氨基酸添加对亚热带森林红壤氮素转化的影响

裴广廷，马红亮,*，林 伟，高 人，尹云锋，杨柳明

1 湿润亚热带山地生态国家重点实验室培育基地，福州 350007 2 福建师范大学地理科学学院，福州 350007

氨基酸添加对亚热带森林红壤氮素转化的影响

裴广廷1,2，马红亮1,2,*，林 伟1,2，高 人1,2，尹云锋1,2，杨柳明1,2

1 湿润亚热带山地生态国家重点实验室培育基地，福州 350007 2 福建师范大学地理科学学院，福州 350007

氨基酸；土壤水分；森林土壤；氮素转化

在森林生态系统中，氮是植物吸收最多的必需营养元素，土壤氮素转化在有机质的分解、土壤供氮能力及有效氮的维持中扮演着重要的角色，强烈影响着森林生产力[1]。除了温度和水分外，外源性N素输入也是影响森林土壤氮素转化的关键因子之一，在自然条件下，凋落物归还和氮沉降是森林土壤N最主要的来源[2]。已有研究表明，氨基酸是凋落物归还土壤过程中有机氮分解的重要产物，也是大气有机氮沉降的组成部分[3]，氨基酸-N不仅能在土壤中迅速矿化成无机氮，而且与无机氮存在着密切的动态转化关系，对土壤氮素保持和迁移转化过程起重要作用[4]，因此在近年来引起了众多学者的关注。

1 材料与方法

1.1 供试土壤

土壤采自福建省建瓯万木林自然保护区(118°02′—118°09′E，27°02′—27°03′N)，土壤为山地红壤。研究区属中亚热带季风气候，样地海拔390m，坡向330°，坡度20°，郁闭度为0.8，年平均降水量为731.4 mm，年平均气温19.4 ℃，相对湿度81%，全年无霜期达227 d，植物群落众多，植被以常绿阔叶林为主。乔木层中主要的树种有浙江桂(Cinnamomumchekiangense)、假蚊母树(Distyliopsisdunnii)、少叶黄杞(Engelhardtiafenzelii)、桂北木姜子(Litseasubcoriace)等，优势树种为浙江桂(Cinnamomumchekiangense)。灌木层比较稀疏，主要有杜茎山(Maesajaponica)、薄叶山矾(Symplocosanomala)、沿海紫金牛(Ardisiapunctata)等。而草本层主要有草珊瑚(Sarcandraglabra)、飞扬草(Euporbiahirta)和狗脊蕨(Woodwardiajaponica)类等。样地附近1 km内没有农业活动，无人为的氮输入[16]。在样地的上、中、下坡随机选取10个采样点，采集样地表层(0—15cm)土壤，挑除石块和凋落物，充分混匀土壤带回实验室，过2 mm筛，装自封袋保存于4 ℃冰箱中待用。土壤基本理化性质为：pH值(4.15±0.01)，土壤饱和持水量(673.59±12.43)g/kg，全碳(39.56±0.49)g/kg，全氮(2.80±0.04)g/kg，C/N比值(14.13±0.27)，铵态氮(32.73±1.08)mg/kg，硝态氮(16.06±0.14)mg/kg，亚硝态氮(0.11±0.01)mg/kg，可溶性有机氮(40.76±5.41)mg/kg，速效钾(72.15±4.32)mg/kg，速效磷(2.01±0.06)mg/kg。

1.2 实验处理

表1 氨基酸基本理化性质Table 1 The physicochemical characteristics of amino acids

1.3 测定方法

1.4 计算方法和数据处理

土壤可溶性有机氮含量的计算[19]：

土壤N2O-N产生量的计算方法[16]：

F=k·v/m·c· 273/(273+T)

式中,F表示气体N2O-N产生量(μg/kg)；k为常数，N2O-N取1.248；v为培养瓶容量体积(mL)；m为干土重(mg)；c为N2O气体浓度(μL/L)；T为培养温度(℃)。

采用 Excel 2003和origin 7.5对数据进行处理和作图，测定结果均以土壤干重计算。运用SPSS 18.0中单因素方差分析(One way ANOVA)中的最小显著差异法(LSD)分析不同处理之间的差异显著性，用曲线估计选择最优拟合方法分析土壤pH值和可溶性有机碳与氮素之间的相关性，并采用三因素重复测量方差(氨基酸、含水量与时间为主因素)进行影响因素分析。

2 结果与分析

图1 两种含水量条件下不同氨基酸处理土壤铵态氮的变化Fig.1 Dynamics of incubated with amino acids under two soil moisture conditionsCK：对照；Glu：添加谷氨酸处理；Lys：添加赖氨酸处理；Ala：添加丙氨酸处理；Met：添加甲硫氨酸处理；均值：36d培养时间段内的平均值(n=6);折线图中所有数值均是平均值±标准偏差(n=3)

图2 两种含水量条件下不同氨基酸处理土壤硝态氮的变化

2.3 不同氨基酸处理土壤可溶性有机氮(SON)特征

如图3所示，氨基酸添加处理土壤SON含量呈先降低后升高趋势。60%WHC条件下，Glu、Lys、Ala、Met在第2天迅速降低至与CK差异不显著，并在第8天降至最低且分别比CK下降了14.61%、16.24%、42.95%(P<0.05)、84.24%(P<0.01)。Glu、Lys、Ala到12d(Met到16d)回升至与CK含量相当。除了第8天Ala显著低于Glu和Lys，Glu、Lys、Ala三者之间无显著差异。

90%WHC条件下，Glu、Lys、Ala、Met同样在第2天迅速降低至与CK差异无显著，并在12d降至最低。除了第16天Met、Ala显著高于CK和Glu(P<0.05)，第2天后Glu、Lys、Ala、Met均与CK无显著差异，且Glu、Lys、Ala三者之间差异不显著。

图3 两种含水量条件下不同氨基酸处理土壤可溶性有机氮的变化Fig.3 Dynamics of SON incubated with amino acids under two soil moisture conditions

2.4 不同氨基酸处理土壤氧化亚氮(N2O)排放特征

从图4可看出，60%WHC条件下，土壤N2O-N释放量在第8天最大，随后迅速降低，CK、Glu、Lys、Ala、Met最大值依次为22.03、22.99、23.46、22.08、16.00μg/kg。Glu、Lys、Ala 三者与CK差异不显著，且三者之间无显著差异。Met在第8天显著低于CK(P<0.05)，随后又显著高于CK(P<0.05)，然而从0至36d平均值看，Met(10.65 μg/kg)大于CK(8.46 μg/kg)，总体上增加了N2O排放的可能性。

当土壤含水量增至90%WHC，N2O-N释放量在第2天迅速增至最大值，CK、Glu、Lys、Ala、Met最大值依次为273.43、312.99、308.97、399.50、193.12 μg/kg，是60%WHC最大值的100多倍。Glu、Lys、Ala 三者与CK差异不显著，且三者之间无显著性差异。与CK相比，Met表现与60%WHC时相似，并在第36天降低至与CK无显著差异，Met的36d平均值(87.95 μg/kg)仍大于CK(68.10μg/kg)。

图4 两种含水量条件下不同氨基酸处理土壤氧化亚氮的变化Fig.4 Dynamics of N2O-N incubated with amino acids under two soil moisture conditions

2.5 土壤pH值的变化及其与土壤氮素相关关系

如图5结果所示，60%WHC条件下，从0至12d土壤pH值迅速增大，随后变化平缓。氨基酸添加处理的土壤pH值均高于CK处理，在第2天、12天、36天Glu、Lys、Ala、Met均与CK达到显著差异(P<0.05)，在各氨基酸处理中Met处理的土壤pH值较高。90%WHC条件下，土壤pH值在短暂(2d)的降低后又升高，与60%WHC相比变化幅度更大。除第2天的Ala和第12天的Lys略低于CK外，氨基酸处理的土壤pH值均大于CK处理，第8天后Met均显著高于CK(P<0.05)，Glu、Lys、Ala处理之间差异不显著(P> 0.05)。

图5 两种含水量条件下不同氨基酸处理土壤pH值的变化Fig.5 Dynamics of soil pH incubated with amino acids under two soil moisture conditions

图6 两种含水量条件下不同氨基酸处理土壤pH值与土壤氮素的相关关系Fig.6 Relationship between soil pH and soil nitrogen in different soil moisture conditions

2.6 土壤可溶性有机碳(SOC)的变化

由于土壤SOC含量与土壤氮素无明显相关性，在此只对土壤SOC含量的变化特征进行分析。从图7中可知，在两种土壤含水量条件下，土壤SOC含量随时间的变化趋势均为先降低后升高再降低。60%WHC条件下，Lys、Ala、Met土壤SOC含量在第8天均显著大于CK处理(P<0.05)；第12、16天氨基酸处理降低为低于CK处理。90%WHC条件下，土壤SOC含量在第12天最大，在第8、12天氨基酸处理均大于CK处理且Ala与CK差异显著(P<0.05)，第16天氨基酸处理均低于CK处理，于第36天各处理降至最低且无显著差异。

图7 两种含水量条件下不同氨基酸处理土壤可溶性有机碳的变化Fig.7 Dynamics of SOC incubated with amino acids under two soil moisture conditions

2.7 多因素统计分析

表2 氨基酸、培养时间、土壤含水量对土壤氮素含量和pH值以及可溶性有机碳含量影响的重复测量方差分析(P)

Table 2 Results of repeated measures ANOVA on the effects of amino acid N addition, incubation time, soil moisture content and their interactions on soils nitrogen, soil pH and soluble organic carbon

影响因素Impactfactor铵态氮NH+4-N硝态氮NO-3-N可溶性有机氮SON氧化亚氮N2O土壤pH值SoilpH可溶性有机碳SOC氨基酸Aminoacid<0．001<0．001<0．0010．860<0．0010．441培养时间Time<0．001<0．001<0．001<0．001<0．001<0．001含水量Soilmoisturecontent0．001<0．0010．013<0．001<0．0010．003氨基酸×培养时间Aminoacid×Time<0．001<0．001<0．0010．650．1030．004氨基酸×含水量Aminoacid×Soilmoisturecontent0．0390．009<0．0010．8610．2340．354含水量×培养时间Soilmoisturecontent×Time<0．001<0．001<0．001<0．001<0．001<0．001氨基酸×培养时间×含水量Aminoacid×Time×Soilmoisturecontent0．2300．010<0．0010．6230．0140．105

3 讨论

3.1 氨基酸添加对土壤氮素含量及转化的影响

3.2 氨基酸理化性质与土壤氮素转化的关系

4 结论

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Effects of amino acid additions on nitrogen transformation in subtropical forest soil

PEI Guangting1,2, MA Hongliang1,2,*, LIN Wei1,2, GAO Ren1,2, YIN Yunfeng1,2, YANG Liuming1,2

1CultivationBaseofStateKeyLaboratoryofHumidSubtropicalMountainEcology,Fuzhou350007,China2SchoolofGeographicalSciences,FujianNormalUniversity,Fuzhou350007,China

Research on the nitrogen cycle of forest soils has traditionally focused on the mechanisms regulating the turnover of inorganic N. However, the key role of organic N in soil nitrogen transformation tends to be overlooked. Over recent decades, researchers have assessed the relative importance of organic N on the nutritional requirements of plants in forest ecosystems. Most studies have revealed that soil amino acids are important sources of organic N in forest ecosystems. Although the fluxes of organic N in forest ecosystems have been studied in detail, we have a poor understanding about the role of amino acids in soil nitrogen transformation in the subtropical region of China. In this study, subtropical broad-leaved forest soil was collected from Wan Mulin Natural Reserve located at Fujian Province, southeast China. We selected four types of amino acids, including L-Glutamic acid, L-Lysine, L-Alanine, and L-Methionine as the study materials, which represented acidic, basic, neutral, and sulfur amino acids, respectively. Soils were incubated for 0, 2, 8, 12, 16, and 36 days in the laboratory after adding 0and 40mg N /kg amino acid. Soil moisture was maintained at 60%WHC (water-holding capacity) or 90%WHC. Ammonium N, nitrate N, soluble organic N, nitrous oxide, soil pH, and soluble organic C content were determined. Data were subjected to analysis of variance (ANOVA) with the SPSS version 18.0, and significant differences between treatments were compared by the LSD test atP<0.05.The results showed that soil NH+4-N content significantly increased with the addition of amino acids, with the repression of NH+4-N production under high soil moisture content conditions (90%WHC) being relieved to some extent. Soil pH was increased by the addition of amino acids, and was closely correlated with soil NH+4-N and NO-3-N. These results support the finding that an increase in soil pH may promote N mineralization in acidic forest soils. Acidic, basic, and neutral amino acids increased NH+4-N production in soil, but had little or no influence on NO-3-N production and nitrous oxide emission. Soil nitrification was significantly inhibited by the addition of methionine, resulting in the accumulation of NH+4-N. Nitrous oxide emission from soil as a whole increased with the addition of methionine. The decrease in SON under the amino acid treatments was more evident under 60%WHC than 90%WHC conditions. The turnover of amino acids in forest soil is very rapid, with NH+4-N being the major N form in soil. Nitrogen transformation in forest soil is probably related to the decomposed products of amino acid mineralization, rather than the charge of amino acids. These findings indicate that nitrogen transformation varies with amino acid type, and that the mechanism inhibiting methionine during nitrification needs further research. In conclusion, amino acids might represent the intermediate products between organic nitrogen and mineral nitrogen, regulating nitrogen transformation in forest soils.

amino acid; soil moisture content; subtropical forest soil; nitrogen transformation

国家自然科学基金项目(40901115, 41271282, 31070549, 31170578)；教育部创新团队项目(IRT0960)；福建省高校杰出青年科研人才培育计划(JA12058)和福建师范大学优秀青年骨干教师培养基金资助(fjsdjk2012069)

2014- 05- 11; < class="emphasis_bold">网络出版日期:

日期:2015- 05- 18

10.5846/stxb201405110957

*通讯作者Corresponding author.E-mail:mhl936@163.com

裴广廷，马红亮，林伟，高人，尹云锋，杨柳明.氨基酸添加对亚热带森林红壤氮素转化的影响.生态学报,2015,35(23):7774- 7784.

Pei G T, Ma H L, Lin W, Gao R, Yin Y F, Yang L M.Effects of amino acid additions on nitrogen transformation in subtropical forest soil.Acta Ecologica Sinica,2015,35(23):7774- 7784.