHE）, Lactic Dehydrogenase （LDH）, Glutamicoxalacetic Transaminase （GOT） and Glutamatepyruvate Transaminase （GPT） were determined and then their correlations with fiber digestibility and the apparent digestibility of Ca, R Met and Cys were analyzed. The results showed that the activity of AKP took on a significant downtrend as the increasing of Leymus chinensis proportion （P〈0.05）. There was a negative correlation between the AKP activity and the digestibility of crude fiber （CF）, neutral detergent fiber （NDF） and acid detergent fiber （ADF） （P〈0.05）. However, there was a significant positive correlation between the AKP activity and the apparent digestibility of Ca, Met and Cys （P〈0.05）. Moreover, the activities of the other five enzymes had no significant correlation with the digestibility of CF, NDF, ADF, and the apparent digestibility of Ca, Met and Cys （P〉0.05）.

Genetic Dissimilarity of Clonal Populations of Leymus chinensis (Trin.) Tzvel in Heterogeneous and Homogeneous Habitats in Southwestern Heilongjiang Province of China

Leymus chinensis （Trin.） Tzvel is the characteristic of the Eastern Asia, and is a perennial herbaceous rhizome species on L. chinensis steppe of the Northern China, the Eastern Mongolia, and area of Outer-Baikal of Russia. It has both vegetative and sexual reproductions, and results in complexity of the population structure. Thus, it is difficult to identify distinct clones. Author used the randomly amplified polymorphic DNA （RAPD） technique to identify the clonal structure of heterogeneous and homogeneous habitats in two populations ofLeymus chinensis, analyzed 260 ramets samples using 12 primers and 60 polymorphie markers （reproducible RAPD bands）. The results proved elonal diversity described using PD, D, and E was higher in the HCS habitat than that in the HPS habitat. The PD, D, and E in the HCS of Songzhan population were 0.21, 0.90, and 0.91, respectively, whereas the PD, D, and E in the HPS of Songzhan population were only 0.09, 0.68, and 0.77, respectively; the PD, D, and E in the HCS of Yongle population were 0.19, 0.92 mad 0.90, respectively, correspondingly, these measures in the HPS of Yongle population were only 0.09, 0.63, and 0.79, respectively. The results also indicated that clonal population ofL. chinensis in HPS habitat had lower genetic dissimilarity index than that in the HCS habitat.

Seed Germination and Callus Induction in Leymus chinensis of Different Seed Colors

[ Objective] To explore the effects of different seed colors on seed germination and callus induction of Leymus chinensis. [ Method ] According to the color of mature seeds of Leymus chinensis, they were divided three color types, namely, pale yellow, yellow and black. Their seed germination and callus induction were observed. [ Result] The pale yellow Leymus chinensis seeds had higher germination rate （32.5%） and rate of callus induction （28.5%）. Based on the results of the TI＇C method and electrical conductivity, the seed viability was decreased with the deepening seed color. [ Conclusion] The study laid the foundation for establishing highly efficient plant regeneration system of Leymus chinensis.

De novo Transcriptome Analysis in Leymus mollis to Unveil Genes Involved in Salt Stress Response

Leymus mollis,a wild relative of wheat,is very tolerant to salt stress,and has been considered as a valuable genetic resource for wheat breeding.However,the genetic basis for salt tolerance of this species is still largely unknown.In this study,de novo sequencing,assembly and analysis of L.mollis transcriptome in response to salt stress was performed.A total of 110,323 and 112,846 unigenes were generated for the NaCl-free(CK)and 180 mM NaCl-treated(CT)library,respectively.For the two libraries,73,414 unigenes were successfully annotated in five common protein databases,and 7521 differentially expressed genes(DEGs)between CK and CT libraries were identified.GO enrichment analysis of the DEGs showed that the significantly enriched GO terms were predominantly involved in environmental adaptation(including“response to abiotic stimulus”,“response to water deprivation”),regulation of signaling pathway(such as“regulation of abscisic acid mediated signaling pathway”,“regulation of cell communication”),and photosynthesis(including“response to light stimulus”,“photosynthesis,light harvesting”and“chlorophyll metabolic process”).KEGG pathway enrichment analysis showed that“mRNA surveillance pathway”,“RNA transport”and“plant hormone signal transduction”were predominantly enriched pathways,followed by several secondary metabolic pathways,photosynthesis,carbohydrate metabolism and lipid metabolism.In addition,DEGs related to osmotic stress,ion homeostasis and oxidative stress,including four dehydrins,five aquaporins,an LmNHX2 and several antioxidant enzymes or proteins genes,were found to be up-regulated in response to salt stress.These results will be helpful for further studies on the molecular mechanisms of salt responses in L.mollis.

Separation and cleaning of Leymus chinensis seed threshing material based on gas-solid coupling

The aim of this study was to improve the cleaning performance of the Leymus chinensis seed threshing material separation and cleaning device,and to clarify the movement law and characteristics of the Leymus chinensis seed threshing material during the cleaning process.A numerical simulation of the separation and cleaning process of Leymus chinensis seed threshing material was performed using the computational fluid dynamics discrete element approach.According to the streamline distribution of the gas-solid coupling,the movement of Leymus chinensis seeds during the cleaning process was examined.Additionally,the average speed and quantity of Leymus chinensis seed threshing material in different separation and cleaning zones were studied over time.Meanwhile,the distribution principle of the threshing material was obtained,and a verification test of the under-sieve distribution was conducted.The test results showed that the numerical simulation was consistent with the distribution trend of the under-sieve.The cleaning performance verification test showed that the impurity content and the loss rate of the separation and cleaning device were 27.3%and 3.3%,where the test results,compared with those of the numerical simulation,showed a reduction of 1.5%and 0.8%,respectively.It is feasible to apply the theory and method of gas-solid coupling to simulate the separation and cleaning process of Leymus chinensis seeds.

降水量和短期极端干旱对典型草原植物群落及优势种羊草(Leymus chinensis)叶性状的影响

植物叶性状在植物响应环境变化中具有重要作用。在气候变化的背景下,典型草原植物叶性状如何响应降水格局与短期极端干旱还不十分清楚。利用野外控制试验,研究了降水量(323 mm和236 mm)和短期极端干旱(生长季减雨66%和生长季干旱60 d)对典型草原植物群落及优势植物羊草(Leymus chinensis)叶性状的影响。结果表明:降水格局显著影响着植物群落和羊草的叶性状(P<0.05),短期极端干旱对典型草原群落和羊草叶面积具有显著影响(P<0.05)。随着降水量的减少,群落和羊草的叶面积与叶干物质含量降低,而比叶面积与叶片氮含量增加。降水格局与短期极端干旱交互作用显著影响着群落的叶面积与叶片氮含量(P<0.05),323 mm降水量下短期极端干旱显著降低了叶面积,266 mm降水量下生长季干旱60 d增加了叶片氮含量。降水格局与短期极端干旱交互作用也显著影响着羊草叶面积与比叶面积(P<0.01),323 mm降水量下短期极端干旱降低了叶面积,266 mm降水量下生长季干旱60 d显著增加了比叶面积。回归分析表明,不同处理下羊草叶面积、叶干物质含量、叶片氮含量能较好地解释群落叶性状。典型草原植物群落通过优势植物的主要叶性状改变来适应降水格局变化,而通过叶面积改变来适应短期极端干旱。

大赖草(Leymus racemosus)结实格局

连续2年对新疆阿勒泰地区荒漠植物大赖草(Leymus racemosus)居群(公路附近沙丘平坦处,P1;农田周围沙丘平坦处,P2;周围积水沙丘中下部,P3;多个沙丘中间平坦处,P4;多个沙丘中间隆起处,P5)、小穗间和小穗内的结实格局进行了比较研究。结果表明:(1)2011年大赖草的穗长、穗宽、总花数、结实率和大种子比率都高于2012年,小种子数低于2012年;2年的结实率在5个居群间均表现为P2>P3>P1>P5>P4。(2)每花序内不同小穗的穗宽、总花数和结实率表现为中部>下部>上部。(3)每小穗均有3.7±0.56朵花、0.6±0.09粒种子,小穗基部的结实率较高。大赖草结实率在年际和不同环境下波动较大,水分和温度是影响其结实格局的主要因素;小穗间及小穗内的资源分配符合资源竞争假说。大赖草花多果少的结实格局是适应荒漠资源贫瘠、干旱少雨气候条件的一种生殖保障。

Seasonal variation in carbon exchange and its ecological analysis over Leymus chinensis steppe in Inner Mongolia

Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were -7.4 and 5.4 g·m-2·d-1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were -12.8 and 5.8 g·m-2·d-1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m-2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m-2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200μmol·m-2·s-1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.

Effect of water stress on ecosystem photosynthesis and respiration of a Leymus chinensis steppe in Inner Mongolia

Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003-2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production (FGEP) and ecosystem respiration (Reco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting FGEP and Reco in 2003, whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004. Under wet conditions, Reco showed an exponentially increasing trend with temperature (Q10 = 2.0), but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress (Q10=1.6). Both heat and water stress can cause decrease in FGEP. The sea-sonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m-2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands.