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Degradation of meadow ecosystems in the largest alpine region of the world, i.e., the Qinghai-Tibetan Plateau (QTP), is a crucial ecological issue that has ardently discussed in recent years. Many factors, such as livestock overgrazing, climate change and overpopulation of small mammals are treated as important factors that cause the degradation of meadow ecosystems in the QTP. However, there are few hypotheses focus on the potential role of plant compensatory growth on meadow degradation. We proposed a compensatory growth-related hypothesis to understand the potential degradation process of meadow ecosystems in the QTP. We discussed that there are two stages of meadow degradation, i.e. the beginning stage of meadow degradation that is triggered by high-strength overcompensation; and the intensification stage of meadow degradation, which are driven by external factors such as climate warming, small mammals and thawing of permafrost.The mechanism of meadow degradation driven by plant compensatory growth is the asynchronism of plant consumption and the availability of soil nutrients. Our hypothesis that plant compensatory growth drives meadow degradation under the overgrazing condition requires re-examination and modification by testing the balance between soil nutrient cycling rates and the strength of plant compensatory growth in alpine regions. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition may alter physiological process of plants in grassland ecosystem. However, little is known about the response mechanism of individual plants in alpine regions to N deposition. We conducted a field experiment, and three treatments including 0 kg Nha-1year−1 (CK), 8 kgNha-1year−1 (Low N), and 72 kg N ha-1 year−1 (High N) were established to simulate N deposition in alpine meadow of Qinghai-Tibetan plateau. Our objectives were to determine the influence of N deposition on photosynthesis of different functional types of herbage species in alpine meadow, and finally characterize the links of plant productivity and photosynthesis with soil nutrients. The results showed that responses of alpine plants were species-specific under N deposition. Compared with grass species Agropyron cristatum and forb species Thalictrum aquilegifolium , the sedge species Carex melanantha was much more sensitive to N deposition; a lower N load (8 kgNha-1year−1) can cause a negative effect on its photosynthesis and productivity. Additionally, N deposition can promote plant N uptake and significantly decreased the C (carbon)/N (nitrogen) ratio. Compared with CK and low N deposition, high N deposition inhibited the photosynthesis and growth of the forb species Thalictrum aquilegifolium and sedge species Carex melanantha. In all three functional types of herbage species, the grass species A. cristatum tended to show a much higher photosynthetic capacity and better growth potential; thus, suggesting that grass species A. cristatum will be a more adaptative alpine plants under N deposition. Our findings suggested that plant photosynthetic responses to N deposition were species-specific, low N deposition was not beneficial for all the herbage species, and N deposition may change plant composition by the differential photosynthetic responses among species in alpine grassland. Plant composition shift to grass-dorminant in alpine regions might be attributed to a much higher photosynthetic potential and N use efficiency of grass species. Image 1035 • The photosynthesis of alpine plants species-specifically response to N deposition. • The responses of the alpine plants to nitrogen deposition was closely related to soil N. • Sedge species may sensitively response to N deposition. • Grass species might have a much higher photosynthetic capacity and better growth potential. [ABSTRACT FROM AUTHOR]

The plateau pika ( Ochotona curzoniae ) is considered a keystone species on the Qinghai–Tibetan Plateau (QTP). Under a moderate burrow density condition, we investigated plant community and soil properties surrounding pika's burrows in comparison to the control sites (without pika's burrows) in an alpine meadow ecosystem. The results demonstrated that plant biomass, especially aboveground biomass around pika's burrow, was improved. The contents of available soil nutrients around the pika's burrow were improved as well. The highest aboveground biomass and highest contents of NH 4 -N, available phosphorus and available potassium was detected at the back of the burrow. The compositions of plant community were not changed significantly around the pika burrow, excluding at the front of the burrow. Our findings revealed that the activities of plateau pika can improve the production of alpine meadow and increase the soil fertility at individual burrow level when the burrow density was not out of control. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Plateau (QTP) is experiencing increasing nitrogen (N) deposition, which may have great impacts on the physical, chemical, and biological factors that determine the stabilization of soil organic carbon (SOC). However, few studies have been conducted to quantify the relative contributions of these factors to SOC stabilization at various N addition levels in alpine habitats. We established a N manipulation experiment from 2015 to 2016 in an alpine meadow on the QTP to examine the impacts of N addition gradients on SOC stabilization under different scenarios of N deposition including 8, 24, 40, 56, and 72 kg N ha−1 yr−1. Using solid-state 13C NMR spectroscopy, we assessed the changes in the chemical composition of SOC. We measured soil aggregate size fractions, iron ions, soil microbes, and soil chemicals to investigate their contributions to SOC stabilization. We found that there were response thresholds of SOC to N addition in this alpine meadow on the QTP. The critical level of N addition for the change of SOC was close to 16 kg N ha−1 yr−1 plus the natural atmospheric N deposition (approximately 8 kg N ha−1 yr−1). N addition affected SOC stabilization in this alpine meadow mainly by affecting soil aggregates and soil microbes. These results of this study suggest that an exogenous N input lower than the critical load is beneficial for C sequestration in this alpine meadow on the QTP. This is potentially important for understanding the influences of atmospheric N deposition on soil properties, with subsequent effects on SOC stabilization on the alpine meadow of QTP and similar fragile ecosystems worldwide. • There were response thresholds of SOC to N input in alpine meadows. • The critical load of N input was close to 16 kg N ha−1 yr−1 for SOC change. • N input affected SOC stability mainly by affecting soil aggregates and microbes. [ABSTRACT FROM AUTHOR]

• No functional traits connected both phylogeny and environmental factors. • N addition at 8 kg N ha-1year−1 filtrated the species of the gramineae. • N addition at 72 kg N ha−1 year−1 filtrated the species of non-gramineae. • Potassium in normal year and phosphorus in warm year were main factors of environmental filtering. Nitrogen (N) deposition and warming leads to environmental gradients that shape plant communities and ecological diversity, space is treated as an equally important variable as the environmental variables in the environmental gradients. The Qinghai-Tibetan Plateau (QTP) is very sensitive to large increases in N deposition rates and warming. Environmental gradients caused by N deposition and spatial factors act as environmental filtering in community assembly by affecting plant functional traits and phylogeny. To investigate the effects of environmental filtering caused by N deposition on the community assembly in alpine meadows, we randomly placed and fertilized at 6 levels of N addition (no N addition, 8 kg N ha-1year−1, 24 kg N ha−1 year−1, 40 kg N ha−1 year−1, 56 kg N ha−1 year−1 and 72 kg N ha−1 year−1) both in a normal (normal precipitation and normal temperature) year and a warm (normal precipitation and warm) year. We used the fourth-corner analysis and extended RLQ (R stands for a matrix of environmental variables by samples, L stands for a species-cover-by-samples matrix and Q stands for a species-by-traits matrix) through multiple factors (soil factors, spatial heterogeneity, species traits, phylogenetic factor) to examine the effects of environmental filtering on the community assembly in alpine meadows. The results demonstrated that all soil variables showed a clear gradient and were affected by simulated N deposition; N addition at 8 kg N ha-1year−1 can filtrate the species of the gramineae, but N addition at 72 kg N ha−1 year−1 can filtrate the species of non-gramineae, the main factors of environmental filtering were potassium in normal year and phosphorus in warm year. With the increase of N deposition rate in alpine meadow of QTP, non-gramineous plants will be favored first, but eventually gramineous plants will occupy the dominant position in the QTP. Rational mitigation strategies should be developed for different climate change scenarios of alpine grasslands on the QTP according to their responses to the N addition gradients and climate change scenarios in the future. [ABSTRACT FROM AUTHOR]

Mining is well-known as one of the most aggressive human disturbances leading to massive and irreversible damages to natural ecosystems. However, the influence mechanisms of open-pit mining on plant communities and soil properties of alpine meadow on the Qinghai-Tibetan plateau are not well understood. In this study, we used structural equation modeling (SEM) to study the influence mechanisms in the disturbed areas of the Qulong copper mine. Our results revealed that the soil parameters of alpine meadow have been significantly changed by mining activities. SEM results showed that Plantago depressa Willd. was more suitable for growing in current soil conditions due to its tolerance to heavy metals than other dominant species, which meant that it would substitute the current two dominant species (Kobresia myosuroides (Villars) Fiori and Blysmus sinocompressus Tang et Wang) in the future and become the most important dominant species in the study area. Unfortunately, the Shannon-Wiener index, Alatalo evenness index and M-Gordon stability index are relatively low in the plot with Plantago depressa Willd. as the dominant species. In a word, the fragile alpine meadow ecosystem may degenerate in the future due to plants and soil disturbed by mining activities. Further, eight targeted recommendations were proposed to protect alpine meadow on the Qinghai-Tibetan plateau. Image 1 • Soil parameters had been significantly changed by mining activities. • Plantago depressa Willd. will become the most important dominant species. • The fragile alpine meadow ecosystem may degenerate in the future. • Eight targeted recommendations were proposed to protect alpine meadow. We confirmed the degradation trend of dominant species and plant communities in alpine meadow of the Qinghai-Tibetan Plateau under the disturbance of mining activities. [ABSTRACT FROM AUTHOR]