Xiaofen Wang

The North China Plain has a typical winter wheat–summer corn double-cropping pattern. The effects of nutrient deficiency conditions on the root characteristics and yield of summer corn in the double-cropping system were studied for four years. Long-term monotonous fertilization patterns undermine crop rotation systems and are detrimental to the sustainability of agricultural production. To complement the development of rational fertilization strategies by exploring the response of crop rotation systems to nutrient deficiencies, an experiment was conducted in a randomized complete block design consisting of five treatments with three replicates for each treatment: (1) an adequate supply of nitrogen and phosphate fertilizers and potash-deficient treatment (T1); (2) an adequate supply of nitrogen and potash fertilizers and phosphorus-deficient treatment (T2); (3) an adequate supply of phosphorus and potash fertilizers and nitrogen-deficient treatment (T3); (4) nutrient-sufficient treatment for crop growth (T4); and (5) no-fertilizer treatment (CK). The results showed that different nutrient treatments had significant effects on the root length density (RLD), root surface area density (RSAD), and root dry weight density (RDWD) in summer corn. At the physiological maturity stage (R6), the root indexes of RLD, RSAD, and RDWD were significantly higher in the 0–20 cm soil layer in T4 compared to CK, with an increase of 86.2%, 131.4%, and 100.0%, respectively. Similarly, in the 20–40 cm soil layer, the root indexes of T4 were 85.7%, 61.3%, and 50.0% higher than CK, with varied differences observed in the other nutrient-deficient treatments. However, there was no significant difference among the treatments in the 40–60 cm layer except for T4, whose root index showed a difference. The root fresh weight and root dry matter in T4, T3, T2, and T1 were increased to different degrees compared with CK. In addition, these differences in root indexes affected the annual yield of crops, which increased by 20.96%, 21.95%, and 8.14% in T4, T2, and T1, respectively, compared to CK. The spike number and the number of grains per spike of T4 were 10.8% and 8.3% higher than those of CK, which led to the differences in summer corn yields. The 1000-kernel weight of T4, T2, and T1 were 9.5%, 8.8%, and 7.4% higher than that of CK, whereas the determining nutrient was nitrogen fertilizer, and phosphorus fertilizer had a higher effect on yield than potassium fertilizer. This provides a theoretical basis for the effect of nutrient deficiency conditions on yield stability in a double-cropping system.

Agricultural Jiaosu (AJ) is a method of recycling agricultural wastes for improving soil properties, promoting plant growth, and enhancing plant stress resistance. However, the underlying mechanism by which AJ improves plant stress resistance needs to be determined. Therefore, in this study, two treatments of AJ spraying and water spraying were set up to determine the enzyme activities related to the stress resistance of pak choi after 30 days of growth, and the potential mechanism of AJ’s influence on the stress resistance of pak choi was revealed by transcriptome, metabolome, and rhizome microbiome analyses. Microbial community analysis revealed that the application of AJ does not alter microbial abundance in the rhizosphere; however, it can improve microbial diversity and enrich Actinobacteriota, Proteobacteria, and Firmicutes in the pak choi rhizosphere. Metabolomic analysis revealed that these phyla were significantly positively correlated, with highly upregulated metabolites. Our findings suggest that AJ recruits beneficial microorganisms (BMs) in the rhizosphere and stimulates the expression of genes and metabolites involved in phenylpropanoid and glucosinolate biosynthesis, as well as glutathione and alpha-linolenic acid metabolism pathways. The use of AJ could considerably minimise the use of pesticides and fertilisers and improve the quality of the ecological environment.

Indigenous soil microbial biomass (ISMB) plays a key role in maintaining essential functions and biodiversity of soil health. One of the critical unknowns is how the indigenous microorganisms respond to different fertilizers which is directly related to agricultural production. Therefore, we used Mi-Seq sequencing and network analyses to compare the response of ISMB to biogas residue and chemical fertilizers. The results showed that crop production was profoundly influenced by levels of ISMB present and is further dependent on the strategy of fertilizer application. Higher ISMB primarily manifests through retention of richer microbial abundance, a balanced community structure, and tightened co-occurrence within a certain proportion of Nitrospirae, Rhizophlyctidaceae, and Gemmatimonadetes. Compared to chemical fertilizer, biogas residue resulted in higher production with more strongly linked nodes such as Actinobacteria, Chloroflexi and Gemmatimonadetes. Under the same level of ISMB, the microbial diversity was richer and co-occurrence was tighter when biogas residues were applied compared with chemical fertilizer. In addition, the higher level of ISMB with biogas residue applied had a lower abundance of potential fungal pathogens in both bulk and rhizosphere soil compared with chemical fertilizer. This study provides critical data to understand the influence of ISMB and biogas residue on soil ecological system.

Microbial communities for bioconversion of lignocellulose have received widespread attention. Many cellulose-degrading microbial communities have been enriched from different sources. Combining two microbial communities with acidic and basic properties (acid–base combination) is a technique used alongside restricted enrichment culturing. Understanding how changes to microbial communities result in community’s structure and function is important for mechanistic reconstruction of microbiomes. In this study, we analyzed changes in microbial community structure to elucidate determination of the mechanisms of acid–base combination. We found that after restricted enrichment, the bacteria that were primarily retaining included not only those that decompose and utilize lignocellulose, such as Clostridium and Pseudomonas, but also synergistic microbiota such as Alkalobacillaceae. When the proportion of these two types of bacteria was unbalanced, the degradative ability of the microbial community was low, or pH changes of it did not compound regular changes, which may lead to the failure of restricted enrichment. Microbial communities were re-constituted by acid–base combination, whereby the degrading and synergistic strains were adjusted to a more appropriate proportion. The acid–base combination fixed the instability of microbial communities caused by the randomness of restrictive screening enrichment; it provided an effective method for obtaining high-quality lignocellulose-degrading microbial community.

Root rot caused by the pathogenic fungi of the Fusarium genus poses a great threat to the yield and quality of medicinal plants. The application of Agricultural Jiaosu (AJ), which contains beneficial microbes and metabolites, represents a promising disease control strategy. However, the action-effect of AJ on Fusarium root rot disease remains unclear. In the present study, we evaluated the characteristics and antifungal activity of AJ fermented using waste leaves and stems of medicinal plants, and elucidated the mechanisms of AJ action by quantitative real-time PCR and redundancy analysis. The effects of AJ and antagonistic microbes isolated from it on disease suppression were further validated through a pot experiment. Our results indicate that the AJ was rich in beneficial microorganisms (Bacillus, Pseudomonas, and Lactobacillus), organic acids (acetic, formic, and butyric acids) and volatile organic compounds (alcohols and esters). It could effectively inhibit Fusarium oxysporum and the half-maximal inhibitory concentration (IC₅₀) was 13.64%. The antifungal contribution rate of the microbial components of AJ reached 46.48%. Notably, the redundancy analysis revealed that the Bacillus and Pseudomonas genera occupied the main niche during the whole inhibition process. Moreover, the abundance of the Bacillus, Pseudomonas, and Lactobacillus genera were positively correlated with the pH-value, lactic, formic and butyric acids. The results showed that the combined effects of beneficial microbes and organic acid metabolites increased the efficacy of the AJ antifungal activity. The isolation and identification of AJ’s antagonistic microbes detected 47 isolates that exhibited antagonistic activities against F. oxysporum in vitro. In particular, Bacillus subtilis and Bacillus velezensis presented the strongest antifungal activity. In the pot experiment, the application of AJ and these two Bacillus species significantly reduced the disease incidence of Fusarium root rot and promoted the growth of Astragalus. The present study provides a cost-effective method to control of Fusarium root rot disease, and establishes a whole-plant recycling pattern to promote the sustainable development of medicinal plant cultivation.