Biology and Fertility of Soils最新文献

Antibiotic resistance has emerged as a global threat to public health. However, the current information is insufficient to understand how other pollutants, such as fungicides and nanoplastics, affect the spread of antibiotic resistance genes (ARGs) among bacteria in the soil. Here, our findings revealed that polyethylene nanoplastics (PENPs) prolonged the persistence of pyraclostrobin (PYR) in the soil by 13 days, increased PYR bioaccumulation in earthworm (Eisenia fetida) by 8.4%, and reduced its weights by 26.8%. PYR alone or combined with PENPs significantly increased the microbiome diversities of earthworm guts, while PENPs alone decreased those but increased the relative abundances of Proteobacteria and Firmicute. PYR and/or PENPs enhanced the diversity and abundance of ARGs in earthworm guts, the range of ARG hosts, and the complexity of ARGs and antibiotic-resistant bacteria coexistence network. The abundance of plasmid-origin ARG-harboring contigs in PYR, PENP, and PYR + PENP treatments was 1.5-, 3.8-, and 2.4-fold higher than that in the control, respectively. Overall, PYR and/or PENPs specifically disturbed the antibiotic resistome in earthworm guts by altering the bacterial community composition and richness, increasing the abundance of mobile genetic elements (MGEs) and ARGs, and modifying the co-occurrence pattern of ARGs-MGEs, particularly plasmids.

A large fraction of the Mediterranean soils is threatened by losses of organic matter and biodiversity, which could compromise the provision of soil ecosystem services and the stability of ecosystems in the face of climate change. In this work we explore several hypotheses related to the role of C inputs and microbial diversity on soil multifunctionality and its resistance to drought in degraded Mediterranean soils. We designed a factorial experiment to test the effect of the addition of an organic amendment and of microbial diversity (using four inoculants with different abundance and diversity of soil microbiota), on the resistance of soil functionality against drought in pot mesocosms. Pots were sown with a forage mixture (Lolium rigidum and Medicago polymorpha), and plant productivity, soil chemical properties, and microbial activity and diversity were measured before and after a simulated drought event. The amendment favored soil moisture, enhancing the stability of the productivity of M. polymorpha. In contrast, the manipulation of inoculation load had a limited effect on the resistance of microbiological activity. Indeed, microbial functioning was highly resistant to reduced water inputs, probably related to the prevalence of Gram positive bacteria. Besides, the effect of microbial diversity on soil multifunctionality was limited. Structural equation modelling confirmed that the enhancement of multifunctionality after soil amendment was attributed to the direct effect of organic C on soil moisture and chemical fertility. In these degraded soils, physico-chemical limitations are the major drivers of soil multifunctionality rather than bacterial or fungal diversity.

Low-light stress has become an important factor limiting crop yield and quality improvement. Appropriate phosphorus (P) addition can enhance soil microbial activity and nutrient availability, thereby alleviating the negative impacts of low-light stress. However, the role of crop rhizosphere microorganisms in the mitigation of low-light stress by P addition in agroecosystems remains unclear. In this study, three light conditions (normal light, S0; moderate low-light stress, S1; severe low-light stress, S2) and three P addition levels (0 kg ha^− 1, P0; 35 kg ha^− 1, P1; 70 kg ha^− 1, P2) were applied to analyze the combined effects on the rhizosphere microbial diversities, compositions, co-occurrence patterns, and assembly mechanisms during critical growth stages (flowering, filling, and maturity stages). The results showed that both low-light stress and P appreciably affected rhizosphere microbial community composition, with P promoting the proliferation of rhizosphere beneficial microbes under low-light stress. Low-light stress reduced rhizosphere microbial α-diversity, and S2 simplified microbial networks. In contrast, P1 increased bacterial network complexity, connectivity, and stability. Indicator taxa analysis revealed that P1 increased the abundance of shared and specific species in rhizosphere microbial networks. Under S1, P1 enhanced keystone taxa abundance. Community assembly analysis indicated that bacterial communities were governed by deterministic processes, whereas low-light stress reduced fungal stochasticity, which was increased by P addition. These findings highlight that P addition under low-light stress can enhance the tolerance of Tartary buckwheat rhizosphere microbial community by modulating rhizosphere microbial diversity, composition, and network stability, providing insights into alleviating low-light stress.

Exudates are the medium through which plants adapt to complex soil environments, however, the mechanisms of how different types of root exudates increase maize yield and phosphorus (P) use efficiency (PUE) throughout the entire growth period remains unknown. In this study, we designed an experiment to examine the effects of continuous addition of exudate substances on maize growth and P uptake over the entire growth period. The addition of succinic acid, luteolin, and inositol significantly increased maize biomass, particularly root biomass. Specifically, the treatment with added succinic acid increased maize yield by 11.6% and PUE by 8%. Additionally, we found that different exudate substances significantly altered the soil bacterial and fungal communities, thereby increasing soil P bioavailability. The microbial co-occurrence networks revealed that Actinobacteriota and Proteobacteria keystone ASVs, enriched by the addition of succinic acid, luteolin, and inositol, were significantly associated with maize P uptake. Furthermore, at the V12 stage (Twelve leaves unfolded), the addition of exudate substances significantly increased alkaline phosphatase activity, and at the R6 stage (Maturity), soil available P content was significantly elevated, enhancing soil P bioavailability. These findings provide evidence for future exploration of the interaction mechanisms between plants and soil microbes and optimizing nutrient management strategies in farmland.

The immediate responses of soil microbial communities to non-catastrophic typhoon disturbances remain largely unclear, despite soil microorganisms are key contributors to ecosystem functioning and sensitive indicators to forest disturbances. To address this gap, we simultaneously investigated soil microbial communities beneath bamboo forest (BF), Chinese fir forest (CF), secondary broadleaf forest (SF) and mixed forest (MF) in the subtropical mountain area of southeastern China before and after typhoon disturbances. Typhoon disturbances significantly altered the composition of soil microbial communities, decreasing bacterial diversity by 12.3% and network robustness by 22.6% in the topsoil, while increasing fungal diversity by 75.0% and network robustness by 33.2% in the litter layer. Notably, these indices returned to the per-typhoon levels post-disturbance. Meanwhile, typhoon disturbances increased the abundance of functional guild on bacterial cellular processes, fungal dung saprotrophs and plant saprotrophs in the topsoil. Moreover, the immediate responses of microbial community composition and diversity to typhoon disturbances were more pronounced in the CF and SF, and bacterial communities were more responsive in the topsoil, while fungal communities were more responsive in the litter layer. Additionally, soil temperature was the primary driver of microbial communities in the topsoil, while litter cellulose and calcium concentrations were key factors in the litter layer. Besides, carbon and nutrient concentrations were also significantly correlated with the composition of taxa and functional guilds of soil microbial communities. In summary, the immediate responses of microbial communities to typhoon disturbances vary considerably depending on forest types and soil horizon, with rapid recovery following typhoon events.

Measuring bacterial and fungal biomass may offer insights into agroecosystem health. Nevertheless, few studies have directly compared the ability of different methods to assess the abundance of these two microbial groups and their ratio (F/B ratio). This study compared the ability, precision, and repeatability of three commonly used laboratory methods - phospholipid fatty acid (PLFA) analysis, quantitative PCR (qPCR), and droplet-digital PCR (ddPCR) - alongside a commercially available microbial carbon testing tool (microBIOMETER^®), to assess the F/B ratio and microbial abundance in agroecosystem soils. We also reviewed recent literature on common measurement and reporting practices. PLFA and ddPCR provided the most reliable outcomes, with PLFA being the most precise, repeatable, and widely used (81% of reviewed studies). However, significant variability in analytical procedures exists between laboratories, and key details, such as storage conditions, are often underreported. MicroBIOMETER^® can offer a low-cost option for assessing total microbial biomass, but did not match PLFA results in determining the F/B ratio. ddPCR offered better precision than qPCR but had a narrower dynamic range. Therefore, optimal approach is to use the two methods in parallel. In conclusion, we recommend future studies adopt PLFA analysis as the primary method for assessing microbial abundance and F/B ratio of soils, as PCR-based measurements are influenced by several unavoidable biases. Furthermore, we suggest improvements to the PLFA method to ensure more reliable comparisons across laboratories. Altogether, our study gives guidelines for improving the monitoring of F/B ratio and microbial abundance in agroecosystems.

Many yet undiscovered plant growth-promoting bacteria are proposed to be harboured in the nitrogen-limited boreal forest. These bacteria are suggested to increase plant growth not only due to their ability to fix nitrogen but also through other growth-promoting properties. Therefore, this study looked at the plant growth promotion potential of endophytic bacteria isolated from boreal forest conifer Scots pine (Pinus sylvestris) needles. Seven assays were used to measure the potential plant growth-promoting abilities of two newly isolated bacteria in this study and seven additionally selected bacteria isolated in our previous study. The three best-performing bacteria were used, either individually or in a consortium, to assess growth promotion on four common crop species. The greenhouse study included the presence of native soil and seed microbiota and used naturally nutrient-abundant soil. The results showed that while all bacteria were capable of multiple plant growth-promoting properties in the in vitro assays, they did not promote plant growth in the in vivo experiment as inoculated plants had similar or decreased chlorophyll content, root and shoot length and dry biomass compared to control plants. Our results show that bacterial plant growth-promoting potential does not always translate into successful plant growth increase in in vivo conditions and highlight the need for a better understanding of plant-bacteria interaction for the future establishment of successful bacterial bioinoculants.

Denitrification is the key process leading to production and loss of nitrogen gases from soils. Its main drivers are N availability and soil water content, but interactions with other elements, such as carbon and phosphorus, can also influence N₂O formation. So far, robust information on the effects of P and the historical context of P addition on N₂O sources remains limited. To address this knowledge gap, we conducted a mesocosm chamber experiment using isotopic approaches to investigate N transformations and N₂O sources following P fertilizer addition in soils with varying histories of P fertilization (low and high P). Differences in long-term fertilization affected C, N, and P availability as well as microbial community composition and nutrient cycling processes. Initially, microbes in both soils were C-limited with slightly higher C availability and microbial respiration in high P soils. Low P availability in low P soil did not restrict denitrification. In contrast, long-term P-unfertilized soil had higher N₂O losses compared to high P soil, which were further stimulated with P addition. Glucose addition alleviated C limitation and strongly promoted microbial growth and respiration, but did not affect N₂O emissions among treatments. Bacterial denitrification and nitrifier denitrification were the main N₂O forming processes, while dissimilatory nitrate reduction to ammonium (DNRA) contributed to NO₃⁻ reduction, but only slightly to N₂O formation.

The mechanisms by which phosphorus (P) availability regulates the priming effect (PE) induced by the addition of leaf litter with different qualities remain unclear. Here, soil samples from a subtropical Pinus massoniana forest were added with/without P and/or high- and low-quality ¹³C-labeled leaf litter. The samples were then incubated in the laboratory for 75 days to assess the PE, microbial community composition, enzyme activity, and microbial carbon use efficiency (CUE). The results showed that litter addition led to a positive PE. High-quality litter inputs stimulated microbial activity but reduced microbial CUE, resulting in a higher PE intensity. By contrast, the PE exhibited a decrease with P addition. Such finding indicates that strategies for obtaining P, such as microbial decomposition of soil organic matter, may be reduced. The random forest analysis revealed that microbial CUE is the dominant factor regulating PE, accounting for 62% of the variation in PE, and it exhibited a negative effect on PE. Collectively, our findings emphasize that P availability regulates PE by decreasing microbial decomposition and increasing CUE, highlighting its essential role in carbon-climate feedbacks.

How photosynthetic carbon input regulates the microbial processes involved in carbon incorporation into soil organic carbon (SOC) and its stabilization during grassland degradation remains unclear. We utilized ¹³C to trace photosynthetic carbon incorporation into SOC and its pools, particulate (POC) and mineral-associated (MAOC) organic carbon, and carbon assimilation by soil microbes across five stages of alpine grassland degradation (S0, without grazing; S1, moderate grazing; S2–S4, light, moderate, and heavy degradation). As grassland approached S4, SOC in the top layer decreased by 53% compared with that in S3. A similar trend was observed in the middle and bottom soil layers, corresponding to a significant decrease in POC (decreased by 54, 40, and 35% in the top, middle and bottom layer, respectively) and carbon incorporation into POC (decreased by 83, 24, and 91% in the top, middle and bottom layer, respectively). A rapid decrease in MAOC was observed in S4, and carbon incorporation into MAOC decreased abruptly in the middle (10–20 cm) and bottom (20–30 cm) soil layers of S3. More than 57% of the incorporated carbon was concentrated in the top (0–10 cm) layers of S0-S4, whereas the middle and bottom layers of S3 and S4 exhibited nearly zero carbon incorporation. During degradation, fungal groups exhibited a downward trend in photosynthetic carbon assimilation, which was associated with their decreasing contribution to carbon incorporation into SOC. However, a relatively high proportion of bacteria participated in carbon assimilation at all soil depths at each stage, suggesting that more bacteria became active in decomposing the original SOC with decreasing carbon input. Our study successfully links aboveground and belowground processes which are crucial to comprehensively understand ecosystem responses to climate change and human activities.