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Recently, the Qinghai–Tibetan Plateau has experienced significant warming. Climate warming is expected to have profound effects on plant community productivity and composition, which can drive ecosystem structure and function. To explore effects of warming on plant community productivity and composition, we conducted a warming experiment using open top chambers (OTCs) from 2012 to 2014 in alpine meadow and alpine steppe habitat on the central Qinghai–Tibetan Plateau. We measured aboveground net primary productivity (ANPP), community composition and species diversity under ambient and two levels of artificially warmed conditions across three years. Our results showed that warming significantly stimulated plant growth in the alpine meadow, but reduced growth on the alpine steppe. The increase of ANPP in alpine meadow was a result of an increase of plant height under warming. Warming-induced drought conditions were primarily responsible for the observed decrease of ANPP in an alpine steppe. Plant community composition and species diversity were not influenced by warming in alpine meadow. Alternatively, in alpine steppe, cover of graminoids and forbs significantly declined while legumes substantially increased under warming, subsequently resulting in rapid species losses. Changes in soil moisture were responsible for observed changes in graminoids and legumes in the alpine steppe. Overall, experimental results demonstrated that warming had a positive impact on plant community structure and function in alpine meadow and had a negative impact on these characteristics in an alpine steppe. This work highlights the important role of soil moisture for regulating plant productivity and community composition response to warming in the alpine steppe. In particular, the deep-rooted, drought resistant plants may increase in a warmer future in the central Qinghai–Tibetan Plateau. These changes may reduce habitat quality for the local community of grazers because many of the species that increased are also unpalatable to grazers. [ABSTRACT FROM AUTHOR]

Changes in climate have caused impacts on ecosystems on all continents scale, and climate change is also projected to be a stressor on most ecosystems even at the rate of low- to medium-range warming scenarios. Alpine ecosystem in the Qinghai-Tibetan Plateau is vulnerable to climate change. To quantify the climate change impacts on alpine ecosystems, we simulated the vegetation distribution and net primary production in the Qinghai-Tibetan Plateau for three future periods (2020s, 2050s and 2080s) using climate projection for RCPs (Representative Concentration Pathways) RCP4.5 and RCP8.5 scenarios. The modified Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ model) was parameter and test to make it applicable to the Qinghai-Tibetan Plateau. Climate projections that were applied to LPJ model in the Qinghai-Tibetan Plateau showed trends toward warmer and wetter conditions. Results based on climate projections indicated changes from 1.3 °C to 4.2 °C in annual temperature and changes from 2% to 5% in annual precipitation. The main impacts on vegetation distribution was increase in the area of forests and shrubs, decrease in alpine meadows which mainly replaced by shrubs which dominated the eastern plateau, and expanding in alpine steppes to the northwest dominated the western and northern plateau. The NPP was projected to increase by 79% and 134% under the RCP4.5 and RCP8.5. The projected NPP generally increased about 200 g C·m − 2 ·yr − 1 in most parts of the plateau with a gradual increase from the eastern to the western region of the Qinghai-Tibetan Plateau at the end of this century. [ABSTRACT FROM AUTHOR]

To analyze CO2 fluxes under conditions of climate change in an alpine meadow on the central Qinghai–Tibetan Plateau, we simulated the effect of warming using open top chambers (OTCs) from 2012 to 2014. The OTCs increased soil temperature by 1.62°C (P < 0.05), but decreased soil moisture (1.38%, P < 0.05) during the experiments. The response of ecosystem CO2 fluxes to warming was variable, and dependent on the year. Under conditions of warming, mean gross ecosystem productivity (GEP) during the growing season increased significantly in 2012 and 2014 (P < 0.05); however, ecosystem respiration (ER) increased substantially only in 2012 (P < 0.05). The net ecosystem CO2 exchange (NEE) increased marginally in 2012 (P = 0.056), did not change in 2013(P > 0.05), and increased significantly in 2014 (P = 0.034) under conditions of warming. The GEP was more sensitive to climate variations than was the ER, resulting in a large increase in net carbon uptake under warming in the alpine meadow. Under warming, the 3-year averages of GEP, ER, and NEE increased by 19.6%, 15.1%, and 21.1%, respectively. The seasonal dynamic patterns of GEP and NEE, but not ER, were significantly impacted by warming. Aboveground biomass, particularly the graminoid biomass increased significantly under conditions of warming. Soil moisture, soil temperature, and aboveground biomass were the main factors that affected the variation of the ecosystem CO2 fluxes. The effect of warming on inter- and intra-annual patterns of ecosystem CO2 fluxes and the mechanism of different sensitivities in GEP and ER to warming, require further researched. [ABSTRACT FROM AUTHOR]

[Display omitted] Structural information of grassland changes on the Tibetan Plateau is essential for understanding alterations in critical ecosystem functioning and their underlying drivers that may reflect environmental changes. However, such information at the regional scale is still lacking due to methodological limitations. Beyond remote sensing indicators only recognizing vegetation productivity, we utilized multivariate data fusion and deep learning to characterize formation-based plant community structure in alpine grasslands at the regional scale of the Tibetan Plateau for the first time and compared it with the earlier version of Vegetation Map of China for historical changes. Over the past 40 years, we revealed that (1) the proportion of alpine meadows in alpine grasslands increased from 50% to 69%, well-reflecting the warming and wetting trend; (2) dominances of Kobresia pygmaea and Stipa purpurea formations in alpine meadows and steppes were strengthened to 76% and 92%, respectively; (3) the climate factor mainly drove the distribution of Stipa purpurea formation, but not the recent distribution of Kobresia pygmaea formation that was likely shaped by human activities. Therefore, the underlying mechanisms of grassland changes over the past 40 years were considered to be formation dependent. Overall, the first exploration for structural information of plant community changes in this study not only provides a new perspective to understand drivers of grassland changes and their spatial heterogeneity at the regional scale of the Tibetan Plateau, but also innovates large-scale vegetation study paradigm. [ABSTRACT FROM AUTHOR]

• The relative abundance of soil rare biosphere was stable under climate changes. • The specific soil microbial taxa strongly related to soil rare biosphere. • The rare biosphere strongly explained variations of soil available nitrogen. Ecological roles of "rare biosphere" (RB) were rarely discussed in alpine grassland ecosystems. We explored the roles of RB and specific taxa of soil bacteria and fungi in regulating soil nutrients and aboveground biomass of an alpine meadow and alpine steppe under warming and enhanced rainfall scenarios on the Qinghai-Tibetan plateau. In the context of alpine meadow and alpine steppe, the relative abundance of bacterial RB was ∼40% in the bacterial community, and it was <10% for fungal RB in the fungal community. The relative abundance of the RB of soil bacteria and fungi were not changed by warming or enhanced rainfall. All specific bacterial taxa and over 90% specific fungal taxa belonged to the RB. The RB, including the most specific taxa, explained many more variations in the contents of soil NO 3 -N and NH 4 -N than the high abundant microbial species under warming and enhanced rainfall conditions. The aboveground biomass of the alpine meadow and steppe were strongly affected by the contents of soil NO 3 -N, available phosphorus and total nitrogen under the condition of warming and enhanced rainfall. Our findings suggest that the robust soil microbial RB plays an important role in regulating the content of soil available nitrogen, which could profoundly affect aboveground plant biomass of alpine grassland ecosystems under climate change conditions. [ABSTRACT FROM AUTHOR]

Grassland cover is strongly influenced by climate change. The response of grassland cover to climate change becomes complex with background climate. There have been some advances in research on the sensitivity of grassland vegetation to climate change around the world, but the differences in climate sensitivity among grassland types are still unclear in alpine grassland. Therefore, we applied MODIS NDVI data and trend analysis methods to quantify the spatial and temporal variation of grassland vegetation cover on the Qinghai-Tibet Plateau. Then, we used multiple regression models to analyze the sensitivity of fractional vegetation cover (FVC) to climatic factors (Temperature, Precipitation, Solar radiation, Palmer drought severity index) and summarized the potential mechanisms of vegetation sensitivity to different climatic gradients. Our results showed (1) a significant increasing trend in alpine desert FVC from 2000–2018 (1.12 × 10−3/a, R2 = 0.56, p < 0.001) but no significant trend in other grassland types. (2) FVC sensitivity to climatic factors varied among grassland types, especially in the alpine desert, which had over 60% of the area with positive sensitivity to temperature, precipitation and PDSI. (3) The sensitivity of grassland FVC to heat factors decreases with rising ambient temperature while the sensitivity to moisture increases. Similarly, the sensitivity to moisture decreases while the sensitivity to thermal factors increases along the moisture gradient. Furthermore, the results suggest that future climate warming will promote grassland in cold and wet areas of the Qinghai-Tibet Plateau and may suppress vegetation in warmer areas. In contrast, the response of the alpine desert to future climate is more stable. Studying the impact of climate variation at a regional scale could enhance the adaptability of vegetation in future global climates. [ABSTRACT FROM AUTHOR]

Alpine ecosystems are known to be sensitive to climate change and human disturbances. However, the knowledge about the changes of their underground microbial communities is inadequate. We explored the diversity and structure of soil bacterial and fungal communities using Ilumina MiSeq sequencing in native alpine grasslands (i.e. the alpine meadow, alpine steppe) and cultivated grassland of the Qinghai-Tibetan Plateau (QTP) under three-year treatments of overgrazing, warming and enhanced rainfall. Enhanced rainfall rather than warming significantly reduced soil microbial diversity in native alpine grasslands. Variable warming significantly reduced it in the cultivated grassland. Over 20% and 40% variations of microbial diversity could be explained by soil nutrients and moisture in the alpine meadow and cultivated grassland, separately. Soil microbial communities could be clustered into different groups according to different treatments in the alpine meadow and cultivated grassland. For the alpine steppe, with the lowest soil nutrients and moistures, < 10% variations of microbial diversity was explained by soil properties; and the soil microbial communities among different treatments were similar. The soil microbial community in the cultivated grassland was varied from it in native grasslands. Over 50% variations of soil microbial communities among different treatments were explained by soil nutrients and moisture in each grassland type. Our results suggest that climate change and human activities strongly affected soil microbial communities by changing soil nutrients and moistures in alpine grassland ecosystems. [ABSTRACT FROM AUTHOR]

Phenology is an important indicator of plant responses to environmental changes and is closely correlated with biomass production. However, how changes in phenological events affect plant biomass production when exposed to changing temperature and precipitation remain unclear.We conducted a 4‐year manipulative experiment of warming and precipitation addition to explore phenology–biomass interactions under climate change in a dry alpine meadow on the central Qinghai–Tibetan Plateau from 2015 to 2018.In dry and warm years, warming delayed phenology and precipitation addition advanced them. Warming decreased the biomass of Kobresia pygmaea in 2018 and the biomass of Poa pratensis in 2015, 2017 and 2018. However, precipitation addition significantly increased the biomass of Poa pratensis and Potentilla multifida in most of the experimental years. Phenological changes regulated the responses of biomass to treatments. Specifically, delay of green up of P. pratensis and delay of withering of K. pygmaea induced by warming can increase biomass production, but it can be offset by the direct negative effects of warming on biomass.Synthesis. Here we show how warming‐induced drought tend to decrease the biomass production of graminoids and the negative effects of warming on the biomass of P. pratensis and K. pygmaea were partially offset by green up postponement and withering postponement respectively. Our results highlights phenology is a crucial regulator for biomass production under climate change. Hence, both direct and indirect effects of warming and precipitation addition on phenology and biomass cannot be ignored when predicting biomass responses to climate change. [ABSTRACT FROM AUTHOR]

• Warming and water addition increase L. chinensis biomass and reduce S. krylovii. • Community biomass is remained unchanged under warming and water addition. • Warming increases L. chinensis biomass by affecting SA and GA. • S. krylovii steppe may be replaced by L. chinensis in warmer and wetter future. Dominant species play a crucial role in regulating plant community structure and productivity. Climate change affects community productivity by changing plant traits and resource use efficiency. However, the response of the productivity of a dominant species to warming and precipitation addition and the related effects on community biomass production in semi-arid grasslands remain unclear. We conducted a ten-year warming and precipitation addition study of a semi-arid steppe in Inner Mongolia, China. We examined the responses of community composition, biomass production, and trait and resource use efficiency of two dominant species, Leymus chinensis (rhizome grass) and Stipa krylovii. The results show that warming and precipitation increased the biomass of L. chinensis and decreased the biomass of S. krylovii. Community biomass production was unchanged under warming and precipitation from the contrasting changes in the two dominant species. Warming significantly increased the leaf area (LA) of L. chinensis and S. krylovii compared to that in ambient conditions, while it decreased the specific leaf area (SLA) and δ13C of S. krylovii. Increases in temperature stimulated biomass production of L. chinensis by affecting salicylic acid (SA) and GA (gibberellin), and they increased its competitive ability compared with that of S. krylovii. Our results highlight the different responses of L. chinensis and S. krylovii to environmental changes, which stabilised community productivity under warming and precipitation. Our study provides evidence that S. krylovii may be replaced by L. chinensis in steppe climates in the warmer and wetter future. [ABSTRACT FROM AUTHOR]

Microorganisms are the basis for sustaining ecosystem function and are extremely sensitive to global warming and altered precipitation. Nevertheless, the seasonal pattern of the microbial response to a coupled effect of warming and increased precipitation is largely unknown. We set up a six-year manipulative experiment to verify changes in microbial response to warming (approximately 2 °C), increased precipitation (20 %), and their interactive effect in a semiarid steppe in Inner Mongolia. We detected changes in microbial species richness, diversity, community structure, and microbial interactions during different periods of the growing season. The results suggest that warming and increased precipitation had a stronger impact on the microbial community in the early growing season than in the mid- and late growing seasons. In the early growing season, warming significantly decreased bacterial diversity, while increased precipitation did not significantly affect the microbial community. The interactive effect of increased precipitation and warming significantly increased bacterial richness but decreased fungal richness and amplified the dissimilarities among bacterial and fungal communities. Compared to the early growing season, less microbial taxa significantly responded to warming and increased precipitation in the mid- and late growing seasons. Warming weakened species interactions, as evidenced by fewer nodes and links and lower complexity and robustness in the network. Increased precipitation strengthened species interactions and eased the warming-induced negative effect under the interactive effect. Our findings emphasize that more attention should be given to the changes in the microbial community in the early growing season of grassland in Inner Mongolia under future climate change scenarios. • Climate change impacts were more obvious in the early growing season. • The interactive effect increased bacterial richness but reduced fungal richness. • Fewer taxa respond to climate change in the mid and late growing seasons. • Species interactions weakened by warming but enhanced by precipitation addition. [ABSTRACT FROM AUTHOR]

• Alpine meadow had higher CUE and lower WUE than cultivated grassland under warming. • Warming decreased biomass of cultivated grassland in the later of the experiment. • Warming increased ET, did not affect GEP, and decreased WUE in alpine meadow. • Warming decreased NEE, did not alter ER, and decrease CUE in cultivated grassland. Carbon and water use efficiency (CUE and WUE) are crucial indicators of grassland ecosystem responses to climate change. Grass planting is one of the dominant methods of grassland restoration and agricultural production. However, how warming and reclamation impact grassland CUE and WUE remain unclear. Here we examined how warming affected carbon and water processes in natural alpine meadow and cultivated grassland, including gross ecosystem production (GEP), net ecosystem CO 2 exchange (NEE), evapotranspiration (ET), CUE and WUE. We deployed a seven-year warming experiment using open top chambers in alpine meadow and cultivated grassland on the Tibetan Plateau. Our results showed that the alpine meadow had a higher CUE and a lower WUE compared to the cultivated grassland under warming. Warming increased biomass production of the cultivated grassland in the beginning of the experiment but decreased it later in the experiment. Warming increased ET, did not affect GEP, and finally decreased WUE in the natural alpine meadow. In the cultivated grassland, warming decreased NEE, did not alter ER, and resulted the decrease in CUE. Our results highlight that reclamation decreases CUE and warming decreased WUE of alpine meadow. Although grass planting can increase biomass, the negative impacts of warming on carbon and water processes of cultivated grassland should be considered when reclaiming alpine meadow under warmer future. [ABSTRACT FROM AUTHOR]

Our understanding on how soil organic carbon (SOC) storage, crop yield, and yield stability are influenced by climate is limited. To critically examine this, the impact of long-term (≥10 years) application of nutrient management practices on SOC storage, crop productivity, and yield stability were evaluated under different climatic conditions in China using a meta-analysis approach. The cropping area of China was divided into four distinct groups based on local climatic conditions (warm dry, DW; warm moist, WM; cool dry, CD; cool moist, CM). Results indicated that the impact of nutrient management practices on SOC storage, crop yield, and yield stability varies under different climatic zone in China. The use of unbalanced mineral fertilizer (UMF), and balanced mineral fertilizer (BMF) led to a loss in SOC storage by 6%, and 11% under CM climatic zone and gains in DW, WM, and CD climates. Organic fertilizers (OF), combined unbalanced mineral and organic fertilizers (UMOF), and combined balanced mineral and organic fertilizers (BMOF) were able to sustain and enhance SOC storage under all climatic conditions. However, the largest increase in SOC storage across all climates was seen for BMOF. Further, corresponding values of crop productivity and yield stability were also highest for BMOF among all the nutrient management treatments. A linear-plateau model indicated that maximal yield responsive SOC stock (C opt) levels ranged from 33.43 to 45.51 Mg C ha−1 for rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum) production. To enhance and sustain SOC storage, and crop productivity of croplands under different climates, BMOF appears to be the most appropriate nutrient management strategy. Our findings demonstrate that it is essential to optimize nutrient management strategies according to the local climate to protect soil from SOC losses, and for achieving sustainable crop production. • The impact of nutrient managements on SOC storage, crop yield, and yield stability varies under different climatic zones. • Unbalanced mineral, and balanced mineral fertilizer led to a loss in SOC storage by 6%, and 11% under cool moist climate. • Combined balanced mineral with organic inputs is crucial for maximal SOC storage and crop yields under different climates. • Maximal yield responsive SOC stock levels ranged from 33.43 to 45.51 Mg C ha−1 for rice, maize, and wheat production. [ABSTRACT FROM AUTHOR]