Combining the Optimized Maximum Entropy Model to Detect Key Factors in the Occurrence of Oedaleus decorus asiaticus in the Typical Grasslands of Central and Eastern Inner Mongolia.

Grasshoppers pose a significant threat to both natural grassland vegetation and crops. Therefore, comprehending the relationship between environmental factors and grasshopper occurrence is of paramount importance. This study integrated machine learning models (Maxent) using the kuenm package to screen MaxEnt models for grasshopper species selection, while simultaneously fitting remote sensing data of major grasshopper breeding areas in Inner Mongolia, China. It investigated the spatial distribution and key factors influencing the occurrence of typical grasshopper species in grassland ecosystems. The modelling results indicate that a typical steppe has a larger suitable area. The soil type, above biomass, altitude, and temperature, predominantly determine the grasshopper occurrence in typical steppes. This study explicitly delineates the disparate impacts of key environmental factors (meteorology, vegetation, soil, and topography) on grasshopper occurrence in typical steppes. Furthermore, it provides a methodology to guide early warning and precautions for grasshopper pest prevention. The findings of this study will be instrumental in formulating future management measures to guarantee grass ecological environment security and the sustainable development of grassland.

Exclusion of livestock decouples the relationship between plant production and diversity, species richness on complex topography in typical steppe in the Loess Plateau, China.

Grazing is widely used in more than one-forth of global terrestrial ecosystems, with three quarters are distributed on complex topography. Grazing and topography have both resulted in degradation of approximately 49 % of natural grasslands. However, research on the interaction between topography and livestock exclusion on grassland characteristics is scarce. This study was carried out on a typical steppe to explore the effect of topography and enclosure year on vegetation characteristics. Aboveground biomass, and species richness were examined for three different enclosure years (0, 3, and 6 years), on four slopes (0°, 15°, 30°, and 45° slope), and three aspects (flat, shady and sunny). The results indicated that: The aboveground biomass on the 0° slope had a greater value after 6 years of the enclosure. Aboveground biomass increased with the increasing enclosure year, while it decreased with increasing slope except enclosure for 0 year on shady slope. Aboveground biomass on the shady slopes was greater than on the sunny slopes. Species richness of community and perennial plants increased with increasing slope and enclosure year. The annual plants richness inversely correlated with slope and enclosure year. All plant diversity indexes increased with increasing enclosure year. Margalef and Shannon-wiener indexes decreased with increasing slope, while Simpson and Pielou indexes increased. This paper demonstrates that aspect, slope and enclosure affect aboveground biomass by affecting other vegetation characteristics. In conclusion, grassland production can be improved with moderate livestock exclusion under different topography.

Long-term grazing improved soil chemical properties and benefited community traits under climatic influence in an alpine typical steppe.

Grazing and climate change both contribute to diversity loss and productivity fluctuations. Sensitive climate conditions and long-term grazing activities have a profound influence on community change, particularly in high-altitude mountain grassland ecosystems. However, knowledge about the role of long-term continuous grazing management on diversity, productivity and the regulation mechanisms in fragile grassland ecosystems is still rudimentary. We conducted a long-term grazing experiment on an alpine typical steppe in the Qilian Mountains to assess effects of grazing intensity on soil, diversity, productivity and the regulation mechanisms. Plants and soil were sampled along grazing gradients at different distances from the pasture entrance (0, 0.3, 0.6, 0.9, 1.2 and 1.5 km) under the non-growing (WP) and the growing season grazing pasture (SAP). The results revealed that community diversity and biomass did not change significantly on a time scale, while the concentration of soil organic carbon and total phosphorus increased significantly. Heavy grazing (0-0.3 km) decreased community diversity and biomass. Grazing increased soil chemical properties in heavy grazed areas of WP, while the opposite was recorded in SAP. Soil chemical properties explained the largest variances in community diversity and community biomass. The prediction model indicates that grazing in WP mainly affects community diversity through soil chemical properties, and promotes a positive correlation between community diversity and community biomass; in SAP, the direct effect of grazing gradients on community diversity and biomass is the main pathway, but not eliminating the single positive relationship between diversity and biomass, which means that diversity can still be used as a potential resource to promote productivity improvement. Therefore, we should focus on the regulation of soil chemical properties in WP, such as the health and quality of soil, strengthening its ability to store water, sequester carbon and increase nutrients; focus on the management of livestock in SAP, including providing fertilizer and sowing to increase diversity and production in heavily grazed regions and reducing grazing pressure through regional rotational grazing. Ultimately, we call for strengthening the stability and sustainability of ecosystems through targeted and active human intervention in ecologically sensitive areas to cope with future grazing pressures and climate disturbances.

Clipping decreases plant cover, litter mass, and water infiltration rate in soil across six plant community sites in a semiarid grassland.

Water infiltration in the soil is a crucial hydrological function in the land water cycle, especially in the semiarid region where water is relatively scarce. The semiarid grassland in Northern China represents the regional vegetation in the vast area of Eurasian continent and is sensitive to land use change. However, no clear patterns exist regarding the comprehensive examination of water infiltration in relation to clipping across six plant community sites. This study aimed to test the effect of clipping and plant community sites, which were dominated by Agropyron cristatum, Stipa krylovii, Leymus chinensis, Potentilla tanacetifolia, Artemisia frigida, or Lespedeza davurica, on the water infiltration rate in the semiarid grassland. Clipping significantly decreased the water initial, steady, and average infiltration rates by 39.13, 4.36, and 12.46 mm h-1, respectively, across the six plant community sites. Clipping-induced changes in the average infiltration rate positively correlated with the changes in the plant cover (r = 0.60, P < 0.01), litter mass (r = 0.53, P < 0.01), forb functional group ratio (r = 0.46, P = 0.03), and total porosity (r = 0.49, P = 0.02), and negatively with water-holding capacity (r = -0.45, P = 0.03). Further, the water infiltration rate significantly differed among the six plant community sites. The L.davurica site had the highest water initial infiltration rate with a value of 137.63 ± 17.76 mm h-1, while the L. chinensis site had the lowest rate with a value of 74.08 ± 5.26 mm h-1. Principal component analysis showed that the total porosity, litter mass, plant cover, and forb functional group ratio were the main factors affecting water infiltration rates in the control grassland. Overall, our findings suggested that local governments and herders should implement unclipping as a potential sustainable management for improving hydrological function in the semiarid grassland.

Biodiversity and soil pH regulate the recovery of ecosystem multifunctionality during secondary succession of abandoned croplands in northern China.

The 'Grain-for-Green' program in China provides a valuable opportunity to investigate whether spontaneous restoration can reverse the deterioration of grassland ecosystem functions. Previous studies have focused on individual ecosystem functions, but the response of and mechanisms driving variation in ecosystem multifunctionality (EMF) during restoration are poorly understood. Here, we quantified EMF using productivity, nutrient cycling, and water regulation functions along abandoned croplands in a recovery chronosequence (5, 15 and 20 years) and in natural grasslands in the desert steppe and typical steppe. We also analyzed the effects of plant and microbial diversity and an abiotic factor (soil pH) on EMF. Our results showed that EMF increased gradually concomitant with recovery time, shifting toward EMF values comparable to those in natural grasslands in both desert and typical steppe. Similar results were found for the productivity function, the water regulation function, and soil organic carbon. However, even after 20 years of restoration, EMF did not reach the levels observed in natural grasslands. Structural equation modeling showed that the driving mechanisms of EMF differed between the two steppe types. Specifically, in the desert steppe, plant diversity, especially the diversity of perennial graminoids and perennial herbs, had a positive effect on EMF, but in the typical steppe, soil bacterial diversity had a negative effect, while soil pH had a positive effect on EMF. Our results demonstrated that spontaneous grassland restoration effectively enhanced EMF, and emphasized the importance of biodiversity and soil pH in regulating EMF during secondary succession. This work provides important insights for grassland ecosystem management in arid and semi-arid regions.

Detecting Key Factors of Grasshopper Occurrence in Typical Steppe and Meadow Steppe by Integrating Machine Learning Model and Remote Sensing Data.

Grasshoppers mainly threaten natural grassland vegetation and crops. Therefore, it is of great significance to understand the relationship between environmental factors and grasshopper occurrence. This paper studies the spatial distribution and key factors of grasshopper occurrence in two grass types by integrating a machine learning model (Maxent) and remote sensing data within the major grasshopper occurrence areas of Inner Mongolia, China. The modelling results demonstrate that the typical steppe has larger suitable area and more proportion for grasshopper living than meadow steppe. The soil type, above biomass, altitude and temperature mainly determine the grasshopper occurrence in typical steppe and meadow steppe. However, the contribution of these factors in the two grass types is significantly different. In addition, related vegetation and meteorological factors affect the different growing stages of grasshoppers between the two grass types. This study clearly defines the different effects of key environmental factors (meteorology, vegetation, soil and topography) for grasshopper occurrence in typical steppe and meadow steppe. It also provides a methodology to guide early warning and precautions for grasshopper pest prevention. The findings of this study will be helpful for future management measures, to ensure grass ecological environment security and the sustainable development of grassland.

Trace elements apportionment in forage, soil, and livestock in rangeland ecosystems along climatic gradients.

BACKGROUND: Alpine meadows, typical steppes, and deserts are among the globally important rangeland types that are generally distributed along temperature and precipitation gradients. Mineral losses caused by grazing are one of the key factors that can lead to instability or even degradation of these rangeland ecosystems. METHODS: We examined the concentrations of Cu, Fe, Mn, and Zn in soil, forage, and livestock dungs from diverse rangeland types in northwest China, to determine the relationships between these trace elements (TEs) concentrations and climatic factors (i.e., temperature, precipitation, and humidity), and to evaluate the potential risks of TEs deficiencies or excesses in these rangeland ecosystems. RESULTS: Forage Zn concentrations in forage of all three types of rangeland, and Cu concentrations in forage of the alpine meadow did not meet the growth requirements of grazing livestock. Concentrations of Cu, Fe, and Mn in forage and Fe, Mn, and Zn in livestock dungs had quadratic parabola relationships with temperature, precipitation, and humidity, but the relationships between climate factors and Cu, Fe, and Mn concentrations in soil were not significant. In addition, the abilities of the plant to absorb Cu, Fe, and Zn from soil were stronger in the typical steppe than that in the alpine meadows and desert. Also, the abilities of livestock to return TEs to soil were stronger in the alpine meadow than that in the typical steppe and desert. CONCLUSION: We derived a conceptual mode that the ratio of TE concentrations of the plant to soil and of livestock dung to forage represents the abilities of plants to absorb TEs from the soil matrix and livestock to return TEs to soil or to absorb TEs from forage, respectively. Results indicate potentially more serious risks of TEs deficiencies, especially that of Zn than previously considered in typical steppes and desert rangelands.

[Comparison of root traits of Stipa krylovii and Allium polyrhizum under grazing in typical steppe.] / æ”¾ç‰§å½±å“ä¸‹å ¸åž‹è‰åŽŸå ‹æ°é’ˆèŒ å’Œå¤šæ ¹è‘±æ ¹ç³»å±žæ€§æ¯”è¾ƒ.

Plant ecological adaptation is associated with root traits. To clarify the differences of root traits between two dominant species, Stipa krylovii and Allium polyrhizum, under different grazing intensities (light, moderate, and heavy grazing intensities), we measured root traits, including root length, root surface area, root diameter, root volume, root tips, root bifurcations, specific root length, and specific surface area. We analyzed the root morphological patterns of tip proportion, length proportion, surface proportion and volume proportion of both species, and examined their ecological adaptation strategies under grazing. The results showed that grazing inhibited aboveground and belowground growth of S. krylovii, but promoted belowground growth of A. polyrhizum. In addition, the effects of grazing on belowground part of S. krylovii was greater than aboveground part. These results indicated that the growth of S. krylovii was maintained by the aboveground part and that of A. polyrhizum was maintained by the belowground part under grazing. Root length, root bifurcations, root surface area and root tips were the main factors affecting root traits of S. krylovii, while root length, root surface area and root volume were the main factors affecting root traits of A. polyrhizum. S. krylovii could adapt to grazing stress by increasing length proportion, surface proportion and volume proportion of diameter class of 0-0.7 mm, while A. polyrhizum by increasing the length proportion, surface proportion and volume proportion of diameter class of 1.4-1.8 mm. The study on the differences of root traits between S. krylovii and A. polyrhizum could help provide a scientific basis for controlling grassland degradation.

Spontaneous grassland recovery on abandoned croplands in northern China: Different vegetation patterns in desert and typical steppe.

Passive restoration (without any intervention) has been proposed as an effective strategy for grassland restoration in abandoned croplands. However, whether the vegetation in abandoned croplands can change towards the desired state and the time needed to reach a relative stable state are context-dependent. We investigated three abandoned croplands with different recovery times (5, 15 and 20 years) and one natural grassland in each of two different types of steppe (desert steppe and typical steppe) in the agro-pastoral ecotone of northern China to assess the restoration potential of grassland on abandoned croplands. Above- and below-ground biomass as well as species biodiversity increased gradually with increasing recovery time. After 20 years of restoration there was no significant difference between abandoned cropland and natural steppe in the typical steppe site, but above- and below-ground biomass and species biodiversity were still lower in abandoned cropland in the desert steppe site. At the beginning of restoration, the communities were dominated mainly by annual species, especially in the desert steppe. As recovery time increased, the biomass and richness of perennial graminoids and forbs increased significantly and replaced annual species as the dominant species. In both desert steppe and typical steppes, species similarity between restored and natural steppe increased over time, suggesting that previously cultivated grassland recovered towards the desired state. Our results indicate that 20 years was sufficient time for the restoration of croplands in the typical steppe, but more time may be needed in the desert steppe.

Increased precipitation enhances soil respiration in a semi-arid grassland on the Loess Plateau, China.

BACKGROUND: Precipitation influences the vulnerability of grassland ecosystems, especially upland grasslands, and soil respiration is critical for carbon cycling in arid grassland ecosystems which typically experience more droughty conditions. METHODS: We used three precipitation treatments to understand the effect of precipitation on soil respiration of a typical arid steppe in the Loess Plateau in north-western China. Precipitation was captured and relocated to simulate precipitation rates of 50%, 100%, and 150% of ambient precipitation. RESULTS AND DISCUSSION: Soil moisture was influenced by all precipitation treatments. Shoot biomass was greater, though non-significantly, as precipitation increased. However, both increase and decrease of precipitation significantly reduced root biomass. There was a positive linear relationship between soil moisture and soil respiration in the study area during the summer (July and August), when most precipitation fell. Soil moisture, soil root biomass, pH, and fungal diversity were predictors of soil respiration based on partial least squares regression, and soil moisture was the best of these. CONCLUSION: Our study highlights the importance of increased precipitation on soil respiration in drylands. Precipitation changes can cause significant alterations in soil properties, microbial fungi, and root biomass, and any surplus or transpired moisture is fed back into the climate, thereby affecting the rate of soil respiration in the future.

Phytolith-occluded carbon sequestration potential in three major steppe types along a precipitation gradient in Northern China.

Phytolith-occluded carbon (PhytOC) is an important long-term stable carbon fraction in grassland ecosystems and plays a promising role in global carbon sequestration. Determination of the PhytOC traits of different plants in major grassland types is crucial for precisely assessing their phytolith carbon sequestration potential. Precipitation is the predominant factor in controlling net primary productivity (NPP) and species composition of the semiarid steppe grasslands. We selected three representative steppe communities of the desert steppe, the dry typical steppe, and the wet typical steppe in Northern Grasslands of China along a precipitation gradient, to investigate their species composition, biomass production, and PhytOC content for quantifying its long-term carbon sequestration potential. Our results showed that (a) the phytolith and PhytOC contents in plants differed significantly among species, with dominant grass and sedge species having relatively high contents, and the contents are significantly higher in the below- than the aboveground parts. (b) The phytolith contents of plant communities were 16.68, 17.94, and 15.85 g/kg in the above- and 86.44, 58.73, and 76.94 g/kg in the belowground biomass of the desert steppe, the dry typical steppe, and the wet typical steppe, respectively; and the PhytOC contents were 0.68, 0.48, and 0.59 g/kg in the above- and 1.11, 0.72, and 1.02 g/kg in the belowground biomass of the three steppe types. (c) Climatic factors affected phytolith and PhytOC production fluxes of steppe communities mainly through altering plant production, whereas their effects on phytolith and PhytOC contents were relatively small. Our study provides more evidence on the importance of incorporating belowground PhytOC production for estimating phytolith carbon sequestration potential and suggests it crucial to quantify belowground PhytOC production taking into account of plant perenniality and PhytOC deposition over multiple years.

Response of Vegetation and Soil Characteristics to Grazing Disturbance in Mountain Meadows and Temperate Typical Steppe in the Arid Regions of Central Asian, Xinjiang.

Grazing is one of the most common causes of grassland degradation, therefore, an assessment of soil physicochemical properties and plant nutrients under grazing is important for understanding its influences on ecosystem nutrient cycling and for formulating appropriate management strategies. However, the effects of grazing on grassland soil physicochemical properties and plant nutrients in mountain meadow and temperate typical steppe in the arid regions are still unclear. Therefore, we investigated the vegetation nutrient concentrations of nitrogen, phosphorus and potassium (N, P, and K) as well as soil physicochemical properties in the topmost 40 cm depth soil, to evaluate how these factors respond to grazing disturbance in a mountain meadow and temperate typical steppe within a mountain basin system in arid regions. Our results revealed that the soil bulk density values at depth of 0-40 cm increased after grazing in the mountain meadow and temperate typical steppe, whereas the soil water content decreased in the mountain meadow and increased in the temperate typical steppe after grazing. In the mountain meadow, soil total N and available P in addition to vegetation N and P concentrations increased in response to high-intensity grazing, while soil available N, available K and vegetation K decreased after grazing; in addition, soil pH, soil total P and K showed no significant changes. In the temperate typical steppe, the soil total P, soil available N, P, and K, and vegetation N, P, and K increased under relatively low-intensity grazing, whereas soil pH and soil total K showed no significant changes except for the deceasing soil total N. Our findings showed the different responses of different grassland ecosystems to grazing. Moreover, we propose that further related studies are necessary to better understand the effects of grazing on grassland ecosystems, and thereby provide a theoretical basis for the sustainable use of animal husbandry and ecological restoration of grasslands.

AM fungal diversity and its impact across three types of mid-temperate steppe in Inner Mongolia, China.

Arbuscular mycorrhizal (AM) fungal diversity was measured in three different natural mid-temperate steppe types: the meadow steppe, typical steppe, and desert steppe. In these steppe soils, 24 AM fungal species from eight genera were identified, in which Glomus had the highest relative abundance. Funneliformis geosporus, Glomus microaggregatum, and Septoglomus constrictum had high relative abundance and were found widely across varying soil depth and steppe type. Meadow steppes had significantly higher AM fungal species richness compared to typical steppes and desert steppes, but there was no significant difference between typical steppes and desert steppes. AM fungal spore density, two Bradford-reactive soil protein (BRSP) fractions, and extraradical hyphal length densities (HLDs) were significantly different among the three steppe types. Alkaline phosphatase and acid phosphatase activity, urease activity, and soil bacterial and actinomycotic quantity were significantly related to the AM fungal spore density and species richness in these arid and semi-arid steppes. Therefore, steppe types could influence the distribution pattern of AM fungal diversity and the content of glomalin-related soil protein (GRSP).

Grazing exclusion promotes grasses functional group dominance via increasing of bud banks in steppe community.

To understand the bud banks response to grazing exclusion, we conducted a demographic experiment in long-term grazing exclusion (20 year and 30 year) typical steppe. Results showed that grass functional group constituted the vast majority of the aboveground vegetation and belowground bud bank in all treatments. Long-term grazing exclusion significantly increased total aboveground biomass (2.5 and 2.6 times in 20y and 30y grazing exclusion grasslands, respectively), and decreased total stem density (31% and 37% in 20y and 30y grazing exclusion grasslands, respectively). Grazing exclusion for 20 and 30 years increased grass aboveground biomass respectively by 6.0 and 8.0 times, and decreased grass stem density by 38% and 33%. Grazing exclusion had different effects on belowground bud density of grass and forb functional group. Long-term grazing exclusion significantly increased plant buds and bud bank size (25% and 37% in 20y and 30y grazing exclusion grasslands, respectively), especially for grass functional group (49% and 95% in 20y and 30y grazing exclusion grasslands, respectively), but had no significant effects on forb bud density. Changes of aboveground community were significantly related to changes of belowground bud bank under both grazing and grazing exclusion grasslands. The bud bank density of grass functional group was significantly positive with total (R2 = 0.33, P < 0.05) and grass aboveground biomass (R2 = 0.36, P < 0.01), while negative related with total (R2 = -0.27, P < 0.05) and grass stem density (R2 = -0.22, P < 0.05). Grazed grasslands, 20y and 30y grazing exclusion grasslands all were not meristem limited and had large reserve bud banks, which would completely replace the aboveground stem population during the growing season. These findings indicate that grazing exclusion could not only improve a large bud bank for grassland restoration but also improve the dominance of grass functional group by increasing grass belowground bud banks in typical steppe community. We propose that the belowground bud bank might be a good approach to indicating potential succession direction of aboveground community.

[Moderate grazing increases the abundance of soil methane-oxidizing bacteria and CH4 uptake rate in a typical steppe of Inner Mongolia, China.] / é€‚åº¦æ”¾ç‰§å¢žåŠ å† è’™å¤å ¸åž‹è‰åŽŸç”²çƒ·æ°§åŒ–èŒä¸°åº¦å’Œç”²çƒ·å¸æ”¶.

Microbial oxidation is the only biological sink of atmospheric methane (CH4). It is essential to understand the variation of CH4 fluxes among different grassland use types for developing low-emission management system. Here, we measured the CH4 flux and the soil methane-oxidizing bacteria abundance in a typical steppe under grazing, mowing and fencing management in central Inner Mongolia, with the aims to determine the effects of these grassland use types on CH4 flux, and to test the hypothesis that pmoA functional gene abundance regulates CH4 fluxes. The measurements were conducted on the experimental grassland that had experienced four grassland use treatments over five years. The treatments were whole growing season grazing from May to September (T1), spring and summer grazing (twice in May and July)(T2), autumn mowing (T3) and enclosure (T0). We measured CH4 flux using static chamber method, and quantified the abundance of pmoA functional genes using molecular techniques. Moreover, we measured plant biomass and soil physicochemical properties. The results showed that moderate grazing significantly enhanced CH4 uptake rate and the methane-oxidizing bacteria abundance (i.e., the pmoA gene copy number per gram of dry soil). The pmoA gene copy number ranged from 6.9×104 to 3.9×105 per gram of dry soil in growing season. The CH4 uptake rate was (68.21±3.01) µg·m-2·h-1 under T1, which was 22.1%, 37.5% and 30.9% higher than that under T2, T3 or T0 , respectively. The CH4 uptake rate was positively correlated with abundance of CH4 oxidizing bacteria and soil sand content, but negatively correlated with soil silt content, soil moisture, NH4+-N and NO3--N content, and plant biomass. These results suggested that the steppe ecosystem is a CH4 sink under all land-use types in central Inner Mongolia, and that moderate grazing would enhance methane-oxidizing bacteria abundance and CH4 uptake by improving soil sand content, reducing soil mineral nitrogen content and plant production in the typical steppe ecosystem. These results were of significance for the development of low-emission grassland management system.

[Dynamics of CO2 and N2O in Seasonal Frozen Soil Profiles for a Typical Steppe in Inner Mongolia].

In order to evaluate the effect of grazing on the mechanism for greenhouse gas emissions in the seasonal frozen soils for a typical steppe in Inner Mongolia, variations of N2O and CO2 concentrations in different soil layers were monitored by an in situ gas collection system. Three conditions were selected:ungrazed since 1979 (UG79), ungrazed since 1999 (UG99), and continuously grazed (CG). The results showed that the profile soil N2O and CO2 concentrations demonstrated a significant spatio-temporal distribution. ① The average concentrations of CO2 in the soil profile of the three conditions were:CO2 in the growth period > in the freezing-thawing period > in the freezing period. The CO2 concentrations in the growing period were much higher than in the freezing-thawing period and freezing period. The CO2 concentration was the highest in the UG79, and the lowest was in the CG. The concentration of CO2 in different soil layers was ordered as 20 cm ≥ 50 cm ≥ 35 cm ≥ 10 cm ≥ 5 cm at the UG79 and UG99 sites, and 50 cm ≥ 35 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm at the CG site. ② The spatial and temporal variation of N2O concentration in the soil profile was different from that of CO2. While the UG79 and UG99 sites showed a "single peak type" change, the CG site had a "bimodal" pattern. The N2O concentration of the three conditions increased sharply during the soil freezing-thawing period, and the N2O was also released weakly during the growing season at the CG site (P<0.05). The average N2O concentration of the CG was significantly higher than that of UG79 and UG99 (P<0.05). The results show that the concentration of N2O in different soil layers was ordered as follows:UG79:20 cm ≥ 50 cm ≥ 35 cm ≥ 10 cm ≥ 5 cm; CG:50 cm ≥ 35 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm, and UG99:35 cm ≥ 50 cm ≥ 20 cm ≥ 10 cm ≥ 5 cm. The results concluded that grazing decreased the profiled soil CO2 concentration and increased N2O concentration, which provides a basis for the accurate estimation of greenhouse gas emissions in the seasonal frozen soil in grasslands.

Defoliation and arbuscular mycorrhizal fungi shape plant communities in overgrazed semiarid grasslands.

Overgrazing substantially contributes to global grassland degradation by decreasing plant community productivity and diversity through trampling, defoliation, and removal of nutrients. Arbuscular mycorrhizal (AM) fungi also play a critical role in plant community diversity, composition, and primary productivity, maintaining ecosystem functions. However, interactions between grazing disturbances, such as trampling and defoliation, and AM fungi in grassland communities are not well known. We examined influences of trampling, defoliation, and AM fungi on semiarid grassland plant community composition for 3 yr, by comparing all combinations of these factors. Benomyl fungicide was applied to reduce AM fungal abundance. Overgrazing typically resulted in reduced dominance of Stipa Krylovii, contributing to degradation of typical steppe grasslands. Our results indicated trampling generally had little effect on plant community composition, unless combined with defoliation or AM fungal suppression. Defoliation was the main component of grazing that promoted dominance of Potentilla acaulis over Stipa krylovii and Artemisia frigida, presumably by alleviating light limitation. In non-defoliated plots, AM fungi promoted A. frigida, with a concomitant reduction in S. krylovii growth compared to corresponding AM suppressed plots. Our results indicate AM fungi and defoliation jointly suppress S. krylovii biomass; however, prolonged defoliation weakens mycorrhizal influence on plant community composition. These findings give new insight into dominant plant species shifts in degraded semiarid grasslands.

Effects of grazing exclusion on the grassland ecosystems of mountain meadows and temperate typical steppe in a mountain-basin system in Central Asia's arid regions, China.

Grazing exclusion has been proposed as a method of restoring degraded grassland ecosystems. However, its effectiveness remains poorly understood in mountain-basin grasslands in arid regions. Thus, we investigated the plant community characteristics, C and N storage levels, and soil organic carbon and total nitrogen concentrations and storage within the upper 0-40 cm soil layer in a grazed grassland (GG) and a fenced grassland (FG) with grazing exclusion in mountain meadow (MM) and temperate typical steppe (TTS) habitats in a mountain-basin ecosystem in an arid region of Central China, which are both vital grassland resources for livestock grazing and ecological conservation. In MM, our investigation revealed that grazing exclusion was beneficial to the productivity, coverage, height, diversity, and C and N storage of aboveground plants. However, grazing exclusion was not an effective option for soil C and N sequestration. In TTS, grazing exclusion effectively improved the plant productivity, coverage, height, plant and soil C and N sequestration, although it was not beneficial for maintaining plant diversity. Our findings suggest that reduced or rotational grazing may be a better choice than grazing exclusion in MM. In addition, considering the trade-off between biomass productivity and species diversity in TTS, short-term grazing exclusion should be considered. Additionally, grazing exclusion should be combined with other appropriate measures rather than operating on a standalone basis.

Drought and grazing drive the retrogressive succession by changing the plant-plant interaction of the main species in Inner Mongolia Steppe.

Plant-plant interactions play a key role in the function and structure of communities. The combined effect of drought stress and grazing disturbance on shaping plant-plant interactions is still poorly understood, while this combination is common in semiarid ecosystems. Four species including Stipa grandis, which is dominant in the typical steppe, and Stipa krylovii, Artemisia frigida, and Cleistogenes squarrosa, which are dominant species in the S. grandis degraded communities, were selected as study targets. We conducted a competition experiment (uniformly dense monoculture or mixture, respectively) under controlled conditions, including both drought stress and mowing disturbance, and calculated the relative interaction index (RII) of tiller number and RII of biomass for each species under each condition. (a) Under the same condition, the RII of tiller number and that of biomass for the same species usually showed reverse trends. (b) Mowing disturbance rather than drought stress played a negative role in influencing S. grandis' or S. krylovii's RII of tiller number and played a positive role in influencing A. frigida's RII of biomass. (c) Drought stress rather than mowing disturbance played a positive role in influencing C. squarrosa's RII of tiller number. (d) Neighbor species significantly influenced S. grandis' RII of tiller number, S. krylovii's RII of tiller number, A. frigida's RII of tiller number and biomass, and C. squarrosa's RII of biomass. These results could provide an explanation for why S. krylovii, A. frigida, and C. squarrosa can replace S. grandis and become the dominant species when S. grandis communities undergo a process of degradation due to overgrazing or climatic drought in natural communities. The present study provided powerful evidences for species replacement in the typical steppe of Inner Mongolia and elucidated the driving mechanisms of S. grandis communities' retrogressive succession.

Response of soil methane uptake to simulated nitrogen deposition and grazing management across three types of steppe in Inner Mongolia, China.

The response of soil methane (CH4) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) in Inner Mongolia, China. The experiment was designed with four simulated N deposition rates such as 0, 50, 100, and 200kgNha-1, respectively, under grazed and fenced management treatments. Results showed that the investigated steppes were significant sinks for CH4, with an uptake flux of 1.12-3.36kgha-1 over the grass growing season and that the magnitude of CH4 uptake significantly (P<0.05) decreased with increasing N deposition rates. The soil CH4 uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH4 uptake by 4.7-40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH4 uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH4 uptake and soil temperature was found in this study, whereas no significant relationship between soil moisture and CH4 uptake occurred. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH4 exchange processes and for evaluating the climate change feedback on CH4 soil uptake.