Publications

Agroecosystems occupy large areas of the land surface and arable soil food webs are of significant importance for global cycling of carbon (C) and nitrogen (N). In a field experiment we labeled maize plants (Zea mays L.) in 13CO2 atmosphere and by K15NO3 fertilization. During 25days, the incorporation of 13C and 15N was traced in plant compartments, soil and soil arthropods, as well as 13C in microbial phospholipid fatty acids (PLFAs) and nematodes. Highlighting the importance of root-derived resources in agroecosystems, 13C was incorporated into all food web compartments, including microorganisms (PLFAs), nematodes and arthropods. The amount of incorporated 13C (as compared to unlabeled samples) markedly decreased along the food chain with ∆13C decreasing from 500‰ in plant roots and 900‰ in microbial PLFAs, to less than 40‰ in nematodes and arthropods. Incorporation of 13C into fungal PLFAs considerably exceeded that into bacterial PLFAs, highlighting the importance of soil fungi as compared to bacteria in C cycling. Fertilizer-derived 15N uniformly increased with time in plant compartments and soil arthropods, indicating that N is distributed homogeneously in the soil food web. High channeling of both root-derived 13C and fertilizer-derived 15N to higher trophic levels by fungi, and intensive feeding on fungi by soil animals highlight the central role of saprotrophic fungi in C and nutrient fluxes in soil food webs of arable ecosystems.

Aim Microbial carbon use efficiency ( CUE ) is one of the key indicators for the formation and release of soil carbon. CUE can be divided into exogenous CUE ( CUE ex , efficiency in using external carbon sources measured by e.g. 13 C or 14 C labeling) and endogenous CUE ( CUE en , efficiency in using internal carbon sources measured by 18 O labeling). Global changes strongly influence CUE, which response depends on the carbon source. However, the effect size and drivers of CUE ex and CUE en responses to global changes remain unclear, leading to large uncertainties when forecasting terrestrial carbon cycling. We aimed to quantify the magnitude and direction of microbial CUE ex and CUE en responses to global changes. Location Global. Time Period 2011–2024. Major Taxa Studied Soil microorganisms. Methods Database containing 213 paired microbial CUE ex and 155 paired microbial CUE en data was integrated and meta‐analysed to assess the impacts of global change factors on microbial CUE. Additional information gathered encompassed latitude, longitude, climate, plant properties, soil properties, microbial properties and experimental conditions. Results We found that CUE ex decreased with absolute latitude, while CUE en showed the opposite trend. Warming reduced CUE ex and CUE en by 3.6% and 16.5%, respectively. Drought increased CUE ex by 7.9%, but decreased CUE en by 14.3%. Nutrient inputs consistently decreased CUE ex by 5.0%–17.1%, while nitrogen and nitrogen combined with phosphorus and potassium inputs increased CUE en by 25.5% and 43.1%, respectively. Aridity index, soil pH and cation exchange capacity were the main factors influencing microbial CUE ex . In contrast, microbial respiration and growth rates, followed by microbial biomass, were the major predictors of microbial CUE en . Main Conclusions Biogeochemical models should account for the opposite spatial patterns of microbial CUE ex and CUE en , as well as their respective specific drivers under global changes, to accurately predict microbial responses to various carbon sources.

Microbial-mediated thickening of the organic layer at the soil–water interface limits the bioavailability of nutrients and protects organic matter.

Coastal wetlands contribute to the mitigation of climate change through the sequestration of "blue carbon". Microbial necromass, lignin, and glycoproteins (i.e., glomalin-related soil proteins (GRSP)), as important components of soil organic carbon (SOC), are sensitive to environmental change. However, their contributions to blue carbon formation and the underlying factors remain largely unresolved. To address this paucity of knowledge, we investigated their contributions to blue carbon formation along a salinity gradient in coastal marshes. Our results revealed decreasing contributions of microbial necromass and lignin to blue carbon as the salinity increased, while GRSP showed an opposite trend. Using random forest models, we showed that their contributions to SOC were dependent on microbial biomass and resource stoichiometry. In N-limited saline soils, contributions of microbial necromass to SOC decreased due to increased N-acquisition enzyme activity. Decreases in lignin contributions were linked to reduced mineral protection offered by short-range-ordered Fe (FeSRO). Partial least-squares path modeling (PLS-PM) further indicated that GRSP could increase microbial necromass and lignin formation by enhancing mineral protection. Our findings have implications for improving the accumulation of refractory and mineral-bound organic matter in coastal wetlands, considering the current scenario of heightened nutrient discharge and sea-level rise.

No abstract is provided for this article.

A paddy soil, with microbial biomass considerably reduced by chloroform fumigation, was treated with low-crystalline ferrihydrite and high-crystalline goet

No abstract is provided for this article.

Afforestation is an important strategy to increase soil organic carbon (SOC) stocks and stabilize soils against degradation and erosion. While the area under afforestation has increased globally during the last 20 years, the dynamics of SOC accumulation due to afforestation are still poorly known, as it cannot be directly compared to that in cropland. The goals of this study were: i) to investigate the dynamics of SOC accumulation after afforestation on the Loess Plateau; ii) to determine SOC contents and distribution in density fractions and aggregates most strongly affected by afforestation; and iii) to analyze the relationships between old and new SOC in relation with afforestation periods. A chronosequence of forest plots aged 1, 5, 12 (with Chinese pine, Pinus tabulaeformis Carr.) and 30 years (with white poplar, Populus alba L.) were selected within the large scale “Grain for Green” project. A maize field nearby was chosen as a control, which represents the land use prior to afforestation. At each location, soils were sampled at depths of 0–10 and 10–30 cm, respectively and aggregates were fractionated into <250, 250–2000 and > 2000 μm sizes, which were subsequently separated into light (ρ < 1.85 g cm−3) and heavy (ρ > 1.85 g cm−3) density fractions. SOC content was generally higher in afforested soils than in cropland and increased with stand age. The mean SOC accumulation rate was 0.11 g C kg−1 year−1 for the 0–10 cm layer of the 30-year-old forests, whereas the maximum rate was found for 5-year-old forest at 0.24 g C kg−1 year−1. For each period of afforestation, the maximum SOC content was recorded in the macroaggregates. The C turnover of the light fraction (calculated based on δ13C of SOC) peaked in the large macroaggregates and ranged from 21 to 23 years). Whereas SOC turnover in the heavy fraction, peaked in the microaggregates at a relatively longer period of 46 to 70 years. We conclude that the initial SOC accumulation under afforestation occurs mainly in the macroaggregates, with a faster turnover compared with microaggregates. During the first 30 years of afforestation, the SOC accumulation and stabilization is ongoing mainly in the upper 10 cm, while the C sequestration in 10 to 30 cm depth needs much longer time.

Spatial heterogeneity of soil bacterial community depends on scales.The fine-scale spatial heterogeneity of bacterial community composition and functions remains unknown.We analyzed the main driving factors of fine-scale spatial patterns of soil bacterial community composition and carbon metabolic functions across a 30 m × 40 m plot within a Korean pine forest by combining Illumina 16S rRNA sequencing with Biolog Ecoplates based on 53 soil samples.Clear spatial patterns in bacterial community composition and metabolic functions were observed in the forest soil.The bacterial community composition and metabolic functions both showed distance-decay of similarity within a distance of meters.Structural equation model analysis revealed that environmental variables and geographic distance together explained 37.9% and 63.1% of community and metabolic functions, respectively.Among all environmental factors, soil organic carbon (SOC) and root biomass emerged as the most important drivers of the bacterial community structure.In contrast, soil pH explained the largest variance in metabolic functions.Root biomass explained the second-largest variance in soil bacterial community composition, but root traits made no difference in metabolic functions variance.These results allow us to better understand the mechanisms controlling belowground diversity and plant-microbe interactions in forest ecosystems.

Improving nitrogen (N) acquisition by crops from soil is essential to reduce fertilization rates whilst maintaining yields. Plants can adapt their nutrient acquisition strategies according to N availability, which also affects soil microbial community structure, functions and activities and relies on the supply of carbon (C) for energy. We hypothesized that N deprivation would create hotspots of N- and C-acquiring hydrolase activities in maize rhizosphere through the effects of altered root exudation on the rhizosphere bacterial community. We grew maize under three N fertilization rates and combined soil zymography with the identification of rhizosphere microbial communities and non-targeted metabolic profiling of root exudates to explore enzyme hotspot formation. The rhizosphere extents of β-1,4-glucosidase (BG) and β-N-acetylglucosaminidase (NAG) activities decreased after N fertilization, narrowing by 48% and 39%, respectively, under typical field N application rates compared to zero application. Rhizosphere extents of enzyme activities were more sensitive to altered N supply than changes in the rates of enzyme activities: BG activity decreased by ∼10%, while NAG activity was unaffected. Decreases in the activities of both hydrolases and their rhizosphere extents caused by N addition correlated with reduced abundances of oligotrophs. The relative abundances of oligotrophic bacteria (e.g., Acidobacteria) decreased, while copiotrophs (e.g., Pseudomonadota and Patescibacteria) increased under the highest N application rate. Co-occurrence networks of the rhizosphere bacterial community revealed that functional units increased with BG activity, while an efficient and denser co-occurrence network supported expansion of its rhizosphere extent. The metabolic profiles of root exudates changed according to the N application rate, suggesting that their chemistry was regulated by the plant in response to N supply. The composition of root exudates and dissolved organic C and nitrate contents explained the largest variations in NAG hotspots in the rhizosphere. In summary, maize actively adjusts the composition of root exudates to increase interactions with rhizosphere bacteria, thereby stimulating hydrolase production and activities, and altering their rhizosphere extents to mobilize N and energy (C) in a larger soil volume, under conditions of N deficiency.

We grew rice in phosphorus (P) deficient subtropical paddy soil in a field study and used 13 CO 2 continuous labelling to investigate photosynthetic carbon (C) partitioning and allocation under FLOOD versus WET/DRY conditions, with and without P fertilization (80 mg P kg −1 ). The plants and soil were sampled after each of three WET/DRY cycles to determine 13 C allocation in above- and belowground plant biomass, microbial biomass, the rhizosphere, and bulk soil. Irrespective of water management, P-fertilized plants had higher biomass and P content and more total 13 C in the rice-soil system, especially the 13 C incorporation into the shoots (51%–96%), than samples without P fertilization. Root and bulk-soil 13 C were largely independent of both P fertilization and water management. However, by the third sampling, P fertilization had increased the amount of 13 C and microbial biomass 13 C in the rhizosphere soil (RS) by 28% (WET/DRY) and 95% (FLOOD), and by 47% (WET/DRY) and 50% (FLOOD), respectively. The WET/DRY condition had significantly higher microbial biomass and 13 C contents than FLOOD condition only in the RS. These results indicate that a well-established aboveground plant biomass following P fertilization is required to increase belowground C allocation. Thus, WET/DRY conditions, like FLOOD conditions, can provide moisture sufficient for unhindered P availability in rice-paddy system.

Uncertainty remains over what properties of biochar and which groups of microorganisms are responsible for the direction and magnitude of observed biochar‐induced priming effects (PE). We selected maize straw, grass, peanut shells and sugar cane as feedstocks to produce biochar at 300, 400 and 500°C by slow pyrolysis, and carried out an 80‐day soil–biochar incubation experiment to investigate biochar‐induced soil PE by adopting isotopic techniques. Irrespective of pyrolysis temperature, grass‐derived biochar (Grass‐B) induced the largest PE (348 to 1214 mg C kg −1 soil), whereas peanut shell‐derived biochar (Peanut‐B) induced the smallest (−135 to 261 mg C kg −1 soil) PE. The intensity of PE was largely determined by the feedstock and was closely related to the proportion of cellulose and lignin in it. The bacterial and fungal communities at days 8 and 40 were investigated by high‐throughput sequencing of 16S rRNA and ITS genes. Biochar additions explained 54.0 and 52.9% of the total variation in bacterial and fungal community structure, respectively. The bacterial Actinobacteria and Firmicutes were dominant during the initial phase of the PE (at day 8), whereas the fungal Sordariomycetes and Tremellomycetes were abundant after the longer phase of incubation at day 40. A succession from bacterial community (used the available C fraction of biochar) to fungal community (used the recalcitrant C fraction of biochar and soil organic C) might occur during the PE, together with the alternation of apparent PE to real PE. Highlights Feedstock type determines biochar‐induced priming effects (PE). A succession from bacterial to fungal community occurred. Actinobacteria and Firmicutes used biochar available C during the early stage. Sordariomycetes and Tremellomycetes were associated with the later real PE.