Research on soil bacterial community assembly and function under different straw returning practices in arid and semi-arid agricultural ecosystems over multiple years

Introduction

Straw return has gained attention for its potential to improve soil quality and crop yields, particularly in semi-arid regions like the Tumu Chuan Plain Irrigation Area. Soil bacteria play a crucial role in regulating soil biological processes, and understanding how straw return affects bacterial populations can guide better agricultural management practices.

Methods

We investigated the impact of continuous straw return on soil bacterial communities using 16S rRNA gene sequencing. Four treatments were applied: Farmers' shallow rotation (CK), straw incorporated with deep tillage (DPR), straw incorporated with subsoiling (SSR), and no-tillage mulching straw return (NTR). Bacterial community structure, metabolic pathways, and assembly mechanisms were analyzed using Bugbase and PICRUSt2 for phenotypic and metabolic pathway predictions.

Results

The study found that straw return practices significantly altered the relative abundance and life history strategies of bacterial phyla, mainly influenced by soil organic matter (SOM) and enzyme activity. The K-strategist to r-strategist ratio was highest in CK (2.06) and lowest in SSR (1.89). DPR and NTR treatments significantly changed bacterial community structure compared to CK (p < 0.05), resembling SSR. Predictions showed that DPR and NTR enhanced carbohydrate and amino acid metabolism and promoted more stable bacterial networks, with homogenous selection and drift effects. Bacterial aggregation in all treatments was driven by random processes, with varying aggregation levels: CK (20%), DPR (38.6%), SSR (16.5%), and NTR (30.7%).

Discussion

The study demonstrates that continuous straw return practices significantly impact soil bacterial communities. DPR and NTR notably improved microbial diversity, bacterial cooperation, and ecosystem stability. These findings provide valuable insights for sustainable agricultural practices in semi-arid regions, enhancing soil microbial ecology and soil health through strategic straw return.

Soil bacterial community response to cover crop introduction in a wheat-based dryland cropping system

The incorporation of cover crops into cropping systems is important for enhancing soil health in agricultural systems. Soil microbes contribute to soil health by supplying key nutrients and providing protection against plant pests, diseases, and abiotic stress. While research has demonstrated the connection between cover crops and the soil microbiology, less is known regarding the impact of cover crops on the soil microbial community in semi-arid regions of the Northern Great Plains. Our objectives were to evaluate changes in the soil bacterial community composition and community networks in wheat grown after multi-species cover crops. Cover crops were compared to continuous cropping and crop/fallow systems and the effects of cover crop termination methods were also evaluated. Cover crops consisted of a cool season multispecies mix, mid-season multispecies mix, and a warm season multispecies mix, which were grown in rotation with winter wheat. A continuous cropping (wheat/barley) and wheat/fallow system were also included along with cover crop termination by grazing, herbicide application, and haying. Cover crop treatments and termination methods had no significant impact on microbial community alpha diversity. Cover crop termination methods also had no significant impact on microbial community beta diversity. Families belonging to the phyla Actinobacteria, Bacterioidota, and Proteobacteria were more abundant in the cool season cover crop treatment compared to the warm season cover crop treatment. Co-occurrence network analysis indicated that incorporation of cool season cover crops or mid-season mixes in a wheat-based cropping system led to greater complexity and connectivity within these microbial networks compared to the other treatments which suggests these communities may be more resilient to environmental disturbances.

Soil bacterial community response to cover crops, cover crop termination, and predicted climate conditions in a dryland cropping system

Soil microbial communities are integral to highly complex soil environments, responding to changes in aboveground plant biodiversity, influencing physical soil structure, driving nutrient cycling, and promoting both plant growth and disease suppression. Cover crops can improve soil health, but little is known about their effects on soil microbial community composition in semiarid cropping systems, which are rapidly becoming warmer and drier due to climate change. This study focused on a wheat-cover crop rotation near Havre, Montana that tested two cover crop mixtures (five species planted early season and seven species planted mid-season) with three different termination methods (chemical, grazed, or hayed and baled) against a fallow control under ambient or induced warmer/drier conditions. Soil samples from the 2018 and 2019 cover crop/fallow phases were collected for bacterial community 16S rRNA gene sequencing. The presence and composition of cover crops affected evenness and community composition. Bacterial communities in the 2018 ambient mid-season cover crops, warmer/drier mid-season cover crops, and ambient early season cover crops had greater richness and diversity than those in the warmer/drier early season cover crops. Soil microbial communities from mid-season cover crops were distinct from the early season cover crops and fallow. No treatments affected bacterial alpha or beta diversity in 2019, which could be attributed to high rainfall. Results indicate that cover crop mixtures including species tolerant to warmer and drier conditions can foster diverse soil bacterial communities compared to fallow soils.

Weed Communities in Winter Wheat: Responses to Cropping Systems under Different Climatic Conditions

Understanding the impact of biological and environmental stressors on cropping systems is essential to secure the long-term sustainability of agricultural production in the face of unprecedented climatic conditions. This study evaluated the effect of increased soil temperature and reduced moisture across three contrasting cropping systems: a no-till chemically managed system, a tilled organic system, and an organic system that used grazing to reduce tillage intensity. Results showed that while cropping system characteristics represent a major driver in structuring weed communities, the short-term impact of changes in temperature and moisture conditions appear to be more subtle. Weed community responses to temperature and moisture manipulations differed across variables: while biomass, species richness, and Simpson’s diversity estimates were not affected by temperature and moisture conditions, we observed a minor but significant shift in weed community composition. Higher weed biomass was recorded in the grazed/reduced-till organic system compared with the tilled-organic and no-till chemically managed systems. Weed communities in the two organic systems were more diverse than in the no-till conventional system, but an increased abundance in perennial species such as Cirsium arvense and Taraxacum officinale in the grazed/reduced-till organic system could hinder the adoption of integrated crop-livestock production tactics. Species composition of the no-till conventional weed communities showed low species richness and diversity, and was encompassed in the grazed/reduced-till organic communities. The weed communities of the no-till conventional and grazed/reduced-till organic systems were distinct from the tilled organic community, underscoring the effect that tillage has on the assembly of weed communities. Results highlight the importance of understanding the ecological mechanisms structuring weed communities, and integrating multiple tactics to reduce off-farm inputs while managing weeds.