Priming Effect In Soil Research Articles

Soil microbiome-induced changes in the priming effects of 13C-labelled substrates from rice residues

Knowledge gap exists to understand the soil CO2 emission and microbial group response to substrates of whole plant residues and derived biochar. We used 13C-labelled substrates (rice straw, roots and biochar) to track influences of their decomposition on soil priming effect (PE) and phospholipid fatty acid (PLFA) composition during one-year incubation. Organic substrates at 1% (w/w) level increased soil pH, available nitrogen (AN) and available phosphorus (AP), especially during the first 45 days of incubation. After incubation, 44% of the added straw was mineralized to 13CO2, followed by roots (~35%) and biochar (~5%). Straw and roots amendment caused positive PE during 4–360 day of the incubation, where a lowest value of 41.9 mg C kg−1 was observed. Biochar amendment caused negative PE during 56–150 day of the incubation, where a largest value of −99.0 mg C kg−1 was observed. Analysis of 13C-labelled PLFA enabled the differentiation of microbial groups during substrates utilization. Gram positive bacteria (G+) and general bacteria groups were dominated in co-metabolizing both the native soil organic carbon (SOC) and substrates after straw and roots amendment. Gram negative bacteria (G−), especially identified by PLFA biomarkers cy17:0 and cy19:0, preferentially utilizes the 13C-labelled biochar but not promoting soil priming effect. Soil pH, SOC, AN and AP all explained changes of total and 13C-labelled PLFA contents (>75%, p < .05). Evidences showed that biochar is best in sequestering soil C pool, followed by straw and roots, and soil microbial groups in utilization of organic substances mediated SOC mineralization.

Correction to: Effects of nitrogen addition on DOM-induced soil priming effects in a subtropical plantation forest and a natural forest

The original version of this article, unfortunately, contained an error. In Figure 2 - panel d, incorrect image was published and this is now presented correctly in this article.

Biochar-Induced Priming Effects in Young and Old Poplar Plantation Soils

The priming effect (PE) induced by biochar provides a basis for evaluating its carbon (C) sequestration potential in soils. A 60 days’ laboratory incubation was conducted, which involved the amendment of biochar (1% of soil mass) produced from rice straw at 300ºC (B300) and 500ºC (B500) to young (Y) and old (O) poplar plantation soils, with the aim of studying the responses of biochar-induced PEs to poplar plantation ages. This incubation included six treatments: Y + CK (control), Y + B300, Y + B500, O + CK, O + B300, and O + B500. Carbon dioxide (CO2) emissions were significantly increased (p < 0.05) in the B300 amended soils, while it was decreased in the B500 amended soils compared to the CK. The primed CO2 emissions were 2.35 times higher in the Y + B300 than the O + B300 treatments, which was measured to be 18.6 and 5.56 mg C·kg-1 with relative PEs of 12.4% and 3.35%, respectively. However, there was little difference between the primed CO2 emissions in Y + B500 and O + B500 treatments, which were measured to be -24.9 and -29.6 mg·C·kg-1 with relative PEs of -16.6% and -17.8%, respectively. Dissolved organic carbon (DOC) was significantly lower in the young poplar plantation soil than that in the old poplar plantation soil regardless of biochar amendment throughout the incubation, indicating greater C-limit of soil microorganisms in the young poplar plantation soil. Using 13C isotope tracing, neither B300 nor B500 decreased native soil-derived DOC, which indicated that the negative B500-induced PEs were not due to a reduction in the availability of native soil-derived C. In conclusion, the response of biochar-induced PEs to poplar plantation age depends on biochar types while soil available C indirectly affects biocharinduced PEs. Further studies should focus on how the interactive effects between soil C availability and microbial community impacts biochar-induced PEs.

Effects of nitrogen addition on DOM-induced soil priming effects in a subtropical plantation forest and a natural forest

Dissolved organic matter (DOM) plays a key role in soil organic matter (SOM) decomposition via the priming effect (PE). The DOM-induced soil PE is closely related to nutrient availability, especially nitrogen (N). Regardless of the widespread of chronic N addition, how elevated N deposition affects DOM-induced PEs remains poorly understood. To fill this knowledge gap, we studied the effects of N addition, 13C-labeled leaf-DOM (herein DOM) addition, and leaf-DOM plus N addition (DOM+N) on soil PEs in soils of a subtropical Chinese-fir (Cunninghamia lanceolata) plantation and a natural Castanopsis carlesii forest (hereafter referred to as Chinese-fir soil and Castanopsis soil, respectively). Soil properties (e.g., soil organic C, total N, available phosphorus, and ratio of C and N), dissolved organic C (DOC), soil microbial biomass C (MBC), phospholipid fatty acid (PLFA), and enzyme activities were also investigated, because these parameters predominantly affect the intensity and direction of soil priming. The addition of DOM induced positive PEs in the Castanopsis soil but negative PEs in the Chinese-fir soil. In addition, DOM addition increased MBC and fungal abundance and the activities of phenol oxidase (PhOx) and peroxidase (Perox) in the Castanopsis soil but not in the Chinese-fir soil. Compared with DOM-only addition, DOM+N addition significantly enhanced PEs in the Chinese-fir soil but not in the Castanopsis soil. Furthermore, compared with DOM-only addition, DOM+N addition significantly increased MBC, abundance of fungi and AMF, fungi to bacteria ratio (F:B), and activities of four enzymes [β-glucosidase (βG), N-acetyl glucosaminidase (NAG), PhOx, and Perox] in the Chinese-fir soil but not in the Castanopsis soil. The DOM+N addition also had a significant effect on composition of main microbial groups in the Chinese-fir soil but not in the Castanopsis soil. These results suggest the enhanced PE following DOM+N in the Chinese-fir soil was likely mediated by enhanced enzyme production associated with increased fungal abundance. Our study highlights that the effects of increases of DOM on soil C cycling is largely affected by N availability and mediated by the effects on the abundance of soil microbial groups and enzyme activities. Our result also demonstrated a case in which effects of DOM and N addition on soil C cycling differ between a Castanopsis forest and a Chinese-fir plantation forest, with Chinese-fir soil being more sensitive to N addition. This is an important finding that needs to be taken into consideration in estimating the soil C pools.

The soil priming effect: Consistent across ecosystems, elusive mechanisms

Organic matter input to soils can accelerate the decomposition of native soil carbon (C), a process called the priming effect. Priming is ubiquitous and exhibits some consistent patterns, but a general explanation remains elusive, in part because of variation in the response across different ecosystems, and because of a diversity of proposed mechanisms, including microbial activation, stoichiometry, and community shifts. Here, we conducted five-week incubations of four soils (grassland, piñon-juniper, ponderosa pine, mixed conifer), varying the amount of substrate added (as 13C-glucose, either 350 or 1000 μg C g−1 week−1) and either with no added nitrogen (N), or with sufficient N (as NH4NO3) to bring the C-to-N ratio of the added substrate to 10. Using four different ecosystems enabled testing the generality of mechanisms underlying the priming effect. The responses of priming to the amount and C-to-N ratio of the added substrate were consistent across ecosystems: priming increased with the rate of substrate addition and declined when the C-to-N ratio of the substrate was reduced. However, structural equation models failed to confirm intermediate responses postulated to mediate the priming effect, including responses postulated to be mediated by stoichiometry and microbial activation. Specifically, priming was not clearly associated with changes in microbial biomass or turnover, nor with extracellular enzyme activities or the microbial C-to-N ratio. The strongest explanatory pathways in the structural equation models were the substrate, soil, and C-to-N ratio treatments themselves, with no intermediates, suggesting that either these measurements lacked sufficient sensitivity to reveal causal relationships, or the actual drivers for priming were not included in the ancillary measurements. While we observed consistent changes in priming caused by the amount and C-to-N ratio of the added substrate across a wide array of soils, our findings did not clearly conform to common models offered for the priming effect. Because priming is a residual flux involving diverse substrates of varying chemical composition, a simple and generalizable explanation of the phenomenon may be elusive.

Global ecological predictors of the soil priming effect

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios.

Global ecological predictors of the soil priming effect

Global ecological predictors of the soil priming effect

Biogeochemical responses of soil ecosystems to raw coal pollution in Xuanhua, China

China is the world’s largest coal producer and consumer. Despite extensive studies on coal-burning pollution, the effect of raw coal pollutants caused by transportation and turnover on soil along the road received little attention. The main purpose of the study was to clarify the biogeochemical response of soil ecosystems to raw coal pollution. The raw coal and unpolluted soil from the coal distribution area in Xuanhua, China were collected for the incubation experiments. Combined with the determination of soil physicochemical properties, including pH, electric conductivity, soluble ions, dissolved organic carbon, and available heavy metals, the biogeochemical responses of soil to raw coal pollution, such as soil enzyme activities (β-glucosidase, alkaline phosphatase, and Urease), microbial community composition, and soil respiration, were systematically studied. In addition, a q-PCR analysis of the urease was performed to clarify the inhibitory mechanism of urease by coal pollution. Furthermore, a simple field investigation was carried out to confirm the incubation results. Raw coal pollution not only changed the soil physicochemical properties but also made the available Zn, Ni, and Co accumulate significantly. A positive priming effect in soil with the low-dose raw coal addition was trigged, but soil respiration rate and soil enzyme activity, such as β-glucosidase and alkaline phosphatase, were inhibited to different degrees with the increased pollution. Urease activity also decreased under the higher coal contamination, which was due to inhibition of ureC gene expression. In addition to the slight soil acidification caused by coal pollution, microbial communities and diversity was also found to be affected. The relative abundances of the microorganisms related to urease, alkaline phosphatase, and β-glucosidase changed accordingly. The incubation results are in good agreement with the field survey results. Low-dose raw coal pollution can trigger the soil positive priming effect. However, as the coal pollution increased, the β-glucosidase, alkaline phosphatase, and urease in the soil were inhibited to varying degrees. The compounding effects of soil acidification, increased electric conductivity, and the accumulation of available heavy metals such as Zn, Ni, and Co are the key causes for the biogeochemical response of soil to coal pollution.

Microbial mechanisms of the contrast residue decomposition and priming effect in soils with different organic and chemical fertilization histories

We integrated chemical, enzymatic, isotopic and molecular approaches to investigate both straw decomposition and its priming effect (PE) on native soil organic carbon (SOC) decomposition in soils with 23 years of application of chemical fertilizer (NPK) and partial substitution of chemical fertilizer by organic manure (NPKM). We found that NPK and NPKM past application significantly increased decomposition of straw. The increases in straw decomposition were not correlated with the abundances of microbiome assimilating straw carbon, but were significantly correlated with abundances of total bacteria, fungi and activities of cellulose-degrading enzymes. In addition, application of NPK did not change straw-induced PE while application of NPKM markedly reduced PE. The variation of PE with different past fertilization was correlated with the abundance of residue-stimulated fungi. The unchanged PE with NPK application in the presence of enriched nutrients and reduced pH was probably due to residue-promoted growth of acid-tolerant SOC-decomposing taxa (unclassified bacteria families belong to Acidobacteria GP3, Gamaproteobacteria and WPS-2 and unclassified fungal families belong to Chaetothyriales and Agaricomycetes). Our research sheds light on the complex processes of carbon transformation in the soils undergoing different long-term nutrient management.

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

The priming effect is well acknowledged in soil systems but the effect of nitrogen (N) fertilization remains elusive. To explore how N modifies the priming effect in soil organic matter (SOM), one in situ experiment with 13C labeled glucose addition (0.4 mg C g-1 soil, 3.4 atom % 13C) was conducted on soil plots fertilized with three gradients of urea (0, 4 and 16 g N m-2 yr-1). After glucose addition, the soil CO2 concentration and phospholipid fatty acid (PLFA) were measured on day 3, 7, 21 and 35. The study found that N fertilization decreased soil CO2, PLFA and the fungi to bacteria ratio. Glucose triggered the strongest positive priming in soil at 0 g N m-2 yr-2, meanwhile N fertilization decreased SOM-derived CO2. Soil at 4 g N m-2 yr-2 released the largest amount of glucose-derived carbon (C), likely due to favorable nutrient stoichiometry between C and N. Stable microbial community biomass and composition during early sampling suggests “apparent priming” in this grassland. This study concludes that N fertilization inhibited soil priming in semi-arid grassland, and shifted microbial utilization of C substrate from SOM to added labile C. Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Litter carbon and nutrient chemistry control the magnitude of soil priming effect

Abstract Plant litter inputs can promote the decomposition of soil organic matter (OM) through the priming effect (PE). However, whereas leaf litter chemistry has long been identified as the primary driver of litter decomposition within biomes world‐wide, little is known about how litter chemical traits influence the occurrence and strength of the PE. Here, we studied the effects of 15 co‐occurring C3 leaf litters of contrasting chemistry on C4 soil respiration by analysing changes in 13C natural abundance during early and later stages of litter decomposition (up to 125 days). Besides an apparent PE of 16% in the first 3 days, soil C respiration was increased by 24% on average with leaf litter addition in the initial stage of decomposition (4–26 days) and by 8% at later stages (27–125 days). Most interestingly, soil PE related well to initial litter chemistry and the dominant factors influencing the magnitude of the PE changed with decomposition stage. In the early stage of decomposition, litter leachate C content and litter hemicellulose concentration were positively correlated with the strength of the PE, whereas tannin concentration was negatively associated with soil PE. Together, tannin and hemicellulose explained half of the observed variation in the PE (R2 = 0.58). In the later phase of decomposition, lignin and lignin:N ratios were negatively related to the PE, whereas Ca, K and Mg concentrations were positively related to the PE; lignin alone gave the best prediction of the PE (R2 = 0.58) at later decomposition stages. Our findings provide evidence that the magnitude and direction of the PE is influenced by the chemistry of OM inputs and suggest that, as decomposition proceeds differently among litter of contrasting chemistry, litters can also have variable effect on soil PE through time. The predictive power of litter chemical traits on soil PE opens new perspectives for improving our mechanistic understanding of soil PE and improving our abilities to model soil C dynamics at variable scales. A plain language summary is available for this article.

Priming effects of soil organic matter decomposition with addition of different carbon substrates

The addition of organic substrates can change the decomposition rate of soil organic matter (SOM), which is termed as “priming effect.” The objective of this study was to explore the priming effects of SOM decomposition with the addition of different organic carbon substrates, including glucose, oxalic acid, and tannin. We hypothesized that with additions from labile to recalcitrant carbon substrates, the soil priming effects changed from positive to negative. Representing from labile to recalcitrant carbon substrates, glucose, oxalic acid, and tannin were added to soil, respectively. Physicochemical properties of soil, carbon dioxide emission rate, soil organic carbon in the labile and recalcitrant carbon pools, microbial biomass carbon (MBC), and microbial community diversity and structure were measured in different treatments. Results showed that the addition of glucose and tannin produced positive priming effects, while the addition of oxalic acid led to a negative priming effect. The addition of glucose and tannin significantly increased the MBC. The addition of glucose significantly promoted the carbon decomposition in both the labile and recalcitrant soil carbon pools. The addition of tannin greatly promoted carbon decomposition in the labile carbon pool and slightly decreased carbon decomposition in the recalcitrant carbon pool of the soil. However, the addition of oxalic acid reduced the MBC and resulted in insignificant changes of the different soil carbon pools. The addition of organic carbon substrates reduced the soil microbial community diversity, especially the addition of glucose. The different priming effects of the treatments with glucose and tannin were attributable to the different phases in the succession of SOM decomposition processes. The treatment with oxalic acid reduced the soil pH, resulting in inactive microbial growth and reproduction. The addition of both glucose (labile carbon) and tannin (recalcitrant carbon) produced positive priming effects. In contrast, the addition of oxalic acid produced a negative priming effect. Except the treatment with tannin, the hypothesis was successfully tested. The results from this study should be useful to better understand the turnover processes of soil carbon pools with exogenous carbon inputs.

Crop residue-derived dissolved organic matter accelerates the decomposition of native soil organic carbon in a temperate agricultural ecosystem

Crop residue-derived dissolved organic matter (DOM) plays an important role in soil carbon (C) cycling. To investigate the effects of maize residue-derived DOM and urea additions on the native soil organic carbon (SOC) decomposition and soil net C balance a pot experiment was carried out during the winter wheat growing season in the North China Plain (NCP). The results showed that adding maize residue-derived DOM alone (RDOM) or together with urea (RDOM + N) accelerated the decomposition of native SOC and resulted in a net SOC loss. The net loss of SOC was 3.90 ± 0.61 and 3.53 ± 0.48 g C m−2 in RDOM and RDOM + N treatments, respectively. The stimulatory effect of per unit DOM-C addition on the native SOC decomposition was 0.25 ± 0.05 and 0.45 ± 0.07 for the RDOM and RDOM + N treatments, respectively. Increases in the microbial biomass and the activity of β-glucosidase, invertase and cellobiohydrolase as well as soil mineral N content were responsible for a more intense priming effect in DOM-amended soils. The positive relationship between primed soil C and soil available N (R = 0.76, P < 0.05) suggested that the stimulation of decomposition of native SOC by DOM addition would be enhanced by nitrogen fertilizer application.

Determining the Stability of Sugarcane Filtercake Biochar in Soils with Contrasting Levels of Organic Matter

Sugarcane filtercake is a nutrient-rich residue produced prior to sugarcane distillation and is commonly disposed of by applying directly to agricultural fields, often causing high decomposition and leaching rates. Transforming this material into biochar could improve its stability in the soil. In this 92-day incubation study, filtercake biochar produced at 400 °C (BC400) and 600 °C (BC600) was used to trace biochar stability when mixed with two soils with different organic matter levels: an agricultural field (1.2% carbon (C)) and a forest (2.8% C) soil. Based on δ13C isotope analysis, biochar decreases in the field soil mostly occurred in the coarse silt fraction. In contrast, biochar decreases in forest soil appeared to be more equally distributed in all particle size fractions. A negative priming effect in biochar-amended soils was noticeable, mainly in the forest soil. Cumulative CO2 emissions were greater in soils with BC400 than in those with BC600 for both field and forest soils, while adding biochar increased CO2 emissions only in field soils. This increase did not appear to affect native soil organic matter pools. High-temperature filtercake biochar could thus be a more stable alternative to the current practice of raw filtercake applications.

Shifts in priming partly explain impacts of long‐term nitrogen input in different chemical forms on soil organic carbon storage

Input of labile organic carbon can enhance decomposition of extant soil organic carbon (SOC) through priming. We hypothesized that long-term nitrogen (N) input in different chemical forms alters SOC pools by altering priming effects associated with N-mediated changes in plants and soil microbes. The hypothesis was tested by integrating field experimental data of plants, soil microbes and two incubation experiments with soils that had experienced 10years of N enrichment with three chemical forms (ammonium, nitrate and both ammonium and nitrate) in an alpine meadow on the Tibetan Plateau. Incubations with glucose-13 C addition at three rates were used to quantify effects of exogenous organic carbon input on the priming of SOC. Incubations with microbial inocula extracted from soils that had experienced different long-term N treatments were conducted to detect effects of N-mediated changes in soil microbes on priming effects. We found strong evidence and a mechanistic explanation for alteration of SOC pools following 10years of N enrichment with different chemical forms. We detected significant negative priming effects both in soils collected from ammonium-addition plots and in sterilized soils inoculated with soil microbes extracted from ammonium-addition plots. In contrast, significant positive priming effects were found both in soils collected from nitrate-addition plots and in sterilized soils inoculated with soil microbes extracted from nitrate-addition plots. Meanwhile, the abundance and richness of graminoids were higher and the abundance of soil microbes was lower in ammonium-addition than in nitrate-addition plots. Our findings provide evidence that shifts toward higher graminoid abundance and changes in soil microbial abundance mediated by N chemical forms are key drivers for priming effects and SOC pool changes, thereby linking human interference with the N cycle to climate change.

Microbial stoichiometric flexibility regulates rice straw mineralization and its priming effect in paddy soil

Nitrogen (N) and phosphorus (P) availability plays a crucial role in carbon (C) cycling in terrestrial ecosystems. However, the C:N:P stoichiometric regulation of microbial mineralization of plant residues and its impact on the soil priming effect (PE), measured as CO2 and CH4 emission, in paddy soils remain unclear. In this study, the effect of soil C:N:P stoichiometry (regulated by the application of N and P fertilizers) on the mineralization of 13C-labelled rice straw and the subsequent PE was investigated in a 100-day incubation experiment in flooded paddy soil. N and P additions increased straw mineralization by approximately 25% and 10%, respectively. Additions of both N and P led to higher CO2 efflux, but lower CH4 emission. With an increase in the ratios of DOC:NH4+-N, DOC:Olsen P, and microbial biomass C:N, 13CO2 efflux increased exponentially to a maximum. Compared with sole straw addition, exclusive N addition led to a weaker PE for CO2 emission, whereas exclusive P addition induced a stronger PE for CO2 emission. In contrast, CH4 emitted from native soil organic matter (SOM) was reduced by 7.4% and 46.1% following P and NP application, respectively. Structural equation models suggest that available N had dominant and direct positive effects, whereas microbial biomass stoichiometry mainly exerted negative indirect effects on PE. The stoichiometry of soil enzyme activity directly down-regulated CH4 emission from SOM. Microbes obviously regulate soil C turnover via stoichiometric flexibility to maintain an elemental stoichiometric balance between resources and microbial requirements. The addition of straw in combination with N and P fertilization in paddy soils could therefore meet microbial stoichiometric requirements and regulate microbial activity and extracellular enzyme production, resulting in co-metabolism of fresh C and native SOM.

Degradability of raw and post-processed chars in a two-year field experiment

The object of the present work was to analyse the degradation dynamics of four chars and a digestate applied to a sandy soil as well as possible initial priming effects on the mineralisation of soil organic carbon in a two-year field experiment. For that purpose, soil carbon content, soil respiration and the corresponding carbon isotopic abundances were repeatedly measured throughout two consecutive vegetation periods. In order to quantify and separate the amount and the degradation of the substrate-derived carbon and to assess soil priming effects, isotopic mixing models were applied to soil-derived and substrate-derived carbon, and to the respired CO2.Pyrolysis char was degraded with decreasing intensity over time with an estimated half-life of about 80years. HTC (HydroThermal Carbonisation) char showed a high degradation during the first year but, during the second year, the remaining recalcitrant pool was degraded much slower with a half-life between 49 and 61years. Digestate was degraded at a constant intensity with a half-life of about 14years. When the chars were fermented before being applied to the soil, the initial degradation of HTC char was reduced, but on the two-year scale, the degradation of both chars was higher than for untreated chars, yielding a half-life between 11 and 15years, comparable to digestate. The results showed considerable stability of the untreated pyrolysis and HTC chars under field conditions, and moreover, no net influence of chars as well as of digestate on the degradation of soil organic carbon after two years.

The priming effect generated by stoichiometric decomposition and nutrient mining in cultivated tropical soils: Actors and drivers

The priming effect (PE) in soil, when induced by a fresh carbon supply, is believed to result from two different mechanisms, “stoichiometric decomposition” and “nutrient mining”, and contributes to either long-term SOM stabilization or depletion. Understanding how to affect the balance between both mechanisms can provide valuable insight into agroecology, especially in Southern countries where organic matter management is the primary method of fertilizing cultivated plots. Therefore, the objective of this study was to investigate the bacterial actors in each mechanism and the influence of three drivers in Malagasy Ferralitic soils: the quality of the inducing substrate, the quality of the SOM, and the soil nutrient status. Three different agricultural Ferralitic soils, characterized by different levels of NH4 and PO4 availability, different SOM size fractionation profiles, and different bacterial communities, were amended with three types of 13C-labeled organic substrate (glucose, wheat residue, and rice residue) and the PE was measured at two incubation times (7 and 42 days). The results showed that a PE generated by stoichiometric decomposition was mainly induced by the polymerized fraction of crop residues, especially in soil enriched by decaying plant tissues, mineral N, and its associated decomposers guild such as Verrucomicrobia, α- and δ-Proteobacteria and Actinomycetes. Conversely, when this young SOM pool was reduced, the PE was mainly generated by N mining, especially when induced by soluble compounds and when N was limiting but P was available.

Feedstock determines biochar‐induced soil priming effects by stimulating the activity of specific microorganisms

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.

Effect of Contrasting Trophic Conditions on the Priming Effect in Gray Forest Soils

Priming effects initiated by the addition of 14С glucose have been compared for humus horizons of soils existing under continuous input of fresh organic substrates and for buried soil horizons, in which entering of organic matter has been essentially limited. The effect of microrelief on the manifestation of priming effect in the humus horizons of gray forest soil on microhigh and in microlow has been estimated. Humus horizon in soils on microhigh, not activated by glucose, produced two times more СО2 in comparison with soils of microlow. However, the introduction of glucose canceled the effect of microrelief on СО2 emission. The intensity of absolute priming effect correlated with the Сorg pool, initial microbial biomass, and enzyme activity, decreasing from humus horizons to the buried ones, and did not depend on microrelief. The effect of microrelief was observed, when assessing the priming effect relative to control (soil not activated by glucose): the value of relative priming effect was 1.5 times greater in А horizon of gray forest soil in microlow in comparison with that on microhigh being the result of increasing activity of enzymes.