Soil Biology & Biochemistry最新文献

The rhizosphere is a typical soil microbial hotspot, however, not a homogeneous entity. Due to root functional differentiation, different root functional modules (i.e., absorptive roots and transport roots) can play distinct roles in microbial necromass formation and subsequent soil organic carbon (SOC) sequestration by influencing microbial metabolic activity in the surrounding soil. Yet, how microbial metabolic traits mediated by different root functional modules regulate the accumulation of microbial necromass C (MNC) in the rhizosphere remains poorly understood. Herein, we quantified and compared the differences in the contribution of MNC to SOC between the rhizosphere of two root functional modules, and explored the role of microbial metabolic traits in influencing the contribution of MNC to rhizosphere SOC in different root functional modules in two spruce (Picea asperata Mast.) plantations. Our findings revealed that absorptive roots exhibited a significantly higher contribution of MNC to SOC (32.9-37.5%) compared to transport roots (27.7-30.5%) in the rhizosphere. This suggests that absorptive roots possess a greater ability to promote MNC accumulation in the rhizosphere than transport roots. This observation was mainly attributed to the difference in the trade-offs between microbial growth and investment traits between the two root functional modules. Specifically, the rhizosphere of absorptive roots had greater microbial C use efficiency (CUE), faster growth and turnover rates, lower respiratory quotients and biomass-specific enzyme activity than did those of transport roots, suggesting that absorptive roots support greater microbial growth yields and subsequently greater necromass production. Collectively, our findings demonstrate that the contribution of MNC to SOC in the rhizosphere largely depends on the trade-offs of microbial metabolic traits mediated by root functional differentiation. Our study also provides novel and direct empirical evidence supporting the need to integrate function-based fine root classifications with the different contributions of MNC to SOC sequestration in the rhizosphere into land surface models of C cycling.

Soil microorganisms can do both, mineralize and synthesize organic and condensed phosphate (P) species. Whereas P mineralization has been extensively studied, few studies have assessed the biological synthesis of organic P species, which can potentially accumulate in soil. The goal of this study was to investigate biotic and abiotic P transformations, particularly the synthesis of organic P species, upon water-soluble P addition in the organic (O) horizons of two beech forest sites with contrasting P availability.

The two O horizons (low-P and high-P) were subjected to four different nutrient addition treatments (Control without addition, CN, P, and CNP additions) in an incubation experiment of up to 104 days. We combined isotopic tracing (³³P-labelled P addition and ¹⁸O-enriched soil water) into sequentially extracted P pools with the characterization of organic P species (solution ³¹P nuclear magnetic resonance (NMR) spectroscopy) and soil respiration measurements.

The P availability of the two O horizons shaped the microbial response to the nutrient additions. In the low-P O horizon, P addition stimulated microbial activity together with the increase of organic (phosphodiesters and phosphonates) and condensed (polyphosphates) P species, most likely from microbial origin. In the high-P O horizon, microbes were unaffected by the added P and abiotic processes controlled its fate. CN addition had no effect on P fate in the high-P O horizon but reduced the transformation of added P into organic P and increased soil-derived P in the resin P pool in the low-P O horizon. The ¹⁸O isotopic values in phosphate of the resin P pool suggest that the released P was biologically cycled.

Our study confirms with a unique multi-analytical approach the microbial synthesis of phosphodiesters, phosphonates, and polyphosphates upon inorganic P addition under low P availability.

Associations of iron (hydr)oxides (FeOx) with organic carbon are vital in regulating the stability of soil organic carbon (SOC). Like SOC, FeOx is chemically dynamic in soils, particularly under anaerobic conditions. However, previous research has not clarified how the stability of FeOx (goethite versus ferrihydrite) and the formation pathway of FeOx-OC associations (adsorption versus coprecipitation) affect the stability of FeOx-bound OC and, subsequently, the priming effect (PE) under anaerobic conditions. With an aim to bridge this gap, we incubated paddy soils for 80 d under anaerobic conditions after adding free ¹³C-glucose, ferrihydrite- or goethite-bound ¹³C-glucose formed by either adsorption or coprecipitation. Compared with the free glucose addition, the FeOx-bound glucose addition increased ¹³CO₂ production by 8%–21% but reduced ¹³C–CH₄ production by 7%–10%. Ferrihydrite-bound glucose was mineralised more than goethite-bound glucose; this is consistent with its lower crystallinity facilitating reduction and, thus, higher OC bioavailability. Glucose induced a negative priming effect (PE) for CO₂ but a positive PE for CH₄, whereas FeOx-bound glucose showed the opposite trend. This may be because FeOx-bound glucose provides an energy source and electron acceptor for Fe-reducing bacteria; this promotes the dissimilating reduction of iron and combines with an aggravated microbial P limitation resulting from the FeOx input. The crystallinity of FeOx affected the amount of primed CH₄ rather than its formation pathway. In conclusion, the crystallinity of FeOx controls the stability of FeOx-OC associations and the PE of SOC decomposition under anaerobic conditions.

Root exudate composition can influence rhizosphere microbial recruitment and is tightly controlled by plant genetics. However, little research has profiled root exudate in vegetable crops or determined their role in rhizosphere microbial community and metabolite composition. It is also not well understood how root exudates and resulting rhizosphere dynamics shift across plant trait diversity and with the development of novel crop genotypes. To address these knowledge gaps, this study paired metabolomics and microbiome analyses to evaluate associations between the composition of exudates, soil bacterial and fungal communities, and soil metabolites across four genotypes of organically produced carrot of differential breeding histories, including two experimental genotypes. Plant genotypes modified soil microbial diversity and composition, and differentially recruited bacterial taxa. Bacterial rhizosphere recruitment from bulk soil was genotype and root exudate-mediated, while fungal recruitment was not. Moreover, root exudate composition was distinct in an heirloom genotype and a novel nematode resistant genotype, compared to other genotypes tested. Root exudate and rhizosphere metabolite composition was decoupled, and soil metabolites more strongly associated with fungal than bacterial communities. Taken together, the results of this study suggest that novel crop trait diversity and breeding histories hold consequences for the functional potential of soils through the diversification of root exudate mediated plant-microbe interactions.

Accurate representation of the chemical diversity of litter in ecosystem-scale models is critical for improving predictions of decomposition rates and stabilization of plant material into soil organic matter. In this contribution, we conducted a systematic review to evaluate how conventional characterization of plant litter quality using proximate analysis compares with molecular-scale characterization using ¹³C NMR spectroscopy. Using a molecular mixing model, we converted chemical shift regions from NMR into fractions of carbon (C) in five organic compound classes that are major constituents of plant material: carbohydrates, proteins, lignins, lipids, and carbonylic compounds. We found positive correlations between the acid soluble fraction and carbohydrates, and between the acid insoluble fraction and lignins. However, the acid-soluble fraction underestimated carbohydrates, and the acid insoluble fraction overestimated lignins by 243%. We identified two sources of uncertainties: i) disparities between litter chemical composition based on hydrolysability and actual chemical composition obtained from NMR and ii) conversion factors to translate proximate fractions into organic constituents. Both uncertainties are critical, potentially leading to misinterpretations of decay rates in litter decomposition models. Consequently, we recommend including explicit substrate chemistry data in the next generation of litter decomposition models.

Climate-induced changes in thinning snowpack can greatly impact soil freeze-thaw patterns and water supply. These effects may influence the soil microbial diversity and the key ecological functions mediated by microorganisms, thereby altering the cycling of nutrient in the ecosystem. A snow-exclusion experiment to explore the effects of snow removal on soil microbial diversity and functionality in Larix gmelinii forest. Control (natural snowfall), SR (complete snow removal) and SR-SR (complete snow removal, with snow returned for water supplementation at the end of winter) were represented three experimental treatments. The results showed that: snow removal resulted in more severe soil frost in winter. Soil nitrogen availability was higher in the snow removal plots compared to control plots in freeze-thaw period. Fungal diversity was not affected by snow removal, neither the α diversity of bacteria. However, snow removal did alter the bacterial community structure. These changes of the above did not persist into the growing season. SR-SR significantly reduced soil multifunctionality during freeze-thaw period, whereas SR did not. However, SR and SR-SR resulted in significantly higher soil multifunctionality than was observed in control during early growing season. Additionally, a widespread increase in the abundance of nitrogen cycling genes was observed in the SR and SR-SR plots during the freeze-thaw period and the early growing season, respectively. Snow removal significantly affected soil multifunctionality, which can be explained by changes in the microbial biomass, bacterial community structure and network complexity. Furthermore, snow removal significantly altered soil water content, temperature, and dissolved carbon, nitrogen. dbRDA and random forest analysis showed that soil water content, temperature, and total nitrogen as drivers of soil microbial community structure and multifunctionality. This study highlights that snow removal altered soil nitrogen availability, microbial community diversity, and multifunctionality during freeze-thaw period. However, these changes did not result in cross-seasonal legacy effects.

Straw and nutrients retained in soil are crucial for priming effect (PE) and consequently for soil organic matter (SOM) turnover. However, the mechanisms by which carbon (C), nitrogen (N), and phosphorus (P) and their stoichiometric ratios impact microbial communities and regulate the PE intensity remain controversial, particularly in the flooded rice soils. In this work, the PE dynamics and microbial life strategies were measured over 100 days following an analysis of C:N:P stoichiometry after ¹³C labeled straw and nutrient inputs. P was the most limiting nutrient for microorganisms in Straw + N, and soil organic matter (SOM) decomposition was thus reduced by 18%. This was evidenced by: (i) the highest stoichiometric imbalance of C:P (0.97) between available resources and microbial biomass, (ii) the highest dissolved organic C (DOC):Olsen P ratio (140), and (iii) the lowest bacterial abundance. In contrast, lowering the soil C:P ratio (65) under straw + NP accelerated SOM decomposition. Compared to straw + N, the bacterial gene abundance increased by 170% under straw + NP, and the relative abundance of Y-strategists (Firmicutes, Betaproteobacteria, Gammaproteobacteria and Bacteroidetes) was 6.8 times greater than that of straw + N, suggesting that P was a major limiting factor for microbes in this paddy soil. With the depletion of available C during incubation, bacterial gene abundance decreased for 9 times, and the abundance of Firmicutes decreased from 39% to 19%, the abundance of Deltaproteobacteria increased from 20% to 24%, indicating a shift from Y-strategists to A-strategists and acquiring the resources from SOM and inducing positive PE. Our study elucidates the complex and dynamic linkages between C, N and P and their available ratio in resources, and evidence changes in the microbial community structure and PE.

Generative AI (GenAI) is becoming a valuable tool for enhancing efficiency and can be used to help foster critical thinking skills among students and possibly assist in hypothesis generation. GenAI can excel at improving original content and to make it more accessible to broader audiences. While GenAI can create stunning images, inaccuracies persist, even with well-designed prompt engineering. Likewise, challenges persist in GenAI processing nuanced information accurately, highlighting the need for foundational knowledge and critical thinking when creating prompts and interpreting GenAI responses.

Soil carbon (C)-degrading extracellular enzyme activities (EEAs) are important regulators in targeting litter and soil organic carbon (SOC) decomposition in territorial ecosystems. However, the responses of enzymes involved in C-cycling to short-term litter input manipulations in different forest ecosystems remain unclear. Here, we examined oxidative C-degrading EEAs (Ox-EEAs), hydrolytic C-degrading EEAs (Hy-EEAs) and their ratios (Ox-to-Hy C EEA ratios) at topsoil (0–10 cm) and subsoil (10–30 cm) after two years of litter manipulations (i.e., Detritus Input and Removal Treatments-DIRT: control, CK; double litter, DL; no roots and double litter, NRDL; no litter, NL; no roots, NR; no roots and no litter, NRNL) in a coniferous forest (Pinus yunnanensis) and a broad-leaved forest (Quercus pannosa) in subalpine area of Southwest China. The litter addition did not significantly affect Ox-EEAs, Hy-EEAs, and their ratios in two forest soils. In contrast, the litter removal significantly decreased Hy-EEAs and slightly affected Ox-EEAs in coniferous forest soil, whereas they increased Ox-EEAs and slightly affected Hy-EEAs in broad-leaved forest soil. Consequently, the Ox-to-Hy C EEA ratios were significantly enhanced by litter removal in both two forest soils. This different variation in Ox-EEAs and Hy-EEAs under litter removal in two forest soils could be attributed to initial soil properties, where soil properties (e.g., pH, total nitrogen [TN], NO₃⁻-N, SOC) with lower C: N ratios in coniferous forest were more likely to promote Hy-EEAs. Whereas microbial parameters (e.g., microbial biomass C) and soil properties (e.g., dissolved organic C) mainly regulated Ox-to-Hy C EEA ratios at topsoil and subsoil in broad-leaved forest, respectively. Overall, our findings revealed different mechanisms and associated drivers on enzymes involved in C-cycling under short-term litter input manipulation of the subalpine coniferous forest and broad-leaved forest soils, which further strengthened our understanding of C-cycling in forest soils.

There is a knowledge gap surrounding how drought and wildfire, two increasingly frequent disturbances, will alter soil fungal communities. Moreover, studies that directly compare ambient and drought-treated soil fungal communities in the context of wildfire are exceptionally scarce. We assessed the response and recovery of soil fungal communities and functional guilds in two sites – a grassland and a coastal sage shrubland – after a severe wildfire burned a long-term drought experiment. We collected soil samples at four collection dates over an eight-month period after wildfire and amplified fungal DNA. We predicted that fungal communities within the drought and ambient treatments would differ significantly across collection dates owing to differing responses to post-wildfire conditions. Richness was stable across collection dates, regardless of precipitation treatment, in both sites. Differences between treatments were significant at every collection date with respect to taxonomical community composition. Differences in community composition between collection dates within each treatment were also significant. Additionally, the monotonic trends of drought and ambient communities over time differed in strength and direction. Differences in shrubland functional guild composition across collection dates and contrasting trends suggest a drought-dependent shift after the fire. Overall, we conclude that drought mediates how soil fungal communities respond after a wildfire in the long term, however drought effects may differ across ecosystems.