Kobresia Meadow Research Articles

Risk zoning of Gynaephora alpherakii (Lepidoptera: Lymantriidae) on the Qinghai-Tibetan Plateau.

Gynaephora alpherakii (Grum-Grschimailo) (Lepidoptera: Lymantriidae) is a major pest in alpine meadow areas in the Qinghai-Tibetan Plateau (QTP) and causes severe losses in the local livestock production industry. Assessing areas at high risk for G. alpherakii infestation is critical for the effective management of this pest. In this study, an ensemble distribution model was used to analyze areas suitable for G. alpherakii on the QTP. Risk zoning was performed based on the vegetation and environmental conditions in areas with high-occurrence points, and differences between high-occurrence points and other occurrence points were compared. The results revealed that the suitable areas for G. alpherakii on the QTP amounted to 28.27 × 104 hm2, accounting for 10.94% of the total area of the QTP; the area of high-risk was 19.07 × 104 hm2, and these areas were located mainly in the eastern part of the QTP. Qinghai Province had the highest risk, accounting for 77% of the total area identified as high-risk. In terms of habitat, G. alpherakii preferred alpine Kobresia meadows, which have abundant sunshine, loose soil, and scarce precipitation. This study supports efforts to manage G. alpherakii outbreaks and contributes to the ecological protection of the QTP.

Biocrust-reduced soil water retention and soil infiltration in an alpine Kobresia meadow

Abstract. Biocrust is a key component of ecosystems and plays a vital role in altering hydrological processes in terrestrial ecosystems. The impacts of biocrust on hydrological processes in arid and semi-arid ecosystems have been widely documented. However, the effects and mechanisms of biocrust on soil hydrological processes in alpine ecosystems are still poorly understood. In this study, we selected two meadow types from the northern Qinghai–Tibet Plateau: normal Kobresia meadow (NM) and biocrust meadow (BM). Both the soil hydrological and physicochemical properties were examined. We found that, in the 0–30 cm soil layer, soil water retention and soil water content in NM were higher than those in BM, whereas the 30–40 cm layer's soil water retention and soil water content in NM were lower than those in BM. The topsoil infiltration rate in BM was lower than that in NM. Furthermore, the physicochemical properties were different between NM and BM. The 0–10 cm soil layer's clay content in BM was 9 % higher than that in NM, whereas the 0–30 cm layer's soil capillary porosity in NM was higher than that in BM. In addition, the 0–20 cm layer's soil total nitrogen (TN) and soil organic matter (SOM) in NM were higher than those in BM, implying that the presence of biocrust may not favor the formation of soil nutrients owing to its lower soil microbial biomass carbon and microbial biomass nitrogen. Overall, soil water retention was determined by SOM by altering the soil capillary porosity and bulk density. Our findings suggest that the establishment of cyanobacteria crust biocrust may not improve soil water retention and infiltration, and the soil in cyanobacteria crust meadows could be more vulnerable to runoff generation and consequent soil erosion. These results provide a systematic and comprehensive understanding of the effects of biocrust on the soil hydrology of alpine ecosystems.

Self‐stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

AbstractBackgroundsGrazing prohibition and reduced grazing intensity, as two important “vegetation close‐to‐nature recovery” methods, have been suggested as economical and effective technologies for enhancing forage production. However, numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows, but not in others. To reveal the mechanism behind this phenomenon, we proposed a series of experiments.MethodsWe monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai‐Tibet Plateau for 6 years. We estimated the relationships between the plant community and soil nutrients and obtained the following results.ResultsAll measured variables were positively correlated with each other. The plant community structure had higher path coefficients to aboveground biomass, soil organic matter, total nitrogen, and nitrate nitrogen than to other factors. The plant community structure played an important role in response to grazing intensity. Different plant functional groups (PFGs) had different responses to grazing intensity, which led to plant community re‐establishment or re‐organization under different grazing intensities. Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs, and the ratio of Kobresia biomass (including Kobresia humilis and Kobresia pygmaea) to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities. With Kobresia pygmaea as the dominant species, the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass. If Poaceae is the dominant PFG, grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.ConclusionsTherefore, the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.

Precipitation and local adaptation drive spatiotemporal variations of aboveground biomass and species richness in Tibetan alpine grasslands.

The Tibetan Plateau contains the highest and largest alpine pasture in the world, which is adapted to the cold and arid climate. It is challenging to understand how the vast alpine grasslands respond to climate change. We aim to test the hypothesis that there is local adaptation in elevational populations of major plant species in Tibetan alpine grasslands, and that the spatiotemporal variations of aboveground biomass (AGB) and species richness (S) can be mainly explained by climate change only when the effect of local adaptation is removed. A 7-year reciprocal transplant experiment was conducted among the distribution center (4950m), upper (5200m) and lower (4650m) limits of alpine Kobresia meadow in central Tibetan Plateau. We observed interannual variations in S and AGB of 5 functional groups and 4 major species, and meteorological factors in each of the three elevations during 2012-2018. Relationships between interannual changes of AGB and climatic factors varied greatly with elevational populations within a species. Elevation of population origin generally had a greater or an equal contribution to interannual variation in AGB of the 4 major species, compared to temperature and precipitation effects. While the effect of local adaptation was removed by calculating differences in AGB and S between elevations of migration and origin, relative changes in AGB and S were mainly explained by precipitation change rather than by temperature change. Our data support the hypothesis, and further provide evidence that the monsoon-adapted alpine grasslands are more sensitive to precipitation change than to warming.

Spatial–Temporal Correlation Considering Environmental Factor Fusion for Estimating Gross Primary Productivity in Tibetan Grasslands

Gross primary productivity (GPP) is an important indicator in research on carbon cycling in terrestrial ecosystems. High-accuracy GPP prediction is crucial for ecosystem health and climate change assessments. We developed a site-level GPP prediction method based on the GeoMAN model, which was able to extract spatiotemporal features and fuse external environmental factors to predict GPP on the Tibetan Plateau. We evaluated four models’ behavior—Random Forest (RF), Support Vector Machine (SVM), Deep Belief Network (DBN), and GeoMAN—in predicting GPP at nine flux observation sites on the Tibetan Plateau. The GeoMAN model achieved the best results (R2 = 0.870, RMSE = 0.788 g Cm−2 d−1, MAE = 0.440 g Cm−2 d−1). Distance and vegetation type of the flux sites influenced GPP prediction, with the latter being more significant. The different grassland vegetation types exhibited different sensitivity to environmental factors (Ta, PAR, EVI, NDVI, and LSWI) for GPP prediction. Among them, the site located in the alpine swamp meadow was insensitive to changes in environmental factors; the GPP prediction accuracy of the site located in the alpine meadow steppe decreased significantly with the changes in environmental factors; and the GPP prediction accuracy of the site located in the alpine Kobresia meadow also varied with environmental factor changes, but to a lesser extent than the former. This study provides a good reference that deep learning model is able to achieve good accuracy in GPP simulation when considers spatial, temporal, and environmental factors, and the judgement made by deep learning model conforms to basic knowledge in the relevant field.

Kobresia pygmaea meadows as disclimax communities in the same geographic and climatic environments in Qinghai–Tibet Plateau, China

Abstract Kobresia meadows are the main pastures for animal husbandry on the Qinghai–Tibet Plateau, and may represent alternative steady states associated with different grazing intensities. The ability of other plant communities to succeed these meadows remains unclear. In this study, the historical data of plant communities were analyzed in terms of the soil profile, and the present characteristics were identified by investigating their plant communities. Four types of steady states were identified, corresponding to grazing intensities of >11, 8–11, 5.5–8 and <5.5 sheep/ha. Drought alpine swamp meadows and shrub meadows could succeed to K. pygmaea meadows and K. humilis meadows under overgrazing, and their total biomass and edible biomass (estimated by Gramineae and Cyperaceae) decreased with increasing grazing intensity. The regime shift of the states occurred at a grazing intensity of 8–11 sheep/ha. This value thus represented the threshold of significant change in the production and ecological service function in the Kobresia meadow succession process. In general, increasing grazing intensities can adversely affect the service ability of meadows for livestock production and ecosystem stabilization. Our results revealed the potential degraded succession process of the alpine Kobresia meadow and the succession direction in the restoration process of degraded meadows. Additionally, this study provided a theoretical basis for evaluating the fitness between the livestock bearing capacity and carrying capacity in steady states and academic reference for policy setting pertaining to the utilization of Kobresia meadows in a sustainable development framework.

Neighboring plant community attributes drive rhizobiome assemblages of a focal plant in a Kobresia meadow

The rhizosphere microbiome (i.e., rhizobiome) plays critical roles in modulating plant performance and fitness. Although plants in natural environments are inevitably affected by neighboring plants, less is known about how attributes of neighboring plant communities affect the rhizobiome of a focal plant. We evaluated the impacts of neighboring plant community attributes (e.g., above- and belowground plant species richness, identity, biomass and composition) on the richness and community composition of rhizosphere archaea, bacteria and fungi associated with Kobresia setchwanensis in an alpine meadow on the eastern Qinghai-Tibetan Plateau. We found that the richness of neighboring plant species both above- and belowground was poorly related to the rhizobiome richness of the focal plant. In contrast, the dissimilarity in aboveground rather than belowground plant community composition was positively correlated with the dissimilarity in the rhizobiome community composition. Aboveground plant community attributes posed stronger effects than belowground attributes on rhizobiome richness and community composition. The identities of neighboring plant species were the most important predictors of rhizobiome richness and community composition. Structural equation modeling further indicated that the effects of neighboring plant community attributes on the rhizobiome composition could be direct or indirect, by impacting bulk soil microbial communities. Our study provides empirical evidence that neighboring plant community attributes are important determinants of the rhizobiome communities of the focal plant in natural environments.

Effects of Climatic Variability on Soil Water Content in an Alpine Kobresia Meadow, Northern Qinghai–Tibetan Plateau, China

Soil moisture dynamics play an active role in ecological and hydrological processes. Although the variation of the soil water moisture of multiple ecosystems have been well-documented, few studies have focused on soil hydrological properties by using a drying and weighing method in a long time series basis in the Qinghai-Tibet Plateau (QTP). In this study, 13 year (2008–2020) time-series observational soil moisture data and environmental factors were analyzed in a humid alpine Kobresia meadow on the Northern Qinghai–Tibetan Plateau. The results showed no significant upward trend in soil water content during the 2008–2020 period. In the growth season (May–October), the soil water content showed a trend of decreasing firstly, then increasing, and finally, decreasing. Correlation analysis revealed that five meteorology factors (temperature, humidity, net radiation, dew point temperature, and vapor pressure) and a biomass element (above-ground biomass) had a significant effect on the soil moisture, and air temperature impacted the soil water variation negatively in 0–50 cm, indicating that global warming would reduce soil moisture. Humidity and net radiation made a difference on shallow soil (0–10 cm), while dew point temperature and vapor pressure played a role on the deep soil (30–50 cm). Above-ground biomass only effected 30–50 cm soil moisture variation, and underground biomass had little effect on the soil moisture variation. This indirectly indicated that below-ground biomass is not limited by soil moisture. These results provide new insights for the rational allocation of water resources and management of vegetation in alpine meadows, in the context of climate change.

The Process of Soil Nutrient Stabilization in Micro-Patches in Alpine Kobresia Meadows

Micro-patches are the basic unit of grazing ecosystems; the characteristics of these micro-patches are relatively stable in species under different grazing intensities in the same vegetation, but obviously different in terms of the distribution pattern. This leads to differentiation of plant community numerical characteristics under different grazing intensities. Understanding the driving force of soil nutrient variation in micro-patches under grazing disturbances will help us comprehend the regulation strategy and adaptation mechanisms of the ecosystem against over-disturbance. We designed four scales: spatial (three typical micro-patches), temporal serial (6 years), a degradation succession process (four key degradation stages), and recovery treatment (three treatments: the original grazing intensity based on herder preferences, half of the original grazing intensity, and zero grazing). The soil nutrient characteristics used to estimate stabilization were the typical soil total nutrient content (soil organic matter [SOM], total nitrogen [TN], total carbon [TC], inorganic carbon [IC], total phosphorus [STP], total potassium [TK], and pH), and available soil nutrients (NH4+, NO3−, phosphorous [avP], and potassium [avK]). Variations in the SOM, TC, IC, TN, STP, avK, and NO3− levels in the main root distribution layers (0–20 cm) on the spatial scale were 69.8–79.7%, 61.4–80.35%, 49.8–79.58%, 60.52–76.34%, 46.44–89.89%, 45.5–71.36%, and 59.21–65.38%, respectively, which accounted for the largest variation in the four scales, based on multivariable analysis. The variations in the avP and NH4+ content of the main root distribution layers (0–20 cm) at the temporal scale were 46.42–67.93% and 48.11–64.55%, respectively, which accounted for the greatest variation in the four scales, based on a multivariable analysis. Upon comparing the degradation succession stages and recovery treatment in each stage, we found that the variation in avP, avK, STP, TN, TC, SOM, TC, and TN content was greater at the degradation succession scale than at the recovery treatment scale. The soil nutrient content of the micro-patches exhibited the smallest decrease in the Gramineae-Kobresia transformation (G-KP) micro-patch, followed by the Gramineae micro-patches (G) and Kobresia micro-patches (KP). The number of G micro-patches decreased with increasing grazing intensity whereas the number of KP micro-patches increased. When the number of KP micro-patches increased to a certain degree, the number of G-KP micro-patches then increased as well. G-KP micro-patches, characterized by cracking in the mattic epipedon in alpine meadows, increased with the grazing intensity increasing in a certain degree in K. pygmaea meadows with mattic epipedon cracking (CP); the latter buffered the nutrient variation and maintained the soil nutrients’ relative stability in the ecosystem. Thus, CP formed the buffer stage for maintaining self-stabilization during a regime shift and was considered the withstanding stage during the alpine Kobresia meadow degradation process.

Comparison of Fourteen Reference Evapotranspiration Models With Lysimeter Measurements at a Site in the Humid Alpine Meadow, Northeastern Qinghai-Tibetan Plateau.

Evapotranspiration is a key component in the terrestrial water cycle, and accurate evapotranspiration estimates are critical for water irrigation management. Although many applicable evapotranspiration models have been developed, they are largely focused on low-altitude regions, with less attention given to alpine ecosystems. In this study, we evaluated the performance of fourteen reference evapotranspiration (ET0) models by comparison with large weight lysimeter measurements. Specifically, we used the Bowen ratio energy balance method (BREB), three combination models, seven radiation-based models, and three temperature-based models based on data from June 2017 to December 2018 in a humid alpine meadow in the northeastern Qinghai–Tibetan Plateau. The daily actual evapotranspiration (ETa) data were obtained using large weighing lysimeters located in an alpine Kobresia meadow. We found that the performance of the fourteen ET0 models, ranked on the basis of their root mean square error (RMSE), decreased in the following order: BREB > Priestley-Taylor (PT) > DeBruin-Keijman (DK) > 1963 Penman > FAO-24 Penman > FAO-56 Penman–Monteith > IRMAK1 > Makkink (1957) > Makkink (1967) > Makkink > IRMAK2 > Hargreaves (HAR) > Hargreaves1 (HAR1) > Hargreaves2 (HAR2). For the combination models, the FAO-24 Penman model yielded the highest correlation (0.77), followed by 1963 Penman (0.75) and FAO-56 PM (0.76). For radiation-based models, PT and DK obtained the highest correlation (0.80), followed by Makkink (1967) (0.69), Makkink (1957) (0.69), IRMAK1 (0.66), and IRMAK2 (0.62). For temperature-based models, the HAR model yielded the highest correlation (0.62), HAR1, and HAR2 obtained the same correlation (0.59). Overall, the BREB performed best, with RMSEs of 0.98, followed by combination models (ranging from 1.19 to 1.27 mm day−1 and averaging 1.22 mm day−1), radiation-based models (ranging from 1.02 to 1.42 mm day−1 and averaging 1.27 mm day−1), and temperature-based models (ranging from 1.47 to 1.48 mm day−1 and averaging 1.47 mm day−1). Furthermore, all models tended to underestimate the measured ETa during periods of high evaporative demand (i.e., growing season) and overestimated measured ETa during low evaporative demand (i.e., nongrowing season). Our results provide new insights into the accurate assessment of evapotranspiration in humid alpine meadows in the northeastern Qinghai–Tibetan Plateau.

Changes and Relationships between Components in the Plant-Soil System and the Dominant Plant Functional Groups in Alpine Kobresia Meadows Due to Overgrazing

In the last several decades, overgrazing has led to various changes in the plant communities, soil nutrients and soil microbial communities in alpine Kobresia meadows, which contain various plant communities coexisting on the Qinghai–Tibet Plateau. Investigating the variations in the biomass and concentration of nutrients in the plant–soil system in these communities may improve understanding of the biochemical responses and adaptation strategies they use to resist disturbances due to overgrazing. We therefore assessed 12 factors across four grazing intensities in alpine Kobresia meadows to explore the following three questions. (1) What the responses are in alpine Kobresia meadows to overgrazing. (2) How they affect plant–soil systems in alpine Kobresia meadows under overgrazing. (3) What factors can be used to evaluate the effects of overgrazing on the ecosystem health status of alpine Kobresia meadows. The results gave the following answers to the above questions. (1) Overgrazing caused the total aboveground biomass to decrease from 333.2 ± 17.4 g/m2 to 217.4 ± 30.2 g/m2, the coverage of plant functional groups of Gramineae and Cyperaceae to decrease from 74.2 ± 3% to 22.5 ± 1.9%, and the total belowground biomass to increase from 4028.5 ± 7.3 g/m2 to 6325.6 ± 24.8 g/m2. (2) Overgrazing resulted in variations in plant–soil systems at three levels. The concentrations of carbon (C) in soil nutrients and plant communities, explained 50.9% of the variation of biomass in plant functional groups; the concentration of soil available nutrients, explained 22.2% of the variation; and the ratio of C and N in shoots and soil total N, explained 11.0% of the variation. (3) The variations in C/N stoichiometry in total soil nutrients and soil microorganisms were 3.4–8.4% and 2.0–3.0%, respectively, and the load of (ammonium-nitrogen (NH4+-N) + nitrate-nitrogen (NO3–-N)) to growth of roots tissue increased from 84.1 ± 5.0 g/m2/(mg/kg) via 99.0 ± 1.3 g/m2/(mg/kg) to 86.1 ± 2.1 g/m2/(mg/kg) at 0 to 40 cm soil in an alpine meadow with grazing intensities rising. Overgrazing would thus increase the deficit of those two kinds of inorganic N on roots growing by 11.4%, 17.7% and 2.4% as grazing rates increased by 93.3%, 126.7% and 213.3%, respectively, compared to a meadow grazed at the lowest rate in the research. We concluded that the alpine meadow changed its distribution of biomass in the plant community, which increased the limiting nutrient deficit on production and altered the concentration and ratio of C and N. This destroyed the original balance to enable the plant community to resist overgrazing. Plot “KH”—a pasture with a grazing intensity next to the lowest one—was the key state in which persistent overgrazing could increase the limiting nutrient load on plant community production, change the dominant position of functional plant groups and species, and lead to plant community degradation. Using ratio of Gramineae to Cyperaceae or Kobresia humilis to K. pygmaea to monitor plant community succession could indirectly estimate these limiting nutrients deficit and balance, and their strategy for incorporating matter into roots and shoots. However how to use those outward characteristics to assess the ecosystem health requires further studies.

Evaluation of actual evapotranspiration measured by large‐scale weighing lysimeters in a humid alpine meadow, northeastern Qinghai‐Tibetan Plateau

AbstractThe accurate estimation of evapotranspiration (ET) is essential for assessing water availability and requirements of regional‐scale terrestrial ecosystems, and for understanding the hydrological cycle in alpine ecosystems. In this study, two large‐scale weighing lysimeters were employed to estimate the magnitude and dynamics of actual evapotranspiration in a humid alpine Kobresia meadow from January 2018 to December 2019 on the northeastern Qinghai‐Tibetan Plateau (QTP). The results showed that daily ETa averaged 2.24 ± 0.10 mm day −1 throughout the study period, with values of 3.89 ± 0.14 and 0.81 ± 0.06 mm day−1 during the growing season and non‐growing season, respectively. The cumulative ETa during the study period was 937.39 mm, exceeding precipitation (684.20 mm) received at the site during the same period by 37%, suggesting that almost all precipitation in the lysimeters was returned to the atmosphere by evapotranspiration. Furthermore, the cumulative ETa (805.04 mm) was almost equal to the maximum potential evapotranspiration estimated by the FAO‐56 reference evapotranspiration (ET0) (801.94 mm) during the growing season, but the cumulative ETa (132.25 mm) was 113.72% less than the minimum equilibrium ETeq) (282.86 mm) during the non‐growing season due to the limited surface moisture in frozen soil. The crop coefficient (Kc) also showed a distinct seasonal pattern, with a monthly average of 1.01 during the growing season. Structural equation model (SEM) and boosted regression tree (BRT) show that net radiation and air temperature were the most important factors affecting daily ETa during the whole study period and growing season, but that non‐growing season ETa was dominated by soil water content and net radiation. The daily Kc was dominated by net radiation. Furthermore, both ETa and Kc were also affected by aboveground biomass.

Modelling and assessment of climate change and policy response – the distribu tion and area of

How the suitable distribution of a given grassland type will respond to policy implementation and climate change is a prerequisite and the basis for effective grassland management and sustainable development. The maximum entropy (MaxEnt) model as a comprehensive evaluation method at species level was successfully used to simulate the temporal and spatial changes in the geographical distribution of Kobresia meadow in China’s Three-River Headwaters (TRH) region under the context of policy implementation and climate change. There were three main findings. First, there are the six dominant environmental variables affecting the distribution of Kobresia meadow (these being elevation, precipitation variation coefficient, March precipitation, April precipitation, April minimum temperatures, and May minimum temperatures: their threshold values are 3500–4000 m, 86–100, 8.5 mm, 12 mm, –3.5°C and 1.5°C, respectively, which indicate the most suitable conditions for Kobresia meadow distribution). Second, under current (2005–2014) climate conditions, the suitable distribution of Kobresia meadow gradually decreases from east to west, with the largest area in the east. Implementation of the ecological conservation policy in the TRH has greatly improved the ecological environment in lower elevation and high population areas. This has benefited the growth of Kobresia meadow and enlarged its suitable areas. Third, compared with the current distribution, areas suitable for Kobresia meadow will increase by 25.4–33.0% in the 2050s (2041–2060) and 17.4–33.0% in the 2070s (2061–2080) under four Representative Concentration Pathway (RCP) scenarios. More importantly, from the 2050s to the 2070s, areas suitable for Kobresia meadow will decrease or stabilise, bringing new challenges for protection and utilisation.

Response of Soil Microbial Communities to Warming and Clipping in Alpine Meadows in Northern Tibet

In order to explore responses of soil microbial communities among different alpine meadows under warming and clipping, soil microorganisms of three alpine meadow sites (low altitude: 4313 m, alpine steppe meadow, 30°30′ N, 91°04′ E; mid-altitude: 4513 m, alpine steppe meadow, 30°31′ N, 91°04′ E; and high altitude: 4693, alpine Kobresia meadow, 30°32′ N, 91°03′ E) were measured using the phospholipid fatty acid (PLFA) method. Both warming and clipping significantly reduced PLFA content and changed the community composition of soil microbial taxa, which belong to bacterial and fungal communities in the alpine Kobresia meadow. Warming significantly reduced the soil total PLFA content by 36.1% and the content of soil fungi by 37.0%; the clipping significantly reduced the soil total PLFA content by 57.4%, the content of soil fungi by 49.9%, and the content of soil bacteria by 60.5% in the alpine Kobresia meadow. Only clipping changed the total fungal community composition at a low altitude. Neither clipping nor warming changed the microbial community composition at a moderate altitude. Soil temperature, soil moisture, and pH were the main factors affecting soil microbial communities. Therefore, the effects of warming and clipping on soil microbial communities in alpine meadows were related to grassland types and soil environmental conditions.

Carbon and water fluxes and their coupling in an alpine meadow ecosystem on the northeastern Tibetan Plateau

Alpine meadow is one of the most widely distributed vegetation types on the Tibetan Plateau—the Earth’s Third Pole. Characterizing the carbon and water vapor fluxes in alpine meadow ecosystems is of particular importance for elucidating the mechanisms underlying the carbon budget and water cycle in high-altitude areas, especially under changing climatic conditions. Thus, the quantitative relationships between carbon and water fluxes and environmental drivers were examined based on a continuous eddy covariance (EC) dataset from 2013 to 2015 over the alpine Kobresia meadow on the northeastern Tibetan Plateau. The results show that (1) the net ecosystem CO2 exchange (NEE) was − 152.89 g C m−2 year−1, − 197.69 g C m−2 year−1, and − 160.09 g C m−2 year−1 from 2013 to 2015, respectively, suggesting that this alpine meadow ecosystem is a strong and consistent carbon sink. (2) Both the multiple stepwise regression analysis (MSRA) and the structural equation model (SEM) analysis confirmed the dominant role of Ts in controlling the carbon flux and that of Rn in controlling the water vapor flux. (3) The inherent water use efficiency (IWUE = GPP×VPD/ET) and underlying water use efficiency (uWUE = GPP×VPD0.5/ET), which incorporates the vapor pressure deficit (VPD) effect, better described the carbon-water coupling characteristics at daily and hourly scales than did the traditional water use efficiency (WUE = GPP/ET). These findings highlight the dominant climatic factors controlling CO2 and water vapor exchanges and contribute to our knowledge of the land surface-atmosphere exchange in alpine meadows on the Tibetan Plateau.

Moderate grazing promotes the root biomass in Kobresia meadow on the northern Qinghai-Tibet Plateau.

Grazing is an important modulator of both plant productivity and biodiversity in grassland community, yet how to determine a suitable grazing intensity in alpine grassland is still controversy. Here, we explore the effects of different grazing intensities on plant biomass and species composition, both at community level and functional group level, and examines the productivity–species richness relationship under four grazing patterns: no grazing (CK), light grazing (LG), moderate grazing, (MG) and heavy grazing (HG), attempt to determine a suitable grazing intensity in alpine grassland. The results were as follows. The total aboveground biomass (AGB) reduced with increasing grazing intensity, and the response of plant functional groups was different. AGB of both sedges and legumes increased from MG to HG, while the AGB of forbs reduced sharply and the grass AGB remained steady. There was a significant positive relationship between productivity and species richness both at community level and functional group level. In contrast, the belowground biomass (BGB) showed a unimodal relationship from CK to HG, peaking in MG (8,297.72 ± 621.29 g/m2). Interestingly, the grassland community tends to allocate more root biomass to the upper soil layer under increasing grazing intensities. Our results suggesting that moderate levels of disturbance may be the optimal grassland management strategy for alpine meadow in terms of root production.

Nitrogen controls the net primary production of an alpine Kobresia meadow in the northern Qinghai-Tibet Plateau.

Net primary production (NPP) is a fundamental property of natural ecosystems. Understanding the temporal variations of NPP could provide new insights into the responses of communities to environmental factors. However, few studies based on long‐term field biomass measurements have directly addressed this subject in the unique environment of the Qinghai‐Tibet plateau (QTP). We examined the interannual variations of NPP during 2008–2015 by monitoring both aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP), and identified their relationships with environmental factors with the general linear model (GLM) and structural equation model (SEM). In addition, the interannual variation of root turnover and its controls were also investigated. The results show that the ANPP and BNPP increased by rates of 15.01 and 143.09 g/m2 per year during 2008–2015, respectively. BNPP was mainly affected by growing season air temperature (GST) and growing season precipitation (GSP) rather than mean annual air temperature (MAT) or mean annual precipitation (MAP), while ANPP was only controlled by GST. In addition, available nitrogen (AN) was significantly positively associated with BNPP and ANPP. Root turnover rate averaged 30%/year, increased with soil depth, and was largely controlled by GST. Our results suggest that alpine Kobresia meadow was an N‐limited ecosystem, and the NPP on the QTP might increase further in the future in the context of global warming and nitrogen deposition.

Characterization of Root Architectures and Soil Macropore Networks Under Different Ecosystems Using X-ray CT Scanning in the Qinghai Lake Watershed, NE Qinghai–Tibet Plateau

The objectives of this study were to visualise and quantify the soil macropore networks and root architectures within intact soil columns under different ecosystems and to investigate the influences of roots on soil macropore network characteristics. Intact soil columns with diameters of 110 mm and lengths of 400 mm were taken from alpine Kobresia meadow, interspace meadow patches of Potentilla fruticosa shrubs, Potentilla fruticosa shrubs and Artemisia sphaerocephala shrubs in the Qinghai Lake watershed of the NE Qinghai–Tibet Plateau. A Philips medical X-ray CT scanner was used to simultaneously visualise and quantify the soil macropore networks and root architectures. The results showed that macropores and taproots were concentrated in the top 0–150 mm. The root volume density of the P. fruticosa shrub was greater than that of the interspace meadow patches of P. fruticosa shrub and that of the alpine Kobresia meadow. The macroporosity and the root volume density of the soils under the P. fruticosa shrub patches were significantly greater than those in the soils under the other sites. The root volume density was significantly correlated with the macroporosity for the A. sphaerocephala shrubs (R2 = 0.88) and the P. fruticosa shrubs (R2 = 0.73). There were significant positive correlations between the volume density, branch density and mean angle of the roots and those of the macropores. Shrub roots invasion played an important role in the formation of macropores. The root volume density was the most important factor for the quantified characteristics and distributions of the macropores.

Measurements and Modeling of the Water Budget in Semiarid High‐Altitude Qinghai Lake Basin, Northeast Qinghai‐Tibet Plateau

AbstractWater budget plays an important role in ecological functions and biogeochemical cycles on the Qinghai‐Tibet Plateau (QTP). However, the key factors that govern the water budget across spatiotemporal scales in natural conditions are poorly understood, especially in the alpine region. To advance our understanding of how and why the water budget varies at the ecosystem and catchment scales, this study measured and modeled the main water budget components in the Qinghai Lake Basin (QLB) and further investigated the key factors for evapotranspiration and streamflow. The results showed that most monthly precipitation from June to September was greater than the corresponding evapotranspiration from the high‐altitude Kobresia meadow (KMd.) and Potentilla fruticosa shrub (PFSh.) ecosystem, and vice versa for the low‐altitude Achnatherum splendens steppe (ASSt.) ecosystem. The mean annual proportions of evapotranspiration of precipitation for the KMd., PFSh., and ASSt. ecosystems were 0.83, 1.06, and 1.02, respectively, from 2014 to 2015. The study highlights that the high‐altitude KMd. ecosystem is the main contributing area for runoff generation in the QLB. From ASSt. to PFSh. and then to the KMd. ecosystem, the key factors for evapotranspiration switched from water conditions to temperature conditions with the increase in elevation. The future scenario of climate warming and precipitation increase may cause a rise in evapotranspiration and streamflow in the QLB. Moreover, the increasing precipitation may be consumed mainly by evapotranspiration in the high altitude with low slope and by transfer into streamflow in the area with high slope.

A prognostic phenology model for alpine meadows on the Qinghai–Tibetan Plateau

Phenology models are useful tools to study phenology shifts and their responses to climate change. Multiple factors including temperature, precipitation, photoperiod, insolation, and snow can affect the phenology of alpine grasslands on the Qinghai–Tibetan Plateau (QTP), but most models applied on the QTP have only considered the influences of temperature or temperature and precipitation. This study presents a multi-factor-driven phenology model, the Alpine Meadow Prognostic Phenology (AMPP) model, based on the Growing Season Index (GSI), to predict both leaf onset and offset dates of QTP alpine meadows at the community scale. Five factors including daily minimum air temperature, precipitation averaged over the previous month, photoperiod, global solar radiation, and snowfall were combined into an integrated index, the Alpine Meadow Growing Season Index, to quantify climatic limitations on foliar development of QTP alpine meadows. A case study was conducted using the observed leaf onset and offset dates of dominant species in QTP Kobresia meadows from 1989 to 2016. The root-mean-square errors (RMSEs) of modeled leaf onset and offset dates from the AMPP model were 6.9 d and 11.0 d, respectively, decreasing by 13.8%–48.9% and 7.6%–47.1% compared with the null model and seven other phenology models. The correlation coefficients between the predicted and observed leaf onset and offset dates were 0.75 and 0.34, respectively, higher than the 0.50–0.68 and −0.22–0.11 from other models. The RMSE ranges of predicted leaf onset and offset dates among three different sites were 2.9 d and 1.1 d, respectively, lower than or equal to the 3.6–12.4 d and the 1.1–6.9 d from other models. Results indicated that the AMPP model clearly improved the prediction accuracy and simulation of the interannual variability of leaf onset and offset dates and showed more robust simulations at different sites. Moreover, this model can be easily embedded into most ecosystem process models and applied to other alpine or subalpine grasslands once it has been adapted to their requirements.