The priming potential of biochar products in relation to labile carbon contents and soil organic matter status

Recognition of biochar as a potential tool for long-term carbon sequestration with additional agronomic benefits is growing. However, the functionality of biochar in soil and the response of soils to biochar inputs are poorly understood. It has been suggested, for example, that biochar additions to soils could prime for the loss of native organic carbon, undermining its sequestration potential. This work examines the priming potential of biochar in the context of its own labile fraction and procedures for their assessment. A systematic set of biochar samples produced from C4 plant biomass under a range of pyrolysis process conditions were incubated in a C3 soil at three discrete levels of organic matter status (a result of contrasting long-term land management on a single site). The biochar samples were characterised for labile carbon content ex-situ and then added to each soil. Priming potential was determined by a comparison of CO₂ flux rates and its isotopic analysis for attribution of source. The results conclusively showed that while carbon mineralisation was often higher in biochar amended soil, this was due to rapid utilisation of a small labile component of biochar and that biochar did not prime for the loss of native organic soil organic matter. Furthermore, in some cases negative priming occurred, with lower carbon mineralisation in biochar amended soil, probably as a result of the stabilisation of labile soil carbon.     

Identification of labile and stable pools of organic matter in an agrogray soil

The intensity of decomposition of the organic matter in the particle-size fractions from a agrogray soil sampled in a 5-year-long field experiment on the decomposition of corn residues was determined in the course of incubation for a year. The corn residues were placed into the soil in amounts equivalent to the amounts of plant litter in the agrocenosis and in the meadow ecosystem. A combination of three methods—the particle-size fractionation, the method of ¹³C natural abundance by C3–C4 transition, and the method of incubation—made it possible to subdivide the soil organic matter into the labile and stable pools. The labile pool reached 32% in the soil of the agrocenosis and 42% in the meadow soil. Owing to the negative priming effect, the addition of C4 (young) carbon favored the stabilization of the C3 (old) carbon in the soil. When the young carbon was absent, destabilization or intense decomposition of the old organic matter was observed. This process was found even in the most stable fine silt and clay fractions.     

Addition of Leucaena-KX2 mulch in a shaded coffee agroforestry system increases both stable and labile soil C fractions

Agroforestry systems have the potential to increase sequestration of atmospheric carbon dioxide (CO₂) as soil organic carbon (SOC) because of the increased rates of organic matter addition and retention. However, few studies have characterized the relative stability of sequestered SOC in soil. We characterized SOC storage in aggregate size and chemical stability classes to estimate the relative stability of SOC pools after the addition of Leucaena-KX2 pruning residues (mulch) from 2006 to 2008 in a shaded coffee agroforestry system in Hawaii. Soil samples were separated by microaggregate isolation, density flotation and dispersion, and acid hydrolysis, resulting in five distinct fractions that differed in relative stability: coarse particulate organic matter (POM), fine POM, microaggregate-protected POM, silt + clay hydrolyzable soil organic matter (SOM), and silt + clay non-hydrolyzable SOM. With mulch addition, the fine POM fraction increased. There was also a shift in the proportion of SOC to more stable silt + clay fractions. In the absence of mulch there was no significant change in SOC fractions. Given that the turnover time of SOC in silt + clay fractions is on the order of decades to centuries, the potential benefits of active shade management and mulching compensate for the loss of C sequestration in tree biomass from pollarding.     

Chemical composition of organic matter in a deep soil changed with a positive priming effect due to glucose addition as investigated by 13C NMR spectroscopy

Fresh organic carbon becomes more accessible to deep soil following losses of surface soil and deep intentional incorporation of crop residues, which can cause the priming effect and influence the quality and quantity of SOC in deep soil. This study determined the priming effect due to addition of water-dissolved ¹³C-labeled glucose (0.4 g C kg⁻¹ soil) to a soil taken from 1.00 to 1.20 m depth. The changes in chemical compositions of SOC in soils without (G₀) and with (G_0.4) glucose addition during a 31-d incubation were investigated with solid-state ¹³C cross polarization/total sideband suppression (¹³C-CP/TOSS) and CP/TOSS with dipolar dephasing nuclear magnetic resonance (NMR) techniques. No glucose remained in the soil after 21 days of incubation, with 48% being completely mineralized into CO₂ emission and 52% being incorporated into SOC. The native SOC was decomposed by 0.23% more in G_0.4 than in G₀. The NMR spectra demonstrated that both labile and recalcitrant organic compounds in SOC changed during the incubation, but in different manners in G₀ and G_0.4. During the incubation, the -(CH₂)_n-abundance in G₀ did not change over time, but in G_0.4 it decreased from Day 0 to Day 21 and then increased from Day 21 to Day 31, suggesting shifts of soil microbial communities only in G_0.4. After the incubation, in G₀ the abundances of ketones/aldehydes and nonpolar alkyl C increased, but those of aromatic C–C and protonated O-alkyl C (OCH) decreased; In G_0.4, the abundances of NCH and protonated O-alkyl C (OCH) increased, but those of nonpolar alkyl C and nonprotonated aromatic C–O and ketones/aldehydes decreased. Such inconsistent changes in recalcitrant compounds between G₀ and G_0.4 indicated that glucose addition likely primed the decomposition of aromatic C–O and suppressed the formation of ketones/aldehydes. We have demonstrated for the first time that the priming effect of SOC decomposition in the deep soil was involved with larger notable changes in both labile and recalcitrant structures of native SOC due to glucose addition compared with that without glucose addition.     

外加碳、氮对黄绵土有机质矿化与激发效应的影响

应用14C标记的葡萄糖和麦秸,15N标记的(NH4)2SO4和Ca(NO3)2对生黄绵土、菜园黄绵土土壤有机质的矿化与激发效应进行了研究。结果表明,外加有机质,特别是外加易分解的葡萄糖,和外加氮源,特别是外加(NH4)2SO4,对两种黄绵土土壤的有机质矿化与激发效应都有明显的促进作用,土壤有机质的矿化是高肥力菜园黄绵土高于低肥力生黄绵土,而有机质矿化的激发效应却是低肥力生黄绵土高于高肥力菜园黄绵土。外加有机质与外加N同时施入土壤时,外加N对外加有机质的矿化与激发效应同样有明显的促进作用,并发现外加有机质与外加N在促进土壤有机质矿化与激发效应过程中表现出正交互作用。激发效应对土壤肥力的更新和培养有积极作用。     

外加碳、氮对土壤氮矿化、固定与激发效应的影响

本文利用14C和15N对中国生黄绵土(坡地黄绵土)、菜园黄绵土和瑞典耕作草甸土的土壤氮矿化、固定与激发效应进行了研究。结果表明,外加碳、氮能促进土壤氮的矿化、固定与激发效应;促进作用的大小次序为外加NH4-15N大于外加NO3-15N,外加葡萄糖+NH4-15N大于外加葡萄糖+NO3-15N,外加麦秸+NH4-15N大于外加麦秸+NO3-15N,外加葡萄糖+NH4-15大于外加麦秸+NH4-15,外加葡萄糖+NO3-15N大于外加麦秸+NO3-15N;低肥力土壤高于高肥力土壤。在本文中提出了土壤净矿化氮的激发效应、土壤生物固定氮激发效应和土壤总矿化氮的总激发效应的概念,认为土壤氮的总激发效应更能反映土壤氮激发效应的实质。     

Response of labile organic C and N pools to plastic film removal from semiarid farmland soil

To examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5‐yr cultivation in the 0‐ to 20‐cm layer. Significant increases in extractable organic C (EOC), KMnO₄‐oxidizable C (KMnO₄‐C) and C management index (CMI) in the 0‐ to 20‐cm layer, and light fraction organic C and EOC in the 20‐ to 40‐cm layer were observed in response to plastic film removal after the 1‐yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO₄‐C and CMI were also observed after five years in the 20‐ to 40‐cm layer. Moreover, KMnO₄‐C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages.     

The inhibiting effect of nitrate fertilisation on methane uptake of a temperate forest soil is influenced by labile carbon

Upland soils are the most important terrestrial sink for the greenhouse gas CH₄. The oxidation of CH₄ is highly influenced by reactive N which is increasingly added to many ecosystems by atmospheric deposition and thereby also alters the labile C pool in the soils. The interacting effects of soil N availability and the labile C pool on CH₄ oxidation are not well understood. We conducted a laboratory experiment with soil columns consisting of homogenised topsoil material from a temperate broad-leaved forest to study the net CH₄ flux under the combined or isolated addition of NO ₃ ^? and glucose as a labile C source. Addition of NO ₃ ^? and glucose reduced the net CH₄ uptake of the soil by 86% and 83%, respectively. The combined addition of both agents led to a nearly complete inhibition of CH₄ uptake (reduction by 99.4%). Our study demonstrates a close link between the availability of C and N and the rate of CH₄ oxidation in temperate forest soils. Continued deposition of NO ₃ ^? has the potential to reduce the sink strength of temperate forest soils for CH₄.     

Immobilized-S, microbial biomass-S and soil arylsulfatase activity in the rhizosphere soil of rape and barley as affected by labile substrate C and N additions

Bulk and rhizosphere soil of rape and barley grown in a calcareous soil were pre-incubated for 7 days at 20 °C with Na₂³⁵SO₄ to partially label soil organic S. The soils were then incubated for 7 days more with increasing levels of two C sources as organic acids (succinic and malic acids) and as glucose (from 0 to 640 mg C kg⁻¹ soil) with or without increasing levels of N (from 0 to 15 mg N kg⁻¹ soil) in the form of ammonium nitrate, in order to mimic rhizodeposition inputs into soil. A second incubation experiment with a single highest dose of the used substrates was undertaken and two destructive soil samplings on days 17 and 35 were carried out. Both incubation experiments showed the intensities of S immobilization in the order: barley rhizosphere>rape rhizosphere>bulk soil. Glucose addition generated positive S priming effects in all studied soils after one week of incubation. Significant correlation coefficients were observed between immobilized-S and microbial biomass-S (r=0.95,p<0.001), arylsulfatase activity (ARS) and microbial biomass-S (r=0.65,p<0.05) on day 17 but not on day 35, whereas significant correlation coefficients were found between arylsulfatase activity and immobilized-S at both days 17 (r=0.79,p<0.01) and 35 (r=0.75,p<0.01). A marked decline of biomass-S noted in substrate-amended treatments at day 35 suggests a quick turnover of this compartment followed by its incorporation into the organic S. Finally, with organic acids high values of ARS per unit of biomass-S were recorded over the two studied dates in the rhizosphere soil of rape. It is concluded that the rhizosphere microbial biomass under rape exhibited more efficient arylsulfatase activity and hence greater turnover of organic S than that under the barley rhizosphere soil.     

Organic matter decomposition and carbon content in soil fractions as affected by a gradient of labile carbon input to a temperate forest soil

Labile carbon (C) input to soils is expected to affect soil organic matter (SOM) decomposition and soil organic C (SOC) stocks in temperate coniferous forests. We hypothesized that the SOM...     

The effect of boreal forest composition on soil respiration is mediated through variations in soil temperature and C quality

Getting a better understanding of CO₂ efflux from forest soils is critical for increasing our comprehension of the global C cycle. We examined the influence of two common boreal tree species, either in pure stands (BS = black spruce; TA = trembling aspen) or in mixtures (MW = BS + TA mixedwood), on total (R_S), heterotrophic (R_H) and autotrophic soil respiration (R_A) and their relationship with soil temperature and moisture, distance to the nearest tree, labile and total soil organic C (SOC), and root content. Stand-specific soil respiration–temperature models were developed to estimate annual soil CO₂ efflux. Soil temperature was the main factor explaining R_S and its components, followed by labile and total SOC. These three variables were significantly affected by forest composition, while no difference in soil moisture, distance to the nearest tree and root content was observed between stand types. A reciprocal forest floor transplant experiment showed that the influence of stand types on mineral soil temperature was due to a difference in light penetration rather than forest floor characteristics. Annual R_S and R_H were significantly greater in MW and TA than in BS, whereas annual R_A was greater in BS and MW than in TA. Temperature sensitivity (Q₁₀) of both R_S and R_H was significantly higher in BS than in MW and TA, suggesting that CO₂ efflux from BS soils could be increased more under climate warming than that from the other stand types. Our results show evidence that boreal forest composition affects soil CO₂ efflux and that litter quality is not the only factor explaining the differences between stand types. The influence of forest composition on soil CO₂ efflux would be mediated through effects on soil temperature as well as on factors affecting the accumulation and the quality of SOC.     

Negative priming effect on mineralization in a soil free of vegetation for 80 years

The priming effect (PE) is a complex process corresponding to a modification of mineralization rates of soil organic matter (SOM) following inputs of fresh organic matter (FOM). The priming effect can be either positive or negative (i.e. an acceleration or retardation of SOM decomposition) and is controlled by several factors such as microbial community composition, SOM chemical structure and nutrient availability. The first objective of our experiment was to study negative or positive PE of stabilized SOM. The second was to identify the role of FOM decomposers in the PE of stabilized SOM. We incubated, for 39 days, a fallow soil free of vegetation for 80 years amended with ¹³C‐cellulose and inoculated with a FOM‐decomposing community. The soil contained stabilized SOM. The PE of the stable organic matter was always negative and tended to be more negative when the FOM‐decomposing community was added. This suggests that for this particular soil, SOM mineralization was not limited by energy. Moreover, as the inoculation of a FOM‐decomposing community led to a more negative PE, we assume that the FOM‐decomposing community facilitated the access of FOM to the indigenous bare soil community.     

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.     

Fungi mediate long term sequestration of carbon and nitrogen in soil through their priming effect

It is increasingly recognized that soil microbes have the ability to decompose old recalcitrant soil organic matter (SOM) by using fresh carbon as a source of energy, a phenomena called priming effect (PE). However, efforts to determine the consequences of this PE for soil carbon and nitrogen dynamics are in their early stage. Moreover, little is known about the microbial populations involved. Here we explore the consequences of PE for SOM dynamics and mineral nitrogen availability in a soil incubation experiment (161 days), combining the supply of dual-labeled (¹³C and ¹⁴C) cellulose and mineral nutrients. The microbial groups involved in PE were investigated using molecular fingerprinting techniques (FAMEs and B- and F-ARISA). We show that mean residence time of SOM pool controlled by the PE decreased from 3130 years in the subsoil, where the availability of fresh carbon is very low, to 17-39 years in the surface layer. This result suggests that the decomposition of this recalcitrant soil C pool is strictly dependent on the presence of fresh C and is not an energetically viable mean of accessing C for soil microbes. We also suggest that fungi are the predominant actors of cellulose decomposition and induced PE and they adjust their degradation activity to nutrient availability. The predominant role of fungi can be explained by their ability to grow as mycelium which allows them to explore soil space and mine large reserve of SOM. Finally, our results support the existence of a bank mechanism that regulates nutrient and carbon sequestration in soil: PE is low when nutrient availability is high, allowing sequestration of nutrients and carbon; in contrast, microbes release nutrients from SOM when nutrient availability is low. This bank mechanism may help to synchronize the availability of soluble nutrients to plant requirement and contribute to long-term SOM accumulation in ecosystems.     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

稳定性液体氮肥在保护性耕作黑土中施用效果

氮肥利用率低是制约我国东北黑土区玉米产业高效稳定发展的重要因素,以尿素硝铵溶液(UAN)为原料,硝化抑制剂2-氯-6(三氯甲基)吡啶微胶囊(CPCS)为材料,制备稳定性液体氮肥,研究其对黑土区玉米氮素吸收与利用和生长发育的影响。以2-氯-6(三氯甲基)吡啶传统乳油剂型(CPEC)为对照,制备了0.5%CPCS-UAN、1%CPCS-UAN、2%CPCS-UAN 3种稳定性液体氮肥。田间试验设置6个处理:不施氮肥(N0)、UAN(N180)、1%CPEC-UAN(N180)、0.5%CPCS-UAN(N180)、1%CPCS-UAN(N180)和2%CPCS-UAN(N180)。在春玉米生育期内测定土壤无机氮动态变化及植株氮素吸收量,并在成熟期测定产量及其构成因素。2020和2021年田间试验结果显示,与UAN处理相比,CPCS-UAN处理能显著提高玉米产量和植株吸氮量,其中1%CPCS-UAN处理表现最优,玉米产量增加6.38%～8.35%,吸氮量增加24.12～31.70 kg/hm²;与传统乳油剂型1%CPEC-UAN处理相比,1%CPCS-UAN处理玉米产量增加5.39%～6.30%,吸氮量增加17.51～18.98 kg/hm²,CPCS-UAN处理增产的主要原因是单穗粒数和百粒重的增加。在玉米整个生育期CPCS-UAN处理0～20 cm土层土壤的铵态氮和硝态氮整体呈现逐渐降低的趋势,其土壤铵态氮含量在各个生育时期均高于其他处理。CPCS-UAN处理能显著降低氮肥表观损失率,增加氮肥表观利用率,其中1%CPCS-UAN处理的土壤氮肥表观损失率最低,为33.2%～34.0%,氮素表观利用率最高,为40.9%～49.6%。在黑土中,CPCS配合UAN制成的稳定性液体氮肥可以有效抑制玉米生育期内铵态氮向硝态氮转化,减少氮素损失,增加植株吸氮量,提高氮肥利用率和玉米产量。     

Old soil carbon is more temperature sensitive than the young in an agricultural field

Changes in the carbon stock of soil in response to climate change would significantly affect the atmospheric carbon dioxide concentration and consequently climate. The isotopes of carbon provide a means to study the temperature sensitivities of different soil carbon fractions. Where C3 vegetation has changed for C4, soil organic matter (SOM) from the different origins have different ¹³C/¹²C ratios. Relying on this feature, we took soil samples from a control field and a field where ordinary grain (C3) vegetation was replaced by maize (C4), 5 years ago. We measured the respiration rate and the ¹³C/¹²C ratio of the CO₂ produced by the samples at different temperatures. Based on these measurements, we quantified that Q₁₀ was 3.4-3.6 for the total CO₂ production while it was 2.4-2.9 at 20 °C for the maize-derived young carbon and 3.6 for the older C3-derived carbon. Our results suggest that climatic warming will accelerate especially the decomposition of the large pool of old soil carbon in these fields.     

设施菜田土壤pH和初始C/NO3– 对反硝化产物比的影响

【目的】设施菜田土壤反硝化作用是N₂O排放和氮素损失的重要途径。本研究通过室内厌氧培养试验,在不同pH和初始C/NO₃–条件下,比较设施菜田土壤反硝化氮素气体排放及产物比的变化特征。【方法】以设施菜田土壤为研究对象,通过添加一定量低浓度的酸碱溶液调节土壤pH分别为酸性、中性和碱性条件,调节后的实测pH分别为5.63、6.65和7.83;同时以谷氨酸钠作为有效性碳,除未添加有效性碳作为对照处理 (CK) 外,其他有效性碳与硝酸盐 (C/NO₃–) 的比值分别调节为5∶1、15∶1和30∶1,三种pH条件下均设置 4 个 C/NO₃– 水平,每个水平3次重复。利用自动连续在线培养系统 (Robot系统),在厌氧条件下监测不同处理土壤产生的 N₂O、NO、N₂和CO₂浓度的动态变化,通过计算N₂O/(N₂O + NO + N₂)指数估算反硝化过程N₂O的产物比。【结果】增加土壤的pH能显著减少设施菜田土壤N₂O和NO的产生量,酸性 (pH 5.63) 土壤的N₂O、NO产生量峰值在不同初始C/NO₃– 比下均显著高于中性 (pH 6.65) 和碱性 (pH 7.83) 土壤 (P < 0.05)。中性和碱性土壤在高C/NO₃– 下有利于减少反硝化过程N₂O的产生,而酸性土壤条件下差异并不显著。中性土壤条件下增加有机碳含量会降低NO产生量,而在酸性和碱性土壤上有机碳的添加对NO产生量没有显著影响。土壤pH和初始C/NO₃– 比对土壤N₂O的产生有极显著的交互效应 (P < 0.001)。酸性和中性土壤上添加有机碳能够显著增加土壤N₂的产生速率 (P < 0.05),且与对照相比,不同pH的土壤添加有机碳后均显著促进反硝化过程中N₂O向N₂的转化。在不同初始C/NO₃– 下碱性土壤的CO₂产生量显著高于酸性和中性土壤,同时与对照相比,添加有机碳显著增加了土壤的CO₂产生量 (P < 0.05)。酸性土壤的N₂O产物比在不同初始C/NO₃– 下均极显著高于碱性土壤 (P < 0.01),且不同初始C/NO₃– 下的土壤N₂O产物比随pH的增加显著下降,二者呈极显著线性负相关关系 (P < 0.01)。【结论】土壤pH降低是设施菜田土壤N₂O和NO排放量较高的重要原因。而且,增加初始土壤有效碳含量促进了土壤的反硝化损失,并在中性和碱性土壤中N₂O的产生量减少。土壤pH升高和初始C/NO₃– 增加均降低了产物比,但增加了土壤反硝化作用速率。在利用N₂O排放通量和产物比估算土壤反硝化氮素损失时,土壤pH和有效碳含量是必须考虑的两个重要因素。