环境科学研究  2017, Vol. 30 Issue (11): 1706-1714  DOI: 10.13198/j.issn.1001-6929.2017.03.01

引用本文  

黄敏, 段军波, 周开来, 等. 典型设施环境条件对土壤活性有机碳及腐殖物质碳的影响[J]. 环境科学研究, 2017, 30(11): 1706-1714.
HUANG Min, DUAN Junbo, ZHOU Kailai, et al. Effects of Typical Greenhouse Factors on Labile Organic Carbon and Humus Substance Carbon in Soil[J]. Research of Environmental Sciences, 2017, 30(11): 1706-1714.

基金项目

国家自然科学基金青年科学基金项目(41101210);中国留学基金委资助项目(留金发[2014]3012)

责任作者

作者简介

黄敏(1973-), 女, 湖北荆州人, 副教授, 博士, 主要从事土壤环境和区域生态研究, huangmin@whut.edu.cn

文章历史

收稿日期:2017-04-20
修订日期:2017-07-13
典型设施环境条件对土壤活性有机碳及腐殖物质碳的影响
黄敏 , 段军波 , 周开来 , 刘茜 , 梁荣祥 , 黄永炳     
武汉理工大学资源与环境工程学院, 湖北 武汉 430070
摘要:为明确设施环境对土壤有机碳形态变化的影响,选取武汉城郊设施土壤为研究对象,分别设置环境温度(4、10和25℃)、土壤酸化(土壤pH分别为6.89、6.11和5.30)和土壤盐渍化[土壤w(可溶性盐分)分别为1.90、3.05和5.01 g/kg]3种典型设施环境条件,通过为期90 d的室内模拟强化试验,研究以上3种典型设施环境条件对土壤活性有机碳动态变化、腐殖物质碳组成及有机碳矿化率的影响.结果表明:与4℃的对照处理相比,随着设施环境温度升高,土壤w(MBC)(MBC为微生物生物量碳)和w(ROOC)(ROOC为易氧化有机碳)呈上升趋势,25℃时的最大增幅分别达19.43%和55.56%;而土壤w(DOC)(DOC为可溶性有机碳)总体呈先升后降的趋势,10℃下最大增幅为17.23%,25℃下最大减幅为60.89%.与对照土壤[pH为6.89,w(可溶性盐分)为1.90 g/kg]相比,土壤pH为5.30的酸化处理下w(MBC)和w(ROOC)平均降幅分别为29.80%和5.93%,土壤w(可溶性盐分)为5.01 g/kg的盐化处理下的平均降幅分别为35.64%和6.26%,而酸化和盐化使土壤w(DOC)较对照的平均增幅分别达58.19%和119.73%.此外,设施环境温度提高会降低土壤有机碳矿化率和HU(胡敏素碳)所占比例,其HA/FA(胡敏酸碳富里酸碳含量之比)较对照增加了1.05倍;而土壤酸化和盐化会使有机碳矿化率较对照分别增加3.78和7.80倍,其HA/FA较对照分别降低了65.72%和73.21%.可见,提升设施环境温度、减缓或改善设施土壤的酸化及盐化问题,均有利于设施土壤的固碳减排.
关键词设施土壤    活性有机碳    腐殖物质碳    有机碳矿化率    设施环境条件    
Effects of Typical Greenhouse Factors on Labile Organic Carbon and Humus Substance Carbon in Soil
HUANG Min , DUAN Junbo , ZHOU Kailai , LIU Xi , LIANG Rongxiang , HUANG Yongbing     
School of Resources and Environmental Engineering, Wuhan University of Technology, Wuhan 430070, China
Abstract: Both labile organic carbon and humus substance carbon are main carbon pools in soil, and they play essential roles in soil carbon cycling. The effects of three typical greenhouse parameters including environmental temperature (4, 10 and 25℃), soil acidification (pH 6.89, 6.11 and 5.30) and salinization (1.90, 3.05 and 5.01 g/kg for soluble salt) on organic carbon in the greenhouse soil were investigated through laboratory experiments. The dynamics of microbial biomass carbon (MBC), dissolved organic carbon (DOC) and readily oxidizing organic carbon (ROOC) in greenhouse soil were determined during 90 days' incubation period. The soil humus substance carbon at the 90th day and the mineralization rate of organic carbon at the 12th day were also analyzed. The results showed that, compared with the control (at 4℃), the contents of MBC and ROOC in greenhouse soil increased significantly with the rising of environmental temperature, with maximum increases of 19.43% and 55.56% at 25℃, respectively, whereas the contents of DOC increased by 17.23% at 10℃ and decreased by 60.89% at 25℃. Both acidification and salinization of greenhouse soil could reduce the contents of MBC and ROOC while increasing the content of DOC. Compared with the control (at pH 6.89 and 1.90 g/kg for soluble salt), the contents of MBC and ROOC in acidified soil (pH 5.30) decreased by 29.80% and 5.93% on average, while the ones in salinized soil (5.01 g/kg for soluble salt) decreased by 35.64% and 6.26% on average, respectively. In contrast, the contents of DOC increased by 58.19% and 119.73% on average in acidified soil (pH 5.30) and salinized soil (5.01 g/kg for soluble salt), respectively. Helpfully, the increase in environmental temperature reduced the mineralization rate of soil organic carbon and decreased the percentage of humus carbon (HU), whereas the ratio of humic acid carbon/fulvic acid carbon (HA/FA) at 25℃ was 1.05 times higher than the control. Compared with the control, the mineralization rate of organic carbon in acidified soil (pH 5.30) and salinized soil (5.01 g/kg for soluble salt) increased by 3.78 and 7.80 times, respectively. However, the ratio of HA/FA decreased by 65.72% and 73.21%, respectively. Therefore, increasing environmental temperature and preventing greenhouse soil from acidification and salinization would be efficient strategies to sequestrate carbon and thus reduce CO2 emissions from greenhouse soils.
Keywords: greenhouse soil    labile organic carbon    humus substance carbon    mineralization rate of organic carbon    greenhouse environmental factors    

土壤有机碳是陆地生态系统的主要碳库,具有调控土壤结构、养分供应以及温室效应等作用[1-3],土壤有机碳动态最初往往通过其活性部分的变化表现出来[4].土壤活性有机碳是指土壤中具有一定溶解性、移动快、不稳定、易分解矿化,对植物和土壤微生物活性较高的那部分碳素[5],其中,土壤MBC(微生物生物量碳)、DOC(可溶性有机碳)和ROOC(易氧化有机碳)均属于表征土壤活性有机碳的常见形态[6].土壤活性有机碳对温室气体排放的贡献率较大,对气候、土壤和植被变化的响应极为敏感,其含量高低直接影响土壤微生物的活性,进而影响土壤固碳能力[7-8].土壤腐殖物质是进入土壤的有机物料在微生物和酶的作用下而形成的一类高分子有机混合物,它对土壤结构具有重要的调节功能. HS(腐殖物质碳)是土壤有机碳的核心组分,根据其溶解性差异又分为FA(富里酸碳)、HA(胡敏酸碳)和HU(胡敏素碳)等成分[9].其中,HA和HU结构复杂且难以降解,其有机碳被认为是土壤固定的惰性或稳定性有机碳[10]. HA/FA(胡敏酸碳与富里酸碳含量之比)是表征有机质腐殖化程度的重要指标,该比值越大,说明腐殖质品质越好[11].

设施土壤是在长期覆盖栽培和高度集约化管理等条件下,一种受人为作用强烈的土壤.因其长期处于“高温、高湿、高蒸发、无降水淋洗”等环境中,加之高度连作、连续大量施肥、盲目灌溉等农艺措施[12],导致设施土壤往往出现酸化、盐渍化及养分失衡等问题[13],这也是当前制约设施土壤可持续利用的关键因素.设施栽培属于反季节栽培,一般在月均气温低于10 ℃以下的冬春季进行,而设施环境温度往往比当季露天气温高4~17 ℃[14].温度对土壤w(TOC)、w(MBC)、w(DOC)和w(ROOC)影响显著,其中环境温度升高(5 ℃升至35 ℃),土壤w(TOC)增加7.55%[15].调查显示,设施菜地土壤pH一般在4.96~ 7.97之间[12];而土壤在一定pH范围内,w(TOC)与土壤pH呈极显著相关(P=0.01)[16].土壤盐渍化、富盐基离子的土壤环境也不利于有机碳的积累[17].有关土壤有机碳组分的形成转化,当前主要集中在露天自然的旱地[18]、水田等湿地[19]、草地[20]等土壤上.而设施土壤的环境条件特殊,其有机碳转化过程往往不同于自然条件下的露天土壤.因此,该研究以武汉近郊的设施菜地土壤为研究对象,结合实际存在的土壤酸化及盐渍化问题,探讨环境温度、土壤酸化和盐化3种典型因素对土壤活性有机碳及腐殖物质碳变化的影响规律,以期为设施土壤有机质管理和有机碳固定、改善区域环境提供理论依据.

1 材料与方法 1.1 试验材料

供试土壤采自武汉市近郊东西湖区石榴红村的设施蔬菜基地的表层(0~20 cm)土壤.该基地设施种植历史已超过20 a,设施面积约70 hm2,设施蔬菜类型主要有豇豆、茄子、辣椒、西红柿、黄瓜、萝卜等.土样采集方法采用“S”形线路随机多点混合而成,装入塑料袋中带回实验室及时研磨,过2 mm筛后置于4 ℃下保存备用.该设施土壤为灰潮土,pH为6.89,w (可溶性盐分)为1.90 g/kg,w(AP)为80.18 mg/kg,w(TP)为2.43 g/kg,w(TOC)为9.97 g/kg.

1.2 试验方法 1.2.1 试验设计

将供试土壤用蒸馏水调节其含水量至饱和持水量的45%后,置于25 ℃恒温恒湿条件下预培养7 d.称取若干份500 g(以烘干基计)预培养的新鲜土样,设置环境温度、土壤酸化及盐化3种因素,每种因素又分别设置3个水平:①环境温度,分别为4 ℃(CK)、10 ℃和25 ℃;②土壤酸化,pH分别为6.89(CK)、6.11和5.30;③盐化程度,w(可溶性盐分)分别为1.90 g/kg(CK)、3.05 g/kg和5.01 g/kg.各处理均设3次重复.其中,土壤pH用1 :9稀HNO3溶液和饱和KOH溶液进行调节,土壤可溶性盐分用两种混合盐溶液调配而成〔混合盐溶液1,配方为32.80 g/L Ca(NO3)2;混合盐溶液2,配方为3.02 g/L NaHCO3、6.00 g/L MgSO4、9.91 g/L Na2SO4、3.21 g/L NaCl、5.57 g/L KCl、5.13 g/L KNO3〕.各处理土样含水量最后均调至其饱和持水量的50%.各处理土壤分别装入2.5 L密封塑料罐,其中温度处理置于相应温度的培养箱内,酸化和盐化处理均在25 ℃条件下培养.在90 d培养期间,每隔2~3 d打开塑料罐通风换气一次.定期取样,分析土壤w(MBC)、w(DOC)和w(ROOC),培养结束时测定土壤HS组分碳含量.

另外,称取各处理50 g(以烘干基计)土样置于密封塑料杯,瓶中放入40 mL 0.5 mol/L NaOH溶液,在上述条件下一并培养. 12 d后测定NaOH溶液对CO2的吸收量.各处理亦设3次重复.

1.2.2 测定方法

土壤w(MBC)采用氯仿熏蒸提取法[21]测定,w(MBC)测定中未熏蒸土样提取液中有机碳含量即为w(DOC). w(ROOC)采用高锰酸钾氧化法[22]测定.土壤有机碳矿化量可由培养12 d后NaOH溶液对CO2的吸收量换算得到[23].土壤HS先用Na4P2O7·10H2O与NaOH混合液浸提,再用调节提取液pH而分离出FA、HA和HU等组分[24],再以重铬酸钾氧化法[21]测定土壤提取液中各HS的有机碳含量.

1.2.3 数据处理

试验结果均以3次重复的平均值±标准差表示,并采用软件Origin 9.0进行作图.

2 结果与分析 2.1 环境温度对土壤活性有机碳变化的影响

图 1(a)可知,90 d的培养期内,土壤w(MBC)随环境温度的升高呈现出先减后增的趋势.在4、10和25 ℃ 3种环境温度下,土壤w(MBC)在培养前5 d均较起始期有所降低,说明土壤微生物存在着对环境温度变化的适应期.第5天时,与4 ℃的对照处理相比,25 ℃下土壤w(MBC)增加19.43%,而10 ℃下却减少72.70%.在培养前中期(0~60 d),3种环境温度下w(MBC)差异显著(P < 0.05),但到第90天,这种差异则不明显(P> 0.05).土壤w(DOC)随培养时间延长总体上呈增加趋势,而随环境温度的升高出现先增后减的趋势〔见图 1(b)〕.培养至第12天时,3种环境温度下w(DOC)差异性最大(P < 0.01),与4 ℃对照相比,10 ℃下土壤w(DOC)增加17.23%,25 ℃下减少60.89%.从图 1(c)可知,土壤w(ROOC)随培养时间延长总体呈上升趋势,并随环境温度的升高而增加,且3种环境温度下土壤w(ROOC)存在显著差异(P < 0.05).从第12天到培养结束,与对照处理相比,10和25 ℃处理土壤w(ROOC)最大增幅分别为35.39%和55.56%.

环境温度/℃: 1—4; 2—10; 3—25. 图 1 不同环境温度下土壤活性有机碳含量的动态变化 Fig.1 Dynamics of labile organic carbon in greenhouse soils under different conditions of envieronmental temperature
2.2 酸化对土壤活性有机碳变化的影响

培养期间不同土壤pH条件下活性有机碳组分含量的动态变化如图 2所示.土壤酸化会显著降低w(MBC),且在培养中期(12~60 d)3种pH处理土壤w(MBC)均存在显著差异(P < 0.05),但培养结束时的差异不显著(P> 0.05)〔见图 2(a)〕.与土壤pH为6.89的对照土壤相比,整个培养阶段,土壤pH为6.11和5.30处理下土壤w(MBC)平均降幅分别为12.43%和29.80%,其中培养中期分别为14.31%和37.92%.从图 2(b)可知,土壤w(DOC)随培养时间延长总体呈上升趋势,且酸化使土壤w(DOC)增加.培养期间,3种pH下土壤w(DOC)在均存在显著差异(P < 0.05).第40天时酸化对土壤w(DOC)影响最大,与土壤pH为6.89的对照土壤相比,土壤pH为6.11和5.30的土壤w(DOC)分别增加了73.34%和58.19%.由图 2(c)可知,所有处理的土壤w(ROOC)一直维持在1.67 g/kg以上,酸化使土壤w(ROOC)显著降低,但在整个培养阶段,两种酸化处理土壤w(ROOC)差异并不显著(P>0.05).与对照相比,土壤pH为6.11和5.30的土壤w(ROOC)平均降幅分别为10.98%和5.93%.

土壤pH: 1—6.89; 2—6.11; 3—5.30. 图 2 不同pH条件下土壤活性有机碳含量的动态变化 Fig.2 Dynamics of labile organic carbon in greenhouse soils with different pH
2.3 盐化对土壤活性有机碳变化的影响

盐化对设施土壤活性有机碳各组分的影响与酸化的效应类似(见图 3):①土壤w(MBC)随土壤盐化程度的加重而显著降低〔见图 3(a)〕;第40天时盐化对土壤w(MBC)影响最大,与w(可溶性盐分)为1.90 g/kg的对照土壤相比,w(可溶性盐分)为3.05和5.01 g/kg处理下土壤w(MBC)分别降低了37.54%和55.92%;第40天后,3种盐分处理的处理土壤w(MBC)差异性逐渐缩小,培养结束时各处理土壤w(MBC)无显著差异(P>0.05),但整个培养阶段,土壤w(MBC)平均降幅分别达18.63%和35.64%. ②土壤w(DOC)随土壤盐化程度加重而显著增加〔见图 3(b)〕,第40天时,与对照相比,w(可溶性盐分)为3.05和5.01 g/kg处理的土壤w(DOC)分别增加98.92%和119.73%,培养结束时各处理土壤w(DOC)差异亦不显著(P>0.05).盐化程度加重总体上使土壤w(ROOC)降低〔见图 3(c)〕,培养12 d后,与对照土壤相比,w(可溶性盐分)为3.05和5.01 g/kg处理的土壤w(ROOC)分别降低4.76%~26.61%和15.47%~21.77%,而整个培养阶段,土壤w(ROOC)平均降幅分别为13.42%和6.26%.

w(可溶性盐分)/(g/kg): 1—1.90; 2—3.05; 3—5.01. 图 3 不同盐化程度下土壤活性有机碳含量的动态变化 Fig.3 Dynamics of labile organic carbon in greenhouse soils with different salinization degree
2.4 不同设施环境条件对土壤有机碳矿化的影响

表 1可知,环境温度从4 ℃升至25 ℃时,土壤有机碳矿化率由5.32%降至0.90%,降低了83.08%.可见设施环境温度的提升可阻滞土壤有机碳矿化,这有利于设施土壤中有机碳的固定.土壤酸化和盐化过程均可促进土壤有机碳矿化,不利于设施土壤有机而碳的积累.如当土壤pH从6.89降至5.30,土壤有机碳矿化率由0.90%增至4.31%,增加了3.78倍;w(可溶性盐分)从1.09 g/kg增至5.01 g/kg时,其土壤有机碳矿化率增加7.80倍.

表 1 不同设施环境下土壤有机碳矿化率和腐殖物质的HA/FA Table 1 The organic carbon mineralization rate and the ratio of HA/FA in greenhouse soils humus substance under three greenhouse factors
2.5 不同设施环境条件对土壤腐殖物质碳组成的影响

培养结束时不同处理土壤HS碳组分及其变化情况如图 4所示.设施土壤HS碳组分中,w(HU)(7.30~8.71 g/kg)最高,其次是w(HA)(2.07~2.52 g/kg),w(FA)(0.25~0.83 g/kg)最低.由图 4(a)可知,与4 ℃的对照相比,25 ℃处理土壤w(HA)增加11.01%,而w(FA)降低了46.81%;10 ℃处理土壤w(HA)下降8.81%,而w(FA)与对照差异不显著(P>0.05). 10和25 ℃处理土壤w(HU)均显著低于对照. HA/FA随温度升高而增加,与对照相比增加1.05倍(见表 1),设施环境温度的提升可促进土壤腐殖质品质的改善.由图 4(b)可见,与pH为6.89的对照土壤相比,酸化处理土壤的w(HA)和w(HU)均降低,而pH为6.11和5.30处理的土壤w(FA)分别提高20.00%和1.60倍.土壤HA/FA随pH减小而降低,与对照相比降低65.72%(见表 1).由图 4(c)可知,与对照相比,盐化处理下w(HA)和w(HU)均显著降低,平均降幅分别达9.56%和5.17%,而w(可溶性盐分)为3.05和5.01 g/kg处理的土壤分别升高了2.32和1.32倍,w(FA)较对照显著升高(P < 0.05).土壤HA/FA随盐化加重而呈降低趋势,与对照相比最大降幅为73.21%(见表 1).

图 4 不同设施环境条件对土壤腐殖物质碳含量的影响 Fig.4 Effects of three greenhouse factors on humus substance carbon concentrations in greenhouse soils
3 讨论 3.1 不同设施环境条件对土壤微生物量碳的影响

土壤活性有机碳对环境变化具有高度敏感性,但不同组分土壤活性有机碳对环境温度、土壤pH和盐分等因素变化的响应敏感性存在差异[25].土壤MBC是土壤有机质中最活跃和最易变化的部分,与土壤有机碳转化有密切关系,其含量高低是衡量土壤质量优劣的重要指标[26].设施栽培一般在温度较低的冬春季进行,设施环境温度往往比当季露天气温高4~17 ℃[14].该研究中将4 ℃设为冬季室外气温的对照处理,研究结果显示,环境温度升至10和25 ℃时,土壤w(MBC)随环境温度的升高呈现出先减后增的趋势. Verburg等[27]的研究结果也与此类似.低温环境下升温(如从4 ℃升至10 ℃),土壤微生物呼吸强度增大,所消耗的有机物质高于其自身形成的生物量,最终导致土壤w(MBC)下降[14];而在温度较高环境下升温(如从10 ℃升至25 ℃),微生物活性显著增强,其生物量形成速率要高于其呼吸强度,导致土壤w(MBC)增加.土壤酸化和盐渍化现象是设施栽培中的常见问题.按半干旱半湿润区土壤盐化程度分级标准[12],该研究中土壤1.90、3.05和5.01 g/kg的可溶性盐分含量可对应为轻度、中度和重度这3种盐化程度,结果显示土壤酸化和盐化程度加剧均降低了土壤w(MBC).酸化和盐化破坏了土壤微生物原有的生活环境,对土壤微生物产生胁迫作用,抑制了微生物增殖,造成土壤w(MBC)下降[28-29].该研究显示,土壤MBC对土壤酸化与盐渍化的响应类似,并随酸化过程和盐化程度加剧而下降.盐分含量增加可提高土壤中碳降解胞外酶的活性,从而促进土壤有机碳的分解[30].该研究结果也显示,设施环境升温使土壤有机碳矿化率降低,这与大多数研究结果[31]相悖,可能与设施土壤的酸化与盐化问题有关. Beltrán-Hernández等[32]的研究结果显示,高盐分条件下土壤CO2释放量是低盐分条件下的2倍左右.该研究中,酸化和盐化均提高了设施土壤有机碳矿化率,会造成土壤CO2释放量增加,加剧设施环境的温室效应.

3.2 不同设施环境条件对土壤可溶性有机碳的影响

土壤DOC是微生物的底物,在养分循环[18]和环境保护[33]方面有重要作用.土壤腐殖质、植物凋落物、根系分泌物和微生物的代谢产物均是其重要来源[34].土壤w(DOC)一般不超过土壤有机碳总量的2%,但其含量和性质能够反映土壤有机碳的稳定性[35].温度显著影响土壤DOC转换,且温度敏感性随着培养时间延长有降低趋势[36].该研究结果显示,温度对设施土壤w(DOC)的影响在不同温度段存在差异.温度增高促进降解土壤基质微生物的活性增强,难降解的有机碳在微生物作用下易于转化为DOC[37];与此同时,温度与土壤呼吸强度成正比,温度升高能够加速土壤微生物的生物周转,促进土壤有机碳的分解.该研究结果显示,土壤w(DOC)变化对土壤酸化与盐化的响应类似,均随酸化和盐化程度加剧而上升. Clark等[38]等研究结果也与此类似. pH可影响土壤中矿物的吸附能力,土壤有机碳大部分为酸性组分,在低pH条件下,易与其他物质如钙镁化合物发生中和反应,从而增加土壤w(DOC)[39].土壤盐分通过影响微生物生活环境而驱动土壤w(DOC)变化,Van Heemst等[40]研究发现,土壤w(DOC)与盐分存在负相关线性关系.土壤DOC作为易于被微生物吸收利用的有机碳源,其含量高低直接影响土壤微生物活性及有机碳矿化率.山榉林土壤DOC的损失与土壤呼吸产生的ρ(CO2)呈极显著线性相关(R=0.79,P < 0.01)[41],笔者所得研究结果也显示,设施土壤酸化或盐化均提高了土壤w(DOC)和有机碳矿化率,结合设施土壤w(MBC)的动态变化来看,设施土壤酸化或盐化不利于微生物对DOC的同化,对土壤CO2的减排不利.

3.3 不同设施环境条件对土壤易氧化有机碳的影响

土壤ROOC作为土壤有机碳中周转最快的组分,是土壤养分的潜在来源及土壤微生物活动的重要能源,常作为表征土壤肥力变化的重要指标[42]. Hassan等[43-44]研究表明,土壤w(ROOC)与温度呈正相关,但温度敏感性随着培养时间延长有降低趋势,笔者所得结果也显示温度升高可提高设施土壤w(ROOC).与环境温度的影响相反,设施土壤w(ROOC)均随土壤的酸化和盐化加剧而呈下降趋势,张仕吉等[45]研究结论也与此相似.原因可能在于酸化或盐化成为了设施土壤微生物类群和活性的胁迫条件,而不利于土壤ROOC的周转与形成.另外,ROOC作为土壤中最易被氧化且活性较高的有机碳,其含量高低能显著影响设施土壤固碳能力及温室气体的排放,有研究[46]显示,土壤有机碳矿化率与土壤w(ROOC)呈显著正相关.综上,设施环境温度的提升、设施土壤酸化或盐化的减缓与改善,均有利于设施土壤的固碳减排.

3.4 不同设施环境条件对土壤腐殖物质碳组成的影响

土壤HS是有机质的主体,它作为土壤的重要碳库,在土壤有机碳的循环转化中起重要作用.土壤HS的传统分组包括HA、FA和HU等组分[47]. w(HS)的多少取决于形成量和分解量的相对大小,而土壤环境条件决定着HS的形成是以HA为主,还是以FA为主[48].该研究结果显示,温度、土壤pH和盐分对土壤HS碳影响并不显著(P>0.05),但温度升高使HA/FA增加,而使w(HU)下降.这表明设施环境温度的提升有利于土壤腐殖质品质的改善,而温度升高增强了微生物活性,可能促进惰性HU碳向其他形态的转化.随土壤酸化和盐化加剧,HA/FA值降低,土壤酸化和盐化降低了土壤微生物活性,HA在结构上脂肪族侧链减少,芳化度增加,土壤有机碳腐殖化程度降低[48]. HS碳是土壤有机质中最难降解的部分,其种类组成直接影响设施土壤有机质品质及固碳减排潜力.

4 结论

a) 与4 ℃对照相比,设施环境温度在4~25 ℃范围内提升条件下,土壤w(MBC)和w(ROOC)最大增幅分别为19.43%和55.56%;土壤w(DOC)和有机碳矿化率均降低.与对照土壤〔pH为6.89,w(可溶性盐分)为1.90 g/kg〕相比,随设施土壤酸化和盐化程度的加重,土壤w(MBC)和w(ROOC)平均降幅分别为34.78%和6.92%;土壤w(DOC)最大增幅分别为58.19%和119.73%;有机碳矿化率分别了增加3.78和7.80倍.

b) 设施栽培中温度升高、土壤酸化或盐化这3种典型环境条件对土壤HS的影响存在差异,其中温度升高,土壤HA/FA较对照可提高1.05倍,有利于改善土壤腐殖质品质,而土壤酸化和盐化使土壤HA/FA较对照分别降低65.72%和73.21%,对土壤腐殖质品质不利.

c) 综合分析可知,提升设施环境温度、减缓或改善设施土壤的酸化及盐化问题,均有利于设施土壤的固碳减排.

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