Distribution pattern of Caragana species under the influence of climate gradient in the Inner Mongolia region, China

There is a strong climate gradient in the Inner Mongolia region, China, with solar radiation and air temperature increasing but precipitation decreasing gradually from the northeast to the southwest. Sixteen Cara- gana species exist in the Inner Mongolia region. These Caragana species exhibit a distribution pattern across moisture zones and form a geographical replacement series. In order to examine the mechanisms responsible for Caragana species distribution pattern, we selected 12 Caragana species that exhibit a distinct distribution pattern across multiple moisture zones in the Inner Mongolia region, and determined the relationships between the leaf ecological and physiological traits of these Caragana species and the aridity index and solar radiation. Along with the climatic drought gradient and the solar radiation intensification from the northeast to the southwest, leaf eco- logical characteristics of Caragana species changed drastically, i.e. the leaf shape gradually turned from flat into tegular or tubbish; the leaf hair became denser, longer and lighter in color; the leaf area, leaf biomass and specific leaf area （SLA） decreased significantly; the leaf thickness and the ratio of leaf thickness to leaf area increased sig- nificantly; and the leaf chlorophyll content decreased significantly. As the climatic drought stress increased, osmotic potentials of the main osmotic adjustment substances and the cytoplasmic ion concentration of Caragana species increased significantly. Meanwhile, the total and free water contents and water potential of leaves decreased sig- nificantly; the ratio of bound to free water increased significantly; the stomatal conductance and transpiration rate reduced significantly; and the water use efficiency （WUE） increased significantly. In addition, with the intensification of climatic drought stress, peroxidase （POD） and superoxide dismutase （SOD） activities in leaves increased significantly. As a result, the malondialdehyde （MDA） content increased while the oxygen free radical content decreased. Our results showed that most of the leaf ecological and physiological traits of the 12 Caragana species varied in accordance with the climatic drought gradient in the Inner Mongolia region, which reflected the adaptation of the Caragana species to the local climate conditions. With relatively more active metabolism and faster growth, the Caragana species in the northeast had strong competitive abilities; on the other hand, with stronger resistance to climatic drought stress, the Caragana species in the southwest could survive in harsh environments. Based on our results, we con- cluded that both the environmental gradients and the adaptive responses of Caragana species to their environments played important roles in the formation of the Caragana species distribution pattern across the Inner Mongolia region.

Comparisons of plant calcium fraction between two different vegetation zones in semi-arid region

To explore the characteristics of plant calcium(Ca) fraction, we analyzed 91 plant species in the Ningxia Habahu National Nature Reserve in Yanchi County of Ningxia and 84 plant species in Zhenglan Banner of Inner Mongolia. Results show that, for the two regions, there is no significant difference between Ca fraction for the same growth type, and between water soluble Ca content or between hydrochloric acid soluble Ca content for plants of the same ecosystem and between hydrochloric acid soluble Ca content for plants of the same family. In similar vegetation zones, there is a significant difference among hydrochloric acid soluble Ca content for different growth types in Yanchi County and Zhenglan Banner,which was the highest for annual herbs and the lowest for perennial herbs. There is a significant difference between acetic acid soluble Ca content and between hydrochloric acid soluble Ca content for sandy land and grassland ecosystems in Yanchi County. There is a significant difference among the same Ca fraction of different families in the same region. Thus, the characteristics of plant Ca fraction are results of long-term adaptation to the environment.

Impacts of grazing and mowing on reproductive behaviors of Stipa grandis and Stipa krylovii in a semi-arid area

Disturbance can affect biomass allocation of plants,but can it influence plant reproductive behavior?To address this issue,we performed field plant community investigations and explored the reproductive behaviors of Stipa grandis and Stipa krylovii in response to grazing and mowing treatments at Maodeng pasture of Xilinguole League of Inner Mongolia,China during 2007–2009.The results showed that,with a similar niche width for the two plant species under mowing and grazing treatments,mowing significantly increased the ratio of ramet to genet number of S.krylovii and the carbon to nitrogen ratio of S.grandis,and grazing significantly decreased the ratio of vegetative to reproductive tiller biomass of S.grandis and increased the ratio of vegetative to reproductive tiller number of S.krylovii.Regression analysis showed that the significantly positive effect of root to shoot biomass ratio was stronger on the ratio of vegetative to reproductive tiller number of S.grandis than on that of S.krylovii.These results indicated that grazing and mowing influenced the reproductive manner and the process of sexual reproduction of S.grandis and S.krylovii.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Features on N/P ratio of plants with different functional groups between two types of steppe in semi-arid area

The differences in nitrogen/phosphorus(N/P)ratios of different functional groups in ecology are more helpful in explaining species competition and community dynamics.Based on the functional groups of plant growth type,carbon metabolism pathway,root type and phylogenetic type,we analyzed characteristics of leaf N/P ratios of 77 species in Sanggendalai(typical grassland zone)of Zhenglan Banner,Inner Mongolia,China and 91 species in the Habahu National Nature Reserve(desertified grassland zone)in Yanchi County of Ningxia,China.The results show that the N/P ratio(16.91)of C3 plants in the desertified steppe was significantly larger than that(12.72)in the typical steppe,but there was no significant difference between the N/P ratios of C4 plants in the two zones.There was no significant difference in N/P ratios between C3 plants and C4 plants in the same zone.Similarly,the N/P ratio(16.60)of dicotyledons in desertified steppe were significantly higher than that(12.98)in typical steppe,while differences in N/P ratios between monocotyledonous plants of the two zones was not significant,and there existed no significant difference in N/P ratios between dicotyledonous and monocotyledonous plants in the same zone.The N/P ratio had significant difference between gramineous and non-gramineous plants in the typical steppe but not in the desertified steppe,but there existed no significant difference in N/P ratios among different root types of perennial herbaceous plants in the same type of steppe or between two types of steppe.Thus,different features on the N/P ratios of C3 plants and dicotyledonous plants between typical steppe and desertified steppe may lead to different growth status of plants,and the N/P ratio stoichiometric of the same plant functional group may be a foundation of the changes of a plant community.

Epichloë内生真菌对宿主羽茅生长和竞争力的影响与土壤微生物多样性有关

Epichloë内生真菌存在于许多禾草的地上部分组织中,地上内生真菌和地下土壤微生物都能影响植物的生长,但关于二者同时对植物生长和竞争力影响的研究却很少。本文旨在研究地上部分内生真菌对宿主禾草的生长和竞争能力的作用是否受到土壤微生物的影响。本文以感染Epichloë内生真菌(EI)和不感染内生真菌(EF)的羽茅(Achnatherum sibiricum)以及大针茅(Stipa grandis)为植物材料,采用湿筛法获得具有不同多样性的微生物接种物。试验采用3因素随机区组设计:一是羽茅的内生真菌感染状况,包括EI和EF;二是土壤接种物的微生物组成,包括混合微生物组分(高多样性)和小型微生物组分(低多样性);三是种植方式,包括单独种植、单种和混种。植物种植16周后测定了植物生长和竞争状况。当羽茅单株或单种种植时,内生真菌对羽茅的生长和种内相互作用无显著影响,但内生真菌显著缓解了土壤微生物对羽茅单株种植时的抑制作用。当羽茅与大针茅混种时,内生真菌和土壤微生物对羽茅的种间竞争力具有显著的交互作用,当接种小型微生物组分时,内生真菌显著提高了宿主植物的种间竞争力;而当接种包含大型微生物的混合微生物组分时,内生真菌对宿主种间竞争力无显著影响。方差分析表明,内生真菌和土壤微生物交互作用对羽茅种间竞争力的贡献比内生真菌和土壤微生物的贡献均大。

Using functional trait diversity to infer community assembly mechanisms:an exclosure experiment as an example

Aims The Qinghai-Tibetan Plateau has a mean altitude exceeding 4000 m and covers about 2.5 million km2.More than 60%of this area is alpine grassland.Exclosures have been widely used in this region to study the sustainable use of grassland resources.We used patterns of functional trait diversity to infer the effects of exclosures on com-munity assembly in alpine meadows.Methods We studied functional diversity using five traits under grazing and three enclosed(exclosure)plots(3,8,and 18 years old)in an alpine meadow on the Qinghai-Tibetan Plateau.We quantified the strength of the community assembly processes by comparing the observed functional trait diversity with a null model that assumes random community assembly.Important findings We found evidence for deterministic assembly processes for plant communities in exclosures.The changes in CWM of the five traits from grazing land to 18-year exclosure indicated that environmen-tal filtering occurred due to the exclosures.Multivariate functional diversity(MFDis and MPDses),and functional diversity of individual traits,including that of leaf area,leaf weight and aboveground bio-mass(FDis of leaf area,leaf weight,and aboveground biomass),increased gradually from grazing land to the 18-year exclosure,and the values of the 18-year exclosure were significantly greater than null expectation.This can be interpreted to indicate that exclosures resulted in greater competitive interaction between species.These results suggest that the effect of exclosures on community assembly is more deterministic than stochastic in this meadow.

Effects of endophyte infection on the competitive ability of Achnatherum sibiricum depend on endophyte species and nitrogen availability

Aims the leaves of almost all terrestrial plant species are colonized by endophytic fungi.compared to agronomic grasses,which usually harbor few endophytes,native grasses generally possess greater endophyte species diversity.Existing studies examining endophyte effects on natural grasses under competition normally considered the infection status(infected or uninfected),and rarely considered endophyte species.Methods We examined the effects of endophyte infection and of endophyte species on the interspecific competitive ability of a subdominant species,Achnatherum sibiricum,at two nitrogen levels(high ni-trogen and low nitrogen).Achnatherum sibiricum plants infected by two different species of endophyte(Epichloësibirica and E.gansuensis)and uninfected plants were grown in monoculture and binary mixtures with a dominant species,Stipa grandis(six individuals per species for monocultures and three+three in-dividuals of each species in mixtures).Shoot and root biomass,tiller number and total phenolic concentration were measured after 3 months.Moreover,the aggressivity index was calculated to compare the competitive ability of A.sibiricum relative to S.grandis.Important Findings Both E.gansuensis(Eg)-and E.sibirica(Es)-infected A.sibiricum plants showed a greater competitive ability than the uninfected plants under high nitrogen supply,while the opposite result oc-curred under low nitrogen supply.At high nitrogen levels,Eg plants had a higher tiller number and a greater shoot biomass in-hibitory effect on S.grandis than Es plants had when growing in mixture,while Es plants showed better root growth performance than Eg and uninfected plants under mixture conditions at all ni-trogen levels.A higher concentration of phenolic compounds in Eg plants than in Es plants might contribute to the higher inhibi-tory effect of Eg plants on competing plants.Our study indicates that the interaction between endophyte infection and nitrogen availability can alter the competitive ability of the host plant A.sibiricum but that these two endophyte species work in different ways,which may influence the coexistence of A.sibiricum with the dominant species.