Prediction of the potentially suitable areas of Ligularia virgaurea and Ligularia sagitta on the Qinghai-Tibet Plateau based on future climate change using the MaxEnt model.

Ligularia virgaurea and Ligularia sagitta are two species of poisonous plants with strong invasiveness in natural grasslands in China that have caused considerable harm to animal husbandry and the ecological environment. However, little is known about their suitable habitats and the key environmental factors affecting their distribution. Although some studies have reported the distributions of poisonous plants on the Qinghai-Tibet Plateau (QTP) and predicted their potential distributions at local scales in some regions under climate change, there have been few studies on the widespread distributions of L. virgaurea and L. sagitta. In this study, we recorded 276 and 118 occurrence points of L. virgaurea and L. sagitta on the QTP using GPS, and then used the MaxEnt model to predict the distribution of suitable habitats. Results showed that (1) under current climate conditions, L. virgaurea and L. sagitta are mainly distributed in southern Gansu, eastern Qinghai, northwestern Sichuan, eastern Tibet, and southwestern Yunnan, accounting for approximately 34.9% and 39.8% of the total area of the QTP, respectively; (2) the main environmental variables affecting the distribution of suitable habitats for L. virgaurea and L. sagitta are the Human Footprint Index (52.8%, 42.2%), elevation (11%, 4.4%), soil total nitrogen (18.9%, 4.2%), and precipitation seasonality (5.1%, 7.3%); and (3) in the future, in the 2050s and 2070s, the area of habitat of intermediate suitability for L. virgaurea will spread considerably in northwest Sichuan, while that of high suitability for L. sagitta will spread to eastern Tibet and western Sichuan.

Daily and Seasonal Activity Patterns of Plateau Pikas (Ochotona curzoniae) on the Qinghai-Tibet Plateau, China, and Their Relationship with Weather Condition.

Exploring the activity patterns of small mammals is important for understanding the survival strategies of these animals, such as foraging and mating. The purpose of the present study was to determine the activity of free-living plateau pikas (Ochotona curzoniae) in different months and seasons (cold and warm seasons), with a particular emphasis on the effects of weather condition. Based on a camera-trapping survey conducted from October 2017 to September 2018, we evaluated the activity patterns and activity levels of plateau pikas inhabiting the eastern Qinghai-Tibet Plateau in China. The effects of environmental factors on the activity of plateau pikas were examined using the generalized additive mixed model (GAMM). The results showed that: (1) The plateau pikas exhibited unimodal patterns of activity during the cold season (October-April). During the warm season (May-September), the activity patterns of the plateau pikas were bimodal. Their activity levels were highest in June. (2) During the cold season, their activity levels rose gradually over the course of the day to a peak near noon, and they were not significantly higher after sunrise than they were before sunset. During the warm season, their activity peaks were in the morning and afternoon, and their activity levels were substantially lower after sunrise than they were before sunset. (3) The plateau pikas were more active under conditions with lower ambient temperatures and precipitation during the cold and warm seasons. While relative air humidity was positively correlated with the activity of the plateau pikas during the warm season, wind speed was negatively correlated with the pikas' activity during the cold season. Overall, these results collectively indicate that plateau pikas occupy habitats with cool and less windy microclimates during the cold season, and with cool and moist microclimates during the warm season. Information on the time allocation of pikas' activity levels during different seasons should provide a baseline for understanding their potential for adaptation to climate change.

Alarm Calling in Plateau Pika (Ochotona curzoniae): Evidence from Field Observations and Simulated Predator and Playback Experiments.

Acoustic communication plays a vital role in passing or sharing information between individuals. Identifying the biological meaning of vocal signals is crucial in understanding the survival strategies of animals. However, there are many challenges in identifying the true meaning of such signals. The plateau pika (Ochotona curzoniae) is a call-producing mammal endemic to the Qinghai-Tibet plateau (QTP) and considered a keystone species owing to its multiple benefits in alpine rangeland ecosystems. Previous studies have shown that plateau pikas emit alarm calls as part of their daily activities. However, only field observations have been used to identify these alarm calls of the plateau pika, with no attempts at using playback experiments. Here, we report the alarm calling of plateau pikas through field observations as well as simulated predator and playback experiments in the Eastern QTP from 2021 to 2022. We found that both female and male adults emitted alarm calls, the signals of which comprised only one syllable, with a duration of 0.1-0.3 s. There were no differences in the characteristics between the observed alarm calls and those made in response to the simulated predator. The duration of the alarm call response varied with altitude, with plateau pikas living at higher altitudes responding at shorter durations than those at lower altitudes.

The Complex and Well-Developed Morphological and Histological Structures of the Gastrointestinal Tract of the Plateau Zokor Improve Its Digestive Adaptability to High-Fiber Foods.

The morphological and histological traits of the gastrointestinal tract (GIT) enable the animal to perform some specific functions that enhance the species' adaptability to environments. The plateau zokor (Eospalax baileyi) is a subterranean rodent that mainly forages on plant roots in the Qinghai-Tibet Plateau, but little is known about the mechanism by which the plateau zokor digests roots that have high fiber contents. In this study, we used comparative anatomy methods to compare the morphological and histological traits of the GIT of both the plateau zokor and the plateau pika (Ochotona curzoniae), a small, fossorial lagomorph that forages aboveground plant parts, in order to clarify the traits of the plateau zokor's GIT and to understand its adaptations to high-fiber foods. The results showed that the foods which plateau zokors eat have a higher fiber content than those which the plateau pikas eat. The plateau zokor has a double-chambered and hemi-glandular stomach (the tubular glands are only in the gastric corpus II, and the gastric fundus is keratinized), whereas the plateau pika has a simple, wholly glandular stomach. The gross morphological indicators (organ index and relative length) of the GIT were significantly lower in the plateau zokor than they were in the plateau pika (p < 0.001). However, the thickness of the gastric corpus II mucosal layer and the gastric fundus muscle layer are significantly higher in the plateau zokor than they are in the plateau pika (p < 0.001), and the thickness of each layer of intestinal tissue is higher in the plateau zokor than it is in the plateau pika. Additionally, the small intestinal villi also are higher and wider in the plateau zokor than they are in the plateau pika. Our results suggest that instead of adapting to digest the high-fiber diet by expanding the size of the GIT, the plateau zokor has evolved a complex stomach and a well-developed gastrointestinal histological structure, and that these specialized GIT structures are consistent with an optimal energy-economy evolutionary adaptation strategy.

Environmental stress-discriminatory taxa are associated with high C and N cycling functional potentials in dryland grasslands.

Increasing environmental stress strongly affects soil microbial communities, but the responses of the microbial assembly and the functional potential of the dominant microbial community in the presence of environmental stress in drylands are still poorly understood. Here, we undertook a broad appraisal of the abundance, diversity, similarity, community assembly, network properties and functions of soil microbiomes in 82 dryland grasslands along environmental gradients. We found that the bacterial and fungal diversity and community similarity showed different sensitivities to environmental stress (decreased mean annual precipitation (MAP) and soil nutrient levels and increased soil pH), and MAP was the most important factor influencing microbial community patterns. In addition, the dominant subcommunity of both bacteria and fungi was more sensitive to environmental stress than the nondominant subcommunity. Although increasing environmental stress decreased microbial phylogenetic clustering, it had no effects on the stochastic and deterministic assembly process balance. Moreover, we identified 101 bacterial and 34 fungal environmental stress-discriminatory taxa that were sensitive to environmental stress, and these bacterial markers showed a high correlation with the abundance of carbon (C) and nitrogen (N) cycling-related genes, whereas the taxa classified as connectors in the network were mainly correlated with C degradation genes. Our study shows that the different responses of bacteria and fungi to environmental stress bring challenges to predicting microbial function, but a relatively small number of taxa play an important role in driving C and N cycling-related functional genes, indicating that identifying an organism's phenotypic characteristics or traits of key taxa may improve our knowledge of the microbial response to ongoing global changes.

Increased burrow oxygen levels trigger defensive burrow-sealing behavior by plateau zokors.

Defensive behaviors are a response to immediate and potential threats in the environment, including abiotic and biotic threats. Subterranean rodents exhibit morphological and physiological adaptions for life underground, and they will seal with mounds and additional plugs when their burrow opened. However, little is known about the factors driving this defensive behavior. In this study, we selected a subterranean rodent, plateau zokor (Myospalax fontanieri), as a species to investigate (both in the laboratory and in the field) the possible factors responsible for burrow-sealing behavior. Our results showed that: (1) In the laboratory, the burrow-sealing frequency of plateau zokor in response to five factors were as follows: oxygen (52.63%) > light (34.58%) > temperature (20.24%) > gas flow (6.48%) > sound/control (0%). Except for light, the burrow-sealing frequency in response to other factors was significantly lower than that in response to oxygen (P < 0.05). (2) Burrow-sealing behavior in response to each treatment did not differ significantly between males and females in the laboratory experiment. (3) In the field, during the animal's active periods in both the cold and warm season, the burrow-sealing frequency under the oxygen treatment was higher than that under the light and temperature treatments. Plateau zokors were found not to be sensitive to these treatments during their inactive periods during both the cold and warm season. (4) The latency to reseal the burrow showed no obvious differences between each treatment both in the laboratory and in the field. In conclusion, the main factor that influences the burrow-sealing behavior of plateau zokors is the variation in oxygen concentration, and this defensive behavior is related to their activity rhythm.

Impact of desertification on soil and plant nutrient stoichiometry in a desert grassland.

Grassland degradation resulting from desertification often alters the carbon (C), nitrogen (N) and phosphorus (P) cycles within grassland ecosystems. To estimate the effects of desertification on the C, N, and P concentrations and C:N:P stoichiometry of plants and soil, we examined C, N, and P concentrations in plant tissues (leaves, roots and litter) and soil across five degrees of desertification in the desert grassland of Ningxia, China (control, light, moderate, severe and very severe desertification stages). The C, N, and P concentrations and C:N:P stoichiometry of the leaves, roots and litter differed among the different desertification stages. Desertification resulted in opposing trends between the leaf N concentration and leaf C:N ratio. With the exception of the very severe desertification stage, the leaf N:P ratio decreased over the process of grassland desertification. The soil C, N, and P concentrations and soil N:P and C:P ratios decreased significantly along the grassland desertification gradient. In contrast, the soil C:N ratio remained relatively stable during desertification (10.85 to 11.48). The results indicate that desertification is unfavourable to C and N fixation and has a negative effect on the ecosystem structure and function of desert grassland.

Plant diversity is closely related to the density of zokor mounds in three alpine rangelands on the Tibetan Plateau.

BACKGROUND: Plateau zokor (Myospalax baileyi) is a subterranean rodent endemic to the Tibetan Plateau. This species has been generally viewed as a pest in China due to the competition for food with livestock and also causing soil erosion. As a result, plateau zokor has been the target of widespread poisoning or trapping campaigns designed to control or eliminate it since 1970s. But there is little research on the effect of plateau zokor on plant diversity in alpine rangelands. Therefore, objectively evaluating the positive effects of the plateau zokors disturbance on their living environment and plant communities is of great significance to understand the function of plateau zokor in alpine ecosystem. METHODS: Here, we selected three rangelands (alpine meadow, alpine steppe and alpine shrub meadow) in which plateau zokors are typically distributed on the Tibetan Plateau, and five zokor mound density gradients were selected in each rangeland type to study the effects of the mounds on soil moisture and temperature related to plant species diversity. RESULTS: The results showed that, with the mound density increasing, the soil temperature decreased significantly in all three rangeland types, and the soil moisture significantly increased in all three rangeland types. In the alpine meadow, both the plant diversity and cumulative species richness increased significantly with increasing mound density. The increase in broad-leaved forbs is the main reason for the increase of plant diversity in the alpine meadow disturbed by zokor mounds. In the alpine steppe, the plant diversity decreased significantly with increasing mound density, while the cumulative species richness initially decreased and then increased. In the alpine shrub meadow, the plant diversity first increased and then decreased with increasing mound density as did the cumulative species richness. In conclusion, plateau zokor mounds dominated the distribution of soil moisture and temperature and significantly affected plant diversity in these three rangelands on Tibetan Plateau; the results further deepen our understanding toward a co-evolved process.

Effects of grassland afforestation on structure and function of soil bacterial and fungal communities.

Grassland afforestation strongly influences the structure and function of soil microorganisms. Yet the mechanisms of how afforestation could simultaneously alter both the soil fungal and bacterial communities and its implications for ecosystem management are poorly understood, especially in nitrogen-limited ecosystems. Using high-throughput sequencing of 16S rRNA and ITS rRNA genes, the present study investigated the changes in soil properties and soil microorganisms after afforestation of natural grasslands with Chinese pine (Pinus tabuliformis) on the Loess Plateau in China. Results showed that soil bacterial diversity had no significant differences among the grassland (GL), forest-grassland transition zone (TZ), and forestland (FL), while soil fungal diversity in the GL was significantly higher than that in the FL and TZ (P < 0.05). The proportion of shared OTUs in the soil bacterial community was higher than that in the soil fungal community among the three land use types. The dominant bacterial phylum shifted from Proteobacteria to Actinobacteria, while the dominant fungal phylum shifted from Ascomycota to Basidiomycota after the GL conversion to the FL. The functional groups of ECM fungi increased significantly while biotrophic fungi decreased significantly after grassland afforestation. Both the soil bacterial and fungal communities in the TZ showed great similarity with those in the FL. In addition, among all examined soil properties, soil nitrogen (N) showed a more significant effect on the soil microbial communities. The reduction of soil N after grassland afforestation resulted in both the structure and function changes in soil microbial communities. Our results demonstrated simultaneously differential changes in the composition and diversity of both soil bacterial and fungal communities after afforestation from grasslands to planted forests.

Prediction of aboveground grassland biomass on the Loess Plateau, China, using a random forest algorithm.

Grasslands are an important component of terrestrial ecosystems that play a crucial role in the carbon cycle and climate change. In this study, we collected aboveground biomass (AGB) data from 223 grassland quadrats distributed across the Loess Plateau from 2011 to 2013 and predicted the spatial distribution of the grassland AGB at a 100-m resolution from both meteorological station and remote sensing data (TM and MODIS) using a Random Forest (RF) algorithm. The results showed that the predicted grassland AGB on the Loess Plateau decreased from east to west. Vegetation indexes were positively correlated with grassland AGB, and the normalized difference vegetation index (NDVI) acquired from TM data was the most important predictive factor. Tussock and shrub tussock had the highest AGB, and desert steppe had the lowest. Rainfall higher than 400 m might have benefitted the grassland AGB. Compared with those obtained for the bagging, mboost and the support vector machine (SVM) models, higher values for the mean Pearson coefficient (R) and the symmetric index of agreement (λ) were obtained for the RF model, indicating that this RF model could reasonably estimate the grassland AGB (65.01%) on the Loess Plateau.

Effect of desertification on productivity in a desert steppe.

Desertification, one of the most severe types of land degradation in the world, is of great importance because it is occurring, to some degree, on approximately 40% of the global land area and is affecting more than 1 billion people. In this study, we used a space-for-time method to quantify the impact of five different desertification regimes (potential (PD), light (LD), moderate (MD), severe (SD), and very severe (VSD)) on a desert steppe ecosystem in northern China to examine the relationship between the productivity of the vegetation and soil properties and to determine the mechanism underlying the effects of desertification on productivity. Our results showed that the effects of desertification on TP (total phosphorus) and AP (available phosphorus) were not significant, and desertification decreased productivity in the desert steppe as a result of direct changes to soil physical properties, which can directly affect soil chemical properties. Therefore, intensive grassland management to improve soil quality may result in the long-term preservation of ecosystem functions and services.