Biology and Fertility of Soils最新文献

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.

The current opinion paper aims to revitalize the important methodological approach initiated by Phil Brookes to measure the adenylate energy charge (AEC) of soils, which indicates the energy status of microbial biomass carbon (MBC). Even dormant soil microorganisms maintain high AEC, i.e., (ATP + 0.5 × ADP) / (ATP + ADP + AMP), levels and, thus, rather stable ATP/MBC and adenylate/MBC ratios. New extractants, improved enzymatic tests, and chromatographic systems are available now that could give new impetus to the measurement of adenylates and AEC in soil. The AEC is a useful tool to investigate important and still unsolved questions in soil microbial biochemistry. For example, drying and rewetting cycles of soil lead to AEC fluctuations, where the energy fluxes of ATP hydrolysis and synthesis remain unknown. Decreasing AEC values might give insights into microbial death processes, particularly in combination with amino sugar assays or molecular genetic techniques.

The depletion of P resources is threatening agricultural sustainability and understanding the mechanisms by which land use change can restore soil health is therefore essential. This study investigated the long-term dynamics of soil phosphorus (P) following the conversion of cropland to grassland in northwestern Spain. The research evaluated how increases in soil organic matter (SOM) have influenced soil P forms along a 40-year chronosequence of grassland establishment, revealing a slow but gradual recovery of organic P (Po), mainly as P-monoesters and diesters. Intensive cropland management initially led to the significant loss of organic P through accelerated mineralization, promoting the dominance of inorganic P (Pi) forms. However, grassland establishment led to a gradual increase in the organic P contents, Po: Pi ratios and soil organic carbon (SOC): Po ratios, suggesting that conversion of cropland to grassland can partly mitigate the initial losses and promote P sustainability (improving nutritional P-use efficiency). Although the recovery of P levels and P distribution to the original state is a long-term prospect, the research findings highlight the important role of grassland conservation in sustaining soil nutrient cycles and fostering agroecosystem resilience.

Foxtail millet is a dietary staple cultivated in arid and semiarid regions worldwide but its sustainable cultivation is strongly restricted by continuous cropping obstacles. Here, we compared the performance of foxtail millet, rhizosphere soil fungi communities under non-continuous cropping, and two and eight years of continuous monocultures (C0, C2, and C8, respectively) to explore the underlying mechanisms. The emergence rates and yield of foxtail millet decreased under continuous monoculture, and the magnitude increased with years of the monoculture. The C8 soil slurry alone and in combination with bactericide (Bronopol) significantly suppressed the emergence rates and root length of foxtail millet, whereas the presence of fungicide (Captan) almost entirely attenuated the suppressive effects, indicating that fungi, but not autotoxicity, are responsible for the negative effects of the continuous cropping on the performance of foxtail millet. Eight-year of monoculture decreased the relative abundance of the fungal genera Acaulium, Gymnoascus, Mortierella, Solicoccozyma, and Pseudombrophila, stimulated the relative abundance of the fungal genera Fusarium, Acremonium, and Cephalotrichum. An F. oxysporum strain, YDSi-3, was isolated from the C8 rhizosphere soil, which induced root-rot disease in foxtail millet. The concentrations of phenolic acids, especially cinnamic acid, significantly increased in the C8 rhizosphere soil. The application of cinnamic acid largely increased the abundance of F. oxysporum in C0 soils. Overall, our findings suggest that the negative effects of continuous cropping on foxtail millet may be attributed to pathogenic fungal accumulation because of the phenolic-acid enrichment in the rhizosphere.

Comprehensive understanding of how seabird nesting influences island soil ecosystems and the underlying mechanisms remains limited. Here, the response of soil bacterial communities in biodiversity and functions to the changing soil properties induced by seabird nesting were investigated based on a case study on a subtropical, unpopulated island of China. Results showed that seabird nesting increased phosphorus input. Soil nitrate nitrogen was also significantly increased, while ammonium nitrogen was decreased. Seabird nesting decreased the alpha diversity of soil bacterial communities and led to a more frangible bacterial co-occurrence network. The relative abundances of Acidobacteriota and Proteobacteria were significantly increased, while that of Chloroflexi was significantly reduced. Soil nutrient cycling might also be weakened via the inhibition of functional genes involved in methane metabolism (pfkA, PFK, etc.), phosphonate transporter (phnC, phnE, etc.), and sulfate reduction (soxA, soxX, etc.). In addition, phosphorus dynamic was identified as the key driver of seabird nesting shifting island soil bacterial communities and nutrient cycles.

Nitrifier denitrification (ND) is recognized as an important pathway for N₂O production in agricultural soils, yet its contributions under different moisture contents are poorly quantified. Using an enriched dual isotope (¹⁵N − ¹⁸O) approach, we estimated N₂O production from ND across eight moisture levels (40–120% water-filled pore space, WFPS) in a typical agricultural soil from the North China Plain. Total N₂O flux began to increase when WFPS exceeded 70%, peaking at 100% WFPS, indicating substantial N₂O emission potential in wet soils. In contrast, the N₂O production from ND increased gradually from 40–70% WFPS, rose sharply from 70–90% WFPS, stabilized between 90–100% WFPS, and declined rapidly from 100–120% WFPS. ND contributed approximately 20%, 80%, and 30% of N₂O emissions under low (40–50% WFPS), intermediate (60–70% WFPS), and high (80–120% WFPS) moisture conditions, respectively. Future contributions from ND may increase as irrigation and extreme rainfall events become more frequent under changing climates.