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This study reports on the self-healing behaviour of fly ash and slag engineered geopolymer composites (FA/S-EGC) under external alkaline environments. FA/S-EGC specimens with different pre-damaged strains were subjected to self-healing at different ages and under different healing environments, including air, water, sodium hydroxide (NaOH) solutions of different concentrations and calcium hydroxide (Ca(OH)2) solution. The self-healing ability of FA/S-EGC was evaluated by crack characteristics, tensile properties and natural frequency-based damage factor. In addition, micro-characterisation techniques including SEM-EDS, XRD and FT-IR analyses were used to reveal the self-healing mechanism of FA/S-EGC. The results showed that FA/S-EGC retained strain hardening and multi-cracking behaviour after healing in an external alkaline environment. The healing products of FA/S-EGC in air, water and alkaline environments consisted mainly of the C(N)-A-S-H gel and calcium carbonate (CaCO3), and the phase of the healing products did not change despite the different environments. The self-healing ability of FA/S-EGC in saturated Ca(OH)2 and 7 % NaOH solutions was significantly improved compared to air and water. This is because the low concentration of the alkaline solution promotes the geopolymerisation of unreacted oxides in the matrix, and the Ca(OH)2 solution also promotes the deposition of CaCO3 at the cracks. However, when the NaOH concentration was increased from 7 % to 21 %, FA/S-EGC still showed significant self-healing behaviour in the first seven days, but new damage was produced in the matrix as the healing age increased. This is because the high concentration of NaOH solution leads to depolymerisation of C(N)-A-S-H gels. These results provide scientific recommendations for the application of FA/S-EGC in alkaline environments and for the development of novel healing agents.

Solar-induced chlorophyll fluorescence (SIF) is strongly physiologically associated with vegetation photosynthesis, and has been broadly employed to monitor gross primary productivity (GPP). However, for some understudied ecosystems, such as the alpine grasslands of the Tibetan Plateau (TP), it is highly uncertain about how SIF performs in tracking GPP. Here, by collecting eddy covariance-derived GPP and climatic data at four grassland sites in the TP, the performances of remotely sensed SIF products (CSIF and GOSIF) in estimating GPP at different time scales (8-day, monthly and growing season) were evaluated and compared against reflectance-based greenness vegetation indices (GVIs) and photochemical reflectance indices (PRIs). Moreover, the SIF-GPP relationship was further examined under different water conditions. The results showed that SIF performed best in tracking GPP variations at all temporal scales compared with GVIs and PRIs. With temporal aggregation, the SIF-GPP relationship was markedly enhanced. We further found that both determination coefficient (R2) values and slopes of the SIF-GPP relationship tended to be lower with decreasing soil water content or increasing vapor pressure deficit. This indicates SIF and GPP will be decoupled with aggravating water stress and their relationship is not universal under different water conditions. Morever, integrating soil water content with SIF improved GPP estimation, underscoring the vital role of water availability in influencing the SIF-GPP relationship. This study can boost our understanding on the variant SIF-GPP relationship and suggests that the regulation effect of water availability need be considered to improve the SIF-derived GPP estimation.

A variable future climate would lead to changes in the biomass allocation pattern of plant communities, but its divergent changes under different environments have not been clearly explored, greatly limiting a better understanding of the responsess of grassland ecosystems to environmental changes. Herein, we conducted field samplings at 215 grassland sites in the Qinghai-Tibetan and Inner Mongolian Plateaus to analyze community biomass allocation patterns (specifically, the ratio of root to shoot, R/S) in various grasslands along environmental gradients. We found a gradual increase in R/S from humid to semi-arid and arid environments across both plateaus. In humid environment, soil factor had a significant effect on the R/S of alpine humid grassland, while climate factor had a significant effect on the R/S of humid grassland. In semi-arid environment, both climate and plant factors had significant effects on R/S in semi-arid grassland. In arid environments, climate and plant factors had significant effects on R/S in arid grassland. These findings emphasize the multifaceted role of environmental factors in shaping biomass allocations across diverse ecosystems, enriching our understanding of ecological dynamics. The current results are timely in advancing the fundamental understanding of the mechanisms of biomass allocation in grasslands and are useful for global research on grasslands in different environments.

Abstract Engineered cementitious composites (ECC) show the distinguished characteristics of high post-cracking resistance and ductility. High-strength stainless steel wire rope (HSSSWR) has been successfully used for restoring or strengthening of existing structures. By combining the advantages of these two materials, a new composite system formed by embedding HSSSWR into ECC was proposed and expected to be a promising engineering material for repair or strengthening of structures. To investigate the tensile failure mechanism and mechanical properties of HSSSWR-reinforced ECC, an experimental study on 27 HSSSWR-reinforced ECC plates was conducted considering the effects of the reinforcement ratio of longitudinal HSSSWRs, formula of ECC and width of the plate. Test results revealed that HSSSWR-reinforced ECC exhibit superior post-cracking resistance, deformation capacity and crack-width control capacity. Increasing the reinforcement ratio of longitudinal HSSSWRs can effectively enhance the tensile strength, crack-width control capacity, deformation capacity and tensile toughness of HSSSWR-reinforced ECC. Adding thickener in ECC can significantly improve the crack-width control capacity and deformation capacity of HSSSWR-reinforced ECC due to enhancing uniform distribution of polyvinyl alcohol fibers, but would slightly reduce the cracking stress and maximum tensile stress by bringing small bubbles in the matrix. The tensile properties of HSSSWR-reinforced ECC plates are almost not affected by varying the plate width. Besides, a tensile constitutive model was developed for charactering the stress–strain relationship of HSSSWR-reinforced ECC in tension. Based on mechanical theories and failure characteristics of HSSSWR-reinforced ECC, the model parameters were determined, and calculation equations of cracking stress and tensile strength were proposed. The accuracy of the developed model and calculation equations was verified by test results.

Drought plays a prominent role in affecting ecosystem stability and ecosystem productivity. Based on eddy covariance and climatic observations during 2012–2020, the Fisher discriminant analysis method was employed to accurately detect drought occurrences. Furthermore, the ecosystem water sensitivity and its resistance to drought were quantified to evaluate the ecosystem stability. The results showed that the alpine meadow suffered drought most frequently at the beginning of the growing seasons. However, drought during the peak growing seasons reduced the gross primary productivity (GPP) the most, by 30.5 ± 15.2%. In the middle of the peak growing seasons, the ecosystem water sensitivity was weak, and thus, the resistance to drought was strong, which resulted in high ecosystem stability. At the beginning and end of the peak growing seasons, the ecosystem stability was relatively weak. Ecosystem stability was positively related to the corresponding multiyear average soil water content (SWCave). However, drought occurring during high SWCave periods led to larger reductions in GPP, which indicated that the inhibitory effects of drought on ecosystems were more dependent on the occurrence time of droughts than on ecosystem stability.

AimsLeaf chlorophyll (Chl) is a fundamental component and good proxy for plant photosynthesis. However, we know little about the large-scale patterns of leaf Chl and the relative roles of current environment changes vs. plant evolution in driving leaf Chl variations.LocationsThe east to west grassland transect of the Tibetan Plateau.MethodsWe performed a grassland transect over 1,600 km across the Tibetan Plateau, measuring leaf Chl among 677 site-species.ResultsLeaf Chl showed a significantly spatial pattern across the grasslands in the Tibetan Plateau, decreasing with latitude but increasing with longitude. Along with environmental gradient, leaf Chl decreased with photosynthetically active radiation (PAR), but increased with water availability and soil nitrogen availability. Furthermore, leaf Chl also showed significant differences among functional groups (C4 > C3 species; legumes < non-legume species), but no difference between annual and perennial species. However, we surprisingly found that plant evolution played a dominant role in shaping leaf Chl variations when comparing the sum and individual effects of all the environmental factors above. Moreover, we revealed that leaf Chl non-linearly decreased with plant evolutionary divergence time. This well-matches the non-linearly increasing trend in PAR or decreasing trend in temperature during the geological time-scale uplift of the Tibetan Plateau.Main ConclusionThis study highlights the dominant role of plant evolution in determining leaf Chl variations across the Tibetan Plateau. Given the fundamental role of Chl for photosynthesis, these results provide new insights into reconsidering photosynthesis capacity in alpine plants and the carbon cycle in an evolutionary view.

The Tibetan Plateau (TP) is one of the most important areas for the study of the carbon budgets of terrestrial ecosystems. However, the estimation of the net ecosystem productivity (NEP) remains uncertain in this region due to its complex topographic properties and climatic conditions. Using CO2-eddy-covariance-flux data from 1982 to 2018 at 18 sites distributed around the TP grassland, we analyzed the spatial–temporal patterns of the grassland NEP and its driving factors from 1982 to 2018 using a random forest (RF) model. Our results showed that the RF model captured the size of the carbon sink (R2 = 0.65, p < 0.05) between the observed and simulated values for the validation samples. During the observation period, the grassland acted as a carbon sink of 26.2 Tg C yr−1 and increased significantly, by 0.4 g C m−2 yr−1. On a regional scale, the annual NEP gradually increased from the northwest to the southeast, and a similar pattern was also observed in the long-term trends. Furthermore, the moisture conditions, such as the specific humidity and precipitation, were proven to be the main driving factors of the carbon flux in the southeastern areas, while the temperature predominantly controlled the carbon flux in the northwest. Our results emphasize the net carbon sink of the TP and provide a reliable way to upscale NEP from sites.

Besides its ecological services to China and even Asia, the Qingzang Plateau (QP) hosts a rich variety of wildlife species. During the last century, wildlife population decreased quickly on the QP, driven by human interventions. Recently, wildlife has witnessed rapid recovery mainly propelled by a series of wildlife conservation policies. However, some cautions merit attentions to sustain wildlife restoration and conservation on the QP. This paper casted an overview of environmental and social-economic changes on the QP affecting wildlife subsistence. Results show that QP has been warming, which can benefit wildlife recovery by easing extreme low temperature stresses. The fast growing social economy across the QP lays a solid economic foundation for investing on wildlife protection. Measures such as establishing conservation areas, constructing wildlife pathway corridors, and encouraging herdsman moving out from wildlife rich regions, have boosted wildlife recovery. However, wildlife recovery is constrained by the limited carrying capacity of the ecosystem, left by domestic livestock. Additionally, fences intended to delineate conservation areas or to separate each type of grassland use, have brought about profound side effects on wildlife through fragmentation of their habitats. It is recommended to set up the fence in a more ecological way, which can be achieved by bypassing the wildlife frequent pathway and using materials devoid of steel barb. Only considering both opportunities and problems simultaneously, can the wildlife protection on the QP be sustained.

Modular space structure has become a research hotspot in the aerospace field. In the microgravity and weak damping space environment, modular space structures may continuously vibrate due to the transient excitation caused by satellite attitude adjustment or space debris impact, which will make the structure unstable. Therefore, a passive vibration control method based on band gap design is proposed for the modular space structures. Firstly, a modular spectral element model based on the super element is established, and the modular spectral element model is expanded into modular space structures. Then, band gap characteristics of the modular space structure are analyzed and optimized to improve the wave isolation ability. The numerical simulation shows that the elastic wave in the band gap can be effectively isolated and the band gap is significantly improved by optimizing structural parameters.

Global warming has boosted vegetation growth to a large extent, but this stimulation effect has significantly weakened in recent years. Among the set of possible driving forces, the asymmetric daytime and nighttime warming effect has been largely neglected. To improve our understanding on the relationship between vegetation growth and global warming, this study tries to attribute the respective effects of daytime and nighttime temperature on vegetation growth and reveal their temporal trends in the extratropical Northern Hemisphere (30–90 °N). The results showed there had been significant warming trends in growing season maximum (TMX, 0.37 °C per decade) and minimum temperatures (TMN, 0.38 °C per decade) during 1982–2015, especially in high latitudes of the NH. Under the asymmetric diurnal warming, the effects of TMX and TMN on normalized difference vegetation index (NDVI) exhibited distinct temporal variations between mid- (55 °N). The positive correlation between NDVI and TMX (RNDVI-TMX) weakened in high latitudes, as well as the negative correlation between NDVI and TMN (RNDVI-TMN). However, the RNDVI-TMX and RNDVI-TMN changed little in mid-latitudes. Moreover, the weakening effect of TMX on NDVI was more apparent than that of TMN in high latitudes. The area with significantly (p

Abstract Effects of climate warming and changing precipitation on ecosystem carbon fluxes have been intensively studied. However, how they co‐regulate carbon fluxes is still elusive for some understudied ecosystems. To fill the gap, we examined net ecosystem productivity (NEP), gross ecosystem productivity (GEP,) and ecosystem respiration (ER) responses to multilevel of temperature increments (control, warming 1, warming 2, warming 3, warming 4) in three contrasting hydrological growing seasons in a typical semiarid alpine meadow. We found that carbon fluxes responded to precipitation variations more strongly in low‐level warming treatments than in high‐level ones. The distinct responses were attributable to different soil water conditions and community composition under low‐level and high‐level warming during the three growing seasons. In addition, carbon fluxes were much more sensitive to decreased than to increased precipitation in low‐level warming treatments, but not in high‐level ones. At a regional scale, this negative asymmetry was further corroborated. This study reveals that future precipitation changes, particularly decreased precipitation would induce significant change in carbon fluxes, and the effect magnitude is regulated by climate warming size.

Abstract Global warming exerts profound impacts on terrestrial carbon cycles and feedback to climates. Ecosystem respiration (ER) is one of the main components of biosphere CO2 fluxes. However, knowledge regarding how ER responds to warming is still lacking. In this study, a manipulative experiment with five simulated temperature increases (+0℃ [Control], +2.1℃ [warming 1, W1], +2.7℃ [warming 2, W2], +3.2℃ [warming 3, W3], +3.9℃ [warming 4, W4]) was conducted to investigate ER responses to warming in an alpine meadow on the Tibetan Plateau. The results showed that ER was suppressed by warming both in dry and wet years. The responses of ER to warming all followed a nonlinear pattern. The nonlinear processes can be divided into three stages, the quick‐response stage (W1), stable stage (W1–W3), and transition stage (W4). Compared with the nonlinear model, the linear model maximally overestimated the response ratios of ER to warming 2.2% and 3.2% in 2015 and 2016, respectively, and maximally underestimated the ratio 7.0% and 2.7%. The annual differences in ER responding to warming were mainly attributed to the distinct seasonal distribution of precipitation. Specially, we found that the abrupt shift response of ER to warming under W4 treatment in 2015, which might be regulated by the excitatory effect of precipitation after long‐term drought in the mid‐growing season. This study highlights the importance of the nonlinearity of warming effects on ER, which should be taken into the global‐C‐cycling models for better predicting future carbon–climate feedbacks.

Investigating elevational gradient of climate driving effects on cropland ecosystem net primary productivity (NPP) plays an important role in food security in alpine region. We simulated cropland NPP by coupling a remote sensing model with an ecosystem process model and explored elevational gradient of climate driving effects on it in an alpine region of the southwest China during 1981–2014. The results showed that cropland NPP increased significantly with a rate of 3.85 gC m−2 year−1 year−1 under significant increasing solar radiation and climate warming and drying, among which the increasing solar radiation was the main driving factor of the increasing NPP. The driving effect of climate warming on cropland NPP shifted from negative at low elevations to positive at high elevations, which was caused by the fragile ecosystem characteristics and frequent drought at low elevations and a higher temperature sensitivity of cropland ecosystem at high elevations. Different effects of climate warming on NPP change at different elevations caused different results when we analyzed the climate-driving effects on cropland NPP at different spatial scales. These results reminded us that we should take the elevational gradient of climate driving effects into account when we manage food security in the alpine region.

The vegetation dynamic (e.g., community productivity) is an important index used to evaluate the ecosystem function of grassland ecosystem. However, the critical factors that affect vegetation biomass are disputed continuously, and most of the debates focus on mean annual precipitation (MAP) or temperature (MAT). This article integrated these two factors, used the aridity index (AI) to describe the dynamics of MAP and MAT, and tested the hypothesis that vegetation traits are influenced primarily by the AI. We sampled 275 plots at 55 sites (five plots at each site, including alpine steppe and meadow) across an alpine grassland of the northern Tibet Plateau, used correlation analysis and redundancy analysis (RDA) to explore which key factors determine the biomass dynamic, and explained the mechanism by which they affect the vegetation biomass in different vegetation types via structural equation modelling (SEM). The results supported our hypothesis, in all of the environmental factors collected, the AI made the greatest contribution to biomass variations in RDA , and the correlation between the AI and biomass was the largest (R = 0.85, p

The spread of a computer virus among the Internet of Things (IoT) devices can be modeled as an Epidemic Containment (EC) game, where each owner decides the strategy, e.g., installing anti-virus software, to maximize his utility against the susceptible-infected-susceptible (SIS) model of the epidemics on graphs. The EC game’s canonical solution concepts are the Minimum/Maximum Nash Equilibria (MinNE/MaxNE). However, computing the exact MinNE/MaxNE is NP-hard, and only several heuristic algorithms are proposed to approximate the MinNE/MaxNE. To calculate the exact MinNE/MaxNE, we provide a thorough analysis of some special graphs and propose scalable and exact algorithms for general graphs. Especially, our contributions are four-fold. First, we analytically give the MinNE/MaxNE for EC on special graphs based on spectral radius. Second, we provide an integer linear programming formulation (ILP) to determine MinNE/MaxNE for the general graphs with the small epidemic threshold. Third, we propose a branch-and-bound (BnB) framework to compute the exact MinNE/MaxNE in the general graphs with several heuristic methods to branch the variables. Fourth, we adopt NetShiled (NetS) method to approximate the MinNE to improve the scalability. Extensive experiments demonstrate that our BnB algorithm can outperform the naive enumeration method in scalability, and the NetS can improve the scalability significantly and outperform the previous heuristic method in solution quality.

The lack of ecosystem-scale CO _2 enrichment experiments in alpine regions considerably restricts our ability to predict the feedback of the global carbon (C) cycle to climate change. Here we investigate soil C response in an experiment with 5-year CO _2 enrichment and nitrogen (N) fertilization in a Tibetan meadow (4585 m above the sea level). We found that despite non-significant increase in bulk soil C pool, elevated CO _2 dramatically altered the allocation of C in different soil fractions and soil mineralization potentials. By changing soil microbial composition and enhancing enzyme activities, elevated CO _2 significantly accelerated soil organic matter (SOM) mineralization rates and stimulated the microbial utilization of ‘old C’ relative to that of ‘new C’. Furthermore, N fertilization under elevated CO _2 altered the decomposition process, increased the fungi to bacteria ratio, and decreased the coarse particulate organic matter pool and enzyme activities, indicating that N fertilization counters the CO _2 fertilization effect. Overall, our findings suggest a growing threat of elevated CO _2 in reducing SOM stability, and highlight the key role of N availability in driving soil C turnover under elevated CO _2 .

Grasslands occupy nearly three quarters of the land surface of the Qinghai-Tibet plateau (QTP) and play a critical role in regulating the ecological functions of the QTP. Ongoing climate change and human interference have greatly affected grasslands on the QTP. Differentiating human-induced and climate-driven vegetation changes is vital for both ecological understanding and the management of husbandry. In this study, we employed statistical analysis of annual records, various sources of remote sensing data, and an ecosystem process model to calculate the relative contribution of climate and human activities to vegetation vigor on the QTP. The temperature, precipitation and the intensity and spatial pattern of livestock grazing differed between the periods prior to and after the year 2000, which led to different vegetation dynamics. Overall, increased temperature and enhanced precipitation favored vegetation growth. However, their combined effects exhibited strong spatial heterogeneity. Specifically, increased temperature restrained vegetation growth in dry steppe regions during a period of slightly increasing precipitation from 1986 to 2000 and in meadow regions during a period of precipitation decline during 2000–2011, thereby making precipitation a dominant factor. An increase in precipitation tended to enhance vegetation growth in wet meadow regions during warm periods, and temperature was the limiting factor in Tibet during dry periods. The dominant role played by climate and human activities differed with location and targeted time period. Areas dominated by human activities are much smaller than those dominated by climate. The effects of grazing on grassland pasture were more obvious under unfavorable climate conditions than under suitable ones.

The Tibetan Plateau (TP) has fundamental ecological and environmental significance to China and Asia through its influence on regional and continental climates. In recent years, climate warming has caused unprecedented changes to land surface processes on the TP, which would unavoidably undermine the ecological and environmental functions of the TP. Among the numerous land surface processes potentially impacted by climate warming, the effect of vegetation greenness on surface energy balance is one of the most critical, but has been long ignored. In this study, we investigated the spatial and temporal patterns of land surface albedo (LSA) on the TP and evaluated the vegetation greenness in relation to patterns of LSA. We found that LSA has been decreasing in most of the vegetated grasslands on the TP from 2000 to 2013, as compared to a flat trend for desert area. The regions where LSA has been decreasing were spatially correlated to areas of increased vegetation greenness. Along rising altitude, LSA decreasing rate exhibited an overall decreasing trend. Across the TP, elevated vegetation greenness in grasslands acted as a primary factor pulling down LSA. The driving effects of vegetation greenness on LSA vary with grassland types, as revealed by a more significant relationship between vegetation greenness and LSA for the sparsely vegetated zone (i.e. steppe) than the more densely vegetated zone (i.e. meadow). Furthermore, the driving effect of vegetation greenness on LSA exhibited an obvious dependence on altitude as effects with rising altitude were relatively strong up to 3000 m, then weakened from 3500 m to 5000 m, and then the effects again increased from 5000 to 6000 m. The growing season LSA trend revealed in this study emphasizes the need to give greater attention to the growing season LSA flux in future surface energy balance studies.

Background: In colorectal cancer (CRC), tumor deposits (TD) have been used to guide the N staging only in node-negative patients. It remains unknown about the prognostic value of TD in combination with positive lymph node ratio (LNR) in stage III CRC. Patients and methods: The authors analyzed data from 31 139 eligible patients diagnosed with stage III CRC, including 30 230 from the Surveillance, Epidemiology, and End Results (SEER) database as a training set and 909 from two Chinese hospitals as a validation set. The associations of TD and LNR with cancer-specific survival (CSS) and overall survival (OS) were evaluated using the Kaplan-Meier method and Cox regression models. Results: Both TD-positive and high LNR (value =0.4) were associated with worse CSS in the training [multivariable hazard ratio (HR), 1.50; 95% CI: 1.43-1.58 and HR, 1.74; 95% CI: 1.62-1.86, respectively] and validation sets (HR, 1.90; 95% CI: 1.41-2.54 and HR, 2.01; 95% CI: 1.29-3.15, respectively). Compared to patients with TD-negative and low LNR (value <0.4), those with TDpositive and high LNR had a 4.09-fold risk of CRC-specific death in the training set (HR, 4.09; 95% CI: 3.54-4.72) and 4.60-fold risk in the validation set (HR, 4.60; 95% CI: 2.88-7.35). Patients with TD-positive/H-LNR CRC on the right side had the worst prognosis (P <0.001). The combined variable of TD and LNR contributed the most to CSS prediction in the training (24.26%) and validation (32.31%) sets. A nomogram including TD and LNR showed satisfactory discriminative ability, and calibration curves indicated favorable consistency in both the training and validation sets. Conclusions: TD and LNR represent independent prognostic predictors for stage III CRC. A combination of TD and LNR could be used to identify those at high-risk of CRC deaths. [ABSTRACT FROM AUTHOR]