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Background and aims: The frequent occurrence of extreme rainfall events results in soils experiencing drying–rewetting (DRW) cycles. Such rewetting can lead to a surge in soil CO2 emissions; however, the main regulatory factors involved in this priming effect are unclear. Methods: In this study, we conducted a meta-analysis using data extracted from 43 published papers, to determine the direct regulatory factors involved in the priming effect of soil CO2. Results: The results indicated that the priming effect of rewetting on soil CO2 emissions was influenced by ecosystem type, soil properties, climatic factors, and the number of DRW cycles. The priming effect was the highest in cropland but the lowest in grassland when taking flux values observed before rewetting as the control group. It was also greater in acidic soils (pH < 6.5) and soils with a high clay fraction (clay ≥ 30%) than in other soils. The effect size (lnRR) of soil CO2 emissions was exponentially related to the mean annual precipitation (MAP), and decreased with increases in MAP. In DRW experiments, the priming effect of the first rewetting on soil CO2 emissions was the largest, an effect that gradually decreased with the number of DRW cycles, before disappearing completely. Most importantly, soil moisture influenced the peak time and the pulse time of the priming effect: the greater the change in soil moisture, the longer the peak time duration; the higher the maximum soil moisture content after rewetting, the longer the pulse time duration; and the lower the initial soil moisture content, the bigger the priming effect. Conclusion: Generally, physical mechanisms, especially soil moisture, directly regulate the CO2 priming effect during DRW cycles. Thus, this study provides a theoretical basis for assessing and predicting the impact of future precipitation changes on soil carbon cycling. Future studies should also carefully monitor any changes in soil microorganisms in response to changes in soil moisture during DRW cycles, because these appear to be significantly involved in CO2 release from soils. [ABSTRACT FROM AUTHOR]

Polyploid plants often exhibit enhanced stress tolerance. Switchgrass is a perennial rhizomatous bunchgrass that is considered ideal for cultivation in marginal lands, including sites with saline soil. In this study, we investigated the physiological responses and transcriptome changes in the octoploid and tetraploid of switchgrass (Panicum virgatum L. 'Alamo') under salt stress. We found that autoploid 8× switchgrass had enhanced salt tolerance compared with the amphidiploid 4× precursor, as indicated by physiological and phenotypic traits. Octoploids had increased salt tolerance by significant changes to the osmoregulatory and antioxidant systems. The salt-treated 8× Alamo plants showed greater potassium (K+) accumulation and an increase in the K+/Na+ ratio. Root transcriptome analysis for octoploid and tetraploid plants with or without salt stress revealed that 302 upregulated and 546 downregulated differentially expressed genes were enriched in genes involved in plant hormone signal transduction pathways and were specifically associated with the auxin, cytokinin, abscisic acid, and ethylene pathways. Weighted gene co-expression network analysis (WGCNA) detected four significant salt stress-related modules. This study explored the changes in the osmoregulatory system, inorganic ions, antioxidant enzyme system, and the root transcriptome in response to salt stress in 8× and 4× Alamo switchgrass. The results enhance knowledge of the salt tolerance of artificially induced homologous polyploid plants and provide experimental and sequencing data to aid research on the short-term adaptability and breeding of salt-tolerant biofuel plants. [ABSTRACT FROM AUTHOR]

The relationship between metabolite changes and biological endpoints in response to cadmium (Cd) stress remains unclear. Fountain grass has good Cd enrichment and tolerance abilities and is widely used in agriculture and landscaping. We analyzed the metabolic responses by detecting the metabolites through UPLC-MS and examined the relationships between metabolite changes and the characteristics of morphology and physiology to different Cd stress in fountain grass. Our results showed that under Cd stress, 102 differential metabolites in roots and 48 differential metabolites in leaves were detected, with 20 shared metabolites. Under Cd stress, most of the carbohydrates in leaves and roots decreased, which contributed to the lowered leaf/root length and fresh weight. In comparison, most of the differential amino acids and lipids decreased in the leaves but increased in the roots. Almost all the differential amino acids in the roots were negatively correlated with root length and root fresh weight, while they were positively correlated with malondialdehyde content. However, most of the differential amino acids in the leaves were positively correlated with leaf length and leaf fresh weight but negatively correlated with malondialdehyde content. Metabolic pathway analysis showed that Cd significantly affects seven and eight metabolic pathways in the leaves and roots, respectively, with only purine metabolism co-existing in the roots and leaves. Our study is the first statement on metabolic responses to Cd stress and the relationships between differential metabolites and biological endpoints in fountain grass. The coordination between various metabolic pathways in fountain grass enables plants to adapt to Cd stress. This study provides a comprehensive framework by explaining the metabolic plasticity and Cd tolerance mechanisms of plants. [ABSTRACT FROM AUTHOR]

Miscanthus spp. show excellent application prospects due to its bioenergy potential and multiple ecological services. Annual N export with biomass harvest from Miscanthus, even without fertilizer supplement, do not reduce soil N levels. The question arises regarding how Miscanthus can maintain stable soil N levels. Metagenomic strategies were used to reveal soil N‐cycling‐related microbiome and their functional contributions to processes of soil N‐cycling based on the comparison among the bare land, cropland, 10‐year Miscanthus × giganteus, and 15‐year Miscanthus sacchariflorus fields. The results showed that, after long‐term cropland‐to‐Miscanthus conversion (LCMC), 16 of 21 bacterial phyla and all the archaeal phyla exhibited significant changes. Soil microbial denitrification and nitrification functions were significantly weakened, and N fixation (NF) was significantly enhanced. The biosynthesis of amino acids, especially alanine, aspartate, and glutamate metabolism, in soil N‐cycling‐related microbiome was dramatically promoted. The genus Anaeromyxobacter contributed largely to the NF process after LCMC. Variations in the soil available potassium, available N, organic C, and total N contents drove a functional shift of soil microbiome from cropland to Miscanthus pattern. We conclude that Miscanthus can recruit Anaeromyxobacter communities to enhance NF benefiting its biomass sustainability and soil N balance. [ABSTRACT FROM AUTHOR]

In this work, a series of phthalonitrile/hollow glass microsphere (HGM) composite foams for applications in the high temperature and flame retardant fields were prepared and characterized. First, Blends of bisphthalonitrile (CN) and alicyclic imide compounds synthesized from tetrahydrophthalic anhydride (CC) were prepared and sieved (>100 mesh), based on the Thermal Synergistic Polymerization (TSP) effect between phthalonitrile and the alicyclic imide compounds, namely, the -C≡N of the phthalonitrile compound could be completely and rapidly consumed. Then thermogravimetric analysis and rheological behaviors of different molar ratios of CC/CN blend at different temperatures were investigated. HGM were modified using a silane coupling agent (KH550) to improve the interface interaction between HGM and the resin, thereby improving the properties of composite foam. Finally, a series of composite foams were fabricated and characterized. The performance of the foam prepared by BMC method is much better than that of the foam prepared by “RTM” method. The foam (BMC) shows a density of 0.47 g/cm3 with no obvious volume change and little voids, also exhibits good thermal stability up to 400 °C and low thermal conductivity, and provides UL94 V0-rated flame retardancy with total HR of 21.5 KJ/g.

Revegetation with herbaceous plants has been effective in neutralizing land degradation; however, there is limited understanding about the water use characteristics and influences on soil water dynamics of revegetated species for ecological restoration. Hence, the stable isotopic composition of xylem water, soil water and groundwater was measured to investigate the water uptake patterns of Bromus inermis and Medicago sativa in the semi-arid agro-pasture ecotone in North China. Based on hierarchical clustering analysis of soil volumetric water content (SWC), soil was classified into four layers (0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm) as different water sources. The main sources for Bromus inermis were from 20–30 cm (27.0%) and groundwater (24.2%) in May, to 0–5 cm (33.9%) and 5–10 cm (26.8%) in June, became groundwater (54.7%) in July, and then to 10–20 cm and 20–30 cm in August (23.2% and 20.6%) and September (35.1% and 32.1%). Medicago sativa were from groundwater (52.9%) and 20–30 cm (32.4%) in May, to 0–5 cm in June (61.0%), July (39.9%), August (47.6%), and then to 5–10 cm (77.8%) in September. Regression analysis showed a negative relationship between SWC and contribution of water uptake (CWU) (CWU = −2.284 × SWC + 60.833), when the difference in water isotopes was small among soil layers. Finally, the two grassland types showed distinct soil water dynamics shaped by species-specific water use strategies and associated soil pore properties. These results indicate that water use characteristics are species specific and a species combination with less water competition is recommended for sustainable revegetation of degraded land. [ABSTRACT FROM AUTHOR]

Different vegetation restoration methods may affect the soil's physicochemical properties and microbial communities. However, it is not known how the microbial network's complexity of the bacterial and fungal communities respond to short-term vegetation restoration. We conducted a short-term ecological restoration experiment to reveal the response of the soil's microbial community and microbial network's stability to initial vegetation restoration during the restoration of the degraded grassland ecosystem. The two restoration methods (sowing alfalfa (Medicago sativa, AF) and smooth brome (Bromus inermis, SB)) had no significant effect on the alpha diversity of the fungal community, but the SB significantly increased the alpha diversity of the soil surface bacterial community (p < 0.01). The results of NMDS showed that the soil's fungal and bacterial communities were altered by a short-term vegetation restoration, and they showed that the available phosphorus (AP), available potassium (AK), and nitrate nitrogen (nitrate-N) were closely related to changes in bacterial and fungal communities. Moreover, a short-term vegetation restoration significantly increased the complexity and stability of fungi ecological networks, but the opposite was the case with the bacteria. Our findings confirm that ecological restoration by sowing may be favorable to the amelioration of soil fungi complexity and stability in the short-term. Such findings may have important implications for soil microbial processes in vegetation recovery. [ABSTRACT FROM AUTHOR]

Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] has become the most widely cultivated warm-season turfgrass in northern China because of its low-maintenance requirements. Nitrogen (N) can be applied to plants in a range of formulations. However, preference of nitrogen uptake and the effects of N form on plant growth and nitrogen accumulation has not been established in buffalograss. In this study, we evaluated the effects of different inorganic nitrogen forms (NO3−-N, NH4+-N, and NO3−-N: NH4+-N = 1:1) on growth and nitrogen accumulation in buffalograss seedlings. Results showed that supply of three N forms significantly increased buffalograss seedlings growth, biomass, and N contents of all plant organs compared with the seedlings receiving free nitrogen. Plants achieved better growth performance when they received nitrate as the sole N source, which stimulated stolon growth and increased the biomass of ramets, spacers, and aboveground and total plant biomass, and also allocated more biomass to ramets and more N to spacers. Meanwhile, those plants supplied with the treatment +NH4NO3 displayed a significantly greater N content in the ramet, 15N abundance, and 15N accumulation amount in all organs. These data suggest NO3−-N supplied either singly or in mixture increased vegetative propagation and thus facilitates buffalograss establishment. However, applications of ammonium caused detrimental effects on buffalograss seedlings growth, but +NO3− could alleviate NH4+-induced morphological disorders. Thus, recommendations to increase vegetative propagation and biomass accumulation in buffalograss seedlings should consider increasing NO3−-N in a fertility program and avoiding applications of nitrogen as NH4+-N. [ABSTRACT FROM AUTHOR]

Carbon (C) and nitrogen (N) coupling processes in terrestrial ecosystems have the potential to modify the sensitivity of the global C cycle to climate change. But the degree to which C–N interactions contribute to the sequestration of terrestrial ecosystem C (Cseq), both now and in the future, remains uncertain. In this study, we used a meta-analysis to quantitatively synthesize C and N responses from field experiments on grasslands subjected to simulated warming and assessed the relative importance of three properties (changes in ecosystem N amount, redistribution of N among soil, litter and vegetation, and modifications in the C:N ratio) associated with grassland Cseq in response to warming. Warming increased soil, litter and vegetation C:N ratios and approximately 2% of N shifted from the soil to vegetation and litter. Warming-induced grassland Cseq was the result of the net balance between increases in vegetation and litter C (111.2 g m−2) and decreases in soil C (30.0 g m−2). Warming-induced accumulation of C stocks in grassland ecosystems indicated that the three processes examined were the main contributors to Cseq, with the changes in C:N ratios in soil, litter and vegetation as the major contributors, followed by N redistribution, whilst a decrease in total N had a negative effect on Cseq. These results indicate that elevated temperatures have a significant influence on grassland C and N stocks and their coupling processes, suggesting that ecological models need to include C–N interactions for more accurate predictions of future terrestrial C storage. [ABSTRACT FROM AUTHOR]

The bioenergy crop switchgrass (Panicum virgatum L.) has been recognized as friendly to the soil of cultivated land depending on the previous land use types and management practices. However, the effects of switchgrass establishment on soil properties at a broader depth when it is harvested annually without any fertilization in northern China largely remain unknown. To explore the impacts of unfertilized switchgrass on soil physical and chemical properties, 0–100 cm soil samples were collected from 7-year cropland-to-switchgrass conversion and the bare land (control). The results showed that switchgrass establishment increased soil total and capillary porosity, CFU numbers of the microbial communities (fungi, bacteria, and actinomycetes), contents of microbial biomass (carbon, nitrogen, and phosphorus), and water-soluble organic carbon, and decreased soil bulk density, mostly at 0–60 cm depths, compared to the control values. Notably, the annual harvest of switchgrass insignificantly increased soil total and available nitrogen contents and slightly reduced available phosphorus and potassium contents. In conclusion, long-term cropland conversion to unfertilized switchgrass could ameliorate soil properties and does not cause soil depletion. The output of this study could inspire governments and farmers to make large-scale use of switchgrass in the ecological restoration of abandoned cropland in north China. [ABSTRACT FROM AUTHOR]

The turfgrass species Carex rigescens has broad development and utilization prospects in landscaping construction. However, seed dormancy and a low germination rate have inhibited its application. Furthermore, the molecular mechanisms of seed germination in C. rigescens have not been thoroughly studied. Therefore, in the present study, PacBio full-length transcriptome sequencing combined with Illumina sequencing was employed to elucidate the germination mechanism of C. rigescens seeds under variable temperatures. In general, 156,750 full-length non-chimeric sequences, including those for 62,086 high-quality transcripts, were obtained using single-molecule long read sequencing. In total, 40,810 high-quality non-redundant, 1,675 alternative splicing, 28,393 putative coding sequences, and 1,052 long non-coding RNAs were generated. Based on the newly constructed full-length reference transcriptome, 23,147 differentially expressed genes were identified. We screened four hub genes participating in seed germination using weighted gene co-expression network analysis. Combining these results with the physiological observations, the important roles of sucrose and starch metabolic pathways in germination are further discussed. In conclusion, we report the first full-length transcriptome of C. rigescens , and investigated the physiological and transcriptional mechanisms of seed germination under variable temperatures. Our results provide valuable information for future transcriptional analyses and gene function studies of C. rigescens. [ABSTRACT FROM AUTHOR]

The recretohalophyte Karelinia caspia is of forage and medical value and can remediate saline soils. We here assess the contribution of primary/secondary metabolism to osmotic adjustment and ROS homeostasis in Karelinia caspia under salt stress using multi‐omic approaches. Computerized phenomic assessments, tests for cellular osmotic changes and lipid peroxidation indicated that salt treatment had no detectable physical effect on K. caspia. Metabolomic analysis indicated that amino acids, saccharides, organic acids, polyamine, phenolic acids, and vitamins accumulated significantly with salt treatment. Transcriptomic assessment identified differentially expressed genes closely linked to the changes in above primary/secondary metabolites under salt stress. In particular, shifts in carbohydrate metabolism (TCA cycle, starch and sucrose metabolism, glycolysis) as well as arginine and proline metabolism were observed to maintain a low osmotic potential. Chlorogenic acid/vitamin E biosynthesis was also enhanced, which would aid in ROS scavenging in the response of K. caspia to salt. Overall, our findings define key changes in primary/secondary metabolism that are coordinated to modulate the osmotic balance and ROS homeostasis to contribute to the salt tolerance of K. caspia. [ABSTRACT FROM AUTHOR]

Aim: Planted forests are becoming increasingly common world‐wide for a variety of reasons, including water conservation and carbon sequestration, although the effects of tree plantations on biodiversity are unclear with respect to whether planted ecosystems are "green deserts" or valuable habitats for biodiversity. Location: Global. Time period: 1980–2020. Taxa studied: Flora, fauna and microorganisms. Methods: By conducting a meta‐analysis of 361 observations from 138 sites world‐wide, we explored the global patterns and associated drivers of biodiversity responding to tree plantations by comparing biodiversity levels in plantations and adjacent habitats (primary or secondary forests). Results: Overall, the biodiversity (species richness) and abundance across multitrophic levels in tree plantations were lower than those in primary forests, reached similar values to secondary succession, but varied with plantation and management regimes. Specifically, the biodiversity across multitrophic levels in reforestation was higher than that in afforestation; the biodiversity in mixed, native species and unmanaged plantations was higher than that in monoculture, exotic species and managed plantations. The diversity of vertebrates, invertebrates and plants in reforestation was lower than that in primary forests, whereas belowground biodiversity in reforestation showed no difference from primary forests. Invertebrate diversity in reforestation was lower than that in secondary succession, whereas plant diversity was higher than that in secondary succession. Moreover, the biodiversity in reforestation increased with reforestation age. Furthermore, structural equation models showed that aboveground faunal diversity in reforestation was driven by canopy coverage and plant diversity and that reforestation affected belowground biodiversity mainly by changing soil organic carbon. Main conclusions: Our findings suggest that reforestation by planting mixed native species will be more beneficial to biodiversity. We reveal that biodiversity in intensively managed plantations is significantly lower than that in restoration‐oriented plantations. We highlight that primary forests are not replaceable, but that planted forests might be a reliable way to restore biodiversity rapidly. [ABSTRACT FROM AUTHOR]

Miscanthus × giganteus has attracted much attention and occupied a significant niche as a bioenergy crop to meet the world's energy demand and in the fight against climate change. In this study, a field experiment was conducted to evaluate the yield and biomass characteristics of M. × giganteus over a period of three years from 2013 to 2015 in Beijing, China. M. × giganteus plants showed higher tiller density and litter leaf weight in the third year, whereas no significant difference in plant height was observed among the years. In contrast, a larger number of nodes per plant were recorded in the first year. Biomass yield potential was the highest in the third year (42.3 t ha−1). In addition, plant height (r =.594, p =.042), tiller density (r =.854, p <.01), and number of nodes per plant (r = ‐.589, p =.044) were significantly correlated with biomass yield. Contents of cellulose and lignin were higher in stems, while that of hemicellulose and ash were higher in leaves. M. × giganteus biomass may be used for cellulosic ethanol conversion due to high cellulose and hemicellulose contents and low lignin content and for direct combustion and co‐combustion due to high calorific value (18.5 MJ kg−1). To conclude, our findings indicate that M. × giganteus can be cultivated in northern China as an excellent herbaceous bioenergy crop. Rational utilization of the agronomic characteristics would be helpful to screening and breeding bioenergy grass for promoting bioenergy production in China. Core ideas: Miscanthus × giganteus is suitable for cultivation in northern China.Agronomic traits were significantly correlated with biomass yield.Biomass yield of M. × giganteus increased over a period of three years.Biomass quality exhibited better suitability for ethanol production.High calorific value may be used for direct combustion and co‐combustion. [ABSTRACT FROM AUTHOR]

Pheophytinase (PPH), the phytol hydrolase, plays important roles in chlorophyll degradation. Nevertheless, little attention has been paid to the PPHs in warm-season grass species; neither its detailed function in photosynthesis has been systematically explored to date. In this study, we isolated ZjPPH from Zoysia japonica , an excellent warm-season turfgrass species. Quantitative real-time PCR analysis and promoter activity characterization revealed that the expression of ZjPPH could be induced by senescence, ABA, and dark induction. Subcellular localization observation proved that ZjPPH was localized in the chloroplasts. Overexpression of ZjPPH accelerated the chlorophyll degradation and rescued the stay-green phenotype of the Arabidopsis pph mutant. Moreover, ZjPPH promoted senescence with the accumulation of ABA and soluble sugar contents, as well as the increased transcriptional level of SAG12 and SAG14. Transmission electron microscopy investigation revealed that ZjPPH caused the decomposition of chloroplasts ultrastructure in stable transformed Arabidopsis. Furthermore, chlorophyll a fluorescence transient measurement analysis suggested that ZjPPH suppressed photosynthesis efficiency by mainly suppressing both photosystem II (PSII) and photosystem I (PSI). In conclusion, ZjPPH plays an important role in chlorophyll degradation and senescence. It could be a valuable target for genetic editing to cultivate new germplasms with stay-green performance and improved photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

Miscanthus spp. are increasingly cultivated in cropland worldwide due to their bioenergy potential and multiple ecological services. Effects of long‐term cropland‐to‐Miscanthus conversion without N fertilizer on soil microbiome and N cycling largely remain unknown. We aimed to explore the effects of Miscanthus conversion on soil microbiome and N cycling over a 15‐year period. We analyzed diversity, composition, and abundance of bacterial and archaeal communities using 16S rRNA amplicon sequencing, and abundances of N‐cycling‐related genes using quantitative polymerase chain reaction of 0–10 cm soils collected from bare land, cropland, 10‐year Miscanthus × giganteus, and 15‐year Miscanthussacchriflorus land in Beijing. Conversion decreased soil sand and micro‐aggregate proportion, nitrate N (NiN), available phosphorus levels, conductivity, temperature, and pH, while increasing proportion of soil clay and macro‐aggregate (MAA), soil organic C (SOC), available N (AN), exchangeable Mg2+ (EMg2+), and available potassium (AK) contents as well as microbial C/N. Consequently, diversity, composition, and abundance of soil bacterial community exhibited larger changes than those values of archaeal community after conversion. Soil AP, EMg2+, AK, and SOC were key factors in shifting microbiome from the cropland to Miscanthus pattern. Moreover, abundances of bacterial and archaeal communities and the N fixer gene nifH increased, whereas that of the bacterial ammonia monooxygenase gene decreased. The copies of other N‐cycling‐related genes in the two Miscanthus lands seemed similar to those values of cropland. The nifH copies negatively correlated with soil NiN and positively correlated with AN, EMg2+, ECa2+, SOC, AK, and MAA. We conclude that changes in soil microbiome pattern induced by the variation of soil properties enhance microbial N fixation potential, maintaining stable N levels and robust N cycling with lower N leakage risk after conversion. These results should inspire farmers and governments to large‐scale use Miscanthus on marginal cropland in Northern China. [ABSTRACT FROM AUTHOR]