Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration.

Maize stalk rot, caused by multiple pathogens, is a serious soilborne disease worldwide. Composition of pathogens causing maize stalk rot and resistance of maize inbred lines in Heilongjiang Province, China, are not well understood. In this study, 138 fungal isolates were collected from different maize-producing areas in Heilongjiang Province, which were identified as Fusarium graminearum (23.2%), F. subglutinans (18.9%), F. cerealis (18.9%), Bipolaris zeicola (13.0%), F. brachygibbosum (13.0%), F. temperatum (7.2%), and F. proliferatum (5.8%). Among them, F. graminearum (>20%) was the predominant species among the isolates causing maize stalk rot. B. zeicola had not previously been reported causing maize stalk rot in China. Resistance of 67 maize inbred lines to maize stalk rot was assessed, and 24 lines (35.8% of them) were highly resistant or resistant, indicating that approximately 65% of these lines were susceptible to maize stalk rot. Maize inbred lines were analyzed using simple sequence repeat markers and divided into five genetic groups with 12 pairs of primers. Additionally, analysis of molecular variance indicated that 44.2% of the genetic variation in disease resistance was distributed among populations. This study provides insight into the genetic diversity of inbred maize and may contribute useful information for breeding stalk rot disease-resistant hybrids, and facilitates development of effective strategies for managing this destructive disease complex.

In the context of the carbon peak and carbon-neutral era, it is crucial to effectively utilize maize straw as a resource for achieving carbon (C) sequestration and emission reduction in rural agriculture. Maize straw carbon undergoes two processes after being added to the soil: mineralization (decomposition) and humification (synthesis) by soil animals and microorganisms. These processes contribute to the reintegration of carbon into the agroecosystem’s carbon cycle. However, understanding of the transformation and stabilization of straw carbon, as well as the differences in C fixation capacity in soils with various fertilization treatments in black soils, remains limited. This study aims to quantify the relationship between straw carbon input and organic carbon sequestration in various fertilization treatments of black soil. Based on a long-term positional fertilization trial (45 years) in black soil, ¹³C-labeled maize straw (1.5 g in 120 g of dry soil) was applied and combined with an in situ incubation method using carborundum tubes. Throughout the 360-day trial, we observed the influence of fertilization on soil total organic C levels, organic carbon δ¹³C values, maize straw addition rate, and straw C fixation capacity. The decomposition of straw was most prominent during the initial 60 days of the incubation period, followed by a gradual decrease in the rate of decomposition. Compared with day 0, the SOC δ¹³C value and straw C residue rate were highest in the no-fertilization treatment (CK) after 360 days of incubation. The amount of organic carbon transformed and fixed in the soil was significantly higher in the organic fertilizer treatment (M) compared to other treatments, highlighting the stronger decomposition, transformation, and carbon fixation capacity of straw carbon in the M treatment. Moreover, the highest carbon storage of 43.23 Mg·ha⁻¹ was observed in the M fertilization treatment after 360 days, which was significantly different from other treatments (p < 0.05). The study demonstrates that soil with low fertility exhibits increased sequestration potential for straw carbon. Additionally, organic fertilizer input would increase soil organic carbon storage and facilitate straw carbon conversion.

Soil acidification threatens N availability, but the effects of maize straw and biochar on organic N fractions in acidic black soil are unclear. We examined the effects of straw (1.5%, 3%) and biochar (1%, 2%) with fertilizer on soil acidity, N fractions, and enzyme activities in a pot experiment with soybean. All amendments raised soil pH, but total exchangeable acidity decreased only at high doses (S3, B2). High-dose straw (S3) increased amino acid N by 21.74% and decreased amino sugar N by 33.33%, with urease (+30.1%) and invertase (+29.8%), indicating accelerated organic N mineralization. For inorganic N, S3 raised NH₄⁺-N by 47.0%, while B2 raised NO₃⁻-N by 30.4%, but low doses (S1.5, B1) reduced inorganic N. B2 increased total N (+5.6%) and total acid-hydrolysable N (+2.9%), with unknown N up by 11.9%, but suppressed catalase and dehydrogenase, suggesting N stabilization. Amino acid N correlated positively with available N and invertase, while amino sugar N correlated negatively with available N. Thus, straw promotes labile N, and biochar stabilizes N; high doses are recommended for acidic black soil fertility.

The process of straw decomposition is highly complex and is regulated by a multitude of interacting factors. However, how the straw return rate influences the metabolic byproducts, extracellular enzymes, and microbial communities during straw decomposition remains an unresolved question. To address this, we integrated straw and soil chemistry, amplicon sequencing, untargeted metabolomics, and enzyme assays across four straw return rates (no return, 1/3, 1/2, and the Full treatment) at 30 and 90 d. Straw mass loss was greatest under the 1/2 return treatment at 90 d, reaching 53.7%, whereas soil organic carbon (SOC) and total nitrogen (N) were highest under the 1/3 return, exceeding the control by 17.6% and 17.2%, respectively. This indicates that decomposition and short-term soil C and N accumulation were decoupled. Microbial communities underwent clear temporal turnover, and hydrolytic enzymes increased from 30 to 90 d and were positively associated with mass loss. In contrast, oxidative enzymes showed no positive association with decomposition. Metabolomic profiles shifted from early-stage labile compounds to later-stage aromatic and phenolic compounds, and straw and soil metabolomes were closely coupled in a stage-specific manner (Procrustes M² = 0.15, p = 0.001; Mantel r = 0.69, p = 0.001). Mantel tests further indicated that the metabolome was significantly associated with return rate and SOC. Partial least squares path modeling revealed that the direct and indirect pathways linking return rate, metabolome, enzymes, and decomposition were reorganized between 30 and 90 d. Overall, straw return rate influenced decomposition through stage-dependent biochemical and microbial changes, and straw mass loss and short-term soil C and N accumulation were decoupled, responding nonlinearly and peaking under different return rates.

The soil nutrients, main agronomic indexes, and key yield factors during the maize growth period were studied by using a nutrient expert system to recommend optimal fertilization. The results showed that the fertilizer application had a significant impact on the growth and yield formation of maize, especially the N fertilizer application. N deficiency in maize seriously affected the yield and its component factors, while P and K deficiency had no significant effect on decreasing maize yield. The optimized fertilization treatment (NE) significantly reduced the bald tip length and increased the ear length and the yield of maize by 10.2% compared with the conventional fertilization treatment (FP). NE significantly increased the utilization rate of N, P, and K in maize, which was 20.1%, 12.4%, and 45.4% higher than that of FP. The trend of fertilizer N deficiency was opposite to NE, but P and K deficiency were not obvious. Compared with FP, soil organic matter of NE did not change significantly, and the pH value was increased. Nitrate nitrogen and ammonium nitrogen were decreased by 51.9% and 3.9%, respectively. A significant correlation between maize yield and alkali hydrolyzed nitrogen, organic matter. In conclusion, the optimized fertilization treatment had obvious effects on the growth indicators and yield components of maize, improving the fertilizer utilization rate, and providing technical support for rational fertilization of maize.