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Hereweprovidetheoriginal data of precipitation, Stream discharge, Water Level,air temperatur, soil temeprature, DOC and DIC in an alpine headwater catchment of the Qinghai-Tibetan Plateau.

Saline lakes on the Qinghai–Tibet Plateau (QTP) profoundly affect the regional climate and water cycle through loss of water (E, evaporation under ice–free (IF) and sublimation under ice–covered (IC) conditions). Due to the observation difficulty over lakes, E and its underlying driving forces are seldom studied targeting saline lakes on the QTP, particularly during the IC. In this study, E of Qinghai Lake (QHL) and its influencing factors during the IF and IC were first quantified based on six years of observations. Subsequently, two models were chosen and applied in simulating E and its response to climate variation during the IF and IC from 2003 to 2017. The annual E sum of QHL is 768.58 ± 28.73 mm, and E sum during the IC reaches 175.22 ± 45.98 mm, accounting for 23% of the annual E sum. The E is mainly controlled by the wind speed, vapor pressure difference, and air pressure during the IF, but driven by the net radiation, the difference between the air and lake surface temperatures, wind speed, and ice coverage during the IC. The mass transfer model simulates lake E well during the IF, and the model based on energy achieves a good simulation during the IC. Moreover, wind speed weakening results in an 11.14% decrease in E during the IC of 2003–2017. Our results highlight the importance of E in IC, provide new insights into saline lake E in alpine regions, and can be used as a reference to further improve hydrological models of alpine lakes.

As regional heterogeneity on the Qinghai Tibetan Plateau (QTP), the “greening rate” between alpine steppe in the west and alpine meadow ecosystems in the east is difference during the past several decades. To investigate the difference, the net photosynthetic rate (An) and the supply (mesophyll conductance ( g), stomatal conductance ( g)) and demand (the maximum rates of Rubisco carboxylase activity ( V) and photosynthetic electron transport ( J)) for CO of three plants functional types (PFTs) were measured. Other functional traits and influencing factors were compared among ecosystems along the altitudinal gradients of QTP. The An of the PFTs was simulated under potential future conditions. At high altitudes, grass was found to maintain a relatively stable An by decreasing V, J, and g, while slightly increasing g, compared with that at a low altitude. The An of sedge and shrubs increased with rising V, J and g and g values, resulting in a large increment in the An at low altitudes. Grass seemed to be less sensitive to the environment by reducing the supply of and holding onto CO , while sedge and shrub increased both. Grass and sedge should be divided into two PFTs rather than remaining as one based on their opposite physiological and morphological functions in response to climate change. The ecosystem at 3600 m was transitional. C was likely to be a more dominant factor than T in affecting the An of grass. The order of rising An in PFTs was shrub > sedge > grass and the An of alpine meadow was found to increase more under the two future climate scenarios.

Canopy conductance (Gc) largely regulates carbon/water cycling and land–atmosphere interactions, but quantifying Gc using eddy flux data is limited by the difficulty of partitioning plant transpiration (T) and surface evaporation (E). We introduced an underlying water use efficiency (uWUE) method to partition evapotranspiration (ET) in an oasis maize ecosystem, and cross–compared with the Shuttleworth and Wallace (SW) model, the lysimeter and isotope measurements. We then estimated surface conductance (Gs) by ET and Gc by T partitioned using the uWUE method, followed by a performance evaluation on the Jarvis model parameterized with both Gs and Gc. The results showed that T/ET estimated by the uWUE method was close to the isotope method in the peak growing season of 2012, it showed similar seasonal variations with the lysimeter/eddy covariance method and the SW model throughout this growing season. Daily T partitioned by the uWUE method was in good agreement with the SW model from 2012 to 2015 (r2 = 0.91). Additionally, Gc had more significant seasonal variations than Gs. The Jarvis model parameterized with Gc exhibited superior performance than those with Gs. Our study suggests that the uWUE method can exclude influences of nonstomatal conductances, and will have great potential to provide more reasonable parameterization for simulation of plant stomata.

Shrub is the main vegetation type for vegetation restoration in the Loess Plateau, which plays an important role in the regional ecosystem restoration. Study on the relationships between vegetation and soil water of typical shrub ecosystems are significant for the restoration and reconstruction of ecosystems in the Loess Plateau. Three typical shrub (Hippophae rhamnoides Linn., Spiraea pubescens Turcz., and Caragana korshinskii Kom.) ecosystems were chosen in the Loess Plateau. Field experiments were conducted to investigate the factors that influencing the processes of rainfall interception and root uptake of typical shrubs. S-Biome-BGC model was established based on the Biome-BGC model by developing the rainfall interception and soil water movement sub-models. The model was calibrated and verified using field data. The calibrated S-Biome-BGC model was used to simulate the characteristics of leaf area index (LAI), net primary productivity (NPP), soil water content and the interactions among them for the shrub ecosystems along the precipitation gradients in the Loess Plateau, respectively. The results showed that the predictions of the S-Biome-BGC model for soil water content and LAI of typical shrub ecosystems in Loess Plateau were significantly more accurate than that of Biome-BGC model. The simulated RMSE of soil water content decreased from 0.040~0.130 cm3 cm-3 to 0.026~0.035 cm3 cm-3, and the simulated RMSE of LAI decreased from 0.37~0.70 m2 m-2 to 0.35~0.37 m2 m-2. Therefore, the S-Biome-BGC model can reflect the interaction between plant growth and soil water content in the shrub ecosystems of the Loess Plateau. The S-Biome-BGC model simulation for LAI, NPP and soil water content of the three typical shrubs were significantly different along the precipitation gradients, and increased with annual precipitation together. However, different LAI, NPP and soil water correlations were found under different precipitation gradients. LAI and NPP have significant positive correlations with soil water content in the areas where the annual precipitation is above 460~500 mm that could afford the shrubs growth. The results of the study provide a re-vegetation threshold to guide future re-vegetation activities in the Loess Plateau.

The interface of the Earth’s critical zone is the place where organic carbon is dramatically decomposed and transformed．The dynamics and fate of organic carbon serve as an important foundation to reveal the material transportation in the Qinghai-Tibet Platea critical zones. This research analyzed temperature, soil moisture and stable carbon isotope values (δ13C) of CO2 in different soil layers, measure soil surface respiration using soil respiration measurement system (LI-8100) , and analyzed carbon storage , carbon dynamics and its controlling factors in critical zones in seven typical ecosystems of the Qinghai-Tibet Platea. The results found that the underground carbon content and its controlling factors were very different in different ecosystems on the Qinghai-Tibet Plateau. The main controlling factor of carbon changes was water in alpine steppe and desert ecosystem while it was temperature in alpine meadow. In the meanwhile, this research also measured the maximum carboxylation rate (Vcmax) of dominant plants in each ecosystem, trying to explore the different carbon inputs in different ecosystems. Understanding the impacts of environmental changes on the geochemical cycling of critical zone’s organic carbon in the Qinghai-Tibet Platea would benefit the optimization of carbon cycling model and climate change predictions．

It is generally believed that evapotranspiration at night is too miniscule to be considered. Thus, few studies focus on the nocturnal evapotranspiration (ETN) in alpine region. In this study, based on the half-hour eddy and meteorological data of the growing season (from May to September) in 2019, we quantified the ETN of alpine desert (AD), alpine meadow (AM), alpine meadow steppe (AMS), and alpine steppe (AS) in the Qinghai Lake Basin and clarified the different response of evapotranspiration to climate variables in daytime and nighttime with the variation of elevation. The results show that: (1) ETN accounts for 9.88~15.08% of total daily evapotranspiration and is relatively higher in AMS (15.08%) and AD (12.13%); (2) in the daytime, net radiation (Rn), temperature difference (TD), vapor pressure difference (VPD), and soil moisture have remarkable influence on evapotranspiration, and Rn and VPD are more important at high altitudes, while TD is the main factor at low altitudes; (3) in the nighttime, VPD and wind speed (WS) control ETN at high altitudes, and TD and WS drive ETN at low altitudes. Our results are of great significance in understanding ETN in the alpine regions and provide reference for further improving in the evapotranspiration estimation model.

The Tibetan Plateau (TP) is characterized by the world's highest timberlines, largest altitudinal range of forest distribution, and high warming rates. Whether the growth of most forests benefits from climate warming or is inhibited by warming-induced drought stress is still under debate. To understand this question, we collected tree-ring width (TRW) data from 6762 trees at 203 sites that contain 12 genera over the monsoonal TP (MTP) with an elevation range between 975 and 4478 m a.s.l. All sites were equally split into four transects along their altitudinal ranking. The mean tree growth rate (MTGR) of each transect was developed by assembling standardized TRW records. Our results suggest that MTGRs of the upper three transects (2992–4478 m) were stimulated by an increase in the summer (May-September) minimum temperature and have experienced unprecedented high values since the 1980s over the past three to four centuries. In contrast, warming-associated drought stress resulted in a sharp growth drop and minimum MTGR in the lowest transect (975–2970 m) during the 2000s, which was most pronounced in the Himalayan Mountains. We conclude that the majority of tree growth on the MTP has benefited from recent summer warming. The results are robust regardless of using alternative detrending methods, but still could be susceptible to the small replications of some species, outdated end years, oversimplification of the regional climate conditions, and varying growth response within each transect.

Rainfall interception loss plays an important role in ecohydrological processes in dryland shrub ecosystems, but its drivers still remain poorly understood. In this study, a statistical model was developed to simulate interception loss based on the mass balance measurements arising from the partitioning of rainfall in 2 dominant xerophytic shrub (Hippophae rhamnoides and Spiraea pubescens) communities in the Loess Plateau. We measured throughfall and stemflow in the field under natural rainfall, calculated the canopy storage capacity in the laboratory, and identified key factors controlling these components for the 2 shrubs. We quantified and scaled up the stemflow and the canopy storage capacity measurements from the branches and/or leaves to stand level. The average interception loss, throughfall, and stemflow fluxes account for 24.9%, 72.2%, and 2.9% of the gross rainfall for H. rhamnoides, and 19.2%, 70.7%, and 10.1% for S. pubescens, respectively. Throughfall increased with increasing rainfall for both shrubs; however, it was only correlated with the leaf area index for S. pubescens. For stemflow measured from individual branches, we found that the rainfall amount and basal diameter are the best predictors for H. rhamnoides, whereas rainfall amount and branch biomass appear to be the best predictors for S. pubescens. At the stand level, stemflow production is affected by the rainfall amount for H. rhamnoides, and it is affected by both the rainfall amount and the leaf area index for S. pubescens. The canopy storage capacity of H. rhamnoides (1.07–1.28 mm) was larger than S. pubescens (0.88–1.07 mm), and it is mainly determined by the branches and stems of H. rhamnoides and the leaves of S. pubescens. The differences in interception loss between the 2 shrub stands are mainly attributed to different canopy structures that induced differences in stemflow production and canopy storage. We evaluated the effects of canopy structure on rainfall interception loss, and our developed model provides a better understanding of the effects of the canopy structure on the water cycles in dryland shrub ecosystems.

The sustainability of vulnerable eco-environment over the Silk Road Economic Belt is under threat of climate change, and the identification of vegetation constraints by sub-optimum climatic conditions is critically essential to maintain existing dryland ecosystems. To better understand how the vegetation varies at monthly scale and its effect by climate conditions in different desert areas, this study first investigated the seasonal variation of the normalized difference vegetation index (NDVI). Then, we analyzed the time effects of diverse climatic factors (air temperature, solar radiation, precipitation) on NDVI and estimated the limitation of NDVI by these climatic factors in different desert areas. The result showed that the mean monthly NDVI during 1982–2015 showed a unimodal variation in most desert areas, with high values in late spring and summer over cold arid areas, in early spring or early autumn over hot arid areas, and in summer over polar areas, respectively. Solar radiation and precipitation in cold arid areas presented 1–2 month lag or accumulation effect on NDVI, while precipitation in most hot arid areas showed no remarkable time-lag but 3 month accumulation effect, and all three climate factors in polar areas exhibited 1–3 month accumulation effect. The explanatory power of climatic conditions for vegetation dynamics considering time effects increased by 3.4, 10.8, and 5.9% for the cold arid areas, hot arid areas, and polar areas (i.e., relative increase of 4.1, 25.4, and 8.2%), respectively. The main climatic constraints to vegetation dynamics were the water condition in hot arid areas (>78%) and the temperature condition in polar areas (>67%), while cold arid areas were simultaneously limited by the water and temperature conditions (>76% in total). These results provide a detailed understanding of vegetation variation and ecological projection, which are very important to implement adaption measures for dryland ecosystems over the Silk Road Economic Belt.

The rooting traits of deep-rooted alpine grasses strongly control the redistribution of soil moisture (i.e., the changes in the soil volumetric water content, ΔSVWC), which is the most important water resource supporting vegetation growth in cold semiarid regions. However, due to the difficulty of developing appropriate methods to characterize the hidden structures of root-soil systems, the linkages between root traits and ΔSVWC remain challenging to detect. This study aims to identify how the roots of Achnatherum splendens (A. splendens) affect soil water infiltration and spatiotemporal variations in the rhizosphere under different root densities and rainfall patterns using electrical resistivity tomography (ERT) and dye experiments, as well as to determine the relationship between root traits and soil water redistribution. Manipulative rainfall experiments 5, 10, 20 and 40 mm simulated rainfall were applied to sample plots with no plants (control), single and double A. splendens plantings (BAS, SAS, DAS, respectively). The results of ERT and the dyeing profiles showed that the roots of A. splendens greatly affected infiltration processes and the soil water distribution. The soil water was vertically and laterally funneled along the roots. In SAS, which had a lower root length density (RLD), the soil water accumulated mainly in the shallow layer (0–20 cm), while in DAS, which had a higher total root mass density (RMD), the soil water mainly infiltrated rapidly into the deep soil (>20 cm), especially during the extreme (40 mm) rainfall event. The temporal increases in soil moisture below 20 cm under DAS were higher than that those under BAS and SAS after rainfall for 2 and 24 h. The RMD, specific root length (SRL), specific root surface area (SSA) and RLD were all negatively and significantly correlated with the ΔSVWC at 0–20 cm. At 20–40 cm, the RMD and RLD were positively and significantly correlated with ΔSVWC, whereas the SRL and SSA showed the opposite trend. These findings provide direct evidence of the linkages between A. splendens root traits and ΔSVWC using ERT and the dye tracing method, and this evidence is important for the development of soil-plant-atmosphere continuum (SPAC) models.

Seasonal non-structural carbohydrate (NSC) dynamics in different organs can indicate the strategies trees use to cope with water stress, however, these dynamics remain poorly understood along a large precipitation gradient. In this study, we hypothesized that the correlation between water availability and NSC concentrations in different organs might be strengthened by decreasing precipitation in Pinus tabulaeformis Carr. forests in temperate China. Our results show that the concentrations of soluble sugars were lower in stems and coarse roots, and starch was higher in branches in the early growing season at drier sites. Throughout the growing season, the concentrations of soluble sugars increased in drier sites, especially for leaves, and remained stable in wetter sites, while starch concentrations were relatively stable in branches and stems at all sites. The NSC concentrations, mainly starch, decreased in coarse roots along the growing season at drier sites. Trees have a faster growth rate with an earlier cessation in active stem growth at drier sites. Interestingly, we also found a divergent relationship between NSCs in different organs and mean growing season water availability, and a stronger correlation was observed in drier sites. These results show that pine forests in arid and semi-arid regions of northern China exhibit different physiological responses to water availability, improving our understanding of the adaptive mechanisms of trees to water limitations in a warmer and drier climate.

The sustainability of dryland vegetation growth over the Silk Road Economic Belt is under threat of water shortage, and the determination of water carrying capacity for vegetation is critically essential to balance water supply and water demand for the maintenance of existing ecosystems. To better understand how and why vegetation growth varies in different desert areas, this study first analyzed the spatiotemporal variation of the normalized difference vegetation index (NDVI). Then, we investigated the relationship between NDVI and climatic factors (precipitation, soil water content, air temperature, evapotranspiration), and estimated the threshold NDVI under water balance in different desert areas. Results showed that the higher NDVI was mainly distributed in Kazakhstan, Russia, and Azerbaijan, and it increased in approximately 53% of desert areas from 1982 to 2015 in the whole study region. The mean annual NDVI showed a simultaneous increasing trend in all desert areas from 1982 to 1994, and decreased significantly only in the cold arid desert area (p < 0.01, −0.0067 decade−1) or had no significant change in other desert areas after 1994 (p > 0.01). The climate condition generally appeared as a warming and drying trend in the past 34 years, with varied changing rates in different desert areas. NDVI presented a strong positive relationship with both precipitation and evapotranspiration in most desert areas. The threshold values of the mean annual NDVI under water balance between 1982 and 2015 were approximately 0.1041 (hot arid desert), 0.1337 (cold arid desert), 0.1346 (cold arid semi-desert), 0.0951 (hot arid desert semi-desert), 0.0776 (polar desert tundra), 0.1071 (hot arid desert shrub), 0.1377 (cold arid desert steppe), and 0.0701 (polar desert steppe), respectively. The responses of these threshold values to precipitation were all positive in different desert areas. These results provide an enhanced understanding of vegetation dynamics and ecological conservation, which are of great importance to implementing adaptation and mitigation measures for terrestrial ecosystems over the Silk Road Economic Belt.

Harvesting is a common method in grassland management. With shrub encroachment into grassland, special hydrological and physiological dynamics probably occur in the shrub-grass coexisted ecosystem after harvesting, which remains largely unclear. Therefore, this study aims to identify potential effects of harvesting on soil moisture pattern, phenology dynamics, and water utilization in a shrub encroached grassland. We monitored soil water for a year beneath the Caragana microphylla canopy and interspace grassland after harvesting. The results showed that the soil water content increased under shrubs and grass patches after harvesting, especially under later ones. The water storage in soil of 0&ndash, 100 cm depth increased by 18.9 mm under grass but only 5.5 mm under shrubs. Harvesting also decreased the difference of water storage between shrubs and grass from 19.1 to 5.7 mm. More snowmelt compensation, less evapotranspiration, shorter growing season, and higher water use efficiency may jointly contribute to the water recovery of harvesting soil. This study contributes novel evidence to the ecohydrological impacts of harvesting on shrub-grass co-existed ecosystems, shows application value in controlling shrub encroachment process and provides fundamental insights for the further study on soil water dynamics of similar ecosystems worldwide.

The Grain for Green Project (GFGP) in Chinas Loess Plateau significantly influences regional vegetation growth and water cycles, especially the inter-annual variability of terrestrial evapotranspiration (ET). In this study, we analyzed the spatial-temporal variations of ET and its driving factors before the period of (1982−1997) and after implementing of the GFGP in the revegetation area of the Loess Plateau during 2001−2015. Firstly, three sets of ET products are collected herein, including global flux product evapotranspiration (FLUXNET ET, FET), model simulation WB-MTE-ET (WET) and GLEAM ET (GET). To evaluate the performance of the ET products in the Loess Plateau, we calculated the mean annual streamflow ( Q mod) based on the water balance equation with three sets of ET products against the observed mean annual streamflow ( Q obs) at seven catchments over the Loess Plateau. The results indicated that Q mod estimated from GET shows the best agreement with Q obs in terms of both spatial ( R 2=0.97, P 0.01) and temporal ( R 2=0.94, P 0.01) variations. Thus, we selected GLEAM ET (GET) products in the following analysis. Secondly, we analyzed the trend of annual NDVI and ET in the growing season before and after implementing of the GFGP in the revegetation area using the linear regression. Furthermore, we conducted the stepwise regression analysis to identify the controlling factors that affect the ET changes in the revegetation area during different period. The environmental factors included soil moisture, air temperature, precipitation and averaged Normalized Difference Vegetation Index (NDVI) during the growing season. The results showed that: (1) The inter-annual variability of ET in the revegetation area was significantly increased after implementing of the GFGP compared with that before the GFGP. The inter-annual ET variability also exhibited great spatial differences which showed the highest peak in the regions with annual precipitation ranging from 400 to 600 mm a-1. (2) Compared with the mean air temperature and total precipitation in growing-seasons, the variation of NDVI contributed the most to the changes in ET followed by the soil water content. (3) After implementing of the GFGP, the contribution of the soil water content to ET variation has generally declined, while the contribution of NDVI has increased. This study reveals the influence of the GFGP on the regional water cycle in terms of ET variation, which is of guiding importance to the ecological engineering construction, as well as the rational water resources allocation.

With the increasing temperature and intensified drought, global climate change has profound impacts on tree growth in temperate regions, which consequently regulates terrestrial-atmosphere biogeochemical processes and biophysical feedbacks. Thus, increasing numbers of studies have addressed the long-term annual trends in tree growth and their response to climate change at diverse spatial scales. However, the potential divergence in tree growth trends and growth variability (represented by coefficient of variance) in different seasons across large-scale climate gradients remains poorly understood. Here, we investigated the tree growth trends and growth variability in different seasons across diverse drought conditions in forested regions over northeastern China during the period 1982&ndash, 2015, using both remote sensing observations and in situ tree-ring measurements. We found clear seasonal divergence in tree growth trends during 1982&ndash, 2015, and the apparent increase was mainly observed in spring and autumn, attributed mainly to the increase in spring temperature and autumn solar radiation, respectively, but not in summer. The magnitudes of increasing trends in tree growth decrease with the increase of the multi-year average dryness index (MAI) in semi-arid areas (1.5 &lt, MAI &lt, 4.0) in all seasons. We further revealed that the interannual variability in tree growth was much larger in the semi-arid regions than in the humid and semi-humid regions in all seasons, and tree growth variability was significantly and negatively correlated with the variations in temperature and water deficit. Our findings improve our understanding of seasonal divergence in tree growth trends and provide new insights into spatial patterns in forest vulnerability in a warmer and drier climate.