Eurasian Steppe Research Articles

Endophytic infection increases the belowground over-yielding effects of the host grass community mainly by increasing the complementary effects.

Increases in plant species diversity may increase the community diversity effect and produce community over-yielding. Epichloë endophytes, as symbiotic microorganisms, are also capable of regulating plant communities, but their effects on community diversity effects are often overlooked. In this experiment, we investigated the effects of endophytes on the diversity effects of host plant community biomass by constructing artificial communities with 1-species monocultures and 2- and 4-species mixtures of endophyte-infected (E+) and endophyte-free (E-) Achnatherum sibiricum and three common plants in its native habitat, which were potted in live and sterilized soil. The results showed that endophyte infection significantly increased the belowground biomass and abundance of Cleistogenes squarrosa, marginally significantly increased the abundance of Stipa grandis and significantly increased the community diversity (evenness) of the 4-species mixtures. Endophyte infection also significantly increased the over-yielding effects on belowground biomass of the 4-species mixtures in the live soil, and the increase in diversity effects on belowground biomass was mainly due to the endophyte significantly increasing the complementary effects on belowground biomass. The effects of soil microorganisms on the diversity effects on belowground biomass of the 4-species mixtures were mainly derived from their influences on the complementary effects. The effects of endophytes and soil microorganisms on the diversity effects on belowground biomass of the 4-species communities were independent, and both contributed similarly to the complementary effects on belowground biomass. The finding that endophyte infection promotes belowground over-yielding in live soil at higher levels of species diversity suggests that endophytes may be one of the factors contributing to the positive relationship between species diversity and productivity and explains the stable co-existence of endophyte-infected Achnatherum sibiricum with a variety of plants in the Inner Mongolian grasslands.

Spatial-Temporal Characteristics and Driving Forces of Aboveground Biomass in Desert Steppes of Inner Mongolia, China in the Past 20 Years

The desert steppe serves as a transitional zone between grasslands and deserts, and long-term monitoring of aboveground biomass (AGB) in the desert steppe is essential for understanding grassland changes. While AGB observation techniques based on multisource remote-sensing data and machine-learning algorithms have been widely applied, research on monitoring methods specifically for the desert steppe remains limited. In this study, we focused on the desert steppe of Inner Mongolia, China, as the study area and used field sampling data, MODIS data, MODIS-based vegetation indices (VI), and environmental factors (topography, climate, and soil) to compare the performance of four commonly used machine-learning algorithms: multiple linear regression (MLR), partial least-squares regression (PLS), random forest (RF), and support vector machine (SVM) in AGB estimation. Based on the optimal model, the spatial–temporal characteristics of AGB from 2000 to 2020 were calculated, and the driving forces of climate change and human activities on AGB changes were quantitatively analyzed using the random forest algorithm. The results are as follows: (1) RF demonstrated outstanding performance in terms of prediction accuracy and model robustness, making it suitable for AGB estimation in the desert steppe of Inner Mongolia; (2) VI contributed the most to the model, and no significant difference was found between soil-adjusted VIs and traditional VIs. Elevation, slope, precipitation, and temperature all had positive effects on the model; (3) from 2000 to 2020, the multiyear average AGB in the study area was 58.34 g/m2, exhibiting a gradually increasing distribution pattern from the inner region to the outer region (from north to south); (4) from 2000 to 2020, the proportions of grassland with AGB slightly and significantly increasing trend in the study area were 87.08% and 5.13%, respectively, while the proportions of grassland with AGB slightly and significantly decreasing trend were 7.76% and 0.05%, respectively; and (5) over the past 20 years, climate change, particularly precipitation, has been the primary driving force behind AGB changes of the study area. This research holds reference value for improving desert steppe monitoring capabilities and the rational planning of grassland resources.

Estimation and Climate Impact Analysis of Terrestrial Vegetation Net Primary Productivity in China from 2001 to 2020

The net primary productivity (NPP) of vegetation is an important indicator reflecting the vegetation dynamics and carbon sequestration capacity in a region. In recent years, China has implemented policies to carry out ecological protection. To understand the changes in the distribution of vegetation NPP in China and the influence of climate factors, the Carnegie–Ames–Stanford approach (CASA) model was used to estimate the NPP from 2001 to 2020. In this paper, several sets of measurement datasets and products were collected to evaluate the effectiveness of the model and suggestions were provided for the modification of the CASA model based on the evaluation results. In addition to the correlation analysis, this paper presents a statistical method for analyzing the quantitative effects in individual climatic factors on NPP changes in large regions. The comparison found that the model has a better estimation effect on grassland and needleleaf forest. The estimation error for the evergreen needleleaf forest (ENF) and deciduous broadleaf forest (DBF) decreases with the warming of the climatic zone, while the evergreen broadleaf forest (EBF) and deciduous needleleaf forest (DNF) do the opposite. The changes in total CASA NPP were consistent with the trends of other products, showing a dynamic increasing trend. In terms of the degree of correlation between the NPP changes and climatic factors, the NPP changes were significantly correlated with temperature in about 10.39% of the vegetation cover area and with precipitation in about 26.92% of the vegetation cover area. It was found that the NPP variation had a negative response to the temperature variation in Inner Mongolia grasslands, while it had a positive but small effect (±10 g C) in the Qinghai–Tibet Plateau grasslands. Precipitation had a facilitative effect on the grassland NPP variation, while an increase in the annual precipitation of more than 200 mm had an inhibitory effect in arid and semi-arid regions. This study can provide data and methodological reference for the ecological assessment of large-scale regional and climate anomalous environments.

Impacts of Grazing Disturbance on Soil Nitrogen Component Contents and Storages in a Leymus chinensis Meadow Steppe

Long-term grazing leads to soil degradation in Inner Mongolia grassland. Based on the Hulunbeier meadow steppe, the variation characteristics of soil nitrogen content and storage in soil layers between 0–40 cm, under six different grazing intensities, and the response of vegetation and other physical and chemical properties of soil to grazing were studied. The main results were as follows: (1) Moderate grazing increased soil total nitrogen (TN), soluble total nitrogen (STN) and microbial biomass nitrogen (MBN) contents, while heavy grazing decreased MBN content. In the year with more rain, heavy grazing increased nitrate nitrogen (NO3−-N) content and storage, while less rain increased ammonium nitrogen (NH4+-N) content. (2) The proportion of 0–40 cm nitrogen components showed an upward trend in the year with more rain, and the opposite in the years with less rainfall with the increase of grazing intensity. Soil soluble organic nitrogen (SON) and NO3−-N storages decreased and MBN storage increased in rainy years. (3) Soil nitrogen component contents and storages were correlated with plant growth status, soil moisture (SM) and soil bulk density (SBD), and were significantly negatively correlated with soil temperature (ST) and pH (p < 0.05). The content and storage of soil nitrogen were affected by grazing, soil, vegetation, meteorological and other environmental factors. Moderate grazing was more conducive to the improvement of soil nitrogen storage capacity and the healthy development of grassland.

Combined influence of ENSO and North Atlantic Oscillation (NAO) on Eurasian Steppe during 1982–2018

As the most influential atmospheric oscillation on Earth, the El Niño/Southern Oscillation (ENSO) can significantly change the surface climate of the tropics and subtropics and affect the high latitudes of northern hemisphere areas through atmospheric teleconnection. The North Atlantic Oscillation (NAO) is the dominant pattern of low-frequency variability in the Northern Hemisphere. As the dominant oscillations in the Northern Hemisphere, the ENSO and NAO have been affecting the giant grassland belt in the world, the Eurasian Steppe (EAS), in recent decades. In this study, the spatio-temporal anomaly patterns of grassland growth in the EAS and their correlations with the ENSO and NAO were investigated using four long-term leaf area index (LAI) and one normalized difference vegetation index (NDVI) remote sensing products from 1982 to 2018. The driving forces of meteorological factors under the ENSO and NAO were analyzed. The results showed that grassland in the EAS has been turning green over the past 36 years. Warm ENSO events or positive NAO events accompanied by increased temperature and slightly more precipitation promoted grassland growth, and cold ENSO events or negative NAO events with cooling effects over the whole EAS and uneven precipitation decreased deteriorated the EAS grassland. During the combination of warm ENSO and positive NAO events, a more severe warming effect caused more significant grassland greening. Moreover, the co-occurrence of positive NAO with cold ENSO or warm ENSO with negative NAO kept the characteristic of the decreased temperature and rainfall in cold ENSO or negative NAO events, and deteriorate the grassland more severely.

Refining the evolutionary tree of the horse Y chromosome

The Y chromosome carries information about the demography of paternal lineages, and thus, can prove invaluable for retracing both the evolutionary trajectory of wild animals and the breeding history of domesticates. In horses, the Y chromosome shows a limited, but highly informative, sequence diversity, supporting the increasing breeding influence of Oriental lineages during the last 1500 years. Here, we augment the primary horse Y-phylogeny, which is currently mainly based on modern horse breeds of economic interest, with haplotypes (HT) segregating in remote horse populations around the world. We analyze target enriched sequencing data of 5 Mb of the Y chromosome from 76 domestic males, together with 89 whole genome sequenced domestic males and five Przewalski’s horses from previous studies. The resulting phylogeny comprises 153 HTs defined by 2966 variants and offers unprecedented resolution into the history of horse paternal lineages. It reveals the presence of a remarkable number of previously unknown haplogroups in Mongolian horses and insular populations. Phylogenetic placement of HTs retrieved from 163 archaeological specimens further indicates that most of the present-day Y-chromosomal variation evolved after the domestication process that started around 4200 years ago in the Western Eurasian steppes. Our comprehensive phylogeny significantly reduces ascertainment bias and constitutes a robust evolutionary framework for analyzing horse population dynamics and diversity.

The relative importance of drought stress and neighbor richness on plant–plant interactions shifts over a short time

Exploring how plant–plant interactions between species and their neighbors vary with biotic and abiotic factors is vital to understanding community assembly mechanisms in the context of global changes. In this study, using a dominant species (Leymus chinensis (Trin.) Tzvel.) in the semiarid Inner Mongolia steppe as the target species and ten other species as neighbors, we carried out a microcosm experiment to evaluate how drought stress, neighbor richness and season affected the relative neighbor effect (Cint) (the ability to reduce growth of target species). The factor of season interactively affected the effect of drought stress or neighbor richness on Cint. In the summer, drought stress decreased Cint directly and indirectly by decreasing SLA hierarchical distance and neighbor biomass. In the subsequent spring, drought stress increased Cint, and neighbor richness increased Cint directly and indirectly by increasing neighbor community functional dispersion (FDis) and neighbor biomass. Specifically, SLA hierarchical distance was positively associated with neighbor biomass, while height hierarchical distance was negatively associated with neighbor biomass in both seasons, which increased Cint. These findings show that the relative importance of drought stress and neighbor richness on Cint shifted over seasons, which provides strong empirical evidence of how plant–plant interactions respond to changes in biotic and abiotic factors in the semiarid Inner Mongolia steppe over a short-term time. Furthermore, this study provides novel insight into community assembly mechanisms in the context of climatic aridity and biodiversity loss in semiarid regions.

Opposite response of N2O emissions in different seasons to warming and precipitation addition on a temperate steppe

AbstractClimate change is an important issue that affects both global warming and precipitation, and the main cause is increased N2O emissions. Temperature and moisture are key factors in grassland ecosystem's response to climate change, and they can affect N2O fluxes. To clarify the impacts of warming and precipitation changes on N2O fluxes, an experiment was conducted in a semiarid steppe in Inner Mongolia, China over a nine‐year period (2011–2019). Plant productivity and soil nutrient dynamics were examined concurrently from 2017 to 2019, and N2O fluxes were monitored in response to different treatment conditions: control (C), warming (W), precipitation addition (P), and warming and precipitation addition (WP). The results showed that N2O emissions in the growing season were higher than those in the nongrowing season. Warming and precipitation addition had no significant effect on N2O fluxes compared with ambient conditions. Compared with P treatment, warming increased N2O flux in nongrowing season and decreased it in growing season. N2O flux was positively correlated with soil temperature and moisture (p < 0.05). Warming had a significant positive effect on soil NH4+‐N, whereas additional precipitation had a large positive effect on soil total nitrogen and soil nitrate nitrogen. With the WP treatment, soil microbial biomass nitrogen (MBN) and soil microbial biomass carbon (MBC) increased by 53.8% and 41.9%, respectively. The decrease in N2O emissions during the growing season in the W treatment compared with the P treatment may be largely attributed to the greater dominance of Leymus chinensis. The results highlight that changes in species dominance play an important role in regulating N2O emissions, and that the N2O fluxes in the nongrowing season account for a large proportion of the changes in N2O fluxes. Therefore, The warming effects on N2O emissions during nongrowing seasons should be further investigated.

Yersinia pestis genomes reveal plague in Britain 4000 years ago

Extinct lineages of Yersinia pestis, the causative agent of the plague, have been identified in several individuals from Eurasia between 5000 and 2500 years before present (BP). One of these, termed the ‘LNBA lineage’ (Late Neolithic and Bronze Age), has been suggested to have spread into Europe with human groups expanding from the Eurasian steppe. Here, we show that the LNBA plague was spread to Europe’s northwestern periphery by sequencing three Yersinia pestis genomes from Britain, all dating to ~4000 cal BP. Two individuals were from an unusual mass burial context in Charterhouse Warren, Somerset, and one individual was from a single burial under a ring cairn monument in Levens, Cumbria. To our knowledge, this represents the earliest evidence of LNBA plague in Britain documented to date. All three British Yersinia pestis genomes belong to a sublineage previously observed in Bronze Age individuals from Central Europe that had lost the putative virulence factor yapC. This sublineage is later found in Eastern Asia ~3200 cal BP. While the severity of the disease is currently unclear, the wide geographic distribution within a few centuries suggests substantial transmissibility.

Prehistoric population expansion in Central Asia promoted by the Altai Holocene Climatic Optimum

How climate change in the middle to late Holocene has influenced the early human migrations in Central Asian Steppe remains poorly understood. To address this issue, we reconstructed a multiproxy-based Holocene climate history from the sediments of Kanas Lake and neighboring Tiewaike Lake in the southern Altai Mountains. The results show an exceptionally warm climate during ~6.5–3.6 kyr is indicated by the silicon isotope composition of diatom silica (δ30Sidiatom) and the biogenic silica (BSi) content. During 4.7-4.3 kyr, a peak in δ30Sidiatom reflects enhanced lake thermal stratification and periodic nutrient limitation as indicated by concomitant decreasing BSi content. Our geochemical results indicate a significantly warm and wet climate in the Altai Mountain region during 6.5–3.6 kyr, corresponding to the Altai Holocene Climatic Optimum (AHCO), which is critical for promoting prehistoric human population expansion and intensified cultural exchanges across the Central Asian steppe during the Bronze Age.

At the onset of settled pastoralism – Implications of archaeozoological and isotope analyses from Bronze age sites in the North Caucasus

Bioarchaeological studies provide a valuable contribution to the understanding of the economy and activities of prehistoric populations in mountain regions. The Late Bronze Age in the Caucasus is an epoch of fundamental transformations that is accompanied by the development of a semi-stationary pastoral economy and ultimately by the emergence of combined mountain agriculture. So far, only a few archaeozoological assemblages from this period have been published. The site of Ransyrt-1 in the North Caucasus offers a substantial collection of bone material from the remains of a mountain sanctuary. Analysis of the animal remains as well as preliminary isotopic analyses of strontium, oxygen, and carbon shed light on animal exploitation at this site. Comparisons with slightly later settlements in the North and South Caucasus illustrate the development of intensive livestock management strategies in the Late Bronze Age in this region at the interface between Southwest Asia and the Eurasian steppe.

Morphological and physiological traits of dominant plant species in response to mowing in a temperate steppe.

Mowing is a common grassland management to feed livestock during winter by harvesting hay in autumn in many high latitude regions. Trait-based approach has been used to explain the responses of plant community to disturbance resulting from environmental changes and human activities. However, few studies have focused on the mechanisms underlying responses of grassland ecosystem to mowing from perspective of plant traits. Here, we investigated the effects of mowing on plant community of a temperate steppe in Inner Mongolia of northern China by field experiments to dissect the trade-off between morphological and physiological traits in response to short-term (4 years) and long-term (16 years) mowing. Specifically, we evaluated the two strategies associated with nutrient acquisition of two dominant species in response to mowing by measuring leaf and root morphological traits and physiological traits of root carboxylate exudation, AMF colonization and soil microbial community. We found that long-term mowing, but not short-term mowing, led to an increase in species richness. In addition, mowing decreased overall plant biomass of grassland community, but enhanced and suppressed growth of forbs and grasses, respectively. However, the ratio of forbs to grasses in the community was dependent on mowing duration, such that the forbs became more dominant than the grasses under long-term mowing. Our results revealed that short-term mowing reduced soil microbial biodiversity and root colonization of AMF in the grass Stipa krylovii, while root AMF colonization and carboxylate exudation in the forb Artemisia frigida were enhanced by short-term mowing. In long-term mowing, the functional traits associated with leaf resource conservation (i.e. leaf tissue density) and root resource acquisition were reduced in the grass, while the functional traits related to leaf resource acquisition and root resource conservation were increased in the forb, highlighting the species-specific and divergence in leaf and root traits in the grass and forb of temperate steppe in response to mowing. These novel findings demonstrate that physiological and morphological strategies are main drivers for dominant species in response to mowing in temperate grasslands.

Genetic Diversity of a Heat Activated Channel-TRPV1 in Two Desert Gerbil Species with Different Heat Sensitivity.

Heat sensation and tolerance are crucial for determining species' survival and distribution range of small mammals. As a member of the transmembrane proteins, transient receptor potential vanniloid 1 (TRPV1) is involved in the sensation and thermoregulation of heat stimuli; however, the associations between animal's heat sensitivity and TRPV1 in wild rodents are less studied. Here, we found that Mongolian gerbils (Meriones unguiculatus), a rodent species living in Mongolia grassland, showed an attenuated sensitivity to heat compared with sympatrically distributed mid-day gerbils (M. meridianus) based on a temperature preference test. To explain this phenotypical difference, we measured the TRPV1 mRNA expression of two gerbil species in the hypothalamus, brown adipose tissue, and liver, and no statistical difference was detected between two species. However, according to the bioinformatics analysis of TRPV1 gene, we identified two single amino acid mutations on two TRPV1 orthologs in these two species. Further Swiss-model analyses of two TRPV1 protein sequences indicated the disparate conformations at amino acid mutation sites. Additionally, we confirmed the haplotype diversity of TRPV1 in both species by expressing TRPV1 genes ectopicly in Escherichia coli system. Taken together, our findings supplemented genetic cues to the association between the discrepancy of heat sensitivity and the functional differentiation of TRPV1 using two wild congener gerbils, promoting the comprehension of the evolutionary mechanisms of the TRPV1 gene for heat sensitivity in small mammals.

Spatiotemporal variation and coupling of grazing intensity and ecosystem based on four quadrant model on the Inner Mongolia

Scientific understanding of the coupling relationship between grazing activities and grassland ecosystem is an important foundation for protecting and improving the ecological quality of grassland. This study took the Inner Mongolia Autonomous Region (Inner Mongolia) as the research area, systematically evaluated the grassland ecosystem and grazing intensity status in Inner Mongolia, and evaluated the ecological quality of Inner Mongolia county based on the four quadrant model. The results showed that: (1) The types of landscape patterns in Inner Mongolia were mainly grassland, forest, and desert. During the study period, the overall pattern of the landscape was stable, but problems such as urban expansion needed to be given more attention. (2) The areas with good grassland ecosystem carrying capacity were principally distributed in the eastern and southeastern Inner Mongolia, while the western Inner Mongolia and the northwest region of the Xilingol League were relatively low, and in the period 2000–2010 the ecological quality of the Inner Mongolia grassland in general belonged to the fair, middle level, but had been in a stable state and showed a good direction to improve the trend of ascension. (3) The grazing overload degree (GOD) in Inner Mongolia was significantly different in the region. GOD decreased from northeast to southwest in both periods. And most of the grassland stocking pressure was alleviated during 2000–2010. (4) The results of the four quadrant model analysis showed that there were obvious spatial differences in ecological quality in Inner Mongolia. And about 97% of the research area was located in the first, second, and fourth quadrants, with only 3% located in the third quadrant. From 2000 to 2010, the counties with nearly unchangeable and non-significantly worse accounted for 91.76% and 4.33%, respectively, indicating that the overall grassland ecosystem in Inner Mongolia remained stable and showed a slight improvement trend. This study can provide the necessary reference basis for the scientific formulation of grassland resources-related policies and plans and the promotion of grassland ecological protection in Inner Mongolia.

Movement drives population dynamics of one of the most mobile ungulates on Earth: Insights from a mechanistic model.

Long-distance movements are hypothesized to positively influence population size and stability of mobile species. We tested this hypothesis with a novel modeling approach in which moving herbivores interact with the environment created by a dynamic global vegetation model using highly mobile Mongolian gazelles in the eastern Mongolian grasslands as a case study. Gazelle population dynamics were modeled from 1901 to 2018 under two scenarios, one allowing free movement and one restricting movement. Gazelles were 2.2 times more abundant when they could move freely and were extirpated in 71% of the study area when mobility was restricted. Mobility resulted in greater population increases during times of abundant forage and smaller population decreases during drought. Reduced thermoregulatory costs associated with climate change, combined with an increase in vegetation biomass, increased gazelle abundance. Since high abundances often resulted in overgrazing and, thus, extirpation when movement was restricted, mobility had an important role in maintaining higher densities. The novel modeling approach shows how accounting for not just herbivore but also plant ecophysiology can improve our understanding of the population dynamics of highly mobile herbivores, in particular when examining the effects of habitat and climate change. Since the model simulates herbivores based on general physiological mechanisms that apply across large herbivores and the vegetation model can be applied globally, it is possible to adapt the model to other large-herbivore systems.

Comparison of two contrasting Leymus chinensis accessions reveals the roles of the cell wall and auxin in rhizome development

Leymus chinensis, a perennial native forage grass, is widely distributed in the steppes of Inner Mongolia as the dominant species. The main reproductive strategy of this grass is clonal propagation, which occurs via the proliferation of subterranean horizontal stems known as rhizomes. To elucidate the mechanism underlying rhizome development in this grass, we collected 60 accessions of L. chinensis and evaluated their rhizome development. One accession, which we named SR-74 (Strong Rhizomes), had significantly better rhizome development capacity than the accession WR-16 (Weak Rhizomes) in terms of rhizome number, total and primary rhizome length, and number of rhizome seedlings. Rhizome elongation was positively correlated with the number of internodes in the rhizome, which affected plant biomass. Compared to WR-16, SR-74 had higher rhizome tip hardness, higher abundance of transcripts participating in the biosynthesis of cell wall components, and higher levels of the metabolites L-phenylalanine, trans-cinnamic acid, 3-coumaric acid, ferulic acid, and coniferin. These metabolites in the phenylpropanoid biosynthesis pathway are precursors of lignin. In addition, SR-74 rhizomes contained higher amounts of auxin and auxin metabolites, including L-Trp, IPA, IBA, IAA and IAA-Asp, as well as upregulated expression of the auxin biosynthesis and signaling genes YUCCA6, YUCCA8, YUCCA10, YUCCA11, PIN1, PIN2, UGT1, UGT2, UGT4, UGT10, GH3, IAA7, IAA23, and IAA30. We propose a network between auxin signaling and the cell wall underlying rhizome development in L. chinensis.

Grazing-induced cattle behaviour modulates the secondary production in a Eurasian steppe ecosystem

Livestock-grassland interactions are among the most important relationships in grazed grassland ecosystems, where herbivores play a crucial role in plant community and ecosystem functions. However, previous studies primarily have focused on the responses of grasslands to grazing, with few focussing on the effects of livestock behaviour that in turn would influence livestock intake and primary and secondary productivity. Through a 2-year grazing intensity experiment with cattle in Eurasian steppe ecosystem, global positioning system (GPS) collars were used to monitor animal movements, where animal locations were recorded at 10-min intervals during the growing season. We used a random forest model and the K-means method to classify animal behaviour and quantified the spatiotemporal movements of the animals. Grazing intensity appeared to be the predominant driver for cattle behaviour. Foraging time, distance travelled, and utilization area ratio (UAR) all increased with grazing intensity. The distance travelled was positively correlated with foraging time, yielding a decreased daily liveweight gain (LWG) except at light grazing. Cattle UAR showed a seasonal pattern and reached the maximum value in August. In addition, the canopy height, above-ground biomass, carbon content, crude protein, and energy content of plants all affected cattle behaviour. Grazing intensity and the resulting change in above-ground biomass and forage quality jointly determined the spatiotemporal characteristics of livestock behaviour. Increased grazing intensity limited forage resources and promoted intraspecific competition of livestock, which induced longer travelling distance and foraging time, and more even spatial distribution when seeking habitat, which ultimately led to a reduction in LWG. In contrast, under light grazing where there were sufficient forage resources, livestock exhibited higher LWG with less foraging time, shorter travelling distance, and more specialized habitat occupation. These findings support the Optimal Foraging Theory and the Ideal Free Distribution model, which may have important implications for grassland ecosystem management and sustainability.

Predrought and Its Persistence Determined the Phenological Changes of Stipa krylovii in Inner Mongolia

Clarifying the response of plant phenology to drought duration is helpful for accurately interpreting and predicting carbon sinks in ecosystems. Based on the response of different phenological periods of the dominant species Stipa krylovii to monthly, seasonal, and semiannual time scale drought in the typical steppe of Inner Mongolia from 1983 to 2018, the results revealed that (1) the start of the growing season (SOS) was characterized by an advance–delay–advance pattern, and the heading stage (HOS), flowering stage (FOS), and end of the growing season (EOS) all showed consistent advanced trends, which provided additional insight into the conclusions of previous studies that found the SOS was advanced in arid and semiarid regions. (2) The response mechanism of the SOS to the timing of drought was not consistent. Among the response mechanism, the SOS was delayed because of the January–February drought at different time scales but advanced because of the April drought at different time scales. The HOS/FOS was delayed by the June–July drought at different time scales, and the EOS was advanced by the August–September drought at different time scales. (3) More importantly, the SOS, HOS, FOS, and EOS were affected by predrought and its persistence, and the effects were greater the closer to the phenological periods that drought occurred. (4) At the monthly scale, droughts in January, June, and August were the critical drought periods affecting the SOS, HOS/FOS, and EOS, while seasonal and semiannual scale droughts in February, June–July, and September were the critical periods affecting the SOS, HOS/FOS, and EOS. The results of this study enrich our understanding of how drought at different time scales affects different phenological periods, providing a basis for improving plant phenological models.

Hydrometeorological controls on net carbon dioxide exchange over a temperate desert steppe in Inner Mongolia, China

Understanding the effect of environmental factors on the net ecosystem CO2 exchange (NEE) and the response of NEE to rainfall events is of great significance for an accurate understanding of the carbon cycle for desert steppe ecosystems. Based on the long-term (2011–2018) eddy covariance flux data of a temperate desert steppe in Inner Mongolia, China, this study used path analysis to analyze the combined impact of the environmental factors on NEE. The results showed that during the growing season, vapor pressure deficit (VPD) and soil water content (SWC) was the most prominent environmental factor for the daytime NEE and nighttime NEE, respectively. NEE responds differently to individual environmental factors among multi-year climatic conditions. The size of rainfall event has significant impacts on NEE, it can effectively promote the CO2 uptake of the desert steppe ecosystem when rainfall event size is greater than 5 mm, and the NEE response increased with the rainfall event size. Moreover, NEE peaked approximately 1–3 days after a 5–10 mm rainfall event, while the rainfall event size >10 mm, it would take 3–5 days for NEE to reach a peak value; and yet, small rainfall events (< 5 mm) slightly increased CO2 emissions. During the growing season, carbon uptake increased with monthly rainfall, except in May. Our results are important for understanding the carbon cycle and its control mechanisms in the temperate desert steppe of Inner Mongolia.

Random forest method for analysis of remote sensing inversion of aboveground biomass and grazing intensity of grasslands in Inner Mongolia, China

ABSTRACT The quantification of grassland above-ground biomass (AGB) and grazing intensity (GI) and their distribution in space is of great significance to grassland management and eco-conservation. Remote-sensing technology is widely applied, but it is difficult to measure accurately when monitoring GI. In this study, the neural network, random forest and statistical function models of the relationship between Landsat NDVI and AGB were constructed by field survey and literature data collection in Inner Mongolia grassland, China. By comparing the accuracy among the three models, we constructed a remote-sensing retrieving model of grass AGB. We also estimated the grassland AGB during the peak growing season (August) for Inner Mongolia. Frequency histograms were then made to identify AGB thresholds under four GI levels (light or ungrazed, moderate grazing, overgrazing and extreme grazing) for each of three grassland types (meadow steppe, typical steppe and desert steppe). This study shows that the random forest model simulates grass AGB more accurately than other models. The spatial distribution of AGB in Inner Mongolia grasslands showed a tendency of decreasing from southeast to northwest, with an increasing trend in the last 10 years. The four GI levels in 2021 accounted for 18%, 25%, 36% and 21% of the grasslands in Inner Mongolia, respectively, and over the last 10 years the GI first improved and then deteriorated. This study provides a guideline to remote monitoring for grassland AGB and GI, and supplies scientific support for sustainable management and grassland restoration of large-scale grasslands.