Songnen Grassland Research Articles

松嫩草原不同演替阶段大型土壤动物功能类群特征

PDF HTML阅读 XML下载 导出引用 引用提醒 松嫩草原不同演替阶段大型土壤动物功能类群特征 DOI: 10.5846/stxb201306011266 作者: 作者单位: 东北师范大学地理科学学院,东北师范大学,东北师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（40871120，41171207） Soil macro-faunal guild characteristics at different successional stages in the Songnen grassland of China Author: Affiliation: School of Geographical Science,Northeast Normal University,School of Geographical Science,Northeast Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大型土壤动物处于整个土壤食物网的最顶端，其各功能类群控制着其他动物所需资源的有效性，是土壤生态系统的重要组成部分。为了查明松嫩草原大型土壤动物的功能类群特征，在2006年5-10月期间，逐月对松嫩草原羊草、羊草+虎尾草、虎尾草、碱茅、碱蓬和光碱斑6个演替阶段大型土壤动物的功能类群组成、结构、多样性等特征进行研究。依据其食性将该区土壤动物划分为杂食性、植食性、捕食性和腐食性4个功能类群其中，杂食性土壤动物个体密度所占比例最多为39.16%，植食性土壤动物的类群数所占比例最多为50.00%，腐食性土壤动物个体密度和类群数所占比例均最小，分别为8.09%和12.82%。各功能类群土壤动物个体密度和类群数的相关性不显著（P>0.05）。从水平结构来看，总体上各功能类群土壤动物在羊草群落和羊草+虎尾草群落个体密度和类群数较多，在无植被的光碱斑生境土壤动物的个体密度和类群数较少，植食性土壤动物的个体密度和类群数、杂食性土壤动物个体密度、腐食性土壤动物个体密度和类群数随着群落演替发生显著的变化（P<0.01）。植食性和腐食性土壤动物个体密度和类群数相关性显著（P<0.05）。垂直结构上，0-10 cm土层和20-30 cm土层除捕食性土壤动物个体密度以外，其它各功能类群土壤动物个体密度随着群落演替发生显著的变化（P<0.05或P<0.01）；10-20 cm土层，除腐食性土壤动物个体密度以外，其它各功能类群土壤动物个体密度随着群落演替发生显著的变化（P<0.05或P<0.01）。0-10 cm土层，植食性和杂食性土壤动物个体密度（P<0.05）相关性显著；10-20 cm土层，植食性和腐食性土壤动物个体密度（P<0.05）相关性显著。不同演替阶段对各功能类群土壤动物的多样性影响程度有所不同。4种功能类群土壤动物在羊草群落和光碱斑之间相似性指数较低，个体数量组成在演替初期的羊草群落和演替后期的光碱斑差异比较大。以上研究结果表明，松嫩草原不同退化演替阶段能够降低大型土壤动物功能类群组成和结构复杂性。 Abstract:Soil macro-fauna play an important role in soil ecosystems. They are at the top of the entire food web and regulate the availability of resources for other animals by changing biotic or abiotic materials. Knowledge of soil macro-faunal guild characteristics is crucial to understanding soil food webs. On the Songnen grassland, located on the northeastern grassland area of China, above ground succession of vegetation can markedly change with soil fauna. The effect of this degradation on the structure and diversity of the below ground soil faunal guild is unknown. In the present study, an investigation of the composition, structure and diversity of the soil macro-faunal guild was conducted in the Songnen grassland with six successional stages (Leymus chinensis community; Leymus chinensis+Chloris virgata community, Chloris virgata community, Puccinellia distans community, Suaeda glauca community and Bare alkali-saline patch). Six observations were conducted from May to October 2005 and four samples in a 50 cm × 50 cm area were investigated in six successional stages each time. Hand collection methods were used to collect soil macro-fauna with soil macro-faunal guilds subdivided based on their feeding habits. The results showed that macro-fauna were divided into four guilds based on their feeding habits, i.e., omnivore, herbivore, predator and detritivore. Omnivore and herbivore were the predominant guilds, accounting for 39.16% and 50.00% in term of the total individual and group numbers, respectively. Detritivore occurrence was rare. The correlations between individual and group numbers were not significant (P>0.05). In general, the Leymus chinensis community and Leymus chinensis+Chloris virgata communities had the largest number of individual and group number among the four guilds, whereas the bare alkali-saline patch was rare. Significant successional stage effects were recorded in individual and group numbers of herbivore, individual numbers of omnivore and individual and group numbers of detritivore (P<0.01). There were positive correlations between individual and group numbers of herbivore and detritivore at different successional stages (P<0.05). In the 0-10 cm and 20-30 cm depth, significant successional stage effects were recorded in the individual numbers of guilds, except predator (P<0.05 or P<0.01). In the 10-20 cm depth, significant successional stage effects were recorded in individual numbers of guilds, except detritivore (P<0.05 or P<0.01), and there were positive correlations between individual numbers of herbivore and detritivore at different successional stages (P<0.05). In the 0-10 cm depth, there were positive correlations between individual numbers of herbivore and omnivore at different successional stages (P<0.05), whereas, in the 20-30 cm depth, there were negative correlations between the individual numbers of the four guilds at different successional stages (P>0.05). The results of the different guilds diversity analysis showed successional stages had different influences on diversity. Significant successional stage effects were recorded in the Margalef index (D) of herbivore (P<0.01); the Shannon-Wiener index (H') of omnivore, predator and detritivore (P<0.01); the Simpson index (C) of omnivore and predator (P<0.01 or P<0.05); and the Pielou index (E) of omnivore and predator (P<0.01 or P<0.05). The similarity results showed that the similarities of guilds between the Leymus chinensis and bare alkali-saline patch are lower than the other successional stages. These results suggest that different degenerative succession stages of Songnen grassland can significantly reduce taxonomic diversity and structural complexity within guilds of soil macro-fauna. 参考文献 相似文献 引证文献

Species abundance-Cdistribution relationship and its interpretation in plant communities on the Songnen grasslands, China

* Key Laboratory of Vegetation Ecology, Ministry of Education, Institute of Grassland Science, Northeast Normal Univer- sity, Changchun 130024 Abstract: The species abundance-distribution relationship (SAD) is a key issue in biodiversity science, yet there is no consensus about the mechanism that shape the SAD. The two most widely-recognized explana- tions are Brown's niche breadth hypothesis and metapopulation dynamics theory. To test these two hypothe- ses on the Songnen grasslands, we investigated plant species growth-form composition and interpatch dis- tance in Leymus chinensis-forb community patches in 2007 and 2008. We employed a growth-form adaption index (GAI), a measure of species adaptation, as a surrogate for species niche breadth and employed shortest distance to nearest patch to indicate the dispersal and colonization process of plant species. Two-year data showed that a species' local abundance was positively correlated with this species' regional distribution. Fur- thermore, the SAD showed no obvious variation among years. Both abundance and distribution of a species were closely correlated with plant growth-form; species with higher abundance and wider distributions were mainly comprised of rhizomatous root, erect grass-like stem, or erect dicot stem growth forms. By contrast, species with lower abundance and narrow distributions were mainly comprised of basal rosette stem or bushy root growth forms. GAI was both positively and linearly correlated with abundance and distribution of a spe- cies. A few species were distributed widely, whereas most species were distributed more narrowly. This result directly supports the niche breadth hypothesis. Shortest distance to nearest patch exhibited a negative pow- er-law correlation with both abundance and distribution of a species, whereas no correlation was detected between species composition similarity index and distance of patch pairs, results which failed to support the metapopulation dynamic theory. We argue that dispersal processes may be an important potential mechanism

Response of bacterial community to simulated nitrogen deposition in soils and a unique relationship between plant species and soil bacteria in the Songnen grassland in Northeastern China

Nitrogen (N) deposition greatly affects the above ground biological composition of grasslands and soil properties. However, its influence on the relationship among soil, plant and bacterial communities remain controversy. We calculated Shannon-wiener index to measure the soil bacterial diversity based on denaturing gradient gel electrophoresis, and investigate the roles of vegetation and soil properties on the soil bacterial community under N addition. A three-year simulated N deposition experiment was conducted in a forbs community dominated by Leymus chinensis (Trin.) Tzvel. and Artemisia scoparia Wald. Et. Kit. N was added at five levels (0, 23, 46, 69, 92 kg ha -1 yr -1 ). Our results showed that N addition increased the soil microbial biomass carbon (SMBC) and soil bacterial diversity. Moderate N (23, 46, 69 kg ha -1 yr -1 ) addition increased the soil bacterial diversity, whereas excess N (92 kg ha -1 yr -1 ) addition inhibited it. The SMBC and soil bacterial diversity were related to richness of plant functional groups. In particular, SMBC had positive correlation with biomass of annuals and biennials, suggesting that the effects of the plant community on the soil bacteria could be explained by a relationship between the soil bacterial community and a subset of plant species rather than all species.

Positive Plant Diversity-Soil Stability Relationships are Mediated through Roots in the Songnen Grassland: Chronosequence Evidence

Living plant diversity (excluding the litter issue) may affect below-ground properties and processes, which is critical to obtaining an integrated biodiversity-ecosystem functioning theory. However, related patterns and underlying mechanisms have rarely been examined, especially lacking long-term evidence. We conducted a factorial crossed sample survey to examine the effects of plant diversity on soil stability over succession based on space-for-time substitution in the Songnen Steppes, North-Eastern China. The results indicate that, under natural colonizing conditions, species-poor systems achieved lower soil stability than species-rich systems, regardless of successional stage. However, soil stability was significantly regulated by plant species richness (number), composition (identity), density (abundance), and functional roles. Our results confirm that a long-term positive plant diversity-soil stability relationship exists in steppe succession. In particular, this enhanced effect of biodiversity on soil stability may operate via diversifying plant root traits. Our results may underpin an integrated biodiversity-ecosystem functioning theory, and improve human use and conservation management of natural resources at an integrated ecosystem level.

Response of phytoliths in Phragmites communis to elevated CO2 concentration in Songnen Grassland, China

Research on response of phytolith assembles in Phragmites communis to two treatments is a new idea for studying global change. As P. communis is an important dominant species in the Songnen Grassland and widely distributed in sampling area and produce abundant phytoliths. P. communis was selected as the material and target to find a link between the phytolith variety and elevated CO2 concentration. An OTC (open top chamber) was used to elevate the concentration of CO2, and the phytoliths in P. communis were investigated to identify the effects. The phytolith record reveals the elevation of CO2 concentration can change the ratio of different types and size of phytoliths significantly. The number of silicified stomata and Saddle decreased while hair cell increased after elevated CO2 treatment. Moreover, after the measurement using a particle-size analyzer and under a microscope, phytoliths grow smaller after elevated CO2 treatment. Research on relationship between phytolith and CO2 concentration renews the traditional understanding. This study introduces a different way to study the influence of global change, and the use of common reed could provide basic data for other studies to make regional contrast with the same species.

Effects of Summer Nocturnal Warming on Biomass Production of Leymus chinensis in the Songnen Grassland of China: From Bud Bank and Photosynthetic Compensation

AbstractNocturnal warming has various effects on plant biomass production. To understand how biomass production of the dominant grassland species Leymus chinensis responds to summer nocturnal warming in the eastern temperate Eurasian steppes, we simulated summer nocturnal warming (+4 °C) using a phytotron system for 100 days operated based on the variation of diurnal temperatures over the past 12 years in the Songnen Grasslands. Our results show summer nocturnal warming significantly increased above‐ground biomass production of parent and daughter shoots as well as increased below‐ground root and rhizome biomass production; rhizome biomass increased faster than root biomass leading to an increase in the rhizome biomass to root biomass ratio. Nocturnal warming slightly increased the number of daughter shoots per plant, and significantly increased the number of buds in the below‐ground bud bank and the number and length of rhizomes per plant. Also, the dark respiratory and net photosynthetic rates, Jmax, the rate of triosephosphate utilization and chlorophyll fluorescence parameters (ΦPSII and qP) were significantly higher under nocturnal warming conditions. These findings show that nocturnal warming in this ecosystem improves individual biomass accumulation due to photosynthetic compensation, and may enhance the population density and productivity of L. chinensis by increasing bud number in the below‐ground bud bank during the early stage of ecological succession for grasslands dominated by L. chinensis.

Effects of abscisic acid and brassinolide on photosynthetic characteristics of Leymus chinensis from Songnen Plain grassland in Northeast China.

BackgroundIt has been well demonstrated that plant growth regulators have important functions in multiple physiological processes. ABA and BR play crucial roles in response of crops to stresses. Photosynthetic capacity of Leymus. chinensis treated by various concentrations of ABA and BR in combination was determined. Further more, the mechanisms of ABA and BR treatments and potential for recovery of saline-alkali grasslands were discussed.ResultsAbscisic acid (ABA) and brassinolide (BR) affected leaf gas exchange, growth and biomass of L. chinensis. The application of ABA and BR mixtures, especially that of 0.01 mM ABA and 2 × 10-4 mM BR, increased the net photosynthetic rate, stomatal conductance, water use efficiency, the maximum net photosynthetic rate, light-saturated rate, leaf respiration rate, the maximum RUBP carboxylation rate, the maximum electron transport rate, the maximum triose-phosphate utilization, carboxylation efficiency and the quantum efficiency of PSII and subsequently enhanced density, height and biomass in L. chinensis. We also observed reduction in the light compensation and saturation points following the application of ABA and BR treatments.ConclusionsWe concluded that proper use of plant growth regulators can enhance the plant growth and productivity on the Songnen grassland, which is particularly important for the improvement of saline – alkaline grassland and the yield of grazing lands.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-42) contains supplementary material, which is available to authorized users.

Carbon stocks and storage potential as affected by vegetation in the Songnen grassland of northeast China

Soil organic carbon storage in grasslands reflects a balance between carbon inputs and the rate of its mineralization. The ability of different plant communities to capture, store and release carbon could lead to different carbon storage in grassland soil. In this study, the plant biomass and soil organic carbon (SOC) stocks of seven communities were investigated. SOC concentration differed significantly among the seven communities, varying from 4.08 g C kg−1 for Suaeda glauca community to 9.18 g C kg−1 for Echinochloa phyllopogon community. Over the entire profile to 100 cm, the SOC storage of E. phyllopogon community was highest with the value of 10.09 kg C m−2, while the storage of S. glauca community was lowest with the value of 5.63 kg C m−2. Over 30% of organic carbon was found in the top soils (0–20 cm). Compared to the Leymus chinensis community, halophytic communities have a great potential to store carbon in the Songnen grassland, with a mean value of 2.95 kg C m−2 in the 0–100 cm soil layer. Vegetation has a great effect on the carbon storage of grassland.

Effect of Aboveground Biomass, Temperature and Moisture on Soil Microorganism of Alkali-Saline Grassland

The information on the soil microorganism of alkali-saline grassland was limited. To demonstrate the effect of aboveground biomass, temperature and moisture on soil microorganism of alkali-saline grassland, the soil microbial counts, biomass carbon, diversity index, aboveground biomass, soil temperature and moisture were measured and analyzed in Songnen grassland. The results showed that aboveground biomass, soil temperature and moisture had significant effect (P0.05). To sum up, the change of the soil microbial counts and biomass carbon were related primarily by plant growth.

松嫩草地66种草本植物叶片性状特征

植物叶片功能性状及其相互关系越来越受到关注。以松嫩草地66种草本植物为研究对象,测量叶片干物质含量、比叶面积、叶片厚度、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量,检验性状间的相互关系,比较不同功能群(多年生根茎禾草,多年生丛生禾草,多年生杂类草,1年生或2年生草本)间性状的差异性。结果表明,叶片厚度变异系数最大,比叶面积、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量之间存在显著的正相关关系;叶片干物质含量与叶片磷含量没有显著的相关关系,与其它叶片性状呈显著的负相关关系;叶片厚度只与叶片干物质含量和比叶面积呈显著的负相关关系,与其它叶片性状不相关。叶片干物质含量、比叶面积、叶片厚度、叶片氮、磷含量在4个功能群间差异显著,叶绿素含量和类胡萝卜素含量在各个功能群间差异不显著;多年生根茎禾草和多年生丛生禾草叶片的7个性状差异不显著;多年生根茎禾草和多年生丛生禾草的叶片干物质含量高于多年生杂类草和1年生或2年生草本,其它性状小于这两个功能群。;Leaf traits such as specific leaf area (SLA) and leaf nitrogen concentration (LNC) play important roles in plant functioning and are affected strongly by ecosystem properties and local environmental conditions. Quantifying the relationships between leaf traits and traits differences among plant functional groups has received increasing attentions in plant functional ecology over the past two decades.<br>We measured in total 7 leaf traits: SLA, LNC, leaf dry matter content (LDMC), leaf thickness (LT), leaf phosphorus concentration (LPC), leaf chlorophyll (a+b) content (Chl) and leaf carotenoid content (Cd) among 66 herbaceous species. And we analyzed the correlation between leaf traits and the traits difference among perennial rhizome grass (PR), perennial bunchgrasses (PB), perennial forbs (PF) and annuals/biannuals (AB) in Songnen grassland, Northeast China.<br>The results showed that LT variation (59.1%) was the highest among the 7 leaf traits measured. Pearson correlation showed that SLA, LNC, LPC, Chl and Cd were positively correlated with each other significantly. There was no significant correlation between LDMC and LPC, however, LDMC was negatively correlated with all other leaf traits significantly. LT was only negatively correlated to LDMC and SLA significantly, but not with others. LDMC, SLA, LT, LNC, LPC were significantly different among the 4 plant functional groups analyzed by one-way ANOVA (<em>P</em><0.05). There was no difference between Chl and Cd. PR and PB had no difference among the 7 leaf traits. The LDMC of PR and PB were significantly higher than PF and AB. SLA, LNC, LPC of PR and PB were lower than PF and AB.

Comparison of seed germination and early seedling growth responses to salinity and temperature of the halophyte Chloris virgata and the glycophyte Digitaria sanguinalis

AbstractSalinization is an increasing land degradation issue in the Songnen Grassland of northern China. Effects of salinity and temperature on seed germination and seedling growth of Chloris virgata, a promising halophyte, and Digitaria sanguinalis, a widespread glycophyte were examined in six soil solutions (0, 50, 100, 150, 200 and 250 mm NaCl) and four temperatures (15, 20, 25 and 30°C). Germination percentages and rates of both species decreased significantly at higher salinities, but ungerminated seeds can recover germination upon supply of distilled water. Radicle length, seedling height and the total dry weight of both species generally decreased in a concentration‐dependent manner at 20°C and above as the salinity increased. However, at 15°C, the salt‐treated seedlings showed decreases with a similar magnitude for different salinities. Low salinities seem to stimulate germination and seedling growth of C. virgata compared with the control treatment. Both species were more sensitive to salinity during the seedling stage than the germination stage. Digitaria sanguinalis from the saline Songnen Grassland region seems to develop a halophyte‐like adaptive strategy to some extent. However, C. virgata may still dominate most hyperhaline areas due to its higher salt tolerance.

Water- and Plant-Mediated Responses of Ecosystem Carbon Fluxes to Warming and Nitrogen Addition on the Songnen Grassland in Northeast China

BackgroundUnderstanding how grasslands are affected by a long-term increase in temperature is crucial to predict the future impact of global climate change on terrestrial ecosystems. Additionally, it is not clear how the effects of global warming on grassland productivity are going to be altered by increased N deposition and N addition.Methodology/Principal FindingsIn-situ canopy CO2 exchange rates were measured in a meadow steppe subjected to 4-year warming and nitrogen addition treatments. Warming treatment reduced net ecosystem CO2 exchange (NEE) and increased ecosystem respiration (ER); but had no significant impacts on gross ecosystem productivity (GEP). N addition increased NEE, ER and GEP. However, there were no significant interactions between N addition and warming. The variation of NEE during the four experimental years was correlated with soil water content, particularly during early spring, suggesting that water availability is a primary driver of carbon fluxes in the studied semi-arid grassland.Conclusion/SignificanceEcosystem carbon fluxes in grassland ecosystems are sensitive to warming and N addition. In the studied water-limited grassland, both warming and N addition influence ecosystem carbon fluxes by affecting water availability, which is the primary driver in many arid and semiarid ecosystems. It remains unknown to what extent the long-term N addition would affect the turn-over of soil organic matter and the C sink size of this grassland.

Leaf nitrogen and phosphorus stoichiometry in 80 herbaceous plant species of Songnen grassland in Northeast China

Aims Leaf nitrogen (N) and phosphorus (P) and N : P stoichiometry have been studied intensively in different regions in China. Songnen grassland is a natural region. Its dominant vegetation is meadow, which is determined by soil properties, and its flora is complex. Our objective was to find the stoichiometric patterns for this region. Methods Leaf samples of 80 herbaceous species were collected in Songnen grassland in August 2008. We de- termined leaf N, P, and N : P on both a mass and an area basis and tested the differences according to plant life forms and functional groups. Important findings Leaf N and P concentrations were (24.2 ± 0.96) and (2.0 ± 0.10) mg·g -1 on a mass basis and (13.0 ± 0.54) and (1.0 ± 0.05) mg·cm -2 on an area basis, respectively. N : P was (13.0 ± 0.39). Plant growth was limited by N in Songnen grassland. The concentration of leaf N and P and coefficient of variation were higher in annual plants than in other life forms on a mass basis, and there were no significant differences of leaf N concen- tration on an area basis and N : P between different life forms. Leaf N concentrations both on mass and area bases and N : P of legumes were higher than in other functional groups. There was no significant difference in the leaf P concentrations on an area basis among different life forms or functional groups. Our findings indicate that appro- priately increasing the proportion of legume plants would improve both the yield and quality of primary produc-

松嫩草原虎尾草生境大型土壤动物动态特征

大型土壤动物是陆地生态系统中的重要组成部分，为探讨松嫩草原虎尾草生境大型土壤动物组成及多样性动态特征，于2006年5月、7月和9月进行了调查研究，共获得大型土壤动物427只，隶属2门4纲9目22科，优势类群共3类，为象甲科幼虫、步甲科和蜘蛛目，类群数与个体数在各月份间无显著差异。大型土壤动物在垂直分布上具有明显的表聚性，各层与各月间均存在显著差异。大型土壤动物的多样性指数随季节变化不大，其中9月份多样性指数、丰富度指数、优势度指数最大，7月份均匀性指数达到最大值。 Soil fauna play an important role in terrestrial ecosystems，in order to investigate the diversity of soil macrofauna in Chloris virgata habitat in Songnen grassland, investigations were conducted in the western of Jilin Province in May, July and September 2006. A total of 427 individuals, belonging to 2 phylas, 4 classes, 9 orders and 22 families, were obtained. There were no significant differences both in groups and individuals among 3 dominant groups, which were Curculionidae larvae, Carabidae and Araneida. Soil macrofauna was decreasing obviously with the depth of soil layers, and that there were significant differences among layers and months. The seasonal variations of the diversity indices of soil macrofauna were not significant. In these diversity indices, Shannon-Wiener diversity index, Margalef richness index, Simpson dominance index were highest in September, however Pielou evenness index was higher in July.

松嫩草原榆树疏林对不同干扰的响应

榆树疏林是中国东北松嫩草原沙地植被演替的顶极群落,其对维持物种多样性,保持水土,涵养水源等都发挥着重要的功能。过去20a间,榆树疏林在人为干扰(农耕和放牧)下,其群落结构和物种组成发生了巨大变化。在1983年和2004年,对松嫩草原不同人为干扰下榆树疏林群落结构和物种组成等进行调查,结果显示:农耕和放牧一方面使松嫩草原榆树疏林群落多物种消失、生物量和多样性显著下降、植被结构简单化;另一方面,也是导致建群种--家榆低矮化,灌木化的主要因素。;Elm (Ulmaceae) widely distributes in the temperate zone of northern Hemisphere, especially in Russia, England, America, Denmark etc. Depending on its drought tolerance, salinity adaptation and adaptation to various climates, elm (<em>Ulmus pumila</em>) contributes to the maintenance of savanna-like ligneous plant community in typical grassland region of the north China. This sparse elm community, generally provides with tree canopy covers less than 25% and average height of mature trees lower than 5 m, and appears a complex mosaic landscape as a whole. Elm woodlands are primarily located in the sandlands in Hunshandak, Kerqin and Ordos Plateau of Inner Mongolia, and in Songnen Plains of northeastern China. Elm woodlands offer wide expanses of grazing land for large herbivores. On the other hand, it can be utilized by agriculture cultivation. Some studies demonstrate that elm woodlands play important roles in decreasing soil erosion and stabilizing sand dune. At larger spatial scale, elm woodland is considered as a natural barrier to sandstorm in the eastern Asia. It greatly contributes to alleviating environmental deterioration and maintaining ecosystem stability. In the past two decades, most elm woodlands of the northern China have been over-utilized by grazing or cultivation. Such excessive utilization of elm woodland leads to the decrease in basal area and productivity, the scarcity of <em>U. pumila</em> juveniles, and the increase in species composition of community. This greatly weakens ecological protective functions of elm woodland. Some researchers assumed that the degradation of elm woodland is associated with drought climate, overgrazing and tree cutting. In order to anchor the essential reason that caused degradation of elm woodland, we carried out following experiments: in the Songnen grassland of China (40°30'- 48°05'N, 122°12'-126°20'E), we sampled an undisturbed <em>Ulmus </em>woodland in 1983, and we maintanenced that the <em>Ulmus</em> woodlands were seldom disturbed in past two decades. In 2004, we sampled five sites: the undisturbed site; two farming sites with 40% and 90% crop coverage; and two sites with light and heavy grazing as determined by distance to the nearest village (600 and 200 m, respectively). In each site, we sampled ten 4 m² plots, and species' names, number and aboveground biomass (measured as community productivity) were measured. Species diversity was calculated. We found that: 1) there were not significant species and productivity changes of elm woodland in 1983 and 2004, therefore we concluded that climate changes was not the main reason caused the degradation of elm woodland; 2) in the contrast with the undisturbed elm woodland, the plowing and grazing elm woodlands showed great differences in species composition and productivity. These leaded us to such conclusion that human activities, such as plowing and grazing, directly decreased the productivity and species diversity of elm woodland, and also simplified the structure of elm woodland. 3) Furthermore, high intensity of grazing caused the constructive specie (<em>U. pumila</em>) was thinner and shorter; therefore, elm represented much more shrub-like in grazing elm woodland. Finally, we concluded that human activities were the main and direct reason caused the degradation of elm woodland.

Effects of saline and alkaline stresses in varying temperature regimes on seed germination of Leymus chinensis from the Songnen Grassland of China

AbstractLeymus chinensis is a dominant and most promising grass species in the Songnen Grassland of Northern China. Experiments were conducted to determine the effect of temperature, salinity, alkalinity and their interactions on seed germination. Seeds were germinated at four alternating temperatures (10–20, 15–25, 20–30 and 25–35°C), with saline stress (9:1 molar ratio of NaCl:Na2SO4) and alkaline stress (9:1 molar ratio of Na2CO3:NaHCO3). Germination percentage and rate were inhibited by either an increase or decrease in temperature from the optimal temperature range of 20–30°C, and were also inhibited by an increase in salinity and alkalinity at all temperatures. The inhibitory effects of high salinity on germination were greater at 25–35°C, but seeds were subjected to more stress even though the alkalinity was low under this temperature. Recovery percentage was highest at 400 mm salinity at 20–30°C, but only at 100 mm alkalinity, and 25–35°C also resulted in lower recovery percentage under both stresses. Results suggest that saline stress and alkaline stress have different impacts on seed germination and that saline‐alkaline tolerance of L. chinensis seeds is affected by the interactions of temperature and salinity‐alkalinity. Early July sowing in the field is recommended when temperature is optimal and salinity‐alkalinity concentrations are reduced by the high rainfall.

Response of phytoliths in Leymus chinensis to the simulation of elevated global CO2 concentrations in Songnen Grassland, China

Measuring the response of terrestrial ecosystems to elevated CO2 concentrations is very important for understanding the effects of global change. In this study, OTC (open top chambers) were used to simulate elevated CO2 concentrations in the Songnen Grassland. As well, phytoliths in Leymus chinensis were extracted to study the relationships between phytoliths and CO2 concentration. The results show the rondel is abundant in Leymus chinensis, while the trapeziform polylobate is rare. When phytolith production is increased, the rondel phytoliths grow bigger and the proportions of the different phytolith types changes under high CO2 concentration. These types include elongate hollow, acicular hair cell, square and laminate and are only observed in samples grown under high CO2 concentrations. All this evidence demonstrates that phytoliths in Leymus chinensis are sensitive to CO2 concentration, and indicate that phytolith analysis may have potential use in the study of global change, identifying different ecotypes of Leymus chinensis and for the reconstruction of paleoatmospheric CO2 concentrations.

Vegetation restoration of secondary bare saline‐alkali patches in the Songnen plain, China

AbstractQuestions: What factors limit vegetation restoration of secondary bare saline‐alkaline patches (BSAP) in the Songnen grassland of northeast China? Is there any adaptive approach to promote revegetation in the shortest time possible and at a low cost?Location: Northeast China.Methods: Considering the climate, soil saline‐alkalization and available seed sources, a new approach was adopted to restore vegetation in BSAP, which were formed by the degradation of typical Leymus chinensis grasslands owing to long‐term overgrazing. The experimental treatments included no treatment (CK), fencing (F), fencing+inserting cornstalks (FS), fencing+inserting cornstalks+sowing L. chinensis (FSL) and fencing+inserting cornstalks+sowing Puccinellia chinampoensis (FSP). The assumptions behind inserting cornstalks were not only that they would create safe sites for initial revegetation but also that they would enhance seed input by trapping and containing the seeds from seed movement on the BSAP surface.Results: Seed bank shortage was an important factor limiting initial revegetation in BSAP; seed movement on the BSAP surface could provide the necessary seed source if it were contained by effective measures. Vegetation at the sites FS, FSL and FSP was restored well in terms of the above‐ground biomass and coverage. Inserted cornstalks acted as safe sites that enhanced the plant survival rate in BSAP; they also enhanced the ability to contain seed movement, thus providing a seed source for initial revegetation. Along with initial revegetation, tussocks around cornstalks can provide better safe sites, which in turn can accelerate subsequent vegetation restoration in BSAP.Conclusions: The approach entails the strategic use of diverse seed sources and the construction of safe sites with agricultural byproducts (cornstalks); therefore, it is a low‐cost method and can be used on a widespread scale. The results provide vigorous support in favor of vegetation restoration in BSAP and severely degraded grasslands in the region. In practice, this approach can be used in degraded ecosystems with compacted soil surfaces (including arid and salt‐affected soils) to promote revegetation in various regions.

Changes in photosynthetic and growth characteristics of Leymus chinensis community along the retrogression on the Songnen grassland in northeastern China

Net photosynthetic rate, stomatal conductance, ratio of sub-stomatal to atmospheric CO2 concentration, transpiration rate, and water use efficiency changed significantly and assimilation capacity dropped continuously along the salinization and alkalinization process in the afternoon. Assimilation capacity of L. chinensis leaf correlated negatively with the degree of salinization and alkalinization. The photosynthetic characteristics of L. chinensis determined its community formation. By changing the ratio of chlorophyll a/b in leaves and accumulating soluble saccharides in rhizome, L. chinensis could adapt to the saline-alkali condition.

Seed movement of bare alkali-saline patches and their potential role in the ecological restoration in Songnen grassland, China

The dynamics of soil seed banks and seed movement was investigated in three bare alkali-saline patches in Songnen grassland, Northeast China, for exploring their potential role in the vegetation restoration of bare alkali-saline patches. The results showed that the seed banks and the seed movement in these patches were very similar to each other, and to some extent the seed movement was related to patch-side vegetation there. Seed movement across the soil surface of these bare alkali-saline patches was abundant and dominated by the seeds of pioneer species, such asChloris virgata andSuaeda corniculata, which accounted for over 96% of these trapped seeds. In the contrast, soil seed banks of bare patches were extremely small, in different seasons, especially in May and June, even no any seed have been found, mainly due to lowest retaining capacity of surface soil to those abundant seed movement. Both soil seed banks and seed, movement showed seasonal variation, and usually reached the maximum in October. Soil seed banks of bare alkali-saline patches, which were extremely small and difficult to recruit naturally, may inhibit speed of vegetation restoration. It is suggested that seed movement would be the potential seed source and play a potentially important role in the process of vegetation restoration of bare alkali-saline patches by enhancing the soil retaining capacity to seed movement.