土壤是大气中CO₂的主要源与汇，在缓解温室效应和实现“双碳”目标中发挥着重要作用。近期的研究认为，生物炭还田有望成为减少土壤碳排放和增加土壤碳汇的重要措施之一。该措施的有效性一方面取决于生物炭在土壤中的稳定性，另一方面取决于生物炭对土壤本底有机碳的激发效应和对土壤CO₂排放的影响，然而目前关于生物炭在土壤中的稳定性、生物炭引发的激发效应及其产生机制、以及生物炭对土壤CO₂排放的影响及机制仍不清楚。此外，生物炭施入土壤后，在一系列物理、化学和生物作用下生物炭的性质将发生改变，进而有可能影响生物炭还田在土壤固碳减排中的应用潜力，但是到目前为止，相关的研究相对较少。基于此，本研究以玉米秸秆为原料，在3个不同热解温度（300 °C、450 °C和600 °C）下制备生物炭，并采集了2种不同质地的酸性水稻土（砂质黏壤土和砂质壤土）和1种碱性土壤，采用室内培养实验并结合元素分析、固态¹³C核磁共振分析、高通量测序和稳定碳同位素（δ¹³C）等技术，通过测定生物炭的特性（元素组成、含碳官能团组成和溶解性有机碳（DOC）含量等）、生物炭的累积矿化量、土壤的理化性质（土壤pH、土壤阳离子交换量、土壤营养元素含量、土壤DOC含量和土壤团聚体等）、土壤的微生物特性（土壤酶活性和土壤细菌群落结构）、土壤本底有机碳的累积矿化量和土壤CO₂排放量，研究了生物炭组成结构、土壤质地、田间老化和外源有机质输入对生物炭稳定性的影响；考察了新鲜和老化生物炭对土壤本底有机碳的激发效应，并分析了激发效应的产生机制；探究了新鲜和老化生物炭对不同土壤CO₂排放的影响，并阐述了具体的影响机制。本研究的主要结论如下：

（1）随着热解温度从300 °C升至600 °C，生物炭的碳（C）含量、芳香碳含量、比表面积、总孔容和pH升高，而脂肪碳含量、DOC含量和阳离子交换量降低。在砂质黏壤土和砂质壤土中，生物炭累积矿化量的大小顺序均为：300 °C生物炭 > 450 °C生物炭 > 600 °C生物炭，并且双指数模型的预测结果显示，300 °C、450 °C和600 °C生物炭在土壤中的平均驻留时间分别为：42～45年、75～107年和161～249年。上述研究结果表明，与富含脂肪碳和溶解性碳质组分的低温生物炭相比，富含芳香碳的高温生物炭更加稳定。相较于砂质壤土，砂质黏壤土中黏粒和活性铁/铝氧化物的含量更高，并且3种生物炭在砂质黏壤土中的累积矿化量均低于砂质壤土，这意味着生物炭在富含黏粒和活性铁/铝氧化物的土壤中更加稳定。

（2）田间老化后，300 °C和450 °C生物炭的C含量降低，而氢（H）含量、氧（O）含量、H/C原子比、O/C原子比、(O+N)/C原子比、极性官能团含量和比表面积增加，并且生物炭的O/C原子比和(O+N)/C原子比会随着老化时间的延长而增大。与新鲜生物炭相比，田间老化后300 °C和450 °C生物炭的累积矿化量分别降低了48%～62%和18%～40%。对比不同田间老化时间采集的生物炭的累积矿化量的差异可以发现，当田间老化时间从15个月增至33个月，300 °C和450 °C生物炭的累积矿化量分别增加了38%和35%，并且老化生物炭的累积矿化量与其O/C原子比和(O+N)/C原子比间存在显著正相（R² =0.92，p < 0.01），表明田间老化过程中生物炭O/C原子比和(O+N)/C原子比的提高使得生物炭更易分解，进而能够降低生物炭的稳定性。添加水稻秸秆后，新鲜和老化生物炭的累积矿化量均显著增加，并且水稻秸秆的累积矿化量远高于生物炭，说明外源易降解有机质的输入能够加快新鲜和老化生物炭在土壤中的分解速度，降低生物炭的稳定性。

（3）在砂质黏壤土和砂质壤土中，新鲜生物炭的施用在实验前期（前2～7周）对土壤本底有机碳的矿化无显著影响，随后，显著抑制了土壤本底有机碳的矿化，产生负激发效应。并且在相应老化生物炭处理的土壤（室内老化360天）中也观察到了负激发效应的产生。在砂质黏壤土中，负激发效应的产生主要归因于生物炭引起的土壤微生物特性的变化。在砂质壤土中，负激发效应的产生机制会随着生物炭种类的变化而改变。具体而言：在低温生物炭（300 °C）处理的砂质壤土中，底物转化和土壤微生物特性的变化引起了负激发效应；而在高温生物炭（450 °C和600 °C）处理的砂质壤土中，负激发效应的产生机制主要是生物炭对土壤本底有机碳的吸附作用和生物炭引起的土壤微生物特性的变化。

（4）在新鲜生物炭处理的酸性土壤和相应老化生物炭处理的酸性土壤（室内老化360天）中，低温生物炭（300 °C）显著增加了土壤CO₂排放量，这主要是低温生物炭自身矿化引起的；然而，高温生物炭（600 °C）显著降低了土壤CO₂排放量，这一方面是因为高温生物炭自身矿化产生的CO₂较少，另一方面是因为高温生物炭抑制了土壤本底有机碳的矿化。在新鲜生物炭处理的碱性土壤和相应老化生物炭处理的碱性土壤（室内老化360天）中，低温生物炭（300 °C）显著促进了土壤CO₂排放，这主要是因为低温生物炭加入后提高了土壤DOC的含量，并使得土壤细菌群落从以寡营养型细菌（酸杆菌门）为主转向以富营养型细菌（变形菌门）为主；而高温生物炭（450 °C和600 °C）对土壤CO₂排放的影响会随着生物炭的老化而发生改变，具体而言：新鲜的高温生物炭显著抑制了土壤CO₂排放，这归因于生物炭引起的土壤DOC含量的降低，而老化的高温生物炭则显著促进了土壤CO₂排放，这主要是因为老化的高温生物炭使得土壤细菌群落的优势菌门从酸杆菌门转变为变形菌门。

（5）在酸性土壤和碱性土壤中，新鲜生物炭和老化生物炭都能够提高土壤的碳含量、降低土壤的碳损失量，并且土壤碳损失量的大小顺序依次为：300 °C生物炭处理的土壤 > 450 °C生物炭处理的土壤 > 600 °C生物炭处理的土壤。此外，新鲜和老化生物炭的施用还能够提高土壤总氮、有效磷和速效钾的含量。这表明生物炭的施用有助于提高土壤肥力，促进土壤碳的封存并且高温生物炭的固碳效果要优于低温生物炭。

本研究有助于加深对生物炭稳定性及其固碳减排效应与机制的认识，并且能够为我国固碳减排政策的制定和实施提供理论依据。

Soils act as a major sink and source of atmospheric CO₂ and therefore play an important role in mitigating the greenhouse effect and achieving the ‘dual carbon’ goals. Recent studies have shown that applying biochar to soils can be one of the appealing ways to reduce soil carbon emissions and increase soil carbon sinks. The effectiveness of this way is largely determined by the stability of biochar in soils, the priming effect induced by biochar on native soil organic carbon, and the effect of biochar on soil CO₂ emissions. However, the stability of biochar, the biochar-induced priming effect and its mechanisms, as well as the effects and mechanisms of biochar on soil CO₂ emissions are still unclear. In addition, after application in soils, biochar properties will change due to a series of physical, chemical and biological processes, thus potentially affecting the effectiveness of applying biochar to soils for soil carbon sequestration and CO₂ emission reduction, while few studies to date have been carried out in this area. Therefore, in this study, three different types of biochar were prepared by pyrolyzing maize straw at 300 °C, 450 °C and 600 °C, and two acidic paddy soils with different textures (sandy clay loam soil and sandy loam soil) and one alkaline soil were collected. Thereafter, laboratory incubation experiments were conducted to determine the properties of biochar (e.g., element compositions, carbon-containing functional groups, and dissolved organic carbon (DOC) contents), the cumulative amounts of biochar-carbon mineralized, the soil physicochemical properties (e.g., soil pH, soil cation exchange capacity, soil nutrient element contents, soil DOC contents, and soil aggregates), the soil microbial properties (soil enzyme activities and soil bacterial community structures), the cumulative amounts of native soil organic carbon mineralized, and the cumulative amounts of soil CO₂ emissions using elemental analysis, solid-state ¹³C nuclear magnetic resonance, high-throughput sequencing techniques, stable carbon isotopes (δ¹³C), etc. The main objectives of this study were to: (1) investigate the effect of biochar compositions and structures, soil texture, field aging and exogenous organic matter input on the stability of biochar; (2) examine the priming effect of fresh and aged biochar on native soil organic carbon and analyze the mechanisms for priming effect; (3) explore the effect of fresh and aged biochar on soil CO₂ emissions and clarify the underlying mechanisms. The main findings of this study were summarized as follows:

(1) Increasing the pyrolysis temperature from 300 °C to 600 °C resulted in an increase in biochar’s carbon content, aromatic carbon content, specific surface area, total pore volume, and pH, as well as a decrease in aliphatic carbon content, DOC content, and cation exchange capacity. In both sandy clay loam and sandy loam soils, the cumulative amounts of biochar-carbon mineralized followed the sequence 300 °C biochar > 450 °C biochar > 600 °C biochar. As estimated by the two-pool exponential model, the mean residence times of 300 °C, 450 °C and 600 °C biochar were 42-45 years, 75-107 years, and 161-249 years, respectively. These findings indicated that high-temperature biochar rich in aromatic carbon was more stable than low-temperature biochar rich in aliphatic carbon and DOC. The sandy clay loam soil had more clay and active iron (Fe)/aluminum (Al) oxides than the sandy loam soil, and regardless of biochar type, the cumulative amount of biochar-carbon mineralized was lower in the sandy clay loam soil than in the sandy loam soil, implying that biochar was more stable in soils with more clay and reactive Fe/Al oxides.

(2) After the field aging, for both 300 °C and 450 °C biochar, a decrease was found in their carbon contents, while an increase was observed in their hydrogen contents, oxygen contents, H/C atomic ratios, O/C atomic ratios, (O+N)/C atomic ratios, polar functional group contents and specific surface areas. Moreover, their O/C atomic ratios and (O+N)/C atomic ratios increased with aging time. Compared with fresh biochar, the cumulative amounts of carbon mineralized from aged 300 °C and 450 °C biochar decreased by 48%–62% and 18%–40%, respectively. As the aging time increased from 15 to 33 months, the cumulative amounts of carbon mineralized from 300 °C and 450 °C biochar increased by 38% and 35%, respectively. And significant positive correlations were found between the cumulative amounts of aged biochar-carbon mineralized and the O/C atomic ratios (R²⁼0.92, p< 0.01) as well as the (O+N)/C atomic ratios of aged biochar (R²=0.92.p< 0.01). These findings suggested that the increase in the O/C atomic ratio and (O+N)/C atomicratio of biochar during field aging made biochar more susceptible to decomposition and thus lessstable. Rice straw addition significantly increased the cumulative amounts of carbon mineralizedfrom both firesh and aged biochar, and the cumulative amounts of carbon mineralized from ricestraw were much higher than those firom biochar, indicating that the addition of easily degradable organic matter can accelerate the decomposition of both fresh and aged biochar and reduce biochar stability.

(3) In both sandy clay loam soil and sandy loam soil, fresh biochar had no effect on nativesoil organic carbon mineralization during the first 2-7 weeks and then induced a negative primingeffect on native soil organic carbon; in their corresponding aged samples (aged in soil for 360 days), a negative priming effect induced by biochar on native soil organic carbon was alsoobserved. In sandy clay loam soil, the negative priming effect was mainly attributed to biochar induced changes in soil microbial properties. In sandy loam soil, the mechanisms for negativepriming effect varied with biochar types. Specifically, the negative priming effect induced by low.temperature biochar (300 °C) was attributed to substrate switching and changes in soil microbiaproperties, while the negative priming effect caused by high-temperature biochar (450 °C and 600 °C) was due to the sorption of soil native organic carbon on biochar and changes in soil microbial properties induced by biochar.
(4) In fresh biochar-amended acidic soils and their corresponding aged samples (aged in soilfor 360 days), low-temperature biochar (300 °C) significantly increased soil CO₂ emissions due toits ineralization; while high-temperature biochar (600 °C)significantly reduced soil CO₂ emissions because of its high stability in soil and its negative priming effect on native soil organiccarbon. In fresh biochar-amended alkaline soil and their corresponding aged samples (aged in soifor 360 days), low-temperature biochar (300 °C) significantly increased soil CO₂, emissions, whichwas due to the biochar-induced inerease in soil DOC content and the biochar-induced soil bacteriacommunity shifted from being dominated by Acidobacteriota to being dominated byProleobacteria. However, the effect of high-temperature biochar (450 °C and 600 °C) on alkalinesoil CO₂ emissions changed with biochar aging. Specially, a significant decrease in alkaline soiCO₂ emissions was observed after fresh high-temperature biochar addition, owing to the biocharinduced decline in soil DOC content. However, an opposite trend was found in aged sampleswhich could be attributed to the biochar-induced shift of the dominant soil phylum from Acidobacteriota to Proteobacteria.
(5) In acidic and alkaline soils, both fresh and aged biochar increased soil carbon contentsand reduced soil carbon losses. And the order of soil carbon losses was as follows: 300 °C biocharamended soil > 450 °C biochar-amended soil > 600 °C biochar-amended soil. In addition, bothfresh and aged biochar increased the contents of soil total nitrogen, available phosphorus andavailable potassium. These findings showed that biochar application could help to improve soilfertility and promote soil carbon sequestration, with biochar produced at high pyrolysistemperatures having a high potential for carbon sequestration.
This study helps deepen the understanding of biochar's stability and its potential for soilcarbon sequestration and can provide a theoretical basis for the formulation and implementatiorof policies regarding carbon sequestration and emission mitigation in China.