环境科学  2023, Vol. 44 Issue (12): 6857-6868   PDF    
引用本文
孙昭安, 朱彪. 农田土壤碳循环过程及其量化方法[J]. 环境科学, 2023, 44(12): 6857-6868.
SUN Zhao-an, ZHU Biao. Carbon Cycling Processes in Croplands and Their Quantification Methods[J]. Environmental Science, 2023, 44(12): 6857-6868.
农田土壤碳循环过程及其量化方法
孙昭安1, 朱彪2     
1. 潍坊学院种子与设施农业工程学院, 山东省高校生物化学与分子生物学重点实验室, 潍坊 261061;
2. 北京大学生态研究中心, 城市与环境学院, 地表过程分析与模拟教育部重点实验室, 北京 100871
收稿日期: 2022-12-25; 修订日期: 2023-02-21
基金项目: 国家自然科学基金项目（32072518）；山东省自然科学基金项目（ZR2020QD042）
作者简介: 孙昭安(1985~), 男, 博士, 副教授, 主要研究方向为农田土壤碳氮循环, E-mail: zhaoansun@wfu.edu.cn
通信作者: 朱彪，E-mail: biaozhu@pku.edu.cn
摘要: 已有研究表明除了作物碳（根际沉积碳和秸秆碳）对农田土壤有机碳（SOC）的输入外，土壤碳还来源于土壤自养微生物固定SOC的贡献以及土壤无机碳（SIC）的固定（无机化学途径和微生物的生物矿化途径）.农田SOC的高低主要受到外源作物碳输入和原有SOC分解的平衡作用.作物碳输入在短期内通常促进SOC的分解，呈现正（根际）激发效应.通过整合分析主要作物的根际激发效应和秸秆还田的激发效应的研究，发现作物根系生长和秸秆还田引起的（根际）激发效应大小平均值分别为75%和67%.尽管秸秆还田通过激发效应引起SOC分解的额外释放，但是土壤残留秸秆碳通常大于激发效应导致SOC的额外损失，因此秸秆还田可能增加SOC的储量.在农田系统中，秸秆碳和根际沉积碳往往共存，这导致土壤碳输入和输出至少有3个碳源（根际沉积碳、秸秆碳和土壤碳），由于多碳源体系的区分方法存在挑战，目前这两种作物碳（根际沉积碳和秸秆碳）对SOC分解的激发效应影响是不清晰的.最后，提出了新量化方法，可以多源区分根际CO2排放以及SOC中作物碳输入的碳源，以及区分碱性土壤中无机化学和微生物途径对SIC的贡献.研究有助于提高对农田土壤SOC和SIC输入和输出途径的理解，以及农田土壤碳平衡评估的精确度.
关键词: 土壤碳      根际沉积碳      激发效应      秸秆还田      多碳源体系     
Carbon Cycling Processes in Croplands and Their Quantification Methods
SUN Zhao-an1 , ZHU Biao2     
1. Key Laboratory of Biochemistry and Molecular Biology in University of Shandong, College of Biological and Agricultural Engineering, Weifang University, Weifang 261061, China;
2. Key Laboratory for Earth Surface Processes of the Ministry of Education, Institute of Ecology, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
Abstract: Recent studies have shown that the source of soil carbon(C) includes not only the input of crop C(rhizodeposit- and residue-C) to soil organic C(SOC) but also the contribution of soil autotrophic microorganisms to SOC and the fixation of soil inorganic C(SIC) from the soil inorganic chemical pathway and microbial biomineralization pathway. The level of SOC in croplands is mainly controlled by the balance between the input of crop C and the loss of SOC via decomposition. In the short term, the input of crop C usually promotes the SOC decomposition, showing a positive(rhizosphere) priming effect. We analyzed the literature on the rhizosphere priming effect of major crops and the priming effect of straw additions and found that they were on average 75% and 67%, respectively. The residual straw C in the soil could completely compensate for the SOC loss caused by the priming effect of straw returning. In croplands, rhizodeposit- and residue-C often coexisted, which resulted in at least three C sources(rhizodeposit-, straw-, and soil-C) for soil C input and output. Finally, we proposed a new method to distinguish the contribution of multiple C sources to the CO2 emission and the SOC input in rhizosphere soils, as well as the contribution of inorganic chemistry and microbial pathways to the SIC input in calcareous soils. This review is helpful to improve the understanding of the input and output pathways of SOC and SIC in croplands and to improve the accuracy of soil C assessment in croplands.
Key words: soil carbon      rhizodeposit-C      priming effect      straw returning      multi-carbon source system     

农田土壤固碳指通过人为和自然作用来提高土壤有机碳(soil organic carbon, SOC)[1~3]和无机碳(soil inorganic carbon, SIC)[4~6]储量, 将大气CO2固持在土壤碳库中.以往研究多关注作物光合固碳对SOC的贡献, 其他途径较少关注[7, 8].利用非同位素法研究土壤SOC对不同措施的响应, 根本原理还是把土壤看成黑盒子, 通过不同时间或处理之间差减来量化, 这忽略了各个途径的贡献, 进而导致不同农业措施对土壤固碳的调控机制是模糊的[8~10].碳同位素法是量化土壤外源碳输入和内外源碳输出的有效手段, 包括13/14C标记法和13C自然丰度法[7, 8].外源SOC的输入除了主要源于作物根际沉积碳和作物残体碳外, 还部分来源于土壤固碳微生物(光能和化能自养)的贡献[1, 11](表 1).在秸秆还田下的农田土壤, 作物根际沉积碳和秸秆碳输入是同时存在的: ①通过13/14CO2标记作物地上部, 区分SOC中源于外源根系和原有土壤的比例, 量化根际沉积对SOC的贡献[2, 3, 7, 8]; ②13/14C标记作物残体添加到土壤, 划分SOC中内外源有机碳的比例, 量化作物残体对SOC的贡献[12]; ③C3作物长期种植在C4土壤上(反之亦然, 表 1).以往研究利用13C自然丰度法来量化C3作物残体对SOC的贡献, 准确地说, 这是C3种植体系的贡献, 包括净根际沉积碳部分[7~9, 13, 14]. SOC输入的第2个途径是土壤微生物对大气CO2和根际呼吸的固定, 以前认为这个贡献很小, 然而, 最近发现这个贡献超出以往的估测[1, 6, 15].例如, Ge等[1]通过110 d的密闭14CO2土壤培养试验, 发现土壤光合固碳微生物对旱田和稻田SOC的贡献率分别为0.15%和0.65%, 推算出全球0~20 cm土壤固碳量为0.57~7.3 Pg·a-1[16], 因此, 土壤固碳微生物对SOC的贡献不容忽视.另外, Liu等[6]在野外沙地通过注入13CO2试验, 发现部分SOC直接源于大气13CO2进入土壤中的13CO2和H13CO3-, 其固碳速率为3.276 μg·(kg·d)-1, 结合宏基因组进一步发现, 推测由微生物的化能自养和异养途径来固碳.因此, 随着碳同位素方法结合微生物测序技术在固碳研究中的应用, 研究者们发掘了更多的土壤有机固碳途径.

表 1 13/14C法量化土壤有机和无机固碳的方法总结 Table 1 Summary of methods for quantifying soil organic and inorganic carbon fixation by the 13/14C method

在富含无机碳的碱性土壤上, 由于碱性土壤额外增加了无机固碳途径, 土壤固碳途径比酸性和中性土壤中的途径更加复杂[17].随着13/14C技术在研究土壤固碳的深入, 有研究发现土壤无机固碳既可以通过无机化学途径(非生物途径)[4, 5], 也可通过土壤微生物的生物矿化(biomineralization)途径[6].最近, 丁仲礼等[18]在《中国“碳中和”框架路线图研究》中指出碱性土壤富含钙离子, 通过无机化学途径捕获大气CO2形成碳酸钙沉淀, 即形成次生无机碳(pedogenic carbonate, PIC), 对大气CO2实施封存.在我国西北和华北碱性农田, 由于根际呼吸和作物残体分解释放CO2为PIC形成提供充足碳源, 大量施用含钙镁的化肥、含钙镁盐基离子的秸秆以及灌溉富含钙镁离子的地下水, 以上农业措施为土壤额外输入了Ca2+和Mg2+, 这为PIC形成提供了充足Ca2+和Mg2+源, 因此, 这两个地区农田PIC的累积速率甚至约是SOC累积速率的2倍[17].通过13C两源模型可以划分PIC源与SIC的比例, 结合SIC含量, 进而量化PIC形成量[4, 5].由于短期内PIC形成量很小, 借助13C自然丰度法很难检测到, 因此13C自然丰度法适合量化不同农业措施对PIC形成的长期影响, 不适合研究作物生长和秸秆分解对PIC形成的短期影响[19].借助13/14CO2标记注入土壤环境, 可以定量分析大气CO2进入PIC的碳量, 例如, Gao等[20]发现注入大气CO2的三分之一形成PIC, 土壤无机固碳速率为475.9 mg·(m2·d)-1.根源呼吸进入PIC的碳量是非常低的, 可能低于13C的检测阈值(10-7 mol), 因此采用低检测阈值的14C标记(10-13 mol)可能是个有效方法[7].此外, Liu等[21]最近通过灭菌和不灭菌处理土壤, 结合13CO2饲喂土壤培养75 d, 发现土壤无机固碳不仅通过无机化学途径, 还包括微生物途径, 并且后者远高于前者的贡献(约2倍).以往研究没有考虑微生物的生物矿化途径对无机固碳的贡献, 这可能高估了无机化学固碳途径的贡献, 今后这方面需要更多生物和非生物途径区分研究, 以提高土壤无机固碳评估的精确度[6].

1 作物光合碳对土壤碳输入的贡献及其对土壤有机碳分解的激发效应

13/14C法可以区分SOC中源于“根系新碳”和“土壤老碳”的比例, 定量作物光合碳对SOC的输入.从碳标记物上可以区分为: ①放射性同位素14C, ②稳定同位素13C; 从示踪方法上进一步区分为: ①连续标记(包括人工13/14C标记和自然13C丰度)[7, 9, 22], ②重复脉冲13/14C标记[23~25], ③单次脉冲13/14C标记[26, 27].与13C标记相比, 14C标记具有费用相对便宜和检测阈值低等优点, 但是14C具有放射性, 对环境和人体有辐射风险, 不适合在野外原位应用[7, 26].在所有碳标记方法中, 借助连续人工标记量化SOC输入是最精确的, 但是长时间人工连续标记需要稳定温度、湿度和CO2浓度的标记装置, 这在国内外少数实验室才能实施, 很难在田间做原位标记, 只能在田间和室内做盆栽试验[22, 28, 29].13C自然丰度法是个折中选择, 13C自然丰度法实际上是长期13C低丰度自然标记, 例如通过把C3作物长期种植或将C3残体持续添加到C4土壤上, 根据作物碳和SOC之间δ13C差异, 通过13C两源模型来定量作物碳对SOC的输入, 但是这个方法仅适合研究外源碳长期累积过程[9, 30].如果研究田间单季作物生长对SOC的贡献, 13/14C脉冲标记是个有效手段, 因为脉冲标记持续几个小时, 标记室内的温度、湿度和CO2浓度要求相对易于满足[31, 32].目前在野外和室内广泛应用的有3种脉冲标记量化方法(图 1): ①不同植株在不同关键物候期平行标记, 然后经过相同天数后(示踪期)收获, 这个方法量化的是每个关键生育期的净根际沉积碳的累加[31, 32]; ②不同植株在不同关键物候期平行标记, 一部分标记植株经过短示踪期后(几个小时和几天)收获, 另一部分标记植株在生育期末收获, 这个方法量化不同时期净根际沉积碳到生育期末的残留[26, 27, 33]; ③同一个植株在不同时期(例如相隔两周)脉冲标记, 到生育期末收获, 标记频率覆盖了整个生育期, 标记相对均匀, 这也是连续人工标记的折中选择[23, 24].

图 1 3种13/14CO2脉冲标记方法的示意 Fig. 1 Schematic of three 13/14CO2pulse labeling methods

1.1 根际沉积碳对土壤碳输入的贡献

植物根系生长对SOC输入的贡献主要是以根际沉积碳的形式, 植物根际沉积碳在土壤中的驻留时间远高于残体碳, 例如水稻根际沉积碳的驻留时间约是其残体碳的1.5倍[34].总根际沉积碳包括: ①净根际沉积碳; ②分解的根际沉积碳(根际微生物呼吸)[2, 35, 36].在全球范围内, 三源区分根际呼吸(活根呼吸、根际沉积碳和SOC分解)的研究仍然很缺乏, 数据源比较少, 本文通过整合分析发现作物、草类和树木的根际沉积碳分解占根源呼吸的比例分别为40%、36%和48%(图 2).结合Pausch等[2]整合作物、草类和树木的光合13/14C分配结果(净根际沉积碳占根源呼吸的比例分别为42%、38%和83%), 由此间接估算出3类植物根际沉积碳的净残留与分解的比值分别为1∶1、1∶1和1∶1.7, 这暗示植物总根际沉积碳大约是净根际沉积碳的2~3倍, 因此, 如果忽略根际沉积碳的分解, 这可能导致大幅低估了根系释放到土壤中的碳量.在绝大数光合碳分配研究中仅量化前者, 而对后者的定量分析极少, 这是由于量化后者的技术难度很大, 前提是需要把根际呼吸划分为活根呼吸、根际微生物呼吸和SOC分解[36~38].目前, 区分这3个CO2组分的同位素方法主要有6种: ①同位素稀释法; ②模拟根际沉积碳法; ③根际沉积碳洗脱法; ④土壤14CO2动态释放建模法; ⑤根源呼吸减去根际微生物呼吸释放的14CO2[39]; ⑥根分离法结合13C脉冲标记法[36].以上6种方法都是建立在基本假设上进行区分, 13/14C方法很难精确区分这3个碳源释放的CO2, 这是由于活根和根际微生物呼吸均来源于根系, 进而导致两者释放CO2的同位素值信号相似[36], 并且这两个来源的CO2共存于同一时空.根际激发效应对SOC分解的影响主要归因于根际沉积碳输入对根际微生物的激发[40], 本文推测根际微生物呼吸与根际激发效应呈正相关性[41].由于三源区分根际呼吸的技术限制, 导致根际激发效应的生态学机制解析仍不清晰, 因此, 这亟需进行三源区分根际呼吸以及定量根际微生物呼吸研究.

N表示数据源的数目, 箱式图中的黑色实线和红色虚线分别表示中位数和平均值, 顶部和底部边界分别表示所有数据的75%和25%, 上部和下部误差线分别表示所有数据的95%和5%, 下同; RR(root respiration)和RMR(rhizo-microbial respiration)分别表示活根和根际微生物呼吸对根源呼吸的贡献率; 星号表示RR和RMR贡献率之间的显著性差异(P < 0.05); 整合分析三源区分根际呼吸的数据来源于树木[37, 42~45]、草类[36, 42, 46~50]和作物[35, 38, 39, 51~54] 图 2 活根和根际微生物呼吸对根源呼吸的贡献 Fig. 2 Contribution of live root respiration and rhizo-microbial respiration to root-derived respiration

以往研究在秸秆还田土壤取样, 通过测定13C值来区分SOC中源于秸秆的比例, 认为这是秸秆还田对SOC的贡献[9, 13], 但是, 这忽略了残留根系和根际沉积碳对SOC的贡献, 导致秸秆还田对SOC贡献的高估.例如, 笔者通过整合分析玉米和小麦光合13/14C分配的研究[8], 发现玉米和小麦光合碳转移到地下(根系残体碳和净根际沉积碳)占净光合碳(植株残体碳+净根际沉积碳)的比例分别为19%和23%, 其中根系残体碳的贡献率分别为14%和18%, 净根际沉积碳的贡献率都为5%.因此, SOC中的“作物新碳”确切地说应是整个种植体系(还田秸秆+残留根系+净根际沉积)对SOC输入的贡献.

1.2 作物生长对土壤碳释放的根际效应

根系生长过程中释放根际沉积碳, 一部分根际沉积碳被土壤微生物利用, 改变根际土壤SOC分解的速率, 呈现SOC分解的“根际激发效应”[41, 55].两源区分根际呼吸(根源呼吸和SOC分解)可以用同位素法和非同位素法, 非同位素法原理从本质上就是差减法, 假设种植物和不种植物处理的SOC源CO2释放相等, 这忽略了根际激发效应.因此, 仅可以通过碳同位素法来定量分析根际激发效应[8].Huo等[56]整合分析了31个根际激发效应的研究, 发现根际激发效应增加SOC分解的幅度为59%, 其中木本植物、草类植物和作物的根际激发效应分别为77%、57%和38%.本文进一步细化四大作物(小麦、玉米、水稻和大豆)的根际激发效应, 整合了30个关于四大作物的根际激发效应研究, 发现四大作物根系生长显著增加SOC的分解, 根际激发效应的平均和中位数分别为75%和42%(图 3), 其中小麦根际激发效应最高(平均和中位数分别为162%和111%), 水稻次之(115%和18%), 然后是玉米(60%和38%)和大豆(36%和31%, 图 3).尽管作物根际激发效应增加了SOC的分解, 但是不一定导致SOC储量的降低, 如果根系释放的碳(包括净根际沉积碳和腐烂根系)腐殖化到SOC含量超过正根际激发效应引起的额外SOC释放[33], 根系生长则导致SOC储量增加, 反之亦然[40, 57].如果量化根际土壤SOC的平衡, 这需要同时量化光合碳在植物-土壤系统中的分配和输入, 以及区分根际CO2释放和根际激发效应[8].但是, 同一个试验同时研究这两个主题的比较少[48], 因此, 根际土壤碳平衡的精确量化基础数据依然很少.例如, 对小麦和玉米进行13CO2脉冲标记, 笔者量化了这两个作物根际效应, 发现增加土壤总碳释放分别为0.26 g·kg-1和0.62 g·kg-1[32], 而小麦和玉米净根际沉积碳分别为0.11 g·kg-1[58]和0.25 g·kg-1[59], 所以净根际沉积碳无法弥补正根际效应导致土壤碳的额外释放.总之, 根际效应对SOC平衡的影响是个双刃剑, 取决于正根际激发碳分解和净根际沉积碳输入的平衡作用[53].

不同小写字母表示不同作物根际激发效应之间的显著性差异(P < 0.05); 整合分析作物根际呼吸的数据来源于四大作物小麦[60~67]、玉米[68~76]、水稻[28, 77]和大豆[29, 41, 61, 62, 78~85] 图 3 四大作物生长对SOC分解的根际激发效应 Fig. 3 Rhizosphere priming effect of four major crops on the decomposition of soil organic carbon

另外, 碱性土壤包括SOC和SIC库, 根系生长同时影响SOC和SIC的释放和输入.例如, 在整个作物生长季, 本文发现冬小麦根际效应对SOC源CO2额外释放量是SIC的2.5倍, 而夏玉米生长导致SOC和SIC源CO2额外释放量相等, 所以碱性土壤碳循环不能忽略根际效应对SIC释放的影响[32].相对于SIC含量的背景值, 根系生长对SIC的输入量是相对低的, 通过低丰度13CO2标记很难检测到, 需要高丰度13CO2标记或者低检测限的14C标记来量化(13C和14C检测限分别为10-7 mol和10-13 mol)[7, 19].从目前来看, 根系生长对SIC释放和输入的影响研究是非常少的, 这需要更多的研究者来关注这个问题, 为碱性农田碳中和对策提供基础数据.

1.3 作物残体对土壤有机碳分解的激发效应

在农田系统中, 作物残体还田可以在短期内促进或抑制SOC的分解, 这种现象被称作“激发效应”[86].作物残体包括根系和秸秆, 由于根系含结构性碳组分高于秸秆, 因此根系分解速率低于秸秆, 这可能导致根系对SOC的贡献更大[34, 87].例如, 从作物残体分解角度, Zhu等[34]发现水稻根系和秸秆在土壤中的驻留时间分别为50.3 d和39.5 d; 从作物残体驱动微生物残体对SOC输入角度, Xu等[88]发现玉米根系还田通过微生物残体途径对SOC积累量高于秸秆还田处理.目前, 秸秆还田对激发效应的研究相对较多[86], 较少关注根系还田的激发效应[89], 两者同时研究的更少[34, 88].通过整合分析13/14C秸秆的土壤培养试验, 本文发现3大作物秸秆(小麦、玉米和水稻)对SOC分解的激发效应, 发现平均和中位数分别为68%和53%[图 4(a)], 其中小麦、玉米和水稻秸秆的激发效应的平均值分别为67%、61%和96%, 中位数分别为71%、42%和88%[图 4(a)].因此, 秸秆还田在大部分情况下促进SOC的分解.秸秆还田对SOC含量的影响取决于残留秸秆碳和正激发效应大小的平衡[57, 90], 本文进一步量化了残留秸秆碳与正激发效应, 发现平均比值为13倍[中位数为5倍, 图 4(b)], 这表明残留秸秆碳可以补偿正激发效应导致SOC的额外分解.

不同小写字母表示不同作物秸秆激发效应之间的显著性差异(P < 0.05); 整合分析秸秆还田对激发效应的数据来源于小麦秸秆[91~96]、玉米秸秆[10, 97~108]、水稻秸秆[34, 89, 109~114]和其他农作物秸秆[115~117] 图 4 作物秸秆对SOC分解的激发效应 Fig. 4 Priming effect of crop residues on the decomposition of soil organic carbon

2 量化土壤有机和无机固碳的新方法 2.1 区分作物生长对土壤内外源碳释放和外源碳输入的影响

在秸秆还田下的根际土壤, 外源有机碳的输入包括根际沉积碳与秸秆碳, 这两种作物碳都可以引起SOC分解的激发效应.在酸性土壤上, 根际土壤CO2释放源达到3个, 包括秸秆碳、根源呼吸和SOC, 而在碱性土壤, 根际土壤CO2释放又增加了SIC源, 达到4个.区分根际土壤CO2是量化土壤碳平衡的前提, 而3/4源碳体系的存在给根际土壤CO2的区分带来挑战.土壤残留秸秆碳的输入量化可以用13/14C方法直接划分SOC来源, 也可间接用13/14C方法量化土壤CO2中的秸秆分解碳量, 进而用总秸秆碳投入减去秸秆分解碳来量化秸秆碳的净输入[10].

2.1.1 区分秸秆还田下根际土壤CO2的释放

在酸性土壤上, 3源区分秸秆还田下根际土壤CO2有两种方法[图 5(a)], 第一种方法为平行13C标记秸秆和植株地上部[118], 第二种方法为平行13C标记秸秆[119].第一种方法标记处理为: ①13C秸秆+植株+土壤; ②秸秆+13C标记植株+土壤; ③秸秆+植株+土壤.通过处理1和2与处理3组合, 分别量化秸秆分解量和根源呼吸量, 最后剩余为SOC的分解碳量.第二种方法标记处理为: ①高富集13C作物残体+作物+土壤; ②低富集13C作物残体+作物+土壤.通过利用秸秆碳、根系碳和SOC之间的δ13C差异, 借助13C三元混合模型, 3源拆分秸秆还田下根际土壤CO2的释放[103, 119, 120], 从而量化根系生长对土壤内外源CO2释放的影响.

图 5 区分酸性和碱性土壤在秸秆还田下根际CO2的释放 Fig. 5 Separating CO2 emission from rhizosphere under straw returning in acidic and calcareous soils

在碱性土壤上, 为了4源区分秸秆还田下根际CO2释放, 通过平行13C标记秸秆和植株地上部来实现, 具体标记处理为[图 5(b)]: ①秸秆+13C标记植株+土壤; ②高富集13C秸秆+植株+土壤; ③低富集13C作物残体+作物+土壤; ④秸秆+植株+土壤.第一步通过处理1和4量化根源呼吸的碳量, 在第一步基础上, 通过处理2和3构建13C四元混合模型, 4源拆分根际土壤CO2的释放.

2.1.2 根际沉积碳和秸秆碳对土壤碳输入的贡献

在根际沉积碳和秸秆碳共存下, 除了以木质素和微生物残体形式对SOC输入外[121], 另外在碱性土壤上, 也能以无机化学固碳形式对SIC的输入[4, 17]..通过平行13C标记秸秆和植株地上部, 来量化作物碳对SOC和SIC的贡献, 具体标记处理如下(图 6): ①13C秸秆+植株+土壤; ②秸秆+13C标记植株+土壤; ③秸秆+植株+土壤.根际沉积碳的输入只能用直接方法, 秸秆碳的输入可用直接和间接两种方法来量化(图 6).直接和间接方法都是通过13C平行标记植株地上部和秸秆, 两种方法都需要两源区分SOC(酸性土壤)和SIC(碱性土壤)中源于根际沉积碳的比例, 以及通过称重法来量化残留根系碳, 两种方法区别在于残留秸秆碳对SOC的贡献, 直接方法是通过直接区分SOC中源于秸秆碳的贡献[122], 间接方法是通过秸秆碳投入量减去秸秆碳分解量来计算土壤残留秸秆碳量[10].

(c)量化根际沉积碳和秸秆碳对土壤碳输入的贡献包括: ①直接方法: 土壤碳的净输入=SOC/SIC秸秆碳(1)+ SOC/SIC根际沉积碳(2)+ 残留根系碳(3); ②间接方法: 土壤碳的净输入=(总还田秸秆碳－秸秆分解(1))+ SOC/SIC根际沉积碳(2)+ 残留根系碳(3), 式中下标(1)~(3)分别表示碳输入分别通过13C标记秸秆、13C标记作物和根系收获法来量化; 酸性土壤仅包括SOC组分, 而碱性土壤包括SOC和SIC两个组分 图 6 量化酸性和碱性土壤中根际沉积碳和秸秆碳对土壤的输入 Fig. 6 Quantifying the input of rhizodeposit-C and straw-C into acidic and calcareous soils

2.2 区分次生无机碳中源于无机化学沉淀和微生物形成途径

在碱性土壤, 目前PIC形成多关注无机化学沉淀途径, 较少关注微生物的生物矿化途径对无机固碳的贡献.还田秸秆分解和根源呼吸释放的CO2可能通过无机化学途径[4, 17]和微生物途径[6]被SIC固定.为了区分这两个途径, 可以在不灭菌和灭菌土壤条件下, 设置标记处理: ①高丰度13C标记作物+12C秸秆; ②12C对照作物+高丰度13C秸秆; ③12C对照作物+12C秸秆.在不灭菌条件下, 通过13CO2气体标记作物地上部或者13C标记秸秆添加, 量化PIC源于无机化学和微生物途径的总贡献; 在灭菌环境下, 通过平行标记作物地上部和秸秆, 量化PIC源于无机化学途径的贡献.最后, 不灭菌下PIC中源于根际沉积碳和秸秆碳的贡献减去灭菌下作物碳的贡献, 即得微生物途径的无机固碳贡献(图 7).

图 7 量化在碱性土壤中根际沉积碳和秸秆碳对土壤无机碳的输入 Fig. 7 Quantifying the input of rhizodeposit-C and straw-C into soil inorganic carbon in calcareous soils

3 展望

(1) 一部分根际沉积碳被土壤微生物分解, 引起根际激发效应, 量化这部分碳的前提是需要把根源呼吸进一步区分为活根呼吸和根际沉积碳的分解.由于区分技术限制, 相关研究仍然较少, 这导致总根际沉积碳量化的不确定性.

(2) 碱性土壤包括SOC和SIC库, 根系生长对SIC溶解也产生影响, 由于碱性土壤增加了SIC源CO2的释放, 导致根际土壤CO2释放源达到3个(根系、SOC和SIC).因此, 在碱性土壤, 三源区分根际土壤CO2的释放是量化根际效应的前提.为了提高量化根际土壤碳输出的准确性和模型预测精度, 多源CO2释放区分研究需要进一步加强.

(3) 大部分秸秆还田对激发效应和碳平衡的影响研究仅考虑秸秆单独添加, 然而, 在秸秆还田下的农田, 作物根际沉积碳和秸秆碳共存, 这导致多源碳体系中作物碳输入和输出的量化仍是一个挑战.尤其在碱性土壤, 根际土壤CO2释放源达到4个.本文初步提出了碱性和酸性土壤中作物碳输入和输出量化的新方法.

(4) 在农田“碳中和”目标下, 碱性土壤无机固碳可能是个生态固碳手段, 以往研究多关注无机化学固碳贡献, 伴随着微生物无机固碳途径的发现, 需要重新思考以往无机化学途径固碳的结果, 以往研究是否高估了无机化学固碳的贡献？尤其针对秸秆还田下的根际土壤, 本文初步提出了区分生物和非生物途径对无机固碳贡献的新方法.

4 结论

本文通过文献整合分析发现: 活根呼吸和根际沉积碳分解比值约为2∶3; 在大部分情况下, 作物根系生长和秸秆碳输入增加了SOC的分解, 呈现正(根际)激发效应(平均值分别为75%和67%); 尽管秸秆还田激发土壤SOC的额外分解, 但是多数情况下土壤残留秸秆碳高于SOC额外分解的损失, 因此, 秸秆还田可能导致SOC库的净增加.针对秸秆碳和根际碳共同输入的农田土壤, 本文提出了新量化方法, 这可能有助于提高农田土壤有机和无机碳循环评估的精确度.

参考文献
[1] Ge T D, Wu X H, Chen X J, et al. Microbial phototrophic fixation of atmospheric CO2 in China subtropical upland and paddy soils[J]. Geochimica et Cosmochimica Acta, 2013, 113: 70-78. DOI:10.1016/j.gca.2013.03.020
[2] Pausch J, Kuzyakov Y. Carbon input by roots into the soil: quantification of rhizodeposition from root to ecosystem scale[J]. Global Change Biology, 2018, 24(1): 1-12. DOI:10.1111/gcb.13850
[3] Liu Y L, Ge T D, Zhu Z K, et al. Carbon input and allocation by rice into paddy soils: a review[J]. Soil Biology and Biochemistry, 2019, 133: 97-107. DOI:10.1016/j.soilbio.2019.02.019
[4] Bughio M A, Wang P L, Meng F Q, et al. Neoformation of pedogenic carbonates by irrigation and fertilization and their contribution to carbon sequestration in soil[J]. Geoderma, 2016, 262: 12-19. DOI:10.1016/j.geoderma.2015.08.003
[5] Wang X J, Xu M G, Wang J P, et al. Fertilization enhancing carbon sequestration as carbonate in arid cropland: assessments of long-term experiments in northern China[J]. Plant and Soil, 2014, 380(1-2): 89-100. DOI:10.1007/s11104-014-2077-x
[6] Liu Z, Sun Y F, Zhang Y Q, et al. Soil microbes transform inorganic carbon into organic carbon by dark fixation pathways in desert soil[J]. Journal of Geophysical Research: Biogeosciences, 2021, 126(5). DOI:10.1029/2020JG006047
[7] Kuzyakov Y, Domanski G. Carbon input by plants into the soil. Review[J]. Journal of Plant Nutrition and Soil Science, 2000, 163(4): 421-431. DOI:10.1002/1522-2624(200008)163:4<421::AID-JPLN421>3.0.CO;2-R
[8] 孙昭安, 朱彪, 张译文, 等. 小麦和玉米生长对土壤碳输入和输出的贡献[J]. 农业环境科学学报, 2021, 40(10): 2257-2265.
Sun Z A, Zhu B, Zhang Y W, et al. Contributions of wheat and maize growth to soil carbon input and output[J]. Journal of Agro-Environment Science, 2021, 40(10): 2257-2265. DOI:10.11654/jaes.2021-0295
[9] Meng F Q, Lal R, Kuang X, et al. Soil organic carbon dynamics within density and particle-size fractions of Aquic Cambisols under different land use in northern China[J]. Geoderma Regional, 2014, 1: 1-9. DOI:10.1016/j.geodrs.2014.05.001
[10] 张轩. 13C标记秸秆在土壤中的分解特征及其在土壤团聚体中的分配[D]. 北京: 中国农业大学, 2011.
Zhang X. Decomposition of 13C labeled maize straw and its distribution in soil aggregates[D]. Beijing: China Agricultural University, 2011.
[11] Liao H, Hao X L, Qin F, et al. Microbial autotrophy explains large-scale soil CO2 fixation[J]. Global Change Biology, 2023, 29(1): 231-242. DOI:10.1111/gcb.16452
[12] Meng F Q, Dungait J A J, Xu X L, et al. Coupled incorporation of maize(Zea mays L.) straw with nitrogen fertilizer increased soil organic carbon in Fluvic Cambisol[J]. Geoderma, 2017, 304: 19-27. DOI:10.1016/j.geoderma.2016.09.010
[13] Wang J Z, Wang X J, Xu M G, et al. Contributions of wheat and maize residues to soil organic carbon under long-term rotation in North China[J]. Scientific Reports, 2015, 5. DOI:10.1038/srep11409
[14] Balesdent J, Mariotti A, Guillet B. Natural 13C abundance as a tracer for studies of soil organic matter dynamics[J]. Soil Biology and Biochemistry, 1987, 19(1): 25-30. DOI:10.1016/0038-0717(87)90120-9
[15] Xiao K Q, Ge T D, Wu X H, et al. Metagenomic and 14C tracing evidence for autotrophic microbial CO2 fixation in paddy soils[J]. Environmental Microbiology, 2021, 23(2): 924-933. DOI:10.1111/1462-2920.15204
[16] 陈晓娟, 吴小红, 简燕, 等. 农田土壤自养微生物碳同化潜力及其功能基因数量、关键酶活性分析[J]. 环境科学, 2014, 35(3): 1144-1150.
Chen X J, Wu X H, Jian Y, et al. Carbon dioxide assimilation potential, functional gene amount and rubisCO activity of autotrophic microorganisms in agricultural soils[J]. Environmental Science, 2014, 35(3): 1144-1150.
[17] 苏培玺, 王秀君, 解婷婷, 等. 干旱区荒漠无机固碳能力及土壤碳同化途径[J]. 科学通报, 2018, 63(8): 755-765.
Su P X, Wang X J, Xie T T, et al. Inorganic carbon sequestration capacity and soil carbon assimilation pathway of deserts in arid region[J]. Chinese Science Bulletin, 2018, 63(8): 755-765.
[18] 丁仲礼, 张涛. 碳中和: 逻辑体系与技术需求[M]. 北京: 科学出版社, 2022.
Ding Z L, Zhang T. Carbon neutrality[M]. Beijing: Science Press, 2022.
[19] Gocke M, Pustovoytov K, Kuzyakov Y. Pedogenic carbonate recrystallization assessed by isotopic labeling: a comparison of 13C and 14C tracers[J]. Journal of Plant Nutrition and Soil Science, 2011, 174(5): 809-817. DOI:10.1002/jpln.200900341
[20] Gao Y, Zhang P, Liu J B. One third of the abiotically-absorbed atmospheric CO2 by the loess soil is conserved in the solid phase[J]. Geoderma, 2020, 374. DOI:10.1016/j.geoderma.2020.114448
[21] Liu Z, Sun Y F, Zhang Y Q, et al. Desert soil sequesters atmospheric CO2 by microbial mineral formation[J]. Geoderma, 2020, 361. DOI:10.1016/j.geoderma.2019.114104
[22] Ge T D, Liu C, Yuan H Z, et al. Tracking the photosynthesized carbon input into soil organic carbon pools in a rice soil fertilized with nitrogen[J]. Plant and Soil, 2015, 392(1-2): 17-25. DOI:10.1007/s11104-014-2265-8
[23] Verburg P S J, Kapitzke S E, Stevenson B A, et al. Carbon allocation in Larrea tridentata plant-soil systems as affected by elevated soil moisture and N availability[J]. Plant and Soil, 2014, 378(1-2): 227-238. DOI:10.1007/s11104-013-2017-1
[24] Martens R, Heiduk K, Pacholski A, et al. Repeated 14CO2 pulse-labelling reveals an additional net gain of soil carbon during growth of spring wheat under free air carbon dioxide enrichment(FACE)[J]. Soil Biology and Biochemistry, 2009, 41(12): 2422-2429. DOI:10.1016/j.soilbio.2009.08.018
[25] Roper M M, Fillery I R P, Jongepier R, et al. Allocation into soil organic matter fractions of 14C captured via photosynthesis by two perennial grass pastures[J]. Soil Research, 2013, 51(8): 748-759. DOI:10.1071/SR12375
[26] Sun Z A, Chen Q, Han X, et al. Allocation of photosynthesized carbon in an intensively farmed winter wheat-soil system as revealed by 14CO2 pulse labelling[J]. Scientific Reports, 2018, 8(1). DOI:10.1038/s41598-018-21547-y
[27] Xiao M L, Zang H D, Liu S L, et al. Nitrogen fertilization alters the distribution and fates of photosynthesized carbon in rice-soil systems: a 13C-CO2 pulse labeling study[J]. Plant and Soil, 2019, 445(1-2): 101-112. DOI:10.1007/s11104-019-04030-z
[28] Zhu Z K, Ge T D, Liu S L, et al. Rice rhizodeposits affect organic matter priming in paddy soil: The role of N fertilization and plant growth for enzyme activities, CO2 and CH4 emissions[J]. Soil Biology and Biochemistry, 2018, 116: 369-377. DOI:10.1016/j.soilbio.2017.11.001
[29] Zhang Q F, Feng J G, Li J, et al. A distinct sensitivity to the priming effect between labile and stable soil organic carbon[J]. New Phytologist, 2023, 237(1): 88-99. DOI:10.1111/nph.18458
[30] Dong X L, Singh B P, Li G T, et al. Biochar application constrained native soil organic carbon accumulation from wheat residue inputs in a long-term wheat-maize cropping system[J]. Agriculture, Ecosystems & Environment, 2018, 252: 200-207.
[31] Swinnen J, Van Veen J A, Merckx R. Rhizosphere carbon fluxes in field-grown spring wheat: model calculations based on 14C partitioning after pulse-labelling[J]. Soil Biology and Biochemistry, 1994, 26(2): 171-182. DOI:10.1016/0038-0717(94)90160-0
[32] Sun Z A, Zhu B, Wang F, et al. Rhizosphere effects of maize and wheat increase soil organic and inorganic carbon release in carbonate-rich soils: a three-source 13C partitioning study[J]. Frontiers in Environmental Science, 2021, 9. DOI:10.3389/fenvs.2021.654354
[33] Lu Y H, Watanabe A, Kimura M. Input and distribution of photosynthesized carbon in a flooded rice soil[J]. Global Biogeochemical Cycles, 2002, 16(4). DOI:10.1029/2002GB001864
[34] Zhu Z K, Zeng G J, Ge T D, et al. Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil—Part 1: decomposition and priming effect[J]. Biogeosciences, 2016, 13(15): 4481-4489. DOI:10.5194/bg-13-4481-2016
[35] Swinnen J. Evaluation of the use of a model rhizodeposition technique to separate root and microbial respiration in soil[J]. Plant and Soil, 1994, 165(1): 89-101. DOI:10.1007/BF00009966
[36] Wang R Z, Bicharanloo B, Shirvan M B, et al. A novel 13C pulse-labelling method to quantify the contribution of rhizodeposits to soil respiration in a grassland exposed to drought and nitrogen addition[J]. New Phytologist, 2021, 230(2): 857-866. DOI:10.1111/nph.17118
[37] 宋文琛, 同小娟, 张劲松, 等. 用自然13C丰度法区分人工林根源呼吸的原理与应用[J]. 中国水土保持科学, 2015, 13(4): 37-43.
Song W C, Tong X J, Zhang J S, et al. Partitioning of root respiration and rhizomicrobial respiration in a Robinia pseudoacacia plantation based on 13C natural abundance[J]. Science of Soil and Water Conservation, 2015, 13(4): 37-43.
[38] Werth M, Kuzyakov Y. Three-source partitioning of CO2 efflux from maize field soil by 13C natural abundance[J]. Journal of Plant Nutrition and Soil Science, 2009, 172(4): 487-499. DOI:10.1002/jpln.200700085
[39] Werth M, Subbotina I, Kuzyakov Y. Three-source partitioning of CO2 efflux from soil planted with maize by 13C natural abundance fails due to inactive microbial biomass[J]. Soil Biology and Biochemistry, 2006, 38(9): 2772-2781. DOI:10.1016/j.soilbio.2006.04.032
[40] Dijkstra F A, Zhu B, Cheng W X. Root effects on soil organic carbon: a double-edged sword[J]. New Phytologist, 2021, 230(1): 60-65. DOI:10.1111/nph.17082
[41] Zhu B, Gutknecht J L M, Herman D J, et al. Rhizosphere priming effects on soil carbon and nitrogen mineralization[J]. Soil Biology and Biochemistry, 2014, 76: 183-192. DOI:10.1016/j.soilbio.2014.04.033
[42] Chen C R, Condron L M, Xu Z H, et al. Root, rhizosphere and root-free respiration in soils under grassland and forest plants[J]. European Journal of Soil science, 2006, 57(1): 58-66. DOI:10.1111/j.1365-2389.2006.00782.x
[43] Kelting D L, Burger J A, Edwards G S. Estimating root respiration, microbial respiration in the rhizosphere, and root-free soil respiration in forest soils[J]. Soil Biology and Biochemistry, 1998, 30(7): 961-968. DOI:10.1016/S0038-0717(97)00186-7
[44] Song W C, Tong X J, Zhang J S, et al. Three-source partitioning of soil respiration by 13C natural abundance and its variation with soil depth in a plantation[J]. Journal of Forestry Research, 2016, 27(3): 533-540. DOI:10.1007/s11676-015-0206-x
[45] Song W C, Tong X J, Zhang J S, et al. Autotrophic and heterotrophic components of soil respiration caused by rhizosphere priming effects in a plantation[J]. Plant, Soil and Environment, 2017, 63(7): 295-299. DOI:10.17221/233/2017-PSE
[46] Johansson G. Release of organic C from growing roots of meadow fescue(Festuca pratensis L.)[J]. Soil Biology and Biochemistry, 1992, 24(5): 427-433. DOI:10.1016/0038-0717(92)90205-C
[47] Craine J M, Wedin D A, Chapin III F S. Predominance of ecophysiological controls on soil CO2 flux in a Minnesota grassland[J]. Plant and Soil, 1999, 207(1): 77-86.
[48] Kuzyakov Y, Kretzschmar A, Stahr K. Contribution of Lolium perenne rhizodeposition to carbon turnover of pasture soil[J]. Plant and Soil, 1999, 213(1-2): 127-136.
[49] Kuzyakov Y, Ehrensberger H, Stahr K. Carbon partitioning and below-ground translocation by Lolium perenne[J]. Soil Biology and Biochemistry, 2001, 33(1): 61-74. DOI:10.1016/S0038-0717(00)00115-2
[50] Kuzyakov Y, Domanski G. Model for rhizodeposition and CO2 efflux from planted soil and its validation by 14C pulse labelling of ryegrass[J]. Plant and Soil, 2002, 239(1): 87-102. DOI:10.1023/A:1014939120651
[51] Cheng W X, Coleman D C, Carroll C R, et al. In situ measurement of root respiration and soluble C concentrations in the rhizosphere[J]. Soil Biology and Biochemistry, 1993, 25(9): 1189-1196. DOI:10.1016/0038-0717(93)90214-V
[52] Kuzyakov Y, Siniakina S V, Ruehlmann J, et al. Effect of nitrogen fertilisation on below-ground carbon allocation in lettuce[J]. Journal of the Science of Food and Agriculture, 2002, 82(13): 1432-1441. DOI:10.1002/jsfa.1202
[53] Larionova A A, Sapronov D V, Lopez de Gerenyu V O, et al. Contribution of plant root respiration to the CO2 emission from soil[J]. Eurasian Soil Science, 2006, 39(10): 1127-1135. DOI:10.1134/S1064229306100103
[54] Sapronov D V, Kuzyakov Y V. Separation of root and microbial respiration: comparison of three methods[J]. Eurasian Soil Science, 2007, 40(7): 775-784. DOI:10.1134/S1064229307070101
[55] 孙昭安, 赵诣, 朱彪, 等. 玉米生长对石灰性土壤无机碳与有机碳释放的根际效应[J]. 土壤学报, 2021, 58(4): 998-1007.
Sun Z A, Zhao Y, Zhu B, et al. Rhizosphere effects of maize on inorganic and organic carbon release in calcareous soils[J]. Acta Pedologica Sinica, 2021, 58(4): 998-1007.
[56] Huo C F, Luo Y Q, Cheng W X. Rhizosphere priming effect: a meta-analysis[J]. Soil Biology and Biochemistry, 2017, 111: 78-84. DOI:10.1016/j.soilbio.2017.04.003
[57] Qiao N, Schaefer D, Blagodatskaya E, et al. Labile carbon retention compensates for CO2 released by priming in forest soils[J]. Global Change Biology, 2014, 20(6): 1943-1954. DOI:10.1111/gcb.12458
[58] Sun Z A, Wu S X, Zhang Y W, et al. Effects of nitrogen fertilization on pot-grown wheat photosynthate partitioning within intensively farmed soil determined by 13C pulse-labeling[J]. Journal of Plant Nutrition and Soil Science, 2019, 182(6): 896-907. DOI:10.1002/jpln.201800603
[59] Meng F Q, Dungait J A J, Zhang X, et al. Investigation of photosynthate-C allocation 27 days after 13C-pulse labeling of Zea mays L. at different growth stages[J]. Plant and Soil, 2013, 373(1-2): 755-764. DOI:10.1007/s11104-013-1841-7
[60] Cheng W X. Measurement of rhizosphere respiration and organic matter decomposition using natural 13C[J]. Plant and Soil, 1996, 183(2): 263-268. DOI:10.1007/BF00011441
[61] Cheng W X, Johnson D W, Fu S L. Rhizosphere effects on decomposition: controls of plant species, phenology, and fertilization[J]. Soil Science Society of America Journal, 2003, 67(5): 1418-1427. DOI:10.2136/sssaj2003.1418
[62] Pausch J, Zhu B, Kuzyakov Y, et al. Plant inter-species effects on rhizosphere priming of soil organic matter decomposition[J]. Soil Biology and Biochemistry, 2013, 57: 91-99. DOI:10.1016/j.soilbio.2012.08.029
[63] Wang X J, Tang C X, Severi J, et al. Rhizosphere priming effect on soil organic carbon decomposition under plant species differing in soil acidification and root exudation[J]. New Phytologist, 2016, 211(3): 864-873. DOI:10.1111/nph.13966
[64] 孙昭安. 不同供氮条件下冬小麦生产向土壤碳库的输入及氮素损失特征[D]. 北京: 中国农业大学, 2018.
Sun Z A. Allocation of winter wheat photosynthesized carbon into soil carbon pool at different rates of nitrogen fertilization and nitrogen losses[D]. Beijing: China Agricultural University, 2018.
[65] Xu Q, Wang X J, Tang C X. The effects of elevated CO2 and nitrogen availability on rhizosphere priming of soil organic matter under wheat and white lupin[J]. Plant and Soil, 2018, 425(1-2): 375-387. DOI:10.1007/s11104-018-3601-1
[66] Xu Q, Wang X J, Tang C X. Rhizosphere priming of two near-isogenic wheat lines varying in citrate efflux under different levels of phosphorus supply[J]. Annals of Botany, 2019, 124(6): 1033-1042. DOI:10.1093/aob/mcz082
[67] Yin L M, Corneo P E, Richter A, et al. Variation in rhizosphere priming and microbial growth and carbon use efficiency caused by wheat genotypes and temperatures[J]. Soil Biology and Biochemistry, 2019, 134: 54-61. DOI:10.1016/j.soilbio.2019.03.019
[68] Kuzyakov Y, Cheng W. Photosynthesis controls of rhizosphere respiration and organic matter decomposition[J]. Soil Biology and Biochemistry, 2001, 33(14): 1915-1925. DOI:10.1016/S0038-0717(01)00117-1
[69] Kuzyakov Y, Cheng W. Photosynthesis controls of CO2 efflux from maize rhizosphere[J]. Plant and Soil, 2004, 263(1): 85-99. DOI:10.1023/B:PLSO.0000047728.61591.fd
[70] 何敏毅, 孟凡乔, 史雅娟, 等. 用13C脉冲标记法研究玉米光合碳分配及其向地下的输入[J]. 环境科学, 2008, 29(2): 446-453.
He M Y, Meng F Q, Shi Y J, et al. Estimating photosynthesized carbon distribution and inputs into belowground in a maize soil following 13C pulse-labeling[J]. Environmental Science, 2008, 29(2): 446-453. DOI:10.3321/j.issn:0250-3301.2008.02.029
[71] 李建敏. 氮肥施用对土壤-玉米系统土壤呼吸的影响机制研究[D]. 南京: 中国科学院南京土壤研究所, 2010.
Li J M. Effects of nitrogen fertilizer application on soil respiration in the maize-soil system[D]. Nanjing: Institute of Soil Science, Chinese Academy of Sciences, 2010.
[72] Kumar A, Kuzyakov Y, Pausch J. Maize rhizosphere priming: field estimates using 13C natural abundance[J]. Plant and Soil, 2016, 409(1-2): 87-97. DOI:10.1007/s11104-016-2958-2
[73] Jiang Z H, Liu Y Z, Yang J P, et al. Effects of nitrogen fertilization on the rhizosphere priming[J]. Plant and Soil, 2021, 462(1-2): 489-503. DOI:10.1007/s11104-021-04872-6
[74] Jiang Z H, Liu Y Z, Yang J P, et al. Rhizosphere priming regulates soil organic carbon and nitrogen mineralization: the significance of abiotic mechanisms[J]. Geoderma, 2021, 385. DOI:10.1016/j.geoderma.2020.114877
[75] 莫朝阳, 张鑫林, 杨京平. 根际激发效应对土壤有机碳累积及分解的影响[J]. 浙江大学学报(农业与生命科学版), 2021, 47(4): 527-533.
Mo C Y, Zhang X L, Yang J P. Influence of rhizosphere priming effects on accumulation and decomposition of soil organic carbon[J]. Journal of Zhejiang University(Agriculture & Life Sciences), 2021, 47(4): 527-533.
[76] 俞诺萱. 玉米幼苗根际激发效应对盐分胁迫及氮素添加的响应[D]. 兰州: 兰州大学, 2021.
Yu N X. The response of rhizosphere priming effect to salt stress and nitrogen addition in maize seedling planting[D]. Lanzhou: Lanzhou University, 2021.
[77] 王莹莹. 水分管理对水稻光合碳的分配及其根际激发效应的影响[D]. 沈阳: 沈阳农业大学, 2019.
Wang Y Y. Effects of water management on rice photosynthetic carbon and its rhizosphere stimulating effect[D]. Shenyang: Shenyang Agricultural University, 2019.
[78] Fu S L, Cheng W X. Rhizosphere priming effects on the decomposition of soil organic matter in C4 and C3 grassland soils[J]. Plant and Soil, 2002, 238(2): 289-294. DOI:10.1023/A:1014488128054
[79] Dijkstra F A, Cheng W X, Johnson D W. Plant biomass influences rhizosphere priming effects on soil organic matter decomposition in two differently managed soils[J]. Soil Biology and Biochemistry, 2006, 38(9): 2519-2526. DOI:10.1016/j.soilbio.2006.02.020
[80] Dijkstra F A, Cheng W X. Moisture modulates rhizosphere effects on C decomposition in two different soil types[J]. Soil Biology and Biochemistry, 2007, 39(9): 2264-2274. DOI:10.1016/j.soilbio.2007.03.026
[81] Zhu B, Cheng W X. Rhizosphere priming effect increases the temperature sensitivity of soil organic matter decomposition[J]. Global Change Biology, 2011, 17(6): 2172-2183. DOI:10.1111/j.1365-2486.2010.02354.x
[82] Zhu B, Cheng W X. Nodulated soybean enhances rhizosphere priming effects on soil organic matter decomposition more than non-nodulated soybean[J]. Soil Biology and Biochemistry, 2012, 51: 56-65. DOI:10.1016/j.soilbio.2012.04.016
[83] Zhu B, Cheng W X. Impacts of drying-wetting cycles on rhizosphere respiration and soil organic matter decomposition[J]. Soil Biology and Biochemistry, 2013, 63: 89-96. DOI:10.1016/j.soilbio.2013.03.027
[84] Keith A, Singh B, Dijkstra F A. Biochar reduces the rhizosphere priming effect on soil organic carbon[J]. Soil Biology and Biochemistry, 2015, 88: 372-379. DOI:10.1016/j.soilbio.2015.06.007
[85] Su T Q, Dijkstra F A, Wang P, et al. Rhizosphere priming effects of soybean and cottonwood: do they vary with latitude?[J]. Plant and Soil, 2017, 420(1-2): 349-360. DOI:10.1007/s11104-017-3396-5
[86] 张叶叶, 莫非, 韩娟, 等. 秸秆还田下土壤有机质激发效应研究进展[J]. 土壤学报, 2021, 58(6): 1381-1392.
Zhang Y Y, Mo F, Han J, et al. Research progress on the native soil carbon priming after straw addition[J]. Acta Pedologica Sinica, 2021, 58(6): 1381-1392.
[87] Lu Y H, Watanabe A, Kimura M. Carbon dynamics of rhizodeposits, root- and shoot-residues in a rice soil[J]. Soil Biology and Biochemistry, 2003, 35(9): 1223-1230. DOI:10.1016/S0038-0717(03)00184-6
[88] Xu Y D, Gao X D, Pei J B, et al. Crop root vs. shoot incorporation drives microbial residue carbon accumulation in soil aggregate fractions[J]. Biology and Fertility of Soils, 2022, 58(8): 843-854. DOI:10.1007/s00374-022-01666-5
[89] 刘峰, 王云秋, 张昀, 等. 长期秸秆还田对水稻根系碳矿化与激发效应的影响[J]. 环境科学, 2022, 43(8): 4372-4378.
Liu F, Wang Y Q, Zhang Y, et al. Effect of long-term straw returning on the mineralization and priming effect of rice root-carbon[J]. Environmental Science, 2022, 43(8): 4372-4378.
[90] Liang J Y, Zhou Z H, Huo C F, et al. More replenishment than priming loss of soil organic carbon with additional carbon input[J]. Nature Communications, 2018, 9(1). DOI:10.1038/s41467-018-05667-7
[91] Shahbaz M, Kuzyakov Y, Sanaullah M, et al. Microbial decomposition of soil organic matter is mediated by quality and quantity of crop residues: mechanisms and thresholds[J]. Biology and Fertility of Soils, 2017, 53(3): 287-301. DOI:10.1007/s00374-016-1174-9
[92] Shahbaz M, Kuzyakov Y, Heitkamp F. Decrease of soil organic matter stabilization with increasing inputs: mechanisms and controls[J]. Geoderma, 2017, 304: 76-82. DOI:10.1016/j.geoderma.2016.05.019
[93] Fang Y Y, Nazaries L, Singh B K, et al. Microbial mechanisms of carbon priming effects revealed during the interaction of crop residue and nutrient inputs in contrasting soils[J]. Global Change Biology, 2018, 24(7): 2775-2790. DOI:10.1111/gcb.14154
[94] Shahbaz M, Kumar A, Kuzyakov Y, et al. Priming effects induced by glucose and decaying plant residues on SOM decomposition: a three-source 13C/14C partitioning study[J]. Soil Biology and Biochemistry, 2018, 121: 138-146. DOI:10.1016/j.soilbio.2018.03.004
[95] Shahbaz M, Kumar A, Kuzyakov Y, et al. Interactive priming effect of labile carbon and crop residues on SOM depends on residue decomposition stage: three-source partitioning to evaluate mechanisms[J]. Soil Biology and Biochemistry, 2018, 126: 179-190. DOI:10.1016/j.soilbio.2018.08.023
[96] 刘本娟, 谢祖彬, 刘琦, 等. 生物质炭引起的土壤碳激发效应与土壤理化特性的相关性[J]. 土壤, 2021, 53(2): 343-353.
Liu B J, Xie Z B, Liu Q, et al. Correlation between biochar-induced carbon priming effect in soils and soil physiochemical properties[J]. Soils, 2021, 53(2): 343-353.
[97] Nottingham A T, Griffiths H, Chamberlain P M, et al. Soil priming by sugar and leaf-litter substrates: a link to microbial groups[J]. Applied Soil Ecology, 2009, 42(3): 183-190. DOI:10.1016/j.apsoil.2009.03.003
[98] Cui J, Ge T D, Kuzyakov Y, et al. Interactions between biochar and litter priming: a three-source 14C and δ13C partitioning study[J]. Soil Biology and Biochemistry, 2017, 104: 49-58. DOI:10.1016/j.soilbio.2016.10.014
[99] Chen R R, Senbayram M, Blagodatsky S, et al. Soil C and N availability determine the priming effect: microbial N mining and stoichiometric decomposition theories[J]. Global Change Biology, 2014, 20(7): 2356-2367. DOI:10.1111/gcb.12475
[100] Kerré B, Hernandez-Soriano M C, Smolders E. Partitioning of carbon sources among functional pools to investigate short-term priming effects of biochar in soil: a 13C study[J]. Science of the Total Environment, 2016, 547: 30-38. DOI:10.1016/j.scitotenv.2015.12.107
[101] Qiu Q Y, Wu L F, Ouyang Z, et al. Priming effect of maize residue and urea N on soil organic matter changes with time[J]. Applied Soil Ecology, 2016, 100: 65-74. DOI:10.1016/j.apsoil.2015.11.016
[102] Wang H, Hu G Q, Xu W H, et al. Effects of nitrogen addition on soil organic carbon mineralization after maize stalk addition[J]. European Journal of Soil Biology, 2018, 89: 33-38. DOI:10.1016/j.ejsobi.2018.10.002
[103] Chen Z Y, Kumar A, Brookes P C, et al. Three source-partitioning of CO2 fluxes based on a dual-isotope approach to investigate interactions between soil organic carbon, glucose and straw[J]. Science of the Total Environment, 2022, 811. DOI:10.1016/j.scitotenv.2021.152163
[104] Zhang X W, Zhu B, Yu F H, et al. Long-term bare fallow soil reveals the temperature sensitivity of priming effect of the relatively stabilized soil organic matter[J]. Plant and Soil, 2022. DOI:10.1007/s11104-021-05260-w
[105] Chen X, Lin J J, Wang P, et al. Resistant soil carbon is more vulnerable to priming effect than active soil carbon[J]. Soil Biology and Biochemistry, 2022, 168. DOI:10.1016/j.soilbio.2022.108619
[106] 何伟. 不同施肥模式和盐渍化程度潮土中秸秆转化及其激发效应[D]. 泰安: 山东农业大学, 2022.
He W. Transformation and priming effect of straw in various fertilized and salinized Fluvo-aquic soils[D]. Taian: Shandong Agricultural University, 2022.
[107] 冷雪梅, 钱九盛, 张旭辉, 等. 添加外源有机物对长期不同施肥处理水稻土有机碳矿化的影响[J]. 南京农业大学学报, 2022, 45(1): 103-112.
Leng X M, Qian J S, Zhang X H, et al. Effects of external organic matter input on the mineralization of organic carbon in paddy soils with long-term fertilizations[J]. Journal of Nanjing Agricultural University, 2022, 45(1): 103-112.
[108] 于雅茜, 裴久渤, 刘维, 等. 13C富集玉米根、茎、叶添加对长期不施肥和施肥处理棕壤土壤呼吸的影响及其激发效应[J]. 土壤学报, 2022.
Yu Y X, Pei J B, Liu W, et al. Effects of root, stem and leaf of maize enriched by 13C on brown earth's respiration and their priming effects under long-term fertilization conditions[J]. Acta Pedologica Sinica, 2022. DOI:10.11766/trxb202110300587
[109] Ye R Z, Doane T A, Morris J, et al. The effect of rice straw on the priming of soil organic matter and methane production in peat soils[J]. Soil Biology and Biochemistry, 2015, 81: 98-107. DOI:10.1016/j.soilbio.2014.11.007
[110] Zhu Z K, Ge T D, Luo Y, et al. Microbial stoichiometric flexibility regulates rice straw mineralization and its priming effect in paddy soil[J]. Soil Biology and Biochemistry, 2018, 121: 67-76. DOI:10.1016/j.soilbio.2018.03.003
[111] Wang D D, Zhu Z K, Shahbaz M, et al. Split N and P addition decreases straw mineralization and the priming effect of a paddy soil: a 100-day incubation experiment[J]. Biology and Fertility of Soils, 2019, 55(7): 701-712. DOI:10.1007/s00374-019-01383-6
[112] 罗安焕. 外源秸秆与温度对喀斯特地区土壤有机碳矿化的影响[D]. 贵阳: 贵州大学, 2021.
Luo A H. Effects of exogenous straw and temperature on soil organic carbon mineralization in Karst area[D]. Guiyang: Guizhou University, 2021.
[113] 段建军, 罗安焕, 李瑞东, 等. 温度对贵州喀斯特黄色石灰土有机碳矿化、水稻秸秆激发效应和Q10的影响[J]. 水土保持学报, 2022, 36(5): 265-280.
Duan J J, Luo A H, Li R D, et al. Temperature remarkedly affecting organic carbon mineralization of Karst Yellow Rendzina, priming effect of rice straw, and Q10 in Guizhou Province[J]. Journal of Soil and Water Conservation, 2022, 36(5): 265-280.
[114] Parajuli B, Ye R Z, Szogi A. Mineral N suppressed priming effect while increasing microbial C use efficiency and N2O production in sandy soils under long-term conservation management[J]. Biology and Fertility of Soils, 2022, 58(8): 903-915. DOI:10.1007/s00374-022-01665-6
[115] Li L J, Zhu-Barker X, Ye R Z, et al. Soil microbial biomass size and soil carbon influence the priming effect from carbon inputs depending on nitrogen availability[J]. Soil Biology and Biochemistry, 2018, 119: 41-49. DOI:10.1016/j.soilbio.2018.01.003
[116] Fang Y Y, Singh B P, Farrell M, et al. Balanced nutrient stoichiometry of organic amendments enhances carbon priming in a poorly structured sodic subsoil[J]. Soil Biology and Biochemistry, 2020, 45. DOI:10.1016/j.soilbio.2020.107800
[117] Fang Y Y, Singh B P, Collins D, et al. Nutrient stoichiometry and labile carbon content of organic amendments control microbial biomass and carbon-use efficiency in a poorly structured sodic-subsoil[J]. Biology and Fertility of Soils, 2020, 56(2): 219-233. DOI:10.1007/s00374-019-01413-3
[118] Weng Z, Liu X H, Eldridge S, et al. Priming of soil organic carbon induced by sugarcane residues and its biochar control the source of nitrogen for plant uptake: A dual 13C and 15N isotope three-source-partitioning study[J]. Soil Biology and Biochemistry, 2020, 146. DOI:10.1016/j.soilbio.2020.107792
[119] Sun Z A, Meng F Q, Zhu B. Influencing factors and partitioning methods of carbonate contribution to CO2 emissions from calcareous soils[J]. Soil Ecology Letters, 2023, 5(1): 6-20.
[120] Whitman T, Lehmann J. A dual-isotope approach to allow conclusive partitioning between three sources[J]. Nature Communications, 2015, 6. DOI:10.1038/ncomms9708
[121] 张彬, 陈奇, 丁雪丽, 等. 微生物残体在土壤中的积累转化过程与稳定机理研究进展[J]. 土壤学报, 2022, 59(6): 1479-1491.
Zhang B, Chen Q, Ding X L, et al. Research progress on accumulation, turnover and stabilization of microbial residues in soil[J]. Acta Pedologica Sinica, 2022, 59(6): 1479-1491.
[122] 孙昭安, 张轩, 胡正江, 等. 秸秆与氮肥配比对农田土壤内外源碳释放的影响[J]. 环境科学, 2021, 42(1): 459-466.
Sun Z A, Zhang X, Hu Z J, et al. How different ratios of straw incorporation to nitrogen fertilization influence endogenous and exogenous carbon release from agricultural soils[J]. Environmental Science, 2021, 42(1): 459-466.