● In low-salinity soil, straw-returning did not change necromass contribution to SOC.
● In medium-salinity soil, straw-returning reduced necromass contribution to SOC.
● Straw-returning reduced POC contribution to SOC in low-salinity soil.
● Straw-returning increased POC contribution to SOC in medium-salinity soil.
● Salinity affects the contribution of microbial-derived and plant-derived C to SOC.
Salinization affects microbial-mediated soil organic carbon (SOC) dynamics. However, the mechanisms of SOC accumulation under agricultural management practices in salt-affected soils remain unclear. We investigated the relative contribution of microbial-derived and plant-derived C to SOC accumulation in coastal salt-affected soils under straw-returning, by determining microbial necromass biomarkers (amino sugars) and particulate organic C (POC). Results showed that, straw-returning increased necromass accumulation in low-salinity soil but did not change its contribution to SOC. In medium-salinity soil, straw-returning did not increase necromass accumulation but decreased its contribution to SOC. In low- and medium-salinity soils, the contribution of POC to SOC showed the opposite direction to that of the necromass. These results suggest that under straw-returning, the relative contribution of microbial-derived C to SOC decreased with increasing salinity, whereas the reverse was true for plant-derived C. Our results highlighted that straw-returning reduces the contribution of microbial anabolism to SOC accumulation in salt-affected soils with increasing salinity.
● We studied the effect of nitrogen and biochar on CO2 emission from SOC and SIC.
● Nitrogen increased SIC-derived CO2 by 41% but decreased SOC-derived CO2 by 20%.
● Biochar reduced total soil-derived CO2 by neutralizing nitrogen-induced acidity.
● We proposed a method for 3- or 4-source partitioning CO2 emission from calcareous soils.
Biochar addition generally increases the alkalinity regeneration to resist soil acidification driven by nitrogen (N) fertilization. Calcareous soils contain soil organic carbon (SOC) and inorganic C (SIC). Owing to technical limitations in three-source partitioning CO2, how biochar addition affects SOC- and SIC-derived CO2 emission has not been clarified yet. Therefore, we conducted a 70-day incubation experiment of ammonium-N and maize-straw-derived biochar additions to investigate the N plus biochar impacts on SOC- and SIC-derived CO2 emission. Over the 70-day incubation, we found that the N-only addition increased the SIC-derived CO2 emission by approximately 41% compared with the control, but decreased the SOC-derived CO2 emission by approximately 20%. This suggests that the distinct responses of SIC- and SOC-derived CO2 emission to N-only addition come from N-induced acidification and preferential substrate (N) utilization of soil microorganisms, respectively. Compared with N-only addition, N plus biochar addition decreased the SIC-derived CO2 emission by 17%−20% during the first 20 days of incubation, but increased it by 54% during the next 50 days. This result suggested that biochar addition reduced the SIC-derived CO2 emission likely due to the alkalization capacity of biochar exceeding the acidification capacity of ammonium-N in the short term, but it may increase the SIC-derived CO2 emission induced by the weak acidity produced from biochar mineralization in the long term. This study is helpful to improve the quantification of CO2 emission from calcareous soils.
Soil organic carbon (SOC) is the largest pool of carbon in terrestrial ecosystems and plays a crucial role in regulating atmospheric CO2 concentrations. Identifying the essential relationship between soil bacterial communities and SOC concentration is complicated because of many factors, one of which is geography. We systematically re-analyzed 6102 high-quality bacterial samples in China to delineate the bacterial biogeographic distribution of bacterial communities and identify key species associated with SOC concentration at the continental scale. The type of land use was the principal driver of bacterial richness and diversity, and we used machine learning to calculate its influence on microbial composition and their co-occurrence relationship with SOC concentration. Cultivated land was much more complex than forest, grassland, wetland and wasteland, with high SOC concentrations tending to enrich bacteria such as Rubrobacter, Terrimonas and Sphingomona. SOC concentration was positively correlated with the amounts of soil total nitrogen and key bacteria Xanthobacteraceae, Streptomyces and Acidobacteria but was negatively correlated with soil pH, total phosphorus and Micrococcaceae. Our study combined the SOC pool with bacteria and indicated that specific bacteria may be key factors affecting SOC concentration, forcing us to think about microbial communities associated with climate change in a new way.
● Soil erosion resulted in homogenization of bacterial communities in the watershed.
● Microbial community heterogeneity among erosion sites made soil tracing possible.
● Assembly process results showed that the tracking results can achieve high precision.
● Dryland was the main source of sediment deposition based on the result of FEAST.
Sediment source tracing can accurately provide a theoretical basis for controlling soil erosion effectively, by identifying the most serious types of land use. Traditional sediment tracing methods are based on physical, chemical, biological, and composite fingerprinting, which have not included microbes. As high-throughput sequencing becomes more prevalent, microorganisms can provide more information than what we think. Thus, whether the microorganism can also be used as a special fingerprint factor for sediment source identification during soil erosion, we have tested it by using microbial source tracking tool FEAST to quantify the microbe contribution from five types of eroded land (including dryland, urban, paddy field, forest and grassland) to the depositional areas (Niubitan) in the Yuanjiang basin. The source microbial community in the erosive area was heterogeneous, and assembly process analysis further demonstrated that the source tracking results could reach higher accuracy. The results of FEAST showed that dryland (35.50%), urban (17.21%), paddy field (8.14%), and forest (1.07%) were the major contributors to Niubitan. Our results follow the general soil erosion rules and prove its validity. Taken together, a new perspective is provided by these results for tracing sediment sources in erosion-sedimentary systems.
● Gentamicin initially decreased microbial activity comparative to penicillin higher.
● Recovery was comparatively high in oxytetracycline treated soils.
● Organic amendments improved the resilience indices.
● Unexpectedly the qCO2 decreased in the antibiotic treated soils.
● The static effects of the applied antibiotics were higher than their cidal effects.
This study aimed to describe the static and cidal adverse effects of antibiotics on soil microbial activity resulting from manure application. So, in the present study, the treatments included: without antibiotics; application of gentamicin, oxytetracycline, and penicillin each in different concentrations (50, 100, and 200 mg kg−1 dry soil). They were applied in soils treated with and without organic and mineral conditioners (cow manure, biochar, and nano-zeolite). Soil microbial respiration and metabolic quotient were studied at three time periods (1−7, 7−30, and 30−90 days) during a 90-day incubation of the treated soils. Antibiotics applied to the soil samples significantly decreased soil basal respiration (BR) values compared to those of the control, and the most significant decrease was observed for gentamicin. Gentamicin had a short intensive impact, alleviated by manure and biochar, on soil copiotrophs. After a significant initial reduction in substrate-induced respiration (SIR), gentamicin application then caused a substantial increase in SIR values. Unexpectedly metabolic quotient decreased in the antibiotic-treated soils. This study revealed that the static effects of the applied antibiotics in soil were greater than the cidal effects.
● Bacterial richness declined but fungal richness increased under salinization.
● Bacteria did not become interactively compact or facilitative under salinization.
● Fungi exhibited more compartmentalized and competitive patterns under salinization.
● Fungal stability showed steeper increases under salinization than bacterial stability.
Soil salinization is a typical environmental challenge in arid regions worldwide. Salinity stress increases plant convergent adaptations and facilitative interactions and thus destabilizes communities. Soil bacteria and fungi have smaller body mass than plants and are often efficient against soil salinization, but how the stability of bacterial and fungal communities change with a wide range of soil salinity gradient remains unclear. Here, we assessed the interactions within both bacterial and fungal communities along a soil salinity gradient in the Taklamakan desert to examine (i) whether the stability of bacterial and fungal communities decreased with soil salinity, and (ii) the stability of which community decreased more with soil salinity, bacteria or fungi. Our results showed that the species richness of soil fungi increased but that of soil bacteria decreased with increasing salinity in topsoils. Fungal communities became more stable under soil salinization, with increasing compartmentalization (i.e., modularity) and proportion of competitions (i.e., negative:positive cohesion) as salinity increased. Bacterial communities exhibited no changes in modularity with increasing salinity and smaller increases in negative:positive cohesion under soil salinization compared to fungal communities. Our results suggest that, by altering interspecific interactions, soil salinization increases the stability of fungal not bacterial communities in extreme environments.
● Soil erosion decreased soil microbial CUE and increased microbial uptake of carbon.
● Soil erosion decreased microbial CUE by decreasing substrate C, N and MBC and increasing soil pH.
● Soil microbes had to increase their uptake rate to cope with the loss of substrates with increasing erosion rate.
● Soil microbial respiration increased with increasing degree of erosion.
● Soil microbial growth rate remained relative stable under different degrees of soil erosion.
● Microbial CUE in soil surface was less responsive to erosion than that in deeper soil.
Soil microbial carbon use efficiency (CUE) is an important synthetic parameter of microbial community metabolism and is commonly used to quantify the partitioning of carbon (C) between microbial growth and respiration. However, it remains unclear how microbial CUE responds to different degrees of soil erosion in mollisol cropland. Therefore, we investigated the responses of soil erosion on microbial CUE, growth and respiration to different soil erosion rates in a mollisol cropland in northeast China based on a substrate independent method (18O-H2O labeling). Soils were sampled at four positions along a down-slope transect: summit, shoulder, back and foot. We found microbial CUE decreased significantly with increasing soil erosion rate in 5−20 cm soil, but did not change in 0−5 cm. The decrease of microbial CUE in subsoil was because microbes increased C uptake and allocated higher uptake C to microbial basal respiration with increasing soil erosion rate. Microbial respiration increased significantly with soil erosion rate, probably due to the more disturbance and unbalanced stoichiometry. Furthermore, soil microbes in surface soil were able to maintain their growth rates with increasing degree of erosion. Altogether, our results indicated that soil erosion could decrease microbial CUE by affecting soil physical and chemical properties, resulting in more decomposition of soil organic matter and more soil respiration, which had negative feedbacks to soil C sequestration and climate changes in cropland soil.
● Nematode abundance and footprint show unimodal patterns with precipitation levels.
● MAP governed nematode diversity along the precipitation gradient of agroecosystem.
● Soil pH determined nematode abundance and footprint in low precipitation levels.
Precipitation plays a crucial role in global biodiversity change across terrestrial ecosystems. Precipitation is proven to affect soil organism diversity in natural ecosystems. However, how precipitation change affects the function of the soil nematode community remains unclear in cropland ecosystems. Here, we tested soil nematode communities from different precipitation sites (300 mm to 900 mm) of the agricultural ecosystem. The abundance of total nematodes, fungivores, and plant parasites, together with the footprint of fungivores was significantly affected by mean annual precipitation (MAP) in cropland ecosystem. Plant parasites diversity and footprint showed negative relationships with MAP. The random forest suggested plant parasite footprint was the most responsive to MAP. The structural equation model revealed that MAP affected nematode abundance and footprint indirectly via soil pH; nematode diversity was affected by MAP directly. We conclude that precipitation could act as the main selection stress for nematode diversity among the large gradient of agricultural ecosystems. However, the soil pH may act as a stress factor in determining nematode community and carbon flow in the soil food web. Our study emphasized that using nematode value by trophic group would provide a deep understanding of nematode response to precipitation in cropland ecosystems.
● Soil pH was a key driver of N2O emission and sources in acidic soils.
● N2O emission was significantly positively associated with the ratio of ITS to 16S.
● N2O was significantly correlated with bacterial and fungal community composition.
● Fungi contributed to N2O in highly acidic tea plantations and vegetable fields.
Acidic soil is a main source of global nitrous oxide (N2O) emissions. However, the mechanism behind the high N2O emissions from acidic soils remains a knowledge gap. The objective of this microcosm incubation study was to pin-point the microbial mechanisms involved in N2O production processes in acidic soils. For that purpose, the isotopic signatures and microbial community structure and composition of four soil samples were examined. The results showed that highly acid soils (pH = 3.51) emitted 89 times more N2O than alkaline soils (pH = 7.95) under the same nitrogen (N) inputs. Fungal denitrification caused high N2O emissions in acidic soils. ITS to 16S abundance ratio was positively correlated with cumulative N2O emissions from the tested soils. The highly acid soils (pH < 4.5) showed greater fungal nirK gene abundance and lower abundance of AOA-amoA, AOB-amoA, nirK, nosZ I and nosZ II genes. The unclassified Aspergillaceae fungi (63.65%) dominated the highly acidic soils and was the most strongly correlated genus with N2O emissions. These findings highlight that soil microbial community structures, denitrifying fungi in particular, shaped by low pH (pH < 4.5) lead to high N2O emissions from acidic soils.
● Characterization of mollisol soil DOM by untargeted metabolomics is possible.
● The polarity of the extractants determines the polarity of the extracted DOM.
● Land use patterns affect the biological functions and co-network interaction of DOM.
Mollisol soil is a major contributor to food production. Clarification of the molecular characteristics of dissolved organic matter (DOM) will contribute to the overall understanding and management of mollisol soil. However, the complexity of DOM poses a challenge to understanding its molecular characteristics. In this study, we investigated the molecular characteristics of DOM (< 1000 Da) in mollisol soils with different soil use patterns (forestland and dryland) based on untargeted metabolomics. Here, we confirmed the feasibility of untargeted metabolomics for the molecular characterization of DOM in mollisol soils. DOM in forestland is mainly derived from plant metabolites, and DOM can perform more biological functions. However, DOM in dryland has complex composition and has powerful co-occurrence network interactions due to human activities. Water has better extraction efficiency for polar DOM, while organic reagents can efficiently extract lipid-like DOM, but the polarity of the extractant has less influence on the DOM than the soil physicochemical properties. Meanwhile, 14-dihydroxyzeatin screened based on metabolomics can be used as a potential indicator for corn land. Therefore, untargeted metabolomics can be an effective method to characterize the DOM molecules of mollisol soil, which provides new insights for management of mollisol soil and sustainable agricultural development.
● High-quality and low-quality root litter had contrasting patterns of mass loss.
● Greater litter-derived C was incorporated into soils under high-quality root litter.
● Root litter decay rate or litter-derived C were related to soil microbial diversity.
● Root litter quality had little effect on soil physicochemical properties.
● High root litter quality was the main driver of enhanced soil C storage efficiency.
Decomposing root litter is a major contributor to soil carbon (C) storage in forest soils. During decomposition, the quality of root litter could play a critical role in soil C storage. However, it is unclear whether root litter quality influences soil C storage efficiency. We conducted a two-year greenhouse decomposition experiment using 13C-labeled fine root litter of two tree species to investigate how root litter quality, represented by C to nitrogen (C/N) ratios, regulates decomposition and C storage efficiency in subtropical forest soils in China. ‘High-quality’ root litter (C/N ratio = 26) decayed faster during the first year (0−410 days), whereas ‘low-quality’ root litter (C/N ratio = 46) decomposed faster toward the end of the two-year period (598−767 days). However, over the two years of the study, mass loss from high-quality root litter (29.14 ± 1.42%) was lower than ‘low-quality’ root litter (33.01 ± 0.54%). Nonetheless, root litter C storage efficiency (i.e., the ratio of new root litter-derived soil C to total mineralized root litter C) was significantly greater for high-quality root litter, with twice as much litter-derived C stored in soils compared to low-quality root litter at the end of the experiment. Root litter quality likely influenced soil C storage via changes in microbial diversity, as the decomposition of high-quality litter declined with increasing bacterial diversity, whereas the amount of litter-derived soil C from low-quality litter increased with fungal diversity. Our results thus reveal that root litter quality mediates decomposition and C storage in subtropical forest soils in China and future work should consider the links between root litter quality and soil microbial diversity.
