This study assesses the effects of the atmospheric nitrogen (N) deposition on the N uptake and the long-term water-use efficiency of two C(3) plants (Agropyron cristatum and Leymus chinensis) and two C(4) plants (Amaranthus retroflexus and Setaria viridis) using N and C stable isotopes. In addition, this study explores the potential correlation between leaf N isotope (δ(15)N) values and leaf C isotope (δ(13)C) values. This experiment shows that the atmospheric N deposition has significant effects on the N uptake, δ(15)N and leaf N content (N(m)) of C(3) plants. As the atmospheric N deposition rises, the proportion and the amount of N absorbed from the simulated atmospheric deposition become higher, and the δ(15)N and N(m) of the two C(3) plants both also increase, suggesting that the rising atmospheric N deposition is beneficial for C(3) plants. However, C(4) plants display different patterns in their N uptake and in their variations of δ(15)N and N(m) from those of C(3) plants. C(4) plants absorb less N from the atmospheric deposition, and the leaf N(m) does not change with the elevated atmospheric N deposition. Photosynthetic pathways may account for the differences between C(3) and C(4) plants. This study also shows that atmospheric N deposition does not play a role in determining the δ(13)C and in the long-term water-use efficiency of C(3) and C(4) plants, suggesting that the long-term water-use pattern of the plants does not change with the atmospheric N input. In addition, this study does not observe any relationship between leaf δ(15)N and leaf δ(13)C in both C(3) and C(4) plants.

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IntroductionDrip irrigation is an efficient water-saving system used to improve crop production worldwide. However, we still lack a comprehensive understanding of maize plant senescence and its association with yield, soil water, and nitrogen (N) utilization under this system.MethodsA 3-year field experiment in the northeast plains of China was used to assess four drip irrigation systems: (1) drip irrigation under plastic film mulch (PI); (2) drip irrigation under biodegradable film mulch (BI); (3) drip irrigation incorporating straw returning (SI); and (4) drip irrigation with the tape buried at a shallow soil depth (OI), and furrow irrigation (FI) was used as the control. The plant senescence characteristic based on the dynamic process of green leaf area (GLA) and live root length density (LRLD) during the reproductive stage, and its correlation with leaf N components, water use efficiency (WUE), and N use efficiency (NUE) was investigated.ResultsPI followed by BI achieved the highest integral GLA and LRLD, grain filling rate, and leaf and root senescence rate after silking. Greater yield, WUE, and NUE were positively associated with higher N translocation efficiency of leaf protein responding for photosynthesis, respiration, and structure under PI and BI; whereas, no significant differences were found in yield, WUE, and NUE between PI and BI. SI effectively promoted LRLD in the deeper 20- to 100-cm soil layers, prolonged the GLA and LRLD persistent durations, and reduced the leaf and root senescence rates. The remobilization of non-protein storage N was stimulated by SI, FI, and OI, which made up for the relative inadequacy of leaf N.DiscussionInstead of persistent GLA and LRLD durations and high translocation efficiency of non-protein storage N, fast and large protein N translocation from leaves to grains under PI and BI was found to facilitate maize yield, WUE, and NUE in the sole cropping semi-arid region, and BI was recommend considering that it can reduce plastic pollution.

High yields and low carbon emissions are new challenges for modern crop production. Balancing the crop yield and reducing greenhouse gas (GHG) emissions has become a new field of agronomic technology innovation. Cereal–legume intercropping is a typical diversification planting system, which has been expected to achieve the dual goals of high production and low GHG emissions. However, the synergistic effect of integrating various technologies in an intercropping system on GHG emissions and whether it will achieve the high yield and low emissions goal remains to be determined. Therefore, bibliometric analysis has investigated the worldwide development trend of cereal–legume intercropping designs. The literature on the GHG emissions of the cereal–legume intercropping system was summarized. Additionally, the effects and mechanisms of different agricultural management methods regarding soil nitrous oxide and carbon dioxide emissions in the cereal–legume intercropping system were summarized. The research on GHG emissions of cereal–legume intercropping systems in non-growing seasons must be revised. In situ observations of GHG emissions from intercropping systems in different regions should be strengthened. This work is valuable in supporting and evaluating the potential of GHG reduction in a cereal–legume intercropping system in various farming areas.

As essential approaches for conservation agricultural practices, straw residue retention and crop rotation have been widely used in the Mollisols of Northeast China. Soil organic carbon, root development and microbial community are important indicators representing soil, crop and microbiota, respectively, and these factors work together to influence soil fertility and crop productivity. Studying their changes and interactions under different conservation practices is crucial to provide a theoretical basis for developing rational agricultural practices. The experiment in this study was conducted using the conventional practice (continuous maize without straw retention, C) and three conservation practices, namely, continuous maize with straw mulching (CS), maize–peanut rotation (R), and maize–peanut rotation with straw mulching (RS). Straw mulching (CS) significantly increased soil total organic carbon (TOC), active organic carbon (AOC), and microbial biomass carbon (MBC), but did not promote maize yield. Maize–peanut rotation (R and RS) significantly increased dissolved organic carbon (DOC) in the rhizosphere by promoting root growth, and maize yield (increased by 10.2%). For the microbial community structure, PERMANOVA and PCoA indicated that the bacterial community differed significantly between rhizosphere soil and bulk soil, but the fungal community shifted more under different agricultural practices. The correlation analysis indicated that the rotation system promoted the association between the soil DOC and the microbial community (especially the bacterial community), and straw mulching enhanced the connection between the soil TOC and the fungal community. Some plant growth–promoting rhizobacteria (including Bacillus, Streptomyces, Rhizobium, and Pseudomonas) were enriched in the rhizosphere soil and were increased in the rotation system (R and RS), which might be due to an increase in the soil rhizosphere DOC level. These beneficial microbes had significantly negative correlations with several fungal groups (such as Mycosphaerella, Penicillium, Paraphoma and Torula) that were classified as plant pathotrophs by FUNGuild. These results indicated that ensuring plant root development and improving root–bacteria interactions are of great importance to guarantee crop yield when implementing conservation tillage practices.