Rhizobia cystathionine γ-lyase-derived H2S delays nodule senescence in soybean.

Hydrogen sulphide (H2S) is required for optimal establishment of soybean (Glycine max)-Sinorhizobium fredii symbiotic interaction, yet its role in regulating the nitrogen fixation-senescence transition remains poorly understood. A S. fredii cystathionine γ-lyase (CSE) mutant deficient in H2S synthesis showed early nodule senescence characterized by reduced nitrogenase activity, structural changes in nodule cells, and accelerated bacteroid death. In parallel, the CSE mutant facilitated the generation of reactive oxygen species (ROS) and elicited antioxidant responses. We observed that H2S-mediated persulfidation of cysteine C31/C80 in ascorbate peroxidase (APX) and C32 in APX2 modulated enzyme activity, thereby participating in hydrogen peroxide (H2O2) detoxification and delaying nodule senescence. Comparative transcriptomic analysis revealed a significant up-regulation of GmMYB128, an MYB transcription factor (TF), in the CSE mutant nodules. Functional analysis through overexpression and RNAi lines of GmMYB128 demonstrated its role as a positive regulator in nodule senescence. MYB128-OE inoculated with the CSE mutant strain exhibited a reduction in nitrogenase activity and a significant increase in DD15 expression, both of which were mitigated by NaHS addition. Changes at the protein level encompassed the activation of plant defenses alongside turnover in carbohydrates and amino acids. Our results suggest that H2S plays an important role in maintaining efficient symbiosis and preventing premature senescence of soybean nodules.

Broad environmental adaptation of abundant microbial taxa in Robinia pseudoacacia forests during long-term vegetation restoration.

Vegetation restoration has significant impacts on ecosystems, and a comprehensive understanding of microbial environmental adaptability could facilitate coping with ecological challenges such as environmental change and biodiversity loss. Here, abundant and rare soil bacterial and fungal communities were characterized along a 15-45-year chronosequence of forest vegetation restoration in the Loess Plateau region. Phylogenetic-bin-based null model analysis (iCAMP), niche breadth index, and co-occurrence network analysis were used to assess microbial community assembly and environmental adaptation of a Robinia pseudoacacia plantation under long-term vegetation restoration. The drift process governed community assembly of abundant and rare soil fungi and bacteria. With increasing soil total phosphorus content, the relative importance of drift increased, while dispersal limitation and heterogeneous selection exhibited opposite trends for abundant and rare fungi. Rare soil fungal composition dissimilarities were dominated by species replacement processes. Abundant microbial taxa had higher ecological niche width and contribution to ecosystem multifunctionality than rare taxa. Node property values (e.g., degree and betweenness) of abundant microbial taxa were substantially higher than those of rare microbial taxa, indicating abundant species occupied a central position in the network. This study provides insights into the diversity and stability of microbial communities during vegetation restoration in Loess Plateau. The findings highlight that abundant soil fungi and bacteria have broad environmental adaptation and major implications for soil multifunctionality under long-term vegetation restoration.

The impact of vegetation reconstruction on soil erosion in the Loess plateau.

Vegetation restoration not only extensively reshapes spatial land use patterns but also profoundly affects the dynamics of runoff and sediment loss. However, the influence of vegetation restoration on runoff and sediment yield from a regional perspective are scarce. This study therefore focused on 85 sites within the "Grain for Green" Project (GGP) region on the Loess Plateau, to investigate the impacts of the GGP on soil erosion. The results revealed a notable reduction in sediment loss and runoff due to vegetation restoration. Since the inception of the GGP in 1999, approximately 4.1 × 106 ha of degraded lands have been converted into forestlands, shrublands, and grasslands, resulting in an average annual reduction of 1.4 × 109 m3 in runoff and a decrease of 3.6 × 108 t in annual sediment loss on the whole Loess Plateau, with the GGP contributing approximately 26.7% of the sediment reduction in the Yellow River basin. The reduced soil erosion has mainly been regulated by vegetation cover, soil properties (clay, silt, and sand), slope, and precipitation on the Loess Plateau. The insights gained offer valuable contributions to large-scale assessments of changes in soil erosion in response to vegetation reconstruction and enhance our understanding of the spatial configurations associated with soil erosion control measures.

Effects of co-application of biochar and nitrogen fertilizer on soil profile carbon and nitrogen stocks and their fractions in wheat field.

Applying biochar to nitrogen (N)-fertilized soils is recognized as an effective technique for enhancing soil carbon (C) accumulation and improving agroecosystem sustainability. However, the impact of co-application of biochar and N fertilizer on soil C and N stocks, as well as their fractions, within the 0-60 cm soil profile remains unclear. This study examined the soil C and N fractions as well as stocks in soil profiles, and the primary influencing factors in wheat field with different rates of biochar (0, 20 and 40 t ha-1; B0, B1 and B2) and N application (0, 180 and 360 kg N ha-1; N0, N1 and N2). The results revealed that compared to B0N0 treatment, biochar plus N application increased soil organic carbon (SOC) and dissolved organic carbon (DOC), while N application alone decreased microbial biomass carbon (MBC). SOC in topsoil (0-10 cm) and DOC in subsoil (40-60 cm) were more susceptible to biochar and N application. The combined application of biochar and N enhanced soil N fractions, with NO3--N having the highest sensitivity than the other N fractions, whereas biochar application alone decreased topsoil inorganic N content. Biochar and N application significantly altered soil C stocks (4.33%-42.20%) and N stocks (-1.24%-20.91%) within the 0-60 cm soil layers, and belowground biomass and SOC were the main influencing factors, respectively. The combination of moderate biochar (42.35 t ha-1) and N (277.78 kg ha-1) application was the most beneficial for soil C accumulation in the 0-60 cm depth. These findings indicate the positive impacts of co-applying of biochar and N in agroecosystems on soil C and N accumulations, and highlight the importance of C and N stabilization in both topsoil and subsoil under management practice.

H2 S works synergistically with rhizobia to modify photosynthetic carbon assimilation and metabolism in nitrogen-deficient soybeans.

Hydrogen sulfide (H2 S) performs a crucial role in plant development and abiotic stress responses by interacting with other signalling molecules. However, the synergistic involvement of H2 S and rhizobia in photosynthetic carbon (C) metabolism in soybean (Glycine max) under nitrogen (N) deficiency has been largely overlooked. Therefore, we scrutinised how H2 S drives photosynthetic C fixation, utilisation, and accumulation in soybean-rhizobia symbiotic systems. When soybeans encountered N deficiency, organ growth, grain output, and nodule N-fixation performance were considerably improved owing to H2 S and rhizobia. Furthermore, H2 S collaborated with rhizobia to actively govern assimilation product generation and transport, modulating C allocation, utilisation, and accumulation. Additionally, H2 S and rhizobia profoundly affected critical enzyme activities and coding gene expressions implicated in C fixation, transport, and metabolism. Furthermore, we observed substantial effects of H2 S and rhizobia on primary metabolism and C-N coupled metabolic networks in essential organs via C metabolic regulation. Consequently, H2 S synergy with rhizobia inspired complex primary metabolism and C-N coupled metabolic pathways by directing the expression of key enzymes and related coding genes involved in C metabolism, stimulating effective C fixation, transport, and distribution, and ultimately improving N fixation, growth, and grain yield in soybeans.

C:N:P stoichiometry of plants, soils, and microorganisms: Response to altered precipitation.

Precipitation changes modify C, N, and P cycles, which regulate the functions and structure of terrestrial ecosystems. Although altered precipitation affects above- and belowground C:N:P stoichiometry, considerable uncertainties remain regarding plant-microbial nutrient allocation strategies under increased (IPPT) and decreased (DPPT) precipitation. We meta-analyzed 827 observations from 235 field studies to investigate the effects of IPPT and DPPT on the C:N:P stoichiometry of plants, soils, and microorganisms. DPPT reduced leaf C:N ratio, but increased the leaf and root N:P ratios reflecting stronger decrease of P compared with N mobility in soil under drought. IPPT increased microbial biomass C (+13%), N (+15%), P (26%), and the C:N ratio, whereas DPPT decreased microbial biomass N (-12%) and the N:P ratio. The C:N and N:P ratios of plant leaves were more sensitive to medium DPPT than to IPPT because drought increased plant N content, particularly in humid areas. The responses of plant and soil C:N:P stoichiometry to altered precipitation did not fit the double asymmetry model with a positive asymmetry under IPPT and a negative asymmetry under extreme DPPT. Soil microorganisms were more sensitive to IPPT than to DPPT, but they were more sensitive to extreme DPPT than extreme IPPT, consistent with the double asymmetry model. Soil microorganisms maintained stoichiometric homeostasis, whereas N:P ratios of plants follow that of the soils under altered precipitation. In conclusion, specific N allocation strategies of plants and microbial communities as well as N and P availability in soil critically mediate C:N:P stoichiometry by altered precipitation that need to be considered by prediction of ecosystem functions and C cycling under future climate change scenarios.

Effects of vegetation restoration types on soil nutrients and soil erodibility regulated by slope positions on the Loess Plateau.

Soil degradation is significantly increased driven by soil nutrient loss and soil erodibility, thus, hampering the sustainable development of the ecological environment and agricultural production. Vegetation restoration has been widely adopted to prevent soil degradation given its role in improving soil nutrients and soil erodibility. However, it is unclear which vegetation type has the best improving capacity from soil nutrient and soil erodibility perspectives. This study selected three vegetation restoration types of grasslands (GL), shrublands (SL), and forestlands (FL) along the five slope positions (i.e., top, upper, middle, lower, and foot slope), to investigate the effects of vegetation restoration types on soil nutrients and soil erodibility. All vegetation restoration types were restored for 20 years from croplands (CL). We used comprehensive soil nutrient index (CSNI) and comprehensive soil erodibility index (CSEI) formed by a weighted summation method to reflect the effect of vegetation restoration on the improving capacity of soil nutrient and erodibility. The results showed the vegetation types with the highest comprehensive soil quality index (CSQI) at the top, upper, middle, lower and foot slope were FL (1.92), FL (1.98), SL (2.15), FL (2.37) and GL (3.93), respectively. When only one vegetation type was considered on the entire slope, SL (0.59) and FL (0.59) had the highest CSNI, the SL had the lowest CSEI (0.34) and the highest CSQI (1.89). The CSNI was mainly influenced by soil structure stability index (SSSI), sand content, silt + clay particles, and CSEI was controlled by soil organic matter (SOM), macroaggregates and microaggregates. Moreover, the CSQI was influenced by pH, silt and clay content, and biome coverage (BC). The study suggested the SL were advised as the best vegetation restoration type on the whole slope from improving soil nutrients and soil erodibility.

Plant diversity enhances productivity and soil carbon storage.

Despite evidence from experimental grasslands that plant diversity increases biomass production and soil organic carbon (SOC) storage, it remains unclear whether this is true in natural ecosystems, especially under climatic variations and human disturbances. Based on field observations from 6,098 forest, shrubland, and grassland sites across China and predictions from an integrative model combining multiple theories, we systematically examined the direct effects of climate, soils, and human impacts on SOC storage versus the indirect effects mediated by species richness (SR), aboveground net primary productivity (ANPP), and belowground biomass (BB). We found that favorable climates (high temperature and precipitation) had a consistent negative effect on SOC storage in forests and shrublands, but not in grasslands. Climate favorability, particularly high precipitation, was associated with both higher SR and higher BB, which had consistent positive effects on SOC storage, thus offsetting the direct negative effect of favorable climate on SOC. The indirect effects of climate on SOC storage depended on the relationships of SR with ANPP and BB, which were consistently positive in all biome types. In addition, human disturbance and soil pH had both direct and indirect effects on SOC storage, with the indirect effects mediated by changes in SR, ANPP, and BB. High soil pH had a consistently negative effect on SOC storage. Our findings have important implications for improving global carbon cycling models and ecosystem management: Maintaining high levels of diversity can enhance soil carbon sequestration and help sustain the benefits of plant diversity and productivity.

Hydrogen sulphide alleviates iron deficiency by promoting iron availability and plant hormone levels in Glycine max seedlings.

BACKGROUND: Hydrogen sulphide (H2S) is involved in regulating physiological processes in plants. We investigated how H2S ameliorates iron (Fe) deficiency in soybean (Glycine max L.) seedlings. Multidisciplinary approaches including physiological, biochemical and molecular, and transcriptome methods were used to investigate the H2S role in regulating Fe availability in soybean seedlings. RESULTS: Our results showed that H2S completely prevented leaf interveinal chlorosis and caused an increase in soybean seedling biomass under Fe deficiency conditions. Moreover, H2S decreased the amount of root-bound apoplastic Fe and increased the Fe content in leaves and roots by regulating the ferric-chelate reductase (FCR) activities and Fe homeostasis- and sulphur metabolism-related gene expression levels, thereby promoting photosynthesis in soybean seedlings. In addition, H2S changed the plant hormone concentrations by modulating plant hormone-related gene expression abundances in soybean seedlings grown in Fe-deficient solution. Furthermore, organic acid biosynthesis and related genes expression also played a vital role in modulating the H2S-mediated alleviation of Fe deficiency in soybean seedlings. CONCLUSION: Our results indicated that Fe deficiency was alleviated by H2S through enhancement of Fe acquisition and assimilation, thereby regulating plant hormones and organic acid synthesis in plants.

Hydrogen sulfide and rhizobia synergistically regulate nitrogen (N) assimilation and remobilization during N deficiency-induced senescence in soybean.

Hydrogen sulfide (H2 S) is emerging as an important signalling molecule that regulates plant growth and abiotic stress responses. However, the roles of H2 S in symbiotic nitrogen (N) assimilation and remobilization have not been characterized. Therefore, we examined how H2 S influences the soybean (Glycine max)/rhizobia interaction in terms of symbiotic N fixation and mobilization during N deficiency-induced senescence. H2 S enhanced biomass accumulation and delayed leaf senescence through effects on nodule numbers, leaf chlorophyll contents, leaf N resorption efficiency, and the N contents in different tissues. Moreover, grain numbers and yield were regulated by H2 S and rhizobia, together with N accumulation in the organs, and N use efficiency. The synergistic effects of H2 S and rhizobia were also demonstrated by effects on the enzyme activities, protein abundances, and gene expressions associated with N metabolism, and senescence-associated genes (SAGs) expression in soybeans grown under conditions of N deficiency. Taken together, these results show that H2 S and rhizobia accelerate N assimilation and remobilization by regulation of the expression of SAGs during N deficiency-induced senescence. Thus, H2 S enhances the vegetative and reproductive growth of soybean, presumably through interactions with rhizobia under conditions of N deficiency.

Soil GHG fluxes are altered by N deposition: New data indicate lower N stimulation of the N2 O flux and greater stimulation of the calculated C pools.

The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO2 , CH4 and N2 O emissions increased by an average of 3.7%, 0.3%, 24.3% and 91.3% under N enrichment, respectively, and that the soil CH4 uptake decreased by 6.0%. Furthermore, the percentage increase in N2 O emissions (91.3%) was two times lower than that (215%) reported by Liu and Greaver (Ecology Letters, 2009, 12:1103-1117). There was also greater stimulation of soil C pools (15.70 kg C ha-1  year-1 per kg N ha-1  year-1 ) than previously reported under N deposition globally. The global N deposition results showed that croplands were the largest GHG sources (calculated as CO2 equivalents), followed by wetlands. However, forests and grasslands were two important GHG sinks. Globally, N deposition increased the terrestrial soil C sink by 6.34 Pg CO2 /year. It also increased net soil GHG emissions by 10.20 Pg CO2 -Geq (CO2 equivalents)/year. Therefore, N deposition not only increased the size of the soil C pool but also increased global GHG emissions, as calculated by the global warming potential approach.

Contrasting responses of leaf stomatal characteristics to climate change: a considerable challenge to predict carbon and water cycles.

Stomata control the cycling of water and carbon between plants and the atmosphere; however, no consistent conclusions have been drawn regarding the response of stomatal frequency to climate change. Here, we conducted a meta-analysis of 1854 globally obtained data series to determine the response of stomatal frequency to climate change, which including four plant life forms (over 900 species), at altitudes ranging from 0 to 4500 m and over a time span of more than one hundred thousand years. Stomatal frequency decreased with increasing CO2 concentration and increased with elevated temperature and drought stress; it was also dependent on the species and experimental conditions. The response of stomatal frequency to climate change showed a trade-off between stomatal control strategies and environmental factors, such as the CO2 concentration, temperature, and soil water availability. Moreover, threshold effects of elevated CO2 and temperature on stomatal frequency were detected, indicating that the response of stomatal density to increasing CO2 concentration will decrease over the next few years. The results also suggested that the stomatal index may be more reliable than stomatal density for determination of the historic CO2 concentration. Our findings indicate that the contrasting responses of stomata to climate change bring a considerable challenge in predicting future water and carbon cycles.

Hydrogen sulphide improves adaptation of Zea mays seedlings to iron deficiency.

Hydrogen sulphide (H2S) is emerging as a potential molecule involved in physiological regulation in plants. However, whether H2S regulates iron-shortage responses in plants is largely unknown. Here, the role of H2S in modulating iron availability in maize (Zea mays L. cv Canner) seedlings grown in iron-deficient culture solution is reported. The main results are as follows: Firstly, NaHS, a donor of H2S, completely prevented leaf interveinal chlorosis in maize seedlings grown in iron-deficient culture solution. Secondly, electron micrographs of mesophyll cells from iron-deficient maize seedlings revealed plastids with few photosynthetic lamellae and rudimentary grana. On the contrary, mesophyll chloroplasts appeared completely developed in H2S-treated maize seedlings. Thirdly, H2S treatment increased iron accumulation in maize seedlings by changing the expression levels of iron homeostasis- and sulphur metabolism-related genes. Fourthly, phytosiderophore (PS) accumulation and secretion were enhanced by H2S treatment in seedlings grown in iron-deficient solution. Indeed, the gene expression of ferric-phytosiderophore transporter (ZmYS1) was specifically induced by iron deficiency in maize leaves and roots, whereas their abundance was decreased by NaHS treatment. Lastly, H2S significantly enhanced photosynthesis through promoting the protein expression of ribulose-1,5-bisphosphate carboxylase large subunit (RuBISCO LSU) and phosphoenolpyruvate carboxylase (PEPC) and the expression of genes encoding RuBISCO large subunit (RBCL), small subunit (RBCS), D1 protein (psbA), and PEPC in maize seedlings grown in iron-deficient solution. These results indicate that H2S is closely related to iron uptake, transport, and accumulation, and consequently increases chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants.

Land-use conversion and changing soil carbon stocks in China's 'Grain-for-Green' Program: a synthesis.

The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the 'Grain-for-Green' Program to determine which factors were driving changes to soil organic carbon (SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0-100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0-20 cm) than in deeper soil (20-100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long-term, and therefore, the large scale of land-use change under the 'Grain-for-Green' Program will significantly increase China's C stocks.

Long-term vegetation restoration promotes lignin phenol preservation and microbial anabolism in forest plantations: Implications for soil organic carbon dynamics.

Vegetation restoration contributes to soil organic carbon (C; SOC) sequestration through the accumulation of plant and microbial residues, but the mechanisms underlying this microbially mediated process are not well resolved. To depict the dynamics of plant- and microbial-derived C in restored forest ecosystems, soil samples were collected from Robinia pseudoacacia plantations of different stand ages (15, 25, 35, 45 years old) established on degraded wheat fields. The results showed that the degree of lignin phenol oxidation decreased with increasing stand age (P < 0.05), and hemicellulose-degrading genes were detected at higher relative abundances than other functional gene categories, indicating selective preservation of recalcitrant lignin phenols. Despite both glucosamine (R2 = 0.61, P < 0.001) and muramic acid (R2 = 0.37, P < 0.001) contents trending upward over time, fungal residual C accounted for a greater proportion of SOC compared with bacterial residual C. Accordingly, fungal residual C, which exhibited a similar response pattern as total microbial residual C to vegetation restoration, was considered a major contributor to the SOC pool. These results provided evidence that long-term vegetation restoration enhanced SOC sequestration in R. pseudoacacia forest by promoting the preservation of plant-derived lignin phenols and concomitant microbial anabolism. Partial least squares-discriminant analysis identified two important ecological clusters (i.e., modules) in the fungal network that profoundly influenced lignin phenol oxidation (P < 0.05) and microbial residual C accumulation (P < 0.01). Among the dominant taxa in microbial networks, the bacterial phyla Proteobacteria and Acidobacteriota had potential to degrade recalcitrant C compounds (e.g., cellulose, lignin), whereas the fungal phylum Ascomycota could outcompete for labile C fractions (e.g., dissolved organic C). Findings of this study can enable a mechanistic understanding of SOC stability driven by microbial turnover in restored forest ecosystems.

Revealing nutrient limitation status of microorganisms in the soil of Robinia pseudoacacia plantation through soil stoichiometry and enzyme metrology.

Exploring nutrient limitation in forest soil holds significant implications for forest tending and management. However, current research on nutrient limitation status of microorganisms in Robinia pseudoacacia plantations within the Loess Plateau remains insufficient. To investigate soil microbial nutrient limitation of R. pseu-doacacia plantations on the Loess Plateau, we selected R. pseudoacacia plantations with different afforestation time series (15, 25, 35, and 45 years) and a pile of barren slope cropland (control) in Yongshou County, Shaanxi Province as the research objects. We analyzed the contents of soil organic matter, total nitrogen, and total phosphorus, and the activities of ß-1,4-glucosidase (BG), cellobiose hydrolase (CBH), leucine aminopeptidase (LAP), ß-1,4-N-acetylglucoside (NAG) and phosphatase (AP). We analyzed the soil nutrient limitation by stoichiometry and enzyme metrology. The results showed a shift in soil pH from alkaline to acidic during vegetation restoration process, and that total phosphorus exhibited a gradual decrease over the course of 0 to 25 years. Soil orga-nic matter, total nitrogen and enzyme activities exhibited an increasing trend during the same time frame. However, between 25 and 45 years of age, soil total phosphorus, soil organic matter, total nitrogen, AP and LAP gradually declined while NAG, BG, and CBH initially increased and then decreased. Notably, the values of (BG+CBH)/(LAP+NAG), (BG+CBH)/AP and (LAP+NAG)/AP in R. pseudoacacia plantations were higher than the global average throughout the process of vegetation restoration. In the study area, the vector length was less than 1 and gradually increased, indicating that a progressive increase in microbial carbon limitation during the process of vegetation restoration. The vector angle exceeded 45° and exhibited an overall decreasing trend, suggesting that soil microorganisms were constrained by phosphorus (P) with a gradual deceleration of P limitation, without any nitrogen (N) limitation. The restoration of R. pseudoacacia plantation resulted in significant change in soil physical and chemical properties, while the time series of afforestation also influenced nutrient limitation of soil microorganisms.

Leaf trait responses to global change factors in terrestrial ecosystems.

Global change influences plant growth by affecting plant morphology and physiology. However, the effects of global change factors vary based on the climate gradient. Here, we established a global database of leaf traits from 192 experiments on elevated CO2 concentrations (eCO2), drought, N deposition, and warming. The results showed that the leaf mass per area (LMA) significantly increased under eCO2 and drought conditions but decreased with N deposition, whereas eCO2 levels and drought conditions reduced stomatal conductance and increased and decreased photosynthetic rates, respectively. Leaf dark respiration (Rd) increased in response to global change, excluding N deposition. Leaf N concentrations declined with eCO2 but increased with N deposition. Leaf area increased with eCO2, N deposition, and warming but decreased with drought. Leaf thickness increased with eCO2 but decreased with warming. eCO2 and N deposition enhanced plant water-use efficiency (WUE), eCO2 and warming increased photosynthetic N-use efficiency (PNUE), while N fertilization reduced PNUE significantly. eCO2 produced a positive relationship between WUE and PNUE, which were limited under drought but increased in areas with high humidity and high temperature. Trade-offs were observed between WUE and PNUE under drought, N deposition, and warming. These findings suggest that the effects of global change factors on plants can be altered by complex environmental changes; moreover, diverse plant water and nutrient strategy responses can be interpreted against the background of their functional traits.

Vegetation restoration altered the soil organic carbon composition and favoured its stability in a Robinia pseudoacacia plantation.

Soil organic carbon (SOC) stabilization is vital for the mitigation of global climate change and retention of soil carbon stocks. However, there are knowledge gaps on how SOC sources and stabilization respond to vegetation restoration. Therefore, we investigated lignin phenol and amino sugar biomarkers, SOC physical fractions and chemical structure in one farmland and four stands of a Robinia pseudoacacia plantation. We observed that the content of SOC increased with afforestation, but the different biomarkers had different contributions to SOC. Compared to farmland, the contribution of lignin phenols to SOC decreased in the plantations, whereas there was no difference among the four stand ages, likely resulting from the balance between increasing lignin derivation input and increasing lignin degradation. Conversely, vegetation restoration increased the content of microbial necromass carbon (MNC) and the contribution of MNC to SOC, mainly because microbial residue decomposition was inhibited by decreasing the activity of leucine aminopeptidase, while microbial necromass preservation was promoted by adjusting soil variables (soil water content, clay, pH and total nitrogen). In addition, vegetation restoration increased the particulate organic carbon (POC), mineral-associated organic carbon (MAOC) pools and the O-alkyl C intensify. Overall, vegetation restoration affected SOC composition by regulating lignin phenols and microbial necromass and also altered SOC stabilization by increasing the physically stable MAOC pool during late afforestation. The results of this study suggest that more attention should be given to SOC sequestration and stability during late vegetation restoration.

Inhibitors mitigate N2O emissions more effectively than biochar: A global perspective.

Farmlands receive large amounts of nitrogen (N) from anthropogenic activities, which increase N2O emissions and promote crop productivity. Inhibitor or biochar applications have proven effective in reducing N2O emissions and promoting crop yields worldwide. However, a direct comparison of the response of N2O emissions and crop yields to inhibitor and biochar applications has not been performed. Here, we conducted a meta-analysis of 787 datasets from different locations worldwide to investigate the response of N2O emissions and crop yields to inhibitor or biochar applications for different climate factors and experimental conditions and determine the key influencing factors. We found that inhibitor applications (37.4 %) resulted in larger N2O emission reductions than biochar applications (20.2 %), but there was no difference in the crop yield improvement (5.8 % and 5.4 %, respectively). Nitrification inhibitor (NI) applications reduced N2O emissions by 40.8 %, a larger reduction than that of urease inhibitor (UI) applications (24.3 %) and the combination of NI and UI applications (36.4 %); 3,4-dimethylpyrazole succinic (DMPSA) was the most effective NI in reducing N2O emissions (50.7 %). We also found that NI applications were more effective in reducing N2O emissions than biochar applications in different climates and experimental conditions (N source, N rate, cropland type, and soil texture). In addition, the N rate was the most important factor impacting N2O emissions and crop yields when inhibitors were applied, whereas the experimental duration had the largest influence on N2O emissions under biochar applications. Moreover, soil factors were also related to N2O emissions under biochar applications or inhibitor applications. Our findings indicate that inhibitors are more effective in reducing N2O emissions than biochar worldwide.

Temporal shifts in root exudates driven by vegetation restoration alter rhizosphere microbiota in Robinia pseudoacacia plantations.

Plant-soil-microbiota interactions mediated by root exudates regulate plant growth and drive rhizosphere microbial feedbacks. It remains unknown how root exudates affect rhizosphere microbiota and soil functions in the course of forest plantation restoration. The metabolic profiles of tree root exudates are expected to shift with stand age, leading to variation in rhizosphere microbiota structure, and in turn, potentially altering soil functions. To unravel the effects of root exudates, a multi-omics study was conducted using untargeted metabonomic profiling, high-throughput microbiome sequencing and functional gene array. The interactions among root exudates, rhizosphere microbiota and nutrient cycling-related functional genes were explored under 15- to 45-year-old Robinia pseudoacacia plantations in the Loess Plateau region of China. Root exudate metabolic profiles, rather than chemodiversity, markedly changed with an increase in stand age. A total of 138 age-related metabolites were extracted from a key module of root exudates. The relative contents of six biomarker metabolites, such as glucose-1-phosphate, gluconic acid and N-acetylneuraminic acid, increased distinctly over time. The biomarker taxa (16 classes) of rhizosphere microbiota varied in a time-sensitive manner, which played potential roles in nutrient cycling and plant health. Nitrospira, Alphaproteobacteria and Acidobacteria were enriched in the rhizosphere of older stands. Key root exudates influenced functional gene abundances in the rhizosphere via direct effects or indirectly through biomarker microbial taxa (e.g., Nitrososphaeria). Overall, root exudates and rhizosphere microbiota are essential for soil function maintenance in R. pseudoacacia plantation restoration.