Search

Enhancing the terrestrial ecosystem carbon sink (referred to as terrestrial C sink) is an important way to slow down the continuous increase in atmospheric carbon dioxide (CO

Silage maize (Zea mays L.) is one of the most important forages in the world, and its yield and quality properties are critical parameters for livestock production and assessment of forage values. However, relationships between its yield and quality properties and the controlling factors are not well documented. In this study, we collected 5,663 observations from 196 publications across the country to identify the relationships between yield and quality properties of silage maize and to assess the impact of management practices and climatic factors on its yield and quality in China. The average dry matter yield of silage maize was (19.98±6.93) Mg ha

The hybrid coupled shear wall (HCW) with replaceable coupling beam (CB) is an optimal component to recover buildings promptly after a severe earthquake. However, the reinstallation may be difficult or impossible with an identical CB because of the inelastic relative dislocation between two wall piers. This study proposes a novel HCW with different reinforcement ratios in the connection, which was tested under cyclic loading. After the test, the bolt holes can be located through terrestrial scanning, which is then utilized to fabricate a new CB that can accommodate the deformation between two wall piers. The newly replaced HCW system was also tested. As a result, all virgin test specimens fail in web fracture and show a significant inelastic chord rotation of 0.2 rad, exhibiting an excellent energy dissipation capacity. Meanwhile, the new method to locate the bolt holes after the test is feasible. The replaced HCW fails in the pull-off of anchor bars and shows poor seismic behavior due to the unpatched concrete cover in the connection. To improve the energy dissipation for the replaced HCW, high-strength grouting in the connection can be used and high-strength material can be used to replace the usual anchor bolts.

Most of China’s historic districts are located in urban centers with excessive building density and possess rich historical, cultural, scientific and aesthetic value. However, historic districts lack infrastructure and specific plans for emergency response compared to modern residential areas in cities, creating a social inequity trap for the residents in both. In addition, as valuable material cultural heritage, the usual conservation of local culture and the ecological environment conflict with anti-epidemic requirements. This study proposes a system of strategies for responding to public health emergencies that can address the above issues. Through the methods of policy refinement and the application of the concept of normal and disaster time conversion, the strategic system was constructed, including five major aspects: emergency preparedness programs at the planning level, installation of modulized variable devices, environmentally friendly health protection, disaster prevention preparation at the spatial level, and plant configuration. It is beneficial to improve the disaster prevention system for special urban communities and provide a reference for emergency planning in the future regeneration process of historic districts.

An effective computational approach that can simultaneously deal with several complexities in geometries, material properties, and size effects is of non-trivial yet important tasks for the design and optimization of device components in micro- and nano-electromechanical systems. This study is devoted to the development of such an effective computational approach, which is formed by integrating the modified couple stress theory into isogeometric analysis framework. The proposed approach is applied to mechanical problems of laminated Timoshenko curved microbeams, i.e., anazlying static bending, natural frequency and transient response. The developed method enables to describe and examine nontrivial features in both material and geometrical properties of laminated curved microbeams. Geometries of curved microbeams and displacement approximation are accurately described by the non-uniform rational B-spline basis functions. For laminated composites, the material coupling is taken into account with the use of equivalent elastic modulus; and the deepness term is properly included in laminate stiffness parameters. In addition, the small-scale size effects are captured with the use of modified couple stress theory. The accuracy and performance of proposed method are demonstrated through several numerical examples, in which the static bending, free vibration and transient response of laminated curved microbeams are considered under effects of some factors such as aspect ratios, lay-ups, boundary conditions and size dependence.

Soil microbes assemble in highly complex and diverse microbial communities, and microbial diversity patterns and their drivers have been studied extensively. However, diversity correlations and co-occurrence patterns between bacterial, fungal, and archaeal domains and between microbial functional groups in arid regions remain poorly understood. Here we assessed the relationships between the diversity and abundance of bacteria, fungi, and archaea and explored how environmental factors influence these relationships. We sampled soil along a 1500-km-long aridity gradient in temperate grasslands of Inner Mongolia (China) and sequenced the 16S rRNA gene of bacteria and archaea and the ITS2 gene of fungi. The diversity correlations and co-occurrence patterns between bacterial, fungal, and archaeal domains and between different microbial functional groups were evaluated using α-diversity and co-occurrence networks based on microbial abundance. Our results indicate insignificant correlations among the diversity patterns of bacterial, fungal, and archaeal domains using α-diversity but mostly positive correlations among diversity patterns of microbial functional groups based on α-diversity and co-occurrence networks along the aridity gradient. These results suggest that studying microbial diversity patterns from the perspective of functional groups and co-occurrence networks can provide additional insights on patterns that cannot be accessed using only overall microbial α-diversity. Increase in aridity weakens the diversity correlations between bacteria and fungi and between bacterial and archaeal functional groups, but strengthens the positive diversity correlations between bacterial functional groups and between fungal functional groups and the negative diversity correlations between bacterial and fungal functional groups. These variations of the diversity correlations are associated with the different responses of microbes to environmental factors, especially aridity. Our findings demonstrate the complex responses of microbial community structure to environmental conditions (especially aridity) and suggest that understanding diversity correlations and co-occurrence patterns between soil microbial groups is essential for predicting changes in microbial communities under future climate change in arid regions. acceptedVersion

1. The quantification of the allocation of nitrogen (N) and phosphorus (P) among plant organs is essential to improve our understanding of plant growth, life-history strategies, and ecosystem nutrient and energy cycles. However, allocation strategies of N and P between terrestrial plant leaves and fine roots are unclear. 2. Here, we compiled a global dataset comprising 807 terrestrial plant species to analyze the stoichiometric scaling of N and P between leaves and fine roots across species, families, plant groups, biomes, and locations. 3. We found that N and P, and N:P ratios manifest different scaling exponents (α-values) between leaves and fine roots. Specifically, overall αN and αP were >1 and, This work was funded by the European Research Council Synergy project SyG-2013-610028 IMBALANCE-P, the Catalan Government grants AGAUR-2020PANDE00117 and SGR 2017-1005, the Spanish Government grant PID2019-110521GB-I00, the Fundac ió n Ra mó n A reces gr a nt ELEMEN TA L-CLIM ATE, t he N at io na l Sc ie nc e Fund for Excellent Young Scholars (31822010), the B iod iver s it y Sur ve y a nd A ssess me nt Pro ject o f t he M inis tr y o f Ecology and Environment, C hina (2019HJ2096001006), National Scientific and Technological Program on Basic Resources Investigation (2019FY102002) and the Innovation Base Project of Gansu Province (20190323).

Precast pre-stressed concrete composite slabs have been widely used in recent years owing to excellent mechanical properties and cost savings. The low accuracy of visual observation and the complexity of actual measurement make the determination of the precise information of structural safety difficult. This article presents an acoustic emission study on the precast pre-stressed concrete composite slab under static loading. First, the correlation between acoustic emission hits (or energy) and crack width (or deflection) was obtained and compared in detail. Second, the stiffness of this composite slab was predicted using the acoustic emission amplitude. Third, a novel analysis method for damage fracture classification is proposed, which is based on the traditional parameter and fuzzy C-means clustering. This method can be used to determine visual crack emerging, rebar yielding, and eventual failure mode by an acoustic emission parametric analysis without involving visual inspection or mechanical measurement. It can be effectively used for fracture characterization and health monitoring of composite slabs.

Microbial stoichiometry and its potential driving factors play crucial roles in understanding the balance of chemical elements in ecological interactions and nutrient limitations along the aridity gradient. However, little is known about the variation in these features along the aridity gradient due to the lack of comprehensive field investigations. Additionally, previous studies focused on the topsoil (0–10 or 0–20 cm); however, the minimum sampling depth for topsoil could impact the results of the vertical distribution of microbial stoichiometry. In the present study, we measured the variation in microbial stoichiometry, examined the major influential factors (climatic, edaphic, and biotic factors) along an aridity gradient, and determined whether the sampling depth affected microbial C : N : P stoichiometry. From the topsoil to the subsoil, the microbial C : N, C : P, and N : P ratios varied from 6.59 to 6.83, from 60.2 to 60.5, and from 9.29 to 8.91, respectively. Only the microbial C : N ratio significantly increased with soil depth. The microbial C : N ratio significantly increased with increasing aridity in both topsoil and subsoil, while the microbial N : P ratio decreased along the aridity gradient only for the topsoil. This result implied that drought-stimulated microbes tend to be more N conservative, especially those in topsoil. Among all the factors, the soil organic carbon (SOC) content and the fungi-to-bacteria ratio exerted the largest influence on the microbial C : N, C : P, and N : P ratios at both soil depths, implying that the substrate supply and microbial structure together controlled the microbial stoichiometry. The results also revealed that the aridity index (AI) and plant aboveground biomass (AGB) exerted negative impacts on the microbial C : N ratio at both soil depths, and the effects of AI decreased in the subsoil. The results of this study suggested that the flexibility of the microbial N : P ratio should be considered when establishing the sampling depth for microbial stoichiometry study.

Changes of soil organic matter (SOM) stability in alpine ecosystems can alter carbon release from the soil and consequently feed back to climate change. We sought to explore the altitudinal patterns of SOM stability and their relationships with climatic, vegetational and edaphic factors. We combined a number of biological, thermal, chemical, molecular and isotopic indices to characterize SOM stability in two soil layers (0–10 and 10–30 cm) of alpine grassland along two altitudinal gradients of 3200–4200 m (Haibei) and 4400–5200 m (Damxung) on the Tibetan Plateau, respectively. There were significant altitudinal variations in SOM stability between the two transects. Greater biological, chemical and isotopic indices of SOM stability were observed in the middle altitude in Haibei, while opposite results were observed in Damxung. Except for a decreasing trend of SOM stability along altitudinal gradient in subsurface soils (10–30 cm) in Damxung, there was no significant altitudinal trend of thermal and molecular indices of SOM stability. The multiple indices of SOM stability were mutually associated and all showed greater SOM stability in subsurface soils than in surface soils across regions and altitudes. Along the altitudinal gradient, SOM stability showed opposite unimodal patterns in Haibei and Damxung, and had higher values in subsurface soils than in surface soils of the alpine grassland. Climatic, vegetational and edaphic factors collectively control SOM stability rather than just temperature or precipitation.

Changes in species composition across communities, i.e., β-diversity, is a central focus of ecology. Compared to macroorganisms, the β-diversity of soil microbes and its drivers are less studied. Whether the determinants of soil microbial β-diversity are consistent between soil depths and between abundant and rare microorganisms remains controversial. Here, using the 16S-rRNA of soil bacteria and archaea sampled at different soil depths (0–10 and 30–50 cm) from 32 sites along an aridity gradient of 1500 km in the temperate grasslands in northern China, we compared the effects of deterministic and stochastic processes on the taxonomic and phylogenetic β-diversity of soil microbes. Using variation partitioning and null models, we found that the taxonomic β-diversity of the overall bacterial communities was more strongly determined by deterministic processes in both soil layers (the explanatory power of environmental distance in topsoil: 25.4%, subsoil: 47.4%), while their phylogenetic counterpart was more strongly determined by stochastic processes (the explanatory power of spatial distance in topsoil: 42.1, subsoil 24.7%). However, in terms of abundance, both the taxonomic and phylogenetic β-diversity of the abundant bacteria in both soil layers was more strongly determined by deterministic processes, while those of rare bacteria were more strongly determined by stochastic processes. In comparison with bacteria, both the taxonomic and phylogenetic β-diversity of the overall abundant and rare archaea were strongly determined by deterministic processes. Among the variables representing deterministic processes, contemporary and historical climate and aboveground vegetation dominated the microbial β-diversity of the overall and abundant microbes of both domains in topsoils, but soil geochemistry dominated in subsoils. This study presents a comprehensive understanding on the β-diversity of soil microbial communities in the temperate grasslands in northern China. Our findings highlight the importance of soil depth, phylogenetic turnover, and species abundance in the assembly processes of soil microbial communities.

The transmissible locus of stress tolerance (tLST) is a genomic island which confers resistance to heat and chlorine. In this study, we determined that the tLST is frequent in genomes of those Enterobacteriaceae that occur in association with plants as well as the intestines of humans and animals and are relevant as nosocomial pathogens, e.g., Klebsiella and Cronobacter species. The tLST is more frequent in environmental and clinical isolates of Klebsiella pneumoniae than in animal isolates, and heat and chlorine resistance of tLST-positive strains of K. pneumoniae matched the resistance of tLST-positive strains of Escherichia coli. The function of 13 tLST genes was determined by assessing the heat and chlorine resistance of E. coli MG1655 mutants. The deletion of sHsp20, clpKGI, sHspGI, pscA, pscB, and hdeDGI reduced both heat and chlorine resistance; deletion of kefB reduced only chlorine resistance. Genes coding for heat shock proteins sHsp20, clpKGI, and sHspGI decreased the oxidation of cytoplasmic proteins, while kefB decreased the oxidation of membrane lipids. The fitness cost of the tLST for E. coli MG1655 was assessed by pairwise competition experiments with isogenic tLST-positive or tLST-negative strains. The tLST imposes a fitness cost that is compensated for by frequent and lethal challenges with chlorine. All core genes need to be present to maintain the ecological advantage relative to the fitness cost. Taken together, core tLST genes are necessary to provide protection for E. coli against heat and chlorine stress, and the selective pressure for the tLST maintains core genes. IMPORTANCE The transmissible locus of stress tolerance (tLST) is a genomic island comprising 10 core genes that occurs in diverse Enterobacteriaceae and confers resistance to heat and chlorine. Experimentation described in the manuscript describes the physiological function of the core genes by characterization of the resistance of 13 single-knockout (KO) mutants and by characterization of protein and membrane oxidation in these strains after chlorine challenge. Results identify tLST resistance as a genomic island that is specific for those Enterobacteriaceae that occur in plant-associated habitats as well in the intestines of vertebrates. In addition, the ecological function of the genomic island was characterized by large-scale genomic analysis and competition experiments of wild-type and mutant strains. Results suggest that tLST-mediated resistance to chlorine may contribute to the persistence of nosocomial pathogens in hospitals.

Xanthomonas is a notorious plant pathogen causing serious diseases in hundreds of plant hosts. Xanthomonas species are equipped with an array of signal transduction systems that regulate gene expression to survive in various harsh environments and successfully infect hosts. Although certain pathogenicity-associated regulators have been functionally characterized, signal transduction systems always function as a regulatory network which remains to be elucidated in Xanthomonas. This study used a systematic approach to characterize all identified pathogenicity-associated regulators in Xanthomonas oryzae pv. oryzae (Xoo), including a transcriptional regulator with unknown function, and their interactive regulatory network. RNA sequencing was used in elucidating the patterns of the 10 pathogenicity-associated regulators identified. Results revealed that each pathogenicity-associated regulator has cross talk with others and all these regulators function as a regulatory network, with VemR and PXO_RS20790 being the master pathogenicity-associated regulators and HrpX being the final executant. Moreover, regulome analysis showed that numerous genes other than genes in pathogenicity islands are finely regulated within the regulatory network. Given that most of the pathogenicity-associated regulators are conserved in Xanthomonadales, our findings suggest a global network of gene regulation in this evolutionarily conserved pathogen. In conclusion, our study provides essential basic information about the regulatory network in Xoo, suggesting that this complicated regulatory network is one of the reasons for the robustness and fitness of Xanthomonas spp. IMPORTANCE The host plant infection process of pathogenic bacteria is a coordinating cellular behavior, which requires dynamic regulation at several levels in response to variations in host plants or fluctuations in the external environment. As one of the most important genera of plant-pathogenic bacteria, Xanthomonas has been studied as a model. Although certain pathogenicity-associated regulators have been functionally characterized, interactions among them remain to be elucidated. This study systematically characterized pathogenicity-associated regulators in Xoo and revealed that cross talk exists among pathogenicity-associated regulators and function as a regulatory network in which a hierarchy exists among the regulators. Our study elucidated the landscape of the pathogenicity-associated regulatory network in Xanthomonas, promoting understanding of the infection process of pathogenic bacteria.

A novel and effective computational approach within the context of isogeometric analysis (IGA) is developed for analyzing size-dependent mechanical behaviors of functionally graded (FG) microbeams. To capture the size effects, an extension of quasi-3D theory is established to integrate with the modified couple stress theory. The nonuniform rational B-spline (NURBS) basis functions are employed and can directly meet the first-order derivative demand of the quasi-3D theory, where four variables are involved at each node. In this new setting, both normal and shear deformations are considered, while the shear correction factor is avoided. Numerical examples are studied, in which the effects of several factors, including material gradient factor, boundary conditions, parameter of material length scale, and aspect ratio, on deflections, stresses, and fundamental frequencies of FG microbeams are explored.

A two-directional functionally graded microbeam model is developed for natural frequency and mechanical bending analysis by using NURBS–based isogeometric analysis combined with a non-classical quasi-3D beam theory (NCQ3BT). Material parameters of microbeam continuously and smoothly change along thickness and axial directions. The small size effects are seized with the modified couple stress theory. In the NCQ3BT, both normal and shear deformations are considered without the need for the shear correction factor. The high-order continuity of NURBS directly meets the demand of C1-continuity in the NCQ3BT. Numerical results prove the superior performance and accuracy of the developed approach. The influences of material gradient factors along the axial and thickness directions, material length scale factor, boundary condition, and other aspect ratios of two-directional FG microbeams on mechanical behavior are investigated.

Steel-concrete composite beams (CB) with precast hollow-core slabs (HCSs) have been widely used in long-span structures for its high bending capacity, good ductility, lightweight, and fast construction. A novel assembled monolithic CB with a cast-in-place (CIP) reinforced concrete layer poured on the precast HCSs (CBCH) was proposed in this study. Eight full-scale flexural tests were conducted majoring in the parameters of span (L = 6.0 m and 8.4 m), degree of shear connection (λDS = 100%, 70%, and 30%), width of CBCH (B = 2100 mm and 1800 mm), and thickness of CIP concrete layer (hCIP = 60 mm and 20 mm). Three typical failure modes were observed: i.e. flexural failure, longitudinal shear failure in the shear span, and peeling failure occurring between the precast HCS and CIP concrete layer. The results indicate that the λDS and hCIP can significantly affect the failure modes, flexural capacity, and ductility; the B has a slight influence on the bending behavior of CBCH. In addition, an extensive parametric study was conducted according to the test results. To elevate the bending capacity of CBCH, relative formulas are proposed, and agree well with the results of test and parametric study. Based on the theoretical and FE analysis, the partial shear specimens with λDS ≥ 85% can achieve almost the same performances as the full shear specimens (λDS = 100%). However, a λDS = 100% and the minimum hCIP = 60 mm are recommended to ensure the integrity of the CBCH in engineering practice.

Shrub encroachment is a critical environmental issue in arid and semi-arid landscapes. However, due to the complicated effects of shrub characteristics and environmental variables, ecological consequences of shrub encroachment significantly differ in different regions. As a result, although the phenomenon of shrub encroachment is widespread in the grasslands of northern China, its ecological consequences and associated drivers have not been well documented at the regional scale. We explored the effects of shrub encroachment on ecosystem structures (herb richness and abundance) and functioning (above- and belowground biomass, and soil carbon and nitrogen content) and evaluated the relative importance of climatic variables (temperature and precipitation) and shrub characteristics (cover, area, and height) as drivers of these effects. Based on field data from 53 sites that stretch across approximately 3000 km in northern China, we conducted the relative interaction intensity (RII) of the response variables between shrub patches and grassy matrix, and then used the structural equation modeling (SEM) to assess the relative importance of chosen drivers on the ecological consequences. Shrub encroachment increased the landscape heterogeneity by decreasing the richness, abundance and aboveground biomass of herbs, while by increasing the soil carbon and nitrogen content. The SEM explained 25–43% of the variation in shrub characteristics and 5–34% of the variation in the effects of shrub encroachment. Shrub height had greater effects on the RII of herb richness, soil carbon and soil nitrogen content, and the standardized total effects were 0.48, 0.25 and 0.18, respectively. Precipitation and temperature positively affected the impacts of shrub encroachment on herb richness, abundance, biomass, and multi-indexes. However, the direct effects of climate could be partially mediated by indirect effects via shrub characteristics. The height, size and cover of shrub patches significantly influenced the community structures and functioning of grassland ecosystems. The increasing aridity could potentially exacerbate the negative consequences of shrub encroachment in arid regions. Our results also demonstrated that the effects of climate variables on grassland ecosystems could be mediated by shrub management.

Widespread shrub encroachment in grasslands can lead to changes in soil aggregates and soil organic carbon (SOC), especially in deep soils. Soil aggregates physicochemically protect SOC and thus affect soil carbon sequestration. Characterizing the changes in soil aggregates and their organic carbon associated with shrub encroachment is critical for evaluating the ecological consequences of shrub encroachment in different grasslands. In this study, we investigated soil aggregates of various sizes and their associated organic carbon at maximum soil depths of 5 m in shrub patches and neighboring grass matrix in two types (desert and typical) of grasslands in Inner Mongolia, China. The mean weight diameter (MWD) of the soil aggregates was similar between the shrub patches and grass matrix in both grasslands. However, the proportion of each aggregate size fraction to whole soil in the shrub patches was significantly lower than that in the grass matrix in the desert grasslands, while there was no significant difference between the shrub patches and grass matrix in the typical grasslands. In addition, the organic carbon content of aggregates in the shrub patches was greater than that in the grass matrix in deep soil layers (>50 cm) but was lower in the topsoil (0–10 cm depth) in the desert grasslands. However, the organic carbon content of aggregates at all soil depths was greater in shrub patches than in the grass matrix in typical grasslands. Our results suggest that the effects of shrub encroachment on the soil aggregate proportion and associated organic carbon vary at different soil depths and in different grassland types. The results of this study also suggest that it is necessary to determine the size structure and its relation to carbon content for soil aggregates to accurately predict SOC dynamics with shrub encroachment.

In this paper, we present numerical investigations on static bending and free vibration behaviors of spatially curved functionally graded (FG) microbeam using isogeometric analysis (IGA). The material properties change continuously along the thickness direction. The small scale effects are captured using the modified couple stress theory while microbeam kinematics are described by Timoshenko beam theory, and the spatially curved microbeam is represented by the Frenet–Serret bases. The geometries of curved microbeams are exactly represented with the non-uniform rational B-spline (NURBS) basis functions, and the same basis functions are applied to obtain displacement field approximation. Numerical examples are presented and computed results are then compared with reference methods to show the accuracy of the developed method. The effects of some factors including material gradient factor, material length scale parameter, and boundary conditions on the mechanical behaviors of spatially curved FG Timoshenko microbeams are investigated.

Grassland is the indispensable natural resources which covers a large area of terrestrial China and plays an important role in the ecological construction, ecological security, and food security of the country. The size of the grassland, i.e., grassland area, is its important natural property, which is the basis to estimate total grassland biomass and productivity. Therefore, an accurate estimate of the grassland area is of great importance in reasonable protection and utilization of the grassland resources. However, the estimated area of China’s grasslands varies greatly among different studies due to different data sources and grassland definitions. Climate determines geographical distribution of natural vegetation, and thus the distribution of a vegetation type can be retrieved based on regional characteristics of climate. In the semi-arid and arid regions of northern China, precipitation is the major limiting factor of vegetation distribution, especially for grassland. On the other hand, normalized difference vegetation index (NDVI) data well reflects the vegetation coverage and is strongly correlated with precipitation in the arid and semi-arid regions. Therefore, the distribution and area of grasslands can be retrieved using the relationship between precipitation and NDVI in the recognized regions of the grassland. For these reasons, we first roughly divide grasslands into two categories according to their concentrative degree of distribution: contiguous temperate grassland (northern grassland) and discrete subtropical grassland (southern grassland), and then quantify the range and area of the grasslands in these two different regions. Because the grassland distribution in the southern regions cannot be directly determined by climatic variables, we use the vegetation map of China to determine the range and area of the grasslands. For the northern grasslands, we first determine the thresholds of mean precipitation in the ecotones between grasslands and forests and between grasslands and desert vegetation, based on vegetation distribution in the vegetation map of China, and then use the precipitation thresholds to make sure the distributional limits of the grasslands. By conducting a regression analysis between average precipitation and the NDVI average value of vegetation growing season (May–September) over the past 30 years (1982–2011), we estimate the NDVI threshold for grassland and retrieved its potential distribution. The precipitation and NDVI thresholds for the grassland distribution in our study area are estimated to be 102–437 mm and 0.12–0.61 unit, respectively. Finally we document an estimate of the total grassland area of 293×104 km2 in China, with a small variation of 290×104–295×104 km2 over the past 30 years. Uncertainties remain in our estimations because the area might be overestimated or underestimated at regional scale. For instance, a part of deserts in northern Xinjiang was falsely determined as sparse grassland, because the NDVI values of these deserts exceeded the thresholds for grassland; and in the northern Tibetan Plateau, the sparse desert grassland, showing NDVI values lower than 0.05, was falsely determined as desert. Nevertheless, our estimate is generally consistent with that from the vegetation map of China and land cover data of China in 2010. Overall, this study develops a useful methodology which estimates the range and area of the grasslands based on the thresholds of precipitation and NDVI values and generates reliable estimates of the total grassland area in China.

Plant nitrogen (N) and phosphorus (P) content regulate productivity and carbon (C) sequestration in terrestrial ecosystems. Estimates of the allocation of N and P content in plant tissues and the relationship between nutrient content and photosynthetic capacity are critical to predicting future ecosystem C sequestration under global change. In this study, by investigating the nutrient concentrations of plant leaves, stems, and roots across China's terrestrial biomes, we document large-scale patterns of community-level concentrations of C, N, and P. We also examine the possible correlation between nutrient content and plant production as indicated by vegetation gross primary productivity (GPP). The nationally averaged community concentrations of C, N, and P were 436.8, 14.14, and 1.11 mg·g-1 for leaves; 448.3, 3.04 and 0.31 mg·g-1 for stems; and 418.2, 4.85, and 0.47 mg·g-1 for roots, respectively. The nationally averaged leaf N and P productivity was 249.5 g C GPP·g-1 N·y-1 and 3,157.9 g C GPP·g-1 P·y-1, respectively. The N and P concentrations in stems and roots were generally more sensitive to the abiotic environment than those in leaves. There were strong power-law relationships between N (or P) content in different tissues for all biomes, which were closely coupled with vegetation GPP. These findings not only provide key parameters to develop empirical models to scale the responses of plants to global change from a single tissue to the whole community but also offer large-scale evidence of biome-dependent regulation of C sequestration by nutrients.

The long-term stressful utilization of forests and grasslands has led to ecosystem degradation and C loss. Since the late 1970s China has launched six key national ecological restoration projects to protect its environment and restore degraded ecosystems. Here, we conducted a large-scale field investigation and a literature survey of biomass and soil C in China's forest, shrubland, and grassland ecosystems across the regions where the six projects were implemented (∼16% of the country's land area). We investigated the changes in the C stocks of these ecosystems to evaluate the contributions of the projects to the country's C sink between 2001 and 2010. Over this decade, we estimated that the total annual C sink in the project region was 132 Tg C per y (1 Tg = 1012 g), over half of which (74 Tg C per y, 56%) was attributed to the implementation of the projects. Our results demonstrate that these restoration projects have substantially contributed to CO2 mitigation in China.

The hybrid coupled wall (HCW) with steel coupling beam (CB) has been widely used in high-rise buildings due to its good ductility and energy dissipation capacity. The HCW with replaceable CB is an optimal component to recover buildings promptly after a severe earthquake. However, the seismic behavior of the HCW with replaceable CB and the reasonable reinforcement ratio in connections to satisfy the design concept of replaceable structure have not been investigated. In this study, a novel HCW subassembly with replaceable endplate-steel CB having different reinforcement ratios in the connections was proposed and tested under cyclic loading. Then, an identical CB was reinstalled and the replaced HCW system was also tested. The results showed that increasing the horizontal or vertical reinforcement ratio in connections significantly enhanced the seismic behavior of HCWs, ensuring the CB to act as a fuse during the test. Increasing the vertical reinforcement ratio could effectively provide a constraint effect on anchor bars and ensure the wall pier to remain elastic, thus satisfying the replaceable requirements. Additionally, the replaced HCW showed similar seismic behavior to the virgin one. Lastly, relevant design methods and recommendations are proposed for the HCW with replaceable CB according to the test results.