Background: Peanut (Arachis hypogaea L.) is an important oil and economic crop. Calcium modulates plants in response to abiotic stresses and improves plant resistance to pathogens. Enrichment of beneficial microorganisms in the rhizosphere is associated with plant disease resistance and soil development. The purpose of this study was to analyze the differences in peanut rhizosphere microbial community structure between the calcium treatment and the control during two growth stages and to explain why calcium application could improve the resistance of peanuts to soil-borne pathogens. Results: The 16S rDNA amplicon sequencing of rhizosphere microbiome showed that calcium application significantly enriched Serratia marcescens and other three dominant strains at the seedling stage. At the pod filling stage, ten dominant stains such as Sphingomonas changbaiensis and Novosphingobium panipatense were enriched by calcium. Serratia marcescens aseptic fermentation filtrate was mixed with PDA medium and inoculated with the main soil-borne pathogens in the seedling stage, which could inhibit the growth of Fusarium solani and Aspergillus flavus. The aseptic fermentation filtrate of Novosphingobium panipatense was mixed with PDA medium and inoculated with the main soil-borne pathogens in the pod filling stage, which could inhibit the growth of Sclerotium rolfsii and Leptosphaerulina arachidicola. Conclusions: Calcium application increases the resistance of peanuts to soil-borne pathogens by enriching them with specific dominant bacteria.

Excessive nitrogen and insufficient calcium could significantly impact peanut yields. This study investigated the effects of nitrogen and calcium fertilizers on nutrient absorption, utilization, and yield; experiments were conducted using the peanut cultivar from Xianghua 2008 in a split-plot arrangement with two calcium fertilizer levels (Ca₀: 0 and Ca₁: 568 kg CaO ha⁻¹) in the main plots and six nitrogen fertilizer gradients (N₀: 0, N_45.0: 45.0, N_90.0: 90.0, N_112.5: 112.5, N_135.0: 135.0, and N_157.5: 157.5 kg N ha⁻¹) in subplots between 2015 and 2016 in Changsha, China. We examined the impact of different rates of calcium and nitrogen fertilizers on the net photosynthetic rate (Pn), agronomic traits, dry matter quality, yield and yield composition, nutrient accumulation, and distribution. The combined application of calcium and nitrogen fertilizers significantly affected the yield and yield components, Pn, main stem height, dry matter, and nutrient accumulation. Under the same calcium level, nitrogen application significantly increased the main stem height and Pn and promoted the accumulation of dry matter and nutrients in the plant, particularly in the kernel. Under the same nitrogen treatment, calcium significantly increased Pn and promoted the accumulation of dry matter, calcium, and magnesium. The pod yield increased gradually with an increasing nitrogen application rate (0–112.5 kg ha⁻¹) and peaked at N_112.5, increasing by 52.3–138.0% compared with N₀. However, excessive nitrogen application (N > 112.5 kg ha⁻¹) decreased the pod yield. Under different nitrogen fertilizer levels, calcium application increased pod yields by 11.5–29.6% by promoting Pn, nutrient uptake, accumulation in the individual plant, and nutrient accumulation in the kernel. Therefore, this study suggested that adjusting the calcium (568 kg ha⁻¹) and nitrogen (112.5 kg ha⁻¹) fertilizer rates significantly improved peanut growth and productivity by enhancing photosynthetic efficiency and nutrient accumulation in calcium-deficient acidic red soil.

Slaked lime has been used to remediate contaminated agricultural soils as an in situ chemical immobilization amendment for a long time. However, the effects of slaked lime on peanut and soil cadmium (Cd) levels remain poorly understood with respect to remediating Cd-contaminated soil. In this study, six rates of slaked lime (e.g., 0, 300, 600, 900, 1200 and 1500 kg ha⁻¹) were applied to evaluate the effects of slaked lime treatments on soil pH and the growth, Cd accumulation and physiology characteristics of peanut, which were in Cd-contaminated soil, and 0 kg ha⁻¹ was taken as the control. The results indicated that slaked lime application significantly increased soil pH and reduced total Cd contents in peanut tissues at all growth stages. As the rates of slaked lime were increased, kernel biomass increased in the maturity stage, which increased peanut yields. The irregular variations in catalase, peroxidase, and superoxide dismutase activities and chlorophyll and malondialdehyde contents that were observed at all growth stages may be due to the interactions among soil pH, Ca nutrients and Cd, etc. In summary, slaked lime is suitable as an in situ chemical immobilization amendment to increase Cd immobilization and peanut yields in Cd-contaminated soil.

The application of nitrogen fertilizer is crucial to the growth and biological nitrogen fixation of peanut, especially in the seedling stage where nodules have not yet formed. However, it is still uncertain how much initial nitrogen fertilizer should be applied to promote peanut root growth, nodule formation, and biological nitrogen fixation (BNF). There, a 2-year pot experiment was conducted using Huayu 22 (HY22, large-grain cultivar) and Huayu 39 (HY39, small-grain cultivar) as experimental materials to research the effects of different initial nitrogen fertilizer application rates on peanut root growth (root weight, root length, root mean diameter, root activity) and biological nitrogen fixation capacity (nodule number, nodule weight, biological nitrogen fixation, and nitrogen fixation potential per plant). N₀, as control, four initial nitrogen fertilizer application rates were established: 15 kg·hm⁻² (N₁₅), 30 kg·hm⁻² (N₃₀), 45 kg·hm⁻² (N₄₅), and 60 kg·hm⁻² (N₆₀). The present results showed that the nodule number, nodule dry weight, nitrogenase activity, and biological nitrogen fixation of the HY22 cultivar under the N₁₅ treatment were higher compared to those under other treatments over the two growing seasons. In addition, the cultivar of HY39 treated with the N₁₅ treatment also increased the nitrogen fixation potential per plant and BNF relative to other treatments. Although the application of 60 kg·hm⁻² nitrogen increased the root surface area and root volume, it decreased the nitrogenase activity, nodule dry weight, and nitrogen fixation potential per plant of HY22 and HY39 varieties in both growing seasons. Above all, an initial nitrogen application of 15 kg·hm⁻² may be the optimal treatment for promoting peanut nodule formation and biological nitrogen fixation.

Peanut is an important oil and economic crop in China. The rainy season (April–June) in the downstream Yangtze River in China always leads to waterlogging, which seriously affects plant growth and development. Therefore, understanding the metabolic mechanisms under waterlogging stress is important for future waterlogging tolerance breeding in peanut. In this study, waterlogging treatment was carried out in two different peanut cultivars [Zhonghua 4 (ZH4) and Xianghua08 (XH08)] with different waterlogging tolerance. The data-independent acquisition (DIA) technique was used to quantitatively identify the differentially accumulated proteins (DAPs) between two different cultivars. Meanwhile, the functions of DAPs were predicted, and the interactions between the hub DAPs were analyzed. As a result, a total of 6,441 DAPs were identified in ZH4 and its control, of which 49 and 88 DAPs were upregulated and downregulated under waterlogging stress, respectively, while in XH08, a total of 6,285 DAPs were identified, including 123 upregulated and 114 downregulated proteins, respectively. The hub DAPs unique to the waterlogging-tolerant cultivar XH08 were related to malate metabolism and synthesis, and the utilization of the glyoxylic acid cycle, such as L-lactate dehydrogenase, NAD⁺-dependent malic enzyme, aspartate aminotransferase, and glutamate dehydrogenase. In agreement with the DIA results, the alcohol dehydrogenase and malate dehydrogenase activities in XH08 were more active than ZH4 under waterlogging stress, and lactate dehydrogenase activity in XH08 was prolonged, suggesting that XH08 could better tolerate waterlogging stress by using various carbon sources to obtain energy, such as enhancing the activity of anaerobic respiration enzymes, catalyzing malate metabolism and the glyoxylic acid cycle, and thus alleviating the accumulation of toxic substances. This study provides insight into the mechanisms in response to waterlogging stress in peanuts and lays a foundation for future molecular breeding targeting in the improvement of peanut waterlogging tolerance, especially in rainy area, and will enhance the sustainable development in the entire peanut industry.

The dual challenges of global climate change and reductions in the amount of arable land represent growing threats to the stability of global human populations. Efforts to further optimize cropping systems to maximize yields while minimizing greenhouse gas emissions in limited land areas have thus emerged as a focus in modern agriculture. Cereal-intercropping management strategies may represent a promising approach to simultaneously addressing both of these challenges in China. We aimed at comprehensively assessing changes in yield, carbon footprint, and net ecosystem economic benefit when transitioning from maize/peanut monoculture to intercropping in a field-scale study in an effort to aid in the development of low-carbon intercropping systems that do not have an adverse impact on Chinese grain yields. Beginning in June of 2018, a randomized complete block design with three treatments was used to initiate this study: (1) peanut monoculture (P), (2) maize monoculture (M), and (3) maize/peanut intercropping (MP). We compared yield, greenhouse gas emissions, carbon footprint and net ecosystem economic benefit. Results over four years showed that the land equivalent ratio associated with MP was greater than 1. All three of these cropping systems were net CO₂ and N₂O sources as well as net CH₄ sinks, with MP generating significantly (p < 0.05) lower N₂O and CO₂ flux as well as smaller seasonal N₂O and CO₂ emissions relative to M. MP additionally reduced the carbon footprint associated with this cropping system by 11.11–31.65% and 30.37–43.62% relative to M and P, respectively. Consistently, MP treatment resulted in respective 70.69% and 26.25% net ecosystem economic benefit (NEEB) increases relative to the M and P conditions while simultaneously enhancing energy use efficiency. In summary, MP systems have potential economic benefit with lower environmental risk alternative to traditional peanut or maize monocropping systems. Converting from peanut or maize monocropping systems to MP systems practices contributed to improved farmland use efficiency, clean production and increased farmers’ income in an agricultural system.