Biology and Fertility of Soils最新文献

The mechanism by which residual straw incorporation affects nitrous oxide (N₂O) and carbon dioxide equivalent (CO₂-eq) emissions throughout the rice season under upland-paddy rotation systems is currently unknown. We aimed to elucidate its effect using a four-year experiment and meta-analysis in southwest China. In garlic–rice (GR) and wheat–rice (WR) systems, residual straw incorporation significantly decreased N₂O emissions (43.6% and 73.5%, respectively) and NO₃⁻-N concentrations, relative abundance of denitrifying bacteria (Anaeromyxobacter, Bacillus and Hyphomicrobium), and copy numbers of the norB and nosZ genes. Ultimately, the soil denitrification rate was reduced during rice tillering and full heading periods, but the soil organic nitrogen accumulation level was increased. The reduction in N₂O also resulted in an average reduction in the total CO₂-eq of the GR (23.4%) and WR (32.9%) systems in 2021–2022. In addition, the meta-analysis results showed that straw incorporation had a generally positive effect on soil N₂O emissions, but this effect was negative during the rice season in upland-paddy rotation systems, which supports the main results of our study. The path analysis results indicated that dry season residual straw incorporation slowed N₂O emissions during the rice season by increasing the soil C/N ratio and downregulating denitrifying microorganisms, thereby inhibiting the denitrification rate. Our findings challenge the understanding that straw incorporation increases greenhouse gas emissions during the rice season and suggest that future estimates of straw incorporation on methane (CH₄) emissions during the rice season should consider the offsetting effect of N₂O.

As the habitats of bacteria, soil pore network and surface properties control the distribution, adhesion, and motility of bacteria in soils. These physical processes in turn influence bacterial accesses to nutrients and bacterial interactions. Our understanding on the pore- and surface-mediated bacterial interactions is currently limited. In this research, we evaluated the effects of soil pore confinement and surface adhesion on conjugation-based bacterial interactions. The interaction was measured by plasmid transfer between donor and recipient cells within the population of soil bacterium Pseudomonas putida. We found that the presence of porous sand media led to a net increase in conjugation frequency compared to sand-free liquid control. The increase is attributed to the facilitated effect of pore confinement on the collision of bacteria within pores. In contrast, bacterial adhesion to sand surfaces under elevated ionic strength conditions decreased the conjugation frequency as a result of mobility reduction on the surface. Such collision and adhesion mechanisms jointly drive the conjugation as a function of pore and surface properties of porous media. These results provide valuable insights into the roles of soil pores and surfaces in regulating horizontal gene transfer, an essential cell-to-cell interaction sustaining key processes of soil ecology and health.

Time dependent deposition of two Azospirillum brasilense strains in sand quantified.

Three inclusions regimes examined: surface, subsurface and premixed.

For surface and subsurface the bacteria accumulated near the point source and remained stagnant in the premixed.

The attachment/detachment numerical model found adequate to describe the time dependent deposition profiles of the bacteria.

Similar to species richness, genotypic richness of plants plays a pivotal role in the structure and function of ecosystems. While the contribution of intraspecific variability to ecosystem function has been well-established, the mechanisms underlying the effect of genotypic richness on nitrogen (N) uptake patten remain poorly understood. We established experimental populations consisting of 1, 4, or 8 genotypes of the clonal plant Hydrocotyle verticillata in microcosms and conducted ¹⁵N-labeling to quantify plant N uptake. NH₄⁺-N uptake rate of the populations with 8 genotypes was significantly higher than that of the populations with 1- and 4-genotypes, while genotypic richness did not influence NO₃⁻-N uptake rate. Increasing genotypic richness also enhanced NH₄⁺-N uptake preference and reduced NO₃⁻-N uptake preference. Additionally, increasing genotypic richness facilitated the transformation of the soil nitrogen pool, resulting in a reduction of total soil N content and an increase in soil NH₄⁺-N, thereby causing a shift in population N uptake preference. Our findings highlight the importance of genotypic richness on both N uptake and N form preference of plant populations. Such intraspecific variability in N uptake and N form preference may further influence population dynamics and ecosystem function.

Soil microbiomes play a pivotal role in shaping plant health and their ability to suppress the pathogens. However, the specific microbial features that confer disease suppression in agricultural soils have remained unknown. In this study, we aim to elucidate the mechanistic roles of soil key bacteria contributing to disease suppression in banana Panama disease by using a comprehensive soil survey focusing on suppressive, and conducive soils. Through an initial field survey across twelve paired locations, we identified five fields with significantly lower pathogen abundances compared to their co-located counterparts. Subsequent greenhouse experiments validated the disease-suppressive nature of soils collected from Jianfeng (JF) and Lingao (LG), both exhibiting low pathogen densities. Furthermore, four OTUs classified as Massilia (OTU44), Flavisolibacter (OTU396), Brevundimonas (OTU632) and Pseudomonas (OTU731), respectively, were identified as key players in suppressing pathogen invasion as they were significantly enriched in suppresive groups and pathogen inoculated treatments. The present results might suggest a vital link between these soil bacteria and pathogen inhibition in banana rhizosphere via a greenhouse experiment. The abundance of nonribosomal peptide synthetase (NRPS) genes, which was responsible for antibiotic synthesis and significantly enriched in the banana rhizosphere after beneficial microorganism inoculation, displayed a significant and negative correlation with pathogen abundance while a positive correlation with relative abundance of Pseudomonas. This result suggests that the up-regulation of NRPS genes may play a key role in bolstering banana plant immunity. These findings not only provide promising biocontrol strategies but also offer valuable insights into the dynamic relationship between soil microbiomes and plant physiology, paving the way for sustainable agriculture and disease management.

Civilian and military activities are sources of water and soil contamination by inorganic and organic contaminants caused by shooting practices, warfare, and/or mechanized military training. Lead poisoning and contaminant bioaccumulation due to spent shots or other related military contaminants have been widely studied for mammals, birds, and plants. Although there are different papers on the impact on earthworms, information on micro and mesofauna (i.e., collembola, nematodes, etc.) is still scarce. Here, we review the published data regarding the impact of civilian and military shooting activities, including war-impacted areas, focusing on soil organisms, from microbial communities to the ecotoxicological effects on terrestrial organisms. One hundred eleven studies were considered where earthworms and enchytraeids were widely studied, especially under ecotoxicological assays with Pb and energetic-related compounds from military explosives. There is a lack of information on soil organism groups, such as mites, ants, or gastropods, which play important roles in soil function. Data from combined exposures (e.g., PTEs + TNT and PTEs + PAHs) is scarce since several studies focused on a single contaminant, usually Pb, when combined contaminants would be more realistic. Ecotoxicological assays should also cover other understudied ammunition elements, such as Bi, Cu, or W.

Soil microbial necromass carbon (MNC) contributes to the long-term stability of soil organic carbon (SOC). However, the response of MNC across aridity gradients remains unclear, especially in vulnerable alpine ecosystems. Here, we examined alpine grasslands from 180 sites spanning a 3,500 km aridity gradient on the Tibetan Plateau to investigate how MNC abundance and composition (contributions of bacterial and fungal necromass carbon) vary with climate. MNC was variable, ranging from 0.55 to 26.95 g kg⁻¹ soil, with higher content observed in humid and dry-subhumid regions than in arid and semiarid regions in the Western Tibetan Plateau. Soil properties were the dominant drivers of MNC, with soil fertility (cation exchange capacity and total phosphorus) and weathering products (clay, silt and iron/aluminum oxides) facilitating MNC accumulation, while a negative correlation was observed between MNC and soil pH. A pivotal aridity threshold of 0.60 underpinned a non-linear decrease in MNC with increasing aridity across soil condition gradients; MNC was negatively correlated with aridity below this threshold and showed no correlation beyond it. Given this pivotal aridity threshold, we delineated the drivers of MNC under conditions of low (aridity < 0.6) versus high (aridity > 0.6) aridity. In low-aridity conditions, MNC accumulation was governed by aridity, soil fertility, weathering products, and pH, whereas in high-aridity conditions, the interplay between soil properties and temperature took precedence. Species richness enhanced carbon accumulation from microbial residues under low-aridity conditions more so than under high-aridity conditions, with fungal necromass carbon consistently being a higher contributor to SOC than bacterial necromass carbon, particularly in humid regions. These findings highlight aridity-driven divergence in MNC and propose that conserving plant diversity may mitigate the adverse effects of aridification on MNC under low-aridity conditions in alpine grasslands.

Emerging scientific evidence has shown that root exudates may trigger the mobilization of soil organic matter (SOM), particularly under nutrient limitation. However, the role of changes in root morphology, metabolism, exudation, and their impact on rhizospheric properties and SOM remain poorly known. To address this issue, we conducted a rhizobox experiment for 50 days in which pre-grown eucalypt plants (120 days-old) were supplied with nutrient solutions providing either limited (0.0 mg L^− 1) or normal N supply (196.0 mg L^− 1). After 48 days, we used a ¹³CO₂ pulse labeling to track the impact of N limitation on C translocation to roots and soil respiration. After the 50th day, we assessed root morphology and metabolism, rhizospheric pH, mineral crystallinity, C and N contents, and the molecular composition of SOM. Under N limitation, eucalypt plants showed reduced photosynthesis, increased their root-to-shoot ratio and root branching, with organic acids prevailing among root metabolites. Overall, N-limited eucalypt plants led to a cascading of changes in the rhizosphere: increased concentrations of recently fixed ¹³C-CO₂, citrate, and N-bearing compounds, whereas soil pH and Fe-bound SOM decreased. These results were not followed by significant changes in microbial biomass, neither fungi: bacteria nor Gram-positive: Gram-negative ratios. Our results show that under N limitation, eucalypt roots exhibited a cascade of morpho-physiological adjustments that ultimately increased the mobilization of some SOM pools. Therefore, the combined impacts of those root morpho-physiological traits on the mobilization of SOM may reduce the overall soil C sink of eucalypt forests under N limitation.

Phosphorus (P) is a key element for energy transfer, and biosynthesis of nucleic acids and cell membranes. The objective of this study was to investigate and quantify P utilization by different grain—maize (Zea mays L.) and soybean (Glycine max L.)—and forage-cover crop brachiaria (Brachiaria ruziziensis) plant species in a low fertility highly weathered Oxisol. Two rates of P (25 and 50 mg kg⁻¹) were applied by water-soluble P fertilizer (triple superphosphate) to each of 12 crop cycles, together with a control (no P added). Measurements included plant biomass production and P uptake for each cycle, and analysis of soil P fractions (including labile and non-labile) and enzymes activities (acid phosphatase and β-glucosidase) were done at the beginning of the experiment and after 3, 6, and 12 cycles. Total biomass production and P uptake/removal were significantly higher for brachiaria than maize and soybean, which was reflected in the P use efficiency (PUE), being higher for brachiaria (57%), compared with maize (26%) and soybean (21%). The higher PUE by brachiaria was partly attributed to higher levels of acid phosphatase and β-glucosidase activities which indicated enhanced biological activity and P cycling under brachiaria. Data from the control treatment clearly demonstrated that all three plant species mobilized stable/occluded fractions of P throughout the experiment, however, brachiaria could produce more using less P. The findings of this study indicated the inclusion of brachiaria in crop rotations as a forage or cover crop/green manure may enhance overall P use efficiency.

Quantifying the gross rates of individual nitrogen (N) processes is critical for understanding the availability, retention and loss of N and its eco-environmental impacts in agricultural ecosystems. Here, we carried out a ¹⁵N tracing study to quantify the influence of soil moisture on the gross rates of ten different N processes in two intensively managed fluvo-aquic soils. Results showed that the gross N mineralization rates were insensitive to changes in soil moisture, ranging from 40 to 120% water-filled pore space (WFPS). Contrarily, the gross ammonium (NH₄⁺) immobilization rates increased exponentially with elevated soil moisture. Specifically, under high soil moisture conditions (i.e., 90–120%WFPS), the gross NH₄⁺ immobilization rates (4.04 ± 0.83 and 0.88 ± 0.28 mg N kg^− 1d^− 1 for the two soils, respectively) were nearly four times higher than those under medium or low moisture conditions (i.e., 40–80%WFPS). Meanwhile, the high WFPS reduced the gross autotrophic nitrification rates (5.92 ± 2.15 and 12.31 ± 3.83 mg-N kg^− 1d^− 1 for the two soils, respectively) to only one-third to one-half of those that were observed under medium or low WFPS. By contrast, the rates of nitrate (NO₃⁻) immobilization increased in one soil whereas they decreased in another under high moisture conditions, and the other N processes (including heterotrophic nitrification and dissimilatory nitrate reduction to ammonium (DNRA)) were negligible throughout the different WFPS. Overall, our results suggest that under highly saturated conditions, the increase in microbial NH₄⁺ immobilization and decrease in autotrophic nitrification are critical for N retention in the fluvo-aquic soils. These findings provide valuable insights into potential alterations in soil N retention or loss under future climate change scenarios, where more intensive irrigation and extreme rainfall events are anticipated.