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Aim: Theoretically, woody biomass turnover time (τ) quantified using outflux (i.e. tree mortality) predicts biomass dynamics better than using influx (i.e. productivity). This study aims at using forest inventory data to empirically test the outflux approach and generate a spatially explicit understanding of woody τ in mature forests. We further compared woody τ estimates with dynamic global vegetation models (DGVMs) and with a data assimilation product of C stocks and fluxes—CARDAMOM. Location: Continents. Time Period: Historic from 1951 to 2018. Major Taxa Studied: Trees and forests. Methods: We compared the approaches of using outflux versus influx for estimating woody τ and predicting biomass accumulation rates. We investigated abiotic and biotic drivers of spatial woody τ and generated a spatially explicit map of woody τ at a 0.25‐degree resolution across continents using machine learning. We further examined whether six DGVMs and CARDAMOM generally captured the observational pattern of woody τ. Results: Woody τ quantified by the outflux approach better (with R2 0.4–0.5) predicted the biomass accumulation rates than the influx approach (with R2 0.1–0.4) across continents. We found large spatial variations of woody τ for mature forests, with highest values in temperate forests (98.8 ± 2.6 y) followed by boreal forests (73.9 ± 3.6 y) and tropical forests. The map of woody τ extrapolated from plot data showed higher values in wetter eastern and pacific coast USA, Africa and eastern Amazon. Climate (temperature and aridity index) and vegetation structure (tree density and forest age) were the dominant drivers of woody τ across continents. The highest woody τ in temperate forests was not captured by either DGVMs or CARDAMOM. Main Conclusions: Our study empirically demonstrated the preference of using outflux over influx to estimate woody τ for predicting biomass accumulation rates. The spatially explicit map of woody τ and the underlying drivers provide valuable information to improve the representation of forest demography and carbon turnover processes in DGVMs. [ABSTRACT FROM AUTHOR]

In this article, a robust cascaded deadbeat predictive speed control method (PSC) is proposed with speed and disturbance observer for the dual three-phase variable-flux permanent-magnet synchronous motor (VF-PMSM) drives. Considering the intrinsic delay in speed loop, an improved predictive speed model has been derived in discrete domain. In turn, a speed observer is proposed for the cascaded PSC to mitigate the issue of this intrinsic delay. In order to improve the system robustness, the torque disturbance observer including the generalized proportional integral observer and the sliding-mode observer has been proposed for parameter variation and load torque perturbation. Furthermore, the stability analysis indicates that the margin of parameter mismatch is determined by the coefficient in the speed observer, which can be expressed as the equivalent gain in discrete domain. The performance comparison between the conventional PSC method and the proposed PSC method has been investigated for parameter robustness. The experimental results are presented to verify the improvements of the proposed PSC method for the dual three-phase VF-PMSM drives under model uncertainty and magnetization manipulation conditions. [ABSTRACT FROM AUTHOR]

The fault-tolerant control method of dual three-phase permanent-magnet synchronous motor (PMSM) drives has gained more and more attention in some applications, such as aircraft system and offshore wind energy system. In this letter, the reason for the torque ripple caused by the standard control method has been investigated in view of the frequency domain after the occurrence of a single open-phase fault. Based on the theoretical analysis, a universal control scheme has been proposed for the dual three-phase PMSM drives with two isolated neutral points, which can be implemented under either healthy condition or fault condition. The key is to modify with a closed-loop controller on harmonic subspace with the notch filter. The proposed method not only realizes the seamless transition between two operation conditions without fault diagnosis but also avoids the reconfiguration of the control structure. Moreover, the system optimization of the minimum copper loss under postfault condition has been integrated into the proposed method. The experimental results are presented to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Position sensorless control of interior permanent magnet synchronous motors (IPMSMs) is of great importance for the sake of the cost reduction and robustness improvement. An improved position sensorless method based on adjustable high-frequency (HF) square-wave voltage injection has been proposed for the IPMSM drive under zero- and low-speed regions. The general detection method of position from positive- and negative-sequence HF current response has been developed by the simple algebraic operations of data at some adjacent sampling instants. In addition, the proposed method not only can retain the advantage of the removal of low-pass filters in current feedback but also can increase the voltage margin of inverter with adjustable frequency setting of HF signal compared with existing square-wave voltage injection methods. Comprehensive experimental results have been given to verify the proposed theoretical analysis. [ABSTRACT FROM AUTHOR]

Fungi and bacteria are the two dominant groups of soil microbial communities worldwide. By controlling the turnover of soil organic matter, these organisms directly regulate the cycling of carbon between the soil and the atmosphere. Fundamental differences in the physiology and life history of bacteria and fungi suggest that variation in the biogeography of relative abundance of soil fungi versus bacteria could drive striking differences in carbon decomposition and soil organic matter formation between different biomes. However, a lack of global and predictive information on the distribution of these organisms in terrestrial ecosystems has prevented the inclusion of relative abundance of soil fungi versus bacteria and the associated processes in global biogeochemical models. Here, we used a global-scale dataset of >3000 distinct observations of abundance of soil fungi versus bacteria in the surface topsoil (up to 15 cm) to generate the first quantitative and high-spatial-resolution (1 km 2) explicit map of soil fungal proportion, defined as fungi/fungi + bacteria, across terrestrial ecosystems. We reveal striking latitudinal trends where fungal dominance increases in cold and high-latitude environments with large soil carbon stocks. There was a strong nonlinear response of fungal dominance to the environmental gradient, i.e., mean annual temperature (MAT) and net primary productivity (NPP). Fungi dominated in regions with low MAT and NPP and bacteria dominated in regions with high MAT and NPP, thus representing slow vs. fast soil energy channels, respectively, a concept with a long history in soil ecology. These high-resolution models provide the first steps towards representing the major soil microbial groups and their functional differences in global biogeochemical models to improve predictions of soil organic matter turnover under current and future climate scenarios. Raw datasets and global maps generated in this study are available at 10.6084/m9.figshare.19556419 (Yu, 2022). [ABSTRACT FROM AUTHOR]

The rotor flux linkage of permanent-magnet synchronous motor (PMSM) is of great importance for monitoring and high-performance control. However, most of the existing online estimation methods need prior knowledge of other PMSM parameters such as stator resistance and dq axis inductance, which are difficult to realize in the rank-deficient models of electrical machines. This article proposes a simple online estimation method of rotor flux linkage for the dual three-phase surface-mounted PMSM (SPMSM) drives with the assistance of injected position offset. The independent estimation model has been developed for the rotor flux linkage by appropriate setting of positon offset between two sets of three-phase windings of dual three-phase SPMSM drives. The proposed method not only has little influence on the output torque and high signal-to-noise ratio for observation, but also offers the superior performance in estimation accuracy irrespective of the influence of VSI nonlinearity. In addition, the proposed position-offset-based method is suitable for the full-speed region including the field-weakening operation. Finally, comprehensive experimental results are presented to verify validity of the proposed method under different working conditions. [ABSTRACT FROM AUTHOR]

In standalone brushless doubly-fed induction generator (BDFIG) power generation systems, unbalanced and nonlinear loads can produce distorted power winding (PW) voltage, and consequently affects the normal operation of other loads and degrades the performance of the power generation system. Although the negative-sequence and harmonic components of the PW voltage can be eliminated by the conventional control methods implemented in either machine-side converter (MSC) or load-side converter (LSC), it causes higher voltage rating of converters and needs more current sensors. In this article, the detailed analysis for the impact of conventional control methods on the voltage rating of the two converters is presented. And then, an improved collaborative control method considering the power converter voltage rating is proposed, in which the MSC can be employed to eliminate the seventh-harmonic voltage of PW, and the LSC can be used to reject the negative-sequence and fifth-harmonic components of PW voltage without extra current sensors. The proportional-integral-resonant controller is applied to the current control loops in both MSC and LSC so as to obtain good current track ability. Comprehensive experimental results based on a 30-kVA BDFIG demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: Shrub encroachment, forest decline and wildfires have caused large‐scale changes in semi‐arid vegetation over the past 50 years. Climate is a primary determinant of plant growth in semi‐arid ecosystems, yet it remains difficult to forecast large‐scale vegetation shifts (i.e. biome shifts) in response to climate change. We highlight recent advances from four conceptual perspectives that are improving forecasts of semi‐arid biome shifts. Moving from small to large scales, first, tree‐level models that simulate the carbon costs of drought‐induced plant hydraulic failure are improving predictions of delayed‐mortality responses to drought. Second, tracer‐informed water flow models are improving predictions of species coexistence as a function of climate. Third, new applications of ecohydrological models are beginning to simulate small‐scale water movement processes at large scales. Fourth, remotely‐sensed measurements of plant traits such as relative canopy moisture are providing early‐warning signals that predict forest mortality more than a year in advance. We suggest that a community of researchers using modeling approaches (e.g. machine learning) that can integrate these perspectives will rapidly improve forecasts of semi‐arid biome shifts. Better forecasts can be expected to help prevent catastrophic changes in vegetation states by identifying improved monitoring approaches and by prioritizing high‐risk areas for management. [ABSTRACT FROM AUTHOR]

This paper proposes an improved coordinated control of standalone brushless doubly fed induction generator (BDFIG) supplying nonlinear loads. Due to the existence of nonlinear loads, the voltage at the point of common coupling becomes distorted with a large number of low-order harmonics, which severely degrades the performance of power generation systems. In order to eliminate the included low-order harmonics, a coordinated control method of harmonic mitigation has been presented in this paper for the control of both machine side and load side converters. Then, a weight factor is introduced to the proposed control method for distributing the contribution of harmonic mitigation between the two converters. Comprehensive experimental results on a 30 kVA BDFIG are presented to verify the proposed control method. [ABSTRACT FROM AUTHOR]

Leaves and roots may differ in nitrogen (N), phosphorus (P) and N:P stoichiometry, which can influence plant growth and ecosystem functioning. As compared to leaves, however, relatively little is known about the N versus P scaling relationship and N:P stoichiometry in root systems, particularly in fine roots.We used a global dataset comprising 1,890 observations for a total of 763 terrestrial plant species in 123 families (spanning 433 sites world‐wide) to examine live fine root N and P concentrations and stoichiometry, and to determine the scaling of N versus P within and across different plant groups and ecosystems.The global geometric mean values of fine root N and P concentrations and N:P ratios were 10.84 mg/g, 0.94 mg/g and 11.55, respectively. Fine root N and P concentrations and N:P ratios varied both within and across plant groups and ecosystems. A 0.82‐power law described the scaling of fine root N with respect to P across the entire dataset and for major plant phylogenetic and functional groups; however, the numerical value of the N versus P scaling exponent declined from the tropics to higher latitudes and varied significantly at different local sites. Soil nutrient account for much of the variation observed in the scaling of fine root N versus P concentration at different local sites.This study advances our knowledge about limiting resource allocation strategies in below‐ground organs and has important implications for modelling plant growth at local, regional and global levels. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Summary: Determining physiological mechanisms and thresholds for climate‐driven tree die‐off could help improve global predictions of future terrestrial carbon sinks. We directly tested for the lethal threshold in hydraulic failure – an inability to move water due to drought‐induced xylem embolism – in a pine sapling experiment.In a glasshouse experiment, we exposed loblolly pine (Pinus taeda) saplings (n = 83) to drought‐induced water stress ranging from mild to lethal. Before rewatering to relieve drought stress, we measured native hydraulic conductivity and foliar color change. We monitored all measured individuals for survival or mortality.We found a lethal threshold at 80% loss of hydraulic conductivity – a point of hydraulic failure beyond which it is more likely trees will die, than survive, and describe mortality risk across all levels of water stress. Foliar color changes lagged behind hydraulic failure – best predicting when trees had been dead for some time, rather than when they were dying.Our direct measurement of native conductivity, while monitoring the same individuals for survival or mortality, quantifies a continuous probability of mortality risk from hydraulic failure. Predicting tree die‐off events and understanding the mechanism involved requires knowledge not only of when trees are dead, but when they begin dying – having passed the point of no return. [ABSTRACT FROM AUTHOR]

Summary: The widely documented phenomenon of nighttime stomatal conductance gsn could lead to substantial water loss with no carbon gain, and thus it remains unclear whether nighttime stomatal conductance confers a functional advantage. Given that studies of gsn have focused on controlled environments or small numbers of species in natural environments, a broad phylogenetic and biogeographic context could provide insights into potential adaptive benefits of gsn.We measured gsn on a diverse suite of species (n = 73) across various functional groups and climates‐of‐origin in a common garden to study the phylogenetic and biogeographic/climatic controls on gsn and further assessed the degree to which gsn co‐varied with leaf functional traits and daytime gas‐exchange rates.Closely related species were more similar in gsn than expected by chance. Herbaceous species had higher gsn than woody species. Species that typically grow in climates with lower mean annual precipitation – where the fitness cost of water loss should be the highest – generally had higher gsn.Our results reveal the highest gsn rates in species from environments where neighboring plants compete most strongly for water, suggesting a possible role for the competitive advantage of gsn. [ABSTRACT FROM AUTHOR]

Summary: The widely documented phenomenon of nighttime stomatal conductance gsn could lead to substantial water loss with no carbon gain, and thus it remains unclear whether nighttime stomatal conductance confers a functional advantage. Given that studies of gsn have focused on controlled environments or small numbers of species in natural environments, a broad phylogenetic and biogeographic context could provide insights into potential adaptive benefits of gsn.We measured gsn on a diverse suite of species (n = 73) across various functional groups and climates‐of‐origin in a common garden to study the phylogenetic and biogeographic/climatic controls on gsn and further assessed the degree to which gsn co‐varied with leaf functional traits and daytime gas‐exchange rates.Closely related species were more similar in gsn than expected by chance. Herbaceous species had higher gsn than woody species. Species that typically grow in climates with lower mean annual precipitation – where the fitness cost of water loss should be the highest – generally had higher gsn.Our results reveal the highest gsn rates in species from environments where neighboring plants compete most strongly for water, suggesting a possible role for the competitive advantage of gsn. [ABSTRACT FROM AUTHOR]

Abstract Plants with crassulacean acid metabolism ( CAM) are increasing their abundance in drylands worldwide. The drivers and mechanisms underlying the increased dominance of CAM plants and CAM expression (i.e., nocturnal carboxylation) in facultative CAM plants, however, remain poorly understood. We investigated how nutrient and water availability affected competition between Mesembryanthemum crystallinum (a model facultative CAM species) and the invasive C3 grass Bromus mollis that co-occur in California's coastal grasslands. Specifically we investigated the extent to which water stress, nutrients, and competition affect nocturnal carboxylation in M. crystallinum. High nutrient and low water conditions favored M. crystallinum over B. mollis, in contrast to high water conditions. While low water conditions induced nocturnal carboxylation in 9-week-old individuals of M. crystallinum, in these low water treatments, a 66% reduction in nutrient applied over the entire experiment did not further enhance nocturnal carboxylation. In high water conditions M. crystallinum both alone and in association with B. mollis did not perform nocturnal carboxylation, regardless of the nutrient levels. Thus, nocturnal carboxylation in M. crystallinum was restricted by strong competition with B. mollis in high water conditions. This study provides empirical evidence of the competitive advantage of facultative CAM plants over grasses in drought conditions and of the restricted ability of M. crystallinum to use their photosynthetic plasticity (i.e., ability to switch to CAM behavior) to compete with grasses in well-watered conditions. We suggest that a high drought tolerance could explain the increased dominance of facultative CAM plants in a future environment with increased drought and nitrogen deposition, while the potential of facultative CAM plants such as M. crystallinum to expand to wet environments is expected to be limited. [ABSTRACT FROM AUTHOR]

Precipitation variability has been predicted to increase in a global warmer climate, and is expected to greatly affect plant growth, interspecies interactions, plant community composition, and other ecosystem processes. Although previous studies have investigated the effect of intra-annual rainfall variability on plant growth and ecosystem dynamics, the impacts of interannual rainfall variability remain understudied. This paper uses satellite data and develops a new mechanistic model to investigate the response of tree-grass composition to increasing interannual rainfall variability in arid to sub-humid ecosystems along the Kalahari Transect in Southern Africa. Both satellite data and model results show that increasing interannual rainfall fluctuations favor deep-rooted trees over shallow-rooted grasses in drier environments (that is, mean annual rainfall, MAP < 900-1000 mm) but favor grasses over trees in wetter environments (that is, MAP > 900-1000 mm). Trees have a competitive advantage over grasses in dry environments because their generally deeper root systems allow them to have exclusive access to the increased deep soil water resources expected to occur in wet years as a result of the stronger interannual rainfall fluctuations. In relatively wet environments, grasses are favored because of their high growth rate that allows them to take advantage of the window of opportunity existing in years with above average precipitation and thus increase fire-induced tree mortality. Thus, under increasing interannual rainfall fluctuations both direct effects on soil water availability and indirect effects mediated by tree-grass interactions and fire dynamics are expected to play an important role in determining changes in plant community composition. [ABSTRACT FROM AUTHOR]

The coexistence of woody plants and grasses in savannas is determined by a complex set of interacting factors that determine access to resources and demographic dynamics, under the control of external drivers and vegetation feedbacks with the physical environment. Existing theories explain coexistence mainly as an effect of competitive relations and/or disturbances. However, theoretical studies on the way facilitative interactions resulting from hydraulic lift affect tree-grass coexistence and the range of environmental conditions in which savannas are stable are still lacking., We investigated the role of hydraulic lift in the stability of tree-grass coexistence in savannas. To that end, we developed a new mechanistic model that accounts for both competition for soil water in the shallow soil and fire-induced disturbance., We found that hydraulic lift favors grasses, which scavenge the water lifted by woody plants. Thus, hydraulic lift expands (at the expenses of woodlands) the range of environmental conditions in which savannas are stable., These results indicate that hydraulic lift can be an important mechanism responsible for the coexistence of woody plants and grasses in savannas. Grass facilitation by trees through the process of hydraulic lift could allow savannas to persist stably in mesic regions that would otherwise exhibit a forest cover. [ABSTRACT FROM AUTHOR]

Plants with crassulacean acid metabolism (CAM) are increasing their cover in many dryland regions around the world. Their increased dominance has been related to climate warming and atmospheric CO fertilization, while the effects of interspecies interactions and the role of CAM plant facilitation by trees and grasses remain poorly understood. Woody plants are known for their ability to directly facilitate CAM plants through amelioration of the abiotic environment. Mechanisms of indirect facilitation of trees on CAM plants in tree-grass-CAM associations, however, have received less attention. It is also unclear whether grasses might facilitate CAM plants in mixed tree-grass-CAM communities. For instance, the inclusion of grasses in tree-CAM associations could enhance hydraulic lift and facilitate CAM plants in their access to shallow soil moisture at the expenses of deep-rooted trees. If this effect outweighs the competitive effects of grasses on CAM plants, grasses could overall facilitate CAM plants through hydraulic lift. Here we develop a process-based ecohydrological model to investigate the direct and indirect facilitation in tree-CAM-grass associations; the model quantifies transpiration of CAM plants when isolated as well as in associations with trees and/or grasses. It is found that woody plants having a high root overlap with CAM plants indirectly facilitate CAM plants by significantly reducing grass transpiration in shaded conditions. For situations of a low-to-moderate root overlap, facilitation may occur both directly and indirectly. Conversely, grasses are unable to indirectly facilitate CAM plants through the mechanism of hydraulic lift because the competitive effects of grasses on CAM plants outweigh the facilitation induced by hydraulic lift. [ABSTRACT FROM AUTHOR]

Quantifying and predicting variation in gross primary productivity (GPP) is important for accurate assessment of the ecosystem carbon budget under global change. Scaling traits to community scales for predicting ecosystem functions (i.e., GPP) remain challenging, while it is promising and well appreciated with the rapid development of trait-based ecology. In this study, we aim to integrate multiple plant traits with the recently developed trait-based productivity (TBP) theory, verify it via Bayesian structural equation modeling (SEM) and complementary independent effect analysis. We further distinguish the relative importance of different traits in explaining the variation in GPP. We apply the TBP theory based on plant community traits to a multi-trait dataset containing more than 13,000 measurements of approximately 2,500 species in Chinese forest and grassland systems. Remarkably, our SEM accurately predicts variation in annual and monthly GPP across China (R2 values of 0.87 and 0.73, respectively). Plant community traits play a key role. This study shows that integrating multiple plant functional traits into the TBP theory strengthens the quantification of ecosystem primary productivity variability and further advances understanding of the trait-productivity relationship. Our findings facilitate integration of the growing plant trait data into future ecological models. Integration of plant functional traits into trait-based productivity theory helps quantify primary productivity in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

The microbial priming effect—the decomposition of soil organic carbon (SOC) induced by plant inputs—has long been considered an important driver of SOC dynamics, yet we have limited understanding about the direction, intensity, and drivers of priming across ecosystem types and biomes. This gap hinders our ability to predict how shifts in litter inputs under global change can affect climate feedbacks. Here, we synthesized 18,919 observations of CO2 effluxes in 802 soils across the globe to test the relative effects (i.e., log response ratio [RR]) of litter additions on native SOC decomposition and identified the dominant environmental drivers in natural ecosystems and agricultural lands. Globally, litter additions enhanced native SOC decomposition (RR = 0.35, 95% CI: 0.32–0.38), with greater priming effects occurring with decreasing latitude and more in agricultural soils (RR = 0.43) than in uncultivated soils (RR = 0.28). In natural ecosystems, soil pH and microbial community composition (e.g., bacteria: fungi ratio) were the best predictors of priming, with greater effects occurring in acidic, bacteria‐dominated sandy soils. In contrast, the substrate properties of plant litter and soils were the most important drivers of priming in agricultural systems since soils with high C:N ratios and those receiving large inputs of low‐quality litter had the highest priming effects. Collectively, our results suggest that, though different factors may control priming effects, the ubiquitous nature of priming means that alterations of litter quality and quantity owing to global changes will likely have consequences for global C cycling and climate forcing. [ABSTRACT FROM AUTHOR]

In this article, the control strategy is studied for the neutral-point-clamped three-level inverter-fed dual three-phase permanent-magnet synchronous motor (PMSM) drive with low switching frequencies. An interleaved finite-control-set model predictive control (MPC) scheme is proposed, where a two-layer MPC is designed to solve the multiobjective optimization problem. The two sets of windings in PMSM are sampled and controlled in an interleaved way so that the control delay and the prediction horizon of the drive system are reduced by half. Moreover, the proposed interleaved control scheme increases the equivalent sampling and control frequency from the perspective of the whole drive system, and thus provides better steady-state performance and dynamic performance. With the switching states of one inverter remaining unchanged, the cross traversal of vector candidate sets between two sets of windings is avoided, and the computational burden can be reduced effectively. Experimental results are given to verify the validity and effectiveness of the proposed interleaved control scheme. [ABSTRACT FROM AUTHOR]

Crossing certain aridity thresholds in global drylands can lead to abrupt decays of ecosystem attributes such as plant productivity, potentially causing land degradation and desertification. It is largely unknown, however, whether these thresholds can be altered by other key global change drivers known to affect the water-use efficiency and productivity of vegetation, such as elevated CO2 and nitrogen (N). Using >5000 empirical measurements of plant biomass, we showed that crossing an aridity (1–precipitation/potential evapotranspiration) threshold of ∼0.50, which marks the transition from dry sub-humid to semi-arid climates, led to abrupt declines in aboveground biomass (AGB) and progressive increases in root:shoot ratios, thus importantly affecting carbon stocks and their distribution. N addition significantly increased AGB and delayed the emergence of its aridity threshold from 0.49 to 0.55 (P  < 0.05). By coupling remote sensing estimates of leaf area index with simulations from multiple models, we found that CO2 enrichment did not alter the observed aridity threshold. By 2100, and under the RCP 8.5 scenario, we forecast a 0.3% net increase in the global land area exceeding the aridity threshold detected under a scenario that includes N deposition, in comparison to a 2.9% net increase if the N effect is not considered. Our study thus indicates that N addition could mitigate to a great extent the negative impact of increasing aridity on plant biomass in drylands. These findings are critical for improving forecasts of abrupt vegetation changes in response to ongoing global environmental change. [ABSTRACT FROM AUTHOR]

Aim: This study aimed to infer the allocation of belowground net primary productivity (BNPP) to sequential soil depths down to 2 m across the globe at a 1 km resolution and assess underlying environmental drivers. Location: Global. Time Period: Contemporary (1932–2017). Major Taxa Studied: Terrestrial plants. Methods: Global datasets including field net primary production (NPP, i.e., the difference between plant assimilated and respired carbon) from 725 soil profiles, root biomass and its depth distribution from 559 soil profiles were compiled and used to infer the depth distribution of BNPP across the globe and digitally map depth‐resolved BNPP globally at 1 km resolution. Drivers of the depth distribution of BNPP were evaluated using machine learning‐based models. Results: Global average BNPP allocated to the 0–20 cm soil layer is estimated to be 1.1 Mg C ha−1 yr−1, accounting for ~60% of total BNPP. Across the globe, the depth distribution of BNPP varies largely, and more BNPP is allocated to deeper layers in hotter and drier regions. Edaphic, climatic and topographic properties (in order of importance) explain >80% of such variability; and the direction and magnitude of the influence of individual properties are soil depth‐ and biome‐dependent. Main Conclusions: The findings suggest that mean annual temperature and precipitation are the two most important factors regulating BNPP across the globe. Soil properties such as soil actual evaporation and total nitrogen also play a vital role in regulating the depth distribution of BNPP. The maps of BNPP provide global benchmarks of depth‐resolved BNPP for the prediction of whole‐profile soil carbon dynamics across biomes. [ABSTRACT FROM AUTHOR]

Savannas are characterized by the coexistence of trees and flammable grasses. Yet, tree-grass coexistence has been labeled as paradoxical-how do these two functional groups coexist over such an extensive area, despite being generally predisposed to excluding each other? For instance, many trees develop dense canopies that limit grass growth, and many grasses facilitate frequent/intense fires, increasing tree mortality. This study revisits tree-grass coexistence with a model of hierarchical competition between pyrogenic grasses, 'forest trees' adapted to closed-canopy competition, and 'savanna trees' that are inferior competitors in closed-canopy communities, but more resistant to fire. The assumptions of this model are supported by empirical observations, including a systematic review of savanna and forest tree community composition reported here. In general, the model simulations show that when savanna trees exert weaker competitive effects on grasses, a self-reinforcing grass community is maintained, which limits forest tree expansion while still allowing savanna trees to persist (albeit as a subdominant to grasses). When savanna trees exert strong competitive effects on grasses, savanna trees cover increases initially, but as grasses decline their inhibitory effect on forest trees weakens, allowing forest trees to expand and exclude grasses and savanna trees. Rather than paradoxical, these results suggest that having weaker competitive effects on grasses may be advantageous for savanna trees, leading to greater long-term abundance and stability. We label this the 'enemy of my enemy hypothesis,' which might apply to species coexistence in communities defined by hierarchical competition or with species capable of generating strong ecological feedbacks. [ABSTRACT FROM AUTHOR]

High altitude wetlands on the Tibetan Plateau have been shrinking due to anthropogenic disturbances and global climate change. However, the few studies that have been conducted on wetlands are inconclusive about the effect of soil moisture on seed banks and potential of seed banks in wetlands with different levels of soil moisture for regeneration of dried wetlands. We investigated seed banks and plant communities along a soil moisture gradient. A structural equation model was used to analyze the direct and indirect effects of soil moisture on seed banks, as well as the relationship between plant communities and seed banks. Although soil moisture had no direct effects on seed bank richness and density and indirect effects on seed banks through plant community, it had indirect effects on the seed bank through soil pH. Soil moisture also did not have direct effects on plant community richness, but it had indirect effects through soil pH. Plant community composition changed with soil moisture, but aboveground plant abundance and seed banks composition did not change. Low similarity exists between plant community and seed banks for all wetlands, and similarity decreased along the moisture gradient. The key factor determining plant community diversity was soil pH, while seed bank diversity was mainly affected by soil pH and plant community diversity with wetland drying. Although potential for regenerating the plant community from the seed bank decreased with an increase in soil moisture, drained wetlands still have enough residual seeds for successful restoration of species-rich alpine meadows. [ABSTRACT FROM AUTHOR]

Functional traits are good predictors of plant responses and adaptations to ever‐changing environments. However, forecasting forest community dynamics is challenging because the relationships among different tree demographic properties (growth, mortality and recruitment) and how functional traits are associated with tree demography remain largely unknown.Here, in a 20‐ha subtropical forest permanent plot, we quantified the rates of tree growth, mortality and recruitment across 53 dominant tree species (diameter at breast height; DBH ≥ 1 cm) from 2005 to 2020. Functional traits that are closely related to plant photosynthesis, nutrients, hydraulics and drought tolerance were measured.We found that tree growth rate (GR) varied independently from rates of tree mortality and recruitment. Hydraulic conductivity was positively correlated with GR (explaining 27% variation—the strongest relationship observed) whereas wood density was negatively correlated with GR. Leaf life span was negatively related to tree mortality. Species with high carbon assimilation rate, nutrient concentration and hydraulic conductivity had high recruitment rates. Leaf turgor loss point was unrelated to plant demography. Principal component analysis revealed that species with quick resource acquisition rates had high rates of growth and recruitment.Our results illustrate that the correlations among tree demographic properties were weak in this subtropical forest with monsoonal climate. Most notably, against expectations, there was no observed trade‐off between growth and mortality. Individual functional traits explained up to 27% of each demographic rate. Variation in recruitment rate was aligned with traits indexing the leaf economic spectrum and also plant hydraulic variation. A better understanding of the role of disturbances on trait–demography relationships would help build a deeper and more nuanced understanding of the ecology of subtropical monsoon forests. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Aim: Fresh carbon (C) inputs to the soil can have important consequences for the decomposition rates of soil organic matter (priming effect), thereby impacting the delicate global C balance at the soil–atmosphere interface. Yet, the environmental factors that control soil priming effect intensity remain poorly understood at a global scale. Location: Global. Time period: 1980–2020. Major taxa studied: Soil priming effect intensity. Methods: We conducted a global dataset of CO2 effluxes in 711 pairwise soils with 13C or 14C simple C sources inputs and without C inputs from incubation experiments in which isotope‐labelled C was used to quantify fresh C‐induced rather than exudate‐induced priming. Results: Soil priming effect intensity is predominantly positive. Soil texture and C content were identified as the most important factors associated with priming effects, with sandy soils from tropical and mid‐latitudes supporting the highest soil priming effect intensity, and soils with greater C content and fine textures from high latitudes maintaining the lowest soil priming effects. The negative association between C content and soil priming effect intensity was also indirectly driven by changing mean annual temperature, net primary productivity, and fungi : bacteria ratio. Using this information, we generated a global map of soil priming effect intensity, and found that the priming was lower at high latitudes and higher at lower latitudes. Main conclusions: Global patterns of soil priming effect intensity can be predicted using environmental data, with soil texture and C content playing a predominant role in explaining in priming effects. These effects were also indirectly driven by climate, vegetation and soil microbial properties. We present the first global atlas of soil priming effect intensity and advance our knowledge on the potential mechanisms underlying soil priming effect intensity, which are integral to improving the climate change and soil C dynamics components of Earth System models. [ABSTRACT FROM AUTHOR]

3 Results 3.1 Characteristics of soil total P concentration across the world Our soil total P concentration database included 5275 measurements from 1894 geographically distinct sites and covered 6 continents, all major biomes, and all 12 USDA soil orders in terrestrial ecosystems (Fig. Besides soil total P concentration and site coordinates, we also included climate variables (i.e., MAT and MAP), vegetation type, and soil physiochemical properties (e.g., SOC, soil clay and sand contents, soil pH) in our database whenever available. Soil chronosequences provide a unique opportunity to isolate the effect of soil age from other soil-forming factors on soil P dynamics and have shown that soil age negatively impacts soil total P concentration (Wardle et al., 2004; Delgado-Baquerizo et al., 2020; Vitousek et al., 2010; Walker and Syers, 1976). In terrestrial ecosystems, to a depth of 1 m from the land surface, most of the P is found in the soil (Zhang et al., 2021). [Extracted from the article]

Aim: The carbon sink in tropical forests is a highly uncertain component of the global carbon budget. An understanding of the processes controlling this sink requires better quantification of carbon allocation, stocks and turnover times. Location: Tropical forests. Time period: 2010–2017. Major taxa studied: Tropical forest ecosystem. Methods: We develop a novel data assimilation system using satellite‐based annual above‐ground biomass derived from L‐band vegetation optical depth with 25 km × 25 km grid spacing, together with leaf area, to constrain the 25 km × 25 km carbon allocation patterns of net primary productivity (NPP) into the wood, leaf and root pools, and their turnover times. Our average data‐driven estimates of these variables are broadly consistent with independent ground‐based estimates of NPP allocation and wood turnover from forest inventory plots. Results: In tropical forest, on average, the NPP allocation into wood (0.30 ± 0.04) is significantly higher than that into leaves (0.24 ± 0.07). From the wet to dry tropics, forest NPP allocation into both wood and leaves declines slightly. The turnover times of forest leaf pools exhibit little spatial variation, whereas the turnover times of wood pools in Africa (median and interquartile range: 50.1‐4.0+5.5 years) are slightly longer than those in South America (48.2‐3.3+4.0 years) and Southeast Asia (48.3‐3.1+5.4 years). Our datasets reveal emergent trade‐offs across climatic and vegetation gradients between growth and life span/turnover for both wood and leaves. The spatial gradients of NPP allocation to wood/leaves are associated with canopy height, adjusted by climate condition and nutrient acquisition. The spatial gradients of wood and leaf turnover times are influenced mainly by climate and leaf characteristics. Main conclusions: Our data‐driven estimates of carbon allocation and turnover times provide a basis for more detailed exploration of these mechanisms in field studies. This highlights that improved model representation of carbon allocation and turnover is necessary for more accurate prediction of future carbon dynamics. [ABSTRACT FROM AUTHOR]

Summary: Nocturnal transpiration is widely observed across species and biomes, and may significantly impact global water, carbon, and energy budgets. However, it remains elusive why plants lose water at night and how to model it at large scales.We hypothesized that plants optimize nighttime leaf diffusive conductance (gwn) to balance potential daytime photosynthetic benefits and nocturnal transpiration benefits. We quantified nighttime benefits from respiratory reductions due to evaporative leaf cooling. We described nighttime costs in terms of a reduced carbon gain during the day because of water use at night. We measured nighttime stomatal responses and tested our model with water birch (Betula occidentalis) saplings grown in a glasshouse.The gwn of water birch decreased with drier soil, higher atmospheric CO2, wetter air, lower leaf temperature, and lower leaf respiration rate. Our model predicted all these responses correctly, except for the response of gwn to air humidity. Our results also suggested that the slow decrease in gwn after sunset could be associated with decreasing leaf respiration.The optimality‐based nocturnal transpiration model smoothly integrates with daytime stomatal optimization approaches, and thus has the potential to quantitatively predict nocturnal transpiration across space and time. [ABSTRACT FROM AUTHOR]

In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grasslands (−38%) than in forests (−10%), which coincided with reduced evapotranspiration and soil water content (SWC). As compared to the 'normal year' of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'. [ABSTRACT FROM AUTHOR]

Combating climate change requires unified action across all sectors of society. However, this collective action is precluded by the ‘consensus gap’ between scientific knowledge and public opinion. Here, we test the extent to which the iconic cities around the world are likely to shift in response to climate change. By analyzing city pairs for 520 major cities of the world, we test if their climate in 2050 will resemble more closely to their own current climate conditions or to the current conditions of other cities in different bioclimatic regions. Even under an optimistic climate scenario (RCP 4.5), we found that 77% of future cities are very likely to experience a climate that is closer to that of another existing city than to its own current climate. In addition, 22% of cities will experience climate conditions that are not currently experienced by any existing major cities. As a general trend, we found that all the cities tend to shift towards the sub-tropics, with cities from the Northern hemisphere shifting to warmer conditions, on average ~1000 km south (velocity ~20 km.year-1), and cities from the tropics shifting to drier conditions. We notably predict that Madrid’s climate in 2050 will resemble Marrakech’s climate today, Stockholm will resemble Budapest, London to Barcelona, Moscow to Sofia, Seattle to San Francisco, Tokyo to Changsha. Our approach illustrates how complex climate data can be packaged to provide tangible information. The global assessment of city analogues can facilitate the understanding of climate change at a global level but also help land managers and city planners to visualize the climate futures of their respective cities, which can facilitate effective decision-making in response to on-going climate change. [ABSTRACT FROM AUTHOR]

The brushless doubly-fed machine (BDFM) without a brush and slip ring has some advantages of high operation reliability and less maintenance cost, which is very suitable for the ship shaft power generation. In this application, the BDFM mainly works on the stand-alone state, in which the power winding (PW) voltage should be controlled directly. The unbalanced load is a typical working state, which mostly results in the unbalance of PW voltage and affects the normal operation of loads severely. The sensorless control strategy can enhance the operation safety under extreme environment and cut down the cost effectively, which is highly desired to be applied in the BDFM-based ship shaft power generation. In this paper, an improved sensorless phase control strategy is proposed, which can work effectively under the unbalanced load condition. First, the sensorless operation is achieved by controlling the $q$ -component of PW voltage, which can realize the phase control simultaneously. Then, the unbalanced compensation is designed in details. Finally, both simulation and experiments have demonstrated that, by the proposed method, the PW voltage phase can be controlled precisely and the voltage unbalance factor is lower than the permissible level. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control method for an asymmetrical-cascaded-multilevel-converter-based hybrid energy storage system (HESS), which includes one battery and several electrical double-layer capacitors (EDLCs). Traditionally, it is challenging to control the power distribution between different cascaded H-bridges by using different energy storage components as dc sources. In this paper, a feedforward space-vector-modulation (FFSVM) technique is used to distribute the active power between the battery and EDLCs. With the proposed voltage feedforward mechanism, the HESS can flexibly operate in the normal operation mode, the high-power output mode, and the reverse power absorption mode. The principle and effectiveness of the improved FFSVM technique are analyzed. Meanwhile, the state-of-charge-balancing mechanisms are introduced. The simulation results obtained in MATLAB/Simulink as well as the experimental results of a hybrid energy storage test bed based on the proposed system are presented to verify its performance. [ABSTRACT FROM PUBLISHER]

Siberia has experienced a pronounced warming over the past several decades, which has induced an increase in the extent of evergreen conifer forest. However, the potential slowing of the trend of increasing surface air temperature (SAT) has produced intense debate since the late 1990s. During this warming hiatus, the Siberian region experienced a significant cooling during the winter season around 10 times that of the Northern Hemisphere (NH) as a whole. This potentially stresses evergreen conifer forests because cooler winters can cause cold-temperature damage and, hence, increase the mortality of young evergreen conifer forests. In this study, the response of Siberian forest composition during the warming hiatus was investigated using satellite observations coupled with model simulations. Observations indicated that from 2001 to 2012, the apparent area of evergreen conifer forest has increased by 10%, while that of the deciduous conifer forest has decreased by 40%. The transition from deciduous to evergreen conifer forest usually occurs through mixed forest or woody savannas as a buffer. To verify the response of evergreen conifer forest, model experiments were performed using an individual-based forest model. Hysteresis of forest change seen in the model simulations indicates that changes in forest composition dynamics under temperature oscillations induced by internal climate variability may not reverse this composition change. As a result, the evergreen conifer forest expansion under climate warming is expected to be a continuing process despite the occurrence of a warming hiatus, exerting far-reaching implications for climate-change-induced albedo shifts in the Siberian forest. [ABSTRACT FROM AUTHOR]

Quantifying soil P fractions is essential for understanding soil P cycling because these fractions are potential sources of bioavailable P. Here, we investigated whether soil P fractions (i.e., labile inorganic P [P], intermediately available P, organic P, occluded P, and apatite P) differed among three tropical forests at different stages of succession (early, middle, and late) in the Dinghushan Biosphere Reserve (DBR), Southern China. We also determined which soil P fractions was closely related to soil microbial and chemical properties in these forests. Soil microbial biomass and chemical properties (except pH, exchangeable Ca, and Mn) were higher in the late successional forest than those in the other two forests. We found that soil organic and occluded P were the dominant fraction in all three forests and together accounted for 78.9, 84.2, and 78.6 % of total P in the early, middle, and late successional forests, respectively. Soil P fractions and acid phosphomonoesterase activity differed significantly among forest successional stages; intermediately available P and organic P (potential sources of labile P) were highest in the late successional forest, occluded P was highest in the middle successional forest, and acid phosphomonoesterase activity significantly increased in middle and late successional forest. Soil labile P fraction and its potential sources (i.e., intermediately available P and soil organic P) were both positively correlated with soil microbial and chemical properties, suggesting that these properties may play critical roles in maintaining high levels of available or potentially available P fractions during this forest succession. Overall, our study indicates that succession in tropical forest ecosystems may not always lead to lower soil P availability. [ABSTRACT FROM AUTHOR]