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Soil drying and rewetting (DRW) events are perceived differently by the soil microbes depending on their adaptation to the previous soil moisture history. Microbes adapted to intense cycles of DRW can experience an experimental DRW event as less harsh than microbes adapted to stable and moist conditions. The perceived harshness in turn can affect the carbon balance after DRW because it can determine the responses of microbial growth (eventually leading to SOC gains) and respiration (SOC loss) after rewetting. These responses have been categorized as “type 1” with immediate fast recovery, or “type 2” with a time lag before fast recovery, due to low and high levels of perceived harshness, respectively. However, we lack a quantitative definition of perceived harshness and how it varies depending on pedoclimatic conditions. Moreover, microbial response types could vary continuously along a continuum from prototypical type 1 to type 2. Therefore, if the shapes of the response curves could be synthesized by using a single function, then the fitted parameters could be used to reflect the harshness levels perceived by the microbes. In turn, these parameters might be combined into an index of harshness with biological interpretation. Relating this index to climatic and edaphic factors would then help to understand the drivers of harshness and microbial recovery after rewetting. To these aims, we described microbial growth with a single logistic function G(t)=Gmax/(1+eb(t-τ)) and respiration with a rescaled gamma distribution R(t)=Ckntn-1e-kt/Γ[n] using data from 15 papers (in total 97 datasets). These functions described well the rates of fungal and bacterial growth, and whole community respiration after rewetting, resulting in a range of shapes consistent with the idea that soil microbial responses form a continuum between types 1 and 2. The product of growth parameters τ (delay time) and b (growth rate at time τ) allowed separating type 1 and 2 responses better than τ or b alone or than any other parameter describing the growth or respiration response. Thus, the product τ×b could be regarded as an effective index to quantify harshness. This index varied depending on soil and experimental conditions: τ×b increased with rewetting intensity (the difference in soil moisture between dry and wet conditions) and declined with higher pH; moreover, bacteria in carbon-rich soils had lower τ×b and thus perceived lower harshness. These results suggest that both fungi and bacteria facing the challenges of acidic soils are also worse adapted to respond to DRW compared to microbes from near-neutral soils. Carbon-rich soils might instead promote bacterial resilience thanks to the more available resources compared to carbon-poor soils. In conclusion, this study places soil microbial responses to DRW along a continuous gradient from fast to slow recovery as quantified by perceived harshness (which in turn is quantifiable by fitting growth and respiration curves to data). Our results help to predict the microbial carbon allocation to growth and respiration at rewetting across ecosystems and environmental conditions.Keywords: soil drying and rewetting, microbial resilience, microbial resistance, growth, respiration

Fatty acid photodecarboxylase is a newly discovered flavin photoenzyme that converts a carboxylic acid into a hydrocarbon and a carbon dioxide molecule through decarboxylation. The enzymatic reactions are poorly understood. In this study, we carefully characterized its dynamic evolution with femtosecond spectroscopy. We observed initial electron transfer from the substrate to the flavin cofactor in 347 ps with a stretched dynamic behavior and subsequently captured the critical carbonyloxy radical. The dominant process following this step was decarboxylation in 5.8 ns to form an alkyl radical and a carbon dioxide molecule. We further identified the absorption bands of two carbonyloxy and alkyl radical intermediates. The overall enzymatic quantum efficiency determined by our obtained timescales is 0.81, consistent with the steady-state value. The results are essential to the elucidation of the enzyme mechanism and catalytic photocycle, providing a molecular basis for potential design of flavin-based artificial photoenzymes.

Cyanobacteriochromes are photoreceptors in cyanobacteria that exhibit a wide spectral coverage and unique photophysical properties from the photoinduced isomerization of a linear tetrapyrrole chromophore. Here, we integrate femtosecond-resolved fluorescence and transient-absorption methods and unambiguously showed the significant solvation dynamics occurring at the active site from a few to hundreds of picoseconds. These motions of local water molecules and polar side chains are continuously convoluted with the isomerization reaction, leading to a nonequilibrium processes with continuous active-site motions. By mutations of critical residues at the active site, the modified local structures become looser, resulting in faster solvation relaxations and isomerization reaction. The observation of solvation dynamics is significant and critical to the correct interpretation of often-observed multiphasic dynamic behaviors, and thus the previously invoked ground-state heterogeneity may not be relevant to the excited-state isomerization reaction.

Vegetation maps are important sources of information for biodiversity conservation, ecological studies, vegetation management and restoration, and national strategic decision making. The current Vegetation Map of China (1:1000000) was generated by a team of more than 250 scientists in an effort that lasted over 20 years starting in the 1980s. However, the vegetation distribution of China has experienced drastic changes during the rapid development of China in the last three decades, and it urgently needs to be updated to better represent the distribution of current vegetation types. Here, we describe the process of updating the Vegetation Map of China (1:1000000) generated in the 1980s using a “crowdsourcing-change detection-classification-expert knowledge” vegetation mapping strategy. A total of 203,024 field samples were collected, and 50 taxonomists were involved in the updating process. The resulting updated map has 12 vegetation type groups, 55 vegetation types/subtypes, and 866 vegetation formation/sub-formation types. The overall accuracy and kappa coefficient of the updated map are 64.8% and 0.52 at the vegetation type group level, 61% and 0.55 at the vegetation type/subtype level and 40% and 0.38 at the vegetation formation/sub-formation level. When compared to the original map, the updated map showed that 3.3 million km2 of vegetated areas of China have changed their vegetation type group during the past three decades due to anthropogenic activities and climatic change. We expect this updated map to benefit the understanding and management of China’s terrestrial ecosystems.

Photosynthetic pigments form light-harvesting networks to enable nearly perfect quantum efficiency in photosynthesis via excitation energy transfer. However, similar light-harvesting mechanisms have not been reported in light sensing processes in other classes of photoreceptors during light-mediated signaling. Here, based on our earlier report, we mapped out a striking energy-transfer network composed of 26 structural tryptophan residues in the plant UV-B photoreceptor UVR8. The spectra of the tryptophan chromophores are tuned by the protein environments, funneling all excitation energy to a cluster of four tryptophan residues, a pyramid center, where the excitation-induced monomerization is initiated for cell signaling. With extensive site-directed mutagenesis, various time-resolved fluorescence techniques, and combined QM/MM simulations, we determined the energy-transfer rates for all donor–acceptor pairs, revealing the time scales from tens of picoseconds to nanoseconds. The overall light harvesting quantum efficiency by the pyramid center is significantly increased to 73%, compared to a direct excitation probability of 35%. UVR8 is the only photoreceptor discovered so far using a natural amino-acid tryptophan without utilizing extrinsic chromophores to form a network to carry out both light harvesting and light perception for biological functions., The light-harvesting network from distal and peripheral to central tryptophans with transfer efficiencies determined from measured energy-transfer rates.

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) associations are critical for host-tree performance. However, how mycorrhizal associations correlate with the latitudinal tree beta-diversity remains untested. Using a global dataset of 45 forest plots representing 2,804,270 trees across 3840 species, we test how AM and EcM trees contribute to total beta-diversity and its components (turnover and nestedness) of all trees. We find AM rather than EcM trees predominantly contribute to decreasing total beta-diversity and turnover and increasing nestedness with increasing latitude, probably because wide distributions of EcM trees do not generate strong compositional differences among localities. Environmental variables, especially temperature and precipitation, are strongly correlated with beta-diversity patterns for both AM trees and all trees rather than EcM trees. Results support our hypotheses that latitudinal beta-diversity patterns and environmental effects on these patterns are highly dependent on mycorrhizal types. Our findings highlight the importance of AM-dominated forests for conserving global forest biodiversity., The relationship of mycorrhizal associations with latitudinal gradients in tree beta-diversity is unexplored. Using a global dataset approach, this study examines how trees with arbuscular mycorrhizal and ectomycorrhizal associations contribute to latitudinal beta-diversity patterns and the environmental controls of these patterns.

Changes in soil carbon (C) and nitrogen (N) stocks following afforestation have been widely studied at different scales. However, soil phosphorus (P) dynamics following afforestation are poorly understood, especially at the regional scale. This paper studied the effects of prior land use (cropland, grassland, and barren land), tree species (conifer, broadleaf, shrub, and mixed), plantation age (young, middle, and old), and climate on soil total phosphorus and available phosphorus stocks change in the top 20 cm following afforestation based on a synthesis of 50 recent publications in northern China. We also considered possible confounding effects between these factors. The results showed that, overall, soil total phosphorus and available phosphorus stocks significantly decreased by 7.3% and significantly increased by 8.8%, respectively, following afforestation. Prior land use was found to be the most important driver in determining changes in soil P stocks. Compared with a significant decrease in P of afforestation of former cropland and grassland, afforestation of barren land caused no clear decrease in P. Tree species was found to have a limited effect on changes in soil P after afforestation, and broadleaf afforestation has a lower P demand than coniferous forests in the studied region. Plantation age did not affect the dynamics of P stocks. Our results showed confounding effects of precipitation, prior land use, and tree species, which impacted the estimates of the drivers of changes in P stocks. These results highlighted the importance of tree species selection and replication across sites that receive different amounts of precipitation.

Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions., Author summary Worldwide, ecosystems are collapsing or in danger of collapse, but the precise causes of these collapses are often unknown. Observational and experimental evidence shows that all ecosystems are characterized by strong interactions between and among species, and that these webs of interactions can be important contributors to the preservation of ecosystem diversity. But many of the interactions–such as those involving pathogenic microorganisms and the chemical defenses that are mounted by their prey–are not easily identified and analyzed in ecosystems that may have hundreds or thousands of species. Here we use our equal-area-annulus analytical method to examine census data from over three million trees in forest plots from around the world. We show how the method can be used to flag pairs and groups of species that exhibit unusual levels of interaction and that are likely on further investigation to yield information about their causative mechanisms. We give a detailed example showing how some of these interactions can be traced to defense mechanisms that are possessed by one of the tree species. We explore how our method can be used to identify the between-species interactions that play the largest roles in the maintenance of ecosystems and their diversity.

Emerging evidence has revealed the distinct role of glypican-1 (GPC1) in mediating cellular signal transduction crucial to tumor progression through its function as a co-receptor/modulator for heparin-binding growth factors. The main objective of this study was to investigate the antitumor effect of a novel mouse anti-human GPC1 monoclonal antibody (anti-GPC1 mAb) on non-small cell lung carcinoma (NSCLC) and associated molecular mechanisms. Results of the in vitro study showed that anti-GPC1 mAb profoundly inhibited the anchorage-independent growth of A549 and H460 NSCLC cells and exhibited relatively high cytotoxic activities towards CCD-19Lu lung fibroblasts, A549/CCD-19Lu and H460/CCD-19Lu coculture spheroids. In the transwell indirect co-culture system, anti-GPC1 mAb treatment significantly decreased the expression of phospho-Src (Tyr416), phospho-Akt (Ser473) and β-catenin in the co-cultured CCD-19Lu lung fibroblasts, and the expression of phospho-MEK (Ser217/221) and phospho-p90RSK (Ser380) in co-cultured A549 cells. When anti-GPC1 mAb was administered to tumor-bearing mice either through tail-vein injection once every 72 hours for 8 doses or through intraperitoneal injection once a week for 3 doses and then once every 10 days for 2 more doses, the inhibitory effect of anti-GPC1 mAb on the growth of orthotopic A549 lung tumors was not statistically significant. Nonetheless, results of Western blot analysis showed significant decrease in the phosphorylation of FGFR1 at Tyr766, Src at Tyr416, ERK at Thr202/Tyr204, RSK at Ser380, GSK3α at Ser21 and GSK3β at Ser9 in tumor samples obtained from tumor-bearing mice receiving the extended-interval dosing of anti-GPC1 mAb. These data implicate that anti-GPC1 mAb treatment impairs the interaction between tumor cells and tumor associated fibroblasts by attenuating the paracrine FGFR signal transduction. In conclusion, although anti-GPC1 mAb alone is not sufficient to inhibit lung tumor growth in vivo, the relatively potent cytotoxicity of anti-GPC1 mAb in lung fibroblasts and its potential inhibitory effect on the paracrine FGFR signal transduction warrant further studies on the combined use of this mAb with targeted therapeutics to improve therapeutic outcomes in lung cancer.

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall species richness (gamma-diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. Here, we provide a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling biases, to compare beta-diversity and species packing across a latitudinal gradient in tree species richness of 21 large forest plots along a large environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogues. This suggests that beta-diversity contributes to the latitudinal species richness gradient as a component of gamma-diversity. Moreover, both niche specialization and niche marginality (a measure of niche spacing along an environmental gradient) also increase towards the equator, after controlling for the effect of topographical heterogeneity. This supports the joint importance of tighter species packing and larger niche space in tropical forests while also demonstrating the importance of local processes in controlling beta-diversity.

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall species richness (gamma-diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. Here, we provide here a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling biases, to compare beta-diversity and species packing across a latitudinal gradient in tree species richness of 21 large forest plots along a large environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogues. This suggests that beta-diversity contributes to the latitudinal species richness gradient as a component of gamma-diversity. Moreover, both niche specialization and niche marginality (a measure of niche spacing along an environmental gradient) also increase towards the equator, after controlling for the effect of topographic heterogeneity. This supports the joint importance of tighter species packing and larger niche space in tropical forests while also demonstrating the importance of local processes in controlling beta-diversity.

ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems ≥1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.

Plants utilize a UV-B (280 to 315 nm) photoreceptor UVR8 (UV RESISTANCE LOCUS 8) to sense environmental UV levels and regulate gene expression to avoid harmful UV effects. Uniquely, UVR8 uses intrinsic tryptophan for UV-B perception with a homodimer structure containing 26 structural tryptophan residues. However, besides 8 tryptophans at the dimer interface to form two critical pyramid perception centers, the other 18 tryptophans’ functional role is unknown. Here, using ultrafast fluorescence spectroscopy, computational methods and extensive mutations, we find that all 18 tryptophans form light-harvesting networks and funnel their excitation energy to the pyramid centers to enhance light-perception efficiency. We determine the timescales of all elementary tryptophan-to-tryptophan energy-transfer steps in picoseconds to nanoseconds, in excellent agreement with quantum computational calculations, and finally reveal a significant leap in light-perception quantum efficiency from 35% to 73%. This photoreceptor is the first system discovered so far, to be best of our knowledge, using natural amino-acid tryptophans to form networks for both light harvesting and light perception., Photoreceptor UVR8 in plants senses environmental UV levels through 26 structural tryptophan residues, but the role of 18 of them was unknown. The authors show, by experiments and computations, how these form a light-harvesting network that funnels the excitation to the pyramid centers enhancing the light-perception efficiency.

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall species richness (gamma-diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. Here, we provide here a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling biases, to compare beta-diversity and species packing across a latitudinal gradient in tree species richness of 21 large forest plots along a large environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogs. This suggests that beta-diversity contributes to the latitudinal species richness gradient as a component of gamma-diversity. Moreover, both niche specialization and niche marginality (a measure of niche spacing along an environmental gradient) also increase towards the equator, after controlling for the effect of topographic heterogeneity. This supports the joint importance of tighter species packing and larger niche space in tropical forests while also demonstrating the importance of local processes in controlling beta-diversity.

Red-light bacteriophytochromes regulate many physiological functions through photoisomerization of a linear tetrapyrrole chromophore. In this work, we mapped out femtosecond-resolved fluorescence spectra of the excited Pr state and observed unique active-site relaxations on the picosecond time scale with unusual spectral tuning of rises on the blue side and decays on the red side of the emission. We also observed initial wavepacket dynamics in femtoseconds with two low-frequency modes of 38 and 181 cm-1 as well as the intermediate product formation after isomerization in hundreds of picoseconds. With critical mutations at the active site, we observed similar dynamic patterns with different times for both relaxation and isomerization, consistent with the structural and chemical changes induced by the mutations. The observed multiphasic dynamics clearly represents the active-site relaxation, not different intermediate reactions or excitation of heterogeneous ground states. The active-site relaxation must be considered in understanding overall isomerization reactions in phytochromes, and such a molecular mechanism should be general.

Foundation species structure forest communities and ecosystems but are difficult to identify without long-term observations or experiments. We used statistical criteria--outliers from size-frequency distributions and scale-dependent negative effects on alpha diversity and positive effects on beta diversity--to identify candidate foundation woody plant species in 12 large forest-dynamics plots spanning 26 degrees of latitude in China. We used these data (1) to identify candidate foundation species in Chinese forests, (2) to test the hypothesis--based on observations of a midlatitude peak in functional trait diversity and high local species richness but few numerically dominant species in tropical forests--that foundation woody plant species are more frequent in temperate than tropical or boreal forests, and (3) to compare these results with data from the Americas to suggest candidate foundation genera in northern hemisphere forests. Using the most stringent criteria, only two species of Acer, the canopy tree Acer ukurunduense and the shrubby treelet Acer barbinerve, were identified in temperate plots as candidate foundation species. Using more relaxed criteria, we identified four times more candidate foundation species in temperate plots (including species of Acer, Pinus, Juglans, Padus, Tilia, Fraxinus, Prunus, Taxus, Ulmus, and Corlyus) than in (sub)tropical plots (the treelets or shrubs Aporosa yunnanensis, Ficus hispida, Brassaiopsis glomerulata, and Orophea laui). Species diversity of co-occurring woody species was negatively associated with basal area of candidate foundation species more frequently at 5- and 10-m spatial grains (scale) than at a 20-m grain. Conversely, Bray-Curtis dissimilarity was positively associated with basal area of candidate foundation species more frequently at 5-m than at 10- or 20-m grains. Both stringent and relaxed criteria supported the hypothesis that foundation species are more common in mid-latitude temperate forests. Comparisons of candidate foundation species in Chinese and North American forests suggest that Acer be investigated further as a foundation tree genus.

Foundation species play important roles in structuring forest communities and ecosystems. Foundation species are difficult to identify without long-term observations or experiments and their foundational roles rarely are identified before they are declining or threatened. We used new statistical criteria based on size-frequency distributions, species diversity, and spatial codispersion among woody plants to identify potential (“candidate”) foundation species in 12 large forest dynamics plots spanning 26 degrees of latitude in China. We used these data to identify a suite of candidate foundation species in Chinese forests; test the hypothesis that foundation woody plant species are more frequent in the temperate zone than in the tropics; and compare these results with comparable data from the Americas to suggest candidate foundation genera in Northern Hemisphere forests. We identified more candidate foundation species in temperate plots than in subtropical or tropical plots, and this relationship was independent of the latitudinal gradient in overall species richness. Two species of Acer, the canopy tree Acer ukurunduense and the shrubby treelet Acer barbinerve were the only two species that met both criteria in full to be considered as candidate foundation species. When we relaxed the diversity criteria, Acer, Tilia, and Juglans spp., and Corlyus mandshurica were frequently identified as candidate foundation species. In tropical plots, the tree Mezzettiopsis creaghii and the shrubs or treelets Aporusa yunnanensis and Ficus hispida had some characteristics associated with foundation species. Species diversity of co-occurring woody species was negatively associated with basal area of candidate foundation species more frequently at 5- and 10-m spatial grains (scale) than at a 20-m grain. Conversely, Bray-Curtis dissimilarity was positively associated with basal area of candidate foundation species more frequently at 5-m than at 10- or 20-m grains. Our data support the hypothesis that foundation species should be more common in temperate than in tropical or boreal forests, and suggest that in the Northern Hemisphere that Acer be investigated further as a foundation tree genus.

Factors such as clay minerals and micropore structure can lead to the adsorption and retention of chemical agents when the components of surfactant-polymer systems enter porous media. This study aims to clarify the influence of adsorption and retention of surfactant-polymer components on reservoir permeability and oil displacement efficiency and then classify the reservoirs into types. The natural cores of conglomerate reservoirs from the Badaowan Formation in the 7th block are selected as research objects to reveal the adsorption law of surfactant-polymer components on different minerals and different micro pores through the dynamic oil displacement method based on physical model and the N element calibration method. Experimental results show that the adsorption capacity of clay minerals for surfactant-polymer components is significantly higher than that of carbonate and skeleton minerals, and different clay minerals differ in adsorption capacity for surfactant-polymer components depending on their cation exchange capacity and end surface adsorption activity. In addition, the adsorption and retention capacities of reservoirs for surfactant-polymer components are closely related to the type and content of clay minerals. The combination type of clay minerals controls the adsorption activity of surfactant-polymer components, and the values of polymer and the surfactant are quantitatively calculated to be 11.3 and 21.4 mg/g, respectively. The adsorption strength of surfactant-polymer components is controlled by the content of clay minerals. With increasing clay content, the adsorption strength of the polymer ranges from 0.5 to 2.5 mg/cm3, and that of the surfactant ranges from 1.0 to 4.5 mg/cm3. On this basis, the “N element calibration method” is used to determine the occurrence state and content of chemical agents in micropores for different permeability samples after surfactant-polymer binary flooding. Research results show that the polymer and surfactant components mainly have two types of occurrence form in micropores, including the complex pores accumulated by clay minerals and the intersections of small pores and throats. With decreasing reservoir permeability, the number and content of detected N element gradually increase, indicating an increase in the adsorption and retention of polymer and surfactant, and the influence on the reservoir seepage capacity also increases. Finally, the conglomerate reservoirs in the Badaowan Formation from the 7th block are divided into four types after considering the influence of clay minerals and micropore structure on the adsorption and retention of surfactant-polymer components, and the reasonable classification of reservoir types can effectively enhance the oil recovery of surfactant-polymer binary flooding.

The application of green manure is a traditional and valuable practice for agroecosystem management. In northern China, the effects of green manure on production of the region’s major crops have been extensively investigated, but the inconsistent conclusions that these case studies have yielded cannot provide effective guidance for practical local agricultural production. Here, we conducted a meta-analysis to generate a comprehensive evaluation of the effects of green manure on soil properties and crop yield in this region. Our results shown that green manure improves soil quality effectively, decreasing soil bulk density by ∼ 5.6 %, increasing microbial biomass carbon by 28 %, and improving the activities of soil enzymes by 14 % ∼ 39 %. Among the different types of green manure, legume green manure more markedly increased both nitrate and hydrolysable nitrogen, while non-legume green manure more markedly increased available potassium. Soil gravimetric water content was decreased under green manure treatment. Maize yield was significantly increased under green manure by 11 % on the whole, while effects of green manure on wheat and potato were inconsistent. In summary, the application of green manure in northern China can improve soil quality significantly, and proper green manure use can improve cash crop yields.

Aggregated patterns of tree species originate either from the physical forcing of habitat heterogeneity or from community processes. In both cases, spatial structuring plays a functional role in ecosystems. This study examines the spatial patterns of tree species, and discusses the degree to which variation in species distribution patterns depends on topographic variation. We first analyzed the spatial distribution patterns of tree species by using the univariate pair correlation function. We used redundancy analysis to identify the main structures explained by the measured topographic variables. Then, we used variation partitioning in combination with Moran’s eigenvector maps and seven topographic variables to determine the relative importance of the effects of pure topographical, pure spatial, and spatially structured environmental processes on spatial patterns of tree species composition in a large-scale stem-mapping plot located in a diverse heterogeneous tropical karst seasonal rain forest of south China. Although aggregated distribution was the dominant pattern for tree species as we expected in this tropical karst forest, the degree of aggregation was lower than in other tropical or subtropical forests. Most species showed random patterns after controlling for habitat heterogeneity in a parametric heterogeneous Poisson process null model. The seven topographical variables explained about 16.7%, 31.0% and 47.2% of the total variance in species abundances by redundancy analysis for cell sizes of 10 m × 10 m, 20 m × 20 m and 50 m × 50 m, respectively. The pure spatial component was most important at the three spatial scales, which accounted for about one-third of total variance in species composition, while the spatially independent habitat contributed a negligible effect. This indicated that the overall evidence for topographic controls of the tropical tree species spatial pattern was strong, but the explanatory power of the topographic variables was negligible compared to the total variation of pure spatial processes, especially the broad-scale space. The results suggest that topographical and neutral progresses jointly contribute to the maintenance of species composition, and their relative importance varies with spatial scale in the Nonggang tropical karst seasonal rain forest.

Both deterministic and stochastic processes have been linked to forest community assembly; however, their contribution to beta diversity has not been properly explored, and no studies to date have investigated their impacts on sparse depleted soils in forests that contain widespread exposed limestone karst. We found that the pairwise differences in species composition between quadrates was determined by a balanced variation in abundance, whereby the individuals of some species at one site were substituted by an equivalent number of individuals of different species at another site. Both the total beta diversity and its balanced variation in abundance declined with increasing sampling grain size. Our research indicated that environmental differences exert a strong influence on beta diversity, particularly total beta diversity and its balanced abundance variation in larger grain sizes. It was evident that deterministic and stochastic processes worked together, and that deterministic processes were more important than stochastic processes in the regulation of beta diversity in this heterogeneous tropical karst seasonal rainforest of Southern China. However, in future research a functional trait based approach will be required to tease out the relative degree of deterministic and stochastic processes toward an assessment of the temporal changes in species composition.

Tree mortality plays a vital role in forest dynamics and contributes to species coexistence and community assembly. However, the mechanisms that control tree mortality are poorly understood, particularly in species-rich tropical forests. Size-dependent abiotic constraints and biotic interactions act simultaneously to cause tree mortality in natural forests. However, these drivers are often studied independently, which can limit our understanding of how they interact to affect tree mortality in natural forests. We employed a hierarchical Bayesian logistic regression modeling approach to quantify the simultaneous effects of tree size, topography, neighborhoods, and their interactions on tree mortality in a 15-ha fully mapped tropical karst seasonal rainforest in Southern China. Of the variables tested, tree size exhibited the most consistent and strongest negative effect on tree mortality, while topography and neighborhood competition were of secondary importance. Neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering mortality, while only several species showed conspecific negative density dependent on mortality. The topographical wetness index had a significant positive effect on tree mortality. Size-dependent and neighborhood competition-induced tree mortality was stronger for shade-intolerant than for shade-tolerant species, and the size-dependent mortality was the strongest for shrub species among the three growth forms. Our results indicated that the size-dependent effect was the dominant cause of tree mortality; however, neighbors, particularly heterospecific neighbors, had a facilitative effect on lowering tree mortality. Furthermore, the relative importance of these mechanisms for tree mortality differed within life-history strategies guilds. Our study highlighted the value of simultaneously considering the individual and interactive effects of multiple mechanisms toward understanding the dynamics and coexistence of highly diverse metacommunities in harsh environments.

Litter is a vital component of ecosystem functionality, which is inherently linked to net primary productivity and global biogeochemical cycles. To better understand the drivers that modify net primary productivity, we need to disentangle the processes that underly changes in the generation of litter. We employed structural equation models (SEMs) to test for the direct and indirect effects of biodiversity, the stand structural attributes, and abiotic drivers on annual litter production in a tropical karst seasonal rainforest. For this study, annual litter production was evaluated over a five-year period in 90 permanent sample litter traps in a dynamic 15-ha long-term forest plot in Southern China. For each circular plot stand (with central litter traps) we quantified biodiversity, structural variations, basal area, and growth rate, which are important for net primary productivity. The four best-fit SEMs with different metrics of biodiversity for the paths between biodiversity, structural attributes, abiotic drivers, and annual litter production had a similar goodness of fit to the data. They accounted for 42.7–47.8% of the variation in annual litter production, 4.7–16.8% of the variation in stand-level growth rate, 29.3% of the variation in stand-level basal area, 8.2–13.2% of the variation in stand structural variation, and 4.4–6.5% of the variation in biodiversity. Although biodiversity had a positive effect on annual litter production through direct or indirect effects via the stand-level growth rate, abiotic drivers had the strongest impacts on annual litter production. We also found that the structural attributes of the stands had positive effects on the annual litter production; however, only the stand-level growth rate had significant consistently positive effects on annual litter production in the four best-fit SEMs. These results implied that annual litter production is most strongly driven by abiotic factors, followed by stand structural attributes and biodiversity. Theoretically, our study supports that niche differentiation and facilitation might enhance productivity; however, this enhanced capacity is primarily contingent on how abiotic variations are controlled in the sampling of natural karst forest systems. Biodiversity and the conservation of specific habitats should therefore be a key component in the management of forest resources, forest conservation, and sustainability.