Although improved soil quality has been recognized for its role in alleviating crop stress, how soil microbial communities respond to extreme rainfall perturbations during critical maize growth stages remains unclear under field conditions. An 11-year field experiment was implemented in maize under two treatments, i.e., chemical fertilizer alone (CF) and combined cattle manure plus CF (CFM). Rhizosphere bacterial and fungal community mean tolerance breadth, average variation degree, and co-occurrence network were characterized shortly before and after extreme rainfall event bracketing maize silking, together with soil chemical properties, enzyme activities, and maize growth and yield. Compared to the CF control, soil fertility index increased by 265% and multi-functionality by two-fold in the CFM treatment. This at least partially contributed to the greater maize yield resistance to mid-season extreme rainfall event in the CFM treatment, as evidenced by their strong and positive correlations (R2 = 0.85, P < 0.01). Specifically, after experiencing heavy rainfall, the CFM treatment exhibited greater community mean tolerance breadth by 4.2% and reduced the average variation degree of bacterial community compared to the CF control. Soil fertility (R2 = 0.91, P < 0.01) and multifunctionality (R2 = 0.73, P < 0.01) were strongly and positively correlated with bacterial community mean tolerance breadth, but showed no significant correlation with that of fungal community. In consistent, fewer changed taxa in response to rainfall perturbations were identified in maize rhizosphere in the CFM treatment. Bacterial co-occurrence networks complexity decreased in the CF but remained stable in the CFM treatment when comparing those before and after rainfall perturbations. The fungal networks exhibited less complexity across treatments and rainfall events. Furthermore, the CFM (85 ASVs) harbored a greater number of keystone species compared to the CF (30 ASVs), most of which strongly correlated with soil fertility, multifunctionality, and maize yield resistance. The predicted microbial functional traits involved in carbon, nitrogen, and redox metabolism exhibited less changes in response to rainfall perturbations under the CFM treatment, further indicating greater functional resistance than the CF control. Overall, our findings highlighted that, under field conditions, improved soil quality and multifunctionality are associated with greater bacterial community stability against extreme rainfall events during maize critical growth stages, which potentially mitigates yield losses.

Green manure (GM) crops are widely adopted to enhance soil nitrogen (N) stocks under reduced fertilizer input. However, the microbial mechanisms governing N cycling in long-term GM-based rice systems remain insufficiently understood. Through a 31-year field experiment comparing a conventional rice-rice-winter fallow system with full fertilizer rate (F) to GM-integrated rotations (rice-rice-Chinese milk vetch or rice-rice-rapeseed rotation) with 50% fertilizer reduction (50%F + M and 50%F + R), we combined soil basic properties, enzyme activities, and microbial taxonomic and functional profiles. Despite reduced fertilizer input, both GM-inclusive treatments sustained soil total N and soil organic carbon (C), while significantly reduced nitrate reductase activity by 62.8%, pH by 8.1% and C/N ratio by 5.9% on average. The sustained N supply was associated with a functional restructuring of the microbial community, characterized by reductions of gene abundance in dissimilatory nitrate reduction to nitrate (e.g., narH and napA), to ammonia (e.g., nirB and nrfA), and particularly denitrification (norB and nosZ by 9%-17%), indicating a downregulation of N loss pathways. Random forest and correlation analyses identified the GM-induced mild but significant decrease in pH and C/N ratio as the key edaphic drivers of this shift. Lowered pH likely directly inhibited key enzymes like NrfA, while a reduced C/N ratio potentially constrained electron donor availability for energy-intensive reductive pathways. Metagenomic assembly further revealed that 13 out of the 15 bacterial MAGs had collective genes encoding enzymes for multi-step N-transformation potential. Collectively, these changes rewired the soil N cycle toward conservation, maintaining net mineralization and N availability. Our study provides a mechanistic framework for designing sustainable green manure-based cropping systems that harness synergistic soil-microbe interactions to enhance N retention and reduce reliance on synthetic inputs.

Cropping diversification, especially with legume inclusion, has been shown to improve soil organic carbon (SOC) sequestration. However, it remains unexplored how preceding intercropped leguminous green manure affect microbial activity and necromass C contribution to SOC under reduced nitrogen (N) input in subsequent crop rotations. A six-year field experiment was conducted with treatments including maize monoculture (M) and intercropping with lablab bean as green manure (M/L), followed by rapeseed (R) under zero, 100 % and 65 % of recommended N application. The treatments were designated as M-R0, M-R100, M-R65, and M/L-R65. Soils were collected from 0 to 20 cm topsoil and 20-40 cm subsoil after rapeseed harvest for analysis of SOC fractions, microbial necromass carbon (MNC), extracellular enzyme activities, and microbial community. The results showed that preceding maize/legume intercropping M/L-R65 significantly increased the content of SOC, total N, dissolved organic C and N by 14.3-34.1 % in the topsoil compared to M-R100. This increase was associated with higher microbial necromass C content driven by a shift towards K-strategy microorganisms that produce more recalcitrant necromass compounds. In contrast, subsoil SOC levels remained relatively stable in the M/L-R65, despite an increase in MNC content. The lower soil C/N and dissolved organic C/N ratios in the M/L-R65 treatment endorsed soil N enrichment-induced decomposition of particulate organic C (POC) in the subsoil. This was further corroborated by the strong and direct impacts of soil C to N stoichiometry on microbial C pools revealed by PLS-PM analysis. Microbial C use efficiency (CUE) was higher in reduced N input treatments in the subsoil, but this did not translate to increased SOC in the subsoil layer, likely due to the shift in fungal community towards r-strategists. Overall, the study suggests that preceding legume intercropping enhances SOC sequestration in the topsoil of low-N input rapeseed rotation systems through increased microbial necromass C inputs. Moreover, the responses of SOC pools across soil depths are mediated by shifts in microbial life-history strategies.

The black soil region is a crucial commercial grain production base in China. However, long-term intensive cultivation has led to increasingly prominent issues, including declining concentration of soil organic matter, water and soil erosion, and soil compaction. Green manure (also known as cover crops), as a traditional and effective soil improvement measure, possesses a long cultivation history and great development potential in Northeast China. We reviewed the current status of black soil degradation in Northeast China, analyzed the effectiveness of green manure cultivation in addressing the problems of shallow, degraded, and compacted black soil layers. Furthermore, we introduced typical green manure application modes explored in recent years across different areas of Northeast China, including green manure-corn intercropping, green manure-rotating with sweet corn, green manure for saline-alkali land, and green manure after wheat cultivation. In conclusion, green manure cultivation could significantly improve soil structure, increase soil organic matter content, reduce water and soil erosion, and enhance crop yields and ecosystem service. It represented an important approach for the coordinated development of black soil utilization and conservation.

Context: Tiller growth and development are crucial determinants of grain yields in wheat (Triticum aestivum L.). However, the impacts of tiller internode structures associated with carbon (C) and nitrogen (N) partitioning underlying tiller development and the ultimate yield have not yet been fully elucidated. Objective: To investigate the tiller internode structure in association with C and N partitioning between stems and their impacts on tiller growth and mortality and the ultimate yield. Methods: Two wheat cultivars with moderate-tillering (ZM578) and high-tillering (LY502) were grown under field conditions with zero N (N0) and 200 kg N ha-1 (N200). Wheat tillering, C and N partitioning, and the anatomical structures of tiller internodes were investigated. Results: Compared to the N200 supply, N0 suppressed tillering by 46.8 % in ZM578 at the jointing stage and by 34.7 % in LY502, indicating a more pronounced tillering response to N availability in the moderate-tillering cultivar. However, at maturity, ZM578 achieved comparable spike numbers and grain yields relative to LY502. This can be attributed to the 11.8-22.5 % lower tiller mortality rate in ZM578, which strongly depended upon the maximum tiller numbers rather than N availability. Although comparable or even lower leaf area and SPAD readings were observed, ZM578 exhibited higher photosynthetic rates compared to LY502. Moreover, ZM578 allocated a greater proportion of assimilates to the main stem and superior tillers, resulting in larger assimilate accumulation gaps between the main stem and tillers. In parallel with these findings, ZM578 displayed larger vascular bundle and phloem sizes, particularly under N-deficient conditions, primarily due to larger size of individual vascular bundle and phloem. Likewise, assimilate partitioning to late-generated tillers in ZM578 was lower than that in LY502, indicating a reduction in unnecessary assimilate consumption. Conclusion: Tiller internode structure plays a significant role in C and N partitioning, which in turn influences tiller development and the ultimate yield. Implications: The results are informative for creating high-yielding wheat populations through the selection of moderate-tillering cultivars and optimized N management.

The effects of biochar and nitrogen (N) fertilization on soil carbon (C) and nitrogen (N) have been primarily studied in topsoil layers (0-30 cm), leaving a gap in understanding their long-term impact on deeper soil layers. This study investigates the effects of biochar (0 (B0) and 9 t ha(-1) year(-1) (B+)) and nitrogen fertilization (0 (N0) and 300 kg N ha(-1) year-1 (N+)) on soil organic carbon (SOC), soil organic nitrogen (SON), microbial biomass carbon, and microbial biomass nitrogen down to 150 cm. The study was conducted over 8 years in a rice field in northwest China. Results showed that biochar application increased total SOC by 27.0% and 12.2%, with and without nitrogen fertilization, respectively. Approximately 43.5%-51.8% of SOC was stored in the top 30 cm, while significant portions were found in deeper layers, indicating substantial carbon movement beyond the surface soil. Biochar also significantly increased SON in the 105- to 150-cm depth, regardless of N fertilization. These results suggest that failing to consider deep soil layers could lead to underestimations of soil C and N storage in paddy systems. The findings highlight the importance of biochar and nitrogen fertilization for improving carbon sequestration and nutrient cycling in rice paddies, offering insights into sustainable soil management practices.

Salt stress poses a major restricting factor for sustainable agricultural development, limiting crop productivity and adversely affecting crop productivity. Grafting is a commonly used technique to improve the quality and stress resilience of horticultural crops. However, limited research has utilized grafting to explore the role of key mobile mRNAs in response to salt stress for molecular breeding applications. In this study, grafting systems were established between cotton and okra or tobacco. Through these systems, the 60S Ribosomal Protein L19-2 (RL192) mRNA was identified as a mobile molecule moved from cotton (rootstock) to okra (scion). Fluorescence quantification and beta-glucuronidase (GUS) staining analyses showed that GhRL192 expression was significantly induced by salt stress. Silencing GhRL192 in cotton significantly reduced salt stress tolerance, whereas overexpression of GhRL192 in tobacco or Arabidopsis improved seed germination and root development and the survival rate of seedlings under salt stress. This novel grafting strategy between horticultural and agricultural crops provides new insights and methodologies for studying mobile mRNAs that enhance crop stress resistance, yield, and quality. The identification and analysis of GhRL192 mRNA in relation to salt tolerance confirmed the feasibility of this approach, laying the groundwork for further exploration of transport mechanisms and molecular regulatory networks.

Ammonium (NH4+-N) is the predominant form of nitrogen (N) fertilizer, but poses a risk of NH4+ toxicity, adversely affecting plant growth. Photosynthesis, which is closely linked to biomass and yield, is inhibited by NH4+ toxicity, but this effect is alleviated with increasing supplied nitrate (NO3--N) fraction. To understand the mechanism behind NO3--N's alleviation of NH4+-N inhibition on photosynthesis, limiting factors for photosynthetic rate (A) and anatomical characteristics of Brassica napus, an essential oil crop that heavily relies on N fertilizer, were measured. Results revealed that the inhibition of NH4+-N toxicity on A and growth was aggravated under NO3--N deprivation. When the proportion of NO3--N was lower than that of NH4+-N, the decrease of A was dominated by mesophyll conductance (g(m)), with its reduction strongly correlated with increased distance between two neighbouring chloroplasts (Dchl-chl) and decreased chloroplast surface area exposed to intercellular airspace per unit leaf area (Sc). NO3--N supply promoted volume fraction of intercellular air space (f(ias)) and mesophyll surface area exposed to intercellular airspace per unit leaf area (S-m), furtherly enhancing Scand facilitating higher gm. Additionally, Dchl-chl, f(ias), and S-m were more closely related to leaf NO3--N concentration than to NH4+-N. Thus, NO3--N plays a crucial role in mitigating NH4+-N toxicity on A by regulating leaf mesophyll arrangement and morphology. Increasing the proportion of NO3--N in fertilizers provides a strategy for crops at the risk of soil NH4+-N toxicity to maintain high A, furtherly promoting yield and N use efficiency.

Harnessing beneficial plant-microbe interactions in the rhizosphere presents a promising strategy for plants to combat unfavorable environment. However, the mechanisms by which rapeseed (Brassica napus L.) genotypes regulate root-associated microbiota through root metabolites under nitrogen (N) deprivation has not been fully explored. To address this issue, we planted rapeseed genotypes with varying tolerance to N deficiency—G364, which is susceptible, and G294 and ZS11, which exhibit tolerance—under both N-starved (N0) and N-sufficient (N1) conditions in pots. As expected, G364 was the most susceptible to N deficiency, experiencing a 30.8 % reduction in dry biomass when subjected to N deprivation. In contrast, G294 exhibited the greatest tolerance to N-deficiency, with only a 14.1 % decline in biomass due to N deficiency, underscoring its superior N utilization efficiency. The rhizosphere bacterial microbiomes of these genotypes exhibited distinct patterns at the rosette stage. Under N deprivation, the bacterial classes that significantly enriched in the rhizosphere of G294 and ZS11 genotypes were Chloroflexia, Bacilli, TK10, Gammaproteobacteria, and Acidimicrobiia. These microbial enrichments were positively correlated with increased biomass and N uptake in rapeseed. Furthermore, the compositional shifts in the rhizosphere bacterial community were associated with greater intensity of metabolites like flavonoids, amines, terpenoids, steroids, hormones and transmitters etc. Taken together, our study underscores the pivotal role of root metabolites in harnessing the beneficial plant–microbe interactions, thereby potentially improving the N use efficiency of rapeseed. This insight is valuable for manipulating the rhizosphere microbiome for breeding crops aimed at developing varieties with enhanced N efficiency.

Improving the nutrient content of red soils in southern China is a priority for efficient rice production there. To assess the effectiveness of oilseed rape as green manure for the improvement of soil phosphorus nutrient supply and rice yield in red soil areas, a long-term field plot experiment was conducted comparing two species of rape, Brassica napus (BN) and Brassica juncea (BJ). The effects of returning oilseed rape on soil phosphorus availability, phosphorus absorption, and yield of subsequent rice under rice-green manure rotation mode were analyzed, using data from the seasons of 2020 to 2021. The study found that compared with winter fallow treatment (WT) and no-tillage treatment (NT), the soil available phosphorus content of BN was increased, and that of BJ was significantly increased. The content of water-soluble inorganic phosphorus of BJ increased, and that of BN increased substantially. Compared with the WT, the soil organic matter content and soil total phosphorus content of BN significantly increased, as did the soil available potassium content of BJ, and the soil total phosphorus content of BJ was significantly increased compared with NT. The soil particulate phosphorus content of BJ and BN was significantly increased by 14.00% and 16.00%, respectively. Compared with the WT, the phosphorus activation coefficient of BJ was significantly increased by 11.41%. The rice plant tiller number under the green manure returning treatment was significantly increased by 43.16% compared with the winter fallow treatment. The green manure returning measures increased rice grain yield by promoting rice tiller numbers; BN increased rice grain yield by 9.91% and BJ by 11.68%. Based on these results, returning oilseed rape green manure could augment the phosphorus nutrients of red soil and promote phosphorus availability. Rice-oilseed rape green manure rotation could increase rice grain yield.

Winter wheat production is influenced by climate extremes worldwide. Heavy precipitation induced delay of sowing generates limited photothermal resources for wheat early growth. However, how wheat build resilience from stunted seedling growth has not been fully explored. Here, a twelve-year farmers' survey of wheat yield was recorded and four-year field experiments of wheat grown in normal and late-sowing were performed under zero nitrogen (N0) and optimum nitrogen (Opt.N) supply. Wheat growth and N uptake were measured at both vegetative and reproductive stages alongside photothermal resource-use efficiency. Farmers' survey showed 10.4 % yield losses due to delayed sowing compared to the normal. However, four-year field trials revealed that the combination of increasing seeding rates and Opt.N application recovered grain yield of sowing-delayed wheat and even increased by 13.2 % compared to plants in the normal seasons. Although delayed sowing substantially suppressed seedling growth and tillering before winter dormancy, the Opt.N application increased spring tillers by 2.4-fold which were productive at maturity. Further, plant growth and N uptake from jointing to anthesis of sowing-delayed wheat were accelerated by Opt.N, but not by N0 treatment. Delayed sowing significantly shortened the duration of lag phase of grain filling by 3.5 days and by 183 growing degree days compared with the normal, which initiated the linear and fast filling earlier. Increased leaf photosynthesis by 27.4 % during grain filling further supported the fast recovery of grain filling in the sowing-delayed wheat. Concomitantly, the physiological N-use efficiency increased by 46.7 % during grain filling and by 41.5 % at maturity by enhancing N availability and seeding rates, and photothermal resource-use efficiency increased by 1.3- to 1.7-fold for wheat with delayed vs. normal sowing. Overall, these findings highlight the integrated management of nutrient and cultivation to mitigate the impacts of climate extremes on crop productivity through building plant reproductive resilience.

Maize intercropped with leguminous green manure (LGM) has been proven as a sustainable plantation practice for enhancing crop yield and soil fertility. However, a comprehensive understanding of how intercropped legumes coordinate the above- and below-ground performance during maize growth under low to high N application remains elusive. This study aimed to investigate the effects of biological C and N input on soil fertility and maize growth by regulating soil enzyme activities in maize/LGM intercropping systems. A three-year field trial was conducted in northwestern China, where maize was intercropped with two LGMs, namely common vetch and pea, under no N (N0, 0 kg ha- 1) and conventional N (N330, 330 kg ha- 1) applications. The grain yield of intercropped maize ranged from 10.54 to 11.08 t ha- 1, representing a significant increase of 6.6-12.1 % compared to monoculture maize in the N0 treatment. Nitrogen application substantially increased maize grain yield by 39.2-52.0 % across cropping systems relative to the N0 treatments, while minor differences were observed in maize yield between cropping systems in the N330 treatments. Compared with monoculture maize, intercropped with LGMs increased C input by 16.7-79.2 % at maize V9 stage and 81.1-140.3 % at the R6 stage. The biological N fixation of intercropped LGMs was 62.7-89.5 kg ha- 1 and 8.0-12.8 kg ha- 1 in the N0 and N330 treatments, respectively. Biological C and N input greatly facilitated soil enzyme activities and the associated nutrient cycling, consequently improving soil fertility. Soil organic matter and total N in the intercropping systems significantly increased by 4.4-14.3 % relative to monoculture across maize growth stages, irrespective of N levels. Furthermore, increased soil fertility was closely associated with nutrient stoichiometry, which in turn facilitated maize nutrient uptake and shoot recovery growth in the intercropping systems. Overall, these findings highlight that increased biological C and N input to belowground enhances soil C and nutrient cycling by regulating the involved enzyme activities, which in turn improves maize nutrient uptake and growth, forming a coordinated loop of C and nutrient flow in the maize and legume intercropping systems. Maize intercropped with LGMs is a sustainable practice that improves soil fertility and promotes maize growth by augmenting biological C and N input.

Increased atmospheric nitrogen (N) deposition significantly disturbs ecosystem N cycle. Although foliar interception and uptake of N deposition can provide an important alternative N supply to forest ecosystems, the mechanisms regulating foliar N uptake from wet deposition are not fully understood. Here, we selected 19 woody species with a wide range of plant traits from different functional groups and conducted a 15 N isotope labelling experiment through brushing 15 NH 4 + and 15 NO 3 − solution on canopy leaves. Our findings demonstrate that leaves can directly absorb N from wet deposition within a few hours. The average leaf 15 N recoveries were 10% and 28% under 15 NH 4 + and 15 NO 3 − treatments across species, respectively, while twig N recoveries were only 1%–7% of leaf N recoveries. Differences in foliar N uptake efficiency among species were closely associated with leaf traits but were little influenced by meteorological conditions or soil nutrient status. Specifically, plants with higher leaf N concentration, larger specific leaf area and lower wax concentration exhibited higher leaf N recovery. Our results indicated that tree canopies could directly absorb N from atmospheric deposition. We highlight the critical role of leaf traits in determining canopy foliar N uptake, which may consequently influence plant competition under elevated N deposition.

A coordinated increase in the photosynthetic rate (A) and photosynthetic nitrogen use efficiency (PNUE) is an effective strategy for improving crop yield and nitrogen (N) utilization efficiency. PNUE tends to decrease with increasing N levels, but there are natural variations. Consequently, leaf functional N partitioning in Brassica napus genotypes under different N rates was measured to explore the optimized N allocation model for synchronously increasing A and PNUE values. The results showed that genotypes whose PNUE increased with increasing N supply (PNUE-I) produced an approximate A value with a relatively low leaf N content, owing to reduced storage N (N-store) and close photosynthetic N (N-psn) content. Partial least squares path modeling showed that A was dominated by the N-psn content, and PNUE was directly influenced by A and N-store. The A value increased with the N-psn content until the N-psn content exceeded the threshold value. The boundary line of PNUE varied with the N-psn and N-store proportions, indicating that the optimum N-psn and N-store proportions were 51.6% and 40.3%, respectively. The N-store proportion of PNUE-I was closer to the thresholds and benefited from lower increments in Rubisco content and nonprotein form storage N content with improved N supply. Optimized N-store and N-psn trade-off by regulating increments in N-store content with increased N supply, thereby promoting coordinated increases in A and PNUE.

Peanut (Arachis hypogaea L.) is one of the most important crops produced worldwide. Peanut is the dominant crop in the typical upland red soil areas of China; however, phosphorus bioavailability in red soil is very low, which severely affects peanut production. To improve the phosphorus bioavailability, which substantially promotes the green development of peanut production, a peanut–green manure rotation field experiment was conducted with six treatments (milkvetch; radish; brassica rape; mustard rape; winter fallow and no-tillage), commencing in September 2017 in the red soil area of Jiangxi province, China. The results show that compared with no-tillage (NT) treatments, different green manure returning treatments had significant effects on soil pH, soil phosphorus components and available potassium content. The particulate phosphorus and soil available phosphorus contents in the green manure treatments were significantly higher than those in the winter fallow (WF) treatment. Compared with the WF treatment, the content of particulate phosphorous in brassica rape (BR), radish (R) and milkvetch (MV) treatments was significantly increased by 6.55%, 3.66% and 2.50%, respectively; the available phosphorus content in mustard rape (MR), BR, R and MV was significantly increased by 20.93%, 25.60%, 23.76% and 18.10%, respectively. In addition, the total phosphorus content of peanut shell in the MV and R treatment was significantly higher than that in the WF treatment, increasing by 33.47% and 60.66%, respectively. Compared with the WF treatment, the peanut biomass of MR, BR and R treatments increased significantly by 19.51%, 29.83% and 19.77%, respectively. The total phosphorus accumulation in all green manure treatments was higher than that in the WF treatment, and the MV treatment reached a significant level at 18.83%. Based on these results, the particulate phosphorus (PP) and available phosphorus were significantly affected by different green manure treatments; green manure amendment improves peanut phosphorus uptake. The use of green manure (especially milkvetch and brassica rape) can be recommended to improve phosphorus bioavailability and yield of peanut in red soil areas.

Intercropping cereals with legumes is considered a promising option for improving productivity and sustaining soil health. However, the long-term effects of cereal and legume intercropping on soil carbon (C) storage and the physicochemical properties of soil profiles remain elusive. In the present study, an 11-year long-term field experiment was carried out on maize monoculture with zero (control) and conventional 375 kg ha  1 nitrogen (N) application rates (N375), as well as on pea and maize intercropping with zero N (Ps) and a 20% reduction in conventional N (PsN300). The crop yield was obtained each year. The cumulative changes in organic C, bulk density, and other physicochemical properties of the top 20 cm of soil at the beginning and end of the experiment, as well as their spatial changes along the 1 m soil profile at the end, were closely investigated. Greenhouse gas emissions were estimated based on reported emission factors. Pea and maize intercropping under reduced fertilizer N application maintained maize growth and grain yield and increased land use efficiency (land equivalent ratio 1.1) relative to monoculture with farmers' N inputs. After an 11-year intercropping, soil organic C concentrations increased by 6.7-12.4% in the top 0-20 cm layer and organic C stocks increased by 8.3-17.9%, and bulk density decreased by 6.4-14.2%. Intercropped soils with optimal N application (PsN300) sequestrated 14.8% more organic C in the 0-100 cm soil profile, particularly at depths of 40 cm and below, and the bulk density decreased by 7.0% on average compared with the monoculture with farmers' N practices. Such intercropping benefits for soil organic C storage and physical properties in the 1-m profile were associated with greater soil microbial biomass C and N and dissolved organic C and N in the profile. Meanwhile, compared to farmers' N and monoculture, intercropping under reduced N fertilizer application substantially decreased nitrate residues by 30.8% and GHG emissions by 17.8% per hectare or by 15.4% per ton grain yield, which was attributed to less N input, and downregulated enzyme activities involved in soil denitrification. Overall, this study showed that intercropping peas and maize with reduced N inputs is an environmentally sound strategy that improves soil physical quality and enhances deep C storage while reducing greenhouse gas emissions.

Background Decomposition of plant biomass is vital for carbon cycling in terrestrial ecosystems. In waterlogged soils including paddy fields and natural wetlands, plant biomass degradation generates the largest natural source of global methane emission. However, the intricate process of plant biomass degradation by diverse soil microorganisms remains poorly characterized. Here we report a chemical and metagenomic investigation into the mechanism of straw decomposition in a paddy soil. Results The chemical analysis of 16-day soil microcosm incubation revealed that straw decomposition could be divided into two stages based on the dynamics of methane, short chain fatty acids, dissolved organic carbon and monosaccharides. Metagenomic analysis revealed that the relative abundance of glucoside hydrolase (GH) encoding genes for cellulose decomposition increased rapidly during the initial stage (3–7 days), while genes involved in hemicellulose decomposition increased in the later stage (7–16 days). The increase of cellulose GH genes in initial stage was derived mainly from Firmicutes while Bacteroidota contributed mostly to the later stage increase of hemicellulose GH genes. Flagella assembly genes were prevalent in Firmicutes but scarce in Bacteroidota . Wood–Ljungdahl pathway (WLP) was present in Firmicutes but not detected in Bacteroidota . Overall, Bacteroidota contained the largest proportion of total GHs and the highest number of carbohydrate active enzymes gene clusters in our paddy soil metagenomes. The strong capacity of the Bacteroidota phylum to degrade straw polymers was specifically attributed to Bacteroidales and Chitinophagales orders, the latter has not been previously recognized. Conclusions This study revealed a collaborating sequential contribution of microbial taxa and functional genes in the decomposition of straw residues in a paddy soil. Firmicutes with the property of mobility, WLP and cellulose decomposition could be mostly involved in the initial breakdown of straw polymers, while Bacteroidota became abundant and possibly responsible for the decomposition of hemicellulosic polymers during the later stage.

Stem node has been found to be a hub for controlling mineral nutrient distribution in gramineous plants. However, the characteristics of stem nodes associated with whole-plant carbon partitioning in maize (Zea mays L.) and their responses to nitrogen (N) availability remains elusive. Maize plants were grown in greenhouse under low to high N supply. Plant growth, sugar accumulation, and sugar transporters in nodes and leaves, as well as the anatomical structure of nodes, were investigated at vegetative phase. When compared to N-sufficient plants, low-N availability stunted growth and resulted in 49–64% less sugars in leaves, which was attributed to low photosynthesis or the accelerated carbon export, as evidenced by more 13C detected further below leaf tips. Invariably higher sugar concentrations were found in the stem nodes, rather than in the leaves across N treatments, indicating a crucial role of nodes in facilitating whole-plant carbon partitioning. More and smaller vascular bundles and phloem were observed in stem nodes of N-deficient plants, while higher sugar levels were found in the bottom nodes than in the upper ones. Low-N availability upregulated the gene expressions of sugar transporters, which putatively function in nodes such as ZmSWEETs and ZmSUTs at the bottom stem, but suppressed them in the upper ones, showing a developmental impact on node function. Further, greater activity of sugar transporters in the bottom nodes was associated with less sugars in leaves. Overall, these results highlighted that stem nodes may play an important role in facilitating long-distance sugar transport in maize.

Seasonal differences in plant and microbial nitrogen (N) acquisition are believed to be a major mechanism that maximizes ecosystem N retention. There is also a concern that climate change may interrupt the delicate balance in N allocation between plants and microbes. Yet, convincing experimental evidence is still lacking. Using a 15 N tracer, we assessed how deepened snow affects the temporal coupling between plant and microbial N utilization in a temperate Mongolian grassland. We found that microbial 15 N recovery peaked in winter, accounting for 22% of the total ecosystem 15 N recovery, and then rapidly declined during the spring thaw. By stimulating N loss via N2 O emission and leaching, deepened snow reduced the total ecosystem 15 N recovery by 42% during the spring thaw. As the growing season progresses, the 15 N released from microbial biomass was taken up by plants, and the competitive advantage for N shifted from microbes to plants. Plant 15 N recovery reached its peak in August, accounting for 17% of the total ecosystem 15 N recovery. The Granger causality test showed that the temporal dynamics of plant 15 N recovery can be predicted by microbial 15 N recovery under ambient snow but not under deepened snow. In addition, plant 15 N recovery in August was positively correlated with and best explained by microbial 15 N recovery in March. The lower microbial 15 N recovery under deepened snow in March reduced plant 15 N recovery by 73% in August. Together, our results provide direct evidence of seasonal differences in plant and microbial N utilization that are conducive to ecosystem N retention; however, deepened snow disrupted the temporal coupling between plant-microbial N use and turnover. These findings suggest that changes in snowfall patterns may significantly alter ecosystem N cycling and N-based greenhouse gas emissions under future climate change. We highlight the importance of better representing winter processes and their response to winter climate change in biogeochemical models when assessing N cycling under global change.

Carbon (C) quality and quantity and nitrogen (N) availability are known to play a crucial role in influencing diazotroph community structure in soils and they are commonly affected by crop residue management and fertilizer application. However, a full understanding of how C and N interactions contribute to shaping soil diazotroph communities remains elusive. An experiment comparing two different C substrates (rice straw vs. glucose) plus low to high rates of mineral N application was conducted in two paddy soils with contrasting pH (pH = 6.05 and 7.85) with Chinese milk vetch (CMV) growth. Soils were sampled during the full blooming stage of CMV and diazotroph community structure was characterized using the nifH marker gene. The results showed that the diazotroph community responded differently to C substrates (straw and glucose) depending upon the C availability. In both soils, mineral N addition decreased nifH gene copy numbers in the straw-included treatments, but not in the glucose-included soils. Compared to the straw-included soils, glucose addition resulted in less alpha-diversity of diazotroph. Meanwhile, diazotroph community structure was clustered into different groups by the C sources, and marginally affected by N levels. These results suggested that the responses of the diazotroph community to N supply were regulated by C availability. Glucose addition decreased the relative abundance of Bradyrhizobium compared to straw incorporation (16.0%-25.9% vs. 19.5%-38.2%), but significantly increased the abundance of the second most dominant genus Geobacter (12.8%-23.7% vs. 4.1%-8.7%). In addition, the diazotroph diversity and community structure were less responsive to straw, glucose and mineral N addition in the lower vs. high pH soils. Overall, the results suggest that the responses of diazotrophs to N availability rely on C availability in paddy soils, and that C substrates exert a stronger influence than mineral N application in structuring diazotroph communities.