Plant diversity increases spatial stability of aboveground productivity in alpine grasslands.

Plant diversity can significantly affect the grassland productivity and its stability. However, it remains unclear how plant diversity affects the spatial stability of natural grassland productivity, especially in alpine regions that are sensitive to climate change. We analyzed the interaction between plant (species richness and productivity, etc.) and climatic factors (precipitation, temperature, and moisture index, etc.) of alpine natural grassland on the Qinghai-Tibetan Plateau. In addition, we tested the relationship between plant diversity and spatial stability of grassland productivity. Results showed that an increase in plant diversity significantly enhanced community productivity and its standard deviation, while reducing the coefficient of variation in productivity. The influence of plant diversity on productivity and the reciprocal of productivity variability coefficient was not affected by vegetation types. The absolute values of the regression slopes between climate factors and productivity in alpine meadow communities with higher plant diversity were smaller than those in alpine meadow communities with lower plant diversity. In other words, alpine meadow communities with higher plant diversity exhibited a weaker response to climatic factors in terms of productivity, whereas those with lower plant diversity showed a stronger response. Our results indicate that high plant diversity buffers the impact of ambient pressure (e.g., precipitation, temperature) on alpine meadow productivity, and significantly enhanced the spatial stability of grassland productivity. This finding provides a theoretical basis for maintaining the stability of grassland ecosystems and scientifically managing alpine grasslands under the continuous climate change.

Warming differentially affects above- and belowground ecosystem functioning of the semi-arid alpine grasslands.

Rapid climate warming is altering multiple ecosystem functions of alpine grasslands. However, the responses of the above- and belowground ecosystem multifunctionality (EMF) to climate warming might exhibit difference in semi-arid alpine grasslands. Based on manipulative field experiments at an alpine meadow and an alpine steppe, we explored warming effects on the functioning of alpine grassland ecosystems on the Tibetan Plateau. Warming significantly decreased plant diversity and aboveground biomass, but tended to increase belowground biomass, soil carbon, and soil nutrient contents. Experimental warming generally had neutral effects on the EMF of both alpine grasslands. Nevertheless, warming differentially affects the above- and belowground ecosystem functioning of Tibetan semi-arid alpine grasslands, with the aboveground EMF (AEMF) deceased but the belowground EMF (BEMF) increased under warmer conditions. Our results further showed that the negative effect of experimental warming on AEMF was mainly regulated by the changes of plant and soil biodiversity. However, plant productivity had a pivotal role in propelling the positive effect of warming on BEMF. Our results emphasized the potential impacts of plant and soil biodiversity, productivity, and soil nutrients in maintaining the EMF of alpine grasslands, which could offer novel views for sustainable management of Tibetan semi-arid alpine ecosystems.

Warming positively promoted community appearance restoration of the degraded alpine meadow although accompanied by topsoil drying.

On-going climate warming is threatening the ecological function of grassland ecosystems. However, whether warming has positive effects on community microhabitats and appearance, especially in degraded grasslands, remains elusive. To address this issue, we conducted a 2-year field experiment on the severely degraded alpine meadow and undegraded alpine meadow with no warming and warming treatments. Community coverage and height in degraded meadow significantly increased under warming, while these changes were not significant in undegraded meadow. Two-year warming increased the community height of degraded meadow and undegraded meadow by 56.55% and 10.99%, respectively. Warming also increased community coverage by 41.88% in degraded meadow and decreased community coverage by 3.01% in undegraded meadow. Moreover, the response of topsoil temperature to warming was stronger in degraded meadow (6.89%) than in undegraded meadow (- 0.26%), while the negative response of topsoil moisture to warming was weaker in degraded meadow (- 13.95%) than in undegraded meadow (- 20.00%). The SEMs further demonstrated that warming had positive effects on topsoil temperature and community height, while had negative effects on topsoil moisture both in degraded and undegraded meadows. Our results confirm that warming-induced soil drying is an important pathway affecting the community appearance in alpine meadows. These findings highlight that warming has positive effects on community height and coverage and is particularly effective in improving community coverage appearance in severely degraded alpine meadow with topsoil drying.

Warming-driven indirect effects on alpine grasslands: short-term gravel encroachment rapidly reshapes community structure and reduces community stability.

The community stability is the main ability to resist and be resilient to climate changes. In a world of climate warming and melting glaciers, alpine gravel encroachment was occurring universally and threatening hillside grassland ecosystem. Gravel encroachment caused by climate warming and glacial melting may alter community structure and community stability in alpine meadow. Yet, the effects of climate warming-induced gravel encroachment on grassland communities are unknown. Here, a 1-year short-term field experiment was conducted to explore the early stage drive process of gravel encroachment on community structure and stability at four different gravel encroachment levels 0%, 30%, 60%, and 90% gravel coverage at an alpine meadow on the Qinghai Tibetan Plateau, by analyzing the changes of dominant species stability and species asynchrony to the simulated gravel encroachment processes. Gravel encroachment rapidly changed the species composition and species ranking of alpine meadow plant community in a short period of time. Specifically, community stability of alpine meadow decreased by 61.78-79.48%, which may be due to the reduced dominant species stability and species asynchrony. Species asynchrony and dominant species stability were reduced by 2.65-17.39% and 46.51-67.97%, respectively. The results of this study demonstrate that gravel encroachment presents a severe negative impact on community structure and stability of alpine meadow in the short term, the longer term and comprehensive study should be conducted to accurate prediction of global warming-induced indirect effects on alpine grassland ecosystems.

Determining the role of richness and evenness in alpine grassland productivity across climatic and edaphic gradients.

Spatial heterogeneity of climatic and edaphic gradients can substantially affect the grassland productivity function. However, few studies have tested the importance of species richness and evenness on regulating grassland productivity across spatial-scale climatic and edaphic changes. This study examines the complex mechanisms by which species richness and evenness regulate productivity in alpine meadow and steppe. We used field survey data to explore above-ground productivity formation and sensitivity to spatial-scale climatic and edaphic response of alpine grassland based on species richness and evenness. Results showed that the growing season solar radiation was the main driving factor of above-ground biomass and was strongly negatively correlated with above-ground biomass. Furthermore, compared with alpine steppe, above-ground biomass in alpine meadow was more responsive to climatic variables, but less responsive to soil variables. Unexpectedly, we found that the regulation patterns of species richness and evenness on above-ground biomass were different in both habitats by a structural equation model analysis. Our study demonstrated that species evenness and richness were both important in co-regulating above-ground biomass in alpine meadow, whereas species richness mattered more than species evenness in regulating above-ground biomass in alpine steppe. Our results offer further support for species richness and evenness co-regulating grassland productivity across spatial-scale climatic and edaphic gradients, which helps maintain the benefits of plant diversity and alpine grassland ecosystems.

Natural compensation mechanism of soil water infiltration through decayed roots in semi-arid vegetation species.

In arid and semi-arid areas, unsuitable afforestation programs may cause soil water deficit and even, in some cases, deep-soil desiccation and the subsequent death of part of the vegetation. However, the benefits of preferential flow through decayed root channels for supplying water in the dried soil layers are rarely evaluated. This study examines the effects of root channels on soil water content (SWC) and infiltration (initial and steady-state) in two planted species with high drought tolerance, namely: Korshinsk peashrub (Caragana korshinskii Kom.), and red plum apricot (Armeniaca vulgaris Lam.), using bare land as control site and published data from alfalfa (Medicago sativa L.) plots to refine results analysis. The infiltration rates were measured using a double-ring infiltrometer in areas with alive and decayed roots; and methylene blue was used to trace the pathways of water flow. The highest SWC appeared in the Korshinsk peashrub land, whereas the alfalfa grassland had the lowest SWC; and the differences of SWC among treatments were significant at all soil layers. Korshinsk peashrub had the highest steady infiltration rates, which were about 23% and 83% higher than those rates measured in the fruit tree plantation and alfalfa grasslands, respectively. The steady infiltration rates were significantly and positively correlated with the average root diameter and area. Within the same species, the decayed root plots significantly increased the soil water infiltration capacity compared to the alive root plots. Considering the water scarcity conditions of the study area, the preferential flow formed through decomposed roots was conducive to soil water supplement, appearing as a natural compensation mechanism caused by dead vegetation. Our findings contribute to a better understanding of soil water infiltration during root decay of the plants in water-limited ecosystems, and how this dynamic replenishes soil moisture and alleviates soil desiccation.

Characterization of Human Origin Salmonella Serovar 1,4,[5],12:i:- in Eastern China, 2014 to 2018.

The prevalence of Salmonella serovar 1,4,[5],12:i:- among diarrhea patients has increased considerably in many countries around the world, including China. However, the characterization of this serovar of human origin has been less reported from China. We characterized 76 isolates of Salmonella 1,4,[5],12:i:- gained from diarrhea patients from 2014 to 2018 in the Jiangsu Province of eastern China. These isolates fell into a single-sequence type (ST34) determined by multilocus sequence typing (MLST), and into 44 pulsed-field gel electrophoresis band patterns, with 1 pattern (JSSMM015) comprising 12 isolates (15.9%). By means of PCR-based assays, the seven prophage located virulence genes were detected in our Salmonella 1,4,[5],12:i:- isolates with a high rate of gipA, gtgB, sspH1, sspH2, sodC1, and gtgE (93.4-97.4%), and with a moderate rate of sopE (42.1%). In contrast, none of the five plasmid-borne virulence genes (spvC, pefA, mig5, rck, and srgA) was identified. We tested the isolates' susceptibility to 18 antibiotics of 9 categories using the VITEK 2 system. A high proportion (89.5%) of the isolates were multidrug resistant (MDR) strains with full resistance to cefazolin, cefotetan, amikacin, gentamycin, and tobramycin, followed by resistance to ampicillin (88.2%) and ampicillin/sulbactam (80.3%). The resistance to piperacillin/tazobactam, ceftazidime, cefepime, and levofloxacin was scarce (2.6-9.2%). Notably, an isolate from 2018 was resistant to carbapenems. blaTEM-1B and aac(6')-Ib-cr were the most common drug resistance genes presented in cephalosporin- and fluoroquinolone-resistant strains. All Salmonella 1,4,[5],12:i:- isolates were capable of forming biofilm, with 13.2% of them having strong ability. However, no association was indicated between the scale of biofilm formation ability and MDR. Our results indicate that the combination of these characteristics may together provide a selective and competitive advantage to those Salmonella 1,4,[5],12:i:- isolates, contributing to their increasing prevalence observed worldwide.

Detection of antibiotics in the urine of children and pregnant women in Jiangsu, China.

Exposure to low concentrations of antibiotics links to multiple health hazards, such as drug resistance of bacteria, and childhood obesity. In this study, seven antibiotics were measured in the urine of 107 children and 126 pregnant women in Jiangsu Province by ultra-performance liquid chromatography and tandem mass spectrometry (UPLC-MS/MS). The overall urinary antibiotics detection rate was 38.6%. Most (98.3%) of the participants' antibiotics concentrations were no more than 10 ng/mL. Children had a significantly higher detection rate than pregnant women (47.7% vs. 31.0%, P = 0.009), as well as the concentration (95th percentile: 6.49 vs. 4.08 ng/mL, P = 0.002). The detection rates of individual antibiotics ranged from 0.4% to 15.0%, and the concentrations ranged from lower than the limit of detection (LOD) through up to 31.96 ng/mL individually. Two or more antibiotics were detected in 11.2% of the urines. Tetracyclines were more frequently detected than phenicols (30.9% vs.12.4%). Oxytetracycline was the most frequently detected (15.0%). Multivariate logistic regression showed that consuming puffed food every day was associated with a significantly increased likelihood of detection, and higher concentration of overall antibiotics, and of doxycycline. Children were more likely to be detected of doxycycline and florfenicol, and to have elevated concentration of doxycycline, compared with pregnant women. This study highlights the relatively heavier antibiotics exposure in children, and a possible impact of puffed food on it, which needs to be warranted in future studies.

Don't judge toxic weeds on whether they are native but on their ecological effects.

The sharp rise in anthropogenic activities and climate change has caused the extensive degradation of grasslands worldwide, jeopardizing ecosystem function, and threatening human well-being. Toxic weeds have been constantly spreading in recent decades; indeed, their occurrence is considered to provide an early sign of land degeneration. Policymakers and scientific researchers often focus on the negative effects of toxic weeds, such as how they inhibit forage growth, kill livestock, and cause economic losses. However, toxic weeds can have several potentially positive ecological impacts on grasslands, such as promoting soil and water conservation, improving nutrient cycling and biodiversity conservation, and protecting pastures from excessive damage by livestock. We reviewed the literature to detail the adaptive mechanisms underlying toxic weeds and to provide new insight into their roles in degraded grassland ecosystems. The findings highlight that the establishment of toxic weeds may provide a self-protective strategy of degenerated pastures that do not require special interventions. Consequently, policymakers, managers, and other personnel responsible for managing grasslands need to take appropriate actions to assess the long-term trade-offs between the development of animal husbandry and the maintenance of ecological services provided by grasslands.

Soil functional biodiversity and biological quality under threat: intensive land use outweighs climate change.

Climate change and land use intensification are the two most common global change drivers of biodiversity loss. Like other organisms, the soil meso-fauna are expected to modify their functional diversity and composition in response to climate and land use changes. Here, we investigated the functional responses of Collembola, one of the most abundant and ecologically important groups of soil invertebrates. This study was conducted at the Global Change Experimental Facility (GCEF) in central Germany, where we tested the effects of climate (ambient vs. 'future' as projected for this region for the years between 2070 and 2100), land use (conventional farming, organic farming, intensively-used meadow, extensively-used meadow, and extensively-used pasture), and their interactions on the functional diversity (FD), community-weighted mean (CWM) traits (life-history, morphology), and functional composition of Collembola, as well as the Soil Biological Quality-Collembola (QBS-c) index. We found that land use was overwhelmingly the dominant driver of shifts in functional diversity, functional traits, and functional composition of Collembola, and of shifts in soil biological quality. These significant land use effects were mainly due to the differences between the two main land use types, i.e. cropland vs. grasslands. Specifically, Collembola functional biodiversity and soil biological quality were significantly lower in croplands than grasslands. However, no interactive effect of climate × land use was found in this study, suggesting that land use effects on Collembola were independent of the climate change scenario. Overall, our study shows that functional responses of Collembola are highly vulnerable to land use intensification under both climate scenarios. We conclude that land use changes reduce functional biodiversity and biological quality of soil.

Trade-off between surface runoff and soil erosion during the implementation of ecological restoration programs in semiarid regions: A meta-analysis.

The application of ecological restoration programs, related to water resources protection and soil erosion control, may have some undesirable outcomes. An important example is the effect that vegetation restoration may have in reducing surface water resources. After searching peer-reviewed articles, we selected 38 publications from 16 countries in comparable areas - semiarid conditions (aridity index <0.5), surface coverage >50% and fine soil texture - to evaluate the effectiveness of different types of vegetation (i.e., forestland, scrubland and grassland) in regulating runoff and sediment transport. In particular, we used three indices: the runoff reduction effect, the sediment reduction effect and the ratio between runoff and sediment reduction. These indices were calculated from measured data reported in the original articles. Results showed that scrubland had higher runoff reduction effect (59% in gentle slopes; 65% in steep slopes) than in grassland (39% on gentle slopes; 43% on steep slopes) and forestland (33% on gentle slopes; 51% on steep slopes). For the three types of vegetation, the sediment reduction effect was >70%. Concerning the ratios between runoff and sediment reduction, grassland showed the lowest ratios (56% on gentle slopes; 53% on steep slopes) compared to forestland (63% on gentle slopes; 65% on steep slopes) and scrubland (93% on gentle slopes; 81% on steep slopes). Our results indicate that low values of ratios between runoff and sediment reduction are the most suitable because they indicate an effective soil erosion and sediment delivery reduction but maintaining surface runoff. Overall, our study demonstrates that grassland may be the best choice for optimizing the trade-off between catchment water yield and soil conservation during the implementation of ecological restoration programs in semi-arid regions.

Effect of three artificial aging techniques on physicochemical properties and Pb adsorption capacities of different biochars.

Biochar is beneficial for soil amendment, but further research is still required on changes in its physicochemical properties during aging, especially in oxygen-containing functional groups and associated adsorption behaviors. Here, we used two different biochars, apple tree branch biochar and maize stalk biochar, and simulated the aging process by using freeze-thaw cycles, dry-wet cycles, and chemical oxidation methods. We investigated the changes in the physicochemical properties and Pb adsorption behavior of the biochars before and after aging treatments. The characterization results showed that the biochar surface structure changed after aging treatments. In general, the specific surface areas (SSAs) of the two biochars increased after chemical oxidation treatment but decreased after the other two treatments. The elemental content analyses indicated a decrease in the C content and increase in O content after artificial aging. In addition, the content of oxygen-containing functional groups in most biochars is increasing after treatment. The increase or decrease in SSA resulted in an increase or decrease in adsorption sites, respectively, thereby enhancing or reducing the adsorption capacity of the biochar. Furthermore, oxygen-containing functional groups enhanced the Pb adsorption capacity of biochar by complexation of free carboxyl and hydroxyl functional groups with Pb. Our research indicated that aging can lead to changes in the Pb adsorption capacity of biochar and that these changes vary depending on the type of aging and biochar. Our results will help to provide a better understanding of the changes in physicochemical properties and Pb adsorption capacity of biochar during the aging process in soil toward making full use of biochar for soil amendment.

Grazing exclusion promotes grasses functional group dominance via increasing of bud banks in steppe community.

To understand the bud banks response to grazing exclusion, we conducted a demographic experiment in long-term grazing exclusion (20 year and 30 year) typical steppe. Results showed that grass functional group constituted the vast majority of the aboveground vegetation and belowground bud bank in all treatments. Long-term grazing exclusion significantly increased total aboveground biomass (2.5 and 2.6 times in 20y and 30y grazing exclusion grasslands, respectively), and decreased total stem density (31% and 37% in 20y and 30y grazing exclusion grasslands, respectively). Grazing exclusion for 20 and 30 years increased grass aboveground biomass respectively by 6.0 and 8.0 times, and decreased grass stem density by 38% and 33%. Grazing exclusion had different effects on belowground bud density of grass and forb functional group. Long-term grazing exclusion significantly increased plant buds and bud bank size (25% and 37% in 20y and 30y grazing exclusion grasslands, respectively), especially for grass functional group (49% and 95% in 20y and 30y grazing exclusion grasslands, respectively), but had no significant effects on forb bud density. Changes of aboveground community were significantly related to changes of belowground bud bank under both grazing and grazing exclusion grasslands. The bud bank density of grass functional group was significantly positive with total (R2 = 0.33, P < 0.05) and grass aboveground biomass (R2 = 0.36, P < 0.01), while negative related with total (R2 = -0.27, P < 0.05) and grass stem density (R2 = -0.22, P < 0.05). Grazed grasslands, 20y and 30y grazing exclusion grasslands all were not meristem limited and had large reserve bud banks, which would completely replace the aboveground stem population during the growing season. These findings indicate that grazing exclusion could not only improve a large bud bank for grassland restoration but also improve the dominance of grass functional group by increasing grass belowground bud banks in typical steppe community. We propose that the belowground bud bank might be a good approach to indicating potential succession direction of aboveground community.

Studies on the reaction mechanism of Cu/SiC catalytic oxidation for degradation of methyl orange in presence of microwave.

The removal of methyl orange (MO) in a copper-loaded silicon carbide (Cu/SiC) system under microwave (MW) irradiation was studied. Cu/SiC was synthesized by employing an impregnation method and the effects of parameters such as reaction time, catalyst dosage, hydrogen peroxide (H2O2) dosage, microwave power and pH on the rate of degradation of MO were also studied. The obtained results showed that almost complete degradation was obtained in the presence of Cu/SiC catalyst within 8 min of irradiation when 100 mL of MO solution (20 mg/L), 3 ml/L of H2O2, 2 g/L of catalyst dose, 600 W of MW power, and pH 7 were applied. The Cu-bearing catalyst with H2O2 formed a Fenton-like system and the rate of generation of hydroxyl radicals (·OH) was also accelerated by subjecting to MW. From the kinetic analysis, it is revealed that the degradation of MO using the MW-Cu/SiC-H2O2 system follows the pseudo-first-order.

Synthesis of a novel magnetic Caragana korshinskii biochar/Mg-Al layered double hydroxide composite and its strong adsorption of phosphate in aqueous solutions.

Phosphate pollution of aquatic ecosystems is of great concern and requires the development of high-performance materials for effective pollution treatment. To realize efficient phosphate removal from aqueous solution, an easily separable magnetic (Fe3O4) Caragana korshinskii biochar/Mg-Al layered double hydroxide composite (denoted as FCB/MAC) was synthesized via two-step electro-assisted modification for the first time. Subsequently, the physical and chemical properties of FCB/MAC were characterized. Furthermore, the sorption mechanism for phosphate removal was investigated in detail. The results indicated that Fe3O4 and the Mg-Al layered double hydroxide were successfully embedded in the biochar matrix. Moreover, FCB/MAC exhibited a high phosphate adsorption capacity and excellent magnetic properties for easy recovery. The maximum phosphate sorption capacity of FCB/MAC was 252.88 mg g-1, which is much higher than the capacities of most magnetic phosphate adsorbents. In addition, the adsorption kinetics and isotherms indicated that phosphate adsorption by FCB/MAC was controlled by the pseudo-second-order kinetic model and the Langmuir-Freundlich isotherm model. The phosphate adsorption mechanism involves anion exchange, electrostatic attraction, and ligand exchange. After five adsorption-desorption cycles, the phosphate adsorption capacity of FCB/MAC was 25.71 mg g-1 with 51.43% removal efficiency and high recyclability. Thus, the composite prepared in this study is a promising adsorbent for phosphate removal from aqueous solution, and this work provides an excellent reference for constructing novel biochar-based phosphate adsorbents.

Phytoextraction of rhenium by lucerne (Medicago sativa) and erect milkvetch (Astragalus adsurgens) from alkaline soils amended with coal fly ash.

Coal fly ash (CFA) is an industrial waste generated in huge amounts worldwide, and the management of CFA has become an environmental concern. Recovery of valuable metals from CFA is one of the beneficial reuse options of CFA. Rhenium (Re) is one of the rarest metals in the Earth's crust and one of the most expensive metals of strategic significance in the world market. A CFA at the Jungar Thermal Power Plant, Inner Mongolia, China, contains more Re than two alkaline soils in the surrounding region. Pot experiments were undertaken to grow lucerne (Medicago sativa) and erect milkvetch (Astragalus adsurgens) in a loessial soil and an aeolian sandy soil amended with different rates (5%, 10%, 20%, and 40%) of CFA. The results show that plant growth was considerably enhanced and Re concentration in plants was significantly increased when CFA was applied to the alkaline soils at rates of ≤20%; while in some cases plant growth was also markedly enhanced by the 40% CFA treatment, which increased plant Re concentration the most of all treatments. Both lucerne and erect milkvetch showed potential for phytoextracting Re from CFA-amended alkaline soils. Using CFA for soil amendment not only offers a potential solution for the waste disposal problem of CFA, but the phytoextraction of Re by both lucerne and erect milkvetch may also bring an economic profit in the future.

Facile Hydrothermal Synthesis and Enhanced Methane Sensing Properties of Pt-Decorated ZnO Nanosheets.

Pure and Pt-decorated ZnO nanosheets were synthesized via a facile and environment-friendly hydrothermal process, and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS), respectively. Side-heated chemical gas sensors were fabricated with the synthesized ZnO based powders and their sensing properties to methane CH4, an important characteristic hydrocarbon contaminant extracted from power transformer oil with overheating or discharging fault, were systemically investigated. Interestingly, Pt decoration not only obviously increased the gas response of sensor fabricated with the synthesized ZnO nanosheets to CH4, but also effectively reduced its optimum operating temperature. Its highest response to 50 ppm of CH4 was about 63.45 at 240 °C, which was about two times larger when compared with the pure one. Meanwhile, the Pt-decorated ZnO nanosheets sensor exhibited shorter response-recovery characteristic, good linearity in low concentration range and excellent stability towards CH4. Those superior sensing features indicate the synthesized Pt-decorated ZnO nanosheets is a promising candidate for fabricating high-performance CH4 sensor.

Prediction of aboveground grassland biomass on the Loess Plateau, China, using a random forest algorithm.

Grasslands are an important component of terrestrial ecosystems that play a crucial role in the carbon cycle and climate change. In this study, we collected aboveground biomass (AGB) data from 223 grassland quadrats distributed across the Loess Plateau from 2011 to 2013 and predicted the spatial distribution of the grassland AGB at a 100-m resolution from both meteorological station and remote sensing data (TM and MODIS) using a Random Forest (RF) algorithm. The results showed that the predicted grassland AGB on the Loess Plateau decreased from east to west. Vegetation indexes were positively correlated with grassland AGB, and the normalized difference vegetation index (NDVI) acquired from TM data was the most important predictive factor. Tussock and shrub tussock had the highest AGB, and desert steppe had the lowest. Rainfall higher than 400 m might have benefitted the grassland AGB. Compared with those obtained for the bagging, mboost and the support vector machine (SVM) models, higher values for the mean Pearson coefficient (R) and the symmetric index of agreement (λ) were obtained for the RF model, indicating that this RF model could reasonably estimate the grassland AGB (65.01%) on the Loess Plateau.

Species-abundance--seed-size patterns within a plant community affected by grazing disturbance.

Seed size has been advanced as a key factor that influences the dynamics of plant communities, but there are few empirical or theoretical predictions of how community dynamics progress based on seed size patterns. Information on the abundance of adults, seedlings, soil seed banks, seed rains, and the seed mass of 96 species was collected in alpine meadows of the Qinghai-Tibetan Plateau (China), which had different levels of grazing disturbance. The relationships between seed-mass-abundance patterns for adults, seedlings, the soil seed bank, and seed rain in the plant community were evaluated using regression models. Results showed that grazing levels affected the relationship between seed size and abundance properties of adult species, seedlings, and the soil seed bank, suggesting that there is a shift in seed-size--species-abundance relationships as a response to the grazing gradient. Grazing had no effect on the pattern of seed-size-seed-rain-abundance at four grazing levels. Grazing also had little effect on the pattern of seed-size--species-abundance and pattern of seed-size--soil-seed-bank-abundance in meadows with no grazing, light grazing, and moderate grazing), but there was a significant negative effect in meadows with heavy grazing. Grazing had little effect on the pattern of seed-size--seedling-abundance with no grazing, but had significant negative effects with light, moderate, and heavy grazing, and the |r| values increased with grazing levels. This indicated that increasing grazing pressure enhanced the advantage of smaller-seeded species in terms of the abundances of adult species, seedlings, and soil seed banks, whereas only the light grazing level promoted the seed rain abundance of larger-seeded species in the plant communities. This study suggests that grazing disturbances are favorable for increasing the species abundance for smaller-seeded species but not for the larger-seeded species in an alpine meadow community. Hence, there is a clear advantage of the smaller-seeded species over the larger-seeded species with increases in the grazing level.