土壤生物质炭环境行为与环境效应

生物质炭具有高度稳定性和较强的吸附性能,可从气候、地质等多方面对环境产生影响,在全球气候变化、碳生物地球化学循环以及环境系统中发挥着非常重要的作用,长期以来成为国内外大气科学、地质学和环境科学领域研究的热点.作为土壤腐殖质中高度芳香化结构组分的可能来源,生物质炭对增加土壤碳库贮量、提高土壤肥力以及维持土壤生态系统平衡意义重大.本文重点概述了生物质炭特性、生物质炭生物与非生物氧化机理、生物质炭对全球气候变化的影响以及土壤生物质炭环境效应等方面的国内外研究进展,并对今后生物质炭在土壤生态系统中的环境行为和环境效应研究进行了简要的展望.     

生物质炭对土壤氮素循环的影响及其机理研究进展

生物质炭因其特殊的理化性质,具有改良土壤、持留养分、提高肥力及增加土壤碳库贮量的作用,成为土壤生态系统生物地球化学循环和农业固碳减排领域的研究热点.作为一种人为输入的新材料,生物质炭将直接或间接地参与土壤氮素物质的周转,进而对土壤生态系统功能产生深远的影响.本文综述了生物质炭输入对土壤生态系统氮素循环的影响研究,重点概述了生物质炭对土壤氮素物质吸附作用以及硝化作用、反硝化作用和固氮作用等生物化学过程的影响,并对其潜在的机理进行了分析.在此基础上,对今后生物质炭与土壤氮素循环的相互作用进行了展望.     

生物炭对土壤理化和微生物性质影响研究进展

生物炭是生物质原料限氧热解制备的高度芳香化和富含碳元素的黑色固体物质。生物炭所具有的独特的性质使生物炭在土壤改良方面具有很大的潜力, 已成为当前农业科学领域的研究热点。但是, 生物炭的性质受原料和热解温度的影响。生物炭性质和土壤环境条件的差异可在较大程度上影响生物炭改良土壤的效果。因此, 必须根据土壤的主要障碍因子, 选择合适的生物炭施加方案, 以期得到较好的土壤改良效果。综述了近年来国内外有关生物炭对土壤理化和微生物性质影响的研究进展, 探讨了生物炭改变土壤性质的机制和影响因素, 阐述了生物炭研究和应用中存在的一些问题, 从而为生物炭在农业领域的应用提供一定的思路。     

生物炭对土壤有机碳矿化的激发效应及其机理研究进展

近年来由于生物炭具有碳素稳定性强和孔隙结构发达等特性,其在土壤固碳减排方面的作用研究受到广泛关注.然而当生物炭进入土壤环境后最终是增加土壤碳的储存还是促进土壤碳的排放?目前学术界对该问题仍存在争议.生物炭对土壤有机碳的激发效应及其机理研究有待进一步深入开展.本文在分析生物炭自身碳素组分和稳定性、孔隙结构及表面形态特征的基础上,综述了添加生物炭对土壤本底有机碳矿化产生激发效应的研究进展,分别阐述了产生正激发和负激发效应(即促进和抑制矿化)的机制机理,认为正激发效应主要是基于生物炭促进土壤微生物活性增强、生物炭中易分解组分的优先矿化以及由此引发的土壤微生物的共代谢作用,而负激发效应主要是基于生物炭内部孔隙结构和外表面对土壤有机质的包封作用和吸附保护作用、生物炭促进土壤有机-无机复合体形成的稳定化作用、生物炭对土壤微生物及其酶活性的抑制作用.最后对今后相关研究方向进行了展望,以期为生物炭在土壤固碳减排方面的应用提供理论依据.     

生物炭介导植物病害抗性及作用机理

生物炭是生物有机材料在缺氧或限氧条件下经高温热裂解后生成的固体产物，在固碳减排、污染修复、土壤改良等方面具有较大的应用潜力。研究表明，生物炭在植物病害胁迫中也起重要的抗性作用。综述了国内外关于生物炭缓解植物病害的相关研究，重点介绍了生物炭在降低病害和提高植物抗性方面的作用机理。生物炭通过诱导植物增强系统抗性，改良土壤理化特性，改变土壤微生物群落结构，增加土壤有益微生物类群的丰度和活性，吸附病原菌及其产生的有毒物质等来降低病原菌对寄主植物的侵害作用，从而促进植物生长和增强植株抗病性。生物炭对病害的抗病效果与生物炭的原料类型、用量、土壤及病害类型等有关。未来的研究应重点应围绕"生物炭-土壤-植物病害"体系，借助组学手段，深入研究生物炭介导植物病害的分子机理。     

生物质炭对土壤养分淋溶的影响及潜在机理研究进展

农田生态系统中土壤养分淋溶控制一直是农业环境领域的研究热点.生物质炭因其特殊的理化性质,具有增加土壤碳库储量、改善土壤质量和提高作物产量等作用.作为一种外源输入的新型功能材料,生物质炭将直接或间接参与农田生态系统土壤养分循环,并对土壤养分淋溶产生重要影响.本文重点针对生物质炭影响土壤养分淋溶的内在因素(如:生物质炭的物理和化学性质及其与土壤生物的相互作用等)进行分析,并结合生物质炭添加量、土壤类型、土层深度、施肥情况、时间动态变化等外在因素,对生物质炭影响土壤氮磷等养分淋溶情况进行了综述.在此基础上,阐明了生物质炭对土壤养分淋溶的4种潜在影响机制:即通过微孔结构或表面电荷直接吸附养分、通过影响土壤持水能力影响养分淋溶、通过与土壤微生物的相互作用影响养分循环、被吸附的养分优先通过细微生物质炭颗粒发生迁移.最后对生物质炭与土壤养分流失控制领域的研究方向进行了展望.     

生物炭在土壤中的生态效应研究进展

生物炭是一类具有比表面积大、疏松多孔、含碳量极高的固体物质, 近年来, 作为一种新型的环境材料受到广泛的关注。然而, 由于原料种类、制备工艺等诸多因素的影响, 生物炭的应用对土壤生态系统的影响表现复杂多样。在此综述了不同原料制备的生物炭的理化特征, 总结了生物炭对土壤生态系统中植物、土壤动物、土壤微生物生态的影响, 最后针对生物炭的土壤生态效应研究提出展望, 为生物炭正向调控土壤生态系统以及生物炭的合理应用提供参考。     

生物炭及秸秆对水稻土各密度组分有机碳及微生物的影响

生物炭被认为是土壤碳封存的有效手段,但是关于生物炭对土壤不同密度组分有机碳影响的研究报道很少。以南方稻麦轮作区水稻土为研究对象,通过田间小区试验研究了不施有机物(CK)、玉米秸秆还田(CS)、施用300℃热解生物炭(300BC)、施用400℃热解生物炭(400BC)和施用500℃热解生物炭(500BC)处理对土壤轻重组分质量比例,土壤轻重组分有机碳和土壤微生物的影响。结果表明:1)施用生物炭显著提高了土壤轻组的质量比例和土壤轻组有机碳含量,轻组有机碳含量为500BC400BC300BCCSCK,对重组有机碳影响不显著,但重组有机碳在土壤中占重要比例;2)施加生物炭后土壤微生物量相比对照也有提高,但是与施加秸秆处理相比,微生物量提高幅度较小。研究表明,生物炭能提高土壤有机碳含量,尤其提高了土壤轻组有机碳的累积,但由于生物炭特殊的芳烃结构,其轻组组分化学性质稳定,这与传统的土壤有机碳轻组理论不同。与秸秆处理相比,生物炭处理具有较低的土壤微生物量与微生物商,有利于土壤碳的固定。     

生物炭的稳定性及其对矿物改性的响应机制研究进展

生物炭具有高度的碳素稳定性,是一种能有效缓解温室效应的固碳材料.研发碳素持留率高和稳定性强的生物炭对固碳减排具有重要意义.矿物改性处理能对生物炭的稳定性起调控作用,但目前相关研究并未得到足够重视,相应调控机理尚不十分清楚.本研究首先对生物炭稳定性的评价指标进行了归纳,主要包括H/C原子比、O/C原子比、稳定性系数R₅₀、挥发性物质含量、碳素热失重率、碳素(化学)氧化损失率、微生物矿化量等.其次,在分析生物炭稳定性影响因素(如原料类型、炭化条件、外界环境等)的基础上,综述了矿物改性对生物炭稳定性影响的研究进展,并探讨了稳定性增强和减弱的响应机制,认为生物炭稳定性的增强响应主要是基于矿物本身的物理阻隔作用,以及矿物与生物炭之间通过交互作用形成的有机矿物复合体对生物炭起到的保护作用,在一定程度上抑制生物炭的降解;而生物炭稳定性的减弱响应则主要与特殊矿物组分有关,例如含铁矿物组分在高温下促进生物炭的降解.最后对未来的研究方向进行了展望,以期进一步推动生物炭固碳减排技术的发展,并为获得稳定性更强的生物炭提供技术支撑和理论依据.     

玉米秸秆生物炭制备及结构特性分析

为了高效、经济、环保地解决华北平原地区玉米秸秆处置问题并寻求有效途径,该研究以玉米秸秆为原料,采用限氧裂解法在不同温度(200℃、300℃、400℃、500℃)下制备生物炭,并对生物炭的热解动力学、结构形貌、元素组成、比表面积、孔径分布、官能团等理化特征进行了分析表征。结果表明:不同裂解温度制备的生物炭具有不同的差热曲线,其官能团的组成也存在差异,这表明了样品中不同生物质的热解反应过程。随着热解温度的升高,生物炭产率、氢和氧含量下降,同时H/C和(O+N)/C比值也降低,而碳和氮含量却升高,说明生物炭芳香性增强,亲水性和极性减弱,性质趋于稳定。生物炭热重曲线和差热曲线分为三个过程,热解温度高时失重比例低,曲线趋向平缓。生物炭的比表面积、微孔比表面积、中孔体积和微孔体积随着热解温度的升高而增大,但最可几孔径却减小,吸附能力增强。综上所述,400℃的温度制备生物炭,其产率相对较高、结构最稳定、吸附性能最佳,有助于最大程序的利用农业废弃物资源、降低耗能,提高农产品附加值。     

施用生物炭对土壤动物群落的影响研究进展

土壤动物是土壤生物群落不可或缺的组成部分,是调控土壤生态过程重要的生物驱动因子。探明向土壤中施加生物炭对土壤动物群落的影响及二者之间的相互关系,对深刻认识土壤生态系统的运行机制、评价土壤生态服务功能具有重要意义。本文综述了施用生物炭对土壤动物群落的影响及机制,包括生物炭原料、制备温度、施用量的差异对土壤动物群落造成的直接影响,及以生物介导(改变植物生理特性、提高微生物数量)和非生物介导(土壤理化性质的改变)环境条件的改变对土壤动物群落造成的间接影响。低量生物炭添加下(生物炭与土壤质量比＜5%),对土壤动物的生长繁殖和行为活动起促进作用,若施炭量过高(＞10%),则会产生毒害;土壤动物的行为活动也会影响生物炭的稳定性。未来应该加强长期田间定位、时空变异性、多学科交融和分析预测等方面的研究。     

Do biotic interactions modulate ecosystem functioning along stress gradients? Insights from semi-arid plant and biological soil crust communities

Climate change will exacerbate the degree of abiotic stress experienced by semi-arid ecosystems. While abiotic stress profoundly affects biotic interactions, their potential role as modulators of ecosystem responses to climate change is largely unknown. Using plants and biological soil crusts, we tested the relative importance of facilitative–competitive interactions and other community attributes (cover, species richness and species evenness) as drivers of ecosystem functioning along stress gradients in semi-arid Mediterranean ecosystems. Biotic interactions shifted from facilitation to competition along stress gradients driven by water availability and temperature. These changes were, however, dependent on the spatial scale and the community considered. We found little evidence to suggest that biotic interactions are a major direct influence upon indicators of ecosystem functioning (soil respiration, organic carbon, water-holding capacity, compaction and the activity of enzymes related to the carbon, nitrogen and phosphorus cycles) along stress gradients. However, attributes such as cover and species richness showed a direct effect on ecosystem functioning. Our results do not agree with predictions emphasizing that the importance of plant–plant interactions will be increased under climate change in dry environments, and indicate that reductions in the cover of plant and biological soil crust communities will negatively impact ecosystems under future climatic conditions.     

Relating microbial community structure to functioning in forest soil organic carbon transformation and turnover

Forest soils store vast amounts of terrestrial carbon, but we are still limited in mechanistic understanding on how soil organic carbon (SOC) stabilization or turnover is controlled by biotic and abiotic factors in forest ecosystems. We used phospholipid fatty acids (PLFAs) as biomarker to study soil microbial community structure and measured activities of five extracellular enzymes involved in the degradation of cellulose (i.e., β‐1,4‐glucosidase and cellobiohydrolase), chitin (i.e., β‐1,4‐N‐acetylglucosaminidase), and lignin (i.e., phenol oxidase and peroxidase) as indicators of soil microbial functioning in carbon transformation or turnover across varying biotic and abiotic conditions in a typical temperate forest ecosystem in central China. Redundancy analysis (RDA) was performed to determine the interrelationship between individual PFLAs and biotic and abiotic site factors as well as the linkage between soil microbial structure and function. Path analysis was further conducted to examine the controls of site factors on soil microbial community structure and the regulatory pathway of changes in SOC relating to microbial community structure and function. We found that soil microbial community structure is strongly influenced by water, temperature, SOC, fine root mass, clay content, and C/N ratio in soils and that the relative abundance of Gram‐negative bacteria, saprophytic fungi, and actinomycetes explained most of the variations in the specific activities of soil enzymes involved in SOC transformation or turnover. The abundance of soil bacterial communities is strongly linked with the extracellular enzymes involved in carbon transformation, whereas the abundance of saprophytic fungi is associated with activities of extracellular enzymes driving carbon oxidation. Findings in this study demonstrate the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in affecting SOC via microbial regulations.     

植物功能性状与湿地生态系统土壤碳汇功能

湿地生态系统碳平衡对气候变化极为敏感,是陆地生态系统碳循环响应全球变化的重要环节。然而,湿地生态系统碳汇调节机制仍不十分清楚,并且对影响因子的研究多集中在非生物因子上。综述了植物功能性状和功能性状多样性对湿地生态系统土壤碳汇功能的影响,阐明了生物因子对生态系统碳循环响应全球变化的重要性,介绍了植物功能性状对生态系统碳输入和输出过程的影响,简述了植物功能性状多样性的研究现状及其在指示生态系统碳汇功能现状和预测未来趋势等方面的应用。从优势植物、植物种间关系和植物-微生物种间关系3方面总结了植物功能性状多样性直接和间接影响生态系统碳循环的途径。展望了植物功能性状和功能性状多样性与湿地生态系统土壤碳汇功能的研究前景。     

森林凋落物分解及其对全球气候变化的响应

凋落物分解是重要的森林生态系统过程之一,受到气候、凋落物质量、土壤生物群落等生物和非生物因素的综合调控．迄今,有关不同森林生态系统和不同树种地上部分的凋落物动态、凋落物分解过程中的养分释放动态、生物和非生物因素对凋落物分解的影响等研究报道较多,但对地下凋落物的分解研究相对较少．近年来,森林凋落物分解对以大气CO2浓度增加和温度升高为主要特征的全球变化的响应逐步受到重视,但其研究结果仍具有很多不确定性．因此,未来凋落物生态研究的重点应是凋落物分解对土壤有机碳固定的贡献、地上／地下凋落物的物理、化学和生物学过程及其对各种生态因子（例如冻融、干湿交替）及交互作用的响应、凋落物特别是地下凋落物分解对全球气候变化的响应机制等方面．     

Biochar supply-chain and challenges to commercialization

Produced through pyrolysis, biochars are used as a soil amendment. Differences in feedstock and processing result in differentiated products which impact their values in different soil conditions. Despite the enormous potential, biochars have not been widely used. This paper overviews the benefits and potential demand for biochar and features of supply chain, and identifies opportunities for viable introduction of biochars. The value of biochars should be evaluated as a part of the pyrolysis system that coproduces biochars and biofuels. Biochars can improve agricultural productivity and soil functioning and contribute to climate change mitigation through carbon sequestration. Furthermore, it can provide extra benefit by contributing to fire prevention. The cost of biochar system depends on the costs of feedstock acquisition, transportation, and processing. Biochar is most likely to be adopted in locations with marginal land and high-value crop, and near low-cost feedstock sources. The adoption of biochar can be enhanced by compensation for carbon sequestration, further investment in research, and learning of producers to enhance efficiency of the supply chain.     

Biochar stability in soil: meta‐analysis of decomposition and priming effects

The stability and decomposition of biochar are fundamental to understand its persistence in soil, its contribution to carbon (C) sequestration, and thus its role in the global C cycle. Our current knowledge about the degradability of biochar, however, is limited. Using 128 observations of biochar‐derived CO₂ from 24 studies with stable (¹³C) and radioactive (¹⁴C) carbon isotopes, we meta‐analyzed the biochar decomposition in soil and estimated its mean residence time (MRT). The decomposed amount of biochar increased logarithmically with experimental duration, and the decomposition rate decreased with time. The biochar decomposition rate varied significantly with experimental duration, feedstock, pyrolysis temperature, and soil clay content. The MRTs of labile and recalcitrant biochar C pools were estimated to be about 108 days and 556 years with pool sizes of 3% and 97%, respectively. These results show that only a small part of biochar is bioavailable and that the remaining 97% contribute directly to long‐term C sequestration in soil. The second database (116 observations from 21 studies) was used to evaluate the priming effects after biochar addition. Biochar slightly retarded the mineralization of soil organic matter (SOM; overall mean: ?3.8%, 95% CI = ?8.1–0.8%) compared to the soil without biochar addition. Significant negative priming was common for studies with a duration shorter than half a year (?8.6%), crop‐derived biochar (?20.3%), fast pyrolysis (?18.9%), the lowest pyrolysis temperature (?18.5%), and small application amounts (?11.9%). In contrast, biochar addition to sandy soils strongly stimulated SOM mineralization by 20.8%. This indicates that biochar stimulates microbial activities especially in soils with low fertility. Furthermore, abiotic and biotic processes, as well as the characteristics of biochar and soils, affecting biochar decomposition are discussed. We conclude that biochar can persist in soils on a centennial scale and that it has a positive effect on SOM dynamics and thus on C sequestration.     

Ethylene: potential key for biochar amendment impacts

Significant increases in root density, crop growth and productivity have been observed following soil additions of biochar, which is a solid product from the pyrolysis of biomass. In addition, alterations in the soil microbial dynamics have been observed following biochar amendments, with decreased carbon dioxide (CO₂) respiration, suppression of methane (CH₄) oxidation and reduction of nitrous oxide (N₂O) production. However, there has not been a full elucidation of the mechanisms behind these effects. Here we show data on ethylene production that was observed from biochar and biochar-amended soil. Ethylene is an important plant hormone as well as an inhibitor for soil microbial processes. Our current hypothesis is that the ethylene is biochar derived, with a majority of biochars exhibiting ethylene production even without soil or microbial inoculums. There was increased ethylene production from non-sterile compared to sterile soil (215%), indicating a role of soil microbes in the observed ethylene production. Production varied with different biomass sources and production conditions. These observations provide a tantalizing insight into a potential mechanism behind the biochar effects observed, particularly in light of the important role ethylene plays in plant and microbial processes.     

The responses of soil organic carbon mineralization and microbial communities to fresh and aged biochar soil amendments

While biochar soil amendment has been widely proposed as a soil organic carbon (SOC) sequestration strategy to mitigate detrimental climate changes in global agriculture, the SOC sequestration was still not clearly understood for the different effects of fresh and aged biochar on SOC mineralization. In the present study of a two‐factorial experiment, topsoil samples from a rice paddy were laboratory‐incubated with and without fresh or aged biochar pyrolyzed of wheat residue and with and without crop residue‐derived dissolved organic matter (CRM) for monitoring soil organic matter decomposition under controlled conditions. The six treatments included soil with no biochar, with fresh biochar and with aged biochar treated with CRM, respectively. For fresh biochar treatment, the topsoil of a same rice paddy was amended with wheat biochar directly from a pyrolysis wheat straw, the soil with aged biochar was collected from the same soil 6 years following a single amendment of same biochar. Total CO₂ emission from the soil was monitored over a 64 day time span of laboratory incubation, while microbial biomass carbon and phospholipid fatty acid (PLFA) were determined at the end of incubation period. Without CRM, total organic carbon mineralization was significantly decreased by 38.8% with aged biochar but increased by 28.9% with fresh biochar, compared to no biochar. With CRM, however, the significantly highest net carbon mineralization occurred in the soil without biochar compared to the biochar‐amended soil. Compared to aged biochar, fresh biochar addition significantly increased the total PLFA concentration by 20.3%–33.8% and altered the microbial community structure by increasing 17:1ω8c (Gram‐negative bacteria) and i17:0 (Gram‐positive bacteria) mole percentages and by decreasing the ratio of fungi/bacteria. Furthermore, biochar amendment significantly lowered the metabolic quotient of SOC decomposition, thereby becoming greater with aged biochar than with fresh biochar. The finding here suggests that biochar amendment could improve carbon utilization efficiency by soil microbial community and SOC sequestration potential in paddy soil can be enhanced by the presence of biochar in soil over the long run.