Microbial physiology and necromass regulate agricultural soil carbon accumulation

Strategies for mitigating soil organic carbon (SOC) losses in intensively managed agricultural systems typically draw from traditional concepts of soil organic matter formation, and thus emphasize increasing C inputs, especially from slowly decomposing crop residues, and reducing soil disturbance. However these approaches are often ineffective and do not adequately reflect current views of SOC cycling, which stress the important contributions of microbial biomass (MB) inputs to SOC. We examined microbial physiology as an alternate mechanism of SOC accumulation under organic (ORG) compared to conventional (CT) agricultural management practices, where ORG is accumulating C despite fewer total C inputs and greater soil tillage. We hypothesized that microbial communities in ORG have higher growth rates (MGR) and C use efficiencies (CUE) and that this relates to greater MB production and ultimately higher retention of new C inputs. We show that ORG had 50% higher CUE (±8 se) and 56% higher MGR (±22 se) relative to CT (p < 0.05). From in situ ¹³C substrate additions, we show that higher CUE and MGR are associated with greater rates and amounts of ¹³C glucose and phenol assimilation into MBC and mineral-associated SOC pools in ORG up to 6 mo after field substrate additions (p < 0.05). ORG soils were also enriched in proteins and lipids and had lower abundances of aromatic compounds and plant lipids (p < 0.05). These results illustrate a new mechanism for SOC accumulation under reduced C inputs and intensive soil disturbance and demonstrate that agricultural systems that facilitate the transformation of plant C into MB may be an effective, often overlooked strategy for building SOC in agricultural soils.     

Effects of single and mixed species forest ecosystems on diversity and function of soil microbial community in subtropical China

Purpose  

The objective of the present study was to evaluate soil microbial community function and diversity among eight single and mixed species forest ecosystems (18-year-old restoration) in subtropical China.     

亚热带松林中强酸性土壤自养和异养硝化作用的研究

The occurrence of nitrification in some acidic forest soils is still a subject of debate. Identification of main nitrification pathways in acidic forest soils is still largely unknown. Acidic yellow soil (Oxisol) samples were selected to test whether nitrification can occur or not in acidic subtropical pine forest ecosystems. Relative contributions of autotrophs and heterotrophs to nitrification were studied by adding selective nitrification inhibitor nitrapyrin. Soil NH₄⁺-N concentrations decreased, but NO₃^--N concentrations increased significantly for the no-nitrapyrin control during the first week of incubation, indicating that nitrification did occur in the acidic subtropical soil. The calculated net nitrification rate was 0.49 mg N kg^-1 d^-1 for the no-nitrapyrin control during the first week of incubation. Nitrapyrin amendment resulted in a significant reduction of NO₃^--N concentration. Autotrophic nitrification rate averaged 0.28 mg N kg^-1 d^-1 and the heterotrophic nitrification rate was 0.21 mg N kg^-1 d^-1 in the first week. Ammonia-oxidizing bacteria (AOB) abundance increased slightly during incubation, but nitrapyrin amendment significantly decreased AOB amoA gene copy numbers by about 80%. However, the ammonia-oxidizing archaea (AOA) abundance showed significant increases only in the last 2 weeks of incubation and it was also decreased by nitrapyrin amendment. Our results indicated that nitrification did occur in the present acidic subtropical pine forest soil, and autotrophic nitrification was the main nitrification pathway. Both AOA and AOB were the active biotic agents responsible for autotrophic nitrification in the acidic subtropical pine forest soil.     

Microbial response of an acid forest soil to experimental soil warming

 Effects of increased soil temperature on soil microbial biomass and dehydrogenase activity were examined on organic (O) horizon material in a low-elevation spruce-fir ecosystem. Soil temperature was maintained at 5  °C above ambient during the growing season in the experimental plots, and soil temperature, moisture, microbial biomass, and dehydrogenase activity were measured during the experiment. An incubation study was also conducted under three temperature regimes, 5, 15, and 25  °C, and under four moisture regimes of 20, 120, 220, and 320% to further evaluate these environmental factors on dehydrogenase activity and microbial biomass. Soil moisture content and microbial biomass controls were significantly lower (30% and 2 μg g^–1 soil, respectively) in the heated plots during the treatment period, suggesting that moisture content was important in controlling microbial biomass. In the incubation study, temperature appeared more important than moisture in controlling microbial biomass and dehydrogenase activity. Increasing temperature between 5  °C and 25  °C resulted in significant decreases in microbial biomass and dehydrogenase activity. Received: 7 August 1998     

Microbial activity in the profiles of gray forest soil and chernozems

Soil samples were taken from the profiles of a gray forest soil (under a forest) and southern chernozems of different textures under meadow vegetation. The microbial biomass (MB) was determined by the method of substrate-induced respiration; the basal respiration (BR) and the population density of microorganisms on nutrient media of different composition were also determined in the samples. The microbial metabolic quotient (qCO₂ = BR/MB) and the portion of microbial carbon (C mic) in C org were calculated. The MB and BR values were shown to decrease down the soil profiles. About 57% of the total MB in the entire soil profile was concentrated in the layer of 0–24 cm of the gray forest soil. The MB in the C horizon of chernozems was approximately two times lower than the MB in the A horizon of these soils. The correlation was found between the MB and the C org (r = 0.99) and between the MB and the clay content (r = 0.89) in the profile of the gray forest soil. The C mic/C org ratio in the gray forest soil and in the chernozems comprised 2.3–6.6 and 1.2–9.6%, respectively. The qCO₂ value increased with the depth. The microbial community in the lower layers of the gray forest soil was dominated (88–96%) by oligotrophic microorganisms (grown on soil agar); in the upper 5 cm, these microorganisms comprised only 50% of the total amount of microorganisms grown on three media.     

Response of soil respiration to nitrogen addition in two subtropical forest types

Anthropogenic activities have increased nitrogen (N) deposition in terrestrial ecosystems, which directly and indirectly affects soil biogeochemical processes, including soil respiration. However, the effects of the increases in N availability on soil respiration are not fully understood. In this study, soil respiration was measured using an infrared gas analyzer system with soil chambers under four N treatments (0, 5, 15, and 30 g N m^-2 year^-1 as control, low N (LN), moderate N (MN), and high N (HN), respectively) in camphor tree and slash pine forests in subtropical China. Results showed that soil respiration rates decreased by 37% in the camphor tree forest and 27% in the slash pine forest on average on an annual base, respectively, in the N-fertilized treatments when compared with the control. No significant differences were found in the soil respiration rate among the LN, MN, and HN treatments in both forest types as these fertilized plots reached an adequate N content zone. In addition, soil microbial biomass carbon (C) content and fine root biomass declined in N-treated plots compared to the control. Our results indicated that elevated N deposition might alter the tree growth pattern, C partitioning, and microbial activity, which further affect soil C sequestration by reducing soil respiration in subtropical forests of China.     

Microbial populations and the activity of the soil under agricultural and agricultural–pastoral systems

The effects of agricultural–pastoral and tillage practices on soil microbial populations and activities have not been systematically investigated. The effect of no-tillage (NT), no-tillage agricultural–pastoral integrated systems (NT-I) and conventional tillage (CT) at soil depths of 0–10, 10–20 and 20–30 cm on the microbial populations (bacteria and fungi), biomass-C, potential nitrification, urease and protease activities, total organic matter and total N contents were investigated. The crops used were soybean (in NT, NT-I and CT systems), corn (in NT and NT-I systems) and Tanner grass (Brachiaria sp.) (in NT-I system); a forest system was used as a control. Urease and protease activities, biomass-C and the content of organic matter and total N were higher (p < 0.05) in the forest soil than the other soils. Potential nitrification was significantly higher in the NT-I system in comparison with the other systems. Bacteria numbers were similar in all systems. Fungi counts were similar in the CT and forest, but both were higher than in NT. All of these variables were dependent on the organic matter content and decreased (p < 0.05) from the upper soil layer to the deeper soil layers. These results indicate that the no-tillage agricultural–pasture-integrated systems may be useful for soil conservation.     

Effect of labile and recalcitrant carbon on heterotrophic nitrification in a subtropical forest soil

Carbon (C) is an important factor controlling heterotrophic nitrification in soil, but the effect of individual C components (e.g., labile and recalcitrant C) is largely unclear. We carried out a C amendment experiment in which either labile C (glucose) or a recalcitrant C (cellulose and biochar) was added to a subtropical forest soil. A ¹⁵N-, ¹³C-tracing and MiSeq sequencing study was performed to investigate soil gross heterotrophic nitrification rates, carbon utilization for soil respiration and microbial biomass production and microbial composition, respectively. After 2 days, results showed a significant increase of gross heterotrophic nitrification rate in glucose (GLU) (on average 3.34 mg N kg⁻¹ day⁻¹), cellulose (CEL) (on average 0.21 mg N kg⁻¹ day⁻¹) and biochar (BIO) (on average 0.13 mg N kg⁻¹ day⁻¹) amendment in comparison with the unamended soil (CK) (on average 0.01 mg N kg⁻¹ day⁻¹; p < 0.05). The contribution of heterotrophic nitrification to total soil nitrification was significantly larger in GLU (average 85.86%), CEL (average 98.52%) and BIO (average 81.25%) treatments compared with CK (average 33.33%; p < 0.01). After 2-month amendment, the gross rates remarkably decreased in GLU (average 0.02 mg N kg⁻¹ day⁻¹), and the contribution to total nitrification (average 8.73%) were significantly lower than that in CK (p < 0.05). A decrease in the proportion of heterotrophic nitrification to total nitrification in soil was also observed in CEL (average 38.40%) and BIO (6.74%) treatments. Nevertheless, BIO amendment (compared to CK, GLU and CEL) showed the highest gross heterotrophic nitrification rate, accompanied by a notably higher abundance of specific heterotrophic nitrifiers, i.e. Trichoderma, Aspergillus and Penicillium. These results point to a stimulatory effect of C addition on soil heterotrophic nitrification in the short term, while the stimulatory impact of C amendment diminishes with the decline in easily available C. In addition, a shift of the microbial composition in the long term can possibly be sustained for longer if additional recalcitrant C is available to heterotrophic nitrifiers. The dynamic response of heterotrophic nitrification to labile and recalcitrant C in this study offered an explanation for the positive effect of plantation and plant root exudation on the process.     

中国亚热带丘陵区马尾松林氧化亚氮排放

The forest ecosystem plays a pivotal role in contributing greenhouse gases to the atmosphere.In order to characterize the temporal pattern of nitrous oxide(N_2O) emissions and identify the key factors affecting N_2O emissions from a Masson pine forest in a hilly red-soil region in subtropical central China,we measured the N_2O emissions in Jinjing of Hunan Province using the static chambergas chromatographic method for 3 years(2010-2012) and analyzed the relationships between the N_2O fluxes and the environmental variables.Our results revealed that the N_2O fluxes over the 3 years varied from-36.0 to 296.7 μg N m~(-2) h~(-1),averaging 18.4±5.6 μg N m~(-2) h~(-1)(n=3).The average annual N_2O emissions were estimated to be 1.6±0.3 kg N ha~(-1) year~(-1).The N_2O fluxes exhibited clear intra-annual(seasonal) variations as they were higher in summers and lower in winters.Compared with other forest observations in the subtropics,N_2O emissions at our site were relatively high,possibly due to the high local dry/wet N deposition,and were mostly sensitive to variations in precipitation and soil ammonium N content.In this work,a multiple linear regression model was developed to determine the influence of environmental factors on N_2O emissions,in which a category predictor of "Season" was intentionally used to account for the seasonal variation of the N_2O fluxes.Such a model explained almost 40%of the total variation in daily N_2O emissions from the Masson pine forest soil studied(P0.001).     

Decline of soil fertility during forest conversion of secondary forest to Chinese fir plantations in subtropical China

The effects of forest conversion on soil fertility are still not well understood in subtropical zones. This issue was addressed by comparing chemical properties of soil in a secondary forest and a Chinese fir (Cunninghamia lanceolata Hooker) plantation at the Huitong Experimental Station of Forest Ecology. Total N, available P, ‐N, cation exchange capacity (CEC) and exchangeable Al³⁺ and H⁺ of soil were significantly lower in the pure Chinese fir plantation (PCP) than in the secondary forest while soil organic carbon (SOC), total K and exchangeable Na⁺ had a tendency to decrease in the PCP. In contrast, soil pH and percentage base saturation (PBS) significantly increased due to forest conversion, and available K, ‐N and exchangeable Ca²⁺, Mg²⁺ and K⁺ tended to increase in the PCP. Some underlying processes responsible for the differences in soil fertility between the secondary forest and the Chinese fir plantation were low litterfall and root input to soil and site preparation in coniferous plantations. There was no significant difference in the effect of slope position on chemical properties of soil in the PCP and the secondary forest. Results indicated that the conversion of secondary forests to coniferous plantations leads to a decline in soil fertility. Copyright © 2010 John Wiley & Sons, Ltd.     

浙江南部亚热带森林土壤植硅体碳的研究

植硅体封存有机碳(Phytolith-occluded organic carbon,Phyt OC)是一种稳定的有机碳形态。它由植物自身硅化作用产生,在植物死亡或凋落后归还于土壤,从而影响森林生态系统稳定性碳库的储量。本文以浙江庆元县5种不同亚热带典型森林立地土壤为研究对象,利用不同土层深度(0~10 cm、10~30 cm、30~60 cm和60~100 cm)土壤样品,分析土壤植硅体含量和植硅体碳含量,并估算土壤中植硅体碳储量。结果表明,毛竹林、杉木林、针阔混交林、阔叶林和马尾松林土壤植硅体含量(土壤剖面平均值)变化范围在8.14~19.74 g kg-1,其中毛竹林土壤植硅体含量最高。而植硅体中Phyt OC平均含量最高的为马尾松林(24.31 g kg-1),最低的为针阔混交林(13.06 g kg-1)。土壤Phyt OC/TOC比值随土层深度增加而急剧增加。统计分析表明,不同林分下土壤硅含量与土壤植硅体含量呈极显著相关关系(p0.01),与土壤Phyt OC含量之间呈显著的正相关关系(p0.05)。我国亚热带毛竹林、杉木林、马尾松林、阔叶林和针阔混交林1 m土体Phyt OC总储量分别为1.988×107、4.025×107、2.575×107、2.542×107和0.340×107 t。     

Microbial performance under increasing nitrogen availability in a Mediterranean forest soil

In forest ecosystems, the external nitrogen (N) inputs mainly involve wet and dry depositions that potentially alter inorganic N availability in the soil and carbon (C) turnover. This study assesses the effect of a slow increase of inorganic N availability on microbial community activity and functionality in a Mediterranean forest soil. A four-month incubation experiment was performed with soil collected from the organic layer of a forest site and fertilized with a solution of ammonium nitrate. The fertilizer was supplied at an equivalent of 0, 10, 25, 50 and 75 kg N ha⁻¹ (0, 0.3, 0.7, 1.3 and 2 mg N g⁻¹ for control N0 and treatments N1, N2, N3 and N4, respectively). The incubation was carried out under optimal conditions, with the addition of the nutritive solution in small aliquots once a week to mimic the phenomenon of N deposition. In order to isolate the effect of N, the pH of the NH₄NO₃ solutions was adjusted to soil pH, and phosphorus was added in order to prevent any nutrient limitation effect. Inorganic N, C-mineralization, the activity of one oxidative enzyme (o-diphenol oxidase) and 8 hydrolitic enzymes (α-glucosidase, β-glucosidase, N-acetyl-β-d-glucosaminidase, cellulase, leucine amino-peptidase, acid phosphatase, butyric esterase and β-xylosidase) and the community level physiological profile (CLPP) were measured and analyzed during the whole incubation and at the end of the experiment as a proxy for microbial decomposition activity. In the first month, the highest N availability (N4) repressed the microbial respiration activity but stimulated microbial enzymatic activity, suggesting a change of C-pathways from spilling to enzymes and biomass investment. The treatments N1, N2 and N3 had no effect in the same period. Throughout the incubation, a general stress condition affected all the treated soils. As a consequence, treated soils exhibited higher respiration rates than the control. This was accompanied by a loss of functional diversity and an end-detected decline in biomass C. Although at the end of incubation most of the soil features showed a clear correlation with the inorganic N pool, the organic C content was strongly affected by different patterns of microbial activity during the experiment: the highest N treatment (N4) showed a lower C loss than the N3 treatment. Overall, the experiment showed how inorganic N availability can potentially alter the C cycle in a Mediterranean forest soil. The effect is non linear, depending on microbial community dynamics, on the community’s ability to adapt given the time scale of the process, and on N supply amount. Our study also revealed a common pattern in the short-term response to N addition in other, similar ecosystems with different climatic conditions.     

Microbial biomass and activity in an agricultural soil with different organic matter contents

Changes in soil fertility caused by various organic and N-fertilizer amendments were studied in a long-term field trial mostly cropped with cereals. Five treatments were included: (I) fallow, (II) cropping with no C or N addition, (III) cropping with N-fertilization (80 kg ha ^?1 yr^?1), (IV) cropping with straw incorporation (1800kg Cha^?1 yr^?1) and N-fertilization (80 kg ha^?1yr^?1), and (V) cropping with addition of farmyard manure (80 kg N + 1800kg Cha^?1yr^?1). The treatments resulted in soil organic matter contents ranging from 4.3% (I) to 5.8% (V). Microbial biomass and activity were determined by chloroform fumigation, direct counting of fungi (fluorescein diacetate (FDA)-staining and Jones-Mollison agar-film technique) and bacteria (acridine orange staining), most probable number determinations of protozoa, esterase activity (total FDA hydrolysis) and respiration. Both biomass estimates and activity measurements showed a highly significant correlation with soil organic matter. Microbial biomass C ranged from 230 to 600 μg C g^?1 dry wt soil, as determined by the fumigation technique, while conversions from direct counts gave a range from 380 to 2260 μg C. Mean hyphal diameters and mean bacterial cell volumes decreased with decreasing soil organic matter content.     

Microbial processes controlling P availability in forest spodosols as affected by soil depth and soil properties

Because carbon dioxide (CO₂) concentration is rising, increases in plant biomass and productivity of terrestrial ecosystems are expected. However, phosphorus (P) unavailability may disable any potential enhanced growth of plants in forest ecosystems. In response to P scarcity under elevated CO₂, trees may mine deeper the soil to take up more nutrients. In this scope, the ability of deep horizons of forest soils to supply available P to the trees has to be evaluated. The main objective of the present study was to quantify the relative contribution of topsoil horizons and deep horizons to P availability through processes governed by the activity of soil micro-organisms. Since soil properties vary with soil depth, one can therefore assume that the role of microbial processes governing P availability differs between soil layers. More specifically, our initial hypothesis was that deeper soil horizons could substantially contribute to total plant available P in forested ecosystems and that such contribution of deep horizons differs among sites (due to contrasting soil properties). To test this hypothesis, we quantified microbial P and mineralization of P in ‘dead’ soil organic matter to a depth of 120 cm in forest soils contrasting in soil organic matter, soil moisture and aluminum (Al) and iron (Fe) oxides. We also quantified microbiological activity and acid phosphomonoesterase activity. Results showed that the role of microbial processes generally decreases with increasing soil depth. However, the relative contribution of surface (litter and 0–30 cm) and deep (30–120 cm) soil layers to the stocks of available P through microbial processes (51–62 kg P ha^?1) are affected by several soil properties, and the contribution of deep soil layers to these stocks vary between sites (from 29 to 59%). This shows that subsoils should be taken into account when studying the microbial processes governing P availability in forest ecosystems. For the studied soils, microbial P and mineralization of P in ‘dead’ soil organic matter particularly depended on soil organic matter content, soil moisture and, to a minor extent, Al oxides. High Al oxide contents in some sites or in deep soil layers probably result in the stabilization of soil organic compounds thus reducing microbiological activity and mineralization rates. The mineralization process in the litter also appeared to be P-limited and depended on the C:P ratio of soil organic matter. Thus, this study highlighted the effects of soil depth and soil properties on the microbial processes governing P availability in the forest spodosols.     

Response of labile soil organic matter to changes in forest vegetation in subtropical regions

Labile soil organic matter (SOM) can sensitively respond to changes in land use and management practices, and has been suggested as an early and sensitive indicator of SOM. However, knowledge of effects of forest vegetation type on labile SOM is still scarce, particularly in subtropical regions. Soil microbial biomass C and N, water-soluble soil organic C and N, and light SOM fraction in four subtropical forests were studied in subtropical China. Forest vegetation type significantly affected labile SOM. Secondary broadleaved forest (SBF) had the highest soil microbial biomass, basal respiration and water-soluble SOM, and the pure Cunninghamia lanceolata plantation (PC) the lowest. Soil microbial biomass C and N and respiration were on average 100%, 104% and 75%, respectively higher in the SBF than in the PC. The influence of vegetation on water-soluble SOM was generally larger in the 0–10 cm soil layer than in the 10–20 cm. Cold- and hot-water-soluble organic C and N were on average 33–70% higher in the SBF than in the PC. Cold- and hot-soluble soil organic C concentrations in the coniferous-broadleaved mixed plantations were on average 38.1 and 25.0% higher than in the pure coniferous plantation, and cold- and hot-soluble soil total N were 51.4 and 14.1% higher, respectively. Therefore, introducing native broadleaved trees into pure coniferous plantations increased water-soluble SOM. The light SOM fraction (free and occluded) in the 0–10 cm soil layer, which ranged from 11.7 to 29.2 g kg⁻¹ dry weight of soil, was strongly affected by vegetation. The light fraction soil organic C, expressed as percent of total soil organic C, ranged from 18.3% in the mixed plantations of C. lanceolata and Kalopanax septemlobus to 26.3% in the SBF. In addition, there were strong correlations among soil organic C and labile fractions, suggesting that they were in close association and partly represented similar C pools in soils. Our results indicated that hot-water-soluble method could be a suitable measure for labile SOM in subtropical forest soils.     

Microbial ethylene production and inhibition of methanotrophic activity in a deciduous forest soil

Production of C₂H₄, but not of CH₄, was observed in anoxically incubated soil samples (cambisol on loamy sand) from a deciduous forest. Ethylene production was prevented by autoclaving, indicating its microbial origin. Ethylene production gradually decreased from 4 to 12 cm soil depth and was not affected by moisture or addition of methionine, a possible precursor of C₂H₄. Oxidation of atmospheric CH₄ in soil samples was inhibited by C₂H₄. Ethylene concentrations of 3, 6 and 10 μl l⁻¹ decreased CH₄ uptake by 21, 63 and 98%, respectively. Methionine and methanethiol, a possible product of methionine degradation, also inhibited CH₄ oxidation. Under oxic conditions, C₂H₄ was consumed in the soil samples. Ethylene oxidation kinetics exhibited two apparent K_m values of 40 μl l⁻¹ and 12,600 μl l⁻¹ suggesting the presence of two different types of C₂H₄-oxidizing microorganisms. Methanotrophic bacteria were most probably not responsible for C₂H₄ oxidation, since the maximum of C₂H₄ oxidation activity was localized in soil layers (2-8 cm depth) above those (8-10 cm depth) of CH₄ oxidation activity. Our observations suggest that C₂H₄ production in the upper soil layers inhibits CH₄ oxidation, thus being one reason for the localization of methanotrophic activity in deeper soil layers.     

Microbial responses of forest soil to moderate anthropogenic air pollution

There is a need to introduce soil microbiological methods into long term ecological monitoring programs. For this purpose we studied the impact of moderate anthropogenic air pollution in polluted and less polluted area districts, forest site types Calluna (CT), Vaccinium (VT) and Myrtillus (MT) and the amount of organic matter, measured as carbon content on the soil respiration activity and the ATP content. The main sources of local air pollutants (SO₂ and NO_x) in the polluted area district were from the capital' region and an oil refinery. Humus (F/H-layer) and the underlying 0 to 5 cm mineral soil samples were collected from 193 study plots located in the 5300 km² study area. We found that the soil respiration rate in humus layer samples was lower in the polluted area district compared to the less polluted one (16.0 and 19.5 μL CO₂ h^?1g^?1 dw, respectively), but the difference occurred only in the dry, coarse-textured CT forest site type. The mineral soil respiration rate and the mineral soil and humus layer ATP content were not affected, by the air pollution. Most of the variations of the biological variables were explained primarily by the soil carbon content, secondly by the forest site type and thirdly by the area division.     

Nitrogen addition change soil N pools with litter removal or not in subtropical forest

ABSTRACT

There are many nitrogen (N) pools in soil, so their availability and different status can give information about bulk soil response to N deposition. However, the different size of N pools in forest soils and the relationship between them have not been well studied under N deposition when considering the role of litter. Here soil in an N-deposition experiment carried out for 5 years in a broad-leaved forest was used as an object to study the response of N pools to N deposition by stepwise extraction using water or solutions containing 0.5 M K₂SO₄, 2.5 M H₂SO₄ (LPI), or 13 M H₂SO₄ (LPII), and calculation of recalcitrant (RC) N pool. Under N control (CT), soil with the presence of litter had a higher N of 23.8–106.8% in the first four pools, but lower of 80.6% in recalcitrant N pool compared with soil with the absence of litter. In the absence of litter, N addition increased soil N in labile pool but decreased N in the RC pool compared to CT and these impacts were greater at high added N (HN) than low-added N (LN) rates. However, in the presence of litter, LN increased the amount of N in the K₂SO₄- extracted pool and HN reduced that in the water extracted pool. Additionally, LN and HN increased TN in the RC pool and HN increased the total soluble N (TSN) in the LPI and LPII pool. N changes in the water extraction pool were attributed to inorganic N, whereas they were NH₄ ⁺ and soluble organic N (SON) in the K₂SO₄-extracted, LPI, and LPII pools. In the presence of litter, HN increased the SON concentration in the K₂SO₄, LPI, and LPII extractions; thus, SON may be a potentially important N form for N availability. These results suggested that N additions improve the accumulation of N in RC pool with the presence of litter. The different effects of N additions on soil N pool or N form in each pool depend on litter present or not.