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Around one third of grasslands in Tibetan Plateau are in different extent of degradation, which is severely harmful for the production, livelihood and ecological security. Degradations of grassland, including structural imbalance and function receding of plant community and deterioration of soil physicochemical properties, are usually caused by natural factors like climate change or human activities like overgrazing. At present, the main measures for grassland restoration include fence enclosure, artificial vegetation cultivation and control of rodent, pest and weed, but all of these measures should be adopted according to degradation stage of the particular grasslands. Restoring the degraded grasslands, balancing the ecological, economic and social functions of alpine grasslands, and achieving the sustainable utilization of alpine grasslands are essential for ecological security, region stabilization and economic development, and the measures should be taken from macro-functions division, scientific development of stockbreeding and education of policies. In order to achieve the sustainable utilization of grassland resources and protection of grassland ecosystems, the adaptive management of alpine grassland ecosystems should be based on ecological theories. This special issue embodies the recent researches on the key processes and mechanisms of grassland degradation and restoration, all of which would provide valuable information for protection and regulation of alpine grassland ecosystem.
Desertification resulting from intensive human activities and climate change has become increasingly severe. Consequently, it is important to study soil physical and chemical properties and enzyme activity for the protection and restoration of grassland ecosystems. In this study, we observed plant community characteristics and analyzed soil physical and chemical properties and enzyme activities along a transect (from more to less degraded) in the Zoige alpine meadow ecosystem. As the degree of degradation increased, the soil bulk density, pH and the alkaline phosphatase (S-ALP) activity also increased, while soil organic carbon, total carbon, available nitrogen, total nitrogen, available nitrogen, total phosphorus, and activities of urease (S-UE), lignin peroxidase (S-Lip), β-glucosidase (S-β-GC) and N-acetyl-β-D-glucosidase (S-NAG) decreased. Soil pH was positively correlated with S-ALP (P<0.01), and negatively correlated with S-Lip, S-β-GC and (S-NAG) (P<0.01). S-ALP was negatively and linearly correlated with S-Lip (P< 0.01, R2=0.27) and S-β-GC (P< 0.05, R2=0.17), indicating that increased S-ALP activity has some inhibitory effect on S-Lip and S-β-GC. Moreover, S-Lip was positively and linearly correlated with S-β-GC (P<0.01, R2=0.59) and S-NAG(P<0.01, R2=0.26), suggesting that S-Lip could promote S-β-GC and S-NAG activities. The findings provide a scientific basis and important reference for further exploration of the dynamics of soil enzyme activity in grassland desertification, Zoige region.
Soil respiration is one of the most important components of the carbon cycle in terrestrial ecosystems. The widely distributed degradation of the alpine meadows on the Tibetan Plateau will impact the soil respiration and carbon cycle. In order to further explore the effects of degradation on the soil respiration of alpine meadows, we measured the soil respiration and related factors of alpine meadows under different levels of degradation in the Beiluhe area, and the relationships between soil respiration and biomass, belowground net primary productivity (BNPP) and soil temperature was analyzed . Our results showed that: 1) Soil respiration of alpine meadows at different levels of degradation showed similar dynamic characteristics during the growing season. Soil respiration increased first and then decreased along the degradation gradient, which reached the maximum under moderate degradation and significantly changed in the middle of the growing season (P < 0.05); 2) There was a significant positive linear correlation between the soil respiration and the aboveground biomass, belowground biomass, and BNPP (P < 0.05); 3) The soil respiration is exponentially correlated with the soil temperature. The temperature sensitivity of the soil respiration changed with the degradation. The Q10 under slight (Q10 = 3.26) and moderate degradation (Q10 = 3.22) was higher than that under non-degraded soils (Q10 = 2.66); however, under severe (Q10 = 2.49) and extreme degradation (Q10 = 1.96), this was lower than that under no degradation. The change in the temperature sensitivity is mainly caused by differences in the soil temperature, belowground biomass, and soil organic carbon content under different degradation levels. The results of this study will help further the understanding of the carbon cycle process of degraded grasslands.
The soil organic matter (SOM) represents the main terrestrial carbon pool and plays a key role in the carbon biogeochemical cycle. However, it is challenging to characterize the SOM at the molecule scale, due to its heterogeneous composition. To isolate the effects of the SOM composition on carbon dioxide emission, correlations were made between the SOM compositions and cumulative CO2 emissions in two alpine grassland soils. The SOM compositions were investigated using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results showed that: 1) the N-compounds were the main chemical components in the two types soils, with values of 38.0% and 52.5%; 2) there was a significant difference in the relative abundance of polysaccharides and terpenes between the two grassland types (P < 0.05); 3) polysaccharides affect the soil carbon dioxide emissions, the equation for which was Y = 86.76X + 344.87 (R2 = 0.63, P < 0.05) (Y is the cumulative CO2 emission, X is the relative abundance of polysaccharides); 4) the relative abundance of polysaccharides, N-compounds, and aromatics are significantly (P < 0.05) correlated with the bacteria, fungi, actinomycetes, gram-negative bacteria, and gram-positive bacteria. These results indicate that the SOM chemical composition of alpine grasslands is directly related to the soil microbial community and cumulative CO2 emission, and the relative abundance of some compounds can be used to analyze the soil respiration under specific incubation conditions, which is important for understanding the characteristics of soil CO2 emissions under different environmental conditions.
Soil microorganisms are an important part of grassland ecosystems. The soil microbial community structure is an effective indicator for reflecting the changes in soil quality. The desertified grassland of the Yellow River source region was the focus of this study, for which Illumina MiSeq sequencing was used to investigate the effects of different human intervention measures [unmanaged plots (CK), planting plots of 4 years (P1), rocky checkerboard sand barriers and planting plots of 4 years (P2), and rocky checkerboard sand barriers and planting plots of 12 years (P3)] on the bacterial and fungal community structures. Our results showed that: 1) for bacteria, the CK and P1 groups were placed into one group, with P2 and P3 in another; for fungi, CK and P1 were grouped first, then clustered with P2, whilst P3 was significantly different from the other three samples; 2) the content of the soil organic carbon and nitrate nitrogen in P3 was significantly higher than that in CK and P2 (P < 0.05), whereas the content of the total soil ammonium nitrogen showed no significant differences in any of the plots (P > 0.05); 3) the plant coverage in P3 was significantly higher than that in CK and P2 (P < 0.05), whilst the above-ground biomass of forbs in P3 was significantly higher than that in CK (P < 0.05). Our research suggests that the rocky checkerboard sand barriers and growing plants are effective measurements for combating desertification in alpine-cold areas. Additionally, the mixed human intervention measure is conducive to the change of the soil microbial community structure, accumulation of soil organic matter, and growth of grass seedlings in the early period of restoration of desertified grassland.
To understand the soil freezing-thawing cycle of alpine meadows in northern Tibet, we monitored the hydrothermal characteristics of alpine grassland soil profiles between 2015 and 2016, based on the Xianzha alpine grassland and wetland ecosystem observation station, and discussed the relationship between the freeze-thaw process and meteorology. The results showed that the soil temperature and moisture in each layer underwent sinusoidal periodic change, and the amplitude of the change varied with the depth. The soil freezing period extended from the beginning of November to the end of April of the next year, and the maximum depth of freezing was about 160 cm. According to the patterns of soil freezing and thawing, the freezing-thawing period was divided into four stages: initial freezing, stable freezing, early ablation, and late ablation. There was a significant correlation between the upper/lower freezing depths and accumulated temperature.
The coupling of water and heat in the freeze-thaw process is an important part of the hydrological cycle in cold regions, and it is an urgent problem that needs to be solved in the fields of agriculture, construction, and ecology in cold regions. We analyzed the freezing-thawing process of frozen soils and water-thermal coupling mechanism. At present, the driving force of water migration is mostly attributed to the soil water potential gradient, with the soil water characteristic curve used to solve the problem. However, this method does not consider the soil temperature, deformation, and physical properties. The hydrothermal coupling model achieves the coupling between water, temperature, and stress, but the feedback mechanisms of the changes in water, temperature, and stress on the soil characteristic parameters are not reflected. The mechanism for ice formation, under the action of multiple fields, is the key to solve the problem of soil frost heave. Meanwhile, we discussed the applicability and accuracy of the three types of current mainstream coupling models: The hydrodynamic, rigid ice, and thermodynamic models. Finally, we analyzed the current problems in the study of hydrothermal coupling in the freeze-thaw process.
Degraded alpine steppe is increasing, which limits the sustainable development of regions. The influences of soil physical and chemical properties on the aboveground biomass and community biodiversity, under the measures of fence restoration, were analyzed in this study. In addition, the critical regulators for plant recovery in degraded grasslands were explored. Consequently, the investigation of grazing exclusion 4, 5, 7, 8, and 9 years were conducted in the Shenza area of Tibet. The findings presented that: 1) In the enclosure steppes, the community biodiversity, aboveground biomass, and vegetation coverage increased at first and then decreased in 7 years. 2) The aboveground biomass and community biodiversity were positively correlated with the soil water content, soil organic matter, soil available nitrogen, and soil total nitrogen while negative relationship was found between the pH and soil bulk density. Our study highlighted that the key to the recovery of degraded grasslands is enhancing the soil water content and nutrients, moreover, seven years of grazing exclusion is the optimum duration in the alpine steppe of Northern Tibet.
Alpine grassland is an important component of the Tibetan Plateau. The degradation of these grasslands affects regional sustainable development. The mechanisms of linkage between soil properties and vegetation traits to the succession process of grassland degradation are still unclear. In the present study, we investigated the correlation of different vegetation characteristics and soil properties with degree of degradation (non-degraded to heavily degraded) of grasslands from across the Tibetan Plateau. The results showed that the aboveground and belowground biomass and the soil properties declined along the degradation gradient. For instance, in heavily degraded grassland, aboveground biomass, below-ground biomass, species richness and species evenness were lower by 42.44%, 60.64%, 21.08% and 8.36%, respectively, compared to non-degraded grasslands. Soil moisture content, organic carbon, total nitrogen and total phosphorus in heavily degraded grasslands were also lower by 33.57%, 45.75%, 22.70% and 11.23%, respectively, compared to non-degraded grasslands. The soil bulk density was 12.12% greater in heavily degraded grasslands than in non-degraded grasslands. In terms of response ratio, we found that vegetation biomass (aboveground biomass and belowground biomass) was positively related with soil properties (organic carbon, total nitrogen and total phosphorus) (P<0.05). The findings indicated that vegetation productivity and soil properties interacted with each other in the process of grassland degradation. In addition, the carbon content loss was more serious than nitrogen and phosphorus content loss.
In order to explore the effects of yak grazing disturbances on alpine meadows in different areas, we analyzed the aboveground biomass (AGB), belowground biomass (BGB), species richness (Richness), Shannon-Wiener index, Simpson index, Pielou index, 0–10 cm soil moisture (SM), and soil organic carbon (SOC) following grazing at different intensities (G1, G2, G3 and G1 < G2 < G3) in Maqu County (grazing intensity: G1 = 13 sheep·ha–1, G2 = 17.6 sheep·ha–1, G3 = 32.5 sheep·ha–1) in Gannan Prefecture, Gansu Province, and in Maqin County (grazing intensity: G1 = 13.2 sheep·ha–1, G2 = 15 sheep·ha–1, G3 = 43.5 sheep·ha–1) in Golog Prefecture, Qinghai Province. The results are as follows: 1) AGB showed a downward trend in both Gannan and Golog with increases in grazing intensity, and AGB in grazing areas was lower than that in no-grazing areas. AGB was significantly lower in Golog than in Gannan following G3 treatment (P < 0.05). Under the same level of grazing intensity, BGB in Golog was distinctly lower than in Gannan (P < 0.05). 2) The species richness, Shannon-Wiener index and Pielou index of plant communities increased with increasing grazing intensity in the Gannan region. Following G1 treatment, Richness, Shannon-Wiener index, Simpson index and Pielou index were significantly higher in Golog than in Gannan (P < 0.05). 3) In the no-grazing area, the AGB of high-quality pasture (grass and sedge) accounted for about 50% of aboveground biomass. With the increase in grazing intensity, the proportion of high-quality pasture was reduced, while the proportion of weeds (edible weeds and poisonous weeds) increased. 4) Following G1 and G2 treatments, soil organic carbon was significantly higher in Gannan than in Golog (P < 0.05). Long-term grazing disturbance significantly reduced soil moisture, and was significantly lower in Gannan than in Golog (P < 0.05). Regional differences have an impact on species diversity, soil organic carbon, and soil moisture. In summary, we conclude that grazing has a greater impact on the vegetation and soil of Gannan.
Vegetation phenology is an important sensor for ecosystem feedbacks on climate change. The study of phenological changes of alpine grassland vegetation on the Tibetan Plateau is of great scientific significance, to reveal the response mechanisms of alpine ecosystems to global climate change. In this study, we selected the 16-day maximum synthetic product MOD13A1 of the MODIS Vegetation Index (VI) from 2001 to 2015. Based on the TIMESAT 3.2 platform, the threshold method was used to extract the vegetation phenological period of the alpine grassland on the Tibetan Plateau, including the start of growth season (SOG), end of growth season (EOG), and length of growth season (LOG). We analyzed the temporal and spatial variations of the vegetation phenology and its driving forces in an alpine grassland of the Tibetan Plateau from 2001 to 2015. The conclusions are summarized as follows: 1) From southeast to northwest, with the deterioration of water and heat conditions and the uplift of topography, the SOG became gradually more delayed, from the 110 days to 170 days. The EOG became gradually more advanced, from the 300 days to 260 days. Finally, the LOG became gradually shorter, from the 300 days to 260 days. However, major differences were noted for the different grassland types. 2) The interannual variation of alpine grasslands showed a tendency for the SOG and EOG to advance, but the LOG increased on the Tibetan Plateau. 3) Altitude is the main factor that affects the phenological heterogeneity of the different grassland types on the Qinghai-Tibet Plateau. Phenology is closely related to altitude between 3 500 m and 5 000 m. With increasing elevation, the SOG of different grassland types became gradually more delayed, the EOG became gradually more advanced, and the LOG became gradually shorter. However, below 3 500 m, the alpine grassland phenology fluctuated greatly with elevation, with no obvious regularity.
In recent years, alpine grassland has become severely degraded in parts of the Qinghai-Tibet Plateau (QTP). This has had a negative effect on livestock production in the region. At some point in the process of the degradation of the grassland, there is a point beyond which it is extremely difficult to restore the grassland. Determining this point in the grassland degradation is an important question for restoration of the grassland. We selected five areas along a gradient from intact to extremely degraded alpine meadows in the permafrost region of the Beiluhe Basin on the QTP to explore the effects of degradation on the above-ground and below-ground biomass of vegetation, and the relative coverage of different plant functional groups (grasses, sedges and forbs). The results showed: 1) as the severity of grassland degradation increased, the relative coverage of grasses and forbs increased while the relative coverage of sedges decreased; 2) there was no significant change in aboveground biomass in the slightly degraded area, and it began to decrease in the moderately degraded area; 3) both belowground biomass and belowground net primary productivity (BNPP) decreased significantly from the moderate degradation stage, and the BNPP moved to deeper layers as the severity of degradation increased; and 4) the relative coverage of sedges and the proportion of BNPP at 0–10 cm soil depth showed a positive correlation with degree of degradation, no significant correlation at 10–20 cm soil depth, and a negative correlation at 20–30 cm and 30–50 cm soil depth. While the relative coverage of forbs at different degrees of degradation and the proportion of BNPP at each soil depth showed an opposite trend to that of sedges, the moderate degradation stage is the critical stage of grassland degradation.
Precipitation-use efficiency (PUE) can be used as an indicator of ecosystem function. This study collected remote sensing data of net primary productivity and meteorological and soil texture data for the Tibetan Plateau for the period from 2000 to 2015. We used regression analysis, correlation analysis and structural equation modeling to characterize the relationships between productivity and precipitation across different soil texture types. NPP was positively correlated with precipitation, and precipitation (|r| = 0.71, P < 0.001) and temperature (|r| = 0.67, P < 0.001). PUE was positively correlated with precipitation (|r| = 0.4, P < 0.001) and temperature (|r| = 0.56, P < 0.001), but temperature had a larger effect on PUE than precipitation. Soil sand content and PUE were positively correlated (|r| = 0.41, P < 0.001), and soil clay content and PUE were negatively correlated (|r| = 0.35, P < 0.001). The results of the structural equation modelling showed that the influence of soil sand content on NPP and PUE was much greater than that of clay content. Therefore, precipitation is the main limiting factor affecting NPP, but the temperature is the main limiting factor affecting PUE. The soil clay content can inhibit the infiltration of precipitation, and improved the PUE of vegetation. We expect the findings of this study to draw attention to the influence of soil texture on PUE and provide scientific theoretical guidance for ecological restoration under different texture conditions.
Litter decomposition is a key process that regulates the carbon and nutrient cycling in terrestrial ecosystems. Most previous studies were conducted in forest and temperate grassland ecosystems, while limited studies have focused on alpine steppe ecosystems. Here, we employed the litter-bag method to study the decomposition of four kinds of alpine steppe species, including Stipa purpurea, Carex moocroftii, Leontopodium pusillum, and Artemisia nanschanica. The results showed significant differences in litter mass loss among plant species and decomposition times. At the end of the experiment, the order of litter mass loss was A. nanschanica (46.69%) > S. purpurea (44.97%) > C. moocroftii (33.55%) > L. pusillum (17.05%). Additionally, the decomposition constant (k) of the four species was between 0.07 and 0.22, the half-life of the litter decomposition was between 3.14 years and 10.50 years, and the turn-over periods were between 13.59 and 45.37 years. The litter N and P dynamics during decomposition largely presented as " cumulation release” and " direct release” patterns. At the end of the experiment, the N and P remaining in the four species were in the order of L. pusillum > C. moocroftii > S. purpurea > A. nanschanica. This study will enrich our understanding of biogeochemistry cycling in alpine steppe ecosystems.
The plateau pika (Ochotona curzoniae) is widely distributed in the source region of the Yellow River Basin (SRYRB) and is a key species in the alpine grassland ecosystem. The spatial distribution of plateau pika and its influence factors are important for understanding the causes of grassland degradation, the formation of " black soil patches”, plateau pika habitat selection, and the role of this species in the ecosystem. In this study, an unmanned aerial vehicle (UAV) was used for obtaining the presence/absence data of plateau pika in the SRYRB. The potential distribution of plateau pika in this region was predicted using 10 different models in the BIOMOD ensemble platform for species distribution modeling. The results show that the application of BIOMOD lowers the uncertainty and improves the prediction performance. The random forest (RF) model could best predict the distribution of plateau pika in this region. This study provides a new method for predicting the potential distribution of plateau pika, the results of which can provide the necessary scientific basis for the protection and control of local plateau pika.
We investigated the relationship between plateau pika (Ochotona curzoniae) burrow entrance densities and soil physical properties, soil chemical properties, species composition and aboveground biomass (AGB) in an alpine grassland in Xianza County. The results indicated that: 1) soil physical properties (soil temperature and soil bulk density) declined as the number of pika burrow entrances increased (P < 0.05), while the number of pika burrow entrances increased as the density of Tibetia himalaica increased; and 2) as burrow entrance density increased, the concentration of soil nutrients (soil total carbon, total nitrogen, total phosphorus, organic carbon, available nitrogen and available phosphorus) increased (although the correlation was not significant at P > 0.05), the diversity of plants decreased (P < 0.05), and the aboveground biomass increased (P < 0.05). Plateau pika preferred warm and dry soils, and grassland where Oxytropis glacialis was present. The increase in the number of plateau pika, up to a certain point, improves the soil nutrient status and increases the aboveground biomass of alpine grasslands.
The density gradient of pika (Ochotona curzoniae) burrows was determined using effective number of caves method (which were expressed from low to high as levelⅠ, Ⅱ, Ⅲ and Ⅳ respectively). To explore the effects of pika activity on the soil and vegetation of alpine meadows in Guoluo Tibetan Autonomous Prefecture, China, the relationships between the density of pika burrows and the total area of patchy bare ground, soil physical characteristics, and vegetation characteristics of alpine meadow were analyzed. The results showed that 1) The number of effective pika burrows across the four gradients was Ⅰ [(4 ± 3)·100 m–2] < Ⅱ[(15 ± 2)·100 m–2] < Ⅲ [(24 ± 2)·100 m–2] < Ⅳ [(37 ± 5)·100 m–2]. 2) The soil water content in the surface layer of the meadows (0–10 cm) was affected by the pika burrow density gradient, and the difference between the gradients was significant (P < 0.05). With an increase in the density gradient of pika, the soil water content decreased sharply and remained below 50% in Ⅱ, Ⅲ, Ⅳ sampling plots. 3)There was no significant correlation between the pika burrow density gradient and the soil compaction of alpine meadows (P > 0.05); only gradient Ⅱ was significantly higher than gradient Ⅰ(P < 0.05), and the other gradients were not significantly different from each other. 4)The effective burrow number had an extremely significant effect on the total area of patch bare ground (P < 0.001), which was the largest at gradient Ⅳ(accounting for 8.75%); 5)The mouse cave density gradient had a significant effect on the coverage of alpine meadow communities (P < 0.001), and the total coverage of plant community at gradients Ⅱ, Ⅲ, Ⅳ(46.55%～41.15%) was significantly lower than gradientⅠ (98.7%); 6) The pika burrow density gradient affected the plant community structure of the alpine meadows. With an increase in the pika burrow density, the populations of Gentiana macrophylla, Elymus nutans, and Veronica eriogyne gradually increased and that of Chamaesium paradoxum, Viola kunawarensis, and Trollius farreri gradually declined, although the populations of the dominant species Kobresia pygmaea and Kobresia humilis did not change. 7) There was no significant difference of plant diversity index between different gradients (P > 0.05). In summary, properly managed pika populations can improve the habitat of the pika and promote the positive succession of the alpine meadow ecosystem. When the disturbance from pikas is too high, the resultant decline in habitat quality will cause the alpine meadow ecosystem to reverse succession.
In order to explore the impact of rodents on alpine grassland ecosystems, we investigated the effect of different densities of plateau pika (Ochotona curzoniae) in the Sanjiangyuan (Source of the Three Rivers) Region in 2016 on different vegetation characteristics (aboveground biomass, underground biomass, species richness) and soil properties. The testing results indicate that the vegetation species richness decreased as pika density increased, and the plant community composition of meadow could be changed by an appropriate density of pika. In addition, as pika density increased, aboveground biomass and underground biomass decreased, but the root: shoot ratio increased. And there were significant differences for soil properties at different soil depths. Most soil properties showed a fluctuating downward trend at the soil depth of 0–20 cm as pika density increased. The soil properties of the areas without pika were significantly different to the areas with high and low densities of pika. Besides, according to the correlation analysis, it is concluded that soil factors are the main drivers of the changes in root: shoot ratio. The findings highlighted that certain levels of pika populations can change the plant community structure and improve soil nutrients, and consequently contribute to the sustainable development of the grassland ecosystem.
Grassland-livestock balance is necessary for the sustainable development of Tibetan grasslands and efficient production of animal husbandry. To alleviate the enormous pressure caused by excessive grazing on natural grasslands and provide an effective way to solve the contradiction between livestock and grass availability, a the field experiment was conducted to select oat varieties that are suitable for cultivation in the Shigatse region of Tibet based on the analysis of dry weight, plant height, leaf-stem ratio, ear length, panicle weight, thousand-seed weight, and nutritional quality of the eight oat varieties; crude protein (CP), ether extract (EE), crude ash (Ash), acid detergent fibre (ADF), neutral detergent fibre (NDF), and lignin (ADL) were also considered. The production performance results showed that the highest yield of Qingyin No.1 was 12 406.95 kg·hm–2, the ear length of Qingyin No.3 was 25.60 cm, and the highest Qingyin No.3 was 159 cm. The nutritional quality results showed that the highest CP content was for Qingyin No. 2 and was 6.4%, the lowest ADF content was for Qingyan No. 1 and was 28.55%. The NDF content of Lean was the lowest (52%), the highest EE content was for Qingyin No. 1 and was 52.7%, the highest Ash content was for Qingyan No. 1 and was 4.97%, and the lowest ADL content was for Qingyin No. 2 and was 24.18%. According to grey relational analysis of yields and nutritional quality, it was concluded that Qingyin No. 1, Qingyin No. 3, and Qingyin No. 2 are more advantageous in the Shigatse region of Tibet, and they are suitable for planting in this region.
Seasonal snow cover is a major factor influencing the structure and function of alpine meadows. It also affects the response of alpine plants to environmental heterogeneity at different levels. We studied the effect of a depth gradient of natural snow on the vegetation in an alpine meadow of Kaka Mountain. Firstly, we measured how soil environmental factors varied under different snow depths. Soil water content under deep snow cover was higher than under shallow snow cover. There were significant differences in total nitrogen content, total phosphorus content, and organic carbon content under deep snow and under shallow snow. The soil particle size also differed under deep or shallow snow, both in the early growing season and in mid-season. By comparison the response of plant leaf traits and height in an alpine meadow to different depths of snow cover, it indicates that Primula purdomii had greater ILM (individual leaf mass) and less SLA under deep snow cover significantly, but Pedicularis kansuensis showed no significant differences of all leaf traits and plant height between different snow cover treatments. Ranunculus tanguticus had greater ILM and plant height but less SLA under shallow snow cover than under deep snow cover. The mid-season flowering species, Leontopodium leontopodioides and Festuca ovina had greater specific leaf area (SLA) under deep snow cover, but Kobresia humilis had better SLA, ILA (individual leaf area) and plant height under shallow snow cover. The later flowering Gentiana sino-ornata indicated similar variation with medium flowering Kobresia humilis. Both ILM and ILA of Saussurea stella were significantly greater under shallow snow cover than deep snow cover. At functional group level, snow depth showed significant effects only on plant height while flowering phenology had significant effects on leaf traits and plant height. For early flowering plants, SLA and plant height were negatively correlated with pH, and between SLA was also negatively correlated with organic carbon, total nitrogen, and sand particle content. For mid-season flowering plants, SLA was positively correlated with pH and sand particle content, and negatively correlated with total phosphorus content. The plant height of mid-season flowering plants was negatively correlated with organic carbon content, total nitrogen content, and total phosphorus content. There was a significant relationship between SLA and plant height in all the different flowering functional groups. The species- and flowering phenology functional-specific response of plant traits on snow depth indicated the survival strategy from different plants in alpine meadows for adapting to environmental change. For the maintenance and management of alpine meadow, it is essential to select appropriate grass cultivars, which can ensure sustainable development of husbandry.
The roots of plants are an important component in desert restoration. To understand the root morphology patterns of grasses being used to recover deserts, we studied grass roots in the Southeast Tibetan Plateau. Roots of the annual grass Avena sativa and the perennial grasses Elymus nutans and Roegneria hirsuta were collected from a field gene bank and sandy land. The tips, forks, average diameter, length, surface, and volume of the grass roots were compared and the ratios of the root tips, length, surface, and volume were analyzed. We discussed the suitability of different root morphologies to desert environments. The results show that the root surface and volume of A. sativa in the field gene bank were significantly higher than those in the sandy land. The root morphology of E. nutans had no significant differences between the field gene bank and sandy land. Additionally, the root tips, forks, length, and surface of R. hirsuta in the field gene bank were significantly lower than those from the sandy land; however, the average root diameter of R. hirsuta was significantly higher. There was a significant decrease in the root volume of A. sativa in the sandy land compared with the field gene bank. However, A. sativa increased the ratios of the root tips, length, surface, and volume, under a diameter of 0.2～0.4 mm, to suit desert environments. E. nutans did not significantly change its root morphology to suit desert environments. R. hirsuta increased the root length, surface, and volume patterns, under a diameter of 0.1～0.2 mm, to suit desert environments by decreasing the root length and surface between 0.7 and 0.8 mm. The root morphology patterns of E. nutans and R. hirsuta are more suitable to desert environments than those of A. sativa.
Allowancing and awarding local herdsmen families for degraded grassland restoration, via grazing exclusion, is an important eco-compensation policy in China. A scientific assessment on how grazing exclusion and climate change affects ecological restoration is essential for improving the layout of enclosures at a broad spatial scale in the future. In this study, we focused on 2 413 enclosures that are distributed in Nagchu and Nagri, Tibetan Autonomous Region, China, and calculated the differences in the means and trends of the Normalized Difference Vegetation Index (DMeanNDVI and DTrendNDVI) in these exclosures between two subperiods, prior to (2000–2009) and after (2010–2017) the current policy of payment for grassland restoration by fencing. The differences in the means and trends of the growing season temperature (GST) and precipitation (GSP) between corresponding subperiods were also calculated, for better understanding of how climatic variables affect NDVI change in fenced grasslands over time and across space. Our results show that exclosures with a ΔMeanNDVI > 0 and ΔTrendNDVI > 0, account for 67.3% and 40.5% of all exclosures on the Northern Tibetan Plateau, respectively, indicating that grazing exclusion has effectively restored these degraded grasslands. The proportion of exclosures with a ΔMeanNDVI < 0 and ΔTrendNDVI < 0 are 22.5% and 31.0%, respectively, indicating that grazing exclusion has negative influences on those fenced grasslands. A ΔMeanNDVI ≈ 0 and a ΔTrendNDVI ≈ 0 can be found in 10.2% and 28.4% of exclosures, respectively, indicating that grazing exclusion by fencing has no evident influence there. In addition, we found that the NDVI of fenced grasslands were correlated with the GST (r = 0.27) and GSP (r = 0.37), and the correlation coefficients of NDVI with GST did not change between the two subperiods. In alpine and desert steppe zones, the correlation coefficients of NDVI with GSP increased from 0.236 in 2000–2009 to 0.370 in 2010–2017. The results of the linear regressions and analyses of variance further indicate that the GST and GSP have significant influences on the NDVI but can explain only a small fraction of its variance (approximately 2%). In summary, the effectiveness of grazing exclusion on the restoration of degraded grasslands showed a heterogeneous pattern over space across the Northern Tibetan Plateau. Therefore, we suggest opening the exclosures where fencing has negative influences, clarifying the optimal time for grazing-exclusion where fencing has positive influences, and exploring the potential effects of other anthropogenic factors where fencing has no evident influences on grassland restoration.
The types and growth statuses of vegetation are considered critical indicators that reflect climate regimes and have received much attention in ecology and climatology. However, studies focusing on climate warming influencing vegetation replacement toward high altitudes and latitudes, from the perspective of the redistribution of vegetation zones, are scarce. This study used AVHRR/GIMMS-NDVI as the indicator to represent the growth status of vegetation zones and chose the Qinghai-Tibetan Plateau (QTP) as the study area, because of its high sensitivity to climate change. The spatiotemporal dynamics of vegetation in the last 35 years, during 1981–2015, were analyzed. Additionally, the responses of vegetation to climate change and human activities were examined by analyzing the relationship between vegetation and climate/anthropogenic influences, using the temperature and precipitation data from 87 metrological stations, assimilated meteorological data, and economic statistical data on the QTP. The results show that ⅰ) on the whole, the growth status has been improving during the past 35 years. This trend was consistent with that of the temperature and precipitation data. However, it is difficult to explain the reasons behind the changes, when taking the QTP as a whole. By dividing the QTP into different sub-regions, from different zoning schemes, the spatiotemporal characteristics are clearly depicted and causes are reasonably explained. ⅱ) The vegetation in the middle and southwestern QTP, with high altitudes, was improving and the warm-humid climate trend was the main reason for this. That is, the frigid climatic conditions at high altitudes have been alleviated with global warming. With the treeline / timberline being lifted and vegetation zones expanding, the NDVI correspondingly increased. ⅲ) The degenerated regions are mainly in the northern and eastern QTP, which have high population/livestock densities. The slowly changing climate regime and anthropogenic influences, e.g., the rapid growth of livestock and population (urbanization), are the main reasons for the vegetation degradation.
Adapting to climate change has become the norm for sustainable development in the context of global change. Farmers are the main basic unit of production in rural areas. Through diagnostic research on the assessment of farmers' adaptation ability to climate change and its limiting factors, the effectiveness of farmers' adaptation and their adaptation ability can be enhanced. Taking 14 administrative villages in the Middle-Lower Huangshui Area of the Tibetan Plateau as a case study, an index system for assessing the adaptation ability of farmers to climate change, based on household survey data, was constructed. The adaptive capacity index model was applied to quantitatively evaluate farmers' adaptability to climate change, with the main restrictive factors of each adaptive capacity area diagnosed and analyzed through the obstacle model. The conclusions showed that 1) farmers in the Middle-Lower Huangshui Area have a more accurate perception of climate change. 2) Adaptability is in a high state, with farmers who have the ability of 0.280 ≤ ACI (adaptive capacity index) < 0.320 are the main body. In this area, from east to west, there is a downward trend of the sample village farmers’ adaptability with altitude. 3) The dimension layer shows that natural ability and economic capacity have a major effect on farmers' adaptability. The indicator layer highlights that the quality of cultivated land, diversity of economic income, methods for obtaining financial assistance, annual income of the family, education level of the labor force, and shortage of crop water are the main limiting factors. 4) The core factor of the adaptability of farmers in the downstream areas of the Middle-Lower Huangshui Area is the annual income of the farmers.