Stipa Grandis Research Articles

Inner Mongolian steppe arbuscular mycorrhizal fungal communities respond more strongly to water availability than to nitrogen fertilization.

Plant community productivity and species composition are primarily constrained by water followed by nitrogen (N) availability in the degraded semi-arid grasslands of Inner Mongolia. However, there is a lack of knowledge on how long-term N addition and water availability interact to influence the community structure of arbuscular mycorrhizal (AM) fungi, and whether AM fungi contribute to the recovery of degraded grasslands. Soils and roots of the dominant plant species Stipa grandis and Agropyron cristatum were sampled under two water levels and N) rates after 8 years. The abundance and diversity of AM fungi remained relatively resilient after the long-term addition of water and N. Variation in the AM fungal communities in soils and roots were affected primarily by watering. AM fungal abundance and operational taxonomic unit (OTU) richness were significantly correlated with average aboveground net primary productivity and biomass of plant functional groups. Hyphal length density was significantly correlated with plant richness, the average biomass of S. grandis and perennial forbs. Both water and plant biomass had a considerable influence on the AM fungal assemblages. The tight linkages between AM fungi with aboveground plant productivity highlight the importance of plant-microbe interactions in the productivity and sustainability of these semi-arid grassland ecosystems.

Interactive effects of elevated CO2 and precipitation change on leaf nitrogen of dominant Stipa L. species.

Nitrogen (N) serves as an important mineral element affecting plant productivity and nutritional quality. However, few studies have addressed the interactive effects of elevated CO2 and precipitation change on leaf N of dominant grassland genera such as Stipa L. This has restricted our understanding of the responses of grassland to climate change. We simulated the interactive effects of elevated CO2 concentration and varied precipitation on leaf N concentration (Nmass) of four Stipa species (Stipa baicalensis, Stipa bungeana, Stipa grandis, and Stipa breviflora; the most dominant species in arid and semiarid grassland) using open-top chambers (OTCs). The relationship between the Nmass of these four Stipa species and precipitation well fits a logarithmic function. The sensitivity of these four species to precipitation change was ranked as follows: S. bungeana > S. breviflora > S. baicalensis > S. grandis. The Nmass of S. bungeana was the most sensitive to precipitation change, while S. grandis was the least sensitive among these Stipa species. Elevated CO2 exacerbated the effect of precipitation on Nmass. Nmass decreased under elevated CO2 due to growth dilution and a direct negative effect on N assimilation. Elevated CO2 reduced Nmass only in a certain precipitation range for S. baicalensis (163–343 mm), S. bungeana (164–355 mm), S. grandis (148–286 mm), and S. breviflora (130–316 mm); severe drought or excessive rainfall would be expected to result in a reduced impact of elevated CO2. Elevated CO2 affected the Nmass of S. grandis only in a narrow precipitation range. The effect of elevated CO2 reached a maximum when the amount of precipitation was 253, 260, 217, and 222 mm for S. baicalensis, S. bungeana, S. grandis, and S. breviflora, respectively. The Nmass of S. grandis was the least sensitive to elevated CO2. The Nmass of S. breviflora was more sensitive to elevated CO2 under a drought condition compared with the other Stipa species.

De novo assembly and transcriptomic profiling of the grazing response in Stipa grandis.

Background Stipa grandis (Poaceae) is one of the dominant species in a typical steppe of the Inner Mongolian Plateau. However, primarily due to heavy grazing, the grasslands have become seriously degraded, and S. grandis has developed a special growth-inhibition phenotype against the stressful habitat. Because of the lack of transcriptomic and genomic information, the understanding of the molecular mechanisms underlying the grazing response of S. grandis has been prohibited.ResultsUsing the Illumina HiSeq 2000 platform, two libraries prepared from non-grazing (FS) and overgrazing samples (OS) were sequenced. De novo assembly produced 94,674 unigenes, of which 65,047 unigenes had BLAST hits in the National Center for Biotechnology Information (NCBI) non-redundant (nr) database (E-value < 10-5). In total, 47,747, 26,156 and 40,842 unigenes were assigned to the Gene Ontology (GO), Clusters of Orthologous Group (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. A total of 13,221 unigenes showed significant differences in expression under the overgrazing condition, with a threshold false discovery rate ≤ 0.001 and an absolute value of log2Ratio ≥ 1. These differentially expressed genes (DEGs) were assigned to 43,257 GO terms and were significantly enriched in 32 KEGG pathways (q-value ≤ 0.05). The alterations in the wound-, drought- and defense-related genes indicate that stressors have an additive effect on the growth inhibition of this species.ConclusionsThis first large-scale transcriptome study will provide important information for further gene expression and functional genomics studies, and it facilitated our investigation of the molecular mechanisms of the S. grandis grazing response and the associated morphological and physiological characteristics.

Ramet Recruitment from Different Bud Types along a Grassland Degradation Gradient in Inner Mongolia, China

Since the contribution of total belowground bud bank and different bud types to community regeneration has rarely been explored, the vegetative offspring recruited from different belowground bud types was investigated in four plant communities along a grassland degradation gradient in northeastern China (Inner Mongolia). This gradient, between 1000 and 1500 m a.s.l., has been caused by overgrazing. It is a Leymus chinensis steppe which occupies about 3.0×10 5 ha. Recruitment from tiller buds was dominant (>80%) in determining the total vegetative offspring density along the whole grassland degradation gradient. However, the proportional contribution of tiller-ramets to total ramet recruitment was significantly greater ( P <0.05) during earlier than later stages of grassland degradation, while that of rhizome-ramets showed an opposite pattern. While the percentage contribution and density of root-derived ramets to total ramet density increased significantly (P <0.05) during the late stages of grassland degradation, those of bulb-ramets kept relatively constant along the whole grassland degradation gradient. The relative contribution of hemicryptophytes (i.e., Achnatherum sibiricum, Cleistogenes squarrosa, Festuca ovina, Koeoleria cristata, Poa annua, Stipa grandis) to total plant species richness decreased, while that of geophytes (i.e., Agropyron cristatum, Carex korshinskyi. Leymus chinensis, Allium anisopodium, A. bidentatum, A. tenuissimum, Astragalus galactites, Cymbaria dahurica, Iris tenuifolin, Potentilla acaulis, P. bifurca , Pulsatilla turczaninovii, Serratula chinensis, Thalictrum aquilegifolium ) increased with the increases of grassland degradation. Our results showed that as grassland degradation increased, changes in the proportion of tiller-, rhizome- and root-derived ramets with respect to total ramet density determined in turn changes in the proportion of hemicryptophytes and geophytes in the study plant communities.

Divergence of above- and belowground C and N pool within predominant plant species along two precipitation gradients in North China

Abstract. The coupling of carbon cycle and nitrogen cycle drives the food web structure and biogeochemistry of an ecosystem. However, across precipitation gradients, there may be a shift in C pool and N pool from above- to belowground because of shifting plant stoichiometry and allocation. Based on previous evidence, biomass allocation to roots should increase with aridity, while leaf [N] should increase. If their effect sizes are equal, they should cancel each other out, and the above- and belowground proportions of the N would remain constant. Here, we present the first study to explicitly compare above- and belowground pool sizes of N and C within predominant plant species along precipitation gradients. Biomass and nutrient concentrations of leaves, stems and roots of three predominant species were measured along two major precipitation gradients in Inner Mongolia, China. Along the two gradients, the effect sizes of the biomass shifts were remarkably consistent among three predominant species. However, the size of the shift in aboveground [N] was not, leading to a species-specific pattern in above- and belowground pool size. In two species (Stipa grandis and Artemisia ordosica) the effect sizes of biomass allocation and [N] were equal and the proportion of N of above- and belowground did not change with aridity, but in S. bungeana the increase in leaf [N] with aridity was much weaker than the biomass shift, leading to a decrease in the proportion of N aboveground at dry sites. We have found examples of consistent N pool sizes above- and belowground and a shift to a greater proportion of belowground N in drier sites depending on the species. We suggest that precipitation gradients do potentially decouple the C and N pool, but the exact nature of the decoupling depends on the dominant species' capacity for intraspecific variation.

Species Composition, Richness and Aboveground Biomass of Natural Grassland in Hilly-Gully Regions of the Loess Plateau, China

In order to study the characteristics of species composition, richness and aboveground biomass of natural grasslands, and then find out the relations between species richness and aboveground productivity of the communities and possible mechanisms to form the relations, four typical grassland communities (Artemisia capillaries (AC), Thymus quinquecostatus (TQ), Stipa bungeana (SB) and Stipa grandis (SG)) along with a succession sequence in hilly-gully regions of the Loess Plateau, China, were investigated by field survey and laboratory analysis. The results were summarized as follows: Different succession stages had different species compositions as well as different proportions of plant life forms and photosynthetic types, and Asteraceae, Poaceae and Leguminosae were their dominant species as well as their dominant perennial herb species; and different succession stages had significantly different species richness and aboveground biomasses. There were many relation patterns (linear positive correlation, unrelated relations and unimodal relations) between the species richness and aboveground biomass in different succession stages and a significant unimodal relation between the species richness and aboveground biomass in all the grassland communities and the highest species diversity appeared at a moderate level of productivity. The results suggest the unimodal relations in all the grassland communities are accumulative results of the relations in each succession stage.

Contrasting responses in leaf nutrient-use strategies of two dominant grass species along a 30-yr temperate steppe grazing exclusion chronosequence

Grazing exclusion practices can be promising restoration techniques where ecosystem degradation follows from rapidly increasing grazing pressure, as widely observed in northern Chinese grasslands. However, the mechanisms of plant-soil interactions responsible for nutrient cycling restoration remain unclear. We examined the functional response of the two most dominant grass species with contrasting nutrient economies to a grazing exclusion chronosequence varying greatly in soil moisture and extractable N and P. The relative biomass of the nutrient acquisitive species Leymus chinensis increased while that of the nutrient conservative Stipa grandis decreased across the chronosequence. Leymus chinensis displayed increasing leaf nutrient concentration and decreasing nutrient resorption with time since grazing exclusion for both N and P. In contrast, S. grandis showed decreasing leaf N and P concentrations and largely stable nutrient resorption. These differences in plasticity, with respect to nutrient stoichiometry and resorption, suggest contrasting abilities of these two dominant species to compete for soil resources and/or differences in their affinity to the changing forms of soil available N and P likely occurring along the restoration gradient. Ecosystem trajectory of change after grazing exclusion appears therefore largely dependent on the nutrient use strategies of co-occurring dominant grassland species.

Soil aggregation and intra-aggregate carbon fractions in relation to vegetation succession on the Loess Plateau, China

Revegetation has been reported to be one of the most effective measures for reducing soil erosion on the Loess Plateau in China. The Yunwu observatory, located in the northwestern Loess Plateau of China, was selected to study the effect of vegetation succession on total carbon (C), aggregate C, and intra-aggregate particulate organic matter-carbon (iPOM-C) concentrations. The vegetation types studied, listed from the shortest to the longest enclosure duration order, were abandoned grazed grassland (Ab.G3), Hierochloe odorata Beauv. (Hi.O7), Thymus mongolicus Ronnm (Th.M15), Artemisia sacrorum Ledeb (At.S25), Stipa bungeana Trin Ledeb (St.B36), and Stipa grandis P. Smirn (St.G56) communities. Five sizes of aggregates were separated using the modified Yoder method (<0.25mm, 0.25–1mm, 1–2mm, 2–5mm and 5–8mm). Fine and coarse iPOM-C concentrations were isolated from the soil aggregates. The results showed that revegetation led to an increase in the percentage of aggregates in small macroaggregates (0.25–2mm) and thereby improved the uniformity of the soil aggregate size distribution. The concentration of bulk soil carbon ranged from 10.1gkg−1 to 29.7gkg−1 during vegetation succession. During the vegetation succession, with the exception of At.S25, the bulk soil carbon and aggregate carbon concentrations increased with recovery time. The fine iPOM-C concentrations were between 0.7 and 14.0gkg−1, which was significantly greater than the coarse iPOM-C concentrations. The coarse and fine iPOM-C concentrations exhibited different trends with vegetation restoration. In conclusion, vegetation restoration caused an increase in small macroaggregates, enhancing the uniformity of the soil aggregate size distribution and inducing greater soil organic carbon sequestration.

Responses of soil nitrogen, phosphorous and organic matter to vegetation succession on the Loess Plateau of China

Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions (particulate organic carbon (POC), humus carbon (HS-C), humic acid carbon (HA-C) and fulvic acid carbon (FA-C)) on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were: (a) abandoned overgrazed grassland (AbG3; 3 years); (b) Hierochloe odorata Beauv. (HiO7; 7 years); (c) Thymus mongolicus Ronnm (ThM15; 15 years); (d) Artemisia sacrorum Ledeb (AtS25; 25 years); (e) Stipa bungeana Trin Ledeb (StB36; 36 years) and (f) Stipa grandis P. Smirn (StG56; 56 years). The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for ThM15. The concentration of NH4-N increased in the medium stage (for ThM15 and AtS25) and decreased in the later stage (for StB36 and StG56) of vegetation restoration. However, NO3-N concentration significantly increased in the later stage (for StB36 and StG56). Carbon fractions had a similar increasing trend during natural vegetation restoration. The concentrations of POC, HS-C, FA-C and HA-C accounted for 24.5%–49.1%, 10.6%–15.2%, 5.8%–9.1% and 4.6%–6.1% of total carbon, respectively. For AbG3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecological function in semiarid grassland ecosystems.

The Characteristics of Plant Communities Along East Eurasian Steppe Transect

The East Eurasian Steppe Transect (EEST) is the first international transect across regions of middle and high latitudes in the eastern Eurasian steppe. The EEST is an ideal platform for researching the response of Eurasian temperate steppe to global change, because of its integrated gradients of temperature and human activities on a large-scale. In this study, basic characteristics of plant communities along the EEST across a latitudinal gradient was analyzed. According to the survey of 58 sampling sites, there are 140 species belonging to 34 families and 94 genera. Of particular note was the finding of Astragalus dalaiensis which has disappeared in the grasslands of China. On the whole, Gramineae plants are dominant with Liliaceae plants in the communities significantly decreasing along the latitudinal gradient from south to north. The Shannon-Wiener index and biomass of communities all decreased along the latitudinal gradient with significant negative linear regressions. The SDR2 (summed dominance ratio based on two factors) of dominant plants in the upper layers of communities, such as Stipa and Leymus chinensis, decreased along the latitudinal gradient from south to north. Especially, the SDR2 of L. chinensis decreased significantly. The SDR2 of Cleistogenes squarrosa, Agropyron cristatum in the lower layers of communities and the indicator species for degradation were not affected. Potentilla acaulis was found mainly in the southern and northern areas. Stellera chamaejasme was found just in a few sites in the southern area of the EEST. In communities of Stipa grandis and Stipa krylovii, annual and biennial species are dominant. The ratio of annual and biennial species in the community is significantly related to the latitudinal gradient. Perennial herbaceous plants and shrubs were not affected. According to the principal component analysis (PCA), with the data from 58×140 dimensions, the first and second components had the lowest proportion, thus indicating that the species compositions and community structures are homogeneous along the EEST. There is a certain degree of spatial differentiation along the EEST due to degradation's differences resulting from the different land uses.

Simulated water fluxes during the growing season in semiarid grassland ecosystems under severe drought conditions

summary To help improve understanding of how changes in climate and land cover affect water fluxes, water budgets, and the structure and function of regional grassland ecosystems, the Grassland Landscape Productivity Model (GLPM) was used to simulate spatiotemporal variation in primary water fluxes. The study area was a semiarid region in Inner Mongolia, China, in 2002, when severe drought was experienced. For Stipa grandis steppe, Leymus chinensis steppe, shrubland, and croplands, the modeled total, daily and monthly averaged, and maximum evapotranspiration during the growing season and the modeled water deficits were similar to those measured in Inner Mongolia under similar precipitation conditions. The modeled temporal variations in daily evaporation rate, transpiration rate, and evapotranspiration rate for the typical steppes also agreed reasonably well with measured trends. The results demonstrate that water fluxes varied in response to spatiotemporal variations in environmental factors and associated changes in the phenological and physiological characteristics of plants. It was also found that transpiration and evapotranspiration (rather than precipitation) were the primary factors controlling differences in water deficit among land cover types. The results also demonstrate that specific phenomena occur under severe drought conditions; these phenomena are considerably different to those occurring under normal or well-watered conditions. The findings of the present study will be useful for evaluating day-scale water fluxes and their relationships with climate change, hydrology, land cover, and vegetation dynamics. 2014 Published by Elsevier B.V.

Restoration and Utilization Mechanism of Degraded Grassland in the Semi-arid Region of Loess Plateau

Grassland degradation results in a series of ecological problems, such as soil and vegetation destruction, strongly inhibiting succession process of grassland. To research how degraded grassland could be recovered and utilized, we monitored the change progress of degraded grassland from secondary bare land to approximate original vegetation by using long-term grazing exclusion. Results showed the recovery succession process could be divided into four stages with the extending of grazing exclusion time. During the process of community succession, the community coverage, plant density, species richness index, diversity index, aboveground biomass, and belowground biomass increased gradually with the maximum level occurring in the 20th year (except for belowground biomass reaching the peak at the 15th year). The aboveground biomass reached the highest value of 520.5 g/m2. During 20-25 years of gazing exclusion, steppe community with the constructive species of Stipa bungeana degraded obviously, and population density of Stipa grandis grew rapidly. After the 26th year of grazing exclusion, steppe community with the constructive species of Stipa grandis grew stably. According to the community succession process, the tendency was Stipa grandis replaced Stipa bungean a. Xerophytic shrubs were aggregately distributed on both sides of the grass channel and community succession entered a new stage. Through several succession stages from 0-26 years of invasion, competition, diffusion, and ecesis, the grassland had entered the subclimax with the constructive species of Stipa grandis . Even decline in grass biomass, improved grass quality and rich species diversity promote the succession of grassland. Vegetation community consisted mainly of Gramineae, Leguminosae and Compositae. Perennial plant, C3 plant, and xerophytic plant could be used to indicate succession process and vegetation recovery. Long-term grazing exclusion had a negative impact on species generation and ecosystem stability. The reasonable enclosing time played an important role in ecological restoration of grassland. Therefore, we put forward an idea that degraded grassland can be utilized after being fenced for 10-15 years, such as mowing once every two years and light grazing (two sheep/hm2). This study would provide scientific evidence for grassland restoration in arid and semi-arid regions.

Effects of Rest Grazing on Organic Carbon Storage in Stipa grandis Steppe in Inner Mongolia, China

This study was aimed to evaluate the potential effects of rest grazing on organic carbon storage in Stipa grandis steppe of Inner Mongolia, China. Using potassium dichromate heating method, we analyzed the organic carbon storage of plant and soil in Stipa grandis steppe after rest grazing for 3, 6, and 9 yr. The results indicated that as the rest grazing ages prolonged, the biomass of aboveground parts, litter and belowground plant parts (roots) of the plant communities all increased, meanwhile the C content of the biomass increased with the rest grazing ages prolonging. For RG0, RG3a, RG6a, and RG9a, C storage in aboveground vegetation were 60.7, 76.9, 82.8 and 122.2 g C m−2, respectively; C storage of litter were 5.1, 5.8, 20.4 and 25.5 g C m−2, respectively; C storage of belowground roots (0–100 cm) were 475.2, 663.0, 1 115.0 and 1 867.3 g C m−2, respectively; C storage in 0–100 cm soil were 13.97, 15.76, 18.60 and 32.41 kg C m−2, respectively. As the rest grazing ages prolonged, the organic C storage in plant communities and soil increased. The C storage of belowground roots and soil organic C was mainly concentrated in 0–40 cm soil body. The increased soil organic C for RG3a accounted for 89.8% of the increased carbon in vegetation-soil system, 87.2% for RG6a, and 92.6% for RG9a. From the perspective of C sequestration cost, total cost for RG3a, RG6a, and RG9a were 2 903.4, 5 806.8 and 8 710.2 CNY ha−1, respectively. The cost reduced with the extension of rest grazing ages, 0.15 CNY kg−1 C for RG3a, 0.11 CNY kg−1 C for RG6a and 0.04 CNY kg−1 C for RG9a. From the growth characteristics of grassland plants, the spring was one of the two avoided grazing periods, timely rest grazing could effectively restore and update grassland vegetation, and was beneficial to the sustainable use of grassland. Organic C storage for RG9a was the highest, while the cost of C sequestration was the lowest. Therefore, spring rest grazing should be encouraged because it was proved to be a very efficient grassland use pattern.

Effects of grazing intensity and topography on species abundance distribution in a typical steppe of Inner Mongolia

Aims Our objective is to determine: 1) how species richness and abundance vary with grazing intensity and topography (i.e., flat vs. slope) in typical steppe of Inner Mongolia grassland, and 2) how common and rare species respond to grazing intensity and what role they play in species diversity maintenance. Methods The study was carried out at the Sino-German grazing experiment site, which was established in June 2004, and located in the typical steppe region of Inner Mongolia grassland dominated by Leymus chinensis and Stipa grandis. The experimental treatments included seven levels of stocking rates (i.e., 0, 1.5, 3.0, 4.5, 6.0, 7.5, 9.0 sheep·hm) and two topographical systems (i.e., flat and slope). Three hundred quadrats (1 m × 1 m each) were investigated on each plot in August 2009, and the total number of species and the number of individuals for each species were measured within each quadrat. The log-normal model, log-series model, and power fraction model were used to fit the observational data. Important findings Our results showed that the species richness and abundance increased at low stocking rates (1.5, 3.0 sheep·hm), but decreased at high stocking rates (7.5, 9.0 sheep·hm) on the flat, which partially supported the grazing optimization hypothesis. The power fraction model well fitted for entire species abundance at most of stocking rates, while the log-normal model only fitted well for entire species abundance just at the high stocking rates. The species richness and abundance decreased greatly with stocking rates on slopes. Abundance 李文怀等: 放牧强度和地形对内蒙古典型草原物种多度分布的影响 179 doi: 10.3724/SP.J.1258.2014.00016 distribution of entire species at each of the stocking rates followed the log-normal function and power fraction function. The groups of common species and the entire species had similar responses in abundance to grazing at each of the stocking rates on both the flat and the slope, which were well fitted by both the power fraction model and log-normal model; whereas the groups of rare species and the entire species had similar richness responses to grazing at each of the stocking rates under both topographical features, which were well fitted by the power fraction model. It is suggested that the effect of grazing on species abundance in plant community depends on common species; whilst grazing effect on species richness depends on rare species. Our findings indicate that the niche partitioning mechanism plays an important role in species abundance maintenance in grassland ecosystems. To restore and maintain a high level of biodiversity and primary productivity in the Inner Mongolia grassland, it is necessary to reduce the excessively high stocking rate at present to a moderate level in future.

Response of the annual biomass production of a typical steppe plant community to precipitation fluctuations

Understanding the relationship between the aboveground net primary production (ANPP) and annual precipitation in arid and semiarid grasslands is crucial for assessing the effects of climate change on grassland ecosystems. The temporal pattern of ANPP, based on long-term data on a semiarid ecosystem in Inner Mongolia, was investigated. The biomass of perennial grasses, perennial forbs and Stipa grandis P. Smirn., showed a positive relationship with annual precipitation. The amount of annual precipitation also changed the annual biomass of 13 other dominant species and consequently the ANPP. The coefficient of variation of the ANPP of the plant community was lower than the coefficient of variation of annual precipitation. Irrespective of the strong inter-annual variation in annual precipitation, the positive relationship found between ANPP and annual precipitation suggests the dependence of ANPP upon hydrological variations in typical steppe. Our findings highlight the importance of dominant perennial species and functional groups in mediating the responses of ANPP to annual precipitation in the typical steppe in northern China.

Establishing the carrying capacity of the grasslands of China: a review

China is rich in grassland resources, with 400 × 106 ha of natural grasslands and 18 main types, mostly distributed in the north-east, north, Qinghai-Tibet Plateau and Xinjiang regions. Grassland-based livestock production is the foundation of the economy in these rural areas. Degradation of grassland has occurred to varying degrees in these regions. Mean overgrazing rates across the whole country were estimated to be ~30% in 2009. Considerable amounts of research have focussed, especially since 2000, on developing better ways of managing Chinese grasslands. Research concerning the relationship between forage production and animal performance, is reviewed for three important national grassland regions. For the three major grassland (steppes) types of Inner Mongolia, the stocking rates proposed as a result of research were 1.0–2.2 sheep units (SU) ha–1 for the western, drier Stipa breviflora desert steppe; 2.0–3.8 SU ha–1 for the steppe of Artemisia frigida and Stipa grandis; and 1.8–4.0 SU ha–1 for the eastern higher-rainfall Leymus chinensis meadow steppe in Hulunbeir. In the Qinghai-Tibetan alpine meadows, the stocking rate of grassland dominated by Edelweiss-Potentilla and Kobresia parva, proposed on the basis of research, was 1.0–5.8 SU ha–1. In Xinjiang’s desert steppe, the stocking rates of Seriphidium transiliense desert steppe were proposed on the basis of research were 1.2 SU ha–1 in spring and 1.8 SU ha–1 in autumn for non-degraded pasture, and 0.3 and 1.2 SU ha–1 for moderate-degraded pasture, respectively. These stocking rates were based on either annual net primary production or desired levels of livestock production and it is argued that there is a need to develop carrying capacities based on a wider range of sustainability criteria and with the most appropriate grazing systems.

Traits related to carbon sequestration of common plant species in a Stipa grandis steppe in Nei Mongol under different land-uses

Traits related to carbon sequestration of common plant species in a Stipa grandis steppe in Nei Mongol under different land-uses

Effects of elevated CO2, warming and precipitation change on plant growth, photosynthesis and peroxidation in dominant species from North China grassland

Warming, watering and elevated atmospheric CO₂-concentration effects have been extensively studied separately; however, their combined impact on plants is not well understood. In the current research, we examined plant growth and physiological responses of three dominant species from the Eurasian Steppe with different functional traits to a combination of elevated CO₂, high temperature, and four simulated precipitation patterns. Elevated CO₂ stimulated plant growth by 10.8-41.7 % for a C₃ leguminous shrub, Caragana microphylla, and by 33.2-52.3 % for a C₃ grass, Stipa grandis, across all temperature and watering treatments. Elevated CO₂, however, did not affect plant biomass of a C₄ grass, Cleistogenes squarrosa, under normal or increased precipitation, whereas a 20.0-69.7 % stimulation of growth occurred with elevated CO₂ under drought conditions. Plant growth was enhanced in the C₃ shrub and the C₄ grass by warming under normal precipitation, but declined drastically with severe drought. The effects of elevated CO₂ on leaf traits, biomass allocation and photosynthetic potential were remarkably species-dependent. Suppression of photosynthetic activity, and enhancement of cell peroxidation by a combination of warming and severe drought, were partly alleviated by elevated CO₂. The relationships between plant functional traits and physiological activities and their responses to climate change were discussed. The present results suggested that the response to CO₂ enrichment may strongly depend on the response of specific species under varying patterns of precipitation, with or without warming, highlighting that individual species and multifactor dependencies must be considered in a projection of terrestrial ecosystem response to climatic change.

Long‐Term Effects of Natural Enclosure: Carbon Stocks, Sequestration Rates and Potential for Grassland Ecosystems in the Loess Plateau

The aim of this study was to better understand the effects of grassland restoration on carbon sequestration at the total carbon stock (plant and soil) scale. The objective of the study was to investigate the temporal carbon sink and sequestration dynamics of grassland ecosystems with five different succession communities, namely, Stipa grandis, Stipa bungeana, Artemisia sacrorum, Thymus mongolicus, and cropland succession in the hilly‐gully region of the Loess Plateau, China. Twenty‐four research papers were analyzed to form the basis of the subsequent field survey conducted at the Yunwu Observatory for Vegetation Protection and Eco‐environment in Ningxia. Following the conversion of cropland to grassland, carbon sequestration values all increased at deeper soil depths of 40–100 cm; carbon stocks within the 0–40 cm profile were largely unchanged. Five time intervals, 0 (cropland) 23, 35, 58, and 78 years yielded carbon stocks of 7.69, 14.58, 16.25, 19.22, and 19.95 kg/m2 at the total carbon stock scale. The main finding indicates that the conversion of cropland to grassland results in significant changes to ecosystem carbon pool properties. This finding has broad implications for the anthropogenic management of terrestrial carbon sequestration at the regional scale.

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.