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.

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.

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 of Leymus chinensis, analyzed 260 ramets samples using 12 primers and 60 polymorphic markers (reproducible RAPD bands). The results proved clonal 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 of L. chinensis in HPS habitat had lower genetic dissimilarity index than that in the HCS habitat.

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.

Role of endogenous hormones,glumes,endosperm and temperature on germination of Leymus chinensis(Poaceae)seeds during development

Aims Leymus chinensis is an original dominant plant in the Songnen grassland,and it has great value for restoration of severely degraded land.However,seeds are dormant,and low germination percentage is a problem for restoring L.chinensis grassland.The mechanism of seed dormancy is not been well understood.The primary aims of the present study were to investigate the dormancy mechanism of L.chinensis seeds(caryopses)with reference to the role of embryo-covering layers,endogenous hormones and temperature.Methods Changes in concentration of the endogenous hormones GA3,indoleacetic acid(IAA),zeatin riboside(ZR)and abscisic acid(ABA)in L.chinensis seeds fromanthesis to maturity weremeasured by the enzymelinked immunosorbent assay method.Germination at different stages of maturity were tested at 16/28
C,5/28
C and 5/35
C for intact seeds with glumes(control),intact seeds with glumes removed(nakedwhole seeds)and intact seeds with glumes and one-half of the endosperm removed(naked-half seeds).Important Findings Of the four endogenous hormones monitored,only the concentration of ZR differed significantly between the beginning and the end of seed development(increased);the GA3/ABA ratio also did not differ.Rank of germination percentage of control at the three temperature regimens was 5/28
C>16/28
C>5/35
C.Germination percentage of the naked-half seeds reached 100%under the three temperature regimens.We concluded that dormancy of L.chinensis seeds is not mainly controlled by endogenous hormones.Germination temperature,mechanical resistance of glumes and inhibition of endosperm are the main factors controlling dormancy and germination of L.chinensis seeds.

Characteristics of phytoliths in Leymus chinensis from different habitats on the Songnen Plain in Northeast China and their environmental implications

The characteristics of phytoliths in Leymus chinensis leaves from five different pH-value habitats from Songnen Plain in China were analyzed to reveal their environmental implications and possible use for quantitative reconstruction of the paleoenvironment. The phytoliths in leaves of L. chinensis from the five habitats showed a non-linear correlation with soil pH. The main types of phytoliths from the different habitats were exactly the same, including silicified stomata, hat-shaped, lanceolate, elongated, multilateral-plate, and tooth-shaped. However, there were significant differences in the contents of each shape of phytoliths among the five habitats. The amount and the volume of weakly tooth-shaped, lanceolate phytoliths and silicified stomata increased with increased pH, while the total amount of phytoliths was reduced. In addition, there were different types of phytoliths in the L. chinensis leaves from the five habitats of different pH, suggesting that the types of phytoliths were controlled, at least in part, by soil pH. The changes of size and percentage of phytoliths were most remarkable at pH 10.15–10.18, indicating that this is the highest pH value that L. chinensis can tolerate.

Genetic Variation and Clonal Diversity of the Two Divergent Types of Clonal Populations of Leymus chinensis Tzvel on the Song Liao Steppe in the West of Northeastern China

The genetic variation and clonal diversity of two divergent types (grey-green and yellow-green) of clonal populations ofLeymus chinensis Tzvel at 14 loci were compared. Total gene diversity (HT) and the coefficient of genetic differentiation (GsT) were all higher for the yellow-green type (HT = 0.270; GsT = 0.186)than for the grey-green type (HT = 0.250; GsT = 0.157) of L. chinensis. Rare alleles usually occurred as heterozygotes rather than homozygotes and significant deviations from Hardy-Weinberg equilibrium were found only at a few loci. This indicated that these two types of populations were mainly out-crossing. Clonal diversity, evenness of clones, and mean clone size were not significantly different between the two types.We found that differences between the clone size and genetic variation of the yellow-green type of popula tions occurred with different climate and habitat population groups. However, for the grey-green type of populations, these genetic variations decreased under conditions of different climate and habitat popula tion groups.

Environmental conditions and genetic differentiation:what drives the divergence of coexisting Leymus chinensis ecotypes in a large-scale longitudinal gradient?

Aims The two coexisting Leymus chinensis ecotypes exhibit remarkable divergences in adaptive strategies under drought and salinity in semi-humid meadows and semi-arid steppes.In order to detect the major genetic and environmental factors dominating the intraspecific phenotype variations and ecotype formation,the questions regarding the two distinct phenotypic forms(ecotypes)in L.chin-ensis were addressed:(i)did environments drive the L.chinensis ecotype formation?(ii)was there a molecular basis for the morphological divergence between the two ecotypes?(iii)which driving force dominated the intraspecies divergence,divergent natural selection,genetic drift or stabilizing selection?Methods We applied a series experiments on demographical,morphological and physiological traits of two Leymus chinensis ecotypes with gray green(GG)and yellow green(YG)leaf color in nine wild sites along a longitudinal gradient from 114°to 124°E in northeast China.The environmental data including mean annual precipitation,mean annual temperature,elevation and soil properties were collected.We compared the differences of morphological,physiological and genetic differentiations between the two ecotypes.Important FindingsThe GG type exhibited stronger fitness than YG type from the population densities,morphological traits(e.g.shoot height,leaf area,leaf and seed weights et al.),leaf mass per area(LMA)and physiological traits[relative water content(RWC),proline,soluble sugar contents].Most of above phenotypes(e.g.total shoot densities,spike length et al.)were significantly correlated with mean annual precipitation,mean annual temperature and soil water content(SWC),rarely a correlated with soil pH and soil nutrient.Transplanted populations showed convergence trend by their leaf chlorophyll contents and osmotic adjustments(proline and soluble sugar contents)in the greenhouse,but still exhibited their divergences between two ecotypes in the outdoor transplantation,suggesting that whether L.chinensis ecotype differentiated could be largely affected by the environmental conditions.Furthermore,by the comparison result of quantitative genetic variation(Q_(ST))values from phenotypes with theoretical neutral genetic differentiation(F_(ST)),differentiation in phenotypic traits greatly surpassed neutral predictions,implying that directional natural selection played a crucial role in L.chinen-sis ecotype differentiation.In addition,microsatellite analysis from Neighbor-joining tree and Bayesian assignment generated into two groups according to ecotypes,indicating molecular genetic differentiation also propelled the two ecotypes divergence.We conclude that L.chinensis population variations were driven by combing divergent natural selection(precipitation,temperature and SWCs)along the large-scale gradient and significantly intrinsic genetic differentiation.

CH_4 uptake flux of Leymus chinensis steppe during rapid growth season in Inner Mongolia,China

The influence of near ground atmosphere CH4 concentration, soil water content, soil Eh, plants, soil temperature, and pH on CH4 uptake flux of Leymus chinensis steppe during rapid growth season was studied using field in-situ measurement in Xilin River basin of Inner Mongolia, China. The results showed that CH4 uptake flux was positively correlated with near ground atmosphere CH4 concentration and soil Eh but negatively correlated with soil water content. Precipitation may decrease the CH4 flux by increasing the soil water content. The average fluxes of three treatments during the observation period were 1.52 (natural conditions, 1.51 (aboveground plants were excluded), and 2.00 mg m?2 d?1 (all plants were removed), respectively. The difference between the CH4 flux of natural condition treatment and that of removing aboveground plants treatment is small, whereas the flux of removing all plants treatment is larger than the other two treatments. This means that the contribution of aboveground plants to CH4 uptake flux is smaller than that of roots or roots-removing process. CH4 uptake flux is not sensitive to soil temperature and the narrow-ranged soil pH (6.36–7.86). The Leymus chinensis steppe acts as a sink for CH4, and thus more studies should be focused on its affecting factors and related mechanisms.

Construction and characterization of the transformation-competent artificial chromosome (TAC) libraries of Leymus multicaulis

Transformation-competent artificial chromosome system is able to clone and transfer genes efficiently in plants.In order to clone genes highly tolerant to barley yellow dwarf virus(BYDV),Aphids,drought and salt from Leymus multicaulis,the two TAC genomic libraries I and II were constructed in vector pYLTAC17 and pYLTAC747H/sacB,which contain about 165000 and 236000 recombinant clones sepa-rately.The genome coverage of the two libraries was totally estimated to be about 3―5 haploid genome equivalents,as size selection of genomic DNA fragments was approximately from 9 to 300 kb.Clones of the genomic libraries were collected as bulked pools each containing 500 clones or so,stored in twelve 96-deep-well plates and then were gridding in triplicate onto a high-density colony hybridization filter with a 3×3 pattern using a GeneTAC?G3 arraying robot after being transferred manually into three 384-well plates.Meanwhile 2501 and 2890 clones of Library in pYLTAC17 and in pYLTAC747H/sacB were stored individually in fourteen 384-well plates and then were automatically gridding in duplicate onto a high-density colony hybridization filter with a 6×6 pattern after a replication of plates.Nineteen positive clones were detected by using the probe glutahione reductase gene of L.multicaulis.TAC libraries constructed here can be used to isolate genomic clones containing target genes,and to carry out genome walking for positional cloning.Once the target TAC clones were isolated,they could be immediately transferred into plant genomes with the Agrobacterium system.

不同盐分对羊草种子萌发和根芽生长的影响

采用水培发芽方法研究了4种中性盐(NaCl、KCl、Na2SO4、K2SO4)和4种碱性盐(NaHCO3、KHCO3、Na2CO3、K2CO3)及其不同浓度培养对羊草种子萌发和根芽生长的影响。结果表明,钠盐对羊草种子萌发和根芽生长的抑制作用明显大于钾盐,碱性盐大于中性盐,二价盐大于一价盐。Na2CO3和NaHCO3浓度≥20mmol·L-1,Na2SO4、K2CO3和KHCO3浓度≥50mmol·L-1,NaCl、KCl和K2SO4浓度≥100mmol·L-1时对羊草种子萌发达到显著抑制水平。羊草根系对盐分的抑制作用具有敏感性,除5mmol·L-1的NaCl、KCl和NaHCO3外,各种盐分浓度对根长均达到显著抑制水平。相同摩尔浓度(以50mmol·L-1为例)下,羊草种子芽长在NaCl、KCl、Na2SO4、K2SO4、NaHCO3、KHCO3、Na2CO3和K2CO3胁迫下分别比对照下降了26%、5.5%、50.7%、11%、38.7%、37.1%、79%和83.9%。高Na+含量和高pH是抑制羊草种子萌发和根芽生长的主要原因。

羊草群落物种多样性与群落特征相关性分析

以呼伦贝尔草甸草原自然保护区作为研究样地,研究不同干扰下羊草(Leymus chinensis)群落物种多样性与群落特征的相关关系。结果表明,刈割和放牧两种干扰方式对羊草群落物种多样性和地上生物量的变化影响明显。刈割区的地上生物量明显高于放牧区;生物多样性的总体趋势是刈割﹥放牧。在两种干扰方式下,群落地上生物量均与Shannon-Wiener多样性指数和Simpson多样性指数呈负相关关系。在刈割干扰下,群落地上生物量与Pielou均匀度指数呈正相关关系,而在放牧干扰下则相反。

施肥对羊草分蘖及养分的影响

为了促进羊草[Leymus chinensis(Trin.) Tzvel.]地下芽库的发生,促进分蘖量增加,提高产草量,对羊草在3种移栽方式不同肥料处理下的形态指标、养分吸收及品质进行了分析研究。结果显示,施肥处理有利于羊草的营养生长。同一移栽方式下,施肥T2处理(N 120 kg/hm^2,P_2O_5120 kg/hm^2,K_2O 60 kg/hm^2)的羊草生长、氮磷钾的吸收、粗蛋白质含量、粗脂肪含量、灰分含量及产量均高于其他施肥处理;粗纤维、无氮浸出物含量低于其他处理;3种移栽方式中以大田育苗移栽的效果较好。适宜的氮磷钾配比和栽培种植方式能够促进羊草的分蘖及提高品质和产量。

羊草功能性状对放牧强度的响应

[目的]探讨呼伦贝尔草原中优势植物功能性状对放牧强度的响应机制。[方法]以内蒙古呼伦贝尔典型草原为研究对象,采用方差分析方法比较不同放牧强度下羊草(Leymus chinensis)12个性状指标的变化。[结果]放牧强度对羊草叶片氮含量、叶片磷含量、叶面积、比叶面积、叶片含水量、叶片干物质含量、叶片厚度、归一化植被指数、叶绿素相对含量及单株重均有显著影响,对光化学反射指数和株高无显著影响。随着放牧强度的增加,叶片氮含量显著降低;轻度放牧的叶片磷含量显著高于中度放牧;轻度放牧的叶面积、比叶面积、叶片含水量、叶片干物质含量和归一化植被指数与中度放牧、重度放牧之间均呈显著差异;中度放牧的叶片厚度和叶绿素相对含量显著高于轻度放牧和重度放牧;轻度放牧和中度放牧的单株重显著高于重度放牧。植物通过对性状的权衡改变其资源利用策略,对不同的放牧强度作出响应。[结论]该研究可为草原生态系统的保护、恢复及重建提供科学依据。

植被盖度和配置方式对土壤风蚀影响的风洞试验

土壤风蚀是中国北方严重的环境问题,植被能够有效控制土壤风蚀。为给土壤风蚀防治方案设计提供依据,在毛乌素沙地南缘以中科1号羊草(Leymus chinensis)为对象,通过野外风洞试验,研究植被盖度(10%、20%、30%和40%)和配置方式(一行一带式、两行一带式、交叉分布式)对风沙流结构和输沙率的影响。结果表明:(1)各层输沙强度随风速增加而递增,随盖度增加而递减;输沙率与盖度符合指数函数关系。风沙流结构出现“象鼻效应”,风速和盖度的增加均使输沙强度峰值的高度层上移。(2)3种配置方式下输沙强度沿垂直高度的变化均呈指数函数分布,两行一带和交叉分布的阻沙效果大于一行一带。(3)从固沙效能最佳和经济效益角度考虑,中科1号羊草应种植盖度约为30%,风速较大的区域使用交叉分布的配置方式。